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November 6

Frames per second

I learned in school that most movies contain twenty four frames per second. This is a two part question:

1. What are the extreme frame rates for human vision--how many are needed in order to detect motion, at what rate does it move two quickly to discern what's happening?
2. What is the "frame rate" of reality? That is to say, is it possible to speak of how quickly my eyes convert what i'm seeing into recognizable images in terms of frame rates?24.147.171.20 (talk) 00:36, 6 November 2008 (UTC)

Our articles frame rate and persistence of vision can hopefully help. The latter talks of a 16fps threshold for film (between flicker and motion image) and that "a critical part of understanding these visual perception phenomena is that the eye is not a camera: there is no 'frame rate' in the eye". Booglamay (talk) - 02:05, 6 November 2008 (UTC)

I recall hearing on the tv show QI that the reason pigeons don't move out of our way (or the way of cars) as quickly is that their 'frame-rate' (or whatever the word is) is much faster than humans, so to them things appear to be moving slower (or something like that) and so the reason they don't get out of the way is that to the thing is 'further' away than it is to us. Could be nonsense but that's what I heard and the show is usually reasonably well researched (being a comedy quiz show about common myths and unusual info). 194.221.133.226 (talk) 09:16, 6 November 2008 (UTC)

The pigeon story sounds like bollocks, IMHO. You are assuming that humans have the "right" frame rate, and species with a lower frame rate will constantly be shocked at how fast everything seems to be moving, and vice versa. Pigeons would be used to their own frame rate. 141.14.217.217 (talk) 11:48, 6 November 2008 (UTC)

Sorry to clarify - it's not that the pigeons are 'shocked', it is that the car is approaching slower so what to us looks like a last-minute get out of the way is to the pigeons plenty of time. I'd try find it on youtube/something as hard to explain, but i'd be surprised if it wasn't based on some truth - the whole role of the show QI is about facts/common mistakes so would be a bit silly. 194.221.133.226 (talk) 14:38, 6 November 2008 (UTC)

That makes no sense - pigeons instinctively know what their frame-rate is so they know how to convert what they see into actual speed, just like we do. The idea that a fast frame-rate corresponds to slow motion only applies if you film at a fast frame-rate and then play it back at a standard one. Either you are remembering incorrectly or QI is talking rubbish (it does happen). --Tango (talk) 15:58, 6 November 2008 (UTC)

To put things a different way, with 194 is proposing, the pigeons are for some reason too 'stupid' to be able to comprehend the speed of a fast moving object. The issue of framerate is an unnecessary distraction and we can never know if it's the cause (I would say it's unlikely, it would just be their brain doesn't compehend fast speeds). For something like a pigeon which AFAIK is resonably intelligent and likely to be preyed upon by a variety of fast moving animals, this would be a major shortcoming and therefore seems unlikely. Nil Einne (talk) 08:51, 8 November 2008 (UTC)

• What are the extreme frame rates for human vision--how many are needed in order to detect motion, at what rate does it move two quickly to discern what's happening?

  The limiting rate that we can distinguish depends on a few things. At the edges of your field of view, you are much more sensitive to flicker than in the center. Secondly, there is a huge variation between individuals. Most (if not all) people can see flicker out of the corners of their eyes at 40Hz. Some are bothered by 50Hz, few at 60Hz - hardly any over 70Hz. But there was one guy I met who (even with the center of his field of view) could see flicker at over 80Hz. His life was miserable because both TV and movies were unwatchable for him. He could use a computer - but only with a very high end video card and a monitor that could be cranked up to refresh at over 100Hz. At the low end, our ability to 'fuse' fast motion into continuous imagery also varies. I hate watching action movies in cinemas because that 24Hz rate doesn't work for me when things are moving fast. Everything becomes very jumbled and essentially unwatchable. But some people can work down to perhaps 15Hz. You can figure out what's happening even as low as 1Hz though. Suppose a lion is rushing towards you through the jungle. You're running and trying to keep an eye on where the thing is. You won't be able to see it all the time - it disappears behind trees - you have to switch back and forth between looking forwards so you don't trip over something - and looking back to see how close the lion is. You can manage to keep a mental 'image' of where the lion currently is between glimpses of it - so long as you get to see it again every few seconds. This ability is what allows you to keep track of what's going on at VERY low frame rates.

• What is the "frame rate" of reality? That is to say, is it possible to speak of how quickly my eyes convert what i'm seeing into recognizable images in terms of frame rates?

  The 'frame rate of reality' is something we discussed in the next question (below) - it's either a meaningless question - or the answer is the planck-time which is around 10^-44 seconds - which is an unimaginably short time. So essentialy, the answer is "there is no such thing". But your eyes don't have "frame rate" - so (as below) the question is moot. SteveBaker (talk) 18:49, 6 November 2008 (UTC)

"Reality,"" or humans' perception of changing visual input, has been modelled as a "continuous flow model" [1] rather than successive frames of movie film or processing steps by a digital computer, so the question may be meaningless. Edison (talk) 05:57, 7 November 2008 (UTC)

Why is there no flicker in real life?

The question above got me thinking: shouldn't there be a flicker from the interference between reality's framerate and my eye's framerate??? Even if reality's is a hundred times higher there should still be barely perceptible flicker, maybe less than once per second depending on how long it takes for the two to get in synch again... —Preceding unsigned comment added by 82.124.214.224 (talk) 02:51, 6 November 2008 (UTC)

See Planck time. The universe's frame rate is at about 5 x 10^-44 seconds. Lets say, for the sake of argument, that your eye can perceive differences in timing of 0.01 seconds. That means that the universe's frame rate at a speed of about 5,000,000,000,000,000,000,000,000,000,000,000,000,000,000 times faster than your eye's frame rate. Good luck finding that "flicker"... --Jayron32.talk.contribs 03:00, 6 November 2008 (UTC)

Neither you, nor the universe, have anything that can really be considered a frame rate. The rods and cones in your retina don't pick up light in synch, which is good, because they don't do it often enough to get a usable frame-rate. The universe becomes less deterministic as you look closer, so talking about anything much smaller than a planck time is pointless, but it's not as if the universe is separated into frames of a planck time each. Also, even if they did have a frame rate, it would just mean that every once in a while the universe would go 5 x 10⁴² + 1 frames instead of 5 x 10⁴². Not really noticeable. — DanielLC 16:47, 6 November 2008 (UTC)

Your eye doesn't have a "framerate" in the way that a TV camera does. Vision is a continuous phenomenon. The "interface" between your eye and your brain isn't a set of 'pixels' being updated at some fixed rate - it's more like "there is a vertical edge moving at 27 degrees per second from left to right across the visual field"...although even that is an over-simplification. There simply isn't enough bandwidth along the optic nerve to pass whole images. Since this isn't a discrete set of events, the idea of "interference" is meaningless. Hence the update rate of your TV (50Hz or 60Hz depending on where you live) doesn't cause 'beat frequency' problems with your visual system as it does when you point a cheap video camera at your TV. The idea of a "frame rate" for reality is even more disturbing. Again, there is no such thing - although I guess if you're forced to come up with something - Jayron32's explanation of the plank time is reasonable. But that's only the smallest measurable interval - because light cannot cross one planck length in less time than that and space is quantized in planck-lengths. I don't think it's the case that everything in the universe progresses one step at a time in perfect sychronism every 5x10^-44 seconds...although it starts to become a meaningless question. SteveBaker (talk) 16:40, 6 November 2008 (UTC)

I'm not sure it's entirely accurate to say "the universe is quantised in planck lengths". We simply don't know what happens on smaller scales, that doesn't mean that nothing happens. --Tango (talk) 18:03, 6 November 2008 (UTC)

Yes - that's true too...which makes it even less accurate to say that time ticks along at the planck time. SteveBaker (talk) 19:13, 6 November 2008 (UTC)

Well, at least it does, in that case, bear some parallels to the motion-picture-camera concept of framerate. When we view a motion picture, we don't know what is going on "between the frames". It could be nothing at all (ala stop-motion animation) or it could be something which is just cannot be recorded as happening (when the camera flicks off, the world doesn't flick off). Likewise, with Planck Time, its not that we can know for a fact that nothing happens in a time interval smaller than this, its just that we can't know what happens in that smaller interval; it is an imperfect analogy to "frame rate", but it works reasonably well, especially in answering the OP's question, and in demonstrating the false assumptions it makes. --Jayron32.talk.contribs 21:18, 6 November 2008 (UTC)

Yeah, the analogy almost works. The main flaw if that frames are set instances equally spaced and you see whatever is happening at that time. That means that an event taking 1/2 the time between frames could either be captured by a frame or fall inbetween two frames. With Planck time, there is no set beginning and end to each interval, so there is no concept of whether a short event happens between frames or not. --Tango (talk) 21:45, 6 November 2008 (UTC)

Indeed. A real film camera will have an adjustable shutter time - so you can either capture short "instants" of time spaced at some interval - or you can leave the shutter open for longer then very rapidly shut it, move the film on and get the shutter open again. This captures all of the action over an extended period - so almost none of the action is "missed" - but the frame is the average of all of the incoming light. Motion blur is the consequence of that. I'm not sure precisely what happens with planck time - but it's possible that it's more analogous to a long shutter time than an infinitely short one. The action would be a smeared statistical mush...which seems intuitively more like we'd expect with quantum theory kinds of events that are always somewhat fuzzy.

The singularity-less black hole

I had a brainwave one day while walking down the street for school that a black hole does not need to have a singularity! My idea was like this: in general relativity, time slows with an increasing gravitational field. Then, in a collapsing star, its mass will never be squeezed into zero volume because the collapse will also be slowed down infinitely when the mass is squeezed into the Schwarzschild radius! Maybe this is why general relativity breaks down in singularities, in the singularity, time goes to the infinites and complex numbers and the universe did not exist at that time! So, perhaps we have to change our definition of black holes into an object with density equal or larger to a certain density(precisely c^6/6G^3M^2 after calculation)! But i didn't use General Relativity. So can anyone who knows General Relativity calculate and tell me is it true or not, please? The Successor of Physics 07:58, 6 November 2008 (UTC)—Preceding unsigned comment added by Superwj5 (talk • contribs) 03:15, 6 November 2008 (UTC)

All objects inside the event horizon collapse to the singularity in finite proper time. The notion of things taking infinite time is an artifact of how things appear to an outside observer trying to use photons to watch someone fall into a black hole. See also black hole and gravitational singularity. Dragons flight (talk) 03:37, 6 November 2008 (UTC)

And to observe things, the best you can do is to use photons, and even gravity travels at c so it makes no difference between what you observe and the slowing of time. Check "http://www.geocities.com/angelto.geo/bhole/blackho.htm"(has changed) "http://www.relatividad.org/bhole/blackho.htm"out and you will know that you are wrong.The Successor of Physics 08:00, 6 November 2008 (UTC)

Somehow I doubt that geocities is the arbiter of all things astrophysics. — Lomn 14:07, 6 November 2008 (UTC)

On that density definition: An event horizon does not form if the mass inside the dense region is moving outward fast enough. That is by the way the trick to escape a black hole, even if you are already in. Blow it up! —Preceding unsigned comment added by 84.187.64.186 (talk) 16:20, 6 November 2008 (UTC)

Of course, the matter making up the black hole is under the same rules as you are, so if the black hole already exists you can't blow it up (other than waiting for Hawking radiation to do the job). You would have to impart the outwards velocity before the event horizon initially formed, which would simply stop the collapse. --Tango (talk) 17:41, 6 November 2008 (UTC)

A black hole is an area of a metric from which no timelike curve leaves. Blowing all matter apart *changes* the metric. There might be some principal obstacles to do this, but the preexisting event horizon is none. —Preceding unsigned comment added by 84.187.77.58 (talk) 08:32, 8 November 2008 (UTC)

Endocannabinoids and autism spectrum

Have endocannabinoids or their absence been implicated or ruled out as part of the mechanism of autism spectrum disorders? NeonMerlin 05:12, 6 November 2008 (UTC)

I don't think that research has been done (know anyone who has been doing their own research/self-medicating? ;) ). Mirror neurons, on the other hand, may play a role in autism. Check out Causes of autism. --Shaggorama (talk) 06:41, 6 November 2008 (UTC)

an imaginary history of time

I recently read A Brief History of Time and was underwhelmed, but curious about one chapter that seems to say: if time is real it has a singularity at the Big Bang, but if time is imaginary we can think of space-time as a smooth hypersphere – or was it the other way round? – and choosing one or the other is a matter of taste. Eh? As a layman not afraid of the occasional bit of math, is there something I can read that makes more sense of this? —Tamfang (talk) 05:42, 6 November 2008 (UTC)

You might enjoy Introducing Time if you're just looking for a quick, accessible read. --Shaggorama (talk) 06:38, 6 November 2008 (UTC)

This is probably heresy of the first degree, but I still haven't read ABHOT. However, what Steven's talking about is basically the choice of basis for your metric of spacetime. If you choose your time variable, t, to be defined in a "conventional" way, then that gives you one expression of the metric - in Minkowski space, you get $ds^{2}=dx^{2}+dy^{2}+dz^{2}-dt^{2}$ - which is just a flat, plain old Riemannian manifold. However, there's nothing stopping you from defining a new time variable, $\tau =it$, and it's fairly easy to show that the metric becomes $ds^{2}=dx^{2}+dy^{2}+dz^{2}+d\tau ^{2}$. Since tau is i times your original t, you can, if you want to, call tau "imaginary time". And other metrics will have similar transformations under such a change of variables. Confusing Manifestation(Say hi!) 22:23, 6 November 2008 (UTC)

what is the temperature of heat (not mainstream).

What is the temperature of pure heat (not mainstream science which says heat cannot exist in pure form). also, is it possible to extract pure heat in solid or gas form, or only liquid? (also not mainstream science persp). thank you! —Preceding unsigned comment added by 82.124.214.224 (talk) 07:17, 6 November 2008 (UTC)

Mu. Your question is nonsensical, since even you seem to grasp that "pure heat" isn't a thing. Heat refers to a type of energy. It is not an object and has no temperature. Dragons flight (talk) 07:40, 6 November 2008 (UTC)

Whats liquid heat look like?124.169.66.245 (talk) 08:40, 6 November 2008 (UTC)

Like this. DMacks (talk) 08:51, 6 November 2008 (UTC)

To pinpoint the first answer, let's see what heat is. Heat is kinetic energy, basically. Atoms in materials oscillate about their equilibrium. The rate of their oscillations is a measure of their temperature, and the overall amount of these microscopic kinetic energies in a piece of material is its heat. There is no kinetic energy other than the energy related to moving bodies. Heat isn't unique in that sense. It's the same issue. Second, there is no mainstream or any other streams from the point of view of physics, and there is no meaning to heat outside the realm of physics. This issue was debated centuries ago, when the notion of flogiston came up, but this possibilty is already over by now. Analogically, there is no meaning to sound outside the context of material as well, since sound waves too, are vibrations in air, liquid or solid. BentzyCo (talk) 09:56, 6 November 2008 (UTC)

I don't understand you guys, I clearly said I wasn't looking for the mainstream scientific perspective! I said it in the title. I said it in my first sentence. I said it in my second sentence. I guess I should have said it after "thank you" as well. As for the answers you guys gave me, I acknowledged them already in the question, saying "mainstream science [...] says heat cannot exist in pure form". So after I've already acknowledged your perspective, and explicitly asked for a different one, why bother to write all that? It's all in the heat article, or in the history of heat under 18th, 19th, and 20th centuries. Why spend time retyping an article?

To reiterarte, I asked a simple question, what is the TEMPEREATURE of pure heat, in liquid form, not from the point of view of scientists who say pure heat is not possible at all. Further, can pure heat be extracted in solid or gas form, or only liquid form -- again, NOT from the point of view of scientists who say pure heat is not possible. Answering hint: you might say 'there is no point of view in the world, held by a single scientist, pseudoscientist, crank, crackpot, or layman, according to which pure heat is possible', though in this case you'd better have a reference for this bold assertion. But if this point of view exists, then that's what I'm asking for -- so if you give an answer that is consistent with the idea that pure heat is not possible, you're NOT answering my question, but only retyping a wikipedia article. (Maybe you could better spend you time adding your thoughts to the heat article in that case?) —Preceding unsigned comment added by 82.124.214.224 (talk) 14:51, 6 November 2008 (UTC)

Temperature is a scientific measurement which relies upon a certain verifiable, falsifiable, universally accepted understanding of material physics. It is incompatible with this nonsense concept of "pure heat". Plasticup ^T/C 15:24, 6 November 2008 (UTC)

Your question cannot be answered because what you are calling "pure heat" is nothing more than nonsense that you made up. It is impossible for anyone to answer what the temperature of something in your imagination would be. Your should consider your insult about "Maybe you could better spend you time..." and realize that you could better spend your time asking questions that can be answered instead of nonsense about stuff you've just made up. -- kainaw™ 15:35, 6 November 2008 (UTC)

Put another way: you're proposing that such a things exists that we as mainstream-science people don't follow. So just what is "pure energy in liquid form"? DMacks (talk) 15:40, 6 November 2008 (UTC)

Red Bull? --LarryMac | Talk 15:58, 6 November 2008 (UTC)

If you ask a question on a SCIENCE desk - and demand non-scientific answers - you are going to get laughed at and soundly denounced as a person of very little brain (which is what is happening right now). The definition of the the word "temperature" and the word "heat" are such that you simply cannot have "pure heat" that's like a physical thing. That's an idea that came in with Phlogiston theory in the 1600's and was proven to be false (and subsequently abandoned) in about the year 1750. You ask for a reference for that - and I suggest you read our article about Mikhail Lomonosov and check the references at the bottom of that article. Even so - if you believed in phlogiston - I don't think your question made sense because even phlogiston didn't have a "temperature". Anyway - if you want an answer from a non-scientist then I suggest you call the Psychic Friends Network - because we can't answer such a nonsensical thing here.

Two and a half centuries of careful experiment has lead to the conclusion that heat is a property of the motion of atoms. The energy we attribute to heat is the kinetic energy of all of those particles bouncing around - and temperature is a measure of that. So when you look carefully at a sufficiently small scale, there is no such thing as heat or temperature - there is just motion. The concepts of heat and temperature are just handy shorthands for this. But that's the scientific answer (and also "The Truth") - evidently you'd prefer to be lied to...so I'll say that the answer is 147.23 degrees centigrade and you'll be just as happy - right?

SteveBaker (talk) 16:29, 6 November 2008 (UTC)

How can heat be a liquid? 216.239.234.196 (talk) 16:31, 6 November 2008 (UTC)

Maybe liquid heat is where liquid smoke comes from. -- kainaw™ 17:37, 6 November 2008 (UTC)

What would be our speed if none of us were here?

Your question is nonsensical and you even insulted people trying to correct you! If you want to ask a nonsensical question then don't ask it on the Wikipedia Science Desk! Please don't insult people trying to help you. You are certainly a person of a tiny brain.----The Successor of Physics 11:11, 7 November 2008 (UTC)

If I understand right, you're asking what (in a hypothetical world) absolute hotness might look like. Now, I could be silly and say [insert sexy movie star name here] embodies absolute hotness, but let's try to answer the question instead.

Initially, it seems like you're asking for the impossible, yes. You're asking for something which is measurable, like "speed" or "distance" or "gallons per second through a pipe", then are asking "what would absolute speed be like?", "what would absolute distance be like?", "what would absolute water flow rate be like?".

Normally, absolutes are the domain of religions. God is allegedly completely good, all-knowing, all-seeing, everywhere, every when, he is the absolute of heat but also of cold, blah blah blah... nonsense words that sound impressive.

But let's try absolute temperature. I think I remember from highschool that heat is from atoms jiggling. The faster they jiggle, the more heat there is. The more atoms you have with the jidggling, the more heat there is. That gif of the rattling things is a good description of heat. The more atoms you have per unit volume, jiggling faster, the more energy you have in heat form. So it's a function of speed and density.

So. Speed. Beyond a certain point, the atoms in a solid get so energetic, they can't keep structure, and they turn to liquid: the solid melts. And then, beyond even that, they fly apart, becoming a gas: the solid boils. Finally, even the gas breaks, as the atoms fall apart, and you get a plasma.

So, "absolute heat" will involve the elements moving at light speed, so it'll be be a plasma, I think. Even atoms couldn't exist in it. However, the denser something is, the more heat it can store, so, it'd have to be as dense as it can possibly be. A black hole. A singularity.

I think, then, "absolute heat" would give you a singularity with the bits inside it moving around at light speed. You couldn't get denser and you couldn't get faster. Except that there's nowhere in the singularity for the bits to move TO. So they'd have to move in synch, the whole singularity vibrating together.

That's the best I can do, anyway. Hope that helps you with your NaNoWriMo god of heat (am I right?) DewiMorgan (talk) 21:29, 8 November 2008 (UTC)

Heat is electromagnetic radiation that is within a certain range of frequencies. If the radiation falls on a solid physical object, it makes the atoms at the surface of the object quiver faster (assuming the body was relatively cool). The increased quivering is passed on to atoms deeper in the body (heat conduction). In the case of a gas or liquid, the atoms are free to move, so they move faster and quiver faster (convection currents can also occur). Thus when an object is hot its atoms quiver or move rapidly. But heat itself is electromagnetic radiation. One more point is that quivering atoms radiate electromagnetic heat, and an object becomes warmer or cooler depending on the net income-outgo of radiant heat.

BLASTing lots of short sequences

Hi,

I want to blast ca. 40,000 70bp (approx) sequences against a particular genome to see which of them are present in the genome. Does anyone know how I could go about this?

Many thanks

141.14.245.167 (talk) 09:16, 6 November 2008 (UTC)

Use an itty-bitty machine gun? --67.185.190.46 (talk) 22:51, 6 November 2008 (UTC)

(To 67.185): The original poster is referring to BLAST, an algorithm for aligning DNA or protein sequences. --NorwegianBlue ^talk 00:50, 7 November 2008 (UTC)

• I would do it the other way around and blast the genome against a large set of peptides. Or you could write a perl script to blast the different sequences... - Mgm|^(talk) 08:06, 7 November 2008 (UTC)

Textile Finishing

What is trubenising? —Preceding unsigned comment added by 203.153.35.130 (talk) 12:22, 6 November 2008 (UTC)

That word give only 90 Google hits. Are you sure that you have spelled it correctly? Plasticup ^T/C 15:33, 6 November 2008 (UTC)

Spelling with a "z" gets 210 ghits. Zain Ebrahim (talk) 16:19, 6 November 2008 (UTC)

Lamictal

One of the effects of a Lamictal overdose is seizures. Can someone please explain to me, in terms of like biology and pharmacology, how an anti-seizure medication can cause seizures? Thanks. —Preceding unsigned comment added by Jamlessness (talk • contribs) 14:12, 6 November 2008 (UTC)

One proposed mechanism (as far as I know there is no conclusive mechanism that is agreed by pharmacists) is that Lamictal stabilises neuronal membranes by inhibiting voltage-sensitive sodium channels and modulates presynaptic transmitter release of excitatory amino acids. My guess would be that an overdose of Lamictal destabilises the voltage-sensitive sodium channels once again and increases the quantity of seizures. —Cyclonenim (talk · contribs · email) 16:50, 6 November 2008 (UTC)

There are several potentially implicated mechanisms. Here is one article that discusses this. Axl ¤ [Talk] 11:01, 8 November 2008 (UTC)

let's try this again.

In a science-fiction alternate universe in which heat was a liquid of some kind that flowed from thing to thing, making it hot, was produced in exothermic reactions, etc, what would be the most plausible temperature for the liquid? If you insist, you can move this question to the humanity section. —Preceding unsigned comment added by 82.124.214.224 (talk) 16:27, 6 November 2008 (UTC)

Since you're talking about some imaginary universe you invented, you can make up whatever rules you like. Asking what's "plausible" doesn't make any sense. Friday (talk) 16:31, 6 November 2008 (UTC)

Are you asking because you're writing some kind of science fiction story? 216.239.234.196 (talk) 16:34, 6 November 2008 (UTC)

If this is for a science fiction story that you're writing, say it's temperature is infinite or that it's so high, it cannot be measured. 216.239.234.196 (talk) 16:41, 6 November 2008 (UTC)

Or, you could say it has negative temperature - I've always thought that sounds like something from sci fi. --Tango (talk) 17:48, 6 November 2008 (UTC)

Wow, you just blew my mind. 216.239.234.196 (talk) 20:51, 6 November 2008 (UTC)

Friday makes a good point, you cannot create an imaginary universe with different rules and then ask us to try and apply real universal laws to it. Why not just pick any temperature if you're writing a story? —Cyclonenim (talk · contribs · email) 16:42, 6 November 2008 (UTC)

I'm fairly certain your question as stated is incoherent. If this imaginary liquid is heat, how can it have a temperature? That's like asking what color is color. Heat is a property of matter, and I think the attempt to try to imagine a property of matter as a form of matter is confusing you. If heat were transfered in this way, the liquid itself wouldn't have a temperature because it imparts temperature. Any attempt to measure its temperature would just cause the thermometer to keep rising with continued exposure. But again, its your imaginary universe, so you can do what you want. If you like, you could just say "heat is only transfered by the exchange of a liquid of 1,000,000K" or something like that, but then you might have a hard time coming up with a reason why this liquid is the only way heat could be exchanged. --Shaggorama (talk) 16:45, 6 November 2008 (UTC)

See Caloric theory. This is not as wacky idea as it may sound, this was once the prevailing scientific theory of heat. You will likely receive some good insight by reading that article... --Jayron32.talk.contribs 17:52, 6 November 2008 (UTC)

Indeed, but I don't think that theory ever tried to give a temperature of the caloric. --Tango (talk) 17:56, 6 November 2008 (UTC)

In part because, as noted, the idea is incoherent. Caloric doesn't have a temperature. It is temperature. --98.217.8.46 (talk) 01:27, 7 November 2008 (UTC)

If you are inventing some 'thing' (a liquid in this case) to which you choose to arbitarily attach the label "heat" - what is the effect (in your imaginary universe) of molecules moving around very quickly? Is that also heat? If so - then it must be a different kind of heat than the kind that appears as a liquid. In such a situation, you'd be well advised to give the properties of your weird liquid a different name - because it's a different kind of thing than heat "really" is. If you claim that it's the SAME thing as the usual meaning - then your liquid has molecules that are moving - and it's not "pure heat" anymore. "Heat" is a word with a meaning. When you give it another meaning, you've just blown the relationship between "heat" and "temperature" because "temperature" relates to the ordinary (atoms moving around quickly) meaning of "heat". So now you're asking us how much of one thing relates to some other thing - when both 'things' are stuff that you've just made up in your head.

Simply forcing something to be true by defining it as true in an imaginary universe means that all connection with fact, logic and reason just got blown away. Without those connections, we can't connect the redefined meaning of "heat" in the context of your imaginary universe with the imaginary definition of "temperature" (which could easily mean "number of migrating swallows per cubic parsec" for all we know!). If you could define the meaning of your word "temperature" in the context of your re-definition of the word "heat" - then perhaps some self-consistent answer might emerge - but it's not the "real" answer because there isn't one.

SteveBaker (talk) 19:10, 6 November 2008 (UTC)

One of the problems with these sorts of "what if just this one thing were different" questions is that it's very easy to get inconsistencies. Scientific theory is constructed to be self-consistent, and changing one rule may make others absurd (in fact proving that a theory leads to contradictions is a major way in which both math and science work). You have to specify what sort of situations you want the new fictional theory to hold, and which you can safely ignore, in order for there to be some semblance of consistency. (And even then, someone will likely find a hole related to something you ignored.) - With that in mind, lets look at heat and temperature. If you take 1L of water, and add a given amount of heat, you raise the temperature. If you take half a liter, you only need half the heat. So it's not the total amount of heat that determines the temperature, it's the "density." If you could "distill" pure liquid heat, the temperature would likely depend on how concentrated you could get it. How much more caloric does 100 L of boiling water have than 100 L of water at freezing? 1 L? 1 mL? 1 nL? The temperature-as-heat-density could vary by orders of magnitudes. You'd have to take into consideration heat capacity as well, though. A given amount of heat applied to 1 L of water doesn't raise the temperature to the same amount as it does when applied to the same amount, either by mass or by volume, of air, metal, or even oil. You'd also need to think about heat of vaporization and heat of fusion. You have to add a lot of heat to ice at 0 C to get it to melt, and once it's melted, the temperature is still at 0 C. One potential dodge is to claim temperature as being the density of "free" caloric, and claim that a certain amount of heat binds to or reacts with the material when it melts/freezes. This can also explain away the heat capacity issue, if you claim that a portion of the caloric doesn't go to increasing the temperature, but binds/reacts with the substance. The temperature of your "pure" caloric would then be related to the hypothesized density, as well and the fraction which gets bound up. (You could even postulate that pure heat has a temperature of near absolute zero, if in your fictional world you say that in pure form caloric "binds to" itself, thus resulting in no "free" caloric, and thus a low "free" caloric density (temperature).) - As mentioned above, once you remove yourself from reality, you can make practically any answer "correct". -- 128.104.112.72 (talk) 19:19, 6 November 2008 (UTC)

In your imaginary universe the "temperature" of a thing might be defined as ([Amount of Liquid Heat] / [Mass of Object]) * [A Constant] = Temperature. If that's how the imaginary scientists in your imaginary world measure "temperature". Then the temperature of pure liquid heat would tend towards positive infinity because of the divide by zero.

Of course, this is all completely meaningless. If your imagination is different than mine, then your imaginary scientists may come up with a completely different formula. APL (talk) 20:08, 6 November 2008 (UTC)

About 42 degrees Q. CBHA (talk) 21:09, 6 November 2008 (UTC)

Why confine yourself to liquid? That's so mundane! Friction wears away the fabric of space letting the heat leak in from another dimension.  :-) Saintrain (talk) 21:36, 6 November 2008 (UTC)

Another dimension? Nonsense! The real answer is much more grim. Friction heat comes from the future. You see, in the far future they stave off the heat death of the universe by sending pockets of heat back in time to what we know as the present day, thus creating an energy gradient in their own time. APL (talk) 13:47, 7 November 2008 (UTC)

That would imply that the heat somehow 'wears out' or otherwise 'goes away' - if it doesn't then they just get it back again from the past and the problem is much worse. I'm also bothered by the fact that if heat is a liquid - we know it can flow through almost anything - that's why the outside of a hot kettle is...hot. So you can't contain it in anything...that would suggest that either this liquid is massless - in which case it should all just float off into space - or it has mass and it would all sink through the earth and sit at the center (which I'm guessing the proponent of this theory will say explains why the earth's core is so hot...although, sadly not why the moon doesn't also have a hot, molten core). There are just too many inconsistencies in a theory like this. It doesn't hold together at all. That's why the Phlogiston theory of heat (which is essentially what this is) was abandoned 250 years ago. SteveBaker (talk) 18:10, 7 November 2008 (UTC)

I HIGHLY recommend you guys search for all of the posts made by the OP's IP address across all the ref. desk boards. The combination of bullheadedness and misunderstanding, spliced with occasional genuine curiosity, is either genius or madness. NByz (talk) 03:56, 8 November 2008 (UTC)

I answered this in your above post, but I'll have another bash at it. The most plausible to me would be that it would have no easily-measurable heat: heat would be an effect of it, not an attribute of it. However, the liquid could get "used up", converted into energy by being absorbed into the thing it was heating, as fast as it could absorb it. Insulators would be things that were very bad at absorbing the heat, which is what you'd have to use to hold the stuff in. If you dipped a thermometer into it, the thermometer would just max out, until the "heat" was all used up. If the thermometer could not absorb all the heat, it would melt, and even boil (both "state changes" involve releases of energy, so would absorb some of the heat liquid). Kinda like why, in the real world, temperature readings are taken "in the shade" - if you take a temperature reading in the sun, you will only measure your thermometer's ability to absorb heat. If you had a bottle of heat-liquid, you'd measure how much you had not in degrees, but in degree-litres or somesuch - the amount you could heat a litre of water with it. Another reasonable thing to measure it in would be watts: people would quite easily say "I've a bottle with 50 kilowatts of heat in". Dilute heat might raise a thermometer to less than the max, maybe, though I don't know what you could dilute heat with... unless you also have a "cold" liquid.

Guess I was wrong about the NaNo God then :) DewiMorgan (talk) 21:42, 8 November 2008 (UTC)

Iron content in apple juice

Not for medical advice or anything but I've been juicing 3 more or less mid sized apples and consuming the juice everyday for the last week or so. Is this amount large enough to induce iron toxicity related disorders? Leif edling (talk) 17:38, 6 November 2008 (UTC)

According to our apple article, 100g of an apple (not juice) has about .12mg or 1% of your suggested daily intake. So it's very very doubtful. -- MacAddct1984 ^{(talk • contribs)} 17:48, 6 November 2008 (UTC)

According to nutrition data, a single large apple has 0.3mg of iron. The recommended dietary allowance is 8mg. So, 3 apples is less than 1mg. Over a week, it is less than 8mg. So, over a week, you are getting less than the RDA for iron. -- kainaw™ 17:45, 6 November 2008 (UTC)

Just saying it isn't a request for medical advice doesn't make it so. "Is this activity I'm doing likely to cause a medical problem?" is a request for medical advice. Our article on apples has the nutritional information including the percentage of recommended daily consumption of iron, see Apple#Health benefits. If you want more than that, ask a doctor. (And you should probably verify the source of the nutritional information as well.) --Tango (talk) 17:47, 6 November 2008 (UTC)

Vox pop here, but a tv nutritionist dumbed it down this way, that it takes five apples today to get you the iron that an apple a day in the 50s gave you. Make of it what you will, Julia Rossi (talk) 21:34, 6 November 2008 (UTC)

Some apples these days are so anemic, they're not even red. —Tamfang (talk) 03:03, 7 November 2008 (UTC)

Apple juice has 0.1 mg of iron per 100 ml according to my nutritional values book. Graeme Bartlett (talk) 21:38, 7 November 2008 (UTC)

It might also be worth pointing out that apples have a little bit of vitamin C, which enhances iron absorption. On that count, though, you might want to be more concerned about oranges. Not that apples and oranges are comparable in any way. SDY (talk) 21:45, 7 November 2008 (UTC)

Too late for a word, I guess, but, referring to Tango 's objections, the words i opened my question with were meant as a sort of a disclaimer to say that if i took the opinion by people replying to my question and it harmed me , i would have none to blame but my foolish self. I don't understand (dont know, rather) why medical advice with proper disclaimers is not allowed on Wikipedia.Leif edling (talk) 16:53, 12 November 2008 (UTC)

Proton Proton Chain

In proton proton chain, gamma ray is gradually released. But is there any fixed energy limit of this ray (i.e range of frequence) or is it same as the common gamma ray?117.201.97.211 (talk) 17:38, 6 November 2008 (UTC)

There is no "common gamma ray" energy. The energy is certainly fixed by conservation of energy. Unfortunately the standard equations for showing fusion and fission reactions don't really show you how the energy is apportioned up in the constituent products. For example, in the standard DT reaction, we see it as this:

D + T = 4He + n + 17.6 MeV

But really the "energy" side of the equation is not just some magical spark (as it is usually depicted, and as it is displayed in the awful illustration at the top of the nuclear fusion page), but in the energy of the products (the neutron flies off with a force of 14.1 MeV, the alpha particle flies off with a kinetic energy of 3.5 MeV). --140.247.243.184 (talk) 18:31, 6 November 2008 (UTC)

Colour of the sky

Two questions:
1. Why is shorter wavelength (i.e. bluer) light subject to more scattering in air than longer wavelengths?
2. Regarding why the sky is bluer overhead than at the horizon, I had a look at this but I still don't understand why the increased scattering of light coming from the horizon makes it lighter.
Thanks, Zain Ebrahim (talk) 17:58, 6 November 2008 (UTC)

Have you seen Rayleigh scattering and diffuse sky radiation? Dragons flight (talk) 18:21, 6 November 2008 (UTC)

Thanks. The external links in those articles helped answer my questions. Zain Ebrahim (talk) 18:11, 9 November 2008 (UTC)

Capsaicin fatality

No, I'm not asking for medical advice. ;) This is just curiosity. There seems to be a large contradiction between the Hot sauce article, in which it's stated that the "heat" caused by Capsaicin is a harmless chemical reaction, and the Capsaicin Toxicity, it's now claimed to be potentially fatal. Is Capsaicin fatal in large amounts because of the body's reaction to it? --Sarcasticninja (talk) 18:44, 6 November 2008 (UTC)

Pretty much everything is toxic in large enough quantities. --Tango (talk) 19:54, 6 November 2008 (UTC)

Indeed, you can even be poisoned by pure water. Capsaicin is harmless in any quantity you are likely to consume in the course of normal eating, even from the dreaded habanero. That doesn't mean that, in large enough quantities, it cannot get toxic. --Jayron32.talk.contribs 21:11, 6 November 2008 (UTC)

My back of the envelope calculations: The world record Naga Jolokia pepperhas about 620 mg of capsaicinoids while a jalapeno of the same weight has about 1.5-5 mg. The lethal dose in mice 47.2 mg/kg, that's about 3300 mg in a 70 kg human. So 5 Naga Jolokia's or 2200 jalepenos could be lethal (extremely rough numbers). The heat is caused by a harmless reaction between your pain receptors in your tongue and the capsaicin, but it has many other effects on your body which taken to extremes could be harmful. -- Mad031683 (talk) 22:33, 6 November 2008 (UTC)

Asuming, of course, that mice toxicity is translatable to human toxicity. There is likely no reason to believe it should be... There are many things toxic in small amounts to one species which are relatively harmless to others (i.e. theobromine toxicity in dogs; humans are not nearly as effected by this chemical.) There is probably little correlation between the LD50 for mice and the LD50 for humans for any given compound... --Jayron32.talk.contribs 23:12, 6 November 2008 (UTC)

While LD50 is hard to measure in humans (the inbred ones don't live in my state :-) ), here is an example of pretty good correlation between human model (in vitro culture) tox data and mouse data:[2]. Admittedly, this is outside my area of expertise, but it seems as though you might be stating the case against animal models for drug toxicity a little too strongly. Any data? --Scray (talk) 00:39, 7 November 2008 (UTC)

Look at this data, culled from our article on Theobromine poisoning:

Animal	Oral toxicity (mg/kg)
	TDLo	LD50
Cat		200
Dog	16	300
Mouse		837
Rat		1265

Assuming that you DON'T have LD50 data for humans, which one of these would you use for a human analog? There's a 6 fold difference in this random sampling of mammals; there is no reason to assume that humans are a closer fit, metabolically, to any one of these mammals. Theobromine is an alkaloid like capsaicin is, I don't expect the toxicity data for that to be any more reliable that theobromine vis a vis animal vs. humans... --Jayron32.talk.contribs 01:31, 7 November 2008 (UTC)

Variation of 6-fold is not that bad. As pointed out earlier in this exchange, the variation in capsaicin levels per pepper are probably comparable, and for many drugs the therapeutic index is much larger than that. These tox data could provide a fair start for dose-finding studies in human trials of a drug (certainly much better than wondering whether the human LD50 is likely to be closer to 0.001, 0.1, 10, or 1000 mg/kg). --Scray (talk) 03:54, 7 November 2008 (UTC)

Cat Scan of Serial Killer's Brain

What would a cat scan of a serial killer's brain look like? Meaning besides those who are not serial killers? --Emyn ned (talk) 21:30, 6 November 2008 (UTC)

Computer tomography of a serial killer's brain would be the same as a normal person's brain. The difference is psychological, not physical. —Cyclonenim (talk · contribs · email) 22:26, 6 November 2008 (UTC)

Usually psychological. I'm not sure about serial killers, but I know some mass murderers (such as Charles Whitman) where later discovered to have brain tumors and similar physical ailments affecting their mental stability. Dragons flight (talk) 22:48, 6 November 2008 (UTC)

• See post hoc ergo prompter hoc. Charles Whitman was discovered to have a brain tumor, and he was also mentally unstable. Not necessarily causitive in his case... --Jayron32.talk.contribs 23:08, 6 November 2008 (UTC)

Actually - we can do one better - and you can see! The Visible Human Project took a corpse, encased it in gelatin - froze it solid and sliced it a fraction of a millimeter at a time - taking photographs at each stage - then reassembling thousands of photos into a 3D computer model. This is better than a CAT scan - you can see exactly what every part of the body looked like without having to be able to interpret the peculiar appearance of CAT scan data. As it happens, the body they used was Joseph Paul Jernigan who was a murderer (OK, only ONE murder - but a pretty brutal one). The project did this to two corpses - one male and the other female. The woman had died of a heart attack - and (as far as we know) lead a more or less blameless life. Comparing the two reveals only the expected differences between men and women.

If you have a strong stomach - you can view the results on many web sites, this one, for example. (Don't say I didn't warn you!) SteveBaker (talk) 23:05, 6 November 2008 (UTC)

I would not be at all surprised to find some structural differences between people whose behavior is normal and those whose behavior is grossly abnormal, like serial killers. WE know that brain damage can cause aberrant behavior, like those with bullet wounds to the brain or those who were the victims of psychosurgery. Similarly brain trauma from alcohol or the effects of Altzheimers, strokes, or abnormal intracranial pressure cause abnormal behavior. Edison (talk) 00:41, 7 November 2008 (UTC)

Unfortunately, such descriptive data does not always work in reverse. Merely because trauma can cause abnormal behavior does NOT mean that abnormal behavior is always caused by trauma. Some people make horendously bad choices, and there isn't always a "cause" for it... --Jayron32.talk.contribs 01:35, 7 November 2008 (UTC)

I would say that people who behave bizarrely are a mixture of those with detectable brain trauma or abnormalities and those without presently detectable brain abnormalities (bad life experiences, chemical imbalances). Edison (talk) 03:41, 7 November 2008 (UTC)

Or sometimes, they are just assholes. When somebody acts in ways that we find incomprehensible, we seek ways to excuse the behavior as beyond their control. See the idea of locus of control. Some people understand that all of their actions are the result of their own consious choosing, others wish to blame every choice they make on factors out of their control. --Jayron32.talk.contribs 04:50, 7 November 2008 (UTC)

The difference is "psychological, not physical"? Well, physical differences in gross structure can manifest as psychological differences. Steve Pinker writes in The Blank Slate, "convicted murderers and other violent, antisocial people are likely to have a smaller and less active prefrontal cortex, the part of the brain that governs decision making and inhibits impulses." --VectorField (talk) 07:40, 13 November 2008 (UTC)

Why don't birds on the power lines get electrocuted

I know I read about this in wikipedia but for the life of me could not figure out how to search for the question or the answer in order to locate that page again. —Preceding unsigned comment added by 12.34.246.35 (talk) 22:08, 6 November 2008 (UTC)

By searching 'bird power line site:wikipedia.org' (Google's "site:" filter is great!), I quickly found this discussion from last June. — Lomn 22:12, 6 November 2008 (UTC)

Because the birds do not complete an electric circuit. In order for electricty to flow, electrons need a complete path either to the source from whence they came, or to the ground. If this condition isn't met, there is no electricity. --Jayron32.talk.contribs 22:15, 6 November 2008 (UTC)

Which is why large birds (eagles, condors, and the like) can get electrocuted: they're big enough that when one lands on a telephone pole, they're likely to touch more than one wire. --Carnildo (talk) 22:56, 6 November 2008 (UTC)

The electricity has a choice - it can either travel a couple of centimeters up one leg of the bird - across it's body and a couple of centimeters back down - or it can take the "short cut" across 1cm of copper. Since electricity flows more easily through copper than through bird - it goes the quick, easy way...and essentially none of the electricity flows through the bird. If the wire midway between the bird's legs were to suddenly snap - the bird would be fried in very short order! If the bird were in contact with the ground and with the wire (a bird with L-O-N-G legs!) then the electricity would find it easier to go through the bird to get to the ground than to go all the way to the far end of the wire, do all the work to drive your PC (or whatever) - then go through your house wiring down to the ground. SteveBaker (talk) 22:54, 6 November 2008 (UTC)

Good answers, but this video is really great for showing what's going on: [3]. --Sean 00:26, 7 November 2008 (UTC)

A bird would get a nasty shock if it landed on a line at a very high voltage, like 345kv or 765 kv, since there would be capacitive current flow with perhaps a big spark when it got close to the wire. The current flow would not be nearly as large as if the bird completed a circuit to ground or to another conductor, so the bird should not get burned up. But I only see birds perched on lower voltage lines. like 12 kv or 4 kv. Not sure about 34 kv. Edison (talk) 00:36, 7 November 2008 (UTC)

Bird on a wire [4]--GreenSpigot (talk) 08:36, 7 November 2008 (UTC)

Ringnecked Parakeet and Alexandrine Parrot

Can these breed together to produce healthy offspring? —Preceding unsigned comment added by 84.71.86.42 (talk) 23:03, 6 November 2008 (UTC)

The answer seems to be yes. [5]

A more extensive search will probably give you some more reliable sources. As we discussed in a previous post [6] hybrids are generally frowned upon by conservation experts and most breeders. Since the Alexandrine Parakeet/Parrot seems to be declining in numbers in the wild, breeding with another Alexandrine would probably be preferable. Lisa4edit (talk) 06:09, 7 November 2008 (UTC)

Negative calorie food

Is there any scientific reason why negative calorie foods can't be artificially produced? Or even just negative calorie additives — e.g. a flavorless substance that would burn calories, that could be, say, added to a cheeseburger to make the net calorie gain only a handful or so? Could one describe what characteristics such a substance would have on a chemical or structural level? It seems to me that such a product could have a variety of medical benefits for the very obese, especially those who are obese to the point that the possibility of an exercise regimen is severely diminished. This would not be the same thing as a substance that was simply zero calories, of course (which seems comparatively straightforward—anything that can't be digested, among other things!). --98.217.8.46 (talk) 23:36, 6 November 2008 (UTC)

TANSTAAFL... likely many of these additives could have undesireable side effects... --Jayron32.talk.contribs 01:21, 7 November 2008 (UTC)

Well you can say that about all additives, even just calorie-free sweetners. Doesn't mean that the positive effects can't outweigh the negative ones. --98.217.8.46 (talk) 13:52, 7 November 2008 (UTC)

There's always Olestra! A little indigestion can't hurt, right? Orlistat is also sort of along the same lines. Both target fats, which are the densest calories, though simple carbohydrates (e.g. sugar) are probably a bigger demon when it comes to empty calories. Chemically or structurally, these substances don't "remove the calorie value", they impair the body's ability to digest the food and turn it into energy (calories). Most normal "negative calorie" foods don't lack calories, they just have calories in a form (e.g. cellulose) that humans can't digest. They're negative only in the net negative sense that you use more energy digesting them than they provide in nutrition. Truly negative calories would mean negative mass: it's not... likely. SDY (talk) 06:41, 7 November 2008 (UTC)

See, what I'm interested in is not thing that can't be digested (which I already indicated above). And I'm not indicating negative mass. What I'm indicating is something that would actually, through the process of digestion, burn a significant amount of calories per mass of food eaten. --98.217.8.46 (talk) 13:52, 7 November 2008 (UTC)

Cestoda is an all-natural calorie-burner. Taken orally, it consumes many of the calories the person ingests. It's widely available in some parts of the world, but with some side-effects, including vitamin deficiency and tissue damage. EverGreg (talk) 12:01, 7 November 2008 (UTC)

Yeah, well... I didn't mean parasites. --98.217.8.46 (talk) 13:52, 7 November 2008 (UTC)

I think to answer this question, we'd need to know what the processes are that use up the most calories in the digestive process. If it's just moving stuff through your gut, then a small rock is a good slimming aid. If it's chewing it, then chewing gum. If it's some chemical reaction, then is there anything that can instigate that chemical reaction without providing calories? Would swallowing lumps of pure cellulose help? Sawdust? Hard to tell without understanding the mechanism. DewiMorgan (talk) 21:53, 8 November 2008 (UTC)

I recall reading a humourous short article (found it: link) about ice which pointed out that it takes more energy to melt and heat ice up to body temperature than you get from consuming it (since it contains no calories). As a result of this, the article claimed, you could totally nullify the calories in a can of Coke just by adding 148 ice cubes to it. Maelin (Talk | Contribs) 15:56, 14 November 2008 (UTC)

Muscle density

Related to a question asked before about chimp strength. They are much smaller than humans, but much stronger. Is this due to the density of their muscles? Are our muscles just bulky, but not very dense? I also read that humans have greater endurance than most other apes. Do animals with dense muscles have less endurance or is endurance due to other factors like lungs, blood flow, etc? 98.221.85.188 (talk) 23:39, 6 November 2008 (UTC)

Don't forget the knuckles. You might enjoy this thread[7] where quotes The Straight Dope[8] gives: In tests at the Bronx Zoo in 1924, a dynamometer--a scale that measures the mechanical force of a pull on a spring--was erected in the monkey house. A 165-pound male chimpanzee named "Boma" registered a pull of 847 pounds, using only his right hand (although he did have his feet braced against the wall, being somewhat hip ... to the principles of leverage). A 165-pound man, by comparison, could manage a one-handed pull of about 210 pounds. Even more frightening, a female chimp, weighing a mere 135 pounds and going by the name of Suzette, checked in with a one-handed pull of 1,260 pounds. ... In dead lifts, chimps have been known to manage weights of 600 pounds without even breaking into a sweat. A male gorilla could probably heft an 1,800-pound weight and not think twice about it.

So, at least knuckles, muscle mass and density, and swinging through the trees all day long possibly. Don't be fooled by that low slung posture when on the ground... Julia Rossi (talk) 05:05, 7 November 2008 (UTC)

What's the trade-off? Evolution would not have stripped us of that strength without giving us something in return. Plasticup ^T/C 06:19, 7 November 2008 (UTC)

Well, you can use food to build muscles, or you can use food to build brains. SDY (talk) 06:43, 7 November 2008 (UTC)

The trade-off? Humans can organize and strategy and develop novel solutions to problems, and coordinate their actions as a group, and build and utilize tools, and improve upon prior advances in ways that no other animal has been shown to do. I'd take a good human brain over the ability to dead-lift 600 lbs any day. After all, why use your own muscles when you can devise a simple lever or pulley to allow you to lift that weight easily... --Jayron32.talk.contribs 17:52, 7 November 2008 (UTC)

These are not related to our muscles. Plasticup ^T/C 06:13, 8 November 2008 (UTC)

First, we didn't get "stripped" of strength. We evolved from frail, little, monkey women. We, and our chimps and gorilla cousins, grew strong later. They grew stronger than we did. Mmmmm. Monkey women.

Second, and with respect, and not to draw too fine a point, but No! No! No! No! No! There are no trade-offs. Evolution is not a process, it doesn't happen in real time and it's not planned. Evolution is what we call the result of individuals reproducing or not. Very few two-foot men 'cause they can't reach the gas peddle; very few nine-foot men 'cause they can't fit behind the wheel. So men tend to be around five-six foot 'cause cars get the girls. That's it. Saintrain (talk) 19:50, 8 November 2008 (UTC)

Endurance, speed, and the ability to walk upright for long periods, among other things. --Carnildo (talk) 21:48, 7 November 2008 (UTC)

Can you be more specific? Are we talking about a different type of muscle? A different configuration? Where can I find more information on this? Plasticup ^T/C 06:13, 8 November 2008 (UTC)

Yes, humans have more endurance, in terms of running, than all other primates (citation Bramble, D.M., Lieberman, D.E. 2004. Endurance running and the evolution of Homo. Nature, Vol 432, November 18, 345-352).--droptone (talk) 12:35, 7 November 2008 (UTC)

The strength of limbs can change radically with the attachment point to the bone. It is a simple lever effect, which gives the usual tradeoff between speed and force. I don't know if that is really the reason, but it fits the data and does not need any biological miracles. A large variation in the structure of muscles between two closely realted species of ape sounds rather improbable. —Preceding unsigned comment added by 84.187.77.58 (talk) 08:49, 8 November 2008 (UTC)

Uranus and neptune surface temp

Which blue planet is colder is it Uranus and Neptune. Those two planets is identical, by blue colors, 4 times bigger than Earth, so would they have the same surface temp, average for both is -210 C or -350 F. Some say Uranus is colder, some say neptune is colder becasue uranus is hazier.--FRWY 23:54, 6 November 2008 (UTC)

Planets are not subject to the same blackbody radiation calculations that stars are; their color is not a product of their surface tempurature. The color is likely solely a result of their atmospheric composition. Their surface temperature is likely subject to a number of factors, including distance from the sun, local greenhouse effect, peculiarities of atmospheric chemistry, internal radioactivity in the planetary core, etc. etc. --Jayron32.talk.contribs 01:19, 7 November 2008 (UTC)

See Uranus (−224 °C) and Neptune (−218 °C). By reading the introductions of both articles, filtering for the right information and then engaging my enormous reasoning capabilities I can tell you that Uranus is colder than Neptune. The planets' colors are irrelevant. Plasticup ^T/C 06:23, 7 November 2008 (UTC)

What's the margin of error for those numbers? 6 degrees isn't a big difference. The variation between different times and places on each planet will be more than that. I think it's probably more accurate to just say they are about the same temperature. --Tango (talk) 10:22, 7 November 2008 (UTC)

November 7

Properties of Water

I was wondering how one may define wet in terms of water and more specifically, would water be classed as wet? For example, something soaked in water would be defined as wet, but would water(or any liquid) itself be classed as wet? 86.9.14.125 (talk) 00:17, 7 November 2008 (UTC)

Wet means covered, soaked with, infused with... a liquid. Liquids are, by definition, covered/soaked/infused with liquids - so they are wet. -- kainaw™ 00:52, 7 November 2008 (UTC)

It's to do with surface tension - and the affinity of water for whatever substance it's trying to wet. "Wet" basically means having a super-thin layer of water on whatever touches the water. If you put your hand into a bucket of dry sand - most of the sand falls off when you take your hand out. With water - you put your hand in the bucket and when it comes out, it's covered in a thin layer of water. That's not true of all liquids - mercury (for example) is a liquid that doesn't wet things at all. If you were to pour some mercury onto your hand, it would flow off and essentially none would remain there. So that's an example of a non-wet liquid. But it's really not that simple - there are surfaces that water doesn't wet - the reason we wax our cars is to alter the affinity of water for the surface and to cause the surface tension to cause water to make little droplets that roll off the car easily. The waxy metal doesn't really get wet - when a water droplet rolls away - the metal underneath is dry. Putting detergent into water lowers the surface tension and lets it wet things that it would ordinarily be unable to...so use soapy water to wash your car. Use plain water for the final rinse to wash off the soapy water and replace it with high-surface tension water that'll bead up and roll off easily.

SteveBaker (talk) 05:15, 7 November 2008 (UTC)

Everyone probably knows this, but mercury is poisonous and can be absorbed through the skin, so don't pour it on your hand. --WikiSlasher (talk) 10:00, 7 November 2008 (UTC)

Yes - that's true. Sadly (or perhaps not), when I was learning chemistry in high-school, this unfortunate fact was not realised - so I've done the experiment many times...it's a great deal of fun - right up to the point where the brain damage kicks in. I recall the year the rules changed...we went from asking the teacher to let us have a half teaspoonfull to play with (it's fun to whack a drop of it with a ruler and watch it "shatter" into tiny little perfect spheres with a mirror surface - that you can push back together again quite easily)...to the day someone broke a thermometer and the building had to be evacuated for an hour while the hazmat crew came in and cleaned it up. Anyway - you may have to take my word for it - but mercury isn't "wet" despite being a liquid...and it has these weird upside-down meniscus's when you pour it into a glass container. (ie when the surface of water meets glass, the water bends up to 'embrace' the glass - but mercury curves downwards as it attempts to avoid contact as much as possible. Mercury is also insanely heavy...somehow your brain just can't adjust to the fact (which may have something to do with that brain damage thing!) - and it always seems very 'alien' stuff. SteveBaker (talk) 18:03, 7 November 2008 (UTC)

Photsensitivity and Effects of UVA Light on Copper Sulfate Solution

My research has shown that a photosensitive jelly-like resin of micromolecules that are exposed to UV light fuse into long cross-linked molecules (polymers). In other words went from mushy to hard.

The same thing with gel use in dentistry and artifical nails. A powder and liquid are mixed, brushed on and "harden" when exposed to UV. They no doubt crystalize.

Based on my earlier assumption, if these things are photsensitive to the effect of UV, wouldn't a solution of copper sulfate be effected by UV (black light/uva). I believe the effect would either accelerate growth and/or crystal size or structure. Two previous response weren't sure of any or little effect.

Any insight on some sources I could consult?

Thank you again,

JM —Preceding unsigned comment added by 206.66.221.83 (talk) 00:53, 7 November 2008 (UTC)

This is not necessarily crystalization. UV light causes increases in polymeric cross linking, which is what happens in the resin. From our article on cross linking, "Cross-linking can also be induced in materials that are normally thermoplastic through exposure to a radiation source, such as electron beam exposure, gamma-radiation, or UV light.". This process is not like crystalization. This is comparing apples to oranges. I am not saying that UV light will not effect crystalization of copper sulfate, indeed you should probably do a controlled experiment to find this our for yourself, though I speculate (see the answer to this same question above) that it will not. The crosslinking process and the crystalization process are entirely unrelated to each other, and you cannot draw parallels between them. --Jayron32.talk.contribs 01:13, 7 November 2008 (UTC)

BTW, if you are looking for some help on crystalization in general, perhaps Arnold L. Rheingold is someone you should attempt to contact. He is, perhaps, the nation's foremost crystalographer and may have some insight into this problem... --Jayron32.talk.contribs 01:15, 7 November 2008 (UTC)

Well, I also conjecture that UV light will accelerate crystallization for a simpler reason. Perfecting the symmetry and shape of the crystals aside, if the evaporation rate of the solvent (pure water in this case) is increased, then the rate of growth will increase, correct? Based on this, and that shorter wavelengths have more energy, I would think that the crystallization would indeed be accelerated (against growth under, say, visible light) because more energy means more heat, and more heat means a quicker rate of evaporation. Am I correct to think of it in such a way?

Again, insight is much appreciated.

Thanks,

JM —Preceding unsigned comment added by 69.251.231.30 (talk) 04:31, 7 November 2008 (UTC)

Not necessarily. Take for example the fact that microwaves cause water to heat up very rapidly, and microwaves are LOWER energy than visible light. There is not a simple "higher energy causes materials to heat up faster" correlation. There is no reason to suspect that UV light at the same intensity as light in the visible spectrum is unlikely to cause any changes in the temperature or evaporation rate of the water. I'm not denying that you may find a change in crystal growth under UV light; however given my understanding of the processes involved, I do not expect it, unless of course I can see data. Data means either find someone who has done this experiment, or do it yourself. --Jayron32.talk.contribs 04:45, 7 November 2008 (UTC)

Interesting, though could you elaborate (thoroughly, if possible, for I am oblivious in this topic) as to why increased energy would not accelerate the solvent's rate of evaporation? And yes I shall conduct the experiment sometime, and I'll report my findings.

Thanks very much, as usual I greatly appreciate your responses.

JM —Preceding unsigned comment added by 69.251.231.30 (talk) 03:20, 8 November 2008 (UTC)

It has to do with modes of energy transfer. Heat is merely molecular motion; faster molecules contain more heat than slower moving molecules. Photons do not usually, in-and-of-themselves, have sufficient momentum to move an entire atom or molecule, and thus do not actually cause molecules to move faster. Photons can cause electrons to move; but at this level of motion, quantum mechanics takes over, and we aren't dealing with a nice intuitive Newtonian world anymore, and quantum mechanics doesn't really cover molecular motion in what we conventionally understand as heat.

The reason microwaves are able to heat water is because of something called dielectric heating. Basically, polar molecules like water can be set "spinning" by the passing waves, and this spinning increases the molecule's kinetic energy, thus heating up the bulk substance. The deal is, in order for this process to work, the wavelength of the light energy has to be "tuned" to the size and shape of the molecule it is working on. Its sort of akin to resonance, in the sense that only specific wavelengths of light will set the molecule spinning. For water, this wavelength is about 12 centimeters, in the microwave range. Other wavelengths simply wont have the effect of heating up the water. Think about it; you can sit a bowl of water in sunlight for hours, and it won't ever boil. It will reach roughly air temperature, but it will never boil. Put it in a microwave oven (and remember, microwaves are longer wavelength than visible light, and thus lower frequency, and thus lower energy), and it will boil in 3 minutes.

The deal with UV light is that it can effect all sorts of chemical processes, because UV light is of an energy necessary to begin to break covalent bonds inside of compounds. However, it has very little effect on other kinds of bonds, specifically the sorts of intermolecular forces that keep water in a liquid state aren't particularly effected by UV light. Also, the sort of ionic bonding that occurs in copper sulfate crystalization wouldn't seem to be particularly susceptible to UV radiation. If you doubt this reasoning, do the experiment. You said you had some blacklights; put a bowl of water in a box with a standard fluorescent bulb and another in a box with your blacklight. Monitor the temperature of the air and of the water in each (evaporation rates will be higher in warmer temperatures, and both lights will generate some heat just due to electrical resistance). If you see greater evaporation in the box with the black light (accounting for any differences in air temperature between the boxes) than you have proved me wrong... --Jayron32.talk.contribs 03:47, 8 November 2008 (UTC)

Ok, thank you very much for that explanation. Two more questions: what are some examples of compounds that could be effected by UV light, and could you specify where I could find information about the breaking of covalent bonds by UV light? I have been searching for books and sources on the internet but have not been able to find much about that.

Thanks,

JM —Preceding unsigned comment added by 144.126.9.247 (talk) 23:02, 8 November 2008 (UTC)

See this google search. I didn't open many of them myself and look that hard, but in the first page of the search, you can see phrases like "The shorter wavelengths or ultraviolet portion of the sunlight spectrum are able to break most covalent bonds..." and "Ultraviolet radiation is powerful enough to break many covalent bonds. Alone it can degrade PCBs, dioxins, polyaromatic compounds, and BTEX (1)." and "Ultraviolet light with a wavelength of 266 nm is capable of breaking the C–C and C–H covalent bonds,...". If you search these more thoroughly, you may be able to get more information about the mechanisms involved. If you need any more help, just ask away! --Jayron32.talk.contribs 01:09, 9 November 2008 (UTC)

Yes that helps me a lot, thank you. While most of the pages I searched through in the Google search you provided didn't go into much detail, it has given me the topic I can go research in a library; bond fission. That aside, could you suggest some sort of easy to obtain compound that has covalent bonds (and can be used as the solute in crystallization through precipitation) which could be broken by UV light, since as you said copper sulfate would not be vulnerable in this way.

JM —Preceding unsigned comment added by 69.251.231.30 (talk) 02:43, 9 November 2008 (UTC)

Table sugar, aka Sucrose, can be crytalized quite easily (sugar crystalized by evaporation is often called rock candy ) and it is a covalently bonded substance. UV light could reasonable be expected to degrade the sucrose molecule, quite likely into fructose and glucose. In fact, the addition of high fructose corn syrup to fudge helps keep large crystals from forming and keeps the fudge a smooth texture; I would imagine that if UV light could be used to generate fructose in situ that would have a similar effect. --Jayron32.talk.contribs 03:05, 9 November 2008 (UTC)

Well, that is all I need to know for now. If I have more questions later on I'll post an entirely new question. You've been a great help, and I thank you for it again.

JM —Preceding unsigned comment added by 69.251.231.30 (talk) 06:56, 9 November 2008 (UTC)

Extinct gull species

Does the current fossil record indicate the existence of extinct gull (or 'proto-gull') species larger than the Great Black-backed Gull? --Kurt Shaped Box (talk) 00:56, 7 November 2008 (UTC)

Only one comes to mind... ;-) --98.217.8.46 (talk) 14:06, 7 November 2008 (UTC)

MWAAAAAK! ;) --Kurt Shaped Box (talk) 20:15, 7 November 2008 (UTC)

Advancing human evolution

What can I do to help advance human evolution, or failing that, advance the evolution of other promising species? NeonMerlin 00:58, 7 November 2008 (UTC)

Genetic engineering for the short term. See technological singularity for the long run. 98.221.85.188 (talk) 01:06, 7 November 2008 (UTC)

Have lots of nookie; encourage all others to do the same? --Jayron32.talk.contribs 01:07, 7 November 2008 (UTC)

Won't that contribute to overpopulation? And isn't overpopulation something that a sufficiently evolved sentient species should be able to avoid? NeonMerlin 03:59, 7 November 2008 (UTC)

Depending on your genetic contribution, the best thing may be to avoid the nookie. Plasticup ^T/C 06:29, 7 November 2008 (UTC)

Except that nookie increases the rate at which new, random genetic variants arise. You'd want to maximize the number of random events to increase the chance that beneficial events would occur. Of course, we'd eventually have to figure out a practical way to develop self-sufficient colonies on other planets, but that's a mere practical concern. If you want to make evolution work better, just make it happen faster! Thus, MOAR SECKS FOR ALL! --Jayron32.talk.contribs 04:03, 8 November 2008 (UTC)

The die-off after over-population reaches critical levels might help to cull the weak. Having nookie is only half of it.

We enjoy the end result, but evolution itself isn't really pleasant. It mostly involves either dieing or just barely not dieing. APL (talk) 13:40, 7 November 2008 (UTC)

You can't "advance human evolution." It will go where it goes, advancing as it may will. If you mean, "try to consciously affect the statistical presence of certain traits in the gene pool over others," take a look at the page on eugenics. There are some ethical, philosophical, and practical issues involved, and whatever you do, you're unlikely to make any difference whatsoever as there are just too many bodies in the gene pool (and a gene pool that doesn't suffer massive shocks—LOTS of death or isolation or forced sterilization or what have you—will tend to revert to the mean over time). As for the other question, I have no idea what you mean by "promising species." --98.217.8.46 (talk) 01:22, 7 November 2008 (UTC)

Evolution no longer means only genetics. Memetics - and all manner of other things are driven by evolution. Some of those work on amazingly short timescales. SteveBaker (talk) 05:07, 7 November 2008 (UTC)

".... to help advance human evolution" you'd have to know what destination you were heading for. Remember the old joke "Yesterday we were close to the brink, today we are one step further."Lisa4edit (talk) 07:51, 7 November 2008 (UTC)

You could try to win a Darwin Award =P --WikiSlasher (talk) 10:03, 7 November 2008 (UTC)

Unfortunately, trying automatically disqualifies you. You need to make it look like an accident. --Tango (talk) 10:25, 7 November 2008 (UTC)

Persue the brightest & healthiest man/woman (depending on on your sex) you can find. If there are others, honest evaluate yourself and if they are better in every other way, then look for someone else. More seriously though, you can't really advance evolution. Evolution is a natural process. Once you start consiciously interfering to achieve a desired outcome (something like artificial selection or eugenics), it's questionable if it's evolution any more IMHO. And evolution doesn't really advance anyway. It just happens and things change. Nil Einne (talk) 11:51, 7 November 2008 (UTC)

Develop a really nasty disease. The people who are left will evolve to have better defences against it. And it would be good for he environment. Set up a dictatorship and do selective breeding. Then you can decide what constitutes more advanced. Set up yet another religion complete with aliens and abductions and have eugenics as a central tenet. I'm sure I could think of some other good ways of improving the genetic stock given a little while to think about it. More interesting I think though is what would you consider as improving people? Dmcq (talk) 18:28, 7 November 2008 (UTC)

Best bet is to try to make the race smarter. Make a really popular movie or book which makes the reader believe it's uncool and unsexy to be stupid, and that it's cool and sexy to be clever. Sort of an anti-forrest-gump movie. Vote for intelligent, pro-intelligence, pro-education politicians. Fight to change education from a system to prepare school-leaving children to obediently fill their predefined roles at the bottom rung in society, to a system that helps them to challenge those roles. DewiMorgan (talk) 22:04, 8 November 2008 (UTC)

That's Lamarckism. Just getting people better educated won't make them evolve. Getting bright people to marry each other won't change things in general (except if we diverge into two different species) Dmcq (talk) 17:41, 9 November 2008 (UTC)

Global warming and climate change.

what is the present reactions in the world due to Global warming and climate change?SAJITH 07:24, 7 November 2008 (UTC) —Preceding unsigned comment added by SAJITHANCHAL (talk • contribs)

See Global warming and Climate change and then look through the categories and links within. The reactions are varied across the world and many nations are taking different stances and positions on how to deal with the threat these cause. Have a look at the Kyoto protocol (or is agreement?) as well. 194.221.133.226 (talk) 09:45, 7 November 2008 (UTC)

Reactions to Global warming and Climate change is dependent on the political orientation of the organization or the individual who will react. Greens tend to be most caution on this issue and strictly favors measures which will reduce green house gas emission, pollution etc. Overall, the world is indifferent with this and the siltation is not hopeful. Otolemur crassicaudatus (talk) 08:48, 8 November 2008 (UTC)

Tangent Galvanometer

I want to wire up a tangent galvanometer, but the thing is, I don't know how to specify the number of loops that I want by connecting the wires in the proper places. For example, there are four knobs for the wires to be connected and three options as to the number of loops (2, 50 and 500).Each number is printed in the middle of two sets of knobs. How do I connect the wires to get 50 loops? Do I connect the wires to the knobs between which 50 is printed? Or do I connect the first wire to the one just before 50, and the last wire to the last knob? Please help. 117.194.225.101 (talk) 10:27, 7 November 2008 (UTC)

Sounds like you would connect one wire to the 50 and the other wire to the common knob. But I have never seen this kind of equipment. If you used 2 and 50 you would get 48 loops. Graeme Bartlett (talk) 21:32, 7 November 2008 (UTC)

That is what I want to know.Is there a common knob at all? And, if I used 2 and 50, wouldn't I get 52 loops? 117.194.226.154 (talk) 03:57, 8 November 2008 (UTC)

I asked this question almost two days back. Am I to take it that no one in the Science Desk has ever seen a tangent galvanometer?? I need the answer by tomorrow, so after that, even if someone does come up with an answer, it'll be of no use to me, because the last practical class of the term will have ended by then. Please hurry! Thanks in advance. 117.194.226.234 (talk) 05:21, 9 November 2008 (UTC)

I think the scarcity of answers may be because the question is specific to a particular instrument that no-one on the help desk has seen.

I'm guessing here but it seems most likely to me

• that the posts on either side of the printed "50" have 50 turns of wire between them,
• that the two posts that have 50 and 2 between them have 52 turns of wire between them,
• that the "end posts" which have 2, 50, and 500 between them have 552 turns of wire between them, and so on.

Depending how resistive the wire is, an ohmmeter might allow you to check how the apparatus is wired. CBHA (talk) 06:18, 9 November 2008 (UTC)

current electricity and magnetism

do the electrons really trace a parabolic path while carrying current?

what is meant by magnetic meidean? —Preceding unsigned comment added by Kunal pdj (talk • contribs) 11:33, 7 November 2008 (UTC)

I wouldn't think that electrons carry current, rather they carry charge and the flow of charge is the current. (Mere semantics, I know...) Electrons in a current typically go through a wire so I can't see how they would trace a parabolic path unless the wire is parabolic. They can however trace a parabolic path as they move through a uniform electric field. --WikiSlasher (talk) 12:05, 7 November 2008 (UTC)

If you're asking about whether or not electrons really trace the classic 'orbital' path like they do in the old Atom illustrations, (Like this one : Image:Flag_of_IAEA.svg) then the answer is "no". See Atom for more discussion on this, but basically they exist in probabilistic clouds around the nucleus and don't really trace any coherent path within that cloud.

_{(As an aside, I can't believe that illustration doesn't appear anywhere in the 'atom' article.)}APL (talk) 13:36, 7 November 2008 (UTC)

impossibility of stable equilibrium in electrostatics

3 point positive electric charges are fixed at the corners of a cube. I have to design an experiment to show that a ninth positive charge placed at the centre of the cube will not be in stable equilibrium. I thought I will place small charged sphere in place of 'ppoint charges'. But how to charge a sphere? I know I can use induction or conduction or friction method to charge them but for that I will need another charged object. How to get a charged object..will they be naturally occuring? Please help..name any experiment to charge objects.. —Preceding unsigned comment added by Sruthi Narasimha (talk • contribs) 12:20, 7 November 2008 (UTC)

By 3, do you mean 8? Algebraist 12:22, 7 November 2008 (UTC)

No, It doesn't make sense. Eight occupied corners give rise to complete equilibrium, since the net field at the center is always 0, as long as the point charges are identical. Nevertheless, the second part of the question isn't clear. Why do you need charging, if you say the ninth is charged ? In whatever positions you choose for the first three, you find two of them symetrical, thus counterbalance each other, leaving the third acting alone. BentzyCo (talk) 13:30, 7 November 2008 (UTC)

Equilibrium is easy, but the question asks for stable equilibrium. That's far harder. --Tango (talk) 14:59, 7 November 2008 (UTC)

I see. I hope that's what the asking user meant, indeed. Anyway, the type of equilibrium is defined by the tendency of the system once it's shifted out of its equilibrium. In the case of a stable one, the ninth charge tends to return to the center of the cube, in order to minimize the potential energy of the system. This is the case assuming 8 identical point charges at the corners, namely the ninth charge would oscillate about the center periodically. In the case of shifting the charge along one of the main diagonals it would oscillate linearly, while in the general case, its oscillations would be spatial. BentzyCo (talk) 16:24, 7 November 2008 (UTC)

No, a charge won't oscillate around the center, whether it's positive or negative. Probably the easiest way to see this is from Gauss's law. There's a stable equilibrium at a point x iff the net force at that point is zero (F(x) = 0) and a small perturbation in any direction leads to a restoring force (for ε sufficiently small, for all |r| = ε, F(x+r) · r < 0). But that implies that the normal force integrated over the sphere of radius ε is nonzero, while by Gauss's law the same integral must be zero, since there's no charge inside the sphere.

In any case, as I said last time, the original poster understands the theory. The question is about actually doing the experiment. I'd answer it except that I don't know anything about doing experiments. -- BenRG (talk) 17:35, 7 November 2008 (UTC)

The "experiment" cannot be done as described. It can be calculated as a "paper experiment", i.e. you can do the calculations to show what the expected results are, however it is literally impossible to do it as described. Here are the problems you will run into:

1. It is impossible to suspend 8 objects, unsupported, in space at the corners of a cube under standard conditions, i.e. in your kitchen. Gravity will just take over. You could POSSIBLY do it in a controlled free fall, such as in orbit aboard a space shuttle, but for practical purposes, your not going to book passage on one just to do this experiment.
2. A point charge is a theoretical construct. You can certainly put an electric charge on object; rub a balloon against your head; viola. However, this has several problems. a) Its not a point charge, but a charged area spread across 3 dimensions b) its not of uniform charge density, that is different parts of the object will have different charges and c) its of an indeterminate magnitude, that is if you repeat the balloon rubbing experiment 8 times, there is no guarantee that each balloon will receive the same amount of electric charge and d) the charge will dissipate over time, as it moves around the object, or just dissapates into the air. The stability of the 8-point equilibrium requires point charges of uniform magnitude; anything other than this exact set up will be unstable from the start, making it impossible to ad your ninth charge in such a way as to do the experiment.

Maybe you should find a different idea to prove experimentally; because I can't fathom a way you could do this to any reliability in real life... --Jayron32.talk.contribs 19:14, 7 November 2008 (UTC)

The experiment ought to work in two dimensions - that's much more do-able. Four charges at the corners of a square with a fifth in the center. By keeping the apparatus horizontal - you can eliminate gravity. By doing it on an air-hockey table you can eliminate friction - and that only leaves air resistance. Alternatively - you could suspend the charges on long strings so they are all at the same level - the restoring force due to the string would have to be negligable - so very long, thin threads would be required. SteveBaker (talk) 12:59, 8 November 2008 (UTC)

Chihuahua and Great Dane

Is there any documentation or photos of a dog that is one half Chihuahua and one half Great Dane? Is it possible?--Emyn ned (talk) 14:10, 7 November 2008 (UTC)

With artificial insemination, it should be possible. Can't say I know what the result would look like, though. --98.217.8.46 (talk) 14:29, 7 November 2008 (UTC)

(EC) It is entirely possible geneticly. One could do it by simple artificial insemination techniques. As far as natural methods, the equipment may not be compatable... --Jayron32.talk.contribs 14:31, 7 November 2008 (UTC)

Male Dachshund x female Afghan Hound works and has happened naturally, FWIW. --Kurt Shaped Box (talk) 20:14, 7 November 2008 (UTC)

I guess, if done naturally, it would have to be a male Chihuahua and a female Great Dane....--Emyn ned (talk) 14:35, 7 November 2008 (UTC)

I think it would need to be even if done by artificial insemination. The puppies might grow too big to fit inside a female Chihuahua resulting in a miscarriage. What size are Great Dane pups? --Tango (talk) 14:55, 7 November 2008 (UTC)

Why do I picture a Chihuahua coming to the door with a dozen roses, a bag of dog-treats, and a step-ladder, and later a very undersatisfied Great Dane? DMacks (talk) 20:36, 7 November 2008 (UTC)

I don't care to speculate about the causes of your warped imagination... ;) --Tango (talk) 00:57, 8 November 2008 (UTC)

Beverly Hills Chihuahua has a fuckload to answer for, s'all I can say... --Kurt Shaped Box (talk) 01:01, 8 November 2008 (UTC)

heating with a gas stove

If someone had electrical heating, which was much more expensive in their area than natural gas (but unfortunately no gas heater was installed in their apartment), couldn't they heat by turning on all four of their stovetop ranges and opening their oven door, putting the oven on full, until their apartment quickly got quite toasty? Or is there some downside I'm not seeing?

I'm NOT asking for legal, medical or any other regulated professional advice! —Preceding unsigned comment added by 82.124.214.224 (talk) 17:19, 7 November 2008 (UTC)

It wouldn't be very efficient. Real gas heaters have all sorts of fans and ducts to move the warm air throughout the house. Just opening up a stove would be a very poor way to heat your house. You'll wind up with a whole bunch of hot air around the stove, and by the time that diffuses throughout your whole home (if it does!) you will have burned a tremendous amount of fuel.

Think of old homes built before central heating. They had a fireplace in every room, and even so they often tended to be rather cool if you weren't standing right next to a fire. APL (talk) 17:33, 7 November 2008 (UTC)

Open fireplaces have a different problem. Hot air rises - so the heat from the fire goes straight up the chimney - however that air has to be replenished from somewhere - so it has to leak in around outside doors and windows. Hence the fire can actually cause the house to be generally colder than it would have been without the fire! The solution (which we have in our open fireplaces is to have a simple heat exchanger built into the grate - through which air from the room is blown - and which exits to the side or above the fireplace. This warms the air in the room using the heat from the fire - which greatly reduces the lost heat - and cuts down on the amount of outside air that gets pulled in. However, it's not perfect.

The problem with the oven is definitely one of circulation of the heat. Putting a small office fan next to the stove might help that. I guess I'd also have nagging worries about combustion by-products from the stove - normally, you'd only operate the stove for an hour or so - but if you're going to have it on for a protracted amount of time - there could be issues here. You should maybe consider installing some carbon monoxide detectors in the kitchen area. SteveBaker (talk) 17:44, 7 November 2008 (UTC)

Granted that fireplaces have more than one problem, house-heating wise. But even a Franklin stove tends to only heat the area around the stove.

I've seen fans on hinges that mount in door-ways. Strategically placed these fans can warm up whole floors of large houses with a small Franklin stove. I'll bet a similar arrangement could work with a gas stove. APL (talk)

Actually, it worked quite quickly (less than 10 minutes). The idea is that I realized that the place got really hot very quickly whenever I was baking something! It's a small place, we're not talking a whole house. —Preceding unsigned comment added by 82.124.214.224 (talk) 18:03, 7 November 2008 (UTC)

There's also a safety issue if you have kids or pets, what with leaving all the burners on the top of the stove on... -- MacAddct1984 ^{(talk &#149; contribs)} 18:10, 7 November 2008 (UTC)

You didn't find that some parts of your apartment were far too hot while others still hadn't warmed up? APL (talk) 19:23, 7 November 2008 (UTC)

I did that and it worked fine for me. That's very probably because of a few special factors in my apartment. Firstly, I was aware of the exhaust fumes and used it only for initial heating, not to keep the temperature permanently. Then there were only a few very small rooms with no doors. And than, the proper heating was itself so poorly designed that nearly everything would be an improvement. 93.132.156.148 (talk) 19:12, 7 November 2008 (UTC)

You could quite easily kill yourself (or the person upstairs) by doing this: either incomplete combustion of the natural gas causes carbon monoxide poisoning, or combustion without enough fresh air coming in causes carbon dioxide poisoning. --Carnildo (talk) 22:06, 7 November 2008 (UTC)

DO NOT DO THIS. Stoves only efficiently vent when closed. If left open to your apartment for long periods of time, toxic gases, as noted above, can build up and harm or kill you. People die this way all the time: [9], [10], [11]. What good is the extra $20.00 per month you will save in heating bills going to do you when you're dead. Don't fuck around with this stuff... --Jayron32.talk.contribs 22:14, 7 November 2008 (UTC)

Personally, I can heat two rooms quite well just by grilling some bacon. Grills aren't intended to work closed, neither are top burners. And I get food cooked at the same time. Yay. Do get any gas devices checked out regularly by qualified technicians. DewiMorgan (talk) 22:11, 8 November 2008 (UTC)

Read above safety notices. A friend of mine used to do this in an apartment that didn't have separate gas metering (in Australia you can only be charged for services that are seperately metered). She put the oven and burners on all day in winter. The place warmed up but it was very humid and there was a lot of condensation on the windows and ceiling. Polypipe Wrangler (talk) 04:36, 9 November 2008 (UTC)

Intensifying Artifical Light, ie from a Flashlight

My son is doing a scientific methodolgy project for school (he is in the 7th grade). His project is determining whether ordinary household light (ie lightbulb, flashlight) could be focused and intesifed by using a series of magnifying lenses. He was hoping he could ultimately focus it to the point where he could burn paper. Is this possisble? Why or why not? He has researched it on the internet but has only found articles on how to convert a Mag Light into a laser using diodes from a DVD burner. Very cool, but not the info he needs. Thanks in advance 63.118.244.130 (talk) 18:42, 7 November 2008 (UTC)

• Whether you could burn paper this way would really depend on the strength of the source light and the strength of the lenses used. (It is possible using a strong magnifying glass and the sun). - 87.211.75.45 (talk) 19:07, 7 November 2008 (UTC)

Artificial or natural isn't a big deal, it's just the intensity (i.e. the amount of energy) of the light. You can't start fires with a magnifying glass and sunlight on a cloudy day, too much has been absorbed already. Your average household flashlight probably doesn't have the power output necessary to ignite things, but I could be wrong. You'd have to look at the total power output of the flashlight and compare it to the point at which paper ignites (451 degrees F, or Fahrenheit 451 if you like). Determining the heat output might be done with a styrofoam container filled with a known amount of water and a thermometer (look at the definition of a calorie), and then compare that to the amount that the lens focuses the rays. A "perfect" lens would focus all energy passing through the glass onto one exact point, but no such perfection exists, and you'd have to know what the best focusing point is (the lensmaker's equation may be of help, but just guessing). Not sure of the exact multipliers involved, since paper will take less energy to warm than water (especially given that water doesn't absorb a lot of light, though reflected sunlight can be used to heat water). You would also have to look at how fast the paper is cooled by the various ways heat transfers. In short, you might be able figure it out, but it would be well beyond 7th grade science. My guess, though, is that a flashlight and an magnifying glass can't make fire from paper, even with black paper, a really strong flashlight, and high power magnifying glass. SDY (talk) 19:10, 7 November 2008 (UTC)

I don't think it's the strength of the magnifying glass that's important, that should just affect how far away the focal point is. The size of the lens determines how much light it actually focuses and thus how likely it is to be able to burn paper. A series of lenses is unneccesary, it won't focus more light than one lens and will actually cause less light to focus because the lenses aren't truly transparent. (It just occured to me you may mean leses next to each other instead of in line, that could help if you could get them to focus on the same spot, which will be difficult). In the end I just don't think you'll be able to get enough light from a flashlight. -- Mad031683 (talk) 20:27, 7 November 2008 (UTC)

Just to clarify, magnifying glasses merely focus or "concentrate" energy; they don't create energy out of nothing. The sun generates sufficient energy to light paper on fire; however there is likely not enough total energy output from a flashlight bulb to generate enough energy to light paper on fire. A typical flashlight bulb draws 10 watts of power. Even if the lightbulb was 100% efficient in turning electricity into light, that would mean it would be maximally capable of 10 joules of energy per second; the paper would be perfectly capable of disipating more than 10 joules of heat per second. This calculation assumes that 100% of the electrical energy was turned into light energy, and that 100% of that light energy could be turned into heat energy. These transitions are going to be far less efficient than that, so it is quite obvious that you couldn't do it with this equipment. --Jayron32.talk.contribs 21:11, 7 November 2008 (UTC)

What the magnifying glass does, though, is that it makes it so that all that energy goes to heating a smaller piece of paper. If you have 10 j/s (very roughly 2.5 calories/second) applied to a microgram of water (10^-6 liters), that microgram of water will evaporate quite rapidly (far less than a second, at any rate). That same amount of energy applied to a microgram of paper will cause it to hit 233 C (451 F), which I assume is the point of spontaneous combustion for paper. SDY (talk) 21:27, 7 November 2008 (UTC)

Except that that microgram of paper is also in contact with other paper, and the air, etc. etc. If you had 1 microgram of paper in a vacuum in isolation, yes, I suppose you could make it burst into flame with an appropriately focused magnifying glass and a flashlight bulb. However, under standard science fair project conditions (i.e. you could do this stuff in your kitchen) its likely impossible to make happen. The question is not whether you could get 10 joules into the paper at a very small point; indeed you could. The question is that whether those 10 joules can be kept in one place long enough to raise the temperature of the paper to its flashpoint. As I said, those 10 joules per second coming in can be easily counteracted by disipating either into the air, or into the rest of the paper itself. You can never build up, in any one spot, enough energy. Also, a microgram of paper is of such a small surface area, you'd have to build a rig isolated from any possible purturbations; any slight motion would move the focus of the lens around and you would not be heating the same point. At those sizes, if you BREATHED on the magnifying glass, it would move enough to make it impossible to do. And again, those 10 joules assumes perfect 100% energy transformations. --Jayron32.talk.contribs 21:43, 7 November 2008 (UTC)

I totally agree, just pointing out that the magnifying glass is not an irrelevant part of the equation and it's not just raw power output that's at issue. I'd actually be curious, thinking about this, if you could even make a liquid-type thermometer (i.e. not the dimetallic type) change temperature by focusing light from a flashlight on the bulb. If you couldn't, that would be a quick-and-dirty way of demonstrating that you couldn't burn paper. SDY (talk) 22:18, 7 November 2008 (UTC)

If I were going to try this, I would start with a small bulb like a two cell flashlight and check how much power it used. Most of the electricity will become heat and no more than about 5% (maybe 2%) will become visible light, but the infrared energy is not included in the lumens of visible light it puts out, and the IR might also contribute to heating. If a flashlight is focussed by a magnifying lens onto the bulb of a thermometer, does it cause the temperature to rise? That is a clue. Do not do experiments which might result in fires or burn injuries without adult supervision, and never aim the output at your skin or your eyes or anything else you can't afford to damage The math and concepts in measuring light are pretty complicated for a 7th grader and for me as well, so I apologize in advance for bringing in numbers , and even more so if I get any calculations wrong. Bright sunlight focussed to the smallest achievable spot will quickly start paper on fire or ignite a match. A 100 watt lightbulb will be a small fraction of the brightness of sunlight. An ordinary flashlight with 2 D cells and a normal flashlight bulb will be a small fraction of the 100 watt light bulb. See [12]. A PR2 flashlight bulb [13], for 2 D cells, uses .5 ampere at 2.38 volts, or 1.14 watts, or 1.14 joules per second, but remember that less than 10 % is likely to be beamed through the lens as visible light energy and infrared, and the glass of the lens might block the infrared. The light output is .8 mean spherical candlepower or 10 lumen. With fresh alkaline batteries the voltage, current, and brightness would be somewhat higher. A 6 volt lantern bulb PR15 [14], would draw .5 amp at 4.82 volts, with 2.0 mean spherical candlepower or 25.14 lumen, from an electrical input of 2.41 watts. A 600 watt projector flood lamp for 120 volt operation would get hot enough to cause serious burns to anyone touching it, and would draw 5 amps at 125 volts, putting out 17000 lumens, or about 1350 mean spherical candlepower. Such a bulb should not be handled with the bare fingers even when cold, since fingerprints cause it to fail in use. The article Sunlight discusses how bright sunlight is, and how much infrared it contains. Bright sunlight hits the earth with as much as 1413 watts per meter. 1000 watts per meter is a common rule of thumb for solar energy calculations at the surface. Sunlight has a luminance of approximately 100,000 candela per square meter at the Earth's surface. A 100 watt light bulb emits about 120 candela or 1500 lumens. Thus the sun is way brighter than a 100 watt bulb which is way brighter than a flashlight bulb. A magnifier just collects the light energy falling on its surface and concentrates it in a smaller area. I have one which is 13 cm across, so it has an area of 13267 square mm. If it did not absorb or reflect any light, and it concentrated the light in a 2 mm spot, which would have an area of about 3.2 sq mm, then the light would be 4145 times as bright in that spot. If the magnifier has an area of 13267/1000000 square meter, or .013 square meter, then it receives about 13 watts of sunlight, and if it concentrates it by 4145, then the little 2 mm spot where the sun's image is formed on the paper is getting hit by enough energy to set it on fire. In reality optical defects, absorption and reflection would reduce the brightness of the spot considerably. A magnifier concentrating or focussing the light from a flashlight bulb or light bulb would similarly be concentrating the light and infrared energy falling on the large area of the lens down to a very small area, the image of the the light bulb. If the amount of energy falling on the lens is small, then even concentrated it will not raise the temperature much. Edison (talk) 22:14, 7 November 2008 (UTC)

Some mistakes in this thread:

• Paper doesn't autoignite at 451°F. I don't know where Bradbury got that idea. It's not only inaccurate but ridiculously overprecise, given that he doesn't even mention the type of paper. Autoignition temperature gives 450°C (not °F). The source it cites says 450°C for rayon fiber, 475°C for cotton.
• The brightness in candelas or lumens is irrelevant here, since those units are based on the sensitivity of the human eye, and human eyes don't figure into this question at all (hopefully!).
• The focal length does matter because the light source has a non-zero size—see below.

As you said, your 13000 mm² magnifying glass only captures about 13 W of sunlight, and I think a magnifying glass that size is more than capable of burning a hole in a piece of paper. Capturing a comparable amount of power from a bright incandescent bulb might be possible. The tricky part is focusing it. The rays coming from the Sun are approximately parallel, and an ideal lens will focus them approximately to a point. But to capture enough power from an incandescent bulb it'll need to be close to the lens, its angular diameter will probably be 100 times the Sun's, and the lens will form a correspondingly larger image. The image diameter is ${\tfrac {d}{r}}({\tfrac {1}{f}}-{\tfrac {1}{r}})^{-1}={\tfrac {d}{(r/f)-1}}$, where d is the diameter of the object, r is the distance to it, and f is the focal length. For the Sun that works out to about 0.01f. Our article claims a typical focal length for a magnifying glass is 25cm, so the image size is around 2-3mm. To get a similar image from an incandescent bulb (5cm diameter?) you'd need r/f ~ 20, which is going to be tricky since r needs to be small. You might be able to do it with a succession of fairly powerful lenses, say two or three with r/f ~ 4. (And come to think of it, you could do better with a clear glass bulb—I was thinking of the frosted type for some reason.) -- BenRG (talk) 02:06, 8 November 2008 (UTC)

Odd, I've seen some other stuff (on the internet, not from reliable sources) that agrees with the 451°F. It's possible that the 450 and 451 (i.e. greater than 450) are from the same tests and Bradbury just used the wrong unit. SDY (talk) 02:19, 8 November 2008 (UTC)

Well, it would be simple enough to test the claim by putting a piece of paper in a standard household oven, if anyone wants to. They usually go up to about 500°F. Of course you want to keep it small, maybe a 1 cm square or even less, so it doesn't make much smoke even if it does burn. Or course, try this at your own risk! --Anonymous, 03:23 UTC, November 8, 2008.

I have set my oven to 550 degrees (F) and have placed a small corner of the Oregon measures voter information booklet for 2008 on a pizza tray. We shall see in a little while whether Bradbury got it wrong. SDY (talk) 03:29, 8 November 2008 (UTC)

For reference, see this picture. The paper did not burn with the oven set at 550 degrees, though it did darken in color. SDY (talk) 03:39, 8 November 2008 (UTC)

Popcorn and Cell Phones

What exactly is happening here?: http://www.dailymotion.com/relevance/search/portable/video/x5odhh_pop-corn-telephone-portable-microon_news Isn't this a health hazard? --Emyn ned (talk) 18:58, 7 November 2008 (UTC)

It's a fake viral video that was aimed to sell Bluetooth devices. Mythbusters did a bit about it on one of their viral video episodes. No need to worry! -- MacAddct1984 ^{(talk &#149; contribs)} 19:19, 7 November 2008 (UTC)

Fake video to advertise bluetooth headsets. More information from Snopes.APL (talk) 19:26, 7 November 2008 (UTC)

Since a cell phone has ~1/1000 the power of a microwave oven, I wonder if a few thousand cell phones in an appropriate enclosure might be able to cook something? I'm sure that 3-4 (like shown in those videos) has no effect. Dragons flight (talk) 19:31, 7 November 2008 (UTC)

How on earth did the company behind these manage to avoid censure? It's blatantly obvious what they're trying to imply in order to sell their products. --Kurt Shaped Box (talk) 19:42, 7 November 2008 (UTC)

And bluetooth involves electromagnetic radiation anyway! Graeme Bartlett (talk) 21:18, 7 November 2008 (UTC)

Perhaps you don't realize it, but Bluetooth operates on the same 2.4 GHz microwave frequency as microwave ovens (but with ~1/100000 the power). The comparison is appropriate except that there isn't nearly enough power involved to damage anything. Dragons flight (talk) 21:35, 7 November 2008 (UTC)

Traditional ship hulls and maximum speed of these

A traditionally shaped ship, propeller-based propulsion and with the distinguishable sleek form, rarely reaches speeds over 30 knots. In fact, it seems outright impossible for any ship of traditional design to reach speeds over 35. See, for the sake of having examples, British battleships and cruisers from the second world war, destroyers of the same (and this) era, indeed any imaginable merchant- or warship of the time. Fast patrol boats, E-klasse, Elco and so forth, have significantly higher speeds. What are the hydrodynamic effects that constrain ship speeds to such an arbitrary range as the 30-35kt one? Note of course that I am fully aware of faster ships, and the aforementioned FPBs may owe their speeds to having so little of their hulls actually down in the wather; jumping on the waves more than plowing through them. Answer, if you can, the question of if there is at all a way to get some Iowa-class battleship to accomplish a speed of 50 knots. :) I thank you for any interest in this matter, and more so for any replies. 80.202.246.253 (talk) 20:08, 7 November 2008 (UTC)

Ocean waves travel at approximately $2.4{\sqrt {\lambda }}$ knots, where lambda is the wavelength in meters. For a 100 meter wavelength, this translates to 24 kt. A ship traveling through the ocean creates its own wave train with a wavelength approximately 1-2 times the length of the ship. For a ship 100 m long, that implies it's wave train is moving ~25-35 kt. As you approach or try to exceed the velocity of your own wave train, you encounter rapidly increasing drag that means further increases in thrust can offer you very little in increasing speed. So, as a practical matter, most large ships are designed not to try an exceed this limit as it eats too much fuel for very little gain. Dragons flight (talk) 21:06, 7 November 2008 (UTC)

The articles on Hull speed and Froude number are relevant here. At hull speed, a ship is basically trying to climb its own increasingly steep bow wave. You can force a higher speed than that by sheer power (essentially forcing the ship into planing). But for large ships, the cost is prohibitive. It's cheaper to just make the ship longer and/or to add a bulbous bow. -- Stephan Schulz (talk) 23:45, 7 November 2008 (UTC)

Exceptionally happy with the answers. :) Thank you! 80.202.246.253 (talk) 14:32, 8 November 2008 (UTC)

Metals for Spaceships

What kind of metals would the spaceships of the future be made out of?

How abundant are these metals on Earth?

Could they be found on the Moon and other satellites? What about asteroids? —Preceding unsigned comment added by 24.125.56.9 (talk) 20:37, 7 November 2008 (UTC)

Titanium is likely of value, but it's not particularly rare here on earth. Like aluminium, the difficulty and expense of titanium is mostly in extracting it and working with it. The "cutting edge" of aerospace nowadays is moving away from metals in general and towards ceramics and carbon fiber composites, which offer better heat resistance or strength for the weight. There are hybrid compounds like Cermet, which uses nickel (common on the earth), molybdenum (not too rare, has been found on the moon), and cobalt (not too rare). The noble metals (e.g. gold) have useful properties, but aren't likely to be used in large quantities. SDY (talk) 21:00, 7 November 2008 (UTC)

Spaceships for the forseeable future will likely be made out of the same metals that are abundant on Earth. Of the 80 or so metals on the Periodic table of elements, only a few are commonly used for structural purposes. Structural metals are ones that are strong enough, but not too brittle, and should be relatively inert. Aluminum, iron, chromium, titanium, cobalt, and nickel are probably your best candidates; though depleted uranium has come into fashion due to its resiliance and strength, it still remains controversial. The Space Shuttle is primarily made of aluminum and titanium, and it seems to work fairly well. --Jayron32.talk.contribs 21:04, 7 November 2008 (UTC)

Why should they made of metal? Might as well make them of ice or some other material that can be used as a fuel and would also provide protection from cosmic rays. Dmcq (talk) 21:45, 7 November 2008 (UTC)

Aluminum is 8.3% by weight of the Earth's crust, thus quite common. It must be separated from elements it is in compoundss with, oxygen and silicon. Bauxite is the ore it is commonly obtained from. Aluminum is also abundant in the lunar surface material, as is iron, magnesium, manganese and titanium. The abundance of these metals varies at different lunar locations. Asteroid mining discusses the possibilities of getting useful materials from asteroids. A 1 km asteroid might contain as much iron ore as is used on earth in 2 years. The lunar surface also contains water, as do some asteroids, which could be used to create fuel and extracted for life support, by the use of external energy sources such as solar. See also Space mining , Space manufacturing , Space-based industry , and In-situ resource utilization. Robots could be useful for such work. Present technology is not quite there yet to unleash robots and have them extract raw materials and build and fuel spaceships and habitats. One drawback is that the robots, if their artificial intelligence were advanced enough to function semi-independently, might decide they should be working for themselves rather than us. Edison (talk) 21:46, 7 November 2008 (UTC)

If you're not going anywhere (asteroid mining stations, orbital colonies) or if you've got energy to spare (Orion-type nuclear propulsion), steel is a likely choice. It's quite abundant and easy to work with. --Carnildo (talk) 22:15, 7 November 2008 (UTC)

Moon Colony

How dependent would a moon colony be on Earth in terms of being provided materials (fertilizers,food,water)? Obviously it depends on its capacity (plant biodomes), but would it be possible to make it completely independent? Thanks for the replies to the last question, by the way. 24.125.56.9 (talk) —Preceding undated comment was added at 23:09, 7 November 2008 (UTC).

I guess it'd be possible to create an independant colony on the moon with exceptional amounts of time and resources initially. It would need a power source (if you want independant, it's got to be solar, hydroelectric or someting similar), food supplies (in a biosphere you can grow everything we do here), water supplies with a way of recycling this water and recycling processes for other materials. I guess a lot also depends on the size of the colony you wish to create. —Cyclonenim (talk · contribs · email) 23:29, 7 November 2008 (UTC)

The Biosphere 2 article might be interesting reading as far as what's possible for autonomy. SDY (talk) 23:34, 7 November 2008 (UTC)

The added difficultly to get from almost self-sufficient (one small shipment of supplies every few months, say) to completely self-sufficient would be enormous and almost certainly not worth it for a lunar colony - the moon just isn't that far away. Power is easy - you just build your colony on a Peak of Eternal Light and use solar power (incidentally, how do you intend to use hydroelectric power on the moon? The energy comes from the sun evaporating water and it then falling as rain...). It's replacing the small but constant loses of water and air that you would need Earth for, but you could get those loses down to a very low level with some effort. As long as you have people travelling between the Earth and Moon reasonable frequently you can easily include some supplies along with the people. There will also be other, less essential, supplies you would need to get shipped in since manufacturing everything locally would be impossible unless your colony was enormous - compare with small island nations, they have all the food and water (and air!) they need, but still import other stuff. --Tango (talk) 01:11, 8 November 2008 (UTC)

Moon colony is an idea of science fiction fans and irrelevant in scientific discussion. Otolemur crassicaudatus (talk) 08:44, 8 November 2008 (UTC)

That was completely uncalled for and entirely incorrect. The creation of a moon colony is very much within the realm of science, as is anything else we might actually wish to do. If you're not going to contribute anything or at least play well with others, perhaps you should focus your efforts elsewhere. You could start by removing your head from your ass. Matt Deres (talk) 16:23, 8 November 2008 (UTC)

You will probably be interested in this http://en.wikisource.org/wiki/Advanced_Automation_for_Space_Missions 93.132.139.211 (talk) 11:04, 8 November 2008 (UTC)

Lunar Atmosphere

Suppose one were to break down lunar rocks with the express intent of freeing oxygen and forming a lunar atmosphere. Due to thermal losses and solar wind ablation, that atmosphere would escape over time, but I am curious what the rate of loss would be. Even at 1/6th Earth gravity, the fraction of molecules in a Maxwell distribution with a velocity above lunar escape velocity is very small (approximately 1 in 10 billion, for 30 amu molecules at 350 K). It's orders of magnitude bigger than the fraction at Earth's escape velocity, but still very small. So, that leads me to wonder, can the moon retain an atmosphere on timescales that are relevant to humans? How long would a 1 bar atmosphere last on the moon? I know it won't last forever, but is the ablation rate 1% per day, 1% per year, 1% per century, etc.?

If it is in the range of 1% per year or longer then it seems like terraforming of the Moon to create an environment where humans can live unprotected might even be possible. Obviously there would be a lot of difficulties with that, and a great many resource challenges to overcome, but I like the idea of people one day looking up at a moon that is green and blue rather than gray. Dragons flight (talk) 02:21, 8 November 2008 (UTC)

The moon's magnetic field is much smaller than Earth's so the impact of the solar wind on the proposed lunar atmosphere will be significant. See Atmosphere of the Moon. Rmhermen (talk) 04:54, 8 November 2008 (UTC)

Sci fi writers have gone with domes containing the air, rather than trying to surround the moon with a breathable atmosphere. They may just have been on to something. Edison (talk) 04:56, 8 November 2008 (UTC)

Maybe they just lacked sufficient imagination. Dragons flight (talk) 05:10, 8 November 2008 (UTC)

Without doing the math, because of the Moon's lower gravity the atmosphere would have to be hundreds of miles (maybe 1000s?) thick to approach 1 atm at the surface (the Earth's is about 100 miles deep). The escape velocity would be much reduced at those elevations. That's also a lot of gas. Domes could be much cheaper. Saintrain (talk) 15:38, 8 November 2008 (UTC)

Of course, one could have a pure oxygen atmosphere at lower pressure. (For American readers, the Mercury and Gemini space capsules had an internal pressure of only 3 psi (about a fifth of an atmosphere) but contained pure oxygen. That gives the same partial pressure of oxygen as sea-level air on Earth.) I haven't done the math either, but needing only a fifth of the pressure makes life a lot easier.

It gets even better — you could populated the Moon with Earthlings adapted to high-altitude conditions. La Paz, Bolivia is a major city (nearly a million residents) sited 3650 m (12,000 ft) above sea level. That puts them above more than a third of the atmosphere, so now we're down to a measly 2 psi of pure oxygen: less than a seventh of sea-level air pressure. TenOfAllTrades(talk) 16:09, 8 November 2008 (UTC)

The escape velocity at 500 km above the moon is only 10% lower than at the surface. Escape velocity does not change rapidly with height. 99.9% of the Earth's atmosphere is below 60 km, by analogy, 99.9% of a lunar atmosphere should be below 360 km. Of course it's a lot of gas. A large fraction of an Earth atmosphere if you really want 1 bar, but who wants cheap. Dragons flight (talk) 16:26, 8 November 2008 (UTC)

I think the key problem isn't maintaining the atmosphere, it's getting it there in the first place. It will escape, but you're probably talking (I'm guessing here, if someone has accurate figures please speak up) 100s or 1000s of years (next to nothing on a geological timescale, but plenty on a human timescale). However, the shear amount of gas required, even if you limit it to pure oxygen, is enormous. Most methods I can think of to build up that kind of atmosphere (chemical reactions with lunar rock, etc) would do so gradually, probably over the same kind of timescale as the atmosphere escaping, so you wouldn't get anywhere. Domes are far, far simpler. An alternative to domes is to build your colony underground - you may need to do something to make the lunar rock above you air tight, but that's not too difficult (easier than building a dome, since the rock can handle the pressure, you just need to fill in the gaps). --Tango (talk) 17:00, 8 November 2008 (UTC)

Actually, making oxygen is straightforward (if ridiculously energy intensive). Melt 100 kg of lunar soil at 2500 C and you release ~8 kg of oxygen gas (which is about 20% of the oxygen in the rock). There are probably ways to make that more efficient and less energy intensive, but the basic idea is there. So to make 1×10¹⁷ kg of oxygen we only need to melt say 5×10¹⁷ kg of rock. Done uniformly, that would mean smelting a 5 m deep layer over the entire moon. Or a 2 km deep layer over 0.25% of the moon. Oh, and that would require the energy equivalent of the Earth's entire electricity generating capacity for the next 3000 years. So there are some practical problems.  :-) But maybe in a few millenia mankind will have solutions to those problems. Dragons flight (talk) 18:52, 8 November 2008 (UTC)

So, like I say, it's going to take in the order of 1000s of years to generate the oxygen and that's roughly the same rate at which it will be escaping, so you don't get anywhere. Until you can generate oxygen significantly faster than it escapes, you're not going to get an atmosphere. --Tango (talk) 20:11, 8 November 2008 (UTC)

Would lunar soil, after over 6000 years of solar radiation, be fully reduced or fully oxidized? That is, how much of the new O2 is just going to oxidize the rocks? Saintrain (talk) 01:36, 9 November 2008 (UTC)

November 8

Deceptive practice?

I was in the supermarket today and I came across non-dairy creamer which displayed prominently "trans fats: zero grams" with a checkmark. Its ingredients are in order: "corn syrup solids, vegetable oil (partially hydrogenated coconut or palm kernel..." (you can view the nutritional information here) According to Wikipedia's article on trans fats, the partially hydrogenated oils are pure trans fats. The serving size is 1 teaspoon, and 225 servings per container. So am I right that this product is basically extremely high in trans fats and that they are exploiting a loophole by making their serving size so small that they are (apparently) allowed to list this as "zero grams of trans fats" obviously intending to give the impression that the product itself has none? If I'm correct, how can this type of deceptive practice be legal? (I'm being a bit rhetorical asking about legality, I know the answer: lobbying). But it's infuriating. 68.237.2.254 (talk) 00:28, 8 November 2008 (UTC)

The Coffee-mate FAQ [15] says the amount of partially hydrogenated oil is "trivial" and meets FDA guidelines for allowing the product to be identified as trans-fat free. Dragons flight (talk) 00:37, 8 November 2008 (UTC)

This is an officially endorsed rounding "error." If it's less than 0.5 grams, it's recorded as zero. It's why Diet Coke has 0 calories instead of 1: the food labeling regulations say to round by 5's. See 21 CFR 101.9. Giving a more exact value is deceptive for most food products, because variations in the raw materials (milk from cow to cow can have different fat content) and variations in manufacturing processes between production plants will give uncertainty. The serving size issue is rather a thorny one, and is the subject of some rancor. The regulatory question is: Is one teaspoon a reasonable amount for a single "serving" of the food? Labeling it as zero is correct from a regulatory standpoint if it is. As for whether the advertisement is illegal, ask a lawyer (preferably one who knows something about 21 USC), because "labeling" (as defined) is a very grey area. SDY (talk) 01:04, 8 November 2008 (UTC)

As you say, it's probably correct from a regulatory standpoint, but it's also clearly misleading. There is a big difference between something being absent and something being present in a quantity below your ability to accurately measure. Advertising laws seem to be very inconsistent in what they consider to be false advertising... --Tango (talk) 01:25, 8 November 2008 (UTC)

There's a difference between things that are illegal and things that are prosecuted. When someone's driving 150 mph in a 20 mph school zone and the next guy behind him is going 25 mph, they've both broken the law, but only one of them is likely to get prosecuted. The advertisement may very well be illegal. SDY (talk) 01:55, 8 November 2008 (UTC)

Deceptive advertising isn't likely a legal issue; it's not a crime in any real sense. It is a violation of regulations, and companies that advertise deceptively can be brought up on civil charges, but probably not criminal ones... --Jayron32.talk.contribs 02:19, 8 November 2008 (UTC)

It's all the same. By violating a regulation (in the US), you are violating the law that the regulation is based on. If you look at a book of the CFR, it'll give an "Authority" (look at the bottom of the page) citation to an actual law (USC = United States Code). When you get to court, you have to prove that the law was broken, you're not actually convicting them on regulations. That they broke the regulation is prima facie evidence that they broke the law, but that doesn't mean they can't argue the point. Civil law has different standards ("Preponderance of the evidence" rather than "beyond a reasonable doubt" for level of proof required) and other quirks but it's still the same legal process. For the record, I am not a lawyer and definitely not speaking for anyone but for my own demented delusions. SDY (talk) 02:28, 8 November 2008 (UTC)

Most deceptive advertising issues in the US are actually handled by the FTC. Only in the event of disputes over FTC judgments would the matter generally be referred to a court at all. The FTC Act, the law governing deceptive advertising, gives the FTC the ability to pursue civil judgments payable to the US government in the event that an advertiser defies FTC orders. Dragons flight (talk) 02:36, 8 November 2008 (UTC)

Hmm. I think I may refer this over to another reference desk, since it's very non-science at this point. SDY (talk) 02:47, 8 November 2008 (UTC)

The thing is, it's almost impossible to guarantee something is absent. For example, in most Western countries we expect all food to be melanime-free but in reality there is an allowed limit. So basically if you say something is absent or a product is free of something, all you are really saying is it's below some limit (for many reasons including the difficulty in testing below that limit, the accuracy of the tests etc). If you don't agree with this, then you are basically saying you don't agree anything should be labelled free or something being absent. If this is your POV, then you are entitled to it, but I'm not convinced it's a view shared by many. Of course, one of the problems is many people don't understand science, and therefore don't realise it's not usually possible to say something is absent with certainty, so you could argue it's only fair that using such terms is banned. Now as to whether the set limit for trans-fats is the right limit, that's a completely different issue. Nil Einne (talk) 08:12, 8 November 2008 (UTC)

I think the key point is that this appears to be an absolute limit, rather than a relative one. A relative limit can be justified in the way you say, there is no justification for an absolute limit in an arbitrary serving size. --Tango (talk) 14:27, 8 November 2008 (UTC)

Sorry I may have misunderstood what's being discussed here. Are you saying that if I sell pure transfat if I can justify having a serving size pf 0.5g or less then I can label the product as transfat free? And that in particular, this product actually has a very high percentage of transfat? If so the I agree it's misleading advertising and although I could be wrong, I'm not convinced it would be acceptable here in NZ. Having said that, I agree with 128 below that while it's misleading, I wouldn't personally be extremely concerned about transfat from something like creamer which for most people is probably not going to add a great amount to your diet. Nil Einne (talk) 12:41, 9 November 2008 (UTC)

That's how I understood what people above were saying. I could be wrong. --Tango (talk) 21:33, 9 November 2008 (UTC)

Aha! I have found this: document (pdf). A "trivial" amount indeed. You use one tablespoon of this stuff (I probably [heretofore] used more than that in one cup) you've got about half of the recommended limit for trans fats in a day (emphasis on limit; none is better). I appreciate the discussion of legality, but I stated in my OP I wasn't really questioning that. As I said, lobbying has secured this type of bullshit carveout. So they're operating within the bounds of the law. That does not reduce their ethical depravity, nor render this any less a deceptive practice.--68.237.2.254 (talk) 10:44, 8 November 2008 (UTC)

There is a problem with this - there is no "recommended limit" for trans fat in the US. The actual recommendation is "as close to none as possible". The 2-g limit comes from a UN recommendation of 1% of total daily calories so for an average 2000 calorie diet, you get the 2 gram number. However, there is suspicion that this 1% figure was merely plucked out of a hat with no scientific backing.[16] The U.S. FDA specifically says that "While scientific reports have confirmed the relationship between trans fat and an increased risk of CHD, none has recommended an amount of trans fat that FDA could use to establish a Daily Value (DV)."[17] Rmhermen (talk) 15:26, 8 November 2008 (UTC)

I'm not quite sure where in the article Trans Fat you got the impression that partially hydrogenated oils are pure trans fats. That is simply not the case. Partially hydrogenated oils are usually a mix of trans unsaturated fatty acids, cis (regular) unsaturated fatty acids and saturated fatty acids. Only a portion of even pure partially hydrogenated fats would be actual trans fats. Furthermore, under Trans_fat#United_States, it discusses the labeling regulations: "However, unlike in many other countries, trans fat levels of less than 0.5 grams per serving can be listed as 0 grams trans fat on the food label." This practice might be a little misleading, because, as you mention, items with a very small serving size may contain an above-average fraction of trans fats, yet still be under the 0.5 g cutoff due to their small size. On the other hand, you probably won't be eating large amounts of foods with small serving sizes, so the total contribution to your diet will still be small. -- 128.104.112.72 (talk) 18:44, 8 November 2008 (UTC)

FDA labelling standards allows Sodium Saccharine to say that it contains "no sodium," since there is less than 1 gram per serving. Edison (talk) 02:56, 11 November 2008 (UTC)

non-flammable comprimise gas mixture for an airship

Hydrogen is flammable, but it lifts very well. Helium isn't flammable, but it doesn't lift as well. What if you were to mix the two gases in a proportion that still allowed for buoyancy, but wasn't flammable? Would this work? Would the gases separate? Would the benefit of increased buoyancy be enough to justify it? Are there any other problems that I'm missing, because it seems to me like a perfect solution to the problem with airships. If this would work, I kinda doubt I was the first to think of it.63.245.152.13 (talk) 02:14, 8 November 2008 (UTC)

Helium is twice as heavy as hydrogen but actually lifts nearly as well in air, because it's the difference to the far heavier air that matters. See Lifting gas#Hydrogen and helium. The main drawback of helium is not lower lift but higher price, especially in the golden era of airships. PrimeHunter (talk) 02:27, 8 November 2008 (UTC)

I've heard that hydrogen, although flammable wouldn't actually be all that bad in airships with proper safety considerations despite the Hindeburg. Hydrogen won't burn without oxygen, but it will ignite readily in a wide range of oxygen proportions. The main issues would be keeping oxygen out, and keeping any escaped hydrogen which is mixed in with regular air from igniting and then compromising the structural integrity of whatever is storing the hydrogen. You may be interested in Hydrogen safety. 152.16.15.23 (talk) 03:17, 8 November 2008 (UTC)

Mixing in helium doesn't really help - it's excluding oxygen that really matters. You don't want the ratio of oxygen to hydrogen to get anywhere close to an explosive mixture. But all that matters is the ratio - after all, hydrogen and oxygen explode even when four fifths of the air is Nitrogen - which in this context is almost as inert as helium. The nitrogen (or helium) simply doesn't matter - it's not involved. It's widely agreed that modern hydrogen balloons could be made very safe - but the negative publicity of the Hindenberg is hard to recover from. FWIW - an amazing number of people survived the Hindenberg because the hydrogen was moving rapidly upwards and away from the gondola when it burned. The material that the envelope was made from (a variant of thermite - which is a pretty good explosive) was a major part of the problem. With modern plastics keeping the oxygen out - monitoring equipment to tell us that there is a problem - safer materials that don't make sparks...and an increasingly dire shortage of helium...we're going to go back to hydrogen balloons - it's just a matter of time. SteveBaker (talk) 03:46, 8 November 2008 (UTC)

The lower explosive limit for hydrogen gas in air is about 4%; that is, a mixture with air that contains at least 4% hydrogen gas will burn. In other words, creating a mix of hydrogen with helium that will be dilute enough not to be flammable means using a mixture that's going to be essentially pure helium anyway. For the extra percent or two of lifting capability it probably wouldn't be worth the extra cost and complexity of mixing gas. TenOfAllTrades(talk) 16:22, 8 November 2008 (UTC)

Putting 4% hydrogen in with your helium would only gain you about half a percent more lift. --Carnildo (talk) 23:08, 10 November 2008 (UTC)

cement production on other planets

Modern civilization is apparently very dependent on cement. I really can't imagine how the modern world would be what it is without it. The thing is, cement is produced from limestone which is produced from biological processes on Earth. In the future, when we colonize other previously lifeless planets, there will surely be lots of rock there, but none of it will be limestone. Limestoneis just calcium carbonate, though. That seems like a pretty simple chemical formula and calcium and carbon are fairly abundant too. So wouldn't it be possible to synthesize lime from non-biological ingredients on a planet with no limestone? Wouldn't it just involve bonding calcium and carbon? Also, how would you go about getting these elements from rocks on other planets? 63.245.152.13 (talk) 02:41, 8 November 2008 (UTC)

There are chemical processes that can produce limestone as well as biological ones. For example, any solution with a sufficiently high pH, high calcium ion presense, and exposure to CO₂ will likely precipitate calcium carbonate (i.e. limestone). Calcite, the basic component of limestone, can be found in Carbonatite, which is essentially igneous marble. The material in cement, quicklime or calcium oxide (or its hydrate known as slaked lime) could be derived from nearly any calcium-rich mineral. It is derived from limestone on earth because it is abundant; but any planet with similar calcium reserves as earth will likely contain compounds which would suffice. --Jayron32.talk.contribs 03:00, 8 November 2008 (UTC)

Actually lime is another name for compounds that are predominantly CaO. CaO is quite common in minerals, but usually only at the ~10% level with Si, Al, or Fe oxides being more prominent. Given enough energy you could extract lime from a wide variety of source materials, but on Earth limestone (CaCO3) is preferred due to the relative ease of processing. Dragons flight (talk) 03:00, 8 November 2008 (UTC)

I wouldn't rule out the presence of calcium carbonate on a planet devoid of carbon based life. The mineral calcite is calcium carbonate and can and does have inorganic origins (although a lot of calcite is in limestone a lot of which is organically originated). Check calcite for more info. 152.16.15.23 (talk) 03:02, 8 November 2008 (UTC)

If you collect water from the polar zone of the moon, you can make cement by adding it to random lunar dust, which has been dehydrated by extreme heat, per the analysis of lunar soil returned by the Apollo expeditions. Edison (talk) 04:54, 8 November 2008 (UTC)

But the idea of colonization of other planets does not exist outside science fiction books. Otolemur crassicaudatus (talk) 08:53, 8 November 2008 (UTC)

At one point walking on the moon only existed in science fiction books. So did heavier than air flight. I could go on. You are correct that at this point in history planetary colonization is fictional, I doubt it will be for long. I fail to see how it matters at all. We're going to have to think about things like this some day. 63.245.144.68 (talk) 13:37, 8 November 2008 (UTC)

I hope you will receive the Nobel Prize next year. Otolemur crassicaudatus (talk) 13:44, 8 November 2008 (UTC)

Why the sarcasm? What did I say?63.245.144.68 (talk) 13:56, 8 November 2008 (UTC)

Not at all. The idea exists in plenty of serious plans written by space agencies and academics. Sure, it hasn't actually been done yet, but it is far more than just fiction. --Tango (talk) 14:20, 8 November 2008 (UTC)

There are always some people within the scientific community who love crackpot ideas, but that does not make them real. There are people who believe some creatures from a distant planet will someday send them a message. Otolemur crassicaudatus (talk) 15:03, 8 November 2008 (UTC)

You think the people running NASA are a bunch of crackpots? They have serious plans to build a lunar colony (well, permanently manned base, at least, I don't know how you define "colony") within the next 10-20 years, as do other space agencies. As for SETI, I think everyone knows it's a long shot, but they think it's worth it - personally, I agree with them. A little time with a radio telescope in exchange for possibly discovering conclusive proof that we're not alone in the universe is worth it. --Tango (talk) 17:04, 8 November 2008 (UTC)

If you redefine everyone who disagrees with you as a crackpot, then everyone who isn't a crackpot will agree with you! APL (talk) 19:15, 8 November 2008 (UTC)

OK, yeah. I see what's going on here now. I suppose you're one of these people who think global warming and evolution are crackpot theories too? Cute. :) 63.245.144.68 (talk) 19:17, 8 November 2008 (UTC)

WHAT MADE YOU BELIEVE I THINK GLOBAL WARMING AND EVOLUTION ARE CRAKPOT THEORIES? Global warming and evolution are proved facts employing scientific method. Extraterrestrial colony is not only practically impossible, it is theoretically impossible also. Otolemur crassicaudatus (talk) 19:51, 8 November 2008 (UTC)

In my experience, people who believe in one pseudoscientific idea tend to beleive in others. I see no reason why establishing colonies on other planets is impossible. 63.245.144.68 (talk) 20:42, 8 November 2008 (UTC)

There's no need to shout. Could you specific which widely accepted theory contradicts the possibility of extra-terrestrial colonies? --Tango (talk) 20:51, 8 November 2008 (UTC)

• First of all, let assume that it is possible to make a base in any other planet. But in that case, the cost for production of the cement (scientific research + cost to maintain a permanent base in the planet + the cost of transportation to earth) will be so high that it will be absurd to use it for commercial purpose on Earth. The International Space Station costs approximately $100 billion while a ton of cement for commercial purpose on Earth costs only $20 (in regard to Thailand).
• Second, in this case we are certainly talking about terrestrial planets since human landing and staying is impossible in gas giants. So the planets we have are Mercury, Venus and Mars. Mercury does not have atmosphere and its surface temperature of Mercury is 442.5 K. So it is impossible to stay in Mercury. Venus has dense atmosphere and the temperature and atmospheric pressure of Venus makes it inhabitable also. The only terrestrial planet close to earth is Mars. See the article Colonization of Mars. It is unknown whether Martian gravity can support human life in the long term. Otolemur crassicaudatus (talk) 21:47, 8 November 2008 (UTC)

"Unknown" is a far cry from "theoretically impossible". I don't think anyone was suggesting exporting the cement to Earth, the idea is to make the cement you need to build the colony locally rather than importing it from Earth at great expense. If you want to make a commercially viable colony you'll need something you can export or a service you can provide (tourism might get you started, but it wouldn't get you very far, astronomy might be good, if someone gets fusion reactors working He-3 might be a valuable export, rocket fuel and servicing for people travelling further afield, although it will be some time before that's useful). In short, a we're a long way off commercially viable colonies, but publicly funded bases are seriously planned and should be around in a few decades (I suspect NASA's estimate is a little optimistic, there are sure to be budget cuts before then that will push it back, there always are, but they or someone else will get there eventually). --Tango (talk) 22:16, 8 November 2008 (UTC)

Why not think about building a distilled water plant in solar core? Are you suggesting these "colonies" in other planets will really serve any purpose on earth (any economic purpose)? Where will you build the colonies - on Venus? On mercury? As I have said above, it i impossible to build base in these two planet. Again see Colonization of Mars#Concerns, "There is likely to be little economic return from the colonization of Mars". Otolemur crassicaudatus (talk) 22:34, 8 November 2008 (UTC)

And again you cannot ignore the gravity issue. Otolemur crassicaudatus (talk) 22:40, 8 November 2008 (UTC)

If you can cover your setup costs somehow (upfront payments by colonists, maybe, if you can get the costs down far enough) you only need sufficient income from exports, etc. to cover the costs of importing the few things you can't make locally. Mars could serve as a base for asteroid mining - I believe it's possible to get raw materials from asteroids to LEO for similar, if not lower, costs than from Earth, they could then be used for building orbital habitats, etc. Mars could also serve as a stepping stone towards the outer solar system, although missions to the outer solar system would probably be primarily scientific. I'm not saying any of this will happen quickly, I don't expect to see any significant population on Mars in my lifetime (I'd hope we send a few people there, though) - the Moon and LEO, maybe. However, it not being commercially viable is very different from it not being theoretically possible, which is what you claimed. Give it 100 years or so, and there may well be sufficient activity in space to make such colonies commercially viable (you're familiar with the quote, "I think there is a world market for maybe five computers"? (I know it's probably apocryphal, but that's not the point) It is very difficult to predict what there will and won't be a market for in the future). --Tango (talk) 23:11, 8 November 2008 (UTC)

Also, you seem to rule out the possibility of ever colonizing anything outside our solar system. I know that leaving this solar system is probably WAYYYYY off, but I'm sure it will be done someday if we last long enough. To me, whether a colony is commercially viable or not doesn't seem to be as important as if it's self-sustaining. Being able to make money off of space colonies will be important, but for some people, establishing a colony on another world would be enough incentive. 63.245.144.68 (talk) 10:28, 9 November 2008 (UTC)

There are massive difficulties involved in colonising other solar systems, the most likely method is generational ships which would need to be truly self-sustaining over 100s or 1000s of years. For a nearby colony you only need to be reasonably self-sustaining and can import a little every now and then to make up for losses, that requires some kind of export to pay for. The setup costs of making a fully self-sustaining colony would probably be so great that you could just invest the extra cash on Earth and use the profits to pay for the imports with plenty to spare. --Tango (talk) 14:15, 9 November 2008 (UTC)

Figuring out how to make concrete on the Moon and Mars is solving the wron problem. We only use concrete here on earth because it's cheap and available. It has lots of horrible problems...it's only reliable in compression - in tension it's positively fragile - it's heavy - it takes vast amounts of energy to produce...all kinds of issues. On another planet, there will be other materials that are cheap and which have other strengths and weaknesses. Who knows? Artificial diamond might be the way to go - or foamed aluminium - it's going to be a matter of fitting in to what we have. So the idea of doing whatever it takes to make concrete is not entirely reasonable. On the moon, we know that the 'sand' particles are very sharp and spikey - and they interlock in interesting ways that the rounded, smooth sand grains here on earth cannot. Using that property of Lunar sand might be the way forward rather than wondering how to process lunar sand to be more like earth sand so we can make earthlike materials. SteveBaker (talk) 17:57, 10 November 2008 (UTC)

An excellent point. There is an argument for sticking with what you know, though. We know all about how to build with concrete, what its limits are, how best to reinforce it, etc., etc.. It may not be worth going through that learning process again with some new building material just because it is slightly easier to make locally. (If it's a lot easier, then it probably would be worth it.) --Tango (talk) 18:01, 10 November 2008 (UTC)

How could thoughtful people of the 15th century possibly assert that colonies in the New World will provide any possible benefit for Europe? They would have had to be a Crotalus horridus to make such a claim. Edison (talk) 02:59, 11 November 2008 (UTC)

Komodo Dragons in North America

Back in the 90s, the local zoo had a few young komodo dragons. This was before they knew that the females could lay eggs without mating. Anyway, let's say if society were to collapse and all the animals in zoos got out, would komodo dragons be able to survive in North America (specifically, I'm in Kansas)? It would only take one female to start a self-perpetuating population, though the population would be almost entirely homogeneous being descended form only one individual. They're tropical reptiles, but would they adapt to a cooler climate? I know monitor lizards can burrow, so couldn't they just curl up in a hole in winter? 63.245.152.13 (talk) 02:50, 8 November 2008 (UTC)

While someone else could tackle the rest of the question, I doubt that the komodo dragons used to a tropical climate are going to be intelligent enough to develop a new behavior like digging a hole. As an example, some lemurs living in North Carolina don't realize that leaving their tails out of their enclosure's heatbox would cause them to get frostbite and require amputation. Their stubby tails are sad to look at but they don't understand that it can actually get that cold because it never gets cool enough in native Madagascar. The situation for a Komodo dragon may be similar in that it would realize it was cold and try to seek somewhere warm, but wouldn't realize that trying to bask outside in the middle of Kansas winter even in the daylight isn't going to heat it up enough. Also keep in mind that any parthenogenic offspring of the female will be male so for perpetuation of the population one of the sons needs to mate with its mother to produce more females. 152.16.15.23 (talk) 04:01, 8 November 2008 (UTC)

Kinda disappointing... I was hoping that when the economy finally crashes and everything goes to hell, I could make a suit of armor and go save little rural farming villages from the local dragon.

If we were talking about florida on the other hand, I would give the komodo dragons a fighting chance. Reticulated pythons have managed to squeeze into the everglades quite nicely. I've heard iguanas are or have already formed some small isolated populations too. 152.16.15.23 (talk) 22:29, 8 November 2008 (UTC)

OK, well, what if a mad scientist genetically engineered...just kidding. :) 63.245.152.13 (talk) 04:38, 8 November 2008 (UTC)

But then again, if there was a large enough original population, couldn't natural selection take over? The lizards with the most cold resistance would survive each winter and after a few decades, they'd have adapted. You know how evolution works. I'd think this would be kind of unlikely with only one female and her parthenogenic offspring, but if several of them escaped....

As you can tell, I really want to live out my childhood fantasies! :D 63.245.152.13 (talk) 04:42, 8 November 2008 (UTC)

Natural selection will not save an ectotherm from a hostile environment. In fact, if it was introduced, the cold would simply eliminate the Komodos in favor of the indigenous species, because it has no adaptations to the cold. bibliomaniac15 04:44, 8 November 2008 (UTC)

I am rooting for them to survive and prosper in the eventuality hypothesized. Why not? Humans survived inhospitable circumstances. Edison (talk) 04:52, 8 November 2008 (UTC)

Aside from the cold problem, what suitable prey foods might Kansas offer that Komodo dragons would be able to catch and swallow? —Preceding unsigned comment added by CBHA (talk • contribs) 05:05, 8 November 2008 (UTC)

Komodo dragons would probably hunt deer, wild turkeys, and other larger animals, as well as scavenging available carrion. Whatever it can ambush is fair game. bibliomaniac15 05:14, 8 November 2008 (UTC)

The Komodo dragon may encounter other problems in Kansas. The diet section of the article Komodo dragon talks about the interesting race-against-time problem encountered by a Komodo dragon that has swallowed a goat (or similar size animal.) They have to digest the meat before it putrefies and poisons them. In a cooler climate than Komodo Island, this may be less of a problem. Or more.

The cooler climate will slow down metabolism and digestion. This may necessitate smaller prey items. 152.16.15.23 (talk) 22:25, 8 November 2008 (UTC)

Also, in Kansas, the virulent bacterial population of the Komodo dragon's mouth (also discussed in the article) would probably be vastly different. The impression I get from the article is that the bacteria are an essential part of the Komodo dragon's "ecology".

IMO, this question cries out for an experimental approach. I wonder whether the Kansas Department of Wildlife and Parks would approve test stocking of Komodo dragons. Aside from the "contribution to scientific knowledge" aspect, this might lead to some unusual and exciting hunting opportunities, especially if Kansas gets a program in place before Nebraska moves in. CBHA (talk) 06:12, 8 November 2008 (UTC)

That was AFTER humans had developed sufficient intelligence which allowed them to survive a large multitude of environments. If you suddenly dump a species in a completely hostile environment, there's a very good chance it's not going to survive. Remember, when we have catastrophic events which lead to a significant change in the environment, we also tend to get mass extinctions. Some species survive the changing environment, but many don't. And while many species have migrated, often they don't migrate to a massively different environment, at least in one go and as far as we know. Even if they do, most species (or genera) who live in a wide multitude of environments appear to have adaptions which enable them to survive resonably okay in these multitide of environments, which therefore likely arose before they were so far widespread. Nil Einne (talk) 07:30, 8 November 2008 (UTC)

Reptiles in temperate or cold climates usually find places to hibernate in winter. Reptiles seem to be pretty widespread, so it stands to reason that at some point komodo dragons had an ancestor that lived in a much cooler climate and therefore had the instinct to hibernate in the winter. Wouldn't it be possible that that latent hibernation instinct could be revived with a bit of natural selection or perhaps just the right stimulus? What we really need to be asking is, how do tropical reptiles usually respond to a cold climate?

Also, half the reason I love the Wikipedia reference desk is because you take insane questions like this seriously. This place kicks ass. :D 63.245.144.68 (talk) 13:27, 8 November 2008 (UTC)

I agree! 152.16.15.23 (talk) 22:25, 8 November 2008 (UTC)

I just learned from the humanities desk that I'm descended from the gods. 63.245.144.68 (talk) 05:18, 13 November 2008 (UTC)

If the mama Komodo dragon found a dry storage site for nuclear waste, where the spent fuel was in stainless steel casks, or even in pools, enough heat would be emitted to keep her quite cozy (without being exposed to a lethal level of radiation). She could live long and prosper. The Wolf Creek Nuclear Generating Station in Burlington, Kansas has 427.3 metric tons of spent nuclear fuel in storage per [18]. This also sounds like the start of a fine 1950's black and white horror movie about mutant Komodo Dragons. Edison (talk) 03:07, 11 November 2008 (UTC)

Relativity's contradiction

Respected sir/ma'am,

I have read special theory of relativity from halliday,resnick and walker's fundamental of physics.After reading that I came across a doubt which my teacher told me that it is contradiction to relativity.But I cannot find contradiction anywhere.

(wrt is with respect to) Question is :-

Suppose 2 observers A and B ,A is at rest wrt ground and B is moving at comparable velocity

v/c doesn't tend to 0.Now if A observe B time for B wrt A increases.But other way round if B

observe A time for A wrt B increases.So time is increasing for both wrt to each other and

they should be of same age for any time interval which doesn't happen.

Pls tell me how to get this logic is right or wrong.

Thanking You! Yours obediently, Harsh Agarwal(harshagg) —Preceding unsigned comment added by Harshagg (talk • contribs) 09:27, 8 November 2008 (UTC)

You are correct - from the viewpoint of each observer, time is passing more slowly for the other observer. This appears to create a paradox if you are still thinking in terms of a Newtonian absolute time. However, in special relativity, neither observer has a privileged viewpoint, and the fact that they each observe time to be passing more slowly for the other observer simply means that their local time co-ordinate axes are at an angle to each other. The apparent difference in time can become a real difference in elapsed time if the observers meet up at some point in the future in the same frame of reference. But to do this, one observer has to accelerate, their histories are no longer interchangeable, and so their viewpoints are no longer symmetrical - see our article on the twin paradox. Gandalf61 (talk) 09:51, 8 November 2008 (UTC)

Gandalf is absolutely right. I think the part you are missing is that, as Gandalf61 says, one of the observers has to accelerate in order for them to end up again at the same point, while the other doesn't. Hence things are not symmetrical, which makes all the difference. Also, you don't have to word your question in the "application" form they teach us in India in fifth standard lol (just kidding, I'm from India too) ReluctantPhilosopher (talk) 10:07, 8 November 2008 (UTC)

What if A and B mirror each other and accelerate at the same rate so as to arrive at a common point? What then? Clarityfiend (talk) 03:04, 9 November 2008 (UTC)

If they reach a common point but still have a non-zero velocity relative to each other then they still have different frames of reference, so there is no paradox. If one observer accelerates so as to reduce their relative velocity to zero then the accelerating observer experiences a real time dilation as per general relativity, so there is a real difference in elapsed time, but no paradox as their histories are not interchangeable. If the observers achieve a zero relative velocity by both accelerating in a symmetrical fashion then they both experience identical time dilation and there is no difference in elapsed time, so once again no paradox. Gandalf61 (talk) 10:24, 9 November 2008 (UTC)

A few questions about immunology

Hello, I would be very grateful if somebody could help me understand four questions about the immune system:

1. Is adaptive immunity acquired even if an infection is treated with antibiotics, or is it necessary for the body to eliminate the pathogens itself?
2. Is it true that adaptive immunity cannot be acquired against UTIs caused by Escherichia coli, since it is not in the body's "interest" to create defences against a bacterium which is important for the gut?
3. If somebody develops immunity against one certain species of bacteria, does that help in any measure against other, related species of bacteria?
4. Lacking an adaptive immune system, does that mean that lampreys are vulnerable to the same pathogens time and again?

Thank you! -Leptictidium (mt) 09:36, 8 November 2008 (UTC)

---

• 1 probab ly yes, because the antibitiocs will have been given well after the start of the infection giving the system plenty of time to respond.
• 2 I think that immunity will not normally be triggered against "food".
• 3 yes if the related bacteria present the same antigens on their surface, but closely related bacteria can appear very different. Graeme Bartlett (talk) 11:43, 8 November 2008 (UTC)

You might find this an interesting read for point number 4. They act like they have an adaptive immune system by responding to infections more rapidly second time around. I'm not sure how this works though, I didn't read the whole article. —Cyclonenim (talk · contribs · email) 12:10, 8 November 2008 (UTC)

---

• 1. Many antibiotics are "bacteriostatic". These antibiotics don't actually kill bacteria, but simply prevent them from growing more. For these antibiotics, the immune system is pretty much essential to eliminate bacteria that are already present; the antibiotics mainly give the immune system a chance to get ahead of the infection.

Other antibiotics are "bacteriocidal", and actually kill bacteria. Even with these antibiotics, it's difficult to treat patients with severe immune defects, though.

• 2. This isn't true. Immune responses to E. coli are common, and fortunately so, because there are several pathogenic strains of E. coli (as well as the commensal strains that are normally present).

However, immune responses to organisms on the surfaces of the body (including the skin and the mucosal lining of the urinary tract, as well as the inside of the gut) are special cases in general. It's not in the body's interests to generate massive immune responses in these areas, because it's normal to have some microbes there (or to have vast numbers of microbes there in the case of the gut). If there was a constant immune response to organisms on our surfaces, our surfaces would be constantly inflamed. There are special forms of adaptive immunity that are specialized for mucosal surfaces, and these will work on urinary E. coli (as well as on pathogens in the gut, and so on). The issue of mucosal surfaces is much more important than the "bacterium that is important in the gut" issue.

• 3. The previous answer (yes if the related bacteria present the same antigens on their surface, but closely related bacteria can appear very different) is exactly correct.

• 4. Lampreys do have an adaptive response, though it is quite different from jawed vertebrates in the molecular details. As such, they do have a memory response to pathogens, though it's slower and perhaps less effective than in jawed vertebrates.

Non-vertebrates do not have adaptive immune responses, and these species are indeed vulnerable to the same pathogens time and again. (It's not quite so simple, because there's evidence that exposure to a pathogen can trigger a general, relatively long-lasting, state of increased immune responsiveness in some insects, so if the insect is exposed to the same, or a different, pathogen in that period it will be more resistant. There are also some claims that some insects may have an adaptive immune response ,wit ha true memory component, though these are rather unconvincing, in my opinion.)

Hope this is helpful. Ian (talk) 17:23, 8 November 2008 (UTC)

So what causes the corn to pop?

Having just read the explanatory responses to the cell-phone/corn popping advert above, I have a little problem understanding how the corn is 'popped'. I do understand why corn pops in normal cooking circumstances. Richard Avery (talk) 10:08, 8 November 2008 (UTC)

Water inside the kernel, coupled with a strong outer shell; water turns to steam inside and can't escape until it builds up enough pressure to cause a mini-explosion. What advert? There's no intentional advertising on this site. You sure you didn't follow a link from an outside site?---68.237.2.254 (talk) 10:46, 8 November 2008 (UTC)

It was this question above about an advertisement. Fribbler (talk) 11:15, 8 November 2008 (UTC)

The popcorn in the cell-phone popping advert is popped by special effect. Somewhere on the internet is the un-edited video, but the jist of it is that already-popped pieces of popcorn are dropped onto a table near a pile of unpopped kernels. The popped kernels are air-brushed out until they hit the table. Once the popped kernels hit the table and bounce upwards, the unpopped kernels are airbrushed out. So it looks like the unpopped kernal has popped and jumped upwards slightly.

It's a rather clever bit of editing. APL (talk) 19:20, 8 November 2008 (UTC)

Found it. Here is a CNN interview with one of the guys who came up with this. Watch how he says it "wasn't about scaring people". Phone popcorn secrets revealed APL (talk) 19:31, 8 November 2008 (UTC)

Great, that simple, (well, if you have the gear) That would explain why some of the participants are looking up to the ceiling before the action gets under way. Many thanks APL. Richard Avery (talk) 19:53, 8 November 2008 (UTC)

Garden burial of animal remains enhances soil fertility?

Beyond the reputed benefits of decaying organic matter, is there anything special about the custom of burying animal remains in one's garden plot? My teenaged daughter cites this from Fried Green Tomatoes in response to a fairly urgent family issue: disposing of a mole's head deposited not far from our doorstep, apparently brought as a trophy/offering by our outdoor cats. I'm actually willing to do this if there's a valid reason. -- Thanks, Deborahjay (talk) 14:04, 8 November 2008 (UTC)

Ask the cat Deborah as it is his/her trophy. If the cat says 'yes' then bury it in your plot. Richard Avery (talk) 17:42, 8 November 2008 (UTC)

With the item remaining in situ for a good 24 hours, all four cats have since showed up as usual and utterly ignored it. I took their behavior as an indication there were no proprietary interests involved nor spirits to propitiate, hence no ceremonial disposition seems required or desired. We'll continue to rely on conventional fertilizing and composting.-- Deborahjay (talk) 18:16, 8 November 2008 (UTC)

opinion on those chairs you sit in with your legs folded under

unfortunately I don't know what to search on, maybe we have an article. How is it to sit in those chairs where your leg folds under you? Does it keep your back straighter, is it more ergonomic, better for long periods in front of a computer, etc? Or is it just a fashion/trend thing?

Obviously I'm NOT asking for legal, medical, or chiropractic advice! —Preceding unsigned comment added by 82.124.214.224 (talk) 15:56, 8 November 2008 (UTC)

I can't answer your question, but I'm assuming (just so everyone understands) that you're asking about kneeling chairs...? TenOfAllTrades(talk) 16:13, 8 November 2008 (UTC)

Yes. Anyone have an opinion on kneeling chairs? —Preceding unsigned comment added by 82.124.214.224 (talk) 16:20, 8 November 2008 (UTC)

Good for the back, but uncomfortable and not very good for the knees. If you are prone to back problems, get a kneeling chair and a conventional one, and switch frequently. Also go to a gym or pool to improve the overall muscle system holding up your back. --Stephan Schulz (talk) 17:08, 8 November 2008 (UTC)

I liked the one my brother used to have. Other than that, I don't have an opinion or reference. Dismas|^(talk) 18:39, 8 November 2008 (UTC)

I've never found one that gave enough room to my long feet. —Tamfang (talk) 03:13, 9 November 2008 (UTC)

Top Elo rating

Is there any theoretical maximal Elo rating in chess?--Mr.K. (talk) 19:03, 8 November 2008 (UTC)

As I understand it, there is no upper limit. The maximum rating is limited by the number of rated players and relative disparity in their skills. Gary Kasparov achieved the highest chess rating of 2851, but some other games using the Elo system have seen ratings over 3100.,

If someone appeared today that could beat modern grandmasters (of Elo 2700) 95% of the time, then the system would give them an Elo of ~3200. If someone then beat that player consistently (and everyone else essentially all the time) then they could get an Elo of 3700, etc. There may be practical limits to how dominating any one player can really be, but the system is open-ended so dominating performances can allow the Elo to climb essentially without limit. Dragons flight (talk) 19:25, 8 November 2008 (UTC)

OK, you could reach a perfect level of play - without any thinkable mistake - that could not be improved anymore...--Mr.K. (talk) 19:48, 8 November 2008 (UTC)

The problem is that the system isn't built upon number of wins, or even how "dominating" or "perfect" those wins are. The two factors involved are whether or not you win or lose, and the difference in ELO rating between you and your opponent. If the winner had a higher rating going into the game, his rating will not go up as much as if the loser had a higher rating going into the game. The rating is largely dependant on who you get to play moreso than how well you play... --Jayron32.talk.contribs 00:34, 9 November 2008 (UTC)

If ELO chess ratings of some players become too high then it may be decided to reduce them. I don't follow chess but remembered reading about Burmese players getting unreasonable high ratings years ago. See [19]. I don't know how it ended or whether this is a common problem. PrimeHunter (talk) 03:31, 9 November 2008 (UTC)

Sex in space

Have people ever had sex in space? Does it work any differently than on Earth? --76.91.56.34 (talk) 21:38, 8 November 2008 (UTC)

of course. people have even had a child! the first space kid. —Preceding unsigned comment added by 82.124.214.224 (talk) 21:43, 8 November 2008 (UTC)

See Sex in space. --Tango (talk) 21:45, 8 November 2008 (UTC)

Centrifuge

Why do heavier objects collect at the walls of a centrifuge? The article doesn't seem to explain why. Thanks! —Preceding unsigned comment added by 76.69.241.185 (talk) 22:45, 8 November 2008 (UTC)

Just as the force of gravity causes heavier- denser-than-water objects to sink (in water), the centrifugal force produced by a centrifuge causes the heavier denser material to drift away from the rotational axis. The advantage of a centrifuge is that, unlike gravity, we can control the centrifugal force by changing the rotational rate or radius of the centrifuge. Common centrifuges can produce forces thousands or 10's of thousands times the force of gravity. -- Tcncv (talk) 01:58, 9 November 2008 (UTC)

Here is an article that seems to have a good explanation. -- Tcncv (talk) 02:07, 9 November 2008 (UTC)

Commenting on Tcncv's reply: it should be denser-than-water & denser material, rather than heavier. BentzyCo (talk) 02:28, 9 November 2008 (UTC)

Good point. I stand corrected. Thank you. -- Tcncv (talk) 02:40, 9 November 2008 (UTC)

Proving evolution with drugs

Doesn't Antibiotic resistance prove evolution? 190.157.120.42 (talk) 23:06, 8 November 2008 (UTC)

yes. --Jayron32.talk.contribs 23:37, 8 November 2008 (UTC)

Just 'yes'? Great then, I just resolved the entire controversy. Spread the word! o_O 190.157.120.42 (talk) 23:59, 8 November 2008 (UTC)

You asked a binary question. If you are unsatisfied with the answer, perhaps you should consider phrasing it differently. --Jayron32.talk.contribs 00:08, 9 November 2008 (UTC)

There really is no doubt among anyone that knows what they're talking about. Evolution is the only plausible explanation for what we see around us. In fact, as your example shows, we know without doubt that evolution does happen, the only possible area of doubt is whether or not evolution is sufficient to explain the variety of species we observe. Studies seem to indicate that it is (there are gaps, but there's no reason to believe we won't fill them in sooner or later). --Tango (talk) 00:10, 9 November 2008 (UTC)

It unquestionably proves natural selection. It does not, IMHO, prove evolution. That would require fossil records. Magog the Ogre (talk) 01:25, 9 November 2008 (UTC)

Natural Selection is merely one of the many mechanisms in which evolution occurs. You don't need a fossil record to witness microbial evolution, since the generations occur on a time scale considerably shorter than the process of fossilization. It sounds like Magog the Ogre needs to read the Evolution article. -- JSBillings 02:13, 9 November 2008 (UTC)

No one seriously doubts that evolution exists. Creationists simply dispute that it is responsible for life as we know it. Breeding disease resistant plants exemplifies evolution but it does not prove that all life evolved from a primordial soup. Plasticup ^T/C 04:38, 9 November 2008 (UTC)

Evolution is proven already; I think what you're really asking is, "would a person who still doesn't believe in evolution, most likely for religious reasons, change their mind upon learning about antibiotic resistance in bacteria"? The answer is probably no, but it will depend on the person. (By "evolution" I mean whatever you meant by it—presumably the origin of species by natural selection, genetic drift, geographic isolation, etc.) -- BenRG (talk) 14:21, 9 November 2008 (UTC)

From the other point of view, the Creationists look at this and consider it "microevolution"—variation within a species, like dog breeding—and distinguish it from "macroevolution"—or actual speciation. Scientists do not generally make that distinction and do not see a hard line between the two concepts. --98.217.8.46 (talk) 15:12, 9 November 2008 (UTC)

I think it's fair to say that the Creationists were backed into their macro- vs. micro- distinction -- God of the gaps style -- when what they consider micro- became patently obvious even to non-scientific people. Presumably even the president of the Answers in Genesis group prefers modern antibiotics to older ones which have long since been overtaken by bacterial evolution. --Sean 15:01, 10 November 2008 (UTC)

A demonstration that I did a LONG time ago demonstrates what's going on. Cut out a few dozen paper squares - each maybe 2"x2". These are our animals. Now take a large pile of coins of random denominations (quarters, dimes, nickels, pennies) and put two onto each paper square animal representing it's genes - one coin on the left of the square, one on the right. (Actually - you don't need real coins - you can just write the values onto the paper instead). Now, play the following game:

• Genetic reproduction: Take pairs of animals at random - let them "make babies" (four babies per pair of parents) - two of the four offspring have coins identical to the left-coin from the 'daddy' animal and the right-coin from the 'mummy'. The other two have the same right-coin as the daddy and the left coin of the momma.
• All of the parents die off and their paper squares and coins are 'recycled'.
• Natural selection: Now - look at the new population of animals and sort them so the ones with the biggest cash value are on your left - ranging down to the ones with the least cash value on your right.
• Sadly, the cheapest ones die young - so eliminate (and 'recycle') the half of the population with the least cash value...the survivors become the parents for the next generation.
• Repeat the process several times.

After a very few generations, almost all of your animals have quarters or perhaps dimes in their genes - and after not many more generations, they are all 50 cent animals.

Interestingly - you can change the rules partway through - and the "environment" can change to suddenly benefit animals that which weigh the least. Because dimes and pennies weigh less than nickels and quarters, you soon get a population of 2c, 11c and 20c animals.

There are other interesting experiments you can do. Suppose that you start your population of animals with none of them having a quarter in their right-side gene. No matter how long you play the game, you'll never get any 50 cent animals...they'll pretty soon all be 35 cent creatures. Now - suppose that every generation, you introduce a mutation. Each generation, pick a couple of animals at random and for each one, replace one of it's "gene" coins with a different one (sometimes a quarter, sometimes a dime, etc). These mutants will mostly be worth less than 35 cents - so they'll get eliminated from the gene pool rather quickly - but once in a while, you'll get a freak mutation that creates an animal with a quarter in it's right gene. In an amazingly small number of generations, this freak will take over the world - and all of your animals will be 50 cent creatures.

SteveBaker (talk) 15:26, 10 November 2008 (UTC)

Any interesting demonstration, but not quite how genetics works, as I understand it. There is no distinction between right and left, they all get mixed up, so if the parents were AB and CD the 4 children should be AC, AD, BC and BD. To demonstrate the affects of mutation, start off with everyone having the same coin (a dime, say) on both sides, and then proceed with the generations as you describe with random mutations which can change dimes to any other coin and see how long it takes before almost everyone is worth 50 cents. --Tango (talk) 17:10, 11 November 2008 (UTC)

November 9

do electric blankets save energy vs. an electric heater?

Is an electric blanke energy-efficient versus my electric heater, because I'm right next to it, and it heats into an insulated place? It seems it would only need to get a fraction of as hot as a normal heater, and there's no such thing as more or less efficient heat generation via electricity -- it's all 100% efficient, isnt' it? (though maybe not directed optimally, but the amount of total heat generation from every x-watt electric blanket pulling y amps is the same, isn't it? —Preceding unsigned comment added by 82.124.214.224 (talk) 02:47, 9 November 2008 (UTC)

if you operate an electric blanket at night and turn the thermostat down, you will probably save considerable energy. You can be cozy under the electric blanket while the house is allowed to become quite cool. When the trade-off is turning up the electric heater (as opposed to a gas furnace) the savings are even clearer. The downside is that some people worry about the small electric field from an electric blanket as an example of EMF Electromagnetic field which is hypothesized to be harmful. An ad for an electric blanket [20] says you can save 10% on your heating bill by turning the thermostat down while you sleep under the electric blanket. Edison (talk) 02:58, 9 November 2008 (UTC)

You appear to be presuming the OP is referring to central heating but I don't see any reason from the question to presume he/she is. The IP looks up to France, where I believe central heating is the norm, so you may be right but there is still the possibility the OP happens to live in a house without central heating. Definitely here in Auckland (or heck NZ) where central heating is relatively rare, it's likely you'd only heat your bedroom when your sleeping. While an electric blanket is still likely to be quite a bit cheaper, the costs savings are probably going to be less. Of course, if your me, a good feather-down duvet is enough for most winter nights in Auckland anyway. Nil Einne (talk) 11:14, 9 November 2008 (UTC)

The answer isn't a "yes" or "no". It is an "it depends". What is the watt rating on your electric blanket? What is the watt rating on your heater? I have a ceramic heater that is 12 watts and an electric blanket that is 35 watts. So, I figure I can run the little heater twice as long as the blanket and get the same energy usage result. So, you want watts to calculate kwatt hours used for some number of hours running each device. -- kainaw™ 03:05, 9 November 2008 (UTC)

I do not believe that you have an electric space heater which draws only 12 watts. Please check the nameplate more closely. I would believe 12 amperes. Electric blankets use far less power than any appliance calling itself an electric space heater. 03:07, 9 November 2008 (UTC)Edison (talk)

I agree with Edison that it is very unlikely that you would have a space heater of any kind that drew only 12 watts. (I would believe 1200 watts, or 12 amps, or somesuch.) In any case, just the rating on the packaging isn't necessarily going to tell you the whole story. Both blanket and heater will likely contain thermostats which regulate their output; neither device is likely to be operating at full power all the time. TenOfAllTrades(talk) 16:59, 9 November 2008 (UTC)

I'm sorry. I didn't mean to imply that I was referring to a space heater. It is a foot heater under my desk. I don't own a space heater. So, all I had to go on in my example is my electric blanket and my foot heater. -- kainaw™ 21:14, 9 November 2008 (UTC)

Unfortunately, heating your feet and heating your bed are rather different tasks, so the example isn't very useful. Space heaters use *enormous* amounts of electricity. --Tango (talk) 21:29, 9 November 2008 (UTC)

I can't even believe a small space heater under the desk only draws 12 watts. That is like a very small light bulb. Edison (talk) 22:00, 9 November 2008 (UTC)

Kainaw called it a "ceramic heater", perhaps it's like a heated ceramic tile that you rest your feet on? That could be quite efficient. --Tango (talk) 22:25, 9 November 2008 (UTC)

That is exactly correct. As I said - I don't have a space heater, so I just used what I did have for the example. My point was that when talking about power consumption, you don't have to guess. You can look at the power rating on the device and calculate rather accurately how much power it will consume over a period of time. -- kainaw™ 00:28, 10 November 2008 (UTC)

I don't think calculating it's that easy though. As you stated, you need to calculate how many kilowatt hours you use, but most heaters aren't on constantly so you'd need to work out how long the heater is actually on, e.g. by timing how long it's on for. I have used several oil filled heaters, either 1kW or 2.4kW. However even if the thermostat's at maximum, they don't usually remain on constantly. (And I personally have never felt the need to turn then on maximum except sometimes when I turn it off after I let it get very hot.) Indeed the 2.4kW one has 3 levels and then a variable thermostat. I'm not sure what the 3 different level setting does, it may adjust the power consumption (as opposed to simply affecting at what temperature the heater turns on and off). The simplest thing would be to get a power consumption metre you can plug the heater into. What is clear is that the electric blanket will win although by how much will vary. (Here in NZ again, our houses tend to be rather poorly insulated which would increase consumption of space heaters a fair amount Nil Einne (talk) 09:30, 10 November 2008 (UTC)

obviously, if the purpose is to heat your body from ambient temp to 65 or something, the less additional mass you have to heat, the more efficient. putting the heater in contact with your body is obviously a step in that direction, compared to heating the mass of air up in the room and wafting it over towards yourself.

on the other topic, yeah, 12 watts sounds about right for something you contact with your body/feet to keep warm, but inadequate for a space heater in anything but a small box (see above) if you think about the heat from a 12 watt bulb. Just for fun; the added heat from AGW currently is estimated about 1.7 watts per square meter, so imagine keeping your tootsies on that little warm tile. it's not insignificant.Gzuckier (talk) 20:23, 11 November 2008 (UTC)

You just reminded me that it is time for our local Darwin award nominees. Every year, about this time, people start setting their rooms on fire - usually killing themselves, by sticking space heaters under their blankets. -- kainaw™ 02:13, 12 November 2008 (UTC)

Speciation in the lab

What new species, if any, have been created in labs? NeonMerlin 03:24, 9 November 2008 (UTC)

See Mycoplasma laboratorium. --Arcadian (talk) 03:48, 9 November 2008 (UTC)

Not seeing species creation, at least not in that article... --98.217.8.46 (talk) 04:14, 9 November 2008 (UTC)

See Speciation#Artificial_speciation. --98.217.8.46 (talk) 04:14, 9 November 2008 (UTC)

spacetime deformation

If you have a supermassive object a great distance away from a planet or something.. The planet will gradually "slide down" the gentle (at that distance) slope of the object's gravity well, right? But a ball falling from a tower on the planet will accelerate far more rapidly than the planet is accelerating. So doesn't that mean that the gravity gradient is steeper locally than relative to the object? In other words, won't the planet just stay slumped in its own deformation of spacetime? Or is this just a trick of relativistic geometry? I know it's common sense that the planet doesn't have to labor up its own gravity well to move anywhere, but does relativity actually explain WHY it doesn't? This is what I mean: http://img204.imageshack.us/img204/2894/wellsbp1.jpg Thanks 71.176.179.91 (talk) 04:32, 9 November 2008 (UTC)

First, gravity wells are a Newtonian thing, not a relativistic thing—see gravity well. In Newtonian gravity the acceleration of an object depends on the net force acting on it, and the net force is just the sum of the individual forces. An object can't exert a net force on itself. So the forces acting on the planet are a bunch of internal forces, which are large but add up to zero (because they point in different directions), plus the force from the distant supermassive object, which is small but nonzero. The net result is an acceleration toward the distant object, and it's the same acceleration as if the internal forces hadn't been there at all. If you like, the object doesn't have to climb out of its gravity well because the gravity well is always instantaneously aligned with the object. Unlike the object itself, the gravity well doesn't have inertia. Gravity acts instantaneously and without any apparent mechanism.

In a relativistic field theory, like Maxwell's electromagnetism or general relativity, the field of an object can't be in constant "communication" with the object because of the light speed limitation. If the object's motion changes, the field won't know about it until some time later. So relativistic fields do have a life of their own, and they do have inertia. If you change the motion of a charged particle it experiences a force due to the delay in updating its own field, and I think this could be described as "laboring up its own potential well". (This force is called the "self-reaction" or "back-reaction", and Wikipedia doesn't seem to have a good article about it.) But that doesn't matter when the particle is being accelerated by gravity, because everything gravitates equally, including fields. The gravity of the distant supermassive object pulls on the planet and the planet's gravity well in equal measure, so the planet doesn't have to fight against the well.

(I should add that I don't actually know if there's a gravitational version of the electromagnetic back-reaction. It's tricky to discuss such things in gravity's case because everything gravitates. You can do electromagnetic experiments by pushing charged objects around with uncharged sticks, but you can't do gravitational experiments by pushing massive objects around with massless sticks. Even light has a gravitational field. It may not even make sense to say that there's a gravitational back-reaction, because there's no way to change an object's motion that the gravitational field won't know about ahead of time.) -- BenRG (talk) 14:02, 9 November 2008 (UTC)

The article self-force looks fine to me; did you not find it? --Tardis (talk) 01:36, 10 November 2008 (UTC)

mechanical reactionless drive?

File:BalloonsReaction.jpg

Supposing you have two spherical balloons full of water connected by a pipe full of water all the way though. if you squeeze one balloon equally in all directions, the pressure change in the pipe will make the other balloon expand equally in all directions. If they were in outer space doing this would not move the system backwards of forewords since all forces cancel out. But hold on-the center of mass has been moved without reaction in violation of Newtons third law of motion. Rotate the deflated balloon around 180 degrees and reverse the process and you have a reactionless drive. Or am I missing something?

--Trevor Loughlin (talk) 06:20, 9 November 2008 (UTC)

You aren't squeezing "equally in all directions" if you have a hole for water to flow through. Dragons flight (talk) 07:14, 9 November 2008 (UTC)

And the apparatus would probably move away from you... Due to viscosity and friction concerns, forces YOU apply will not be 100% returned via the opposing balloon, and there will be a net force away from you that will be unopposed... --Jayron32.talk.contribs 11:30, 9 November 2008 (UTC)

I thought someone would bring up the "hole the water flows through" but since this "hole" is connected to a solid metal tube with water all the way through it (no air bubbles to be displaced) connecting to the other balloon, there is only a pressure change and I assume this would not cause a backwards reaction. As for friction and viscosity, what if you used liquid helium? An easier to understand thought experiment equivalent to the two balloons (in fact more practical) would be two bicycle chains with a j shaped weighted section on two spindles oppositely opposing each other in a reflection at the top of the j to prevent rotation. If both were synchronized and the weighted section was pulled up on the bottom j chain and down on the top, I am sure that the center of mass would move without any reaction in the opposing direction. I will of course try my experiment unless you can convince me I am wasting time and money, but (as with EM drive) a space based test would be the only convincing evidence.

It is not as if I haven't broken fundamental laws of physics before-I have already built and tested in (lucrative) real world applications a Quantum Superluminal Communication Device which violates causality by transmitting USEFUL binary data from the future to the past. But I am not putting the plans for that here because I intend to rule the world using it! —Preceding unsigned comment added by Trevor Loughlin (talk • contribs) 15:34, 9 November 2008 (UTC)

I think you'll find that you can move the center of mass around, but the balloons won't actually move anywhere. And rotating the balloons around is cheating- it requires energy from outside the system 71.176.166.28 (talk) 17:31, 9 November 2008 (UTC)

No, the hole implies a pressure imbalance, which implies a net force, and is what causes water to flow from one side to the other. Dragons flight (talk) 23:06, 9 November 2008 (UTC)

An electric motor with or without a gyro will spin the system. Without a gyro it will move in the opposite direction, but as long as its mass is similar to the reactionless chain assembly it WILL easily rotate the centre of mass.

The change in PRESSURE causing a reaction to spoil this system IS a more serious objection. But this applies to the balloon experiment. What about the chain based experiment in the image above? It also has four linked units to counteract all rotational forces. I will build this unless you can find a flaw.—Preceding unsigned comment added by Trevor Loughlin (talk • contribs)

Regarding the balloon drive, I think the fly in the ointment is the need to "Rotate the deflated balloon around 180 degrees". Is this rotating one balloon or rotating the entire system around the centre of mass? CBHA (talk) 06:12, 10 November 2008 (UTC)

The whole system is rotated by a motor, which will rotate in the opposite direction at the same speed if it is the same weight, but an alternative might be to have two separate motors on each balloon and alternately switch them on when each balloon inflates. The balloons would have to be connected by a U shaped solid tube or they WOULD impart a reaction and spoil the plan, because the balloon would push against the tube as it expanded outwards pushing the whole system backwards. But with a U shaped tube the expanding balloon would push DOWNWARDS forcing the system to ROTATE UPWARDS (not the required sideways movement from the top motor needed when the appropriate balloon has expanded. This problem is eliminated by pairing an opposing (upside down U) reactionless drive as a mirror image,so that each rotation cancels out, as with the chain drive version's. —Preceding unsigned comment added by Trevor Loughlin (talk • contribs) 13:50, 10 November 2008 (UTC)

This is an easy one: The center of gravity (strictly, the center of mass) of the system composed of the two balloons, the water and the pipe would not move as you squeezed the balloon. So the whole machine would move as you squeezed - but then stop when you stopped squeezing. When you release the balloon and the water sloshes back again, the center of gravity still doesn't move - although the machine moves back the other way - and you're back exactly where you were. Rotating the system about it's center of gravity leaves that center of gravity in the exact same place - so there is no net motion and this doesn't buy you anything. To rotate it other than around the center of gravity requires reaction mass...so the only way to propel yourself forwards is to expel reaction mass...pretty much as you'd expect. SteveBaker (talk) 14:56, 10 November 2008 (UTC)

Rotating around a point other than the center of gravity could be accomplished by attaching two such devices at a common rotation point, and have them rotate in opposing directions. Of course, the center of mass would still not be changing position.

The problem of a reactionless drive has existed for ages. It's a staple of science fiction. The Dean drive is the most infamous example of a "real" reactionless drive. ~Amatulić (talk) 22:24, 10 November 2008 (UTC)

AHA-but if the balloons are connected by a U-SHAPED TUBE then this "sloshing back" will create a ROTATIONAL rather than a LINEAR reaction. This "rotational reaction" could be CANCELED OUT by a second version of the U+balloons linked in a mirror image, since the two rotations would be in opposing directions. (I am not talking about the desirable sideways rotation of the whole system created by the motor to spin the smaller balloon about the bigger one, but an undesirable top to bottom spin of the single U which force the centre of mass back to where it started.) —Preceding unsigned comment added by Trevor Loughlin (talk • contribs) 02:30, 11 November 2008 (UTC)

Look - you can make this as complicated as you like - it's NEVER going to work. The whole "every action has an equal and opposite reaction" thing means that you're screwed no matter how complicated you make it. The best you can hope for is to exhaust our patience in breaking down these increasingly bizarre (and useless) contraptions to find the 100% inevitable flaw in them. That doesn't mean that you succeeded in inventing a reactionless drive - it just means that you became boring and we gave up trying to explain one of the most fundamental laws of physics to you. Feel free to consider that this may already have happened. SteveBaker (talk) 04:02, 11 November 2008 (UTC)

I am fully aware of the implictions of Newtons third law of motion, and am skeptical of reactionless drives, otherwise I would have built and patented this design rather than put it in the public domain. However, rather than dismissing it out of hand, look at the diagrams and tell me how it will not work in detail-for example where do the forces NOT counteract, leading to the system moving back to where it started? —Preceding unsigned comment added by Trevor Loughlin (talk • contribs) 05:14, 11 November 2008 (UTC)

Why bother though? Either Newton's laws work and the exercise is meaningless. Or (and this is important) Newton's laws don't work, and the whole thing is even more meaningless, because then we would literally have no way of predicting what your device (or any other device) will do in any untried situation.

If you have outside, physical evidence that Newton might be wrong about something, then that's a whole different story. But this question is simply asking us to use Newton's laws to prove Newton's laws. It's just an exercise in futility. APL (talk) 05:46, 11 November 2008 (UTC)

I agree with SteveBaker. My interest ran out when you suggested a U-shaped tube instead of a straight one, thereby changing the entire configuration.

But if you think the chain drive mechanism has potential, please do not be discouraged by negative comments here. A lot of good ideas have been subjected to negative comments. Go ahead and build one. If it works, I expect NASA or some other space agency will be interested to see the results. CBHA (talk) 05:59, 11 November 2008 (UTC)

I will. If it is going to pass the "swing" test it will need several blocks in series of the four unit drives illustrated so that there is always some momentum, like a four stroke engine (assuming it works) and if it can constantly pull a swing at an angle this might work. —Preceding unsigned comment added by Trevor Loughlin (talk • contribs) 14:21, 11 November 2008 (UTC)

Come on guys, this one is easy. SteveBaker had the answer already. Let's assume frictionless pipes and zero viscosity water just for fun. Look at the first diagram, top left at the top of the section. When you compress the right balloon, it exerts a force against the balloon in every direction, all of which cancel out - except the upward/downward direction, since the water is free to flow down the pipe. It reaches the end of the "down" section and exerts a force downward on the down side of the horizontal pipe section, cancelling out the until-now-uncancelled up force it exerted on the top of the balloon during compression (thus this balloon will move slightly up, keeping the centre of mass fixed as the water travels down). Since it is stuck in the rightmost elbow joint and has stopped going down, it exerts forces on that joint in all the lateral directions too. These all cancel out except for the left/right forces, as the water flows to the left along the pipe. Eventually it reaches the end of the horizontal bit of pipe and exerts a force on the left wall of the pipe, finally cancelling the force it exerted to the right (so the pipe will move slightly right, keeping the centre of mass fixed as the water travels left). More forces in every direction, but the water can flow up into the left balloon. There's a delay between the force on the down side of the left end of the pipe and the force on the top of the left balloon, so this balloon will move slightly downward, keepign the centre of mass fixed at all times. So as you do this you will set the device rotating (in rotation that will be cancelled once you stop pumping water through as the forces cease in reverse order), but its centre of mass remains fixed at all times. Finding the inevitable flaws in "free energy" machines like this is a mildly entertaining but ultimately pointless endeavour. Maelin (Talk | Contribs) 14:41, 11 November 2008 (UTC)

Indeed.

I could come here and describe a Heath Robinson (Rube Goldberg for you Americans) contraption with hundreds of swinging, spinning, spring loaded parts with hydraulic and pneumatic connections using exotic mixtures of non-Newtonian fluids, clockwork parts, gyroscopes, magnets, complicated chemical and biochemical reactions, active electrical parts and photonic circuits, with complex computer software driving them using neural networks and evolutionary algorithms - being driven by a trained parrot...and then ask the people at the science desk to tell me why it doesn't work as a reactionless drive. The result is likely to be exceedingly difficult to analyse at a detailed level - it would result in days of complicated discussions and arrive at the same conclusion. You can't expect us to do that. It's utterly unreasonable - BUT it's also utterly unnecessary.

To analyse your machine (or mine), we simply place an imaginary black box around whatever bizarre contraption we are presented with and boldly assert (per Newton's first law of motion) that the center of gravity of "the system" (the black box) doesn't move no matter what happens inside because "the system" is in a state of motion that it will continue in unless some external force is applied to it.

In the case of a rocket engine - the exhaust from the engine remains inside the box - so the center of gravity of the rocket and all of it's exhaust gasses doesn't move. In the case of a light-sail, the light source, the craft and all of the photons are inside the box - and the box doesn't move. So for the craft to move bodily one way - something else has to go off in the opposite direction to keep the center of gravity of "the system" where it is. Hence there are no "reactionless" drives - per Newton's first law.

If you want to assert that this is not the case then you are explicitly denying Newton's laws - and we're going to laugh at you. If Newtons' laws are somehow incorrect at "human scales" of speed, mass, distance and time - then we're in a much weirder universe than we believe. It's utterly inconceivable that any device you could think up like this could break those laws without doing something relativistic or quantum-level or close to a black hole or in some other way radically 'pushing the envelope' of the realms of experimentation we've done as a civilisation for the past 300 years. Mundane stuff like pipes and liquids and spinning things are just too well tested for the laws to be incorrect at those scales.

The whole beauty of these kinds of fundamental law is that they allow simplification. We don't NEED to calculate the energy in each part of the system, analyse the torque and the tensors and the inertia and all of that stuff. We know for an absolute certainty that if we went to all of that trouble - the answer would be "NO!". We have a simple law of nature that's always proven correct that says that we can shortcut all of that analysis and treat the system as a black box. It's the same deal with perpetual motion machines - the laws of thermodynamics say "NO!". So there you go: "NO!" - and the explanation is very simple indeed. SteveBaker (talk) 15:05, 11 November 2008 (UTC)

I admit that this idea is so simple that it is highly probable that someone must have tested it at some time and failed, though I have made a search. It will not be my highest priority to build! So what do you think the chances of an idea that really does "push the envelope" such as EM drive, has of actually moving a craft in a straight line in space without rockets?

Certainly the device IN THE FIRST DIAGRAM will ROTATE about its centre of mass and not move anywhere when transfering the fluid. Worse still, without any air resistance or gravity it would end up on its SIDE by the time all the fluid is transfered, so instead of the motor being able to swing the small balloon around the big one, and then reverse the process, the motion is now upwards instead of sideways, and another cycle will put the device the wrong way round. But what about the second diagram, when two mirror image units counter each others rotation in the Z-axis? —Preceding unsigned comment added by Trevor Loughlin (talk • contribs) 02:54, 12 November 2008 (UTC)

It's not necessary that someone tested something just like this. You're missing the "big message" here. Newton's first law says that if we draw a line around some kind of 'system' (your machine in this case) then unless some external force operates on it - it's just gonna sit there with it's center of gravity not moving by so much as the diameter of an atom no matter what weird-assed motion it's going through internally.

We've tested all of the parts of standard machines and we know how such things behave. So:

• The chances of a reactionless drive working with 'ordinary stuff' such as you describe is zero - not gonna happen.
• The chances of making a reactionless drive that uses some aspect of relativity or quantum theory (or preferably, both) seem exceedingly slim - the science is pretty well known.
• If I'm pushed into imagining some kind of experiment (likely, just a thought experiement) where there might be some doubt as to whether Newton's law might break unexpectedly - then I guess it's remotely possible that some insanely 'extreme' design that has the mass of three galaxies - or which was just over a 'planck length' long or only works when cooled within a billionth of a degree above absolute zero - or which would have worked within a picosecond of the big bang but cannot work at any time since - or which only works in 17-dimensional space....something like that might maybe expose a new aspect of the laws of motion that could perhaps require a small adjustment to Newton's first law that might just open a chink of hope for a ridiculously impractical reactionless drive.

But I really don't imagine any such thing could ever be remotely practical - simply because everything within the realms of "possible" have been so well researched.

SteveBaker (talk) 05:10, 12 November 2008 (UTC)

One other idea. Supposing you had two spindles with a heavy chain inside a rectangular box, and a motor at each end wound/unwound the chain from one spindle to the other. The box would rotate about its center of gravity due to the spin of the motor at each end. But if we have TWO of these boxes back to back what would happen? Would the box move linearly backwards as the in the opposite direction to the winding of the chain instead of spinning? If it did not, then mass would have been transered without reaction,so it probably would, but I am not sure what would happen. It certainly WOULD move backwards if the chain was pulled in without being still wound on the other spindle. But as long as the chain is attached to the two spindles, it can't move backwards(?), otherwise with large enough spindle and rope the device would move further than its length in any case,violating Newtons third law in any case(?)

LISTEN TO ME. NO! It's Newtons' first phreaking law. You will NEVER come even close to breaking it with any crazy contraption you can come up with. Give it up and go back to squaring the circle, performing a trisection with ruler and compass, making a perpetual motion machine, calculating the last prime number (and the last digit of PI)...those are all just as likely as you coming up with a reactionless drive. SteveBaker (talk) 01:18, 13 November 2008 (UTC)

Look. Whenever you have closed system consisting of one object exerting a force on another object and things moving each other around however you like, all the forces involved will end up balancing each other out perfectly, and the centre of mass of the whole system will continue with the exact same momentum as it had initially. If you have some complicated construction made of pipes and water and balloons and motors to spin bits around and pumps to move the water, no matter how you rig it up, if it's a closed system its centre of mass will stay exactly where it is the whole time. This is unavoidable.

Every time someone proposes a reactionless drive, or perpetual motion machine, or whatever else that will violate conservation of momentum (or conservation of energy, or entropy, or whatever), they have always taken a very basic machine and tacked on bits and altered it until it is sufficiently complicated that they can no longer understand how the forces will cancel each other out, then they say, "lo! a perpetual motion machine!". But it isn't. You can take one thing that isn't a reactionless drive, and staple it to another thing that isn't a reactionless drive, and guess what: you will still not have a reactionless drive. No matter where you move the water, the centre of mass stays the same. No matter how you rotate bits, the centre of mass stays the same. You can't escape conservation laws just by being complicated. Maelin (Talk | Contribs) 11:24, 13 November 2008 (UTC)

If the chain is continuous spiral winding/unwinding should not cause back reaction (I think) and the mirror image device in the same box will prevent rotation.

File:SpiralReaction1.jpg

If the chain was not continuous it would be subject to Newtons third law and not work;

File:SpiralReaction2.jpg

The statement above is about a reactionless drive finding a loophole in Newtons third law, not a perpetual motion machine breaking the first law of motion-that would be a tall order. This machine would use electric motors with either a solar panel or RTG battery as the power supply.

Human brain -> computing power

Hi,

One thing I've wondered is how much memory space does the human brain harbour, in terms of computing power (eg Gigabyte, terabyte, etc.). I'd be interested to know the answer to this! Thelb⁴ 13:07, 9 November 2008 (UTC)

The best answer on this Yahoo! answer is pretty good. —Cyclonenim (talk · contribs · email) 13:55, 9 November 2008 (UTC)

Thanks, that's very interesting! 81.151.36.130 (talk) 14:23, 9 November 2008 (UTC)

But we don't store information like a computer. That explanation vaguely hints at "compression" but I think this misrepresents what we are storing. When a computer stores a video file, it stores every single pixel of every single frame, and every single sample of every audio signal, at some fixed sampling rate (30 frames x 320x240 pixels)/sec, + (44100 audio samples per second). Then, effective compression locates redundancy in these stored data, and removes that redundancy (with some "loss" in the exact representations, sufficiently engineered to be minimally noticeable to a human).

But when a human "remembers" a movie, it doesn't do anything at all like that! If you were asked to recall Pixel (122,61) at Second # 4051 in your favorite movie (that you've watched a dozen times and memorized all the dialog for), you would not be able to do ANYTHING like recall that information. You wouldn't even be able to get a glossy "key-frame", or the blurred-pixel-square representation from Second #4050 at Pixel (128,64) which you would presume is probably close to the request. You might not even be able to remember the color of the main character's shirt. At the same time, if a clever psychology-experimenter made you watch the same movie twice, with the only changed-detail being a different shirt-color on a minor character, there's a significant chance that you would have noticed that detail. How did your brain selectively notice something which you might not be able to recall if directly questioned? Clearly information-storage is selective and complex.

It's really hard to estimate the capacity for human brain's information storage system when we know so little about how it actually works, so I would be very reluctant to assign any numeric estimate of capacity - you're comparing serial, precise machine storage to a mash-up of biological/analog distributed fuzzy storage, where the concept of "one bit" probably does not apply. Nimur (talk) 17:23, 9 November 2008 (UTC)

It doesn't really make sense to discuss the information stored in the brain in terms of bits and bytes, so estimates of storage capacity in terms comparable to those of a computer are pretty misleading. But, your question can be answered, and the answer is surprising: the human capacity to store factual memory appears to be near limitless. A Russian neurologist named Dr. Luria studied a man named Solomon Shereshevskii who apparently had limitless memory. Since then it was taken for granted that the Luria case was an extreme outlier, but in 2006 researchers at UCI discovered first one, then almost immediately afterwards 2 more people with seeming unlimited memory, a condition they termed Hyperthymesia. The speed with which new cases were discovered suggests that this capacity may actually be somewhat common, but like synesthesia, affected individuals may take for granted that they are no different from the rest of the population. --Shaggorama (talk) 22:59, 9 November 2008 (UTC)

I don't believe in this limitless-capacity idea. A poem, even an epic poem, doesn't take much RAM to store. Moby Dick is only about 10⁶ characters long, and state-of-the-art compression algorithms can get it down to 100-200 kilobytes. The pi-memorization world record seems to be 67890 digits, which is only 28190 bytes (10⁶⁷⁸⁹⁰ ≈ 256²⁸¹⁹⁰). That's the record among everyone who's ever participated in these contents; I have a hard time believing that Luria's mnemonist would have done better.

There's a famous paper by Thomas K. Landauer, How Much Do People Remember? Some Estimates of the Quantity of Learned Information in Long-term Memory (Cognitive Science 10, 477–493 (1986), online here), which estimates the total memory capacity at about 10⁹ bits. There's no consensus that he's right, but at least his measurements are based on actual empirical tests of what people remember. The neuron-counting numbers are an attempt (though not a very principled one) to estimate something else, namely the number of bits necessary to describe "the current structure of the brain". But even in an analog computer the number of states is astronomically larger than the number of computational states. The raw physical states don't behave predictably enough for reliable computation. -- BenRG (talk) 13:36, 10 November 2008 (UTC)

Obviously, it's not limitless - but the idea that memory can become fuzzier and less detailed as the memory becomes less and less important does allow it to SEEM limitless because we're able to recall the important details but merely have a broad-brush fuzziness about the less relevant parts. This does indeed suggest that some pretty sophisticated 'lossy compression' is going on - and it's happening on-the-fly. So a new memory pretty much has to displace some older information - but it's not like a computer where you delete an old file to make room for a new one...learning calculus doesn't make you forget your wedding day...what it does is to make you forget the color of your best man's shirt and whether you gave your bride an orchid or a rose. This is more like turning down the JPEG or MP3 'quality' dial on older files to make them take less space so that there is room for new files. SteveBaker (talk) 17:48, 10 November 2008 (UTC)

I mean, I don't really know what to tell you guys. Whether you 'believe' it or not, the cases I described exist. BenRG, the paper you cite is from 1986, which is a pretty old citation for neurology paper. The neuron counting attempts look nice and produce impressive numbers, but they assume an antiquated, folk-scientific principle known as the "Grandmother Neuron," a theory which states that individual objects of memory are stored in their own respective neurons. How memories are encoded is still very, very unclear, but current community consensus is leaning more towards distributed neural network implementation, an idea which makes it very difficult to give an estimate of bits and bytes. If the neural net theory is right, then the net is signficantly greater than the sum of its parts (i.e. can retain more information than the number of involved neurons may suggest). Furthermore, related ideas may be stored in mapped areas, further compressing data. When it comes down to it, the fact remains: the architecture of the brain does not resemble that of contemporary computers, either in hardware or software, so these bitwise comparisons are meaningless to begin with. Obviously the human capacity for memory is not actually limitless: physical constraints on the brain obviously must put a cap on the possible amount of data we can store. But, since we just don't know how the data is stored, there's no good reason to just assume that the memory capacity of the brain necessarily must be exceeded in a human lifetime. Although they are outliers, the 4 cases I described (in particular the latter 3) strongly support this. As far as steveabakers "lossy compression" goes, current theory seems to suggest that its more likely lossy retrieval: memories are stored intact, but are cached in a way that permits for more rapid access of the most pertinent information (and consequently, normal people lose access to alot of the details). If it was just lossy compression, repressed memories wouldn't be so problematic for traumatized individuals: the bad parts just would have been erased/stored poorly. Instead, it seems that the bad parts just often aren't accessed consciously. --Shaggorama (talk) 16:29, 11 November 2008 (UTC)

Bell inequality

I get the idea behind it and I get the experiment and scoring. But I don't really understand the actual implications of the Bell inequality being violated. This is sort of how I understand it.. is one of these correct, or am I totally off? The article is tough!

1. After observing a particle's spin, you can guess its entangled partner's spin (even measuring orthogonally to the first measurement) with better-than-random success by guessing the same as the first particle's spin.
2. After observing a particle's spin, you can guess its entangled partner's spin (even measuring orthogonally to the first measurement) with better-than-random success by guessing the opposite of the first particle's spin.

71.176.166.28 (talk) 14:38, 9 November 2008 (UTC)

Mmm... you've kind of got the implications wrong. If we lived in a world without Bell inequality, you'd have 100% chance of guessing the spins. Then, as Einstein wanted it to be (see EPR paradox), quantum mechanics would allow you to have "complete" knowledge of a given particle despite the Uncertainty Principle, which would mean that Uncertainty Principle was based primarily on issues regarding observation. But lo! Because of Bell inequality you can't just guess the spin—you will be wrong a significant part of the time, and your knowledge of the universe is incomplete, per Uncertainty Principle, and thus Einstein was wrong. Does that clarify things a bit? It actually resolves a fundamental question about QM and the Uncertainty Principle, one that most people thought could never really be resolved (most thought that one's take on whether particles contained all information—but that some of it was just hidden due to UP—was a matter of epistemological opinion, and couldn't be actually tested). --98.217.8.46 (talk) 15:03, 9 November 2008 (UTC)

No, the original poster has it the right way around—the nonclassical correlations in quantum mechanics are stronger than classical correlations at somealmost all angles, meaning that you have a better chance of guessing the spin. E.g. if the two spin measurements are separated by 60° then given the outcome of one you can predict the outcome of the other with 3/4 accuracy in quantum mechanics, while you can't do better than 2/3 in any local classical theory. (That's the specific case used in the gambling-game example I linked below.) Newtonian physics is deterministic, but Bell's theorem applies to any theory that follows the rules of classical probability, even theories that have true randomness or theories in which measurement has an unavoidable effect on the thing being measured. -- BenRG (talk) 17:34, 9 November 2008 (UTC)

Same vs. opposite doesn't matter—it's just a question of how you set up the spins. If you started with the state |↑↑〉 + |↓↓〉 then they'll be the same, if you started with the state |↑↓〉 + |↓↑〉 then they'll be opposite. In practice the easiest way to get a Bell state is from the decay of a spin-0 system, which (by conservation of angular momentum) has to lead to antialigned spins. That's why you'll more commonly hear "opposite" in descriptions. But there's no deep difference—you can turn one into the other by rotating one of the particles 180 degrees, or by simply redefining your coordinate axes. In the remainder of this reply I'll assume equal (not opposite) spins.

I'm not completely sure what you mean by "orthogonal" since orthogonality of wave functions is different from orthogonality in space. (For example the spin states |↑〉 and |↓〉 are orthogonal as wave functions but parallel in space.) But if the spin measurements of the two particles are made at angles differing by 90° in space, then your same-spin guess will be right 50% of the time, i.e. it's no better than flipping a coin. If the measurements are made in the same direction (0°) then you will be right 100% of the time. If the measurements are made in opposite directions (180°) then you will be right 0% of the time. So far there's nothing very surprising here. But quantum mechanics says that, in general, if the separation angle is θ then you will be right cos² (θ/2) · 100% of the time, whereas there's an argument from fairly general classical assumptions that you can't be right more than (1 - θ/180°) · 100% of the time for those other angles, no matter what internal algorithm the two particles are using to decide the outcome of the measurement. (edit to add: sorry, silly mistake here. Obviously if the measurements are separated by more than 90% you can guess the opposite of what you saw and be right more often than that. The formulas should be max(cos² (θ/2), 1 − cos² (θ/2)) and max(1 − θ/180°, θ/180°) (for 0 ≤ θ ≤ 180°). The quantum formula is at least as large as the classical maximum for every θ and it's strictly larger except when θ is a multiple of 90°.)

But I wouldn't worry about it. There are lots of ways of showing that quantum mechanics is nonclassical, and Bell's is not especially clear. He proved too much—it's not necessary to get a result valid for any angle, you just have to show one example of quantum mechanics violating classical assumptions. I like this gambling-game version (which isn't original to me, though that explanation is mine).

All of the above assumes spin ½ particles (like electrons). If you're using spin 1 particles (like photons) then you should divide all of the above angles by two, and your Bell state will look more like |↕↕〉 + |↔↔〉 (or |↕↔〉 + |↔↕〉). -- BenRG (talk) 17:08, 9 November 2008 (UTC)

So the .707 figure means that if you guess "same" for the second particle you'll be correct 71% of the time, instead of the 50% that is the non-QM answer? I guess that makes sense, especially in light of your point about same vs opposite just being a matter of how you set up your axes 71.176.166.28 (talk) 17:41, 9 November 2008 (UTC)

(see my edit above) The probability depends on the angle between the measurements, and I don't think there's any simple angle for which it equals .707 (i.e. there's no simple θ for which cos² (θ/2) = √2/2). The non-QM maximum is 50% at an angle of 90°, and the QM prediction at that angle is also 50%. You need to use some other angle to get a difference. Note that the QM formula is a prediction of quantum mechanics, while the classical formula is not a prediction, it's a maximum over all possible physical theories that satisfy certain assumptions. -- BenRG (talk) 11:33, 10 November 2008 (UTC)

That link is great. So it's saying that if each player had a sheet of paper that says something like:

• If the number you're given is a 1, say YES
• If the number you're given is a 2, say NO
• If the number you're given is a 3, say YES

then they make on average (1 & 2 is +1) + (1 & 3 is -2) + (2 and 3 is +1) = ZERO. But they can actually make more money using entangled particles than with a predetermined answer key? That's amazing! thanks a ton 71.176.166.28 (talk) 18:36, 9 November 2008 (UTC)

Yes, but moreover I'm arguing that they didn't have any better option than to use a crib sheet like that, i.e. it's not just the best crib-sheet-based strategy but also the best strategy of any kind (subject to certain assumptions about the way the world works). -- BenRG (talk) 11:33, 10 November 2008 (UTC)

Is the space shuttle capable of breaking Earth's orbit?

Assuming that they wanted to, is NASA's space shuttle physically capable of breaking out of Earth's orbit? 67.184.14.87 (talk) 15:15, 9 November 2008 (UTC)

I've just done some research into that and I think the answer is "no". The main engines can get the shuttle into Low Earth orbit, they would then need about 3.2km/s of delta-v (according to that article) to reach an escape orbit. As far as I can tell, the only engine they could use for that is the Orbital Maneuvering System, which only carries enough fuel for 0.3km/s of delta-v, far short of what they would need. They also have Reaction control system engines, but I can't find the maximum delta-v for those, I very much doubt it's enough to make up the extra 2.9km/s they would need, though. --Tango (talk) 16:20, 9 November 2008 (UTC)

The main cargo bay should have ample capacity (volume and mass) to store enough extra fuel for escape. As far as I know nobody ever bothered to design a tank to be fit in the cargo bay, and it might also be a major problem to get the fuel from there to the main engines. —Preceding unsigned comment added by 84.187.126.130 (talk) 16:45, 9 November 2008 (UTC)

That's assuming the engines can handle a significantly longer burn. Even if they can, you're talking about a massive retrofit. --Tango (talk) 17:09, 9 November 2008 (UTC)

Maybe things like low energy transfers, Interplanetary Transport Network and gravity assist could eventually reach the needed speed. It would be too slow to be suited for a manned mission. PrimeHunter (talk) 17:00, 9 November 2008 (UTC)

There are dozens of other considerations, such as whether the radios and communications equipment has sufficient range to operate in other orbits; whether the life support systems can sustain longer voyages; if the crew compartment is sufficiently protected from radiation in higher orbits; whether it would be safe or structurally feasible to store fuel in the cargo bay; in short, the space shuttle was designed for its current orbit. With significant modifications, it could probably be retrofitted to do a lot of different things, but a sufficiently re-engineered vehicle would no longer be the space shuttle as we know it. Nimur (talk) 17:03, 9 November 2008 (UTC)

I don't think any of those things would help with getting from LEO to an escape orbit. Low energy transfers, etc, would require reaching a Lagrangian point, I think, which are all far above LEO. A gravity assist isn't going to help, that requires you to pass near a massive object that is in orbit around the object you're orbiting (usually the Sun), the only relevant massive object when you're in LEO is the Earth itself, and you can't get a gravity assist from the object you're orbiting (the moon does, in a sense, via tidal interactions, but it is many orders of magnitude bigger than a space shuttle and even it only gains altitude at a rate of centimetres a century). --Tango (talk) 17:09, 9 November 2008 (UTC)

In space aerodynamics are irrelevant, so they could add on whatever structure and supplies were needed for an extended mission. The extra food, fuel, life support assets, and even extra solid fuel rockets could be taken up in one mission and used in another. I do not think the low earth orbits of the shuttle are significantly less exposed to radiation than places farther from earth. The big problem I see is that the shuttle is designed to be strong enough and aerodynamic enough for reentry,with wings, control surfaces, parachutes, and landing gear, and that makes it more massive than a craft would have to be whose only goal was to get beyond earth orbit with a human crew. Or did someone say the craft should land on another planet, orbit another planet, or return the crew to earth? The devil is in the details of the mission requirements. If you want to send a shuttle out of earth orbit, it is certainly possible with today's technology, as long as you do not expect it to land a crew somewhere and come back. Edison (talk) 21:54, 9 November 2008 (UTC)

Surely when Apollo 11 orbited the moon it could have performed a gravitational slingshot out into space. It would only have taken a small tweak. It's not exactly the space shuttle, but it is ancient technology. Plasticup ^T/C 15:56, 10 November 2008 (UTC)

In fact, the maximum Δv capability of the Saturn V would have caused the Apollo capsules to approach the Moon much faster than they actually did, reducing the trip from three days to one day. The slight problem with that is that the capsules would have been on a hyperbolic lunar orbit, and wouldn't have been able to reduce their speed enough to enter a stable elliptical orbit, so they would have zipped past it.

Going back to the original question, the Shuttle doesn't have enough fuel to get out of Earth orbit right now, but it could have if an extra fuel tank were added inside the orbiter (with the tradeoff of a significant safety risk, orbiter redesign, and a drastically reduced payload capacity), and/or larger SRBs were used. The SSME's should handle it, as they are [supposedly] designed for multiple uses. Titoxd^{(?!? - cool stuff)} 19:12, 10 November 2008 (UTC)

Apollo 11 was launched with much a much bigger rocket than Space Shuttles are. Making bigger rockets isn't that difficult, it's just more expensive. --Tango (talk) 21:49, 10 November 2008 (UTC)

Even with a cargo bay full of fuel - there could still be significant problems: The cargo bay doors MUST open because without them the orbiter doesn't have enough electricity to keep going for more than a few orbits - and it doesn't cool properly without them opened to increase the surface area of the orbiter. I very much doubt they are strong enough to stay open while doing a burn to a higher orbit...so maybe this is still impossible...I'm not sure. Certainly there would be MANY other obstacles...not least, on reentry, the orbiter would be going much faster than it's designed to come in at...so right there is a big problem. Certainly many of the onboard computer systems would have to be reprogrammed (a not inconsiderable task because every flight-critical software function was written independently by several different teams of programmers and the results compared so that software bugs may be eliminated (mostly!). It's not a simple matter. But the shuttle is already being phased out - this could never happen. SteveBaker (talk) 21:56, 10 November 2008 (UTC)

Please source the bit about the bay doors having to be open for electric generation. Solar cells? radiators from fuel cells? The rockets to boost out of earth orbit need not be as powerful as the ones to lift off from Cape Kennedy, so they can be sized to as low a force as the structure can withstand. 1 G of acceleration is certainly within the structural capabilities of every part of the shuttle, since it endures it on earth, and it would allow an amazing velocity over a little time. Reentry? Where? The question was LEAVING earth, not landing safely back at earth or on Mars or elsewhere. The biggest problem, as I stated, is all the extra mass the reentry equipment represents. A craft to leave earth orbit and go BEYOND need not be aerodynamic at all, and need not have wings, landing gear, parachutes, etc, unless a landing stage for Mars or somewhere is desired, and that does not need to be the whole interplanetary craft. Add enough booster rockets, or enough fuel for the present shuttle, and we could get the thing out of earth orbit with today's technology. The program modifications are relatively trivial. Edison (talk) 03:23, 11 November 2008 (UTC)

Inside the cargo bay.

You shouldn't really need a source for that - just take a look at any photo of the shuttle in orbit and note that the inside of the shuttle bay doors are completely covered with thermal radiators and solar cell panels. Those have to be on the inside because they'd never survive launch and reentry if they were on the outside. Here is a (google cache) explanation of how those radiators matter so much in orbit: [21].

I guess, technically, the OP's question doesn't require the successful return of the craft - but in practical terms, it's bloody stupid to send a reusable spaceplane on a one-way trip. It's not unreasonable to assume that the OP was really talking about a return capability - and for that the re-entry issues are surely significant (and, I believe, insurmountable). SteveBaker (talk) 03:50, 11 November 2008 (UTC)

So we get rid of the wings, the landing gear, parachutes, possibly add a landing craft, add whole new rockets and fuel tanks, etc. In what way is this still the Space Shuttle? You've just constructed a whole new interplanetary craft, and yes, we know we have the technology to get to Mars, we've sent numerous probes there. The only difficult bit is life support (and man rating everything), we've done everything else. --Tango (talk) 11:37, 11 November 2008 (UTC)

Yes - exactly. You wouldn't be able to take people to Mars in the shuttle anyway - there isn't remotely the space or facilities you need to allow people to exercise - or to generate spin gravity - and for sure you couldn't carry enough oxygen, food, water, recycling gear, etc. (Particularly because you filled the entire cargo bay with fuel tank already!)...you'd also find so many other little subsystems that you'd have to replace: Are the radios powerful enough to reach earth from that distance? Does the inflight software cope with radio transmission delays greater than a second when communicating with earth-based systems without 'timing-out' and giving up? Can the antenna be pointed with enough precision to aim at a more distant earth?...and that's considering just one of dozens of critical subsystems. SteveBaker (talk) 14:33, 11 November 2008 (UTC)

If the point was simply to leave orbit for the sake of doing it, perhaps a large solar sail could be used. It probably wouldn't require major structural changes to the shuttle. Given enough time, and a large enough solar sail that can be furled and unfurled strategically you could get pretty far away. The shuttle could carry an enormous sail in it's cargo bay and still have room for extra oxygen and water supplies. The longer time frame of the mission could (in part) be offset by a smaller crew.

The problem with this idea, of course, is that there's no good design for a solar sail of that size yet. The obvious designs don't hold up in computer simulations. APL (talk) 16:18, 11 November 2008 (UTC)

There's another potential problem - there is still a significant amount of atmosphere in LEO, atmospheric drag from the sail would probably be greater than the light pressure. You could try having it only open when it would be angled in line with the direction of travel, but I think the best time to have it open is when the light would push the shuttle forwards, rather than up (see the discussion somewhere above about the opposite case of pushing backwards being a better way to de-orbit that pushing down), so it would be extremely inefficient. If it worked at all, it would probably take months to get up to escape velocity, far longer than even a small crew could survive on even a modified shuttle (you could probably do it with major modifications, but then you're back into the realms of it not really be a space shuttle any more). --Tango (talk) 16:33, 11 November 2008 (UTC)

I think that we have established that the answer to the bare question is "Yes, the shuttle could be rocketed out of earth orbit." Other answers are "No, it could not do it as presently configured and equipped, due to a lack of fuel. And the crew could not survive indefinitely, although the habitability could be extended considerably by carrying extra food etc. And since it is built with much of its mass devoted to reentry into the earth's atmosphere, it would be silly to use the energy required to send all that useless mass out of earth orbit." Many of the objections could be answered by a little creative engineering. Do you recall that a Saturn stage was adapted to be a Skylab, and that was a far greater re-purposing than just accelerating the shuttle with sufficient thrust for sufficient time to increase its velocity to that needed for escape. The shuttle has been called the most complicated machine made by humans, and maybe the idea would be just to push it out into the solar system on its own as a monument. The radios aren't powerful enough? Give me a break. More powerful transmitters and more sensitive receivers are not very high technology, and 1970's technology allows communication with probes at the edge of the solar system. The radiators inside the doors must be exposed to space? Then open the doors. There is no wind resistance. The real problem is the lack of a mission or purpose or goal in the project. How much would the target mass be for a manned mission to Mars, compared to the shuttle? Wikipedia articles on space exploration are very short of such numbers. Space shuttle says the mass of the craft is 2,029 metric tons, apparently including the external fuel tanks, loaded, and the solid fuel rockets. The space shuttle orbiter(Endeavor) had an empty weight of 68.6 metric tons, per Space Shuttle orbiter. The proposed Russian Martian Piloted Complex of 1975 would have a mass of 1630 metric tons, apparently the mass when it was assembled in low earth orbit before blasting off for Mars. Edison (talk) 17:06, 11 November 2008 (UTC)

Yes, Skylab was partially adapted from a Saturn V but no-one would describe it as one. You could certainly use the Space Shuttle as a starting point to design and build an interplanetary craft (it probably wouldn't be very wise, though), but it wouldn't be a Space Shuttle afterwards, they would share very little in common. Adapting the Space Shuttle would be far harder than you make out. The crew surviving longer than the week or two Shuttle missions are designed to last would require far more than just carrying extra consumables. You need to consider radiation shielding, room for exercise, room so they don't go stir crazy cramped together in a tiny Shuttle for months, etc. You basically have one cargo bay to work with, it can probably be used to solve each of the problems, but not all of them together. It can't serve as a fuel tank, an extra engine, more pressurised space for the crew and storage for additional consumables all at the same time. Your only option would be to attach more things to the outside which means launching them separately, which means you're even further away from it actually being a Space Shuttle, it would be a larger craft which happens to contain a modified Space Shuttle as one component. --Tango (talk) 17:42, 11 November 2008 (UTC)

I'm reminded of the (terrible) film "Deep Impact". In that film the passenger compartment of the space ship looked like a hastily retrofitted space shuttle, essentially just bolted onto a set of much larger engines (in orbit, apparently.) The design of that ship was my favorite part of that film. APL (talk) 17:57, 11 November 2008 (UTC)

i would so no, a priori, because 1) if it were, they would have done it at some point and 2) conversely, if it were capable of doing that, it would be heavier than if it weren't, and adding excess unneeded weight onto the space shuttle so it could do things it never actually does, and thereby requiring all the extra fuel to hoist the extra mass up into orbit, is a big nono. Gzuckier (talk) 20:12, 11 November 2008 (UTC)

Total ship water displacement

Dear Wikipedians, what might be an educated guess towards how much water the world's shipping displaces? And, I seek to know, how much has the ocean risen from this displacement? Curiously and humourously yours, 80.202.246.253 (talk) 16:55, 9 November 2008 (UTC)

From Displacement (ship), "A floating ship always displaces an amount of water of the same mass as the ship." So, you are essentially asking for an estimate of the total tonnage of shipping (transport/cargo, military, recreational, etc). I would estimate that cargo ships make up the lion's share of worldwide tonnage, with other contributions probably being negligible. If I don't mention it first, Steve Baker will probably have to remind me that this is the Science Desk and not the Speculation Desk, so I would focus my efforts on locating actual reasonable estimates for international shipping before excluding any quantities. Nimur (talk) 17:07, 9 November 2008 (UTC)

Doing the calculation the other way around (working out how much shipping would be required to raise sea levels by a certain amount) is somewhat easier, so I'll do that. According to ocean, the oceans cover approximately 361 million square kilometers. If we ignore curvature (which I think we can for very small increases in sea levels) and assume all coastlines are vertical cliffs (again, reasonable for small increases), we find that a 1mm increase in sea levels would increase the volume by 361 billion metres cubed, corresponding to a mass (ignoring salinity) of 361 trillion kilograms. I'm struggling to find numbers for the mass of container ships, but it seems the biggest has a deadweight tonnage of 300,000, that's not a measure of displacement, but I reckon it gives us a rough order of magnitude at least, so let's say a container ship weights 1 million tonnes, or 1 billion kg. That means we would need 361,000 of the biggest container ships to raise see levels by 1mm. I can't find estimates of how many ships there are, but even with the most generous estimates I can't see the sea level rise caused by all the shipping we have being more than a few millimetres. --Tango (talk) 17:34, 9 November 2008 (UTC)

This says that in 2005, the total deadweight tonnage of the world's bulk cargo ships was 960 million tons - and that, fully laden, that goes up to 7100 million tons...which is 6x10¹²kg - or 6 billion cubic meters of water (OK - that's pure water, not salt) - which falls well short of the 360 billion that Tango estimates we need for a 1mm raise. So roughly 1/60th of a millimeter - which gets us to (as the popular press would be SURE to say) "about the thickness of a human hair". But since global warming has been raising the sea level by about 1.8mm per year for the last century (surely much faster that over the past few years)...I don't think we have to be too concerned about the displacement of our shipping fleet! SteveBaker (talk) 18:29, 9 November 2008 (UTC)

Here is our discussion of this topic from June. — Lomn 15:37, 10 November 2008 (UTC)

Input resistance of nerve fibres

Why is the input resistance of nerve fibres (accroding to cable theory): rinput = 0.5*sqrt(rm*ri) where rm is the membrane resistance and ri is the internal resistance ? 131.111.8.104 (talk) 17:57, 9 November 2008 (UTC)

Nerve fibers conduct nerve impulses electrochemically, not by electrical conduction like a wire or coax cable. The question makes an unwarranted assumption. Edison (talk) 21:44, 9 November 2008 (UTC)

November 10

low-cholesterol heart attacks

I was reading this, which starts

“ People with low cholesterol and no big risk for heart disease dramatically lowered their chances of dying or having a heart attack if they took the cholesterol pill Crestor, a large study found. ”

But goes on to say

“ [the drug] gave clear benefit in the study, but so few heart attacks and deaths occurred among these low-risk people that treating everyone like them in the United States could cost up to $9 billion a year — "a difficult sell," one expert said. ”

I don't get it: the group is already low-risk. Wouldn't they prefer to receive even $1 billion as life insurance payoff to the families of the dead among them than to force the whole group to both take an unneeded pill and pay out $9 billion for the privilege? Or is my logic off... 82.124.214.224

Hi, 82.124.214.224, please sign to avoid confusion. Julia Rossi (talk) 22:36, 9 November 2008 (UTC)

Well, I would prefer to live than give my surviving relatives a million Euro each, but that's just me (a selfish fecking bastard :-) ). But other that that, you are correct. What the article says is that a study proved that there is a benefit. This is proved by many studies very often. But cost-benefit analysis comes in at this point. There are numerous things that we could do to save a few extra lives each year, but the costs are just too high, and the money better spent elsewhere. This appears to be one of those cases. Fribbler (talk) 00:11, 10 November 2008 (UTC)

To the OP; that's the idea. Drug companies are looking for a way to make money off of people that don't need to take their drugs by convincing them that if they don't, they will DIE. Turns out that most statin drugs, while they lower cholesterol, don't actually increase your lifespan, life quality, or otherwise prevent heart attacks in any measurable way. It's the old "correlation is not causation" or post hoc ergo propter hoc problem. People with high cholesterol have more heart attacks; however, there is no mechanistic connection. Turns out, that you can lower cholesterol levels via these drugs and have no appreciable effect on heart attacks. It could very well be that high cholesterol levels are likely a symptom of the underlying health problems, and not the actual cause of them. However, methods that lower cholesterol via lifestyle changes do lower chances of having a heart attack. So, rather than taking drugs to cure a symptom, it's better to change your lifestyle to fix the underlying symptom. However, you will never hear this from the health system because that message doesn't make drug companies any cash... --Jayron32.talk.contribs 03:22, 10 November 2008 (UTC)

Just for the record, check out Cholesterol#Clinical_significance. The connection isn't well understood, and there are some skeptics, but the mainstream opinion is that high cholesterol increases the risk for a heart attack. Saying that there is no connection isn't a "flat earth" opinion, but it's definitely an unusual stance. SDY (talk) 16:08, 10 November 2008 (UTC)

I should note that the linked quote doesn't support your claim. It says that people who take Crestor have a dramatically lower chance of having a heart attack, but these people already have such a low chance that it isn't a big drop in the number of people dying from heart attacks. However our article statins does support your claim Nil Einne (talk) 09:08, 10 November 2008 (UTC)

Except there were TWO problems with the Crestor study cited above (and I am familiar with that 1 study). 1) Its primary sponsor was Astra Zeneca, who, um, makes Crestor. Creates a major conflict of interest problem. 2) The study was stopped early, according to the company because, and I am paraphrasing here, "this drug is so fucking awesome, it would be a crime to stop people from taking it by waiting for the study to finish". However, as noted the number of people effected in a positive way by the drug was so statistically insignificant that the shorter study likely only prevented more reliable data from being obtained. They basically stopped the study early because the results, though likely a statistical abberation, were in their favor. The company who made the drug had nothing to gain by keeping the study going, since increasing the participants would only have averaged out the outliers, and would have reduced the "good results" they got. There have been DOZENS of truly independent studies (i.e. those NOT done and controled by the drug companies) that support the idea that Statins like Crestor don't actually improve quality or length of life. --Jayron32.talk.contribs 15:14, 10 November 2008 (UTC)

Please don't use the RefDesk to spread non-sense like this. The test was ended prematurely because the independent review board concluded the results were so obviously significant (>99.9% chance of reducing major cardiovascular events) that further study was unnecessary and delaying the release of the results was contrary to the interests of public health. Yes, you can criticize them by saying that most of the people in the study would have been healthy anyway, but among that fraction who wouldn't be, it did show a clear benefit in this study. Saying the result were statistically insignificant is simply wrong. Dragons flight (talk) 17:12, 10 November 2008 (UTC)

So according to data extracted from our articles on statins, heart attack and stroke - and this claimed $9 billion cost to treat 300 million people (which seems a little low to me - but let's go with that): $9 billion for 300 million people is just $30 per person per year. They estimate a 60% reduction in risk of a heart attack across the board, a 17% reduction in stroke risk and a possible 50% reduction in colorectal cancer risk - balanced against a new 0.00044% per year risk of the rather nasty (and sometimes fatal) muscle issues that are the major side-effect and an even smaller (and presumably non-fatal) risk of some increased production of liver enzymes. So to put numbers on this: if we dosed every American with this stuff - we'd expect to get around 13,000 new cases of the nasty muscular problems per year - versus maybe 600,000 fewer heart attacks and (since 40% of those are fatal) 240,000 less deaths as a result. The cost of treating a heart attack averages to around $40,000 in the first 90 days - so if the treatment reduces your personal risk of a heart attack by only one part per thousand each year - then it's worth the $30 just in the savings in the cost of treatment. To paint the "big picture": the US spends $110 billion annually on treatment for heart attacks - so the $9 billion cost only has to reduce the number of heart attacks by 10% to be cost-effective...since it's claimed to reduce them by 60% then regardless of the humanitarian issues - the cold cash benefits are hard to deny (IF you believe in the results of the study). Free provision of these drugs could be funded by adding a 50c tax on every burger McDonalds sells...or considerably less if we put the tax on every fat-rich fast food item. SteveBaker (talk) 14:41, 10 November 2008 (UTC)

Or we could use a cheaper generic statin with less of a chance of side effects. Crestor is a bit of a loose cannon, and some groups have even called for yanking the approval on it because there are drugs without the problems. See Crestor#Debate_.26_criticisms. SDY (talk) 16:08, 10 November 2008 (UTC)

Was it $9b to treat everyone, or $9b to treat all the low risk people (with the high risk people already being treated since they're high risk)? If it's just the low risk people then that increases the cost per person (I'm not sure how much by, but I'd guess significantly - how many Americans actually have low cholesterol?). Also, are they recommending statins for children or is it just everyone over a certain age? --Tango (talk) 17:28, 10 November 2008 (UTC)

Thank you very much for your detailed analysis, it is greatly appreciated! (just out of personal interest). Will you tell me if you really mean "600,000 fewer heart attacks", this doesn't at all mesh with my understanding that heart attacks are nearly unheard-of among people with extremely low cholesterol (to begin with, independent of any drug). Will you explain how you arrived at that figure? —Preceding unsigned comment added by 82.124.214.224 (talk) 17:31, 10 November 2008 (UTC)

I haven't checked Steve's arithmetic, but it's important to remember that there are lot of people in the US so even if the risk of an individual having a heart attack is very low you still end up with a fairly large number of heart attacks in total. --Tango (talk) 17:40, 10 November 2008 (UTC)

Ok, I've done my own research and checked Steve's numbers and his look right but they are numbers for the population as a whole, not for low risk groups. So, Steve's conclusion is actually that, if everyone's risk was the same it would be worth treating everyone, but that's a false assumption. Generally speaking, you get better value for money treating high risk people than low risk people, which may well mean it doesn't make good financial sense to treat the lowest risk people. --Tango (talk) 17:55, 10 November 2008 (UTC)

Certainly you get better bang for buck by only treating the needy - but I was attempting to demonstrate that there was essentially nothing to lose (and a heck of a lot to gain) by simply treating everyone regardless of whether they need it or not (a similar argument to putting vitamins in milk or flouride in the water supply). Remember - there is a 'cost' to testing everyone too. Could you give everyone in the USA a cholesterol-level test every year - and pay for that by the savings you get by not treating those who pass it? Would the deaths due to preventable heart attacks amongst the false-negatives be less than the additional deaths due to side-effects from the stattin drug? I don't have numbers - but I strongly doubt it. I doubt you could administer the cholesterol test for less than $30 (it's a blood test - so you need a professional and a clean needle - and you've probably broken the $30 barrier right there) - and because heart attacks are SO common, I bet more people would die from the occasional unnecessary heart attack death following a screwed up test that said "don't take the drug" than would die from the side-effects of taking the drug unnecessarily. So I believe that you're STILL better off treating everyone, regardless. SteveBaker (talk) 21:47, 10 November 2008 (UTC)

don't forget, the study was done, published, and presumably the press releases sent out by the manufacturers of crestor. so, guess what they would answer to the question "wouldn't it be better to just give the money to the people at low risk rather than buy them all crestor?" Gzuckier (talk) 20:09, 11 November 2008 (UTC)

physics

what is meant by magnetic flux and magnetic meridean? —Preceding unsigned comment added by Kunal pdj (talk • contribs) 07:15, 10 November 2008 (UTC)

Have you read magnetic flux? Can't help with the meridean I'm afraid. Feel free to come back if you have more questions. —Cyclonenim (talk · contribs · email) 07:25, 10 November 2008 (UTC)

I'm just speculating here but perhaps the magnetic meridian is like a line of longitude for the Earth's magnetic field, like a line that goes through the north and south magnetic poles. This is just a guess, though. --WikiSlasher (talk) 07:56, 10 November 2008 (UTC)

correct [[22]]. I'm adding it to the meridian article, so magnetic meridian should now give an explanation EverGreg (talk) 09:22, 10 November 2008 (UTC)

scientific names

Hi all,

What are the scientific names of the two macroscopic invertebrae phylum with hard parts which have successfully invaded and thrive in all three major habitat: marine, freshwater and terrestrial.

Thanks —Preceding unsigned comment added by 122.108.248.74 (talk) 08:50, 10 November 2008 (UTC)

"The reference desk is not a service that will do homework for others." Otolemur crassicaudatus (talk) 11:01, 10 November 2008 (UTC)

Indeed. But you could start with our invertebrate article, which has a list of the 9 invertebrate phyla with examples of members of each one. Gandalf61 (talk) 11:29, 10 November 2008 (UTC)

Putting things up your ass

Please don't be put off by the title- it's a serious question!

Am I right in thinking that when you put a drug up your ass, that works by going into the bloodstream. And yet if you put, say, an apple in your ass, you probably wouldn't absorb the apple into your bloodstream - it would just sit there?

If you put a load of sugar up your ass, say in cube form - would that just stay there, or would it absorb into your bloodstream? And would it make you fat? Or energised? Given that it never gets into the stomach.Jacobsen's Ladder (talk) 11:37, 10 November 2008 (UTC)

You can, indeed, absorb things through the rectum and colon. See Enema. I expect you are correct that an apple would not be absorbed, at least not quickly (and if it stayed there too long it would probably do serious harm, see Bowel obstruction). Sugar should be pretty easily absorbed, since it will dissolve in the natural moisture present in the colon and be absorbed into the bloodstream. There should be no difference between absorbing sugar that way and eating it, you would gain the calories and you can either use them or store them as fat. --Tango (talk) 12:10, 10 November 2008 (UTC)

Glucose (also known as dextrose) can be absorbed rectally[23]. Glucose is often used in energy drinks etc because it can be absorbed directly through the intestinal wall when swallowed. Sucrose is the form of sugar in table sugar, and when eaten is broken down into simpler sugars (glucose and fructose) by enzymes in the intestines before being absorbed. Some sucrose would be broken down by enzymes in the lower intestine if administered rectally, but I'm not sure how effective this would be (a quick search doesn't show up any relevant research, though a lot of people are doing funny things to locust rectums[24]). So, glucose administered anally would work, but sucrose would be less well absorbed. The above mainly refers to sugar solutions. If administered in cube form, you would have to wait for it to dissolve, which would slow the process. --Maltelauridsbrigge (talk) 12:13, 10 November 2008 (UTC)

these people did the experiment, though I am not sure that their results are reproducable... --Jayron32.talk.contribs 14:58, 10

November 2008 (UTC)

The rectum is a well accepted route for the administration of both hydrating fluids and drugs. Where drugs are not tolerated orally by the patient or where an infusion by needle is inappropriate then the rectal route serves. Generally the substance needs to be in solution as the interior of the rectum is only moist and a dry substance may not be easily absorbed or it may irritate the mucosa. The glucose, fructose or whatever is not likely to have any greater energising effect than that taken orally. Energy is largely (though not exclusively) a psychogenic phenomenon. Taking lots of sugars or other carbs won't necessarily give you boundless energy. Richard Avery (talk) 16:19, 10 November 2008 (UTC)

I have heard from an unreliable source that you can put cocaine up your ass and it will have the same effect. The advantage will be that you won't destroy your nose or vein due to your addiction. The hole history sounds plausible to me, but I don't know if some people do it actually. 80.58.205.37 (talk) 16:15, 10 November 2008 (UTC)

It wasn't that long ago that the blogs were quickly copying the story of a wife who killed her husband with a 3L sherry enema. You can also find many sources that explain how to use a tampon and alcohol to get drunk without drinking - for those days when you apparently want to get drunk but don't want to hold a glass or can or bottle or box... 16:24, 10 November 2008 (UTC)

I don't think the wife was responsible (although she probably should have stopped him). The man won a Darwin Award, I think. --Tango (talk) 16:37, 10 November 2008 (UTC)

Delivering analgesics by suppository has the advantage of avoiding first pass metabolism. (No puns intended.) Axl ¤ [Talk] 19:04, 10 November 2008 (UTC)

Anyway: the reference desk will not do your homework for you :) --PMajer (talk) 20:32, 11 November 2008 (UTC)

electricity

how many watts is mesaraed as units in india —Preceding unsigned comment added by 118.95.124.242 (talk) 12:56, 10 November 2008 (UTC)

Ministry of Power at this site can be useful for answering your question [[25]]Hope this helps User:Maheshkale

Asperger's and phone conversation - is it talking or just calling?

I red that those with Asperger's Syndrome have anxiety about talking on the phone. I was wondering, is that really right? Or is it just making the call they have problems with?

It seems more intuitive that - if a person has a condition wherein they need things in fixed patterns, need to plan out how things will go if they go out, etc. - that the mere calling of someone on the phone would be the biggest problem, not talking in and of itself. There is actually a lot less nonverbal communication to take into account, and therefore less stuff they have to sort through mentally, when talking on the phone. But, with calling someone, you never know if the person will be there, whether you are interrupting, what their mood will be, etc.. Similar, if someone calls, you don't know who it will be (unless you have Caller ID, what they want, and so on.

So, is it just talking on the phone, or is it instead the anticipation of receiving/making a call that troubles those with Asperger's?209.244.187.155 (talk) 14:45, 10 November 2008 (UTC)

Where did you read that??? No, anxiety about talking on the phone is not one of the symptoms for Asperger's syndrome, and not even a common characteristic. However, somebody with Asperger's could have trouble understanding the "unwritten rules" of talking on the phone, and develop an anxiety. Lova Falk (talk) 15:10, 10 November 2008 (UTC)

Aspergers (and it's big brother: Autism) is a 'spectrum' condition. There are people to be found on all points along the line between normality and autism. Hence, people (such as myself) with Aspergers have a reasonably wide range of issues and it's impossible to speak for everyone who is on that spectrum.

But we can make some generalizations: Interpersonal communication of all kinds is more difficult for aspies than for normal people. Picking up non-verbal cues is the hardest thing for all of us. Hence, on the telephone we are at least on an equal footing to other people - which means that for some of us, using the phone is easier than face-to-face - and using things like eMail and IRC is yet easier (because even tricky things like comprehending the tone of voice is eliminated). However, some Asperger's (myself included) find phone conversations more stressful than face-to-face. In my case, this is because I still don't have an innate mental model of what the other person is feeling or thinking - and the few tricks I've been taught about body posture and facial cues are useless too. So I dislike phone conversations slightly more than I dislike face-to-face conversations - but both are basically unpleasant. Email/forums/IRC is easiest for me. SteveBaker (talk) 16:46, 10 November 2008 (UTC)

Is this compound acidic or basic?

A student has asked me whether acetylcholine is acidic or basic. Acetylcholine is a quaternary ammonium cation, and as such, has a permanent + charge on the N. So I believe this means that it won't gain or lose a proton, regardless of the pH of its environment, and consequently is neither acidic nor basic. But this sort of thing has always confused me, so please let me know if this is wrong before I give out bad information. ike9898 (talk) 14:52, 10 November 2008 (UTC)

Things can be acidic in ways other than the Brønsted–Lowry acid-base theory ("acid is something that loses H+"). If you put this N+ thing in water, how might it interact (remember water exists partially as a mixture of "H+ and OH-")? If you change the balance of H+ and OH-, you're changing the pH of the solution. DMacks (talk) 17:52, 10 November 2008 (UTC)

I suppose it will either remove some free OH- from solution, consequently increasing the ratio of H+ in solution and lowering pH, or it will have no effect at all. How would you describe acidity/basicity of this molecule, short of being quantitative about it? Would you simply call it a weak acid, or it there something more precise you can say? ike9898 (talk) 18:06, 10 November 2008 (UTC)

Asuming that the -NH₃⁺ bit is the most acidic bit, it will have some measurable pKa value. Any solution that has a pH above this number will result in deprotonation of the molecule. According to this page, the Ka of acetylcholine is 1.8e-5, which means the pKa is 4.74. So any solution of a pH greater than 4.74 will deprotonate the -NH₃⁺. In other words, in a pure water solution (pH = 7.00) acetylcholine will be acidic. Cheers. --Jayron32.talk.contribs 17:59, 10 November 2008 (UTC)

The N doesn't have a proton to lose. It has 4 substituets. ike9898 (talk) 18:06, 10 November 2008 (UTC)

You're right. I misread the article. But the pKa of the molecule is measured, so it really is a weak acid. It doesn't matter WHERE the proton comes from. Looking at the structure, the base form of Acetylcholine is likely to be a zwitterion of the form CH3COOCH^-CH2N⁺(CH3)3 or maybe on the next carbon to the right... --Jayron32.talk.contribs 18:13, 10 November 2008 (UTC)

What about the effect cited by DMacks above? Is the + charge going to pull OH- ions out of solution? ike9898 (talk) 18:19, 10 November 2008 (UTC)

I don't see why that would work. After all, Na⁺ ions aren't acidic in any way; they don't "pull" OH^- ions out of water at all... --Jayron32.talk.contribs 18:25, 10 November 2008 (UTC)

Wrong on both counts. That paper is talking about the dissociation constant of a complex with a receptor, not a pKa. Na+ is indeed acidic, although very weak. Acetylcholine is also a very weak acid; you can deprotonate a carbon next to the nitrogen to form a nitrogen ylide, or the carbon next to the ester carbonyl to form an enolate. But both pKa's are greater than 14, which means that the deprotonation will be largely negligible in water. Acetylcholine could also act as a Lewis acid and react with water as RNMe3+ + H2O -> RNMe2 + MeOH + H+, but that's probably not what the OP had in mind because it "destroys" the molecule rather than simply deprotonating it. --Itub (talk) 20:22, 10 November 2008 (UTC)

Good call, Itub. Yes, I was lazy in not fully reading the article. After looking over the structure, there's no reason to assume that ANY of the C-H bonds is particulatly acidic; they certainly don't look much more acidic than, say, the C-H bonds in acetylacetone, which, while being more acidic than alkyl C-H bonds, really doesn't compare to classically defined "acids". --Jayron32.talk.contribs 21:13, 10 November 2008 (UTC)

Bodily fluids in the wash

If i put something in the washing machine with some sort of bodily fluid on it, it feel like im just making a solution of bodily fluids and soaking my clothes in them and this will then rub off on things - i guess my question is to what extent is the true. thanks. 143karbkaz (talk) 15:10, 10 November 2008 (UTC)

143karbkaz, I think we already answered this question here when originally asked by zakbrak341. I like how your user name is the just the reverse of the original. Laenir (talk) 15:44, 10 November 2008 (UTC)

I forget the password for that account, and its a different question - the question for that was do the enzymes in detergent break down the protiens in semen. This is a different question :( 143karbkaz (talk) 15:56, 10 November 2008 (UTC)

When something with stains from bodily fluids is put into a washing machine (note that name - bit of a clue there!) the washing powder will break down the protein of the stain and allow it to become a suspension in the water. Now here comes the cunning bit, the machine then empties all that water away and rinses the clothes twice more so ensuring that no stains or particulate matter is left in the clothes or linen. Semen, saliva and urine are particularly easy stains to remove and in theory the washing machine does make a 'soup' of bodily fluids but it then proceeds to flush it all away and rinse out the clothes thoroughly. I would bet a wad of cash that it would not be possible to detect semen, saliva or urine in washing after a full hot cycle. This is the same system they use in modern hospitals to clean linen. Dang, this modern technology is good! 86.4.187.55 (talk) 16:09, 10 November 2008 (UTC)

I suppose its probably possible to work it out, such a tiny amount and thats dissolved in what 40L of water, work out the concentration of that, then work out how much water the clothes hold after they have been spun, then work out how much solute would be in that, then when thats all dissolved in the next rinse cycle ect. it would be pretty small. But do you think the solute would rub off on things once its dried? —Preceding unsigned comment added by 143karbkaz (talk • contribs) 16:18, 10 November 2008 (UTC)

It's just as well I don't believe in homeopathy...all of that dilution making things more powerful...Urgh! SteveBaker (talk) 16:48, 10 November 2008 (UTC)

I just knew when I saw your name and "dilution" in the edit summary that you were going to make a comment about homeopathy... you're getting predictable! --Tango (talk) 16:56, 10 November 2008 (UTC)

OK. For the sake of thoroughness, lets ACTUALLY see how much spooge is left on your clothes after your last nocturnal emission and if you wash it in a typical washing machine. Lets make some spherical cow-type assumptions. Lets say that the ejaculate is completely and evenly dissolved in the wash water each time the washing machine fills, and lets assume that you do the "double rinse" option on your washing machine. According to Ejaculation, the average event produces 1.5 - 5.0 mL of spunk. Lets just take the high end of that volume. According to this page, a modern "energy star" compliant washer uses 18-25 gallons per load. Doing a quick conversion, and this time lets use the smaller end, so we can maximize the amount of jizz in the washing machine, for our "worst case scenario" wash, we get a metric volume of 68 liters, or 68,000 mL. 5/68,000 means that after the wash cycle, we have .000735 % of our cum left in the wash. After one rinse cycle this reduces to .000000108 % left, and after 2 rinse cycles, that leaves us with .000000000000159 % of our original stain left in the machine. Considering that the average ejaculation features, according to our article on Semen analysis, 60,000,000 sperm per milliliter, or 300,000,000 sperm in our 5 mL test case. Multiplying this by our dilution factor gives us .0000047; which means that there is a 1 in 200,000 (roughly) chance that a single sperm is left in your washing machine after a standard wash cycle, with the double rinse option. And this is ignoring any effect that soap may have on denaturing or destroying the components of the semen. I don't think you have anything to worry about. --Jayron32.talk.contribs 17:50, 10 November 2008 (UTC)

That's got to win some kind of award for the largest quantity of synonyms for sperm used in one paragraph. —Cyclonenim (talk · contribs · email) 18:08, 10 November 2008 (UTC)

I don't follow your calculations. You seem to be assuming that there will be 5ml of liquid left in the washing machine after it drains each time, I expect it is considerably higher. --Tango (talk) 18:10, 10 November 2008 (UTC)

Hense the spherical cow reference. OK. Lets assume that there is really 500 mL of water left after each wash, so I was off by a factor of 10,000. That's still a 1 in 20 chance of finding a single spermatazoa in the wash. I am not concerned... --Jayron32.talk.contribs 18:19, 10 November 2008 (UTC)

There are 3 drainings, so wouldn't you be off by a factor of 1,000,000? That would give an expectation of 5 sperm after the wash. I think your cow is a little too spherical. I think the fact that any sperm would almost certainly be killed by the heat (and perhaps the soap) is more important than the dilution (which is far too difficult to calculate reliably). --Tango (talk) 19:14, 10 November 2008 (UTC)

Actually, the three dilutions I did would be the 5/68,000 500/68,000 500/68,000, to get the 1/20 number. --Jayron32.talk.contribs 19:19, 10 November 2008 (UTC)

What if the machine does not have a special spunk cycle? Edison (talk) 19:59, 10 November 2008 (UTC)

The point of the calculations is to show the rediculousness of the premise of the original question. The idea that when you wash and entire washload of clothes, some of which has a trivial amount of semen on it, that that semen could somehow cover all of the clothes in the wash, "contaminating" them. The idea that you could somehow "coat" an entire washload of clothes with semen (well, using a washing machine. If you and a bunch of friends were REALLY dedicated...) by simply washing clothes is just silly. --Jayron32.talk.contribs 20:39, 10 November 2008 (UTC)

Well, yeah, but our concepts of filth aren't necessarily dictated by logic. Here's a little experiment my roommate showed me back in uni: take a small cup of water, like the little Dixie cup you use at the dentist. Drink a little of the water. Everything okay? Now spit into the cup, as much as you can without actually horking up anything nasty. No need for phlegm, just mouth saliva. See if you can refill the cup to replace what you drank. Okay, now drink the spit water. You know the water is okay because you just drank it and you know the spit is okay because it's yours and it just came from your mouth, yet most people have a very hard time gulping down the mixture and even many that can do it, can only do it as a "dare" type thing. There's nothing in the cup that wouldn't be in your mouth the second you take a swig, but one is filthy while the other is not. No logic there. Matt Deres (talk) 17:45, 11 November 2008 (UTC)

VCR tape to DVD

How do I copy one to the other please?--212.139.78.231 (talk) 17:48, 10 November 2008 (UTC)

Probably better suited for the computing reference desk, but here's a little article which gives you some hints at how to do it. Basically, it requires hardware: Linky —Cyclonenim (talk · contribs · email) 18:05, 10 November 2008 (UTC)

Buy a DVD recorder. My computer came with one installed. --Jayron32.talk.contribs 18:06, 10 November 2008 (UTC)

Do you have a DVD player for your TV that can burn DVDs? If so, just connect your VCR player to the DVD player's input and follow the instructions for burning DVDs. If you don't, and want to use a computer DVD burner you will need a TV tuner card to connect the VCR player into. If you want more details, there are loads of tutorials online, try google. --Tango (talk) 18:07, 10 November 2008 (UTC)

Don't use a standalone DVD recorder. They usually make proprietary discs that are not readable by other machines. I've had two and neither made DVDs that any other machine could view, even the DVD-ROM on my 'puter. Matt Deres (talk) 17:47, 11 November 2008 (UTC)

I agree with Matt..I purchased a standalone and was quite upset to find out the discs would not work in any other player. cheers, 10draftsdeep (talk) 18:26, 11 November 2008 (UTC)

water clock from 2008

http://www.alibaba.com/showroom/Water_Clock/------------15--------------.html

Where would I find an explanation on how these work? —Preceding unsigned comment added by 12.213.224.56 (talk) 18:21, 10 November 2008 (UTC)

Maybe in the article Water clock? --Jayron32.talk.contribs 19:14, 10 November 2008 (UTC)

That article is about old-fashioned mechanical clocks, with gravity driven water as the power source. This questioner is asking about electrically powered digital clocks that use an open container of water as a primitive cell. Possibly a Daniell cell, but I'm not sure. APL (talk) 19:48, 10 November 2008 (UTC)

They run on saltwater batteries. Digital clocks require so little energy that even a "homemade" battery can work. You may also be interested in two potato clocks The Amazing Two Potato Clock. See the brief paragraph here : List_of_battery_types#Homemade_cells. APL (talk) 19:13, 10 November 2008 (UTC)

Please note - the power doesn't come from the water - it comes from the dissimilar metals in the two electrodes reacting with each other via the water. Hence the claims for "potato powered clock" or "lemon powered clock" or (god forbid) "water powered clock" are all just a tad inaccurate. SteveBaker (talk) 21:30, 10 November 2008 (UTC)

Indeed, as Steve notes, the power provided is from the difference in reduction potential between the two dissimilar metals. These set ups are functionally equivalent to ANY other battery, like good old double-a cells, and the salt water/lemon/potato provides NO electromotive force themselves; they only provide the medium in which the required spontaneous chemical reactions happen. --Jayron32.talk.contribs 22:12, 10 November 2008 (UTC)

Galaxy flow

If the galaxies are moving in the same direction, isn't that the same as saying they aren't moving at all? If there was a supermassive object beyond the visible universe, wouldn't it be impossible to receive any effects from it, including gravity? Before any of you mention it: xkcd. — DanielLC 18:23, 10 November 2008 (UTC)

If it were due to a massive object then the galaxies nearer it would presumably be moving faster than those further away, that difference would be meaningful value (as you say, the actual movement of a given galaxy is meaningless since there is no universal frame of reference - in fact, it's the tidal force that has the measurable effect rather than the gravitational force itself). As for it being beyond the observable universe, I agree, if we're observing its gravitational effects then we are observing it so it must be within the observable universe. It could be something more fundamental than just a lot of matter, though, perhaps something to do with the global structure of spacetime? I think we're probably in the unfortunately common situation of a journalist not knowing what they're talking about (New Scientist is generally better than mainstream journalism, but it's far from perfect).--Tango (talk) 18:31, 10 November 2008 (UTC)

The cosmic microwave background defines a privileged state of motion everywhere in the universe, called the Hubble flow: it's only if you're moving with the Hubble flow that the CMB is isotropic. The large-scale net movement (which may not be real) is with respect to that. The part about its being a pull from beyond the observable universe is just speculation (only circumstantially supported by the data), but it makes sense once you understand the ambiguity in the definition of "observable universe". The part of the universe we can actually observe with telescopes is limited to a past light cone extending back to 400,000 (0.0004 billion) years "after the big bang", which is when the primordial soup cooled down enough to become transparent. (See Age of the universe#Explanation for what "after the big bang" means.) If you extend the light cone another 400,000 years back in a naive way, assuming matter/radiation dominance, then the size is not much different—either way you get about 46 billion light years (comoving) in every direction, which is the value in our observable universe article. But most cosmologists think that there was an inflationary epoch a small fraction of a second "after the big bang" during which the growth was dominated not by matter or radiation but by a cosmological-constant-like quantum field and the universe expanded by a factor of 10^{something large} in a very short time. If you extend the past light cone through that, it covers an enormously larger (comoving) area. So the idea is that the net motion is due to something from the pre-inflationary era which is inside our past light cone but well outside the part of the universe that we can actually see. -- BenRG (talk) 20:51, 10 November 2008 (UTC)

I've never heard of "observable universe" being used to mean anything other than the light cone going all the way back to t=0, is it common to define it to stop at the moment of last scattering? --Tango (talk) 21:58, 10 November 2008 (UTC)

It is fairly common, if somewhat inaccurate, to use "observable universe" to mean "visible universe" (i.e. the universe as probed by light). Dragons flight (talk) 22:12, 10 November 2008 (UTC)

I noticed that too.. if we're seeing the gravitational effects of an object, we must be seeing the object itself. Unless, as said above, it's some weird phenomenon independent from the laws of physics as we know them. which is a pretty unreasonable assumption. 72.236.192.238 (talk) 22:34, 11 November 2008 (UTC)

is my scientific methodology sound?

i'd like to test whether a wikipedia article is being suppressed.

my methodology is:

1. identify a control page that
   1. is approximately the same length as the test article
   2. has an inadequate lead section
2. the test article is international law and the arab-israeli conflict, which has an inadequate lead section
3. my hypothesis is that the reason it doesn't meet our wikipedia:lead_section guideline is it's being suppressed
4. to make the test blind, i will pay a paper mill to read both articles and produce a lead section for each that
   1. meets the guidelines of wikipedia:lead_section
   2. incorporate as much of the current lead as possible (to minimize the chances of reversion)
   3. is in line with lead sections of good articles of the same length
5. from two different net cafes i will
   1. create a new wikipedia account
   2. from each account change one of the page's intro to the intro produced by the paper mill
6. if the improved control intro is not reverted/obfuscated but the improved test intro is, i will conclude that the wikipedia article is being suppressed

what do you think of my scientific methodology —Preceding unsigned comment added by 82.124.214.224 (talk) 19:30, 10 November 2008 (UTC)

If you're serious about the scientific aspect, some obvious problems are that two data points don't mean much, and that two encyclopedia articles are different enough that one is not a good control for the other. If you're more interested in improving article content, forget this science experiment and just bring up your concerns on the talk page. There's no need to resort to sockpuppetry or subterfuge- in fact you'll find that doing so makes your work here more difficult rather than easier. Friday (talk) 19:52, 10 November 2008 (UTC)

I'm not interested in doing work here, and I'm not interested in the article I linked -- that's why I've never made an edit. I am interested in (knowing--not changing) whether Wikipedia articles are suppressed! That is useful and good information to know... I'll think about your specific concerns, but please tell me if you have an easy way to improve my test algorithm. —Preceding unsigned comment added by 82.124.214.224 (talk) 20:14, 10 November 2008 (UTC)

Actually: do you have an easy way for me to divine whether Wikipedia articles (such as the one I linked) are being linked, and in a way that is scientific? I don't understand your point that two Wikipedia articles are "different enough" that if the intro paragraph of one is reverted to two short sentences (the latter of which doesn't even make sense) and the control articles aren't, it wouldn't imply that the control article was being suppressed?? The only reason for the control, is to show that reverting a good, obvious improvement doesn't normally go on. How would you feel if the control group were, say, twenty articles?

You haven't defined what suppression is. You're experiment wouldn't prove suppression in any way, because that would mean reading the intent of people who are removing information from the article. There are many good faith reasons to remove text from an article, or to prevent new text from being added, and not all of them imply "preventing people from hearing the TRUTH!". --Jayron32.talk.contribs 21:08, 10 November 2008 (UTC)

Nice attempt to paint me as a conspiracy nut ("the TRUTH"). How about you read what I wrote and come up with a single good faith reason to remove the lead the paper mill would produce from the article itself and based directly on our lead guideline? —Preceding unsigned comment added by 82.124.214.224 (talk) 21:41, 10 November 2008 (UTC)

The use of the word "suppression" is itself perjorative, and implies a deliberate attempt to deceive. I see no evidence of that here, and I also see no evidence that the methodology would test for that. --Jayron32.talk.contribs 22:09, 10 November 2008 (UTC)

Who said anything about deception? I mentioned suppression. If you don't think there's any reason to even suspect it, why don't you take 30 seconds and change the lead paragraph to something sensible, after reading the rest of the article. I am genuinely interested in whether your good-faith attempt will get reverted, and I don't know if it will. Try it! If it does get reverted, we can discuss why, if you still won't think it's suppression...

Removal != suppression. There are many reasons to remove verbage from an article, and suppressing it, which is basically the intentional act of preventing information from becoming public knowledge, is only one of them... --Jayron32.talk.contribs 23:52, 10 November 2008 (UTC)

What is suppression? When one viewpoint surpasses another and thus oppresses the lesser? Wikipedia is built on this. It's the collective ideology of capitalism, the industrial revolution, and Web 2.0: Putting something out there for others to shamelessly improve on. Mac Davis (talk) 23:12, 10 November 2008 (UTC)

No, I mean suppression literally: pushing things down into the bucket. I would like to test whether the mentioned article does this by not having a lead paragraph.

"Pushing things down into the bucket?" As I understood what you meant, I would say the same thing Jayron32 did. Often elimination of words is the best writing technique. Mac Davis (talk) 23:26, 10 November 2008 (UTC)

You're normally absolutely right, and the first thing I do after typing something is cut, cut, cut. In this case however the lead paragraph hasn't just been pruned -- it doesn't exist at all! Look at the "introduction" to international_law_and_the_Arab–Israeli_conflict and you'll see the lead paragraph doesn't exist. For comparison you can read our guideline, and then read the intro section of some good or featured articles. Now do you see why I am interested in whether the missing lead is an act of suppression or not, and would like to test it? I'm not saying it is, or isn't -- here at the reference desk, my question is about the methodology for testing this.... If you'd like to be my volunteer, please, make some improvements to the lead section so I can see if they'll be reverted. To make the study blind, I don't want to make changes myself... —Preceding unsigned comment added by 82.124.214.224 (talk) 23:49, 10 November 2008 (UTC)

How do you intend to control for the different levels of attention the two articles receive? I suspect that any article relating to conflicts in the Middle East will have a large number of unique editors, a large number of edits per day, and appear on a large number of editors' watchlists compared to the typical Wikipedia article. Edits to sensitive topics are also often more successful if they are discussed in advance on the article talk page — a precaution that is often unnecessary for less contentious areas.

In other words, I can think of quite a few confounding factors for your study. Instead of wasting your time and money to generate a meaningless result, perhaps you should try discussing the matter calmly and politely on the relevant talk pages. Accusing editors of 'suppressing' topics (whatever that means) isn't likely to result in the sort of collaborative consensus-building that allows us to create great articles. TenOfAllTrades(talk) 00:01, 11 November 2008 (UTC)

You're right about all that. Let's try it and see how it goes (see my comment below) 82.124.214.224 (talk) 00:23, 11 November 2008 (UTC)

Here's a test: dig into the fossil record and see if there has been any dispute over the contents of the lead. In this case, considering that over the past year there has been only one minor change to that header section, the prior probability of your hypothetical (and amorphous) "suppression" is low. — Scientizzle 00:10, 11 November 2008 (UTC)

I like that test, it proves that no one is digging up the suppressed information. I guess I'll be the first! :) I'm going to do the edit myself and see what happens. I'll post my version here first and you suggest improvement, then I'll post it there. See ya', I'm off to read the article and lead paragraph guideline carefully!—Preceding unsigned comment added by 82.124.214.224 (talk • contribs)

How is something "suppressed" if it's never before been added? The assumption that any reversion of a new addition is an attempt at censorship violates Wikipedia's core behavioral policies, too... If you can improve the article, please do so...but don't disrupt Wikipedia to make a point, okay? — Scientizzle 00:35, 11 November 2008 (UTC)

Okay, I was bold and added this:

The resolutions of major institutions of international law, such as the International Court of Justice, are rejected in the case of the Arab-Israeli conflict by both Israel, the principal state involved in the conflict (there is no Palestinian state), and the United States, another country supporting Israel's decision to do so. This rejection is possible because international laws, unlike the more familiar laws of local and national governments, are neither legislated nor enforced by a sovereign government having jurisdiction and law enforcement powers: there are local and national governments in the world, but no "international government" of the same kind. Instead, countries exercise sovereignty in international affairs, and are bound by the findings of international institutions only insofar as they submit themselves to their authority. At times, nations cooperate easily, and international institutions, as the manifestation of this cooperation, wield considerable power. At other times, such as in the case of the Arab-Israeli conflict, international institutions are less powerful.

with the edit summary "improved lead. Please refer to Wikipedia:Lead_section and make further improvements". We'll see what happens...

Don't post your version here, this is the science ref desk. We're good at science, we're not necessary good with international affairs. The article's talk page is the place to get opinions on changes. Alternatively, you could just update the article and just see if anyone reverts, if they do you can go to the talk page to discuss it then (see WP:BRD). --Tango (talk) 00:42, 11 November 2008 (UTC)

No. I do not think it is sound at all. Not even close.

1. You're going to need to define "suppressed" much better than you've already done.
   1. What does "Suppressed" mean?
   2. Why would this "suppression" manifest itself in the lead of the article?
   3. Are you expecting a particular point of view to be pushed? Or just a general resistance to change?
      1. If the former, which? If the latter why would the Israel article be more susceptible to it?
2. You would need a lot more than two pages to draw any significant conclusions.
3. You would also need your "control" articles to be as heavily watched and edited as your test articles
   1. If the control articles are intended to be non-controversial, this may be very difficult.
   2. How would you measure page watched-ness?
4. You would need your "Essay mill" students to be completely unbiased, and familiar with WP's style.
   1. I bet they'll figure out where you got the articles from.
   2. It would not be a blind study if you copy-edit their leads at all. Even just going through and adding the wikilinking could taint the experiment.
5. You've only described a single-blind experiment. The measurement criteria had better be very well defined ahead of time.
6. You've just now told us, some of the subjects in your experiment, that you intend to run an experiment.

APL (talk) 01:36, 11 November 2008 (UTC)

I was thinking that I shouldn't ask you guys, but I thought it wouldn't really matter, it's a very different circle of people. That's why I didn't ask on the article's talk page though... How important are double-blind studies versus single-blind? Are researchers really that bad when they know what effect they're evaluating?

Yes - in some cases, it makes a big difference. In a drug study where half the people get placebo and the other half get real drugs, it's very hard indeed for the doctor who is handing out the drugs not to say something that will clue the patient in to what's really going on and thereby destroy the placebo effect. Double-blind is the only scientific way to do this kind of study. SteveBaker (talk) 03:26, 11 November 2008 (UTC)

I've made the edit, as you can see. I think it's pretty clear now. Am I wrong to conclude that if it stays (isn't reverted) then the lead had NOT been totally inadequate before my edit BECAUSE of a group of people suppressing the article -- making sure the lead didn't say what's in it -- but for some other reason? Or is this also a wrong conclusion on my part?

The edit in question is here.

So, after discussing your scientific methodology, finding it inadequate, you elect to not even follow your own inadequate procedure? Regardless of what happens here, nothing will be proved, no experiment has been conducted. "Experiment" does not mean "try random stuff and see what happens.".

Incidentally, the lead you added to that article doesn't really seem to be a good summary of the article. It seems more like a brief rant on the implications of the topics of the article, but not really a summary. I don't know enough about the topic to give a fair assessment of that, though. APL (talk) 04:58, 11 November 2008 (UTC)

It would be REALLY tough to suppress an article here on Wikipedia. Remember that all of your changes - and everyone else's are stored in the article's history. If someone "suppressed" something - you can look to your last version - see exactly who changed it, how they changed it and when they changed it. You can go to their Talk: page and ask them why they did that - your question and their answer also remains in the edit history for all eternity. To remove an entire article or do something 'special' to wipe out some editing history would require the decisions of a whole committee of people...fiercely independent people...getting them to agree to suppress something would be all but impossible...and all of those discussions are retained in 'history' pages forever. The paper-trail is very complete and all-but-impossible to alter. Given all of that - it would take a lot of nerve for someone to start methodically suppressing stuff, you could easily create an unbelievable stink (because you can easily prove everything that happened) - and if you're right, people will flock to your side. However, I wish I had a dollar for every time I reverted someone's crappy editing, poor grammar, unreferenced facts, violations of policy/guidelines...and ended up being accused of "suppression". So if you feel something has been inappropriately removed - you've got to go to the talk: page - and ask why. If you disagree with the reasons - then seek to get a consensus of users who agree with your points - if you succeed, you can restore your version and people will defend you if it gets removed again. But if you fail - you'll have a lot of people patiently explaining WHY you're wrong...and you'll simply have to swallow your pride and admit that you're wrong. SteveBaker (talk) 03:26, 11 November 2008 (UTC)

thank you for that... but nothing of mine was removed. can you also explain given that it's not possible to suppress information, why some articles are heinously biased?

Since this whole thing is pretty bankrupt as far as 'science' and experimentation, and, I can't find it right now, but I'm almost positive that there's a WP policy that specifically forbids this sort of experimentation, perhaps this discussion should be brought up in the talk page of the article in question? APL (talk) 05:04, 11 November 2008 (UTC)

(edit conflict) You don't understand NPOV and consider something biased even though it follows it? You're biased and assume anything without the same bias isn't? The articles in question were only written by one or two people and have not been edited for NPOV? The articles in question are the subject of an ongoing edit war and have been locked on The Wrong Version? Making an article NPOV is harder than you think? Making an article NPOV is impossible? There are over a million articles on Wikipedia, so some will be biased? I think people can add to this.

Who said anything about bias? I didn't. Who was that directed to? APL (talk)

APL, I think Wikipedia is only against experimentation that damages it, such as inserting false information. The OP's experiment involves improving Wikipedia. — DanielLC 05:15, 11 November 2008 (UTC)

Fair enough. That may be what I'm thinking of. APL (talk) 05:50, 11 November 2008 (UTC)

Bias (even serious bias) or incompleteness or other defects in a Wikipedia article may be due to the inexperience of the person who created the article, or to "inadequate attention" from other editors, or both. It is not necessarily the result of "suppression". Some articles get little if any attention after they are created. I think a stroll through Wikipedia using the "random article" link will demonstrate that. CBHA (talk) 06:45, 11 November 2008 (UTC)

Bias is a tough thing to judge. What happens is that opinion lies on a line between one extreme and the other - you always regard your own position as being in the middle of the line - so if the article is to the left of where you are - it's biassed. However, for someone who's opinion is to the left of yours - it's balanced. Who's right? Dunno. The solution to bias in Wikipedia is simple - we don't choose the facts - we find references and write what they say in our own words. The opinions of the authors SHOULDN'T matter (although it obviously does sometimes). But if you find an article (especially one with a lot of authors that's been around for a long time) - and you think it's biassed - you should probably take a deep breath and realise that your opinion is not in the center of the spectrum of opinions. For new-ish articles with just a couple of authors - bias can certainly creep in - and it's your responsibility to get in there - talk it out on the discussion page and use FACT with REFERENCES to bring the article into balance and harmony. When you consider the amount of hate and resentment flung around in the articles about John McCain and Barrack Obama - then look at the beautiful pair of articles that were simultaneously brought to featured status in time for the US election day - you've got a pretty good idea of how to do this. You WILL end up agreeing to text that you don't personally approve of - but you'll also have the chance to get the facts in there. Wikipedia is actually a shining beacon of conflict resolution in this regard. SteveBaker (talk) 14:15, 11 November 2008 (UTC)

Speed of Electricity.

http://en.wikipedia.org/wiki/List_of_common_misconceptions states that "Electricity" is fast, but the electrons inside move slow. However I have yet to see an article/document stating the research behind this and blah blah blah. I wanted to know if I could get more accurate sources. I myself have found http://www.eskimo.com/~billb/miscon/speed.html

but I wanted to know if there was a more scientific article on it...

In retrospect the whole list_of_common_misconceptions page has alot of unsourced material but that's not my point. 70.89.49.205 (talk) 19:34, 10 November 2008 (UTC)

Have you looked at the electric current article, particularly the section on drift speed?

List of common misconceptions is actually fairly well sourced, as articles of that class go. In cases where references are not cited, other Wikipedia articles linked in the article have the appropriate citations. If you can contribute sources where needed, please do. ~Amatulić (talk) 19:51, 10 November 2008 (UTC)

See Speed of electricity, which says that the electrons carrying current flow a t a typical rate of millimeters per second, while the impulse when current is switched on travels through copper at almost the speed of light. Electrons start entering one end of the conductor at about the same time they start flowing out the other, but the electrons are not travelling all the way through the wire that fast, because there are so many of the charge carriers present in any small section of wire. The article Drift velocity gives a mathematical explanation of the slow rate with which electrons drift through a conductor. Edison (talk) 19:55, 10 November 2008 (UTC)

Ahh, Thank you for the results, I appreciate your time looking 70.89.49.205 (talk) 20:29, 10 November 2008 (UTC)

It's not such a difficult concept. Imagine a garden hose that's been running for a while. You turn it off, wait a bit, then turn it on again. The instant you turn it on, the water starts flowing out of the other end. Even if the hose is 100' long - the water comes out almost instantly - the delay between turning the water on and getting water out of the end is probably something like the speed of sound in water. Yet the water flow itself is nothing like that fast - a few feet per second probably. It's the same deal with the electrons and the wire. The wire is already "full" of electrons - so when you push one into the wire at the battery end - there is a knock-on effect that pushes one out of the other end at about the speed of light in copper...but the individual electron meanders very slowly along the wire. I read somewhere that there was a good chance that when you put a new battery into a flashlight - there is a good chance that not one of the electrons would make it out of the battery, all the way around the circuit and back into the battery before the battery went dead. I'm not sure that's really true - but as Edison says - at a couple of millimeters per second, it's an amazingly slow process. SteveBaker (talk) 21:17, 10 November 2008 (UTC)

These explanations are still a bit misleading since they suggest that the electrical energy goes in the same direction as the charge carriers, just faster. Actually it's just as happy to go in the opposite direction. When you initially insert a battery into a circuit, it pulls charge carriers from the wire connected to one of its terminals and pushes them into the other. That leads to a cascading effect that travels around the circuit in both directions from the battery, meeting up at the far end of the circuit (the halfway point). If you're modulating the current/voltage to send a message, as with a telegraph or broadband over power lines, the signal travels from sender to receiver along both wires. (I think. There's no reason for it not to, anyway.) -- BenRG (talk) 22:55, 10 November 2008 (UTC)

A very good and profound question, regarding an issue or phenomenon that isn't covered in classical textbooks, either at high-school level or higher, introductory ones. This issue was raised during a course I gave about half a year ago, and drove changing the usual syllabus of the course. SteveBaker's explanation is a very good simplified demonstration. However, the phenomenon of electric current is far more complex. In brief, at least two phenomena are involved here. The 1st of which is the actual motion of free electrons, which is typically very small, as already mentioned before. The 2nd is a result of the appearance of a potential difference or voltage along the conducting wire, which acts as a source of disturbance. This disturbance spreads through a potential gradient in a wavelike manner, namely a pulse (physics). As all waves do, they carry energy delivered to the mettalic atoms of the conductor, thus heating it. The pulse has nothing to do with the actual free electros motion, but manifests itself as a momentary repeated change in their rate of oscillations, propagating along the conductor in approx. 70% of the speed of light. There are differences between the dynamics related to DC & AC, and other phenomena related exclusively to the latter.

To elaborate in depth on the subject, you're invited to look up at: (1) Solid State Physics, (2) Solid State Physics, by Ashcroft & Mermin, (3) Introduction to Solid State Physics, by Kittel. BentzyCo (talk) 23:15, 10 November 2008 (UTC)

Square seconds

According to the article on acceleration, SI measures it in terms of meters per square second (m/s²). What does a square second look like? --67.185.190.46 (talk) 22:31, 10 November 2008 (UTC)

It probably looks similar to what a second looks like. Mac Davis (talk) 22:46, 10 November 2008 (UTC)

Think of it in words. Velocity/speed is in meters per second - how many meters can be covered in one second's time. That is, the change in displacement/distance with respect to time. Acceleration is the change of velocity with respect to time, so it should have units of "meters per second per second." If the velocity changes by 5 m/s in one second, it's acceleration is 5 meters per second, per second. This works out to m/s² (take m/s and divide by s) --Bennybp (talk) 22:47, 10 November 2008 (UTC)

What does a second look like while we're at it? Acceleration is the rate of change of speed - its units are "meters per second, per second" (ie if you are accelerating at 2 ms^-2, your speed will have increased by 4 ms^-1 after 2 seconds), and (ms^-1)^-1 becomes ms^-2. (ec: wow, beaten to the punch - twice.) 81.102.34.92 (talk) 22:50, 10 November 2008 (UTC)

If units are used to describe physical quantities, the "derived unit" of ms^-2 describes how distance and time might be related in this situation. Mac Davis (talk) 23:03, 10 November 2008 (UTC)

Seconds squared by itself is a meaningless unit. However, meters PER second squared is acceleration. One cannot arbitrarily pull part of the unit out of the definition and make it meaningful. For example, let's say your name was John Joseph Smith, and I were to ask "what does ephsmi mean?" That's essentially what the OP's question does to the units; though I admit that it looks like seconds squared is an "operative" part of the unit, it's REALLY just a mathematical convenience. The real physical quantity is (meters PER second) PER second which is mathematically identical to meters PER second squared. --Jayron32.talk.contribs 23:48, 10 November 2008 (UTC)

I chalk it up to either my own personal density or my poor education that I only figured out as an adult that all it means is that for each second the thing is falling, it adds X meters per second to its velocity. --Sean/76.182.94.172 (talk) 00:00, 11 November 2008 (UTC)

Occasionally (rarely) it is pronounced "Meters per second per second", if that helps you at all. APL (talk) 01:38, 11 November 2008 (UTC)

The significance of the exponent is that it implies the distance travelled has a linear relationship with the square of the elapsed time. The fact that the units are in the form distance/time^2 is not a coincidence; it means that the two quantities are related. --Bowlhover (talk) 02:57, 11 November 2008 (UTC)

It's really only a notational convenience. We square (and cube and more) all sorts of peculiar units. The 'volt' and the 'watt' (for example) both have seconds-cubed in their expansions - the units of 'permittivity' have seconds to the fourth power. If your rate of acceleration is changing - you might have seconds-cubed - if the rate at which your rate of acceleration is also changing you have seconds-to-the-fourth power. It's just notation. SteveBaker (talk) 03:12, 11 November 2008 (UTC)

Calling the unit "metres per square second" raises the question: what on earth is a "square second"? It sounds very strange!

In my experience with the terminology, I have never before heard it called that. "Metres per second squared" is usual IME, and (as noted above) that is simply an abbreviated way of saying "metres per second per second". CBHA (talk) 06:59, 11 November 2008 (UTC)

Yeah - I've never heard "meters per square second" either. I suppose that when some people are talking about units of (for example) density, we could talk about kg.m^-3 as "kilograms per cubic meter" rather than "kilograms per meter cubed" - but scientists don't often do that unless they are talking casually to laymen - and they certainly only do it that way when it makes physical sense (which it doesn't with 'squared seconds'). But we need this kind of nomenclature. Saying "meters per second per second" is easier for the layman to understand than "meters per second squared", but when we get into some units, that convention quickly becomes unwieldy. An "ohm" for example would be a "meter meter kilogram per second per second per second per ampere per ampere" - or a "farad" would be an "ampere ampere second second second second per meter per meter per kilogram"! You simply have to use the mathematical convention of calling an object that's multiplied by itself a "square" and an object that's multiplied by itself three times a "cube". We do that just to make the words easier to understand. It doesn't have a physical meaning - but this is math - so it doesn't have to have physical meaning. It all relates back to Dimensional analysis - in which the units can be treated like variables in an equation and can be multiplied and divided - cancelled out or raised to some power as needed. SteveBaker (talk) 13:55, 11 November 2008 (UTC)

Nuclear reactor efficiency numbers

I'm looking for some numbers on nuclear power plant efficiency and I'm having a hard time getting them. Any help? I'd like to compare them to solar, wind, coal, and oil. Mac Davis (talk) 22:45, 10 November 2008 (UTC)

Can you define more precisely what you want? There are different ways to look at it. Fuel is not totally depleted, heat is not totally converted to electricity, capacity is not fully utilized, etc. Dragons flight (talk) 22:59, 10 November 2008 (UTC)

Heat not totally converted to electricity. What is the word for this? Thanks. Mac Davis (talk) 23:04, 10 November 2008 (UTC)

Thermodynamic efficiency, I guess, but I don't see how you can meaningfully compare different types of power plant this way. The important differences are in things like the construction cost, the cost and availability of the fuel, the environmental impact, and the risk of serious accidents, not the amount of waste heat they produce (unless it's enough to be a pollutant, I guess). All else being equal a power plant that produces less waste heat is better, but all else is rarely equal. -- BenRG (talk) 23:27, 10 November 2008 (UTC)

I was thinking economically, a major factor would be how much of the produced heat could be turned into electricity. Might the about the same 30%-50% for all of them? Mac Davis (talk) 00:15, 11 November 2008 (UTC)

It's probably not a big factor economically. Think about it—if the cost of a unit of heat is really different between technologies, then one could be far less efficient and be still be really profitable. What you want from an economic point of view is cost per kWh and things like that. --98.217.8.46 (talk) 01:09, 11 November 2008 (UTC)

I would imagine it would convert heat to electricity identically to coal - the turbine arrangement ought to be pretty similar. Maybe the operating steam temperatures are different - but I kinda doubt it matters. But I'd echo what others have said - the problems with nuclear are not to do with generating the heat...you've got heat to spare...so efficiency isn't really the issue. It's all about cost-of-ownership, safety and waste disposal. But coal also generates low level radioactive waste - and it's worst waste product (the CO2) is still untrappable. The worst that a nuclear plant has ever done (Chernobyl) when criminally badly operated - with all of it's safety gear disabled - didn't really cause any more problems than coal plants do when they are operating ordinarily. SteveBaker (talk) 03:03, 11 November 2008 (UTC)

SteveBaker, very well said. Mac Davis (talk) 22:53, 11 November 2008 (UTC)

I suspect the 100,000+ permanently displaced people would consider the Chernobyl event rather different than what "coal plants do when they are operating ordinarily". Dragons flight (talk) 04:56, 11 November 2008 (UTC)

Um, well, Chernobyl did make a huge area of land uninhabitable and dispersed pretty radioactive materials over a large area. I would consider that qualitatively different than the sorts of ills caused by coal. But it's not really the point, and using Chernobyl to discount all nuclear technology is extremely short-sighted, I am sure we would agree... --98.217.8.46 (talk) 03:13, 11 November 2008 (UTC)

Have you ever flown over Wyoming or Kentuky? Coal mining has rendered huge areas effectively uninhabitable also, and the health effects in these areas (mostly black lung disease but also mining disasters) are much worse overall than those from Chernobyl. Nuclear has a dramatically lower overall impact that coal, even when you count in the criminal negligence of the designers and operators of the Chernobyl plant. -Arch dude (talk) 15:22, 11 November 2008 (UTC)

As SteveBaker said, if the steam turbine technology is comparable between nuclear and coal plants then it can be ignored if all you're doing is comparing those two technologies. What matters for the comparison is the differences between the heat sources, including the plant designs and whether one heat source has a much different cost than the other. If you're trying to get a single efficiency number then you'll have to define what you mean by efficiency. Nuclear fuels can produce more fuel from what is otherwise waste, and can generate electricity without a steam cycle. One can also generate heat with uranium by exploding it, or by stacking it a mile high on geothermal piping. -- SEWilco (talk) 04:06, 11 November 2008 (UTC)

(unindent) A sea level rise of just 20cm could create 740,000 homeless people in Nigeria alone. If you buy into the theory that the unprecedented force of hurricanes in the USA over the past few years is related to global warming - then if even ONE of them was caused by CO2 from coal-fired power stations - then Chernobyl is like a damp squib. Most major hurricanes cause 1000+ deaths (many have caused over 8,000) - Chernobyl caused only 47 immediate deaths (although the increased cancer risk will ultimately have shortened the lives of thousands more). If they hit a major city - hurricanes can easily temporarily displace a million people (Chernobyl displaced only 300,000). Well over 300,000 did not return to New Orleans after Katerina which certainly trumps Chernobyl's 100,000 'permanently displaced' people. The Chernobyl disaster has actually benefitted local wildlife - there are species of wild donkey previously thought to be extinct that are now florishing in the depopulated area. Now think about Polar bears...(no, the cute baby ones...yeah - that's it!). SteveBaker (talk) 15:29, 11 November 2008 (UTC)

geting back to the original question, "Power plants employing saturated or only weakly superheated steam have a thermodynamic efficiency of 35% or less. Such power plants include nuclear power " from the google summary of http://www.freepatentsonline.com/3992884.html although i can't find it on the site now, and "35% to 45%" from http://wiki.answers.com/Q/What_is_the_thermal_efficiency_of_the_nuclear_process_for_generating_electricity_and_how_does_it_matter&src=ansTT. seems in the right ballpark, offhand. Gzuckier (talk) 20:04, 11 November 2008 (UTC)

November 11

How to move energy faster than the speed of light

Imagine you have a easily pliable ring millions of miles in diameter. What if one were to stand in the exact center of this ring with a garden hose and release a perfectly even stream of water for one second while doing a 360. The water would then hit the ring causing it to move in a wave that would cover millions and millions of miles (or whatever circumference you would like) in one second. Is this possible?

Thanks--UhOhFeeling (talk) 06:23, 11 November 2008 (UTC)

Only if you are standing in Philadelphia. CBHA (talk) 07:03, 11 November 2008 (UTC)

Since a ring with a diameter (2xr) of about 2 million miles (1,911,200 miles) is already at a distance (r) of 4 times the average distance of the Moon from earth (238,900 miles) all sorts of factors come into play, including what keeps your pliable ring taut, at what speed it is rotating, the fact that neither a garden hose as delivery system nor water as a liquid would have much chance of meeting your "perfectly even stream" requirement. And that's just for starters. Having someone hop up and down on the surface of the ring might have a better theoretical chance of producing a wave, but nowhere near any speed of light. 76.97.245.5 (talk) 08:01, 11 November 2008 (UTC)

Hypothetical example, assume ideal conditions.--UhOhFeeling (talk) 09:28, 11 November 2008 (UTC)

Doing this with a light beam is much more reliable than with water. Just shine a torch away from you, and quickly rotate so the torch shines in all directions. At long distances from you, the torch beam is moving much faster than light. I thought we had an article mentioning this, and why it is not normally considered to count as FTL (because it doesn't allow superluminal information transmission), but I can't find it. Algebraist 09:54, 11 November 2008 (UTC)

Indeed. Or replace the water with raido waves and you have a pulsar. Suppose pulsar is at A and sweeps its beam between B and C, many light years apart, in a fraction of a second. Then energy is transferred from A to B (or to C) at the speed of light - but no energy is transferred from B to C. Gandalf61 (talk) 10:01, 11 November 2008 (UTC)

I guess it's similar to how the group velocity of light can exceed the "speed of light". The key point, as has been said, is that no information is travelling faster that light speed. --Tango (talk) 11:52, 11 November 2008 (UTC)

That is why you need water (or whatever you want, Hypothetical Example) to impart a force on the pliable strip between B and C creating a physical wave moving faster than the speed of light. Under ideal conditions would this hypothetical work?--UhOhFeeling (talk) 19:58, 11 November 2008 (UTC)

Why bother? Light can push stuff, so you can probably get a wave going with that if you want to. You still won't have superluminal information transfer. Algebraist 20:00, 11 November 2008 (UTC)

Sure Light is fine, Hypothetical. Why won't you have superluminal information transfer is my question. Thanks.--UhOhFeeling (talk) 20:04, 11 November 2008 (UTC)

Because as you stand at A swinging your spotlight (at FTL speeds) from B to C, there's no way that events at B at the time the light hits can influence what you're doing (said events are still way in the future at this point). Thus events at B can't influence C FTL through this mechanism. Algebraist 20:11, 11 November 2008 (UTC)

The "wave" isn't propagating along the ring, it's being caused separately at each point when the beam of water or light hits it, so there is no information going along the ring (well, there will probably be a wave propagating as well, but that will follow along behind at a slower speed). The only information moving if from the centre of the ring to the ring itself, which travels at sub-light speeds (for water) of light speed (for light) but never faster. --Tango (talk) 20:13, 11 November 2008 (UTC)

Why would the wave be following along at a slower speed if the energy hit it in such a way that the wall was being pushed in a way that would create a wave faster than light. Couldn't this wave continue after it's initial trip around on it's own? --UhOhFeeling (talk) 01:27, 12 November 2008 (UTC)

Of course not, any more than dropping a thousand rocks into a pond in a line will create some sort of supersonic ripple that arrives at the other end of the pond immediately. Each rock creates a wave (really a set of waves) that spreads out from its point of impact at a fixed speed, and the presence of other waves is irrelevant. (This isn't very precise for waves on the surface of water, but the idea is correct.) Given that you're trying to make a faster wave, you must be dropping the rocks into the pond with very little time between them: so little time, in fact, that the first rock's waves haven't reached the last rock when it hits! This means that the rest of the pond (in the direction of the line of rocks) will see the wave from the last rock before any of the others have had any effect on it. This is what is meant by the lack of superluminal information: the first rock can't affect the last rock because information about its impact on the water can't get to the last rock's impact.

With the speed of light, the "can't affect" becomes an absolute statement that encompasses all kinds of effects, so it is simply irrelevant to each part of your ring that you have already doused some other part, since the other parts are all too far away to have affected it (yet). At the moment your last bit of water hits the ring, that part of the ring is aware only of that last bit of water, so we can't expect that part of the ring to do anything special like maintain the ludicrous speed of the "wave". (Put differently, there is no single object that we may call "the wave", because it's not causally connected.) Moreover, assuming all the miniwaves propagate at the same speed, no previous part of the wave will ever catch up to the leading edge (where the water hit last), so there won't even be interference at that edge to make anything interesting happen.

In short, the answer is Yes, it's possible, but so what?. The fact that the water was once all in the center with you does not make it one object when it hits the ring, because it too has become causally disconnected. The various events of bits of water striking bits of ring are unrelated, and any "speed" you assign them as a group (by considering the change in position with respect to time of "the most recent place where water has hit") is entirely a construct of your perception.

Finally, note that non-physical speeds such as that of the water-ring contact point are not well defined given the existence of other observers; for an observer moving at an appropriate relativistic velocity, the wetting of the ring may be happening in more than one place at once and be moving in the opposite direction you say it is! --Tardis (talk) 17:11, 12 November 2008 (UTC)

See also Superluminal Scissors (wot, no article?); here, then. --Sean/76.182.94.172 (talk) 13:36, 11 November 2008 (UTC)

Cool article, I'm not sure if it applies here as the information would be directly impacting the surface rather than traveling the length of the scissor edge.--UhOhFeeling (talk) 20:02, 11 November 2008 (UTC)

Is concussion or neck injury common in horned animals?

Or, at least, the ones attacked to their heads?

I suppose the answer is kind of straightforward - the ones who would suffer them were sorted out long ago because they didn't survive - but it's one of those questions I have if I awaken in the middle of the night.

Reading about sheep (redirected from rams), I didn't even find much about their horns, though considering that the article says injuries are one of the main causes of death for them, maybe it does still happen.

I would also think that perhaps said horns are so incredibly thick that the constant head butting never gets through to their skulls. However, I also wonder if that doesn't increase the chance of neck injuries.

Thanks.Somebody or his brother (talk) 13:06, 11 November 2008 (UTC)

See the comments here for some thoughts on the relative resistance of head-butting animals to traumatic brain injury. - Nunh-huh 16:04, 11 November 2008 (UTC)

Which begs the question, if a sheep is concussed, or suffers cognitive impairment, how does one know? It isn't like the sheep was writing novels or working out differential calculus before the injury... --Jayron32.talk.contribs 19:31, 11 November 2008 (UTC)

You could devise some simple tests for the sheep to compare cognition before and after. Even measuring pupil reactivity or something. Plasticup ^T/C 23:48, 11 November 2008 (UTC)

The force of the collision can't "stay" in the horns (unless they deform but that is besides the point...) The force has to dissipate somewhere, which is down the horns, across the head, down the neck, into the body and to whatever is anchoring the animal in place ( In this case the hooves). Here is some info as it related to woodpeckers (http://web.cornell.edu/blogs/theessentials/?p=395) I bet some of it carries over... 152.16.15.23 (talk) 19:48, 11 November 2008 (UTC)

How many cells are in an embryo when it splits into twins?

I understand that identical twins are formed when an embryo splits very early on. How many cells are in the embryo when it splits? Is it always the very first split that results in two embryos? —Preceding unsigned comment added by JeremyStein (talk • contribs) 15:07, 11 November 2008 (UTC)

The article you link to answers yoru question in the first paragraph and the start of the second: "If the zygote splits very early (in the first two days after fertilization), each cell may develop separately its own placenta (chorion) and its own sac (amnion). These are called dichorionic diamniotic (di/di) twins, which occurs 18–36% of the time.[15] Most of the time in MZ twins the zygote will split after two days, resulting in a shared placenta, but two separate sacs. These are called monochorionic diamniotic (mono/di) twins, occuring 60-70% of the time[15]. In about 1-2% of MZ twinning the splitting occurs late enough to result in both a shared placenta and a shared sac called monochorionic monoamniotic (mono/mono) twins.[15] Finally, the zygote may split extremely late, resulting in conjoined twins."

I'm not sure how many cells the earliest splitting equates to, but it's clear that splitting is possible at almost any point in the pregnancy. 137.108.145.10 (talk) 15:35, 11 November 2008 (UTC)

well, i'm not sure that conjoined twins are split later on, so much as twins which have fused later on. the requirement for splitting the embryo is that it must happen early enough so that each cell is totipotent i.e. can take off and start an embryo on its own. this is a handy property for lab tinkering; you take an early embryo, gently take the cells apart, and you have a bunch of identical embryos. repeat as desired. according to our article, this stops at about 4 days. i'm not expert, so i'll accept that. doesn't sound unreasonable. at this point the cells begin to become increasingly specialized; for instance, the first thing is that cells become to think of themselves as one end of the embryo or the other. from fruitfly work, if you then transplant cells from one end to the other things go haywire, but if you move the cells at each end around on the same end, no problem. the specialization then gets more specific from there downhill, like at one point you can swap the future leg and antenna and each will switch to the correct item for where it now is, but the next day it won't. this implies that it's the neighboring cells that somehow tell the developing cells what they're supposed to be, and as each part develops the cells within tell each other what they're supposed to be doing. it's fascinating stuff. caveat: i haven't read anything about it in a decade or so, so this represents state of the art for the end of the last millenium. Gzuckier (talk) 15:53, 11 November 2008 (UTC)

Totipotent cells are present in the morula up to the 16-cell stage. At 32 cells, the morula begins to differentiate. So it isn't necessarily the first split that leads to identical twins. A split anywhere up to 16 cells can lead to identical twins. Axl ¤ [Talk] 11:30, 12 November 2008 (UTC)

basic anatomy

why do you taste eyedrops after applying them to your eyeballs? —Preceding unsigned comment added by 69.246.63.171 (talk) 18:53, 11 November 2008 (UTC)

It's because the drops travel down the nasolacrimal duct into your nasal cavity and from there down onto the back of your tongue. Fribbler (talk) 19:01, 11 November 2008 (UTC)

That's awesome!! Mac Davis (talk) 22:55, 11 November 2008 (UTC)

I wonder if it goes in reverse: i.e. spicy foods causing one's eyes to burn. I still figure the majority of the cause of that is airborn molecules but now I wonder... 152.16.15.23 (talk) 23:58, 11 November 2008 (UTC)

A dentist once injected novocaine into the inside of my cheek and it went up into my eye, which went numb. The tears that came out and ran down my cheek from the stinging tasted of novocaine. She said "oops". --Sean 01:03, 12 November 2008 (UTC)

How does the exchange of virtual photons mediate attractive vs. repulsive coulomb force?

I understand that, in QED, it is the exchange of virtual photons that mediates that coulomb force via the transfer of momentum. However, what I am having difficulty tracking down is how the charge information is carried. (I.e. whether the transfer should function as attractive or repulsive force.) I'm willing to work my way through the technical details if I can just be pointed toward a good online source, such as some scientific journal articles. (The virtual particle FAQ didn't prove useful for me, unfortunately.) Any suggestions? Thank you.—RJH (talk) 20:11, 11 November 2008 (UTC)

pain

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glass recycling projects third world

We live in the Namib desert in Namibia and require information about recycling glass for a community project. Is there a way of reusing the glass bottles to manufacture glass tiles or beads or any other product to either sell to tourists or reuse in a sustainable way? Your advise will be much appreciated.

Johan Raubenheimer <email redacted> —Preceding unsigned comment added by 41.198.48.196 (talk) 21:53, 11 November 2008 (UTC)

Glass is a pretty recyclable material - you just need a sufficiently hot furnace - and people with the right skills to reform the liquid glass into new shapes. I guess in the Namib, the problem will be finding fuel for the furnace. I wonder if it would be possible to make a solar furnace with enough power to do the job? Making glass animals is a pretty easy skill to learn - you can do that with a small propane torch - you don't even need a furnace. If you have someone with the imagination to produce something unique, then you would have something to sell to tourists. The trick will be in finding a compelling and unique art style. If you can find the talent - you could sell the product on the Internet too. Small, high value product that don't have high shipping costs are a great choice for Internet marketting. SteveBaker (talk) 00:06, 12 November 2008 (UTC)

Also see Bottle wall for one use not requiring melting/furnaces. There are others. We used to make vases by coating and/or cutting glass bottles. Get a bunch of people together and brainstorm. 76.97.245.5 (talk) 07:33, 12 November 2008 (UTC)

surface of last scattering

Cosmic_background_radiation#Features says:

Accordingly, the radiation from the sky we measure today comes from a spherical surface, called the surface of last scattering. This represents the collection of points in space (currently around 46 billion light-years from the Earth—see observable universe) at which the decoupling event happened long enough ago (less than 400,000 years after the Big Bang, (13.7 billion years ago)) that the light from that part of space is just reaching observers.

If the event occurred 14 billion years ago in that space, shouldn't it only be 14 billion light-years away instead of 46 billion ly? At first I was thinking that we're moving away so fast that it takes 4 times as long for the light to reach us, but that violates special relativity, right? So how can both those numbers be right? Thanks 72.236.192.238 (talk) 22:44, 11 November 2008 (UTC)

It doesn't violate special relativity because there isn't actually any movement involved, it's just the space inbetween expanding. When we talk about the universe expanding that doesn't mean everything in it is moving outwards it means the actual spacetime itself is expanding. The standard analogy is to think of a balloon. Before you blow up the balloon, draw some dots on it. Now as you blow it up those dots get further and further apart, but none of them has actually moved relative to the balloon. --Tango (talk) 22:56, 11 November 2008 (UTC)

See Metric expansion of space#Understanding the expansion of space. The pictures illustrate a nearly identical situation (light from 12–13 billion years ago, instead of 13.7, from an object that's now 28 billion light years away, instead of 46). -- BenRG (talk) 23:10, 11 November 2008 (UTC)

It is really quite simple (simpler than the above answers make it sound). The thing we see as the surface of last scattering is moving rapidly away from us (Hubble expansion). Today we can see light from it that was emitted 13 billion years ago, and we infer from where it was then and how fast it has been moving that it should now be 46 billion light years away. In other words, it is simply a matter that the separation is believed to have increased a lot during the time it took the initial light to reach us. Dragons flight (talk) 23:40, 11 November 2008 (UTC)

Black knees

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This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis or prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page. --~~~~

If you are concerned about unusual symptoms you experience after physical exertion, you should speak to a medical expert. TenOfAllTrades(talk) 23:24, 11 November 2008 (UTC)

any way to guess how long it took someone to write something?

Resolved

I'm wondering if there is any way to come up with an approximate guess as to how long it took someone to write something. in particular, how could I go about guessing how long it may have taken to write these paragraphs in particular? What about a more general way to guess? —Preceding unsigned comment added by 83.199.126.76 (talk) 23:07, 11 November 2008 (UTC)

Probably the wrong place. Touch typists can manage up to 1k per minute, although 400 characters per minute is more typical. --Stephan Schulz (talk) 23:21, 11 November 2008 (UTC)

Wikipedia on this article cites it at 50-70 words per minute. I guess I'd use that as a baseline but obviously it's going to depend on the individual. —Cyclonenim (talk · contribs · email) 23:25, 11 November 2008 (UTC)

Two things: one, what does "probably the wrong place" mean? Two: why do you both talk about typing speed, when I mean writing speed. We're not talking about chatting (or how I'm writing now), but composition as well....surely it's less than blind typing, especially when we're talking about references as well... Can anyone give me a minute estimate for my above link specifically, and how you made that guess? Thank you!

You're in the wrong place because this problem is not well enough defined to have a useful scientific answer. I gave you a lower limit. Composition speed is often considered half of typing speed, but that of course depends on how well the writer is familiar with the topic and if they know what they actually want to say. You might get some anecdotal evidence at the language or humanities desk. --Stephan Schulz (talk) 00:10, 12 November 2008 (UTC)

Okay, so I cut and paste the paragraphs into a character counter and divided by five, because hte typing speed article says every five characters counts as a word (regardless of actual space locations), and got 1022. So if the guy composed it continuously, and was able to type all that at 60 words per minute, then if composition is half of typing speed (30 wpm) it took him 34 minutes. If he was very thoughtful and typed half as slowly, it took him 68 minutes. And the upper limit is about 15 hours, because that's how long there was between when what he's replying to appeared, and his reply.... So... anywhere from 34 minutes to 15 hours. Can we do ANY better than that?

I think it's pretty clear that the answer is "No". We know the time when the edit was committed - but we don't know when the person started to type it. It's certainly not just a matter of typing speed - thinking speed matters too. Also, if they proof-read and then go back and fix up errors or decide to expand upon a particular thought...there is truly no way to put a number on it. SteveBaker (talk) 23:49, 11 November 2008 (UTC)

Do you agree with my reasoning of between 34 minutes and 15 hours? Can you find a trick to improve it by a TAD? (such as a way to figure out that it's almost certainly less than ten hours -- ALL of us know this intuitively!)

No - I certainly don't agree. We have no idea whether this was bulk cut/pasted from other sources - or whether this was a synthesis of some other document written in advance - or whether this is a very thoughtful piece composed by someone with many interruptions who goes through many drafts before hitting that 'Send' button. Heck, he may have been thinking about this for a year and only just now decided to put his words into print. There is quite simply no way to know - and any kind of speculation is just that: "speculation". SteveBaker (talk) 04:49, 12 November 2008 (UTC)

Thank you. You have me convinced. I realize I can't even have an upper limit of even the lifetime of the poster, since the paragraphs could include cut-and-paste from deceased people as well! :( I guess the conclusion is exactly what you first said, no way to know even approximately. You can put a green checkmak, resolved, next to this question (I don't know how to do it). Thanks!

FYI: You add {{resolved}} just under the title of the question. SteveBaker (talk) 18:11, 12 November 2008 (UTC)

May I ask why it has to be less than 10 hours? And on a second note, sometimes people leave their computer in the middle of typing, so really even 10 hours is possible. —Preceding unsigned comment added by 76.69.241.185 (talk) 00:56, 12 November 2008 (UTC)

I understand that Flaubert wrote Madame Bovary at a rate of about 1 sentence per day. --Sean 01:12, 12 November 2008 (UTC)

At the other end of the spectrum, Anthony Trollope wrote 1000 words an hour, day in, day out for years, according to Brittanica Concise Encyclopedia. Clarityfiend (talk) 04:13, 12 November 2008 (UTC)

Leonhard Euler likely more than that. Mac Davis (talk) 22:22, 12 November 2008 (UTC)

November 12

What shape is this?

I was thinking about this some time ago. Imagine a small room that has a door on each of its six faces. On the center is a flower pot and some clothes that I discarded. If I open and enter any of the doors in this room, I will enter a room with the flower pot and the same clothes that I discarded earlier. My question is, what is the shape of the room? I'm pretty sure it is not 3 dimensional. --Lenticel ^(talk) 00:37, 12 November 2008 (UTC)

I think you have been trapped in a game. In many old 2D games when you went off one side of the screen you reappeared at the other side. Obviously they have upgraded your game to ake advantage of a graphics processor to do 3D. On the other hand you might like to read the bit at the end of Shape of the Universe,we may be in something far weirder. 01:10, 12 November 2008 (UTC)

A room with 4 walls, a floor, and a ceiling could be considered as a cube with six faces. CBHA (talk) 02:43, 12 November 2008 (UTC)

This reminds me of a hemicube. Anyway, I'd say either the room is three dimensional, but the geometry isn't Euclidean, or you're on a three-dimensional analogue of a torus. That is, the surface is three-dimensional. — DanielLC 01:22, 12 November 2008 (UTC)

Topologically speaking, if the room has six walls in addition to floor and ceiling, the floor of the room could be a sphere, a torus, or a projective plane, for example. If it has four walls + floor and ceiling, then the room could be a three-torus or any number of weirder manifolds. Algebraist 01:31, 12 November 2008 (UTC)

Wow, this weirder than I thought. --Lenticel ^(talk) 01:37, 12 November 2008 (UTC)

We could narrow it down further if we knew whether or not going through any of the doors changes you from being right-handed to left-handed, or vice versa (or, equivalently, makes everything else in the room turn into its mirror image, but changing you sounds more fun!). --Tango (talk) 01:46, 12 November 2008 (UTC)

I wonder whether you got this idea from Cube 2: Hypercube which has similarities (but limited logic). PrimeHunter (talk) 01:56, 12 November 2008 (UTC)

Well I got the idea while I was taking a bath earlier today. The cramp bathroom inspired the idea. By the way, the movie seems to be cool. Maybe I'll try to find a DVD version later.--Lenticel ^(talk) 02:18, 12 November 2008 (UTC)

If the answer is "not 3 dimensional", then the word you're looking for is "Hexagon". APL (talk) 14:03, 12 November 2008 (UTC)

It's not a tesseract is it? It's a non-3-dimensional shape which is connected in ways I don't understand. AlmostReadytoFly (talk) 16:35, 12 November 2008 (UTC)

A tesseract is 4D, I don't think we have any reason to believe we're working in 4 dimensions. --Tango (talk) 16:42, 12 November 2008 (UTC)

Potential Energy

For the sake of simplicity, let's consider gravity. Now I understand why the gravitational potential energy of an object has to be negative (as it approaches the source of gravity its potential energy must decrease in order to allow its kinetic energy to increase), but isn't energy the ability of an object to do work? And so it seems odd that an object could have negative energy (when its, say, lying on a table). How would one resolve this apparent contradiction? Thanks. —Preceding unsigned comment added by 76.69.241.185 (talk) 00:46, 12 November 2008 (UTC)

It doesn't have to be negative, you can set the zero of potential energy to be anywhere you like. The maths is often easier if you set the zero to be at infinite distance and thus have it always negative, but it doesn't really matter. All that matters is the change in energy. For an object on a table it would probably make sense to set the zero to be when the object is on the ground, since that's the lowest it can get. If you do that, then when it's on the table it has positive energy and can do work as you would expect. --Tango (talk) 01:04, 12 November 2008 (UTC)

For an object A in a gravitational field of another object B, it makes sense to define a zero of potential energy at very large (infinite) distance between the objects, and to measure the velocity relative to the center of mass (CM) of the system of the two objects. Then, if the TOTAL energy of A is negative, then it is on the bound orbit around CM ; and if the TOTAL energy of A is positive, then it is on the open orbit. Gravitational potential energy of A is always negative. If A performs work, its total energy decreases, but its instant potential and kinetic energy may either increase or decrease, provided their SUM (the total energy) decreases and provided the potential energy stays negative. Now, for the AVERAGE potential and kinetic energies of A in the BOUND orbit, you can apply a so-called virial theorem. For a classical gravitating system, it states that AVERAGE kinetic energy Ekin equals minus half the AVERAGE potential energy, Ekin = -Epot/2 ; or, equivalently, Etot = Ekin + Epot = -Ekin = Epot/2 < 0 . In a two-body system the AVERAGE is determined over a closed orbit; in a many-body gravitational system the strict average is over an infinite time, but for a "very large" finite time the result holds with high accuracy, too. Anyway, since E = Epot/2, body A performing work DE > 0 changes E to E - DE, so makes Epot "more negative" (thta is, larger in its absolute value). That means that Ekin also becomes larger in its absolute value! What happens is, the body A, having lost some energy, moves to a tighter orbit where its total energy is indeed lower (larger in absolute value, and negative) but its mean-square speed is higher. Hope this helps. --Dr Dima (talk) 01:47, 12 November 2008 (UTC)

Camera red eye and white eye

I've noticed that my new camera often causes people to have one red pupil and one white pupil instead of the standard camera red eye. I thought that the red eye was caused by reflection of the red on the back of the eye. So, that doesn't explain how the white eye effect is produced. It never happened with any of my older cameras. So, I am left wondering if it is the camera. Has anyone else here had a camera do this? Is there a fix to make it stop doing it? It is a pain because the auto-removal of red eye doesn't work if the pupil is white. -- kainaw™ 01:41, 12 November 2008 (UTC)

Could it be some weird anti-red eye feature going horribly wrong? Try turning off any weird anti-red eye features and see if it stops happening. --Tango (talk) 01:50, 12 November 2008 (UTC)

Also, have you tried it with different subjects? Maybe the person you are photographing has a strange eye (in which case, they should probably see a doctor!). --Tango (talk) 01:51, 12 November 2008 (UTC)

I have noticed it with more than one person. About 90% of the times I've seen are with my son. But, about 99% of the photos I take are of him. So, there is no reason to think he is more prone to it. I've tried to turn off all weird functions on the camera. It isn't easy to use because it is designed to be so easy to use that it decides what you want and does it for you - refusing to let you decide what you want. Something I did got it to stop blinking the flash 4-5 times before snapping a photo - which often meant that the cool photo of my son would end up being him covering his eyes and turning away from the evil flashing light. -- kainaw™ 02:08, 12 November 2008 (UTC)

This site has any explanation of camera red eye and one reason for white eyes: [26] Rmhermen (talk) 02:11, 12 November 2008 (UTC)

Thanks. It commented on the reflection being common when the pupil is angled away from the camera, towards the nose. Looking back at the photos I didn't manually correct, I can see that the people with one white eye are looking away from the camera and towards their nose. -- kainaw™ 02:40, 12 November 2008 (UTC)

I suppose it's worth asking whether your son is cross-eyed? If the two eyes were not pointing in the same direction - then the reflection off the retina of one, would not occur on the other eye. It's hard to imagine any other reason. SteveBaker (talk) 04:41, 12 November 2008 (UTC)

It's also possible if the camera is close to the person's face, but they're looking at something well behind the camera. I don't know how close the camera would need to be for this. --67.185.190.46 (talk) 06:36, 12 November 2008 (UTC)

My understanding is that if the eye is looking straight at the camera the flash will produce a reflection of the vascular, and thus red, back of the retina. However if the eye is not directly aligned with the camera the reflection is of the less vascular parts of the retina producing a white reflection. I believe the phenomenon of 'red-eye' is a human problem associated with the particular vascular anatomy of the human retina. Perhaps it occurs in other primates. Richard Avery (talk) 08:13, 12 November 2008 (UTC)

Since this is occurring with photos of several people, a medical cause is unlikely. However retinoblastoma can give this appearance. Axl ¤ [Talk] 12:05, 12 November 2008 (UTC)

Now that I had some search terms for Google (thanks), I understand. This happens with children and isn't very uncommon. If a child is looking away from the camera (by about 15 degrees), the eye that is looking towards the nose will turn white. The other will be dim red - not a complete red-eye, but not white either. If you look at eye, you can see the main optic nerve is not dead center in the back of the eye. It is about 15 degrees off center. So, if the child is looking away at just the right angle, you get reflection off the optic nerve, not the nice red part of the eye. Further explanation that I've found from tons of Google hits is that this is limited to children because the size of the whitish area around the optic nerve is larger in relation to the size of the eye than it is in adults. Also, adults tend to look at the camera, not slightly away - so they don't even get in position for this sort of reflection. Since I've been mainly photographing my 1-year old son and his friends, I've been picking up a lot of kids at just the right angle to get the white-eye reflection. -- kainaw™ 13:41, 12 November 2008 (UTC)

Light Has Intelligence?

I saw a "documentary" recently in which a "scientist" stated that light has shown to anticipate experiments in which it is involved. The guy did not seem like a crack pot. What in the world could he be referring to? —Preceding unsigned comment added by 75.67.217.220 (talk) 01:52, 12 November 2008 (UTC)

Perhaps retrocausality? Jkasd 02:16, 12 November 2008 (UTC)

See also, freebasing and crack cocaine. Plasticup ^T/C 02:50, 12 November 2008 (UTC)

I suspect you're thinking of things like the "wave-particle duality" effect and quantum mechanics. Because of the wave–particle duality of light, the results of certain experiments seem to depend on how you are measuring the results - which leads one to kinda imagine that the light in the experiment "knew" how you were ultimately going to measure it - and changed it's behavior beforehand.

I recommend reading Double-slit experiment - and Quantum eraser experiment.

Suffice to say, the light isn't "intelligent" - but it does behave in ways that seem so far from our normal experience that it's almost impossible to get your head around the implications. This stuff leads us into the ideas of parallel universes and all manner of other weirdnesses.

SteveBaker (talk) 04:37, 12 November 2008 (UTC)

I'd guess the Elitzur-Vaidman bomb-tester is closest to what he might have been thinking of Dmcq (talk) 09:04, 12 November 2008 (UTC)

The deal with light is that it is not a particle or a wave, it is its own thing. Its just "light". We have models that treat it like a particle; and those models work to explain some of the behaviors of light. We also have models that treat it like a wave; and those models work to explain some of the behaviors of light. The deal is, that both models fall apart roughly 50% of the time; that is for any set of conditions in which light behaves as a particle, the wave model looks like it doesn't work, and visa-versa. The reality of light is that it doesn't have an analog in the "big" world. You can't say light is like _blank_, where _blank_ is any thing you have the ability to manipulate with your hands. Any "contradictions" in lights behavior, which make it, for example, appear "intelligent" as described (such as the aforementioned Double-slit experiment), are just the result of the faultiness of our models. Its our problem, not light's... --Jayron32.talk.contribs 17:24, 12 November 2008 (UTC)

The trouble is that this is simultaneously a correct - but also intensely frustrating - answer! You're absolutely right - light is something for which we have no analogs - which leaves us no way to explain it that does not tempt us into dangerous extrapolation-from-experience. Ordinary 'stuff' has a mass and you can stop it moving. Then you can stick it on a weighing machine and you know it's mass. When you push ordinary stuff towards light-speed, it gets heavier and heavier - and if you could somehow get it up to light speed, it's mass would be infinite. So the mass of normal 'stuff' is infinite at the speed of light and something reasonable all the rest of the time. Photons, however can only move at the speed of light - but yet they have actual sane, finite masses. Time is similarly warped - so for the photon, time doesn't exist...neither does distance. It's no wonder that it 'misbehaves' in every way imaginable compared to normal 'stuff'. The very nature of the zeroes and infinities that pop up at the speed of light in relativistic calculations pretty much guarantees that light is going to be weird. SteveBaker (talk) 22:05, 12 November 2008 (UTC)

How come garbage explodes only when it's buried?

The old lady told me to take out the garbage earlier (always naggin') so I jokingly said I'll chuck it in the backyard. Then she said "You can't throw it in the backyard, ass-h*le, it'll draw rats!" Then I said, "Fine, I'll bury it! That way I wont have to pay a goddam garbage bill!" Many colorful obscenities later she told me that garbage will explode if buried for a short time. I didnt want to agree with her at the time, but I vaguely remember hearing that's why landfills are vented and have flames shootin out of factory whistle lookin thingamajigs. My neighbor 3 trailers down has had garbage all over his yard for years that wasnt buried and he hasnt had no problems. Not even rats. What gives?Sunburned Baby (talk) 02:28, 12 November 2008 (UTC)

Maybe it explodes on Wednesdays while your friend is at work? —Preceding unsigned comment added by 83.199.126.76 (talk) 02:32, 12 November 2008 (UTC)

Much of our garbage tends to produce methane when it decomposes. When sitting in the open, the gas just floats away. When buried, it builds up in pockets. If, for some reason, the pocket of gas is ignited, it can make a small explosion. Venting natural gas from landfills isn't done just for safety. There are people who buy natural gas, so the landfill companies bottle up the byproduct for profit. So, why not bury your garbage, stick a hose down in it, and funnel off the gas into some empty wine boxes you have laying around. You might make enough to pay for a whole week's worth of lottery tickets. -- kainaw™ 03:06, 12 November 2008 (UTC)

The "some reason" for the gas igniting Kainaw mentioned is often an exothermic reaction in the decomposition process. I tried to find a nice link for you. Although several sites including our Composting page mention the fact that decomposition by anerobic bacteria generates heat, I've failed to find a nice concise description of the process. Anaerobic respiration holds some clues, but not much context. What you get is spontaneous combustion which has a dead end link to Fermentation (biochemistry). Don't get you hopes up for not getting rats when you bury the stuff. I used to live next to a former dump and the critters had no problem burrowing to the larder. You'd just get a chance to ignore what you don't see. Your neighbor who didn't get any might have had a local ecosystem (e.g. snakes, cats, owls etc.) that kept the rat population down to an unnoticeable/non existent size. The amount of biogas you get out of your household waste is not likely to reach marketable amounts unless you wish to build a Mount Trashmore in your back yard. The volume of easily digestible biomass in proportion to stuff that takes decades to break down is likely not very high. To reduce the volume of trash you put out you could deliver glass, plastics, metals and paper to a local recycling center and pepper your back yard with compost barrels (no access for rats) to use the compostable portion of your biodegradable trash. Depending on gas prices and local garbage collection policies and prices you might come out ahead or not. 76.97.245.5 (talk) 07:17, 12 November 2008 (UTC)

Methane as cause of global warming

Im looking for references that Methane in the atmosphere causes much more global warming than co2 and therefore that burning natural gas is good for the earth.--GreenSpigot (talk) 02:58, 12 November 2008 (UTC)

Woooaahh...be very VERY careful how you say that!!

Our Methane article does indeed say (correctly) that "Methane is a relatively potent greenhouse gas with a high global warming potential of 72 (averaged over 20 years) or 25 (averaged over 100 years)." (and there is a reference for that). CO2 has a 'global warming potential' of 1 - so clearly Methane in the atmosphere is a REALLY bad thing.

HOWEVER it is most certainly NOT a good idea to drill for natural gas and burn it in order to save the planet! It's far better to leave it underground where it belongs! Methane deep underground where it's been safely buried for millions of years - is just fine where it is! The only (exceedingly special) time when what you say is correct is if the natural gas is already in the atmosphere - then converting it to CO2 is better than waiting for many decades for it to degrade by itself.

So please don't go around saying "we should all be using natural gas because it's good for the atmosphere" - because nothing could be further from the truth! The kinds of situation we're talking about is when (for example) you have a herd of dairy cows and their poop would normally produce a bunch of methane that would do terrible things to the planet - then it is much better to use that methane as a fuel (both extracting some useful energy - and converting it into much safer CO2 in the process).

SteveBaker (talk) 04:22, 12 November 2008 (UTC)

Methane is more potent per molecule; however, in absolute terms we've added much more CO2 to the atmosphere than methane, so methane has had less of a global warming impact than co2. Dragons flight (talk) 05:53, 12 November 2008 (UTC)

Yes - I agree. This may change as the methane clathrate deposits in the deep oceans begin to melt. There has been some evidence that this exceedingly nasty situation is starting to occur - and (reluctantly) one has to say that burning the stuff as fuel (converting it to CO2) before it can ramp up the greenhouse effect (with the potency of methane) might be a last-ditch way to survive that situation. However, it's a decidedly "non-trivial" problem to do that - and we'd want to be very sure that the runaway melting of these deposits was really going to happen before we took such a drastic step. SteveBaker (talk) 14:57, 12 November 2008 (UTC)

Full moon on birthdays

Over the course of a lifetime of, say, 85 years, how often could one expect their birthday to coincide with the full moon? -- JackofOz (talk) 05:34, 12 November 2008 (UTC)

Three times on average. Dragons flight (talk) 05:54, 12 November 2008 (UTC)

Thanks. How did you work that out? -- JackofOz (talk) 07:29, 12 November 2008 (UTC)

A full moon occurs once every 29.5 days according to its article, so a birthday has one chance in 29.5 of coinciding with one. 85 is almost three times 29.5. (Something for werewolves to look forward to?) Clarityfiend (talk) 07:58, 12 November 2008 (UTC)

Yep, that's what I originally figured. It just felt way too low, so I thought I must have gone wrong somewhere. Depending on where the birthday falls, you might only manage 2 birthday full moons in an 85-year lifetime. Is there any way to work out, for any particular birthday and a given starting year, when the birthday full moons will occur, or do you have to use an ephemeris and do it "manually"? -- JackofOz (talk) 08:22, 12 November 2008 (UTC)

It probably sounds low because the moon changes size quite slowly and appears full to the naked eye (at least mine) for several nights a month. Algebraist 08:25, 12 November 2008 (UTC)

You probably would need an ephemeris; the 29.5 days varies a bit. However, there may be astrological software that can tell you when a solar return (birthday) coincides with a sun-moon opposition (full moon). You would also need to know the place of birth so that you could reduce the time to UT, the time used in most ephemerides.--Shantavira|^{feed me} 08:43, 12 November 2008 (UTC)

Pneumonia

What is the survival rate for untreated bacterial pneumonia if the victim is an otherwise-healthy young adult? --67.185.190.46 (talk) 06:28, 12 November 2008 (UTC)

Untreated, bacterial pneumonia kills ~30% of the afflicted [27]. Dragons flight (talk) 06:45, 12 November 2008 (UTC)

But it's occurrence and observation is, I assume, much higher in the sick and elderly. Being in good physical condition and having a robust immune system bacterial pneumonia may manifest itself as only a cough and I may not even go to the doctor. Any measurements (short of those from controlled experiments) is going to suffer monstrous selection bias. Plasticup ^T/C 15:05, 12 November 2008 (UTC)

Pneumonia describes an illness that necessarily has certain symptoms, i.e. fluid in the lungs, almost always accompanied by fever and some degree of difficulty breathing. If you only have a cough, then you might have an infection, but you do not have pneumonia. Dragons flight (talk) 16:22, 12 November 2008 (UTC)

It's certainly possible that a person whose only symptom is a cough has pneumonia. It's especially possible in the elderly or others with immune dysfunction, but not what you'd expect in the young: I think Darongs flight's point is that those with vigorous immune responses fight off infection before it becomes pneumonia. Since the question asks specifically about the young, we can't give a reasonable answer if the population studied includes the elderly and we don't have the data to correct for age. 30% is certainly high for a young population. - Nunh-huh 17:26, 12 November 2008 (UTC)

Lots of folks (especially kids) get so called walking pneumonia, otherwise identified as atypical pneumonia, often with mycoplasma as the causative agent. As a result of the slow growth rate of this organism, a generally healthy patient can exhibit nothing more than a nagging cough and certain degree of lethargy as they go about their daily business, which doesn't clear up after a long period of time. Most parents I know (who are reasonably frequent consumers of healthcare) are quite familiar with it. I'm not sure how it resolves itself if untreated, what I see is parents who see those symptoms in their kid for a couple of weeks, go to the doc and get the diagnosis, and get it treated with specific antibiotics. But if you're the type of person who avoids doctors unless absolutely necessary, for whatever reason, you probably wouldn't be worried enough to seek attention.Gzuckier (talk) 17:45, 12 November 2008 (UTC)

Query about today's featured picture.

What a fantastic picture, but that apart can anyone explain the blue/green light circle at the rotor tips. I understand that it is caused by lights but what is the purpose of the lights, surely they are not decorative. Are they part of some safety system that shows the position of the rotors at night to prevent..um.. unpleasant accidents? Richard Avery (talk) 08:23, 12 November 2008 (UTC)

Link to the image. Just in case this will not be answered today.--Lenticel ^(talk) 09:32, 12 November 2008 (UTC)

That's definitely an amazing photograph! This pdf linked from the V-22 Osprey talk page mentions "upgrading rotor tip lights & formation lights for improved night vision goggle (NVG) compatibility" and this page also mentions that the "prop-rotors have lights in the rotor tips for night safety." --LarryMac | Talk 14:23, 12 November 2008 (UTC)

See these pictures 1 and 2 of the B-25 Mitchell, an American bomber during the Second World War: it's long been a common practice to have something light at the edges of blades, although as you can see, 60+ years ago they simply painted the propellor tips rather than having lights at the edge. Nyttend (talk) 14:42, 12 November 2008 (UTC)

Certainly it's so that the pilot can visualise where the rotor tips are - that's especially important in this aircraft because it's a tilt-rotor craft - those engine nacelles swivel through roughly 90 degrees between hovering and forward flight. When hovering in confined areas - it's really useful to be able to see that your rotor tip is just about to whack into a tree limb or a lighting pole or something. I strongly suspect that they only turn them on in those specific circumstances because military aircraft don't generally want to be seen at night. SteveBaker (talk) 14:50, 12 November 2008 (UTC)

Thanks guys and gals, kind of what I thought but you have collectively sourced and expressed it so well. Richard Avery (talk) 15:21, 12 November 2008 (UTC)

Mars

How long could an unprotected human survive on the surface of Mars? —Preceding unsigned comment added by 195.188.208.251 (talk) 12:35, 12 November 2008 (UTC)

According to drowning, lack of oxygen takes about six minutes to cause brain death, so at most that long. I think that'll kill you before the cold does, but I don't know for sure. Algebraist 12:57, 12 November 2008 (UTC)

I'm not sure drowning is a fair comparison.

In any case the article on Time of Useful Consciousness, says for altitudes over 50,000ft, you've only got 9 to 12 seconds before you lose the capacity for rational thought. The surface of Mars would be similar or worse. So, you'd want to get back inside pretty quickly. APL (talk) 13:59, 12 November 2008 (UTC)

The atmospheric pressure on the surface of Mars is a shade less than one percent of the air pressure at Earth's sea level. For the purposes of sustaining life, it's better described as a low-quality vacuum than an atmosphere. In that vein, you'll probably be interested in our articles on the Armstrong limit, Human adaptation to space#Unprotected effects, and space exposure. Briefly, you would expect somewhere in the neighbourhood of 10 seconds of useful consciousness. Based on animal experiments, if your friends dragged you into the airlock and repressurized you within about 90 seconds, you'd probably survive without permanent injury. Beyond that threshold, you're probably toast. (I would expect rapid, serious damage to the lungs.) TenOfAllTrades(talk) 15:53, 12 November 2008 (UTC)

What would cause that damage? If you survive the initial decompression (most importantly, don't try and hold your breath), the barotrauma from a difference of (effectively) one atmosphere shouldn't be too extreme. I think it's hypoxia that would kill you by damaging the brain (it important to note that hypoxia is worse in hard vacuum than when drowning - the oxygen is kind of sucked out of you rather than just being used up, hence 90 seconds rather than the 6 minutes Algebraist mentioned). Since the Martian atmosphere isn't much of a thermal conductor (there simply isn't enough of it), the cold would take longer to affect you so we can probably ignore it. --Tango (talk) 16:10, 12 November 2008 (UTC)

From Space exposure : "But severe symptoms such as loss of oxygen in tissue (anoxia) and multiplicative increase of body volume occur within 10 seconds, followed by circulatory failure and flaccid paralysis in about 30 seconds.[1] The lungs also collapse (atelectasis) in this process, but will continue to release water vapour leading to cooling and ice formation in the respiratory tract." APL (talk) 22:13, 12 November 2008 (UTC)

Leaves changing color at different rates

Here in Beaver Falls, Pennsylvania, most leaves have fallen, but there's a large maple with large leaves (I'm guessing Norway Maple) behind my house. Reading Autumn leaf color, I note that the article says that "Often the veins will still be green after the tissues between them have almost completely changed color." However, this tree is odd, with leaves that are more extreme than this: some of its leaves are totally yellow, while leaves farther up the branch are almost totally green still. Is it simply because these leaves are closer to the trunk, or because they're (most of the time) shaded by the leaves at the edge of the tree, or some other reason? And is this an unusual phenomenon, or is it common and I've really not been paying attention all my life? I checked last night, by the way: they really are on the same branch, so it's not as if there are leaves from two trees intermingled. Nyttend (talk) 14:36, 12 November 2008 (UTC)

Leaves change color because the sap is "running", as they say in the maple sugaring industry. Basically, all of the sap (i.e. sugary water) is drained out of the tree into storage in the roots. This makes sense because the roots are insulated by the ground, where as the leaves are basically big heat-dissipators, and so are VERY suceptible to freezing. The process is relatively slow; it can take several days to weeks to complete, depending on the size of the tree. For very large trees, the leaves at the periphery (i.e. farthest from the trunk) are "drained" first, so the leaves there die off earlier. For very large trees, the leaves at the tippy-top can have changed and fallen before those near the bottom and close to the trunk have even begun to start changing. --Jayron32.talk.contribs 17:37, 12 November 2008 (UTC)

Not sure where there's stuff about this but the colour in those leaves is put there to protect the leaf from sunlight whilst the tree absorbs back anything useful. Putting in that golden colour costs the tree. So the outermost leaves and those facing south will be coloured most. You might notice leaf buds are often brown or red too to protect them whilst developing. Dmcq (talk) 18:02, 12 November 2008 (UTC)

human fat

in Volume how does a pound of human fat compere to lard —Preceding unsigned comment added by Seanbaguley (talk • contribs) 15:30, 12 November 2008 (UTC)

Both are slightly more than 0.9g/c^3, a little less than water. Lard is slightly denser. SDY (talk) 15:35, 12 November 2008 (UTC)

length of Vibrio cholerae

What's the typical size, i.e. length of a cholera bacterium? --Ayacop (talk) 16:21, 12 November 2008 (UTC)

2-3 microns in length, 0.5 microns in width. - Nunh-huh 17:15, 12 November 2008 (UTC)

Could you add that to the article Vibrio cholerae? Rmhermen (talk) 23:18, 12 November 2008 (UTC)

yeast need salt?

In order for yeast dough to rise does it need to contain salt? RJFJR (talk) 17:04, 12 November 2008 (UTC)

No. See fermentation. 93.132.179.55 (talk) 17:14, 12 November 2008 (UTC)

Salt is used in baking to control the rate of fermentation, but is not strictly necessary for fermentation proper. However, "without salt, the yeast acts very rapidly and peters out too quickly. Too much salt will stunt yeast activity" [28]. "Salt controls yeast activity to achieve a slow, steady rise and it strengthens the dough structure; eliminating salt can result in a baked bread that has collapsed." [29] - Nunh-huh 17:17, 12 November 2008 (UTC)

Thank you! RJFJR (talk) 18:22, 12 November 2008 (UTC)

Just as an aside, bread made with no salt tastes terrible. Robinh 21:53, 12 November 2008 (UTC)

Strength difference men-woman

What is the strength difference between men and woman?--Mr.K. (talk) 18:52, 12 November 2008 (UTC)

Estimates vary, particularly based on how you define "strength". this USMC report suggests the average woman's strength is 40%-70% of her male counterpart's. This report (with a higher average age) notes 50%, and then proceeds to note that males are also heavier and that strength-per-weight (if you elect to use that sort of "strength" definition) has a completely different result -- they find that males and females are effectively equal in terms of strength-per-muscle-mass. — Lomn 19:41, 12 November 2008 (UTC)

No surprise there, though, right? I don't think it's headline news to announce that folks with bigger muscles tend to be stronger... Matt Deres (talk) 17:29, 13 November 2008 (UTC)

Animal abuse

Wikipedia is preventing me from linking directly to the image I'm talking about. But on that site, encyclopedia dramatica, when you search "Animal Abuse", at the bottom you see an animated gif of a cat in some terrible device that shoots some liquid from the bottom into a chamber that the cat is in. What is that device that the poor cat is in? 98.221.85.188 (talk) 21:06, 12 November 2008 (UTC)

Encyclopedia dramatica is basically a joke site; I would not judge anything I read there too seriously. --Jayron32.talk.contribs 21:12, 12 November 2008 (UTC)

The Pet Spa [30]. Hydromassage, bath, and blowdry machine for dogs and cats. Edison (talk) 21:23, 12 November 2008 (UTC)

That's kind of a relief. But why was the cat so upset when it was in there? Was the water too hot? Was the machine being misused? 98.221.85.188 (talk) 22:04, 12 November 2008 (UTC)

Most house cats can't stand getting their fur wet. There are exceptions to this rule, of course, but I have a hard time imagining your average house cat enjoying a "hydromassage". APL (talk) 22:09, 12 November 2008 (UTC)

What's the problem with linking to Encyclopedia Dramatica? —Preceding unsigned comment added by 83.199.126.76 (talk) 21:51, 12 November 2008 (UTC)

If I'm reading the spam black and whitelists right, you can't link anywhere on ED except the Main Page, because (a) it's a haven for anti-Wikipedia trolls, and (b) it's a haven for trolls in general, and has tended to be linked only to harass someone or to act as a shock site. I may be wrong, but I suspect Main Page was whitelisted only after the actual article on the site finally passed its 1000th deletion review. Confusing Manifestation(Say hi!) 22:33, 12 November 2008 (UTC)

Why is 350°F the standard for cooking food?

Almost every recipe I see wants to be cooked in an oven that is 350°F. Some call for temps up to 450°F. But I've never seen any recipe that calls for a temp outside of these extremes. (I'm sure there are exceptions) What's so special about this temperature range and cooking food? --70.167.58.6 (talk) 22:21, 12 November 2008 (UTC)

Related article or place to start deduction from: Temperature (meat). Mac Davis (talk) 22:30, 12 November 2008 (UTC)

Actually, that article doesn't help.

I think the temperature has more to do with the smoke point or flash point of fats and oils. Lard, for example, has a smoke point of about 370°F. Vegetable shortening smokes around 360°F. You don't want all the fat burning away while the food cooks.

Higher temperatures are useful for different cooking techniques, such as searing the outside of a piece of meat so that the inside continues to cook after it is removed from the oven. ~Amatulić (talk) 22:48, 12 November 2008 (UTC)

Note the temperatures in the Temperature (meat) article are the meat temperatures when cooked, not the oven temperatures.

When oven cooking foods of any significant thickness (such as cakes, pies, roasts of meat, puddings, large potatoes) using too low a temperature will not cook them through to the middle, or will take an unnecessarily long time to do so. Using too high a temperature is likely to result in the outside being dried out or burnt before the centre is cooked. The recommended temperatures are compromises between these two problems. CBHA (talk) 23:04, 12 November 2008 (UTC)

If you'd like to use different temperature settings, try a convection oven. NB Acrylamide is produced in increasing amounts at temperatures exceeding 350 F. The temperature settings of ovens are not a reliable indicator of actual temperatures inside (and those tend to vary significantly from one point in your oven to the other). You may find recipes for conventional ovens that tell you on what rack / distance from the heating element to place your food. To be sure your food is cooked properly use a meat thermometer. To make sure baked goods are done, the traditional method is to stick a knitting needle in and declare it done when no dough sticks to the needle anymore. (OR by my granny :-) 76.97.245.5 (talk) 00:26, 13 November 2008 (UTC)

Generally, 350 deg F is a temperature which is hot enough to encourage the Maillard reaction to occur (aka "browning"), without causing substantial burning to also occur. If you get up into the 500 deg F range, the food will char or burn (i.e. produce ash) which imparts a bitter and unpalatable flavor. Below probably 325-350 deg F, and there is likely not enough heat for the vital Maillard reactions to occur; it's these reactions that produce those brown tasty bits that form when meat is properly cooked. Its also why most slow-cooking methods, such as "crock-pot" cooking, require you to brown the meat seperately before adding to the crock pot. The crock pot gets hot enough to cook the meat (generally up to around 180-190) but never gets hot enough to brown it; which means you miss an entire flavor component of the food. --Jayron32.talk.contribs 03:15, 13 November 2008 (UTC)

anaerobic motor /propulsion

i would like to know whether an anaerobic motor /propulsion really exists. To me anaerobic refers to organisms. furthermore: the described process releases oxygen besides heat . can such a process/reaction called anaerobic? clear question: can an oxygen producing reaction be called anaerobic or what can it be caled instead?

finds in wikipedia: http://en.wikipedia.org/enwiki/w/index.php?title=Special%3ASearch&search=%22anaerobic+propulsion%22&ns0=1&fulltext=Search

http://en.wikipedia.org/wiki/Ictineo#Ictineo_II

http://en.wikipedia.org/wiki/Ictineo_II

thanks--Stefanbcn (talk) 00:38, 13 November 2008 (UTC)

Anaerobic - means "not needing air" (basically) - so any motor that doesn't need air (like an electric motor - or a clockwork motor) is "anaerobic". A coal fired steam engine - or a gasoline powered car is "Aerobic"...it needs oxygen from the air to work. A motor that used some chemical process to produce oxygen and burned that to make motion would probably be called "anaerobic" too. SteveBaker (talk) 00:51, 13 November 2008 (UTC)

Artificial holographic sun

Using sulfur lamps and rotating mirrors, would it be possible to create a false window with a nice holographic landscape, with a completely realistic rectangle of direct false "sunlight" striking the floor/walls? (this is for people with just a brick wall to look at and no direct sunlight) and could mirrors make it plane parallel? —Preceding unsigned comment added by Trevor Loughlin (talk • contribs) 04:34, 13 November 2008 (UTC)

Well, it has been done - some really expensive flight simulators have used laser-projected displays that are bright enough to simulate natural sunlight at real-world candela values - and I've worked on them.

However, it's freakishly expensive and insanely dangerous. Remember that if you stare into the real sun - it's so bright that you will damage your eyes if you don't look away within a few seconds. Now consider a display device (a projection TV or something) that put out enough light to produce that same effect - plus enough to project all of the rest of the world at natural brightness levels too. In fact, it would need more energy even than that because it would have to scan over the scene at least 60 times a second - and the screen itself would not be perfectly, 100% reflective - so the display is putting out a lot more energy than the sun - within the small range of angles that covers the scene. If you think for a moment about the amount of heat that the sun puts out as it shines onto your skin - the display would probably have to chuck out that much heat too!

The result would have to be an amazingly powerful laser or something very similar. If you were to happen to catch a glimpse of the light from the laser itself (rather than it's dispersed, reflected image) - you'd be blinded instantly...no chance to blink or look away. When I worked with such a system a few years ago - everyone who entered the room when it was turned on had to go through a 30 hour laser safety course - the doors had to have automatic locking devices to stop people coming in when the laser was turned on - and there were all manner of handrails and such stopping people from going where the laser was operating. We nicknamed the gigantic water-cooled laser "The Death Ray of Ming the Merciless" because it looked exactly like something from the lair of a 1950's SciFi super-villain.

There is another issue here - which is for an outdoor scene to look completely real (ie not like a super-high-def TV screen) - the light has to appear such as to cause your eyes to focus at the correct depth. For an outdoor scene where nothing comes within (say) about 30 feet of the viewer, it's enough to 'collimate' the light so it appears to come from a source that's infinitely far away. This is tough to do. You either need a dome to project it onto that's at least 30' away - or a curved mirror such that the path from the laser projector to the eye is at least 30 feet - or you need some large, expensive glass lenses that are the size of your window to perform the same task. The difficulty with all of those things is that the scene only looks truly real when your head is at the "designed eyepoint" of the system - if you step a few feet to the side, the illusion is destroyed. It's kinda possible to correct for that - but the viewer needs to be wearing some kind of tracking device - and only one viewer gets a perfect view at a time.

So, yes - it's certainly possible - I've seen it done and the result is highly realistic and extremely compelling. But I don't think we'll see it happening as an entertainment device anytime soon.

SteveBaker (talk) 15:23, 13 November 2008 (UTC)

Bird identification

Hello, I was at Taronga Zoo today and I took a photo of this little sparrow-ish thing. I would be very grateful if someone could help me with identifying its species. Thanks! 122.106.197.159 (talk) 04:43, 13 November 2008 (UTC)

That looks a bit like a silvereye to me. Tonyrex (talk) 06:02, 13 November 2008 (UTC)

rectilinear perspective

Do people actually see in rectilinear perspective, or is this just a convention of western art? For example, I've seen Looney Toons cartoons in which when viewing a tall rectangular building from the bottom, the lines start curving together at the top (rather than pointing straight at the vanishing point). --VectorField (talk) 06:11, 13 November 2008 (UTC) I guess an example of what this would look like can be found at fisheye lens. --VectorField (talk) 06:18, 13 November 2008 (UTC)

See also Perspective (visual) and for Cartesian rectilinear perspectives and variations on this see Perspective (graphical). In traditional Japanese and Chinese art, the perspective is constructed differently, more like parallel perspective. Julia Rossi (talk) 10:05, 13 November 2008 (UTC)

It's more than just convention. The idea is that the canvas should be like a window through which you can see the three-dimensional scene, and if you work that out in detail for a flat canvas (as described in Perspective (graphical)) you get the rules of perspective. It's the flatness of the canvas that matters, not anything going on inside the eye or brain. I don't think that people see in rectilinear perspective (I don't think the idea even makes sense—I think it's an instance of the homunculus fallacy) but the theory of perspective makes no such assumption. It does, however, assume that you stand in the correct location and have only one eye.

If you work out the rules for a cylindrical canvas instead, you get cylindrical perspective. (More precisely, if you follow the correct perspective rules for a cylindrical canvas with the viewer in the center and then unroll it, you get what's normally called cylindrical perspective.) The advantage of a cylindrical canvas is that you can get a wider field of view. A flat canvas is limited to a 180° FOV, and as you approach that limit the canvas size goes to infinity or the distance from canvas to viewer goes to zero, both of which are inconvenient. If you stand at the wrong distance from a large-FOV flat image (and any convenient distance will be wrong) it will look very distorted. A cylinder doesn't have that problem. Any small enough part of a cylinder is roughly flat, and so an unrolled cylindrical perspective is suitable for a very wide image that's meant to be looked at only a bit at a time (walking from side to side). A wide or tall background in a cel-animated TV show will normally be drawn in cylindrical perspective since it's designed to be panned over. -- BenRG (talk) 14:45, 13 November 2008 (UTC)

Oooh! Good question!

Perspective of some kind is a necessary part of any practical visual system. We really do see things that way. The different kinds of perspective come about through the shape of the 'screen' onto which the scene is projected - and the nature of the lens and how it gathers the light.

• In an idealised 'pin-hole' camera, the film (or digital imaging device) is flat - and since light travels in straight lines through a notional zero-sized pin-hole at the front of the camera - and then onto the flat surface inside, all straight lines in the world outside project into straight lines in the image - and we have perfect rectilinear perspective.
• In a practical camera - the lens isn't a pinhole and it has to bend the light to make it focus properly - that results in a non-linear mapping of real world onto the flat film plate - and depending on how much the light is bent, straight edges turn into curves and you no longer have rectilinear perspective.
• In our eyes, the imaging surface (the retina) isn't flat - so straight lines in the real world (like the sides of a tall building) don't project into straight lines on the retina. However, our visual system isn't a matter of a bunch of pixels on the retina being "absorbed" somehow by the brain. It's MUCH more complicated than that. One of the things our visual system does is to compensate for those complicated curves so that we "see" straight lines where the lines are straight...we're not aware of the weird mapping that goes on because of a non-zero pupil diameter and a non-flat retina. We are aware at some level that things seem "smaller" the further they are away - but we're also unconsciously correcting for that - so we don't think that a car is tiny because it's further away. The mathematical fact of perspective has been converted by our visual system into something that takes on different meanings depending on the context about which we are considering them. There are several optical illusions that play on that to demonstrate that we don't "see" what is really there.
• In art, the painting itself is generally flat - and artists generally want to give the impression that the rectangular frame of the painting is like a hole cut into the wall and the art is like an image coming through that hole - which is then percieved by our eyes. So then the mathematically "correct" thing for the artist to do is to pretend that the painting is a pinhole camera image and use rectilinear perspective - and then let our eyes process that image as if it were really light coming through a hole in the wall. Because that image then enters the eye in the same way that the light from a real object would - and the painting "looks real" to us (well, not quite because of issues of depth of focus and "collimation" of the resulting light).
• In 3D computer graphics, (my speciality - I'm a graphics programmer for the games industry) no matter how wide-angle the "virtual camera" becomes - since the screen is flat - and we use rectilinear perspective because the math is simplest that way. Especially - we want to map straight lines onto straight lines - because our graphics algorithms are much simpler that way. And (fortunately) it all looks right for the same reason that art looks right. But we do see "fish-eye distortion" in computer graphics - and this is true even though the computer is translating straight lines into straight lines (actually, the graphics hardware is incapable of directly drawing curved edges - rectilinear perspective is built into the 3D circuitry at a fundamental level!). We perceive wide field-of-view images as distorted (and some people will even go so far as to claim that everything is curved even when that is a physical/electronic impossiblity!) The reason for that is that we are taking an image from a 'virtual camera' with a wide field of view (say 120 degrees) and presenting it on a screen that only subtends (perhaps) 30 degrees at your eye. This is not a natural thing - and our brains have to somehow interpret this as if the image were being seen through a distorting "fish eye" lens when all it's really seeing is through an idealised pin-hole camera. Our mental compensation for that imagined distortion (which is not present in the mathematically "correct" rectilinear perspective) results in a strong impression of curvature.

A similar problem occurs with narrow-angle images (eg taken with a telephoto lens) where the relative lack of perspective foreshortening leaves us with a wrecked sense of distance. Film makers love to use this. In a romantic scene with the moon in the background, they'll pull their camera WAY back from the actors - then zoom WAY into them - and the resulting screwup of our mental idea of perspective makes the moon look HUGE. This is used in action shots too - when the hero is running away from the burning car - which explodes behind him hurling him towards the camera...you place the camera WAY back from the car - put the actor fairly close to the camera and a VERY safe distance from the car...then the telephoto lens screws up the perspective for us - and we think the car is really close. It's still very close to being strictly rectilinear perspective - but our brain's inability to compensate for the distortion that results from the mismatch of the field of view means that we see things in way that they really are not.

SteveBaker (talk) 15:03, 13 November 2008 (UTC)

I think it's interesting that how we see things is generally governed by how we expect to see them. We know what size a car is, so we see it as being that size regardless of how far away it is (to use your example). However, if you're in an unusual situation, for example seeing cars on a road when looking out of the window of a plane, your brain doesn't really know what to expect and you need to consciously work out what you're seeing and you do notice the fact that cars are all so tiny (the standard cliché is to compare them to ants). --Tango (talk) 15:33, 13 November 2008 (UTC)

To put this simply, our eyes use elliptic geometry and a flat canvas uses Euclidean geometry. Trying to put the same picture on both will require some warping. — DanielLC 15:56, 13 November 2008 (UTC)

The extent to which rectilinear perspective correctly replicates a 3D view, at least for a fixed observer and small field of view, can be judged by the success of trompe-l'oeil illusions. Gandalf61 (talk) 16:02, 13 November 2008 (UTC)

Recent coverage of drawing on curved canvases here. —Preceding unsigned comment added by 190.220.104.35 (talk) 19:21, 13 November 2008 (UTC)

Ceiling fan

Hello. If a Ceiling fan is switched on at the wall but it is actually off then does it still use electricity? Sorry if its a stupid question. ```` —Preceding unsigned comment added by AreDeeCue (talk • contribs) 13:49, 13 November 2008 (UTC)

No. The circuit has to be closed to use any noticeable amount of electricity (I'm ignoring cases such as worn out wires sparking against nails in the attic and such). Any switch anywhere in the line that opens the circuit will cause the flow of electricity to stop. -- kainaw™ 13:58, 13 November 2008 (UTC)

Your question implies that there are two (serial) switches to operate the fan? If this is the case, both switches must be on for the fan to work. Therefore the fan is not using electricity. Sometimes the wall-mounted control has an LED to indicate that it is on. However this LED uses a trivial amount of electricity. Axl ¤ [Talk] 14:01, 13 November 2008 (UTC)

The ceiling fans that use an infrared remote (to avoid the need to add house-wiring for houses that don't have a second switch and circuit) DO use a tiny amount of electricity when they're turned on at the wall but off using the remote. Some piece of circuitry has to be powered in order to pay attention to the InfraRed receiver. It's pretty tiny - but with a bajillion appliances around the home all eating small amounts like that - it does add up. The kind of ceiling fan that has a pull-cord to turn it on and off shouldn't be consuming any electricity at all when it's turned off there instead of at the wall. SteveBaker (talk) 14:26, 13 November 2008 (UTC)

Echinoderm diversity

Estimations of the diversity of extants echinoderms vary widely, from 6,000 to 10,000 species, and even reliable sources differ a lot. Which is the most authoritative source on echinoderms, and what figure does it give? Thanks. Leptictidium (mt) 14:56, 13 November 2008 (UTC)

dangerous situation arising from killing germs?

If you kill all the germs in a place germs like to live, won't it just create natural evolutionary pressure toward germs that aren't affected by death? —Preceding unsigned comment added by 83.199.126.76 (talk) 15:22, 13 November 2008 (UTC)

Not being affected by death is tricky, but antibiotic resistance certainly arises in this way. Algebraist 15:47, 13 November 2008 (UTC)

Well - I don't think they can be "unaffected by death" - that's kinda silly! But I guess what you mean is that these critters are not killed by whatever means you've been using to kill off the others. If so - then yes! This happens all the time. In hospitals particularly, there are antibiotics everywhere - in the air and on all of the surfaces. Bacteria are mostly killed by this stuff being everywhere - but one in a trillion (maybe) survives - and this causes an evolutionary effect that results in types of bacteria that are immune to all of the common antibiotics. It is therefore necessary for the drug companies to continually come up with new antibiotics that the bacteria has not yet been exposed to - and which can therefore kill them...until a few more years have gone by. Doctors also recognise this and they don't prescribe the newest and most powerful antibiotics until they know that the older (and by now, better-resisted) have failed. This is an attempt to keep the newer kinds of treatment in reserve for the most resistant bugs. It's not just 'germs' either - strains of rats and mice that are immune to the common kinds of rat and mouse poisons are also appearing. There is no doubt that evolution does this all the time. SteveBaker (talk) 16:52, 13 November 2008 (UTC)

What do you call this camera trick?

OK, I'm not sure how to describe something visual in words, but I will try. In movies and TV shows, they have this camera trick where the object in the forefront (usually a person) stays stationary but the background somehow moves. It seems like some sort of trick of perspective. This technique is usually used to convey shock, something unexpected or when the person makes a sudden realization. Sorry I can't give a better description, but this technique is used enough that hopefully someone will know what this is named. 216.239.234.196 (talk) 15:32, 13 November 2008 (UTC)

Dolly zoom APL (talk) 15:45, 13 November 2008 (UTC)

Yep, that's it! Thank you. (Comment: So they actually move the camera? Wow.) 216.239.234.196 (talk) 15:58, 13 November 2008 (UTC)

I've always heard it called a "Hitchcock zoom" because he was the one who first popularized it. It requires zooming the camera either in or out and simultaneously moving the camera either backwards or forwards. Done correctly (which is tough), the person in the foreground stays at exactly the same size - but the background zooms in or out. It has the effect of separating the character from their surroundings - which Hitchcock used to great effect to get across emotional state and such. Adding 'rim lighting' or other inconsistent lighting for the character is another way to separate a character from the background that Hitchcock used effectively. SteveBaker (talk) 16:57, 13 November 2008 (UTC)

Energy drink ingredients

Do any ingredients in energy drinks other than sugar and caffeine have proven desirable short-term effects? NeonMerlin 15:43, 13 November 2008 (UTC)

You're probably best to just run through the list of ingredients in your favourite energy drink and check the Wikipedia articles. The major active ingredient in guarana is caffeine. Taurine has been shown to axiolytic effects in some animal studies, but no effect on human beings has been observed. The NIH has reported that supplements containing gingko biloba have no measurable benefit when taken as directed. The list goes on, but you can probably find what you're looking for by following the links from Red Bull, Rockstar, and the others. TenOfAllTrades(talk) 16:25, 13 November 2008 (UTC)

Visual acuity of hawk's eye: why/how?

Hi, is there an article that explains why the hawk's eye has such great visual acuity? I can't find any info on WP on such a fascinating subject. Kreachure (talk) 16:52, 13 November 2008 (UTC)

Maybe you should read the article you linked to, then. Matt Deres (talk) 17:41, 13 November 2008 (UTC)

Yeah, thanks, but I was looking for more information, like the one provided by the bird vision article which I just found. Kreachure (talk) 18:09, 13 November 2008 (UTC

I think visual acuity is provided by the number of cone cells in the fovea, and presumably by how other bits of the eye work. Hawks presumably have a higher percentage of cones in the fovea than other species. This is just complete assumption. —Cyclonenim (talk · contribs · email) 18:54, 13 November 2008 (UTC)

resistors

today i encountered with a resistor named 3k9,4k7,and 100R.can any body plz tell me what values of these resistance and what is the type of these resistors . -- 116.71.186.13 (talk) 17:36, 13 November 2008 (UTC)

3900 ohm, 4700 ohm and 100 ohm. It's a funny bit of notation that is standard in the industry, but makes sense easily enough. They're just bog standard resistors as far as I can tell from that information. 137.108.145.10 (talk) 18:56, 13 November 2008 (UTC)

Fructose Malabsorption

Disclaimer: I have no intend to ask for medical advice here. If you think you cannot answer without giving medical advice please just ignore my questions. If you feel obliged to tell me to see a doctor please give me name and address, too, as I have seen many doctors and none of them has even mentioned fructose malabsorption.

The one section of the fructose article (fructose malabsorption#Fructose Metabolism) states that fructose is absorbed using GLUT-2, the rest of the article states it is absorbed by GLUT-5. This seems to be a bit of a contradiction, or can GLUT-2 absorb fructose, too, but GLUT-5 is specialized on it?

It is not clear to me from the articles if fructose is normally (without f.m.) absorbed in the small intestine, the large intestine, or both, and if f.m. affects only the absorption in one of those or both. Fructose#Malabsorption gives the medical advice that Exercise can exacerbate these symptoms by decreasing transit time in the small intestine, resulting in a greater amount of fructose being emptied into the large intestine which I know is not true from my own experiences. Fructose not being absorbed and rotting in the large intestine as well as in the small would account for this experience.

Are ther many different forms of f.m. and is the absorption via GLUT-2/5 totally absent or only reduced?

Fructose is a small molecule, isn't it absorbed by pinocytosis or is it that the pinocytosed amount is too small? Thanks 93.132.177.64 (talk) 19:24, 13 November 2008 (UTC)