::::::A wonderful Star Trek-like solution, but the humans you imagine have little to do with any humans I have ever seen. Make a big dome, put a few thousand humans inside it, wait a few weeks and they'll be in a state of civil war, disrepair, disaster. I don't see us getting off this planet in any major way. The human race will, at some point, go extinct—of that there cannot be any question. Once you accept that it just becomes a question of when and where. --[[Special:Contributions/98.217.8.46|98.217.8.46]] ([[User talk:98.217.8.46|talk]]) 21:12, 31 October 2008 (UTC)
::::::A wonderful Star Trek-like solution, but the humans you imagine have little to do with any humans I have ever seen. Make a big dome, put a few thousand humans inside it, wait a few weeks and they'll be in a state of civil war, disrepair, disaster. I don't see us getting off this planet in any major way. The human race will, at some point, go extinct—of that there cannot be any question. Once you accept that it just becomes a question of when and where. --[[Special:Contributions/98.217.8.46|98.217.8.46]] ([[User talk:98.217.8.46|talk]]) 21:12, 31 October 2008 (UTC)
:::::::There are plenty of remote groups of humans with populations under 1000 who manage just fine. The [[Pitcairn Islands]] had a rough start - but they survived and thrive today with almost no contact with the outside world and only just barely enough genetic diversity to keep going. I don't see the need for passimism in that regard. As for the "humanity" of the humans I imagine - well, I think what matters is our intellects - and what I suggest would preserve that in the purest way possible. You might think we couldn't survive that - yet wikipedians talk via the clunkiest links - form friendships - and seem in every way "human" - even though we rarely meet face to face. If my brain was merely simulated on a big computer - I don't see how you could possibly tell. [[User:SteveBaker|SteveBaker]] ([[User talk:SteveBaker|talk]]) 01:48, 1 November 2008 (UTC)
:::::::There are plenty of remote groups of humans with populations under 1000 who manage just fine. The [[Pitcairn Islands]] had a rough start - but they survived and thrive today with almost no contact with the outside world and only just barely enough genetic diversity to keep going. I don't see the need for passimism in that regard. As for the "humanity" of the humans I imagine - well, I think what matters is our intellects - and what I suggest would preserve that in the purest way possible. You might think we couldn't survive that - yet wikipedians talk via the clunkiest links - form friendships - and seem in every way "human" - even though we rarely meet face to face. If my brain was merely simulated on a big computer - I don't see how you could possibly tell. [[User:SteveBaker|SteveBaker]] ([[User talk:SteveBaker|talk]]) 01:48, 1 November 2008 (UTC)
:::::::::The pitcairns are a rubbish example - [[Pitcairn_rape_trial_of_2004]] [[Special:Contributions/86.150.196.186|86.150.196.186]] ([[User talk:86.150.196.186|talk]]) 15:40, 1 November 2008 (UTC)
== Photons and Phonons ==
== Photons and Phonons ==
Revision as of 15:40, 1 November 2008
Welcome to the science section of the Wikipedia reference desk.
The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.
Yes, it is possible to give birth to half-sibling dizygotic twins. I cannot think of any specific documented cases, but it is possible because sperm survives for about 3 days (5?) in the woman's body. If two eggs are released, and fertilized by sperm from different fathers, there will be two half-sibling twins.CalamusFortis04:04, 26 October 2008 (UTC)[reply]
Yes, the phenomenon is known as Superfecundation. From the article: "The first recorded case was made by John Archer, an American physician in 1810 and is discussed in Williams Obstetrics (1980). According to Archer, a white woman who had sex with a black man and a white man within a short time subsequently gave birth to twins—one white, one of mixed-race. Other cases have been reported since." Among humans this is rare, but in reptiles where sperm can be stored for long periods of time, it's not as uncommon. bibliomaniac1505:41, 26 October 2008 (UTC)[reply]
If memory serves, the honey bee reproduces like that routinely. The queen flies around for a bit, receives sperm from a variety of drones and then lays eggs. --Tango (talk) 14:09, 26 October 2008 (UTC)[reply]
It is not necessary that there be separate fathers for twins to be one black and one white. See the recent Daily Mail story where one man and one woman had fraternal twins, one quite black and one quite white [1]. Its called Genetics. Edison (talk) 21:56, 26 October 2008 (UTC)[reply]
In domestic cats it is not unusual for kittens in a single litter to have a different male begetter. This can sometimes be seen in the different coloration of the kittens. —Preceding unsigned comment added by 98.17.36.129 (talk) 10:42, 27 October 2008 (UTC)[reply]
What year were nutritional supplements first available to the general public for purchase in USA? And where?
What was the first supplement available? —Preceding unsigned comment added by 12.215.237.58 (talk) 02:06, 26 October 2008 (UTC)[reply]
They have always been available. See snake oil for a surprisingly balanced history of that balm, which should give you an idea of the time range involved. From there, it might seem that the next choice would be to determine when the first effective supplement was marketed, but see multivitamin to see how ambiguous the results are for even modern supplements. Matt Deres (talk) 15:48, 26 October 2008 (UTC)[reply]
Well, If it's a Persian rug, the best and easy option is to hang it over a horizontal bar and beat the dust out (best done outside). If you choose to use a vacuum cleaner, use the bare floor setting (so the beaters do not turn). If there is a stain, it is probably best left to a professional, but if you feel brave, and you are sure it its a high quality rug (low quality Persian rugs often are ruined by washing because the colors run) you can give it a deep cleaning by laying it out on some sunny concrete, and using Orvis Horse Soap (sodium Laural sulfate) under running water (from a hose), and scrubbing with a push broom. However, this is best done in warm weater, as the rug will take several days to dry. —Preceding unsigned comment added by Hacky (talk • contribs) 18:58, 26 October 2008 (UTC)[reply]
I've heard of rugs like this being placed face down on the snow and beaten on the back to remove dirt. Face down makes sense since the heavy dirt needs to come back out rather than be forced against the rug's woven base. OR here, but I washed a small carved wool chinese style mat thinking it was quality and all the pastel colours ran out. Another time washed a filthy large oval version face down on the grass and it came out clean and original. Patch testing first might be a good idea. Julia Rossi (talk) 22:15, 26 October 2008 (UTC)[reply]
Shock waves
Is it true that during areal bombing windows and doors of the house should be open in order to "balance" out the pressure after the explosion? That used to be the rule in case of tornadoes, but National Weather Center now advises to keep the windows closed. So what about during bombing from the sky - open or close the windows and doors?
Well, opening doors and windows certainly reduces - or perhaps even eliminates the possibility of the windows blowing out - but doing so must therefore increase the amount of 'over-pressure' entering the interior of the building - which could mean more damage inside than there would have been if the windows had withstood the initial pressure-wave for a while before breaking. That's probably why the advice over tornadoes has changed. SteveBaker (talk) 05:38, 26 October 2008 (UTC)[reply]
The tornado warning was changed because even an F5 tornado doesn't create enough of a pressure differential to cause damage; even a "closed" house will be able to breathe enough to compensate. My understanding is that the idea it helps at all is flawed, not that the net amount of damage was re-assessed. The current wisdom from the NWS is not to close or open the windows but rather, "Never mind them. The tornado will open them if it wants." IOW, get your ass to safety. If I knew/suspected that my neighborhood was going to be bombed and I already had a safe place for myself and family, I would shut and board all windows and doors; the pressure difference will be nothing compared to the blast itself. Matt Deres (talk) 15:37, 26 October 2008 (UTC)[reply]
Don't bother opening the window. The bomb or tornado will open it for you. As for boarding it up, a documentary about a controlled demolition of a building in the downtown of a city showed the contractors putting plywood over the stained glass windows of a church to reduce the chance of the pressure wave breaking them. Boardup is also encouraged when hurricanes are expected, both to protect against wing pressure and flying debris. Sturdy shutters could also be helpful. Edison (talk) 21:50, 26 October 2008 (UTC)[reply]
Controlled demolition is designed to avoid producing large shock waves...the blasts are small and contained and the only "danger to the public and neighbors" I ever hear about it from flying debris. So I call [citation needed]: were they really trying to protect the stained glass from a pressure wave and if so did they actually have an engineering basis for doing so, or were they just protecting from an errant brick? DMacks (talk) 13:12, 27 October 2008 (UTC)[reply]
Unfortunately I do not keep a acrd file of references for every fact presented in every TV documentary I have ever seen. They said it was to increase protection against the pressure wave, since the clearances were marginal. Better safe than sorry. Edison (talk) 19:30, 27 October 2008 (UTC)[reply]
Thanks for the info! I was curious as in Yugoslavia during bombing we used to open doors and windows as I was told that that is done to reduce the pressure. —Preceding unsigned comment added by 72.224.207.32 (talk) 05:17, 27 October 2008 (UTC)[reply]
It's perfectly possible that people in Yugoslavia thought it was a good idea - when in fact it was not. People do a lot of dumb things with the idea that they are doing some good based on 'common sense' reasoning - even when the science points the other way. Drive along any road in Texas and look at the number of pickup trucks where people have either removed or lowered the tailgate "to reduce air resistance" in an effort to get better gas mileage. It SEEMS like a perfectly rational idea - right up to the point when you put a truck into a wind tunnel and find that the manufacturers actually did their homework - and the truck's aerodynamics are better with the tailgate up. However, even though the owner's manual tells you this in words that a child could understand - that doesn't stop hundreds of thousands of truck owners going by "gut instinct" alone. SteveBaker (talk) 14:12, 27 October 2008 (UTC)[reply]
Here: http://www.fourmilab.ch/bombcalc/instructions.html we find that windows will be broken by between 0.2 and 1.0 psi of overpressure - and that walls of a typical house require between 1 and 5 psi to demolish them. That's not really surprising - a 4'x4' pane of glass contains 2300 square inches of glass - so between about 500 and 2300 pounds of force will be applied to it - that's like between 3 and 15 adults standing on it...and it doesn't surprise me that it would break!
So the question is this: If the overpressure outside the building compared to inside is going to exceed the amount needed to break windows - but not be enough to demolish the house - then will opening the doors help? The problem with answering it is this: As the pressure wave travels towards the building, does the pressure rise sharply or more slowly? This matters because if the pressure builds slowly enough, high pressure air will be able to gradually leak into the house through small gaps and equalise the pressure inside and out - thereby preventing the windows from blowing in because of the overpressure...whether the doors are open or not. (Sure, flying debris might take them out anyway - but this is a thought experiment - and I want to imagine there is no debris.) If the pressure builds really quickly then even if the doors are wide open, the high pressure air will not be able to flow through the doorway and around to the insides of the windows before the overpressure reaches 1 psi and they blow out.
Therefore, there must be some middle range of rate-of-pressure-increase at which (with doors closed) the air cannot get in through the small holes fast enough to keep the pressure difference on the two sides of the glass down below 0.2 psi - yet if the doors were opened, the reduced resistance to passage of the air into the house would allow the air to flow into the house fast enough to keep the pressure difference under 0.2 psi - so the windows will be saved. So to answer the question rigorously - we'd need a plot of the rate of change of pressure in the shockwave from whatever kind of bomb we're considering.
However - I'm pretty sure the rate of pressure increase gets less as you get further from the explosion (the actual overpressure also gets less too - but that's not the question here). I'm pretty sure this is true because of the business of low frequency sounds travelling further through the air than high frequencies - so the sharp, high-frequency leading edge of the pressure curve must get softened. So this suggests that there must be some distance from the bomb where leaving the doors open will indeed save your windows. So the idea has some merit.
The problem is though that by leaving your doors open - you are increasing the sharpness of that pressure wave on the things inside the house...such as the interior walls. The thought experiment I did for the windows applies equally to the interior walls. If the 'sharpness' of the overpressure curve is too steep - the interior walls will be destroyed - but if it's gentle enough, they won't. With the outside doors open - the interior walls will feel more sharp overpressure than if the outside doors are shut and therefore slow down the pressurization of the interior. So there is the problem - if you are at the right range from the explosion - opening the doors will save your windows - but MIGHT cause more extensive interior damage. At other ranges, your windows will blow out even with the exterior doors open - but you are making matters much worse for the interior structures of the house. So unless you somehow know in great detail how big the explosion is going to be - and how far away it is - there is no way to know whether it's worth opening your doors or not. Overall, therefore, you're better off leaving them shut.
I would like to make a movie in PyMol based on "mset 1 x60" followed by "mdo 1: turn x,3; turn y,5;" but whereas this makes a rotating molecule on-screen, exporting to PNG files yields only a single file. ----SeansPotato Business11:39, 26 October 2008 (UTC)[reply]
Can you export to .gif format? These can be animated, otherwise you will have to go to .mov or .mp4 format, and then convert to animated .gif or ogg format for use in Wikipedia. Graeme Bartlett (talk) 23:40, 26 October 2008 (UTC)[reply]
PyMol only gives me the option to export movies as a series of PNG images which then have to be put together with another program. The problem is that I am only getting a single frame when there ought to be many. ----SeansPotato Business23:51, 26 October 2008 (UTC)[reply]
"eMovie is a free tool that makes the creation of molecular movies both easy and intuitive via a breakthrough storyboard interface, similar in nature to what is used in the creation of traditional movies. eMovie is a plug-in for PyMOL ...". Seems relevant. --Sean13:21, 27 October 2008 (UTC)[reply]
Free energy idea needs debunking
Ever since I was a kid I've occasionally come up with free energy and wacky propulsion ideas. Ultimately they've all proved to be fatally flawed in some way, based on my misunderstanding of energy conversion. But I can't figure out what's wrong with this new idea. I'll keep it in its simplest terms.
Okay, imagine a glass tank filled with water, like a fish tank. Through electrolysis we can split the water into hydrogen and oxygen. These gases will float up, in air, right? So if we let the gases separately float up two pipes and collect them in upside-down glass jars, we have potential energy at the top. Then if we recombine that into water, suddenly we've got something that wants to run down again, down another pipe gathering momentum until it hits a turbine at the bottom at speed, driving an electric motor, before falling back into the original tank.
Now this wouldn't generate enough energy to do the electrolysis in the first place. But I don't see why we couldn't extend the height of the system to exploit gravity more, say to 10m. The gases will still float up, and the water will still run down, but now the water will gain additional speed because it's falling further, and it will hit the turbine with much more momentum, thus pushing it round much further for the same amount of water.
Why couldn't this idea be extended until the water reaches terminal velocity, to generate a simply huge amount of energy for the same amount of effort put into electrolysis? There must be something I've got wrong. Can anyone share some insight? • Anakin(talk)14:33, 26 October 2008 (UTC)[reply]
Some things wrong which I notice are; when recombined, don't hydrogen and oxygen form water vapour?; why should both gasses rise to the top of the jars (hydrogen is lighter so it will rise above oxygen)? --SeansPotato Business14:43, 26 October 2008 (UTC)[reply]
This is rather simple to debunk on your own if you like experimenting. Get an electric motor and try to split some water. Notice how much energy it takes - as a sanity check, think about the lack of hydrogen as a fuel source. If hydrogen was so eager to split away from oxygen in water, wouldn't it be possible to have hydrogen producers running on tiny batteries in our back yards? Another sanity check - if it was so easy to split water into hydrogen and oxygen and recombine into pure water, wouldn't that be used all over the world to desalinate ocean water? You will find that it takes a lot of energy to split a water molecule. Then, put a water wheel out in the rain and see if a constant rainfall can produce enough electricity to do the job. Of course, it won't. But, you can see how big the gap is between the energy needed and the energy produced. -- kainaw™15:07, 26 October 2008 (UTC)[reply]
Ah, but 'common sense' arguments by analogy have no place in physics. Putting a 'water wheel out in the rain' is – at its heart – essentially how all modern hydroelectric power plants operate. To make it work, we collect a lot of raindrops from a wide area, and concentrate them into lakes and rivers. It's just a question of scale. Similarly, concerns about the energy cost of electrolysis don't immediately sink the proposal — putting a fuel cell on the uphill end of the device allows us to recapture a substantial portion of the energy used for electrolysis when the hydrogen and oxygen recombine into water. Sure, electrolysis takes a lot of energy for a given amount of gas production, but the reverse process also releases a lot of energy. (There's a reason why hydrogen is used as a rocket fuel.)
What we really have in this proposal is (nominally) a method for moving water from a low altitude to a high one. In hydroelectric plants, the energy to drive this process comes from sunlight (ocean water is evaporated, this water vapor eventually condenses and falls at higher altitudes, we capture some of its gravitational potential energy as it flows back to the oceans). In this perpetual motion device, the source of energy is not immediately obvious, but (since in this house, we obey the laws of thermodynamics) we know that there must be unaccounted energy 'leaking' in somewhere. DanielLC, below, has hit on what I think is the explanation — the conditions at the top and bottom are such that the energy costs of inflating bubbles of gas against atmospheric pressure will offset the apparent energy gained by moving the liquid water to a higher altitude. TenOfAllTrades(talk) 16:16, 26 October 2008 (UTC)[reply]
The amount of energy released from burning hydrogen is the same amount used to separate it, assuming the conditions are otherwise the same. Energy is conserved, not destroyed. The problem with your idea is that the conditions aren't the same. The further down the water is, the more pressure it's under and the harder it is to separate into hydrogen and oxygen. The higher up it is, the less pressure it's under and the less energy is released burning it. — DanielLC15:19, 26 October 2008 (UTC)[reply]
I came across a case where a person wanted to bring water up a hill by having the pipe go downwards so the water would get up speed and then rush upwards. Nonsense of course, but even something as silly as that could lead to an idea like the hydraulic ram. So keep up with the wacky ideas and then see if something else occurs to you. Dmcq (talk) 15:46, 26 October 2008 (UTC)[reply]
DanielLC, that sounded like the right explanation at first, but it seems to me that balancing the pressures is a bit of a flimsy way for the universe to ensure that we can't violate the laws of thermodynamics. I mean is it really that much harder to do electrolysis of water under an extra 10m of air pressure, compared to the increase in acceleration provided by gravity when the water falls again?
One way to rule out the pressure problem is to see if there's any conceivable way it could work in the absence of air.
Imagine, for example, a sealed room in a lab with all the air sucked out. The water tank would be the same, but this time, instead of upside-down glass jars to collect the gases in, we'll use two open tubes. The bottom end of each tube would be under the water, around the electrodes to collect the gases. The top ends would just be left open. As the gases bubble out from the electrodes, they would float out of the water then sit and float on its surface (near the bottom of the tubes). Without air in the room, they wouldn't float up any further. But if this process was given enough of a kick-start the tubes would gradually fill all the way up. A littler pipe could run between the two tubes near the top and the gases could be recombined into water again in the middle, providing a perfect stream of water to run down an open shoot again, onto the turbine to generate electricity (which would now spin faster, in the absence of air resistance!).
If there were no air pressure the water would boil. Even if it didn't, the gas released wouldn't just sit there it would spread out to fill the vacuum. --Tango (talk) 18:30, 26 October 2008 (UTC)[reply]
It's very definitely debunked - because the laws of thermodynamics say it's debunked and that's enough.
If you really have to break it down, the fatal theoretical flaw is that the cost of splitting water into oxygen and hydrogen is the cost of breaking the bonds between them PLUS the cost of overcoming the pressure in the water to create the bubbles. When you recombine the gasses at the top end of the equipment, you rejoin those chemical bonds - but you only get back the energy you used to break them - not the energy you used to make the bubbles form. The energy you get back from the flowing water is the same as the additional energy used to create the bubbles in the first place. I used to have a reference for the additional electrical energy it took to do this (as a function of the temperature and pressure of the water) - but sadly, I can't find it right now so you'll have to take my word for it.
The much more obvious practical flaw is that neither electrolysis nor recombining hydrogen and oxygen are remotely close to being 100% efficient - there is friction everywhere in the system and the turbines for recovering power from the flowing water can't ever be close to recovering 100% of the kinetic energy because to do that they'd have to stop the water from flowing - which would block the output of the system.
There comes a point in your life when you've seen enough of these crazy perpetual motion machines. We have a set of thermodynamic laws that step back from the details of the mechanism and do an end-run around all of the detailed explanations. When someone suggests such a system - you may safely start from the principle that it definitely won't work. The details of why are then just an intellectual exercise with little or no practical value.
Neither a solar system or galaxy is a perpetual motion machine. Both start, last a long time, and end. The universe as a whole is debatable. It did begin. Will it end? Most theories say that it will, so it isn't perpetual. However, it is possible that it will keep going forever. -- kainaw™04:15, 27 October 2008 (UTC)[reply]
A perpetual motion machine is usually defined as something that moves perpetually while giving off energy. If you don't include that last bit, a pendulum in a vacuum is a perpetual motion machine (give or take the difficulties in producing a perfect vacuum). --Tango (talk) 11:40, 27 October 2008 (UTC)[reply]
It would have to be a pendulum in a perfect vacuum with a frictionless bearing - which is impossible because anything that bears the weight of the pendulum is going to produce friction of some kind. Worse still: an-anything-in-a-perfect-vacuum is impossible to start with because as soon as you put something into a vacuum - it'll shed a few molecules and you won't have a perfect vacuum anymore. If you ignore the problems of the imperfect vacuum then a simple spinning disk (in a perfect vacuum and someplace where there is no gravity) might
work - except that in our universe, there is ALWAYS some gravity from somewhere.
Solar systems clearly aren't perpetual. The star runs down and explodes or collapses or something...and a galaxy is just a bunch of solar systems - and all of them give off light that they can't get back - so they definitely aren't perpetual. The universe as a whole...well, that's a bit tricky. Entropy is going to cause the universe to change - but arguably, that's an exponential process that never actually goes to zero. (Although a lot depends on things we don't know about like dark energy/matter). However, we can discount the idea of getting 'free energy' this way because if you are considering the universe to be the 'closed system' in thermodynamic terms - then any machine that's supposedly extracting energy from it is a part of the system that the energy is being extracted from - so the laws of thermodynamics are happy about that. SteveBaker (talk) 14:02, 27 October 2008 (UTC)[reply]
Actually, in theory it does work: if your electrolysis device and fuel cell are both 100% efficient, the energy used to split the water is exactly the same as the energy gained from recombining it. You can then extract energy from the water as it flows down to the electrolysis device. It needs to be open to the atmosphere, though, because you're using the gravitational potential energy of the atmosphere to lift the gasses generated to fuel cell. --Carnildo (talk) 22:30, 27 October 2008 (UTC)[reply]
No - even in theory there has to be energy lost due to friction and heat and turbulance and things like that. You can make a thought experiment in which all of those annoying things are magically handwaved away - but that's true of even the simplest of perpetual motion ideas. Connect a magical 100% efficient motor to a magical 100% efficient generator and use magical zero friction bearings and magical zero-resistance wires - and you have a perpetual motion machine. Heck - you don't even need to go that far - pick up any object and set it spinning and in an idealized world, you have perpetual motion. But you can't justify this kind of nonsense on the basis of UTTERLY unreasonable frictionless, lossless parts. As I explained before - to extract 100% of the kinetic energy from the water as it goes through the turbine, the turbine has to utterly stop the liquid from moving. The trouble with that is that the dead stationary water now blocks the output of the turbine. So no matter how far 'out there' you want to go with your 100% efficient turbine 'thought experiment' - it can never extract 100% of the kinetic energy. So as the water enters the tank at the bottom of the machine - ready to be re-electrolysed, it has to have a tiny bit of residual motion - which ultimately leeches energy from the system and causes it to stop. The laws of thermodynamics tell us that even in the uttermost airy-fairy theory, you can't get back 100% of your energy unless you are operating it at the absolute zero of temperature - and it also says that you can't ever get to the absolute zero of temperature - so no machine can ever be 100% efficient...even in theory.
um, the hydrolysis thing is a red herring; all you need to do is let water vapor condense and fall. in fact we do get power from such a system on a big scale, it's called hydroelectricity. Gzuckier (talk) 05:54, 1 November 2008 (UTC)[reply]
transformer
i have tried a lot but dint got a satisfiable answer,so plz tell me wat exactly happens when we apply a heavy ac signal on primary of a single phase transformer ,but keep secondary open.although power at primary is same as in normal cases because input voltage and current will be same.then where does this huge power goes.116.71.185.65 (talk) 16:43, 26 October 2008 (UTC)[reply]
See Transformer. There will also be a little real power dissipated with an open secondary due to eddy currents and due to I2 R losses in the primary winding, due to magnetizing current. Even the humming of an unloaded transformer means that a little power is being consumed to cause vibration of the metal. The real point of misunderstanding in the question is the mistaken assumption that "power at primary is same as in normal case." If "normal case" means a normally loaded transformer, then the comparatively low current into the primary of the unloaded transformer means that the input power is much lower than the normal case. Remember that for an ideal (lossless) transformer, "power in = power out" even though the voltage and current levels vary with the number of turns in the primary and secondary, directly for voltage and inversely for current. Edison (talk) 21:46, 26 October 2008 (UTC)[reply]
How are all sciences interrelated?
Hello,
I am looking for a kind of scheme in which important topics/fields of exact science are related. Most of the articles on scientific subjects (take semiconductor devices for example) relate it to more fundamental topics (quantum physics--> solid state an semiconductor physics) and to applied topics (transistors--> chips etc), but I would like to see all that information on one (perhaps giant) picture. Any ideas?
I have seen that cartoon before: it kind of made me start wondering so it's funny to get as an answer :-). I'm looking for something more in detail, though. —Preceding unsigned comment added by 87.67.44.42 (talk) 20:19, 26 October 2008 (UTC)[reply]
I can kinda imagine the sort of diagram you're looking for - and I'm surprised I couldn't find one anywhere (I did spend a while hunting for one). I kinda imagine a diagram with the words "PHYSICS", "CHEMISTRY", "MATH", "BIOLOGY" and so on in big letters in regions of the diagram - with all of the sub-disciplines (things like "ELECTRONICS") placed in relation to the main topics (eg Electronics straddling physics and chemistry - but nowhere near biology) - perhaps with arrows between sub-disciplines showing how they relate to one-another. I think you could make a coherent diagram like that - but it would be hard to do a perfect job because most things touch mathematics - and (as the XKCD cartoon so elegantly points out), chemistry is technically a sub-field of physics and biology a sub-field of chemistry...so it's not really going to be perfect. However, I was unable to find such a thing (although I'm sure I've seen one someplace in the past). SteveBaker (talk) 13:45, 27 October 2008 (UTC)[reply]
Yeah - that's the kind of thing - but that one only has the sciences that relate directly to chemistry - I was thinking of a much denser diagram with hundreds of fields connected with arrows showing how they interrelate. The annoying thing is that I'm almost sure I've seen something like that. SteveBaker (talk) 23:20, 27 October 2008 (UTC)[reply]
That's indeed what I was looking for. Thanks for help me searching, and if you happened to stumble across something similar I would be happy to know. --Gnorkel (talk) 23:35, 27 October 2008 (UTC)[reply]
Photons released while burning?
Since photons are the carriers of light and when anything (like paper, wood, candle wicks, etc.) burns light is emitted, does this mean that photons are part of the atomic structure of all matter?Terran2034 (talk) 18:50, 26 October 2008 (UTC)[reply]
No. Photons are created whenever energy is released as electromagnetic waves (E=Mc2 - the energy released is converted into the mass of the photons that are carry the energy away). They aren't tucked away inside the atoms waiting to be released. Aside from anything else, photons have to move at the local speed of light which means that they can't be stationary inside the atom. SteveBaker (talk) 19:11, 26 October 2008 (UTC)[reply]
Photons are created or absorbed when an electron in an atom loses or gains energy. In the course of burning, lots of energy is released from the breaking of chemical bonds. This energy, among many other things, causes electrons to move into higher orbitals, where they are in an "excited state". As the electrons "relax" back to their native, or "ground" state, they release photons. Its not that the photons are "part" of the electron; you need to stop thinking of sub-atomic models as having convenient macroscopic analogs. The electron "releases" the photon, but it does not "contain" the photon itself. The electron is releasing "energy", which at this scale is basically exactly the same as releasing mass. Whether you think of light as a "photon" (i.e. a "mass") or as a "wave" (i.e. "energy") depends upon which model best fits your application. Light is light, and it does what it does. Photons are a convenient model for explaining some behaviors of light, but that doesn't mean that photons behave like little billiard balls... --Jayron32.talk.contribs17:10, 27 October 2008 (UTC)[reply]
What do people think is the prime source of (ie largest contributor to) harmonic distortion in a Wien bridge oscillator (Not homework Im researching low distortion oscillators ATM)--GreenSpigot (talk) 20:26, 26 October 2008 (UTC)[reply]
My guess would be due to non linear gain due to the amplifier element being not ideal. If you use ceramic capacitors you may also get non linear response. Graeme Bartlett (talk) 21:11, 26 October 2008 (UTC)[reply]
If you use a light bulb that should be reasonably linear as long as the oscillator is much higher frequency than the response of the filament in the bulb. At audio frequencies you may have some detectable effect. Graeme Bartlett (talk) 20:31, 27 October 2008 (UTC)[reply]
How about Ares? Ares 1 isn't even finished yet. Also, I don't think that there's a Ares 2, 3 or 4. Maybe NASA decided to borrow the Saturn version numbers for the Ares rocket program? 67.184.14.87 (talk) 00:39, 27 October 2008 (UTC)[reply]
Ares IV was planned, but the project was later scrapped. I assume that the same is true of Ares II and III, though perhaps these got no further than rejected proposals. Deor (talk) 10:51, 27 October 2008 (UTC)[reply]
Indeed, it's quite common for some versions to never get past the drawing board or maybe some testing which results in strange orderings. (eg. Apollos 2-6) --Tango (talk) 11:44, 27 October 2008 (UTC)[reply]
I heard of a chemical that can be put into a house's air ducts that will hamper marijuana growth by I think preventing pollination or something. I've read the mj cultivation and indoor cultivation articles and looked on google - does anyone know? —Preceding unsigned comment added by 206.116.59.222 (talk) 02:16, 27 October 2008 (UTC)[reply]
Narking on the cultivator would be a more efficient solution to the problem of having someone in the household cultivating marijuana, of course with its own risks. Edison (talk) 03:06, 27 October 2008 (UTC)[reply]
No, preventing cultivation in the first place is the more efficient solution. Turning in a grower does nothing to prevent the property damage or protect the property owner from legal and property seizure ramifications of owning a marijuana house. Telling potential renters that dope wouldn't grow because of the retardant DOES.
Putting a chemical into a house's air ducts could be a health and safety hazard, and your tenant might have a claim against you in law. There is only a remote chance that a particular tenant would be intending to grow marijuana. Depending on the jurisdiction it would be better to build into the tenancy agreement a right for the landlord to inspect the property at regular intervals, and a heavy financial penalty if they were found to be engaging in an illegal activity. Itsmejudith (talk) 20:35, 27 October 2008 (UTC)[reply]
None of which prevents the landlord from TELLING his tenants that he did this in order to discourage them from undesirable behaviors. Not everyone is smart enough to think these things through to their logical conclusions. SteveBaker (talk) 05:16, 28 October 2008 (UTC)[reply]
Obviously nobody's actually heard of the chemical, because it's safe, it's approved for use, and it's on the market right now. I just can't remember the name of it, and frankly nobody who's felt the need to contribute to this thread has been the remotest bit helpful. Please credit people with a modicum of sense? We're not all looking for a bunch of uninformed or general opinions. Some of us actually know our stuff, we just need a little nudge in the right direction. Don't anyone bother actually answering this question, I won't be back to this page again. —Preceding unsigned comment added by 206.116.59.222 (talk) 13:30, 29 October 2008 (UTC)[reply]
I haven't read Flatland in years, so maybe this is answered there, but anyway: An object in a 2-dimensional land such as flatland would appear from inside the land as a line segment, possibly changing length is the object turned. Except -- the only way it would be visible is if there was some non-zero third dimension ("height") to this figure; otherwise, there would be nothing to see. (Similarly if in the real world you drew a line segment with zero thickness, you wouldn't see anything.) So this implies that there must be a non-zero infinitesimal third dimension. This would then imply that a 3-dimensional world must have an non-zero fourth dimension to be able to actually perceive anything (aside from time: time would apply in the 2-dimensional land as well), and that the fourth dimension world would have a non-zero fifth dimension, and so on. Therefore, the universe has infinite dimensions.
By "see", you are referring to a light particle bouncing/reflecting/emitting from a surface and hitting a sensory organ in some sort of eye. Light particles may be defined as having width, but it is just as easy to define them as a zero-size wave of energy. So, it is not necessary for the surface to have height since the wave of energy coming from it doesn't have to have height. Also, the point of flatland isn't that there isn't height, it is only that the beings living in flatland cannot comprehend or sense height. So, flatland doesn't say there isn't height. In fact, it uses a demonstration of height - shoving your finger through flatland. The beings there will see a weird object that changes shape as your finger moves through and they see it slice by slice. -- kainaw™03:59, 27 October 2008 (UTC)[reply]
Why shouldn't a Flatlander's eye have a one-dimensional retina that sees one-dimensional images? Consider the cross-sectional diagrams you've seen of light entering an eye and forming an image; now take that diagram literally. In our world something with no thickness has no substance, but Flatland is not our world. A four-dimensional observer might make the same comment about our vision that you make about Flatland vision. —Tamfang (talk) 05:29, 27 October 2008 (UTC)[reply]
(I think?) that's what I'm saying - that we shouldn't be able to see each other unless there is another physical dimension in which we are "thick," just as flatlander wouldn't be able to see each other if they really had no height. And that by induction this would continue to an infinite amount of dimensions. But Kainaw's explanation that we don't have to be "thick" in another dimension because light can be a zero-seze wave (that can be absorbed and therefore processed and seen) seems to work for me. zafiroblue05 | Talk05:59, 27 October 2008 (UTC)[reply]
Well, I see two problems in your reasoning. First off, the flatland example only suggests that you need N+1 dimensions to be able to perceive in N dimensions. Once N dimensions are present, perception in N-1 dimensions becomes possible. Nowhere in this argument is an N+2 dimension necessary unless there are beings that percieve in N+1, and so on.
The other problem I see in your reasoning is that your premises are about the nature of perception, but you draw conclusions about the nature of the universe. Our perceptions are structured from sense data we receive from our body and are structured into experience by the mind. How we understand the universe through our perceptions does not need to match up with reality as long as our perceptions remain consistent. Mathematically, we could actually live in a 2D holographic universe, and we wouldn't even know it because our experience is 3D! It's even possible that we don't have accurate access to the content of our minds (a very wierd but fun idea). In the very least, you must concede that the fact that you can watch TV and see more than flashing lights is testament to the fact that our brains perceive depth in our world in ways that at least aren't always accurate. --Shaggorama (talk) 07:21, 27 October 2008 (UTC)[reply]
I think the problem is that you're not seeing things from a truly 2D viewpoint. There is no reason why truly 2D photons coming from a 2D light source should not bounce off a 2D object, be focussed through a 2D lens and land on the viewer's (presumably) 1D retina - thereby forming a 1D image. There is no need for any extra dimensions to make this work. Hence your extrapolation (which in itself is a bit 'iffy') is entirely invalid. Incidentally - the book 'Flatland' was written in 1884 and it's basically crap. You won't learn anything about the nature of a 2D world from it. It's mostly a diatribe about class distinctions and politics - it's sexist as all hell (quite an embarrassment to read, actually) and its ideas about a 2D world are poorly thought out from any kind of scientific perspective. If you want a truly great book on the subject, I strongly recommend "The Planiverse" by A.K.Dewdney. It's by far the best book to cover the idea of a 2D world and it has a really careful treatment of what it would mean to live in two dimensions - the world is fleshed out in great detail with lots of interesting diagrams (you can easily spend 20 minutes looking at the 2D steam engine or the structure of a 2D 'house' or a fishing boat. The appendices to the book cover some serious scientific issues that probably mean that a 2D world with the kind of richness needed to form stars, planets and creatures could probably not exist at all. For example, it's believe that 2D atoms would be unable to form chemical bonds at all. But the book also has a great plot and I recommend it to anyone with an enquiring mind (which means everyone here at the science ref desk!) - read it to your kids too. SteveBaker (talk) 13:34, 27 October 2008 (UTC)[reply]
I think Flatland was being satirical about the sexism thing. Also, who is to say that light and sight work the same in flatland, IIRC, gravity pulls consistently southward, and gets less potent toward the northern latitudes, and rain always "falls" in the same direction. Sliver Slave (talk) 22:43, 28 October 2008 (UTC)[reply]
Urgent need to pee
Suppose someone really really really goes to go but they don't want to because it would be embarrassing (eg, marching in a parade) or very messy to clean up (eg, driving a car) or very both (eg, riding in the boss's car.)
Can a person hurt themself by trying to hold it till they get to an "appropriate" place? Or is it safe to hold on as long as they can?
Second part of the question -- are there any strategies to help people "hold on"? (Please, no suggestions to carry clothespins at all times.)
PS: Just on the off-chance that anyone wants it, I irrevocably agree to release this contribution under the terms of the GFDL. CBHA (talk) 03:26, 27 October 2008 (UTC)[reply]
Spontaneous rupture of the bladder is very rare, but does occur. To quote a case study, one scenario is: "The pathogenesis involves bladder overdistension and thinning of the dome from diuresis. The patient ignores natural cues to void due to alcoholic stupor. Thereafter even trivial increase in intra abdominal pressure like coughing can rupture the bladder." - Nunh-huh03:52, 27 October 2008 (UTC)[reply]
See Tycho Brahe#Death for a well-known case where someone was claimed to have killed himself in this way, although not with a rupture. --Anon, 05:53 UTC, October 27, 2008.
BTW, there is no need to include a statement licensing your contribution under the GFDL. By posting any text to wikipedia, you've already agreed to release your contribution under the terms of the GFDL, without exception. And it is not as odd as it may seem since there are many wikipedia mirrors who mirror our content completely legally. And we archive all reference desk questions so who knows, maybe some day someone will want to publish a book or CD or whatever 09:45, 27 October 2008 (UTC)
I need to go to the toilet now.I bet that was your suggestion. There's probably a word for that like one yawn making everyone else yawn but it 'scapes me now - gotta go :) Dmcq (talk) 16:34, 27 October 2008 (UTC)[reply]
I've heard your kidneys just stop producing urine after a while. If that's correct, you could probably get kind of sick if you let the toxins in your bloodstream build up long enough. I'd consider that hurting yourself. — DanielLC23:42, 27 October 2008 (UTC)[reply]
As a practical matter, wouldn't bladder control give out long before the kidneys ceased to operate (leaving aside the case of someone with kidney disease)? CBHA (talk) 04:45, 28 October 2008 (UTC)[reply]
not too risky as one episode, but doing this as a habit can cause the bladder to stretch, and that makes it weaker. (as the radius of a sphere increases, the projection of the tension of the wall in the radial direction becomes less, until of course at infinite radius the two are perpendicular and the inward pressure is zero no matter how high the tension of the wall) Gzuckier (talk) 06:06, 1 November 2008 (UTC)[reply]
Sorry, but your question isn't clear. If you're asking for medical advice (For example, if you've crammed something into your eye.) then we can't give medical advice but if you're worried then you should probably get to an emergency room.
Sorry OP, APL seems to have confused a question about human anatomy with a request for medical advice. Objects don't really travel down nerves, just chemicals. But, the optic nerve passes through the a hole in the orbit called the optic canal, which does go directly to the brain. A quick browse around google gives the canal a diameter of 4-6mm in adults, so some objects (such as icepicks, as APL gruesomely suggested) can pass through the without damaging the bone. But please, do not stuff anything into your or anyone elses eyes. —Preceding unsigned comment added by 96.231.89.120 (talk) 07:02, 27 October 2008 (UTC)[reply]
I did not entirely assume it was a request for medical advice as you're suggesting. My first sentence was a statement that I didn't find the question clear. The second was an answer for if it was medical advice, and my third and fourth sentences was an attempt to offer an informative link about my best guess of what they were asking about.
However, I had assumed that the article on ice pick lobotomies would at least briefly discuss the route from the eye-socket to the brain. Looking more closely, I see that isn't the case. APL (talk) 07:23, 27 October 2008 (UTC)[reply]
The questioner did not present any intent to either put in or pull out something out of his optic nerve. Sounds unlike medical advice to me. Mac Davis (talk) 19:00, 27 October 2008 (UTC)[reply]
Solar-To-Electric Efficiency (STEE)
In Wiki–page vide-http://en.wikipedia.org/wiki/Solar_power numerous method of harnessing solar energy is explained. But only under sub section- "solar pond" I came across this parameter "Solar-To-Electric Efficiency"(the S-pond has STEE 2%).Whilst under section Photo Voltaics therein, I read
"converted less than 1% of incident light into electricity".
"Parabolic dish systems display the highest solar-to-electric efficiency among CSP"
without any mentioning of any percentage under the same sub-section. Apart from these, there are numerous methods of harnessing solar power. It would be delighting to compile a short article of STEEs of different methods, history, development, breakthroughs, etc.
Would this be a valid contribution (by anyone)? "Solar-to-electric efficiency of different methods".
Yes - anything we can add to the encyclopedia in these areas of increasing importance is worth doing. I would only caution you though that we require our contributors to supply 'references' for every significant fact they provide - so you'd need to come up with reliable references to books, scientific journals, trade magazines and things of that kind to back up most of what you say. Also, if you happen to work for a company that makes or sells those things (so that there might be a conflict of interest) - then you should probably NOT write the article yourself - but rather use the article's Talk: page to pass on information and references to the people who are actually doing the writing. But aside from those two concerns - YES! PLEASE! SteveBaker (talk) 13:18, 27 October 2008 (UTC)[reply]
It's worth noting that the "less than 1%" figure applied to the very first solar cells, which were little more than a nineteenth-century curiosity. Silicon solar cells, developed in the 1950s, started out at roughly 5% efficient. Widely-deployed photovoltaic panels today run from about 12 to 24% efficiency. Costly special-purpose panels (primarily used aboard spacecraft) are better than 30% efficient, while experimental cells have exceeded 40% efficiency in the lab. TenOfAllTrades(talk) 14:15, 27 October 2008 (UTC)[reply]
You also need to be aware that terrestrial and space solar cells efficiencies are computed with a different standards so they cannot be simply compared. The standard for space-faring solar cells includes UV intensities that are not seen on Earth because of atmospheric blocking. Rmhermen (talk) 20:12, 27 October 2008 (UTC)[reply]
I came across Thixotropy which suggests ketchup shows thixotropy. I'm not however certain if this is true (or for that matter, any of the other examples are correct). I believe it is definitely Shear thinning (from a NASA article) but both wikipedia articles note there is a distinction and the terms are often confused (although I presume itcould be both). Searching didn't help because there are far too many references which treat the two as the same thing. I had the same issue previously with with silly putty where there was confusion over whether it showed dilatant or rheopecty (it appears it is a dilatant but the article had inaccurate information for a long while) Nil Einne (talk) 14:12, 27 October 2008 (UTC)[reply]
How is the phase between electric and magnetic waves in a lightwave determined?
Hi,
Consider this image of a lightwave.
What I want to know is how is the phase relationship between E (electric force) and B (magnetic force) determined? How is it measured?
I mean, how do we know the phase is 0° and not, say, 90°?
That's not what I'm asking. I'm trying to understand why it is that the electric force E and the magnetic force B are synchronized. I'm wondering how we know that when E is at maximum, B is at maximum too. I mean, is it possible for E to be to a maximum, and B to be at zero? So this question is about the phase in time, not in space. —Preceding unsigned comment added by InverseSubstance (talk • contribs) 23:14, 27 October 2008 (UTC)[reply]
OK if you look at Sinusoidal plane-wave solutions of the electromagnetic wave equation the equations have a solution. The derivative of the Electric field with respect to z the distance along the travel direction is proportional to the derivative of the magnetic field with respect to time. When you consider the wave is traveling, then z is equivalent to time, and then derivative of E is proportional to derivative of B, ie they are in phase. Do you need a more symbolic expression of this? Graeme Bartlett (talk) 05:46, 28 October 2008 (UTC)[reply]
I Think you will find in normal space or materials that the fields will still be in-phase, for circular or elliptical polarization. The E and B vectors will spin around around the axis of propagation but still be in phase with the other field at 90 degrees in space with it. Graeme Bartlett (talk) 00:51, 29 October 2008 (UTC)[reply]
Why do Budgerigars have such crappy night vision when compared to humans?
Question as topic. From my experience with my own birds, it seems that they are unable to see objects in the dark until they are mere inches away (at which point, the budgie freaks out). If a budgie has a 'nightmare' (or a night fright, or whatever) and falls off its perch, it seems to be completely unable to find it again will flap around wildly and screech until the light is turned on. --Kurt Shaped Box (talk) 18:47, 27 October 2008 (UTC)[reply]
Well, they're not nocturnal birds so the obvious feature (specially adapted eyes) aren't present. In the article under vision here[3] their vision is maybe more strictly designed for full spectrum sunlight. Compare this with human adaptation, making our sight more versatile (sunlight, twilight and night). It'd be interesting to look at a budgie's eyes in terms of size ratio and compare that with human eyes ratio to body size as well. Julia Rossi (talk) 21:43, 27 October 2008 (UTC)[reply]
(after edit conflict)You'd think that a bird as low down in the food chain as the Budgerigar is would at least be physically capable of keeping something of a look out for nocturnal predators when roosting though, wouldn't you? If they are unable to spot a human at a distance of six feet in a room with the lights turned off, what chance would they have in the wild against an owl? --Kurt Shaped Box (talk) 23:13, 27 October 2008 (UTC)[reply]
Humans have about 7 million 'cone' cells that are responsible for daylight, color vision - and between 75 and 150 million 'rod' cells that are there for low light level monochromatic vision. If we didn't need to see in poor lighting conditions, we could either have eyes that were 10 to 20 times smaller (and therefore require less energy and less weight) - or we could have daytime vision that would be 10 to 20 times sharper. So we pay a LARGE price for our night vision. A creature such as a non-nocturnal bird might well do much better without reasonable night vision. SteveBaker (talk) 23:10, 27 October 2008 (UTC)[reply]
Wait, "we could [...] have eyes that were 10 to 20 times smaller"? Surely the area of the retina matters to the quality of our vision? We couldn't just have the same number of cone cells on a smaller retina and expect the same results, could we? Or would a different lens solve this? 79.66.32.150 (talk) 21:44, 30 October 2008 (UTC)[reply]
in fact, the cone cells are concentrated in a very small part of the retina, the fovea. the result of this is the continual movement of the eye to see more than one little area at a time (saccade). this also means that rod cells, spread all over the retina, are responsible for not only night vision, but also the "seeing out of the corner of your eye" thing.Gzuckier (talk) 06:11, 1 November 2008 (UTC)[reply]
Harmonic Vibration
Two part question
1 - Is Sympathetic resonance the same concept as Harmonic vibration - i.e. a sound vibrating an object at a frequency that can eventually cause an object to shatter?
2 - Is it possible to weaponise this concept for use against humans? Could we induce SR/HV in the human skeleton, causing someones bones to shatter into powder?
Vibrations can only be sustained or built up if the Q factor is high. Bones and humans do not have such a response to vibration, so you need to put in very high power. The target will probably be affected less than the shooter. Graeme Bartlett (talk) 20:50, 27 October 2008 (UTC)[reply]
although there is a persistent urban legend about the military developing a weapon to excite specific resonances of the gastric tract to incapacitate the opposition nonlethally. i don't know if that's true, but can personally vouch for having my guts uncomfortably scrambled following the first time my buddy's dad left us alone at home with his macintosh stereo and wharfdale speakers for a few hours. Gzuckier (talk) 06:16, 1 November 2008 (UTC)[reply]
Staying underweight by thinking?
I was reading the article of L (Death Note), and noticed that one line read, "he remains underweight because the brain uses the most calories of any organ in the body." First of all, how much of this is true or false? Like for instance, if one were a deep thinker, would they be able to keep their weight down? What other metabolic functions are involved in this as well? Thanks, Valens Impérial Császár9320:09, 27 October 2008 (UTC)[reply]
While the brain does consume quite a fair share of the body's energy intake, the largest amount of the brain's function is not necessarily consumed by conscious thinking. Large areas of your brain are devoted to lots of unconscious processes, such as regulating all the processes that simply keep you alive. Also, there is no reason to assume that a person who spends more time in "deep thought" (i.e. thinking about really important or difficult problems) exhibits more brain activity than people who spend their time thinking lots about boobies and brands of beer. Also, what is "deep" for one person is not "deep" for another. Bill Belichick likely spends lots of time thinking about different things than does Stephen Hawking, yet each is as likely to spend as much brain activity in his own field. As a last thought, should not spend too much time looking for logical consistency or scientific stringency out of anime. Most of the time, people who write fiction just make stuff up. --Jayron32.talk.contribs20:28, 27 October 2008 (UTC)[reply]
<Anecdotal evidence warning> I remember ending up with terrible headaches after study sprees, exams that (mostly due to lack of preparation) needed a lot of improvisation and after endless hours of chess games. Something that definitely didn't happen after equally long hours of day-dreaming during boring trips. --Taraborn (talk) 22:39, 27 October 2008 (UTC)[reply]
<Not medical advice however much it may look like it warning ;)> My guess would be that you were focusing close up for long periods of time - it's your eyes that caused the headaches, not your brain. You should take regular breaks from close up work and allow your eyes to focus on something in the distance. If you get such headaches regularly, then see a doctor or optician, of course (I did and it worked for me!). --Tango (talk) 23:32, 27 October 2008 (UTC)[reply]
Just because your brain uses more calories than the rest of your body - doesn't mean that you can make it use yet more by doing something differently. SteveBaker (talk) 23:04, 27 October 2008 (UTC)[reply]
Actually, despite a lot of the anecdotal pessimism in the answers so far, the brain actually does consume a huge amount of energy and what you are doing with it does affect how many calories it consumes. "Even at rest, the brain consumes 20% of the body's energy."[4] "During periods of peak performance, adults increase that energy consumption by up to 50%."[5] Thinking "deep thoughts" is probably not enough—doing challenging mental work, though, is more on par. Speculating about whether there is a God by itself is probably not deep enough—trying to rigorously prove it one way or another, working your way through all of the logical ends, probably is. Many "deep thoughts" are pretty cognitively empty unless you back them up with rigor.
Could you keep thin through mental activity? Potentially. It would depend on your overall calorie consumption, size of brain, amount of mental activity, etc. There are also basic metabolic issues that differ from person to person. Clearly just engaging in regular mental activity is not enough for some people—think of Herman Kahn, for example, who was an active thinker by any definition, but he was a complete sybarite and probably far out-consumed any calories burned by thinking (and probably did do enough walking in any case—cutting out normal calorie-burning activities like walking is pretty much the equivalent of chowing down on cake). --98.217.8.46 (talk) 01:14, 28 October 2008 (UTC)[reply]
Studies at MUSC (shown on Mythbusters) use brain activity (which may possibly relate to calorie usage) to identify if a person is telling the truth or not. As shown in the episode, when a person lies, it takes more effort and shows up as more brain activity. So, you could stretch this all very thin and make an unscientific claim that telling nothing but lies will cause the brain to burn more calories. Of course, everyone here should know at least one person who constantly lies without apparently burning many calories. -- kainaw™01:19, 28 October 2008 (UTC)[reply]
Thanks for that, I guess I was thinking of when fat was not so cool, more like now. Also, maybe successful writers can afford more nutrition so it's not about thinking or lying that loses weight but good ol' eating or not. Julia Rossi (talk) 00:18, 31 October 2008 (UTC)[reply]
also: the brain runs on glucose only, and i don't believe there's any pathway to convert fat to glucose, so you could think yourself into starvation but still not lose any fat weight. Gzuckier (talk) 06:17, 1 November 2008 (UTC)[reply]
Analyze a liquid
I currently pay a lot of money for a certain commercially sold product (a special type of cleaning solution, no ingredients listed on the label) and wanted to explore the possibility of creating my own at lower cost. How do I go about reverse-engineering a liquid? Do I lookup "labs" in the Yellow Pages and ask them how much it would cost to come up with the recipe? If yes, how much would such a venture typically cost?
I would assume that the solution is patented, and so I don't know if it would be illegal to produce this yourself. I guess it would probably be OK if you are only using it for yourself.
If I were you, I would look for a cheaper alternative. If you have already searched, and one doesn't exist or it doesn't live up to the standards you expect then I would take further action.
You could ask the company for the ingredients, and I am under the belief that they have to give it to you (I may be wrong) - obviously if you were to do this, make up a lie such as "Could you please provide me with a list of the ingredients that go into your Product XXX. I need this because I clean very sensitive substances that can't come into contact with many commercial cleaning products, and I need to check if your product can be used with these substances." That is a pretty poor lie so don't use it, but I'm sure you can come up with something better.
If they don't tell you, you could get a lab to find out the ingredients. The cost of this could be anything, it depends on how long it would take them to work out the ingredients, which depends on the complexity of the recipe.
Even if you do get the list of ingredients, how do you expect to manufacture it? The ingredients might be impossible for you do get hold of - simply because of the danger. Even if you do get hold of ALL of them, you might need a lot of equipment to manufacture it, including safety equipment. As you would be making this on a small scale this would probably be false economy. Even if we ignore all of these things, the ingredients might not just have to be mixed together, but to go through various processes, for example, heat Ingredient 1 for 5 minutes, then add Ingredient 2 and allow to react for 10 minutes when you will then add Ingredient 3. You would probably not be able to work out what these processes are.
Making it yourself is almost certain to be more expensive. Just go to the supermarket and buy the cheapest cleaner that says it does what you want and try it out, if it doesn't work, buy a more expensive one and work your way up the market until you find something suitable. --Tango (talk) 22:40, 27 October 2008 (UTC)[reply]
Blindly figuring out what is in a liquid could be difficult, especially if the mixture is complex. What is more reasonable would be figuring out the concentrations of the various components based on an ingredients list, which some products do provide. This is what an analytical chemist can do. Alternatively, if the product is patented, you could try searching for the patent information. It might be difficult to read and won't contain everything, but it is a start. What product is it that you are using? --Russoc4 (talk) 22:49, 27 October 2008 (UTC)[reply]
On the subject of patents: To obtain a patent, the patent-holder must specify in detail how to create the patented product. For a liquid, this means specifying precisely what they put into the liquid and in what proportions, and how it was treated if applicable. If he hasn't done this, then there is no patent, and it is perfectly legal to recreate. In that case, it is likely a trade secret, so reverse-engineer to your heart's content if you can find a way to do it ;-) Someguy1221 (talk) 23:01, 27 October 2008 (UTC)[reply]
In many countries, manufacturers and most retailers are required by law to provide you with an MSDS sheet for chemical products. You can also look them up online (just type the product name in full with MSDS in Google). The MSDS will tell you the active ingredients in the product. If I was a gambler, I would bet decent money that the actual cleanser is no different than a dozen others on the shelf. Matt Deres (talk) 23:06, 27 October 2008 (UTC)[reply]
I'm reluctant to divulge precisely which liquid I'm referring to, but it is a unique product and nothing else like it is available. The reason I think I can do this myself cheaper is because after some discussion with the manufacturer (a small family-centered operation) I got the feeling that this is something they mix together themselves in their basement. But it does work as advertised and I'd like to replicate it if possible. —Preceding unsigned comment added by 216.48.176.5 (talk) 14:03, 28 October 2008 (UTC)[reply]
In the U.S. a company has to provide info for the Material Safety Data Sheets which many companies, schools, hospitals, etc have to keep on premises. So if "Farmer Joe's Secret Formula Triple X Lingerie Wash and Engine Degreaser" lists no ingredients, what would a poison control center do if a child drank some and they got a call? There should be a contact for ingredient information, or a MSDS should be available. Edison (talk) 14:40, 28 October 2008 (UTC)[reply]
Uranus disc color
Though Uranus looks pale blue most of the time, could it look bluish-purple sometimes? Since methan gas could make the planet look purple sometimes depend on the sunlight.--Freewayguy22:46, 27 October 2008 (UTC)[reply]
It's always a very tricky matter to talk about absolute color for things like far distant planets. What you'd probably want to know is what color the planet would appear if you were in orbit around it looking down. But sadly, there is VERY little sunlight out that far - and the planet would be exceedingly dim - almost black. So with your dark-adjusted eyes, things would look more blue than they usually do - but pretty much monochromatic. Well, that's not really the answer most people actually DO want - so when NASA shows pictures of these things, they boost the brightness and juice-up the color to show the details...but it's very rare that the pictures were taken with electronics that have similar properties to human eyes - they are often looking in the infra-red or the ultra-violet - or in colors other than the red, green and blue that our eyes can detect. The cameras may not actually have captured any significant reflected light in red, green or blue. So you see a wide variety of 'interpretations' of remote imagery. It's tough to say what's "right" because nothing is really "right". SteveBaker (talk) 01:11, 28 October 2008 (UTC)[reply]
Isn't Saturn very far from the sun too. The photos Voyager taken can be closely right or little off. Well, some iamge from Voyager finds Uranus green or blue-green, Uranus from space may look blue-purple, I was told to be pale blue. For Saturn I was told if blue-silver color, it may be yellow or gold sometimes, this all depends on sunlight and chemical. Neputne looks usually dull blue from Voyager 2, sometimes neptune is VERY blue, maybe a little purple dye sometimes.--Freewayguy02:44, 28 October 2008 (UTC)[reply]
My understanding is that the Voyager crafts use a Vidicon camera - black and white. They put color filters, such as orange and violet, in front of the camera. Then, NASA combines snapshots taken through different filters and apply color "correction" to make the image appear pleasing. It is not a true color of the objects being photographed. -- kainaw™02:51, 28 October 2008 (UTC)[reply]
From this view Neptune's color is blue but duller. This all matters on chemicals, and depends on cluds. For instant Venus may be very yellow sometimes sometimes Venus is white. All spacecraft going through distant palents colors goes in differ color. Jupiter is a distant planet too, sometimes it have black, white, gray, yellow stripes too maybe blue and green.--Freewayguy02:55, 28 October 2008 (UTC)[reply]
What about Jupiter and Saturn. Cassini, pioneer, and Galileo gone through those planets. You said Jupiter and Saturn may not be a true color is it right. Do pineer, Cassini, and Galileo use black-and white cameras like Voyagers, then put into orange-violet filters for NASAS photos. Which spacecraft of Jupiter and Saturn is true colors?--Freewayguy02:55, 28 October 2008 (UTC)[reply]
is tan or gray for Mercury a true color, or all spacecrafts use black-and white for all panets. Mercury is only visit by one spacecraft so far, is those photos true colors for Mercury?--Freewayguy02:59, 28 October 2008 (UTC)[reply]
My question is is almost all the planet in fake color, when spacecraft visit it. Jupiter and Saturn have been visit by at least 5 spacecrafts. If I go orbiting it truly in space will disc be blue, white? Jupiter looks orange through spacecraft Pioneer, Galileo too, or those is not true color either. Do most spacecraft work same way as Voyagers?--Freewayguy03:52, 28 October 2008 (UTC)[reply]
Can you answer this quickly. You seem to lose me a little bit. Gas giant interior is white-hot and generate off mor heat than it gets from the sun, menas it's interior is white, very white, then at each cloud layer they scatter numerous of light waves. The atmospheric layer is thick, menas every point of layers have differ colors. uranus and neptune have methane, I doubt the true color will be black, but maybe not blue. Methane usually makes things look purple, amybe around blue-purple colors to both planets (Uranus maybe a little lighter, Neptune maybe a little darker). jupiter and Saturn is mostly hydrogen gases, and it have a very light interior, part of sky may have white, gray, light brown colors, the disc colro might vary green, orange, yellow paly through every single color. Venus may be perfectly white, all CO2-brightest planet. For Titan may be like burnt orange.--Freewayguy04:34, 28 October 2008 (UTC)[reply]
The gas giant's core produces heat but no light. So that's an irrelevence. It doesn't affect the color. The gas giants don't "glow" - they reflect light just like the rocky planets do. Since they don't glow with their own light - the remainder of your statements are unimportant. SteveBaker (talk) 05:04, 28 October 2008 (UTC)[reply]
Just answer quickly, you seem to be confusing me. I doubt gas giant's sky is black. Which planet have absolute true color or none of them do?--Freewayguy04:41, 28 October 2008 (UTC)[reply]
No - the sky isn't black until you get VERY deep into the atmosphere. Just like here on earth, the materials that make up their atmospheres will scatter sunlight via the Raleigh and Mei scattering mechanisms - so their sky's will appear colored from moderately shallow distances into the clouds up to the outer reaches of the atmosphere when the sky doesn't scatter enough light and it appears black...just like here on earth. But that doesn't affect what I've been telling you. The AMOUNT of sunlight out at Uranus is not enough for humans to see colors. So if you were near Uranus - it would be a very dim, dark swirling mass below your feet. The sun would look like a candle flame 50 or 100 feet away - hardly enough to cast any light on the subject. At those low light levels, we humans don't see colors - just shades of blueish grey...irrespective of the "true" color of the object. We can produce fake color pictures using the various sensors on the spacecraft but to answer the question "what color would it look like"...the answer is more or less "Black". SteveBaker (talk) 05:04, 28 October 2008 (UTC)[reply]
Mercury, Venus, Mars, Jupiter and Saturn are all VASTLY closer than Uranus. You can see them all with small telescopes or binoculars and they are quite bright. Jupiter is five times further from the Sun than we are - sunlight there is 25 times dimmer than here on earth - pretty much the same as the sunlight we get here on Earth on a very cloudy day - so it's obvious that you'd be able to see Jupiter very clearly if you were in orbit above it. Saturn is about ten times further from the sun than we are - so the light there is 100 times dimmer than on earth - but that's still enough to see quite clearly and in full color. The lighting inside your house at night is probably around 100 times dimmer than the sun. But Uranus is twice as far away as Saturn - that's 400 times less sunlight than here on Earth. The sun is only as bright as a candle flame halfway down my backyard...you wouldn't see Uranus at all well until your eyes got dark-adapted - and that means no color vision. Spacecraft use peculiar colored filters so that they can maximise the scientific value of the images they produce. They don't often carry a set of red/green/blue filters in order to produce 'natural-looking' photographs for the benefit of human vision. SteveBaker (talk) 04:55, 28 October 2008 (UTC)[reply]
Aren't we exaggerating the darkness for the outer planets here? Lux tells me there is about 32000 to 130000 lux (but why that range?) in direct sunlight on the Earth and 100 lux in an overcast day, or 50 in a living room. I can see colours in an overcast day, and also inside rooms. That's a factor of about 600 at best, so I would expect to see Uranus and Neptune's colours. If I read lux right, 100 lux would be one hundred candles just one metre away. That seems plenty bright. One candle a metre away (one lux, or the Sun on a planet 178 Astronomical units away) might be the threshold limit. -84user (talk) 21:56, 28 October 2008 (UTC)[reply]
Answering the questions about cameras... From what I've seen - and I am not an expert - all of the probes we've sent out have used black and white cameras. That is actually a bit vague. They can see more than visible light. They can take infrared and ultraviolet photos as well. Filters are used to limit the bandwidth of electromagnetic energy that is collected by the camera. With a set of photos from different filters, it is possible to create a true color photo of what something would look like if it had the same amount of light as we have here on Earth. That is not what normally is produced. Instead, a false-color photo is created. For example, there is a very famous photo of the Horsehead Nebula. Because so many people have seen it, they assume that the colors in that photo are the colors from the nebula. If memory serves, the colors in that photo were created by using one color for oxygen content, one color for hydrogen content, and one color for something else. But, the point of this is not to say that all those photos are fake. They are great photos for what the purpose they are created. Scientists don't care what shade of blue a certain ring around Saturn may be. They want detail about what is in the ring. A false color image created from infrared and filtered snapshots may produce the best visual representation for that purpose. -- kainaw™12:12, 28 October 2008 (UTC)[reply]
A color camera needs three sensors per pixel and a lens that is a compromise design that avoids chromatic aberration. Using a monochrome camera that's sensitive to a broad range of frequencies - with optical filters to narrow that range where required means that you can have a higher resolution, better-focussed, more sensitive AND more flexible design than if you have to compromise the design to be able to capture red, green and blue (or possibly, three different frequencies of infrared, five frequencies of visible light and two more of ultraviolet) simultaneously. A set of filters with a little motor to select which one is in front of the camera is a MUCH more effective design. The only reason you'd want to capture several frequencies at once (like a domestic digital camera) is to get a snapshot of a fast-moving target...but it's rare to need to do that on deep-space missions because everything happens so slowly. Furthermore, because the on-board storage capacity of the spacecraft's computers is limited and the rate that data can be sent back to Earth is HORRIBLY limited - you can't waste storage and bandwidth capturing data that isn't strictly required to meet the scientific goals of the mission. Routinely sending back red/green/blue data is wasteful. SteveBaker (talk) 13:19, 28 October 2008 (UTC)[reply]
Mine is a pinkish-brown color, but its really hard to see without a mirror, or a friend who I trust a WHOLE lot... oh, wait, you meant... OH, never mind... --Jayron32.talk.contribs12:32, 28 October 2008 (UTC)[reply]
By when i get deep into atmospheric layer, does this mean to interior or to space. You said for gas giants for Saturn, Uranus, and Neptune I will see it almost black until I get into atmospheric layer. The clouds scatter some light waves, same as Earth, I thought Earth would look dark blue until I get close to it it will lighten, if I get closer to Saturn, Uranus, and Neptune, by actually diving in atmospheric layer like I'm in their mesosperic layer will they have mix colors between blue, purple, and gray-is that the color of mehtane. Would true color for Mercury and Venus be almost white from space. Mars can look brownish orange sometimes, and the sky I will say close to brown since the atmospheric is much thinner.--Freewayguy22:52, 28 October 2008 (UTC)[reply]
What you mean by low light, Saturn, URanus, and Neptune have a methane haze, though so the disc color would be like between blue, purple, and gray, and the sky close to it is something like this. Lower level, perhaps differ colors. I though sky don't blacken until we get to molecular interior, the next bound. What you mean by "Low light"--Freewayguy22:55, 28 October 2008 (UTC)[reply]
If I bring a flashlight would I see mix shade of blue, purple and gray color, becasue of it's gas. For Mars sky I beleive is closer to brown, sooner up it darkens and darken, until 100 m above it appears nearly black. Mars' atmosph is so thin, it won't be able to scatter as much light wave and Venus and Earth does. Would Venus sky be pale yellow seen from surface and the globe look almost white?--Freewayguy00:01, 29 October 2008 (UTC)[reply]
Can you answer this quickly. Planet itself can't be black either, just loks black for few miles away. That's Pluto and Charon, 3 times further than Uranus. It's ground would look almost black--Freewayguy00:43, 29 October 2008 (UTC)[reply]
A friend said recently his mother - who had Alzheimer's before she died - "thought it was her wedding day each day in her last months." A sweet way to go, to be sure.
In reading the Alzheimer's article I think I understand why - flashbulb memory connected with the fact emotions do seem to be recalled, even in the latter stages of Alzheimer's. My question is: 1. is minea correct presumption; and, 2. If so, how does this explain the person who thinks something more mundane is taking place. For instance, I have heard of non-Alzheimers patients who have thought they were in their home, when in fact they were in a nursing home thousands of miles away. (And, with no reminder of home, i.e.: an old picture that was always sitting out.) But, it is not as if anything special is "going on" for them at that moment. Or, could this be an entirely different part of the brain being triggered when that happens?Somebody or his brother (talk) 23:14, 27 October 2008 (UTC)[reply]
I think the only accurate response to your question is: "we don't know". Its a fair hypothesis though. When the neurons in the brain die during the progression of the disease, those that would normally wire together to form what we can consider to be a "memory unit" may become disrupted. But, as the Hebbian theory goes, "those that fire together, wire together". The neurons that are left are now misfiring, and they are likely to form synapses with other neurons. So neurons that, for example, "store" the memories of your wedding day could get wired up the the neurons that one uses to "store" short term memory. The result is that the person with dementia, almost literally, gets their wires crossed and recalls inappropriate memories in response to mundane cues. It seems intuitive that the "special" flashbulb memories would be the most persistent, and this is why they seem to survive until the end. But its also possible that there is some kind of recording bias. Memories that are meaningful to the caregiver are the most likely to be documented among the jumble of minor memories the person with dementia may recall each day. Its also comforting to think the sufferer is re-living happy times, and so there is a type of positive re-enforcement in the caregiver believing this. Either way, if significant memories really do persist more than other less significant memories, how and why is unknown. Rockpocket08:06, 28 October 2008 (UTC)[reply]
October 28
Alcohol consumption strange side-effects
Hello, all!
I have volunteered and worked with person(s) who have various severities of alcoholism, from merely excessive to outright insane levels of consumption.
I was curious if someone could explain some of the stranger side effects I have witnessed:
1. Brightening of colors -- White colors becoming blinding, yellow becomes white, confusion of black/blue or yellow/green, etc.
2. Having nonexistant conversations -- with people whom are not speaking, or, thinking there is someone in the room speaking to them when there is not. Not a delusion - the person, even when confronted, thinks there is someone talking to them.
3. The ability to drink a large amount of alcohol (1/5 of vodka, etc.), and, in a relatively short amount of time (1 hr.), the person is relatively sober and able to pass a breathalyzer test (.08 BAC). I was under the impression that this is physically/anatomically impossible.
4. Blindness that fades in and out, however, the person remains able to speak clearly without slurred speech and has generally unaffected motor skills.
5. Phantom-limb type symptoms (w/ people who have lost limbs), but only when heavily inebriated.
3. This is not physically impossible for people who regularly consume large amounts of alcohol. Their bodies will eventually become adapted to higher than normal BAC levels and will metabolize alcohol faster, allowing them to consume larger amounts without actually intoxicating themselves. Unfortunately, in order to achieve intoxication, they must drink larger and larger amounts of alcohol, which really damages their livers.CalamusFortis04:09, 28 October 2008 (UTC)[reply]
Also - (for #3) it takes a while for the alcohol in the stomach to make it into the blood stream - and from there into the lungs so it'll show up on the breath tester. Over a very short period, I guess it's just about possible.
For all of the other symptoms: Cell membranes can't block Ethanol - so it can attack any cell in the body. Hence, a huge range of side-effects are possible. Heavy drinkers that have varieties of liver problems will suffer another huge range of symptoms from whatever toxins are in their bodies that a healthy person could metabolise without side-effects - but their broken livers are unable to get rid of fast enough. So the consequences for heavy drinkers go beyond the primary effects of the alcohol and into secondary effects that could be due to medications or other things in their diet that would ordinarily be no problem for a healthy person.
But anyone who's ever had more than a couple of drinks in their lives knows that alcohol screws with your brain...once someones brain is screwed - you shouldn't be at all surprised at all of the blindness, bizarre vision issues, phantom limb stuff and auditory hallucinations. It's like you're taking this very large, delicate and super-sophisticated computer and smashing random bits of it with a hammer...the result is entirely predictable...the computer starts to break down. Precisely HOW it breaks down is a lot less predictable. Brains are massively parallel machines so they don't have a single point of failure. So instead of 'crashing' like your PC probably does when you smash it with a hammer - the brain merely generates incorrect results. Since the ethanol is attacking the entire brain at once - it's impossible to predict which bits are going to break first - or what the consequences will be. So for some people - the vision system gets hit - for others it's the nervous system - for others it's memory or hallucinations or insomnia or hypersomnia. Once the brain is broken somewhere at random, almost anything is possible. SteveBaker (talk) 04:29, 28 October 2008 (UTC)[reply]
..and there is no irreversible equilibrium state in which the properties of all matter and energy are either fixed or in a repeating loop, then logic suggests that any event that could possibly happen will happen an infinite number of times.
(edit conflict) It seems to me the phrase "any event that could possibly happen" is ambiguous. Do you intend this just to mean it is possible to imagine an event happening, or does it mean something stronger than that?
For example, it is possible to imagine a streetcar plunging into the Grand Canyon. However, unless there are streetcar tracks very close to the rim, I suspect it won't happen.
I think the statement as it stands is incorrect, that a lot more things "could possibly happen" than actually do happen. CBHA (talk) 04:40, 28 October 2008 (UTC) (More philosophy than science, ISTM.)
I highly suggest that we don't address this question here. It should be addressed on the science reference desk. Magog the Ogre (talk) 04:45, 28 October 2008 (UTC)
I'll give it a try out there. I guess the purpose of the question is to make you test just how big your minds concept of "infinity" is. Even though there is no logical reason that a streetcar's tracks would lead into a 'Grand Canyon', the very concept of "dividing infinity", to me, always meant that regardless of how small the chance of something is (like for example, atoms with identical properties reforming an infinite number of exact replicas of earth) will happen an infinite number of times in the universe I described.NByz (talk) 06:52, 28 October 2008 (UTC)
I moved this from the misc. desk. I am interested in articles about this type of thinking. Or people shooting it down with better logic.NByz (talk) 06:56, 28 October 2008 (UTC)[reply]
Even in a finite time period in a finite region of space, any event that could possibly happen...could happen. But that says nothing of what will happen. You run into an issue of our own universe. Depending on the ultimate fate of the Universe, and assuming the universe is finite in extent, then not everything may happen. If the universe hits an abrupt end somewhere, then time is finite, and not everything will happen. If the universe is inifinite but suffers heat death or explosive expansion, then the probability of certain events will shrink even closer to zero as time proceeds, and so the infinite time integral of a certain event's probability may still be close to zero. But under certain scenarios, including that the universe is infinite in extent, then yes, it would certainly seem the case that anything that can happen, since it can happen anywhere with some probability, has a probability of 1 of happening somewhere. Your chance of witnessing it may still be close to 0 if it is something dramatically unlikely, like a grand piano appearing out of thin air. For further reading, you may be interested in boltzmann brain and quantum immortality, the latter being on a supposed consquence of the (perhaps) infinitely many, and completely encompassing many-worlds. Someguy1221 (talk) 07:06, 28 October 2008 (UTC)[reply]
Those were cool articles. I guess we'd have to alter some of the assumptions about the universe in order to suggest my conclusion. I'm thinking that this hypothetical universe had no tendency towards entropy, and no eventual state of repetition or 'boredom'; there is always the potential for something to change (but not in some repeating loop or in some way that it has before), but not to the point where each 'state' of the universe was stochastic. Doesn't the fact that 1) something will change between this state of the universe and the next, 2) that the change won't be repetitive (everything isn't just clumping up, or spreading out) and 3) time is infinite mean that, no matter how many units of matter and energy exist in the universe, they will eventually be arranged in every conceivable way?NByz (talk) 08:00, 28 October 2008 (UTC)[reply]
Every way that is reachable from the initial state under the laws of physics, maybe. It may be possible that there are two states which can't be reached from each other without violating the laws of physics - a mathematician would say that the action of the laws of physics on the state of the universe isn't transitive. Of course, those assumptions don't fit with our universe, so this discussion is entirely academic. --Tango (talk) 11:44, 28 October 2008 (UTC)[reply]
Even if time is infinite - it's still likely that it will settle into an eventual steady-state after which no further change will ever happen again. So in the case of the streetcar plunging into the grand canyon - it plunges once, smashes into a million pieces and then stays like that until the Earth is destroyed, the Sun fizzles out, the galaxy collapses into a black hole, the progress of the expansion of space and the demands of entropy cause everything to turn into a uniform, cold sea of particles. That state could then persist off into the infinite future with no possibility of new earths and new streetcars ever being formed, however long you wait. That would imply that we were in the cosmologically brief period between the big bang and the infinite, boring nothingness - and the number of streetcars falling into grand canyons could be completely finite - even utterly unique. Entropy is a harsh mistress.
However, if space is infinite, then it can also be fairly similar everywhere - and in THAT case, every event in every possible variation will happen an infinite number of times as out OP suspects - until the universe changes (due to entropy) into a state where that event is no longer supportable anywhere. SteveBaker (talk) 12:56, 28 October 2008 (UTC)[reply]
It also matters what you mean by "infinite". There are lots of kinds of "infinity". For example, the integers is an infinite set. So aren't the numbers between 1 and 2. However, one is a countable infinity, which allows progress towards the infinite "end". I can get farther along that number line, and can move between defined points on it in a meaningful way, even though the line is a defined infinity. There are also an infinite number of numbers between 1 and 2, and if one were to scrupulously define them all, it would be impossible to make progress. You can't even get to the next 0.1 or 0.01 or 0.001 because there are always an infinite number of finer divisions you can make. This is still infinity, but its not a countable infinity. The problem arises when the two types of infinity are conflated. Tbe classic example of this is Zeno's paradox, which states that motion is impossible because there are always an infinite number of divisions one has to move through to get anywhere, and each of those divisions should take some measureable time to pass through. There seems to be some very "Zeno-like" paradoxes going on in this discussion, and it's why its not getting anywhere. --Jayron32.talk.contribs13:16, 28 October 2008 (UTC)[reply]
What you are saying is true - there are indeed many flavors of infinity - but here we're talking specifically of infinite time or infinite space (or both) - and those are countably infinite in the same way that there are infinite numbers of integers. To express it your way, travelling through space or the progression of time is "progress towards the infinite 'end'" - not the infinite subdivision of a finite bound. Given that this is all we're interested in - I don't see the relevance of your comment and the discussion is working out just fine.
As for Zeno's paradox - it doesn't seem at all paradoxical to me - the finer you slice the distance between Achilles and the tortoise - the smaller the time interval required to cross it. As soon as you slice the distance Achilles has to cross into infinitely many pieces - you reduce the time taken to cross each piece to 1/infinity - which means that you wind up with infinity/infinity as the time it takes to get there...but infinity/infinity is mathematically undefined - it's certainly not necessarily infinite - and in this case, it's most definitely not infinite. Since you can't evaluate that expression - you can't say that Achilles can never catch the tortoise - nor that he can. All you've done is come up with a bizarre formulation for the math that simply isn't the right way to solve the problem. You can take any perfectly sensible question ("What is 2+2?") and screw with the math to come up with a variation that involves various infinities that you can't solve. Is that paradoxical or just the results of the ravings of someone who doesn't understand much math? "What is 2+2?" Well, that's just 2+(2/2 + 2/2) which is just 2+((2/4+2/4)+(2/4+2/4)) which is just 2+(((2/8+....+2/8)))...which I can carry on subdividing into an infinite number of terms. Then I can argue that since we have to add up an infinite number of non-zero terms - the value of 2+2 is infinite...well, that's flat out not true - you have to add up an infinite number of terms EACH OF WHICH is 1/infinity...so you can't solve "What is 2+2?" this way. There are an infinite number of ways I can fail to solve that. x=2+2 ...hmmm...suppose I add infinity to both sides of the equation x+infinity=2+2+infinity=infinity...oh - darn - I can't solve that...therefore there is an exciting paradox that people should still be talking about thousands of years from now!?! It's a bloody stupid argument - yet it's identical to the Zeno "paradox". Zeno's paradox confuses philosophers - but then they are easily confused. Mathematicians and scientists just say "Well - that was a bloody stupid way to calculate when Achilles will catch the tortoise - let's just use the normal laws of motion - express Achilles' position as (velocity x time) - express the tortoise's position the same way - then we have two equations and two unknowns - which we can easily solve to get a perfectly reasonable, finite, time. Ergo the philosphers are wrong - which is no surprise because they are all a pretty useless bunch. Where is this paradox? Philosophers are a waste of space - fuzzy thinking turned into an art form!
A bit unfair, Steve. We have the benefit of twenty-four centuries of work after Zeno, some of it arguably motivated specifically by him. No, Zeno's paradoxes are not particularly paradoxical, once you understand the real numbers, but they weren't really understood until the work of Dedekind and Cauchy and Weierstrass, less than two hundred years ago. Zeno's arguments do ably refute certain views of space, time, and the infinite, that might have been reasonable to hold at the time.
This is what philosophical paradoxes do best; they're not for explaining around the lava lamp so people can say "heavy, man"; they're for showing why certain otherwise reasonable positions have problems. Another good example is the Russell paradox, which lots of people take the wrong message from. The right lesson is that one has to distinguish between the extensional or combinatorial notion of set from the intensional notion of class (or extension of a definable property). That's what we do, these days, working in the von Neumann universe, but this was not clear even to Georg Cantor, though some of his writings can be read, after the fact, as prefiguring it. --Trovatore (talk) 08:50, 29 October 2008 (UTC)[reply]
Russell's paradox is not quite the same thing. Firstly, Russell was a mathematician AND a logician AND a philosopher. I'd argue that he didn't have his philosopher's hat on on the day he came up with the paradox - however, that's a separate matter. Secondly - this paradox is broadly the same as the Barber's paradox (which some suggest Russell invented in order to explain his set-theory paradox to the layman). These non-mathematical versions of the paradox are pretty easy to dismiss. The simplest solution is just that the statement of the paradox is wrong. "Everything I say is a lie" is simply not true...some things I say are lies, some things aren't - this happens to be one of the ones that's a lie. So it's hard to see a paradox in a statement that's just obviously false to begin with. All that happened was that the person stating the paradox said something which isn't true - and forced it upon us by stating it as an axiom in the framing of the question. It's the same deal with the barber who "shaves only those who does not shave themselves"...NO HE DOESN'T because that's simply impossible...we know that he shaves at least one person who shaves himself...so we can prove that the question itself is wrong - and therefore no answer is required of us. All you've done there is the logical equivalent of saying "It is axiomatic that 0=1 ... oh wow! Look what bizarre things just happened to all of my logic."...well DUH...if you make an axiom out of something nonsensical then you're bound to wind up with a nonsensical answer! So the existence of a "set of all sets that do not contain themselves" cannot be axiomatic in any self-consistent system - and you certainly can't derive a proof of the existence of such a set because it clearly can't exist in any halfway reasonable logical system. That's not exactly a paradox - it's a choice of axiom that doesn't match the way the real universe works and therefore produces counter-intuitive results. The cleanest take on this self-referential paradox issue is Godel's incompleteness theorem. It assures us that we can't have 100% self-consistent logical systems with sufficient complexity to do interesting math - and it does it without introducing new axioms. So the INTERESTING part of all this (the fundamental incompleteness of all sophisticated logical systems) is most definitely something that springs from mathematics - not from philosophy's "paradoxes" which are generally quite easy to dismiss using a small amount of clear thinking. SteveBaker (talk) 21:12, 29 October 2008 (UTC)[reply]
I'm afraid you're missing the point a little bit, probably because you don't know the history of the problem. What happened was that Gottlob Frege had proposed a system that he wanted to use to reduce mathematics to logic alone, based (he thought) on Cantor's set theory (though later writers such as Wang Hao have argued that Frege got Cantor wrong). Frege's system (which by the way was completely formalized, not "naive" in the sense that is sometimes suggested) identified sets (collections of objects) with extensions of (presumably definable) properties, and proposed that for every definable property, there was a set that was its extension. He certainly did not propose as an axiom that there was a set of all sets not containing themselves; that was simply a consequence.
It was a reasonable thing to try at the time. You're right, of course, that it was wrong. But it wasn't obvious that it was wrong. It took the paradox to show it.
One last aside — the bit about Gödel isn't quite right. It's perfectly possible to have "100% self-consistent logical systems" that do interesting math, and (we believe) we do have them. It's just that (subject to some technical stipulations) they'll never be able to settle all questions that you might ask. Therefore mathematical truth cannot be identified with provability. --Trovatore (talk) 21:47, 29 October 2008 (UTC)[reply]
Nice Post! I guess, in summary, I had to make too many unrealistic assumptions above to avoid an eventual "steady state", or to include infinite random fluctuations in the universe. It was meant to make you really think about how "big infinity is" and I think (after reading your post, especially!) that the concepts of "big" and "counting" can never really apply to ideas like this (in my hypothetical universe). Frankly, I've always felt that the whole concept of "discreteness" was a human illusion derived from the way we've developed problem-solving skills over our formative generations.NByz (talk) 18:29, 28 October 2008 (UTC)[reply]
The cause of the paradox is the assumption that doing an infinite number of tasks is impossible. However, there is absolutely no reason to make that assumption, philosophers like to make things up without any regard for whether they actually fit observation - as you say, they are a waste of space. --Tango (talk) 15:06, 28 October 2008 (UTC)[reply]
"Even if time is infinite - it's still likely that it will settle into an eventual steady-state after which no further change will ever happen again." — Steve Baker
No large scale change. There are likely to still be individual particles and photons moving around, but on the whole nothing will be changing. --Tango (talk) 16:18, 28 October 2008 (UTC)[reply]
Well - if you take that view - then the OP is correct. Even if there is hardly any motion left - if there is just SOME motion left then eventually (and we have infinite time) an extraordinary coincidence will result in an entire galaxy just like ours forming by sheer unlikely statistical luck - and the street car can crash into the grand canyon again (although it may be painted a slightly different shade of red this time around). Infinity leaves plenty of time for that to happen - however unlikely it is. For what I said to be true (and I still believe it), there has to be a time in the FINITE future when literally the last erg of energy is gone from the entire universe. That's a reasonable assumption because entropy drives things relentlessly in that direction. If Axl chooses to characterise that as time 'ending' or 'stopping' - then I guess that's a position one could take - but I don't see why you can't see it as time continuing along but with no change to measure its passage. However, since we can reasonably assume that the universe is spatially infinite - then the streetcar will smash into the grand canyon an infinite number of times while my finger was pushing down on the last period in this sentence. SteveBaker (talk) 18:26, 29 October 2008 (UTC)[reply]
Just looking for the cheapest way to set up an oscillating reaction for part of my halloween costume. The only one I know of is the Briggs-Rauscher, which is pretty, but expensive to make.
I'm a fidgeter. I seem incapable of sitting still, i'm always bouncing my legs or fiddling with things with my hands, tapping stuff, reposition myself etc. etc. (i know i'm a joy to be near). I'm also slim, naturally slim, and naturally quite fit. Question: How much calories does 'fidgetting' burn. Is it very little or would it be enough to say, i dunno, account for eating a bag of crisps or a chocolate bar? Also whenever i do stuff I do it 'quickly', be it going to the kitchen to get a drink, walking, typing, whatever, is that also likely to increase calorie consumption V someone who does these things more slowly? (Hope not too stupid a question) 194.221.133.226 (talk) 11:45, 28 October 2008 (UTC)[reply]
I don't think fidgeting affects calorie consumption in a major way. Muscles just don't burn calories at all that high a rate unless they are engaged in real activity. Speed of activity can change calorie consumption—a slow walk does not burn as much as a brisk walk. (ergo "power walking"). --98.217.8.46 (talk) 12:00, 28 October 2008 (UTC)[reply]
You can run for a mile on the energy from one sugar cube. This is very depressing and seriously discourages me from doing enough exercise. SteveBaker (talk) 18:16, 29 October 2008 (UTC)[reply]
???? According to [6] there are 25 calories in a sugar cube. According to [7] running a mile uses 100-125 calories depending on your sex and weight. That's 4-5 times the energy of a sugar cube. Exxolon (talk) 20:37, 29 October 2008 (UTC)[reply]
Are there any planned missions to put a satellite around the moon with the resolution great enough to see the Apollo landers?
Are there any planned missions to put a satellite around the moon with enough resolution to see the Apollo landers? Just wondering how soon we can finally put those Apollo hoax conspiracy theories to rest. 12.10.248.51 (talk) 17:03, 28 October 2008 (UTC)[reply]
From Lunar Reconnaissance Orbiter: "...will fly several times over the historic Apollo lunar landing sites, with the camera's high resolution, the lunar rovers and Lunar Module descent stages and their respective shadows will be clearly visible". Gandalf61 (talk) 17:10, 28 October 2008 (UTC)[reply]
See also the Indian craft, Chandrayaan, recently launched, with a 5m resolution, to be followed by the rover mission Chandrayaan II in 2009.
The conspiracy theorists will simple state that the photo evidence is doctored/faked. Short of taking every single conspiracy theorist to the moon there's no solution to the conspiracy (and even then they'd find a way..."it's possible now, but it wasn't then - the materials here were planted in preparation for the trip" etc. etc.). It's a no win situation, they'll carry on being deluded for the rest of their days regardless of any new evidence (there is already ample evidence to show the landings did occur as far as I and many millions of others are concerned). ny156uk (talk) 17:17, 28 October 2008 (UTC)[reply]
As noted, the believers in most conspiracy theories, including the Apollo Hoax conspiracy, believe in the existence of the conspiracy as an a priori fact. They opperate on the assumption that the conspiracy is true, and then all evidence is interpreted based on the belief that it must fit the conspiracy, and not the other way around. Any "proof" of the missions will be discarded or adapted to further prove the conspiracy, not disprove it. A wise man once said "You cannot reason a man out of a conclusion he did not arrive at by reason himself"... --Jayron32.talk.contribs17:22, 28 October 2008 (UTC)[reply]
OK, are there any planned missions to put a satellite around the moon with the resolution great enough to see the Apollo landers NOT BY NASA? Presumably, Russia, China and India would have an interest in exposing the hoax. 12.10.248.51 (talk) 17:57, 28 October 2008 (UTC)[reply]
See the previous response. --Anon, 18:10 UTC, October 28, 2008.
But there is no hoax to expose. The people in charge of the Russian, Chinese and Indian space programs aren't stupid, so they know that. --Tango (talk) 18:20, 28 October 2008 (UTC)[reply]
They are all leftist commie countries. Of course they support the Big Government lies! Who do you think got Kennedy to fund the so-called "space program", and where did that money go? And why is China doing so well now? Makes you wonder... --Demosthenes 18:25, 28 October 2008 (UTC)
It's pretty irrelevent whether they would or would not like to see the hoax debunked - nobody is going to spend all that money just to prove that a few lunatics are...well...lunatics. But no matter what you do - the conspiracy theorists will twist it to their needs. If Russia photographed the landing site - then this would just mean that the Russians have something to hide also! There are actually three distinct groups of conspiracy nuts surrounding the Apollo missions.
Those who believe that neither we nor any robotic missions have ever gotten out of Earth orbit.
Those who believe that robotic landers have sucessfully reached the moon and/or mars - possibly including a robotic "lunar lander" and "moon buggy" identical in design to the Apollo missions - and that would be what this upcoming mission will be photographing (in their view).
Those who believe that only the first couple of moon missions were faked and that the later ones were real.
So even a 100% convincing demonstration that there really are a bunch of lunar landers on the moon could only impress the first group...but they won't be convinced that these photos haven't been faked anyway. Since over 20% of Americans believe it was all a hoax (at least that's less than the 65% who believe the "face" on Mars is 'real' and was constructed by aliens) - there is quite enough room for a large range of sub-conspiracies. SteveBaker (talk) 18:44, 28 October 2008 (UTC)[reply]
BTW, the face on Mars isn't quite as looney as the Apollo hoax conspiracy theory. After all, if I were a civilization living on a dying planet, a giant rock sculpture that can be seen from space might be the way I might try to preserve some record of our civilization and to say to the universe, "We existed.". 12.10.248.51 (talk) 20:02, 28 October 2008 (UTC)[reply]
I once met someone who (it seemed, genuinely) believed that the *moon itself* is a hoax. He claimed that the moonlike object we see in the night sky is at most 'a couple of hundred miles away' and was built by the Nazis in the 1940s as some sort of orbital surveillance platform (later taken over jointly by US and Soviet secret services). Any prior historical references to a moon could easily be attributed to intentional falsification of documentation and the doctoring of photographs.
Omphalos (theology) describes the reasoning that if the Garden of Eden contained fossils and trees with tree rings inside on the day it was created, implying a nonexistent long previous period of existence, then the world could have been created last Thursday complete with eroded mountains and 6 billion people with artificial memories of the preceding Wednesday. Put THAT in your tinfoil hat and smoke it. Edison (talk) 23:27, 28 October 2008 (UTC)[reply]
Fossils? They're the work of Marxist agitators, you know. Pesky blighters are trying to discredit and bring down Judeo-Christianity as a prelude to the revolution. A teacher at my school told us. So it must be true. --Kurt Shaped Box (talk) 23:43, 28 October 2008 (UTC)[reply]
Hey! Tamfang! I wanted to find out what such a comment should have ended with - but it looks like your modem lost carrier before you could tell us what it was. SteveBaker (talk) 03:13, 30 October 2008 (UTC)[reply]
For the most elaborately constructed bogus theory I know of - the Flat Earth Society is hard to beat. They were a serious group of people back in the 1940's - but when spacecraft started getting launched and contrary evidence became harder to deny - they kinda fizzled out and the society became a joke thing that people would join just for the silliness of it. However, they've recently had a major revival - their theories are extremely complex and really quite impressively clever. It takes some serious thinking to find ways to disprove their ravings. You're probably immediately going to think of a dozen ways to prove them wrong - but if you think you have a 'killer argument' - check their FAQ first - I can almost guarantee they've thought of an answer. SteveBaker (talk) 18:14, 29 October 2008 (UTC)[reply]
I recently got in the mail a pamphlet educating me on the great lie of heliocentricism that scientists have been perpetuating for all these years. APL (talk) 19:48, 29 October 2008 (UTC)[reply]
I was accosted in the town centre last year by a man who insisted on telling me, in a passionate and animated matter, about how Triclavianism was 'The Truth' which certain parties were trying to suppress for their own nefarious ends. He had pamphlets too. I took one, but binned it soon after. It leaves me shaking my head that people actually find this kind of thing important enough to worry and/or get upset about. Nothing wrong with taking a scholarly interest, if that's what you're into - but why the need to get all wild-eyed about it with strangers? Yes, I suspect that the answer is something along the lines of "Because they're cranks". --Kurt Shaped Box (talk) 22:26, 29 October 2008 (UTC)[reply]
There are a couple of things that the conspiracists use to discredit that experiment:
There are naturally reflective rocks on the moon - some of which are natural retro-reflectors. When NASA planned the fakery - they scanned the moon with lasers to find naturally reflective spots and chose those as the "landing sites" precisely so this experiment would work.
Many conspiracists do not deny the existance of robotic space missions - it would be fairly easy to land a craft on the moon with retroreflectors on it - hence these are no proof that humans have ever been there.
Some simply claim that all of the places that have bright enough lasers and powerful enough telescopes to do the experiment are operated by people who are in league with NASA - which means that they can fake it EASILY. The fact that they are willing to repeat the experiment for people like Mythbusters is further seen as proof that they are on a mission to squash the "truth tellers".
Waves changing a beach are both constructive and destructive at the same time, as sand is moved from one place and put in another place. The size of the waves determines where the destruction happens. When they are big or high (eg storm surge) they get to places that humans did not plan for and demolish their constructs, and are called destructive. Big waves carry much more energy too. Graeme Bartlett (talk) 20:47, 28 October 2008 (UTC)[reply]
A good place to look at Wikipedia for some of these answers is our article on Coastal erosion. For more details, the work of Orrin H. Pilkey is considered some of the best in the field. He has done some of the most extensive studies of beach erosion, especially with regards to barrier island migration. If Pilkey's work is too advanced, or not directly applicable to your question, another good place to look is in the textbook that your teacher gave you, or in your class notes that you wrote down on the day that your teacher talked about this subject. Cheers! --Jayron32.talk.contribs21:26, 28 October 2008 (UTC)[reply]
In detail, for water that's deeper than about 2 wave-lengths, the individual water molecules are moving around in big vertical circles. As the water gets shallower, there is no room left for the water to circulate like that - so the circular motion gets squashed into an ellipse. This affects the speed of the waves - slowing them down - so refraction of the water occurs...and this is why waves almost always come ashore parallel to the beach - no matter the angle of the beach to the deep-water waves. The slowing down also causes the waves to pile up - which results in the formation of rollers and breakers where the top of the wave is still trying to move at the same speed - while the deeper part is being slowed down by its interaction with the beach underneath. Hence the top of the wave gets ahead of the bottom - and the nice smooth sinusoidal wave gets pushed forwards so that its front is steeper than it's back. In the limit - this structure breaks apart - and that's where the surf comes from. When waves from different directions interfere - the consequences are just the classical 'sum of sine waves' interference patterns - but in three dimensions. The wind also has an effect - skewing the waves around.
You can produce rough simulations of this stuff in a computer very easily (I've done it - and the software is OpenSourced as one of the demos in the PLIB package). But these are only simulations of a generic kind. To calculate the precise shape of a real wave would be difficult because there are an enormous number of variables and much of the detail of the motion would be a consequence of turbulance and other chaotic effects that are literally impossible to calculate precisely.
obsidian, Pumice, Ryolite, Ash. What do these four things have in common? They all come from a volcano! Why they develop differently though, that's what I want to know. Why does cooling magma form 4 different types of stone. Especially obsidian.
Forai (talk) 22:43, 28 October 2008 (UTC)[reply]
We will not do your homework here. Try searching for the answers yourself by typing a key word or phrase (hint: "antibiotics") in the search box near the top left of this page. -- Tcncv (talk) 03:58, 29 October 2008 (UTC)[reply]
Please do not post in ALL CAPS because it is the equivalent of shouting. See the article Antibiotics which discusses side effects and misuses. For "who discovered antibiotics and how" see the History section of Antibiotics as well as Timeline of antibiotics and read about the various antibiotics, who discovered them , how, and when. Questions of "who discovered" something are often subjects of debate. There are many tentative and ultimately abandoned experiments before someone gets it right and comes up with a practical product. Edison (talk) 05:24, 29 October 2008 (UTC)[reply]
Well it was asked on another desk - and I suppose you could say it was answered (there were replies to the question) - but we didn't come up with any satisfactory (yet alone 'compehensive') answer...which is a shame - because I'd quite like to know too. However, I doubt there are many people who respond on the Science desk who don't also patrol the miscellaneous desk - so I doubt we'll get any further here. SteveBaker (talk) 17:23, 29 October 2008 (UTC)[reply]
I for one do not stalk the misc desk. Just because you seem to think you know everything, doesn't mean you can make such generalisations. With regards to the answer, Dmcq's answer actually sounds quite reasonable. Jdrewitt (talk) 07:52, 31 October 2008 (UTC)[reply]
Posting this here because it's the closest RD topic to engineering...
The bridge pictured to the side was badly damaged in flooding this summer, as is obvious; but how properly should the bridge be described? Destroyed, because obviously it can't be used? Or damaged, because 2/3 of the bridge is still there? I'm loth to use "destroyed" because most of it is there; "damaged", because that's not specific enough (after all, minor vandalism to a bridge can legitimately make it "damaged"); "washed out", because (at least to me) that conveys less than this bridge has sustained; and "irreperably damaged" because (aside from the fact that I probably spelled it wrongly) I suppose the state could come along and fix it back up again, so such a pronouncement would be crystalballish and perhaps OR-ish. What's the most accurate term of these, or is there a better? Nyttend (talk) 14:09, 29 October 2008 (UTC)[reply]
If you want to be more descriptive or specific then you'll need to think about phrases like "damaged by having one of three spans destroyed". Incidentally, I think you really needed the language desk because your problem is not one of engineering but of words - but hey, who's worrying. 86.4.187.55 (talk) 14:35, 29 October 2008 (UTC)[reply]
To say that the remaining 2/3s are "functional" is not necessarily accurate either. Any structure that has had a partial collapse may have other non-visible structural problems elsewhere. I would not assume that the standing pieces are "undamaged", they are just "less damaged" than the collapsed span. Nimur (talk) 17:05, 29 October 2008 (UTC)[reply]
Truly - this is neither a science nor an engineering question - it's linguistic - and it belongs on the language desk. I suppose - if forced to describe it - I'd say that one span was destroyed and the other two appear intact. "Damaged" works for me too - and since we didn't say how damaged, there is indeed considerable ambiguity between a small scratch on the commemorative plaque at one end of the scale - and just a small amount of the bridge remaining at the other. So "heavily damaged" might be a better choice. I suppose we really need a word like "incapacitated" ... "non-functional" maybe? But it's not science - nor yet engineering.
To quote (my hero)Richard Feynman who is talking about a walk through the park with his father when he was just a little kid:
" `See that bird?’ he says. ‘It’s a Spencer’s warbler. (I knew he didn’t know the real name.) ‘Well, in Italian, it’s a Chutto Lapittida. In Portuguese, it’s a Bom da Peida. In Chinese it’s a Chung-long-tah, and in Japanese it’s a Katano Takeda. You can know the name of that bird in all the languages of the world, but when you’re finished, you’ll know absolutely nothing whatever about the bird. You’ll only know about humans in different places, and what they call the bird. So let’s look at the bird and see what it’s doing - that’s what counts!' "
So - who cares whether the bridge is "damaged" or "destroyed"? That tells you nothing about the state of the bridge - but only how humans perceive it to be. The real issue - is how much will it cost to repair - and do we want to do that? SteveBaker (talk) 17:20, 29 October 2008 (UTC)[reply]
The reason I ask is that it's notable (on the National Register of Historic Places) and I think I'm going to write an article on it soon; and I was guessing that there might be some sort of specific term used to describe it for use in the article. The article will include this photo, so I'll not need just words. Nyttend (talk) 20:34, 29 October 2008 (UTC)[reply]
One of the more common ways of differentiating between "damaged" and "destroyed" is "Is it cheaper to repair it, or to tear it down and build a replacement?" If it's cheaper to repair, it's been damaged. If it's cheaper to replace, it's been destroyed. --Carnildo (talk) 23:35, 29 October 2008 (UTC)[reply]
But that dichotomy is rooted in the originally designed/intended function, not the thing itself. "The thing" is only damaged, not destroyed, until it's completely reduced to rubble. Rendered unusable as intended and unable to be repaired to such a state ≠ demolished. DMacks (talk) 01:34, 30 October 2008 (UTC)[reply]
Technically - I suppose - general relativity is SLIGHTLY involved - but that's a really silly, misleading and quite utterly useless answer.
For all practical purposes, the answer is "No". Straightforward gravity - per Sir Isaac Newton - suffice to explain the tides without mentioning general relativity. Science has known how tides work perfectly well - and has been able to calculate their properties for a hundred years before Einstein.
The gravity of the moon decreases with the square of the distance from it. Hence, the gravity on the side of the earth nearest the moon is slightly greater than over the rest of the planet - so water is pulled harder towards the moon on that side. It's actually a bit more complicated than that because there are actually TWO high tides - one on the side nearest the moon - and another on the side furthest from it. This is because the earth-moon system rotate around a common center of gravity that's not at the center of the earth - but a bit closer to the moon. If you imagine this pair of large objects spinning around a point somewhere between their centers - than you'll see that the part of the earth that's furthest from the moon is subject to some centrifugal force (yes, I know there is no such thing as centrifugal force - it's a handy shorthand and I have no compunctions in using the term in casual explanations). That centrifugal force throws the water on the side OPPOSITE to the moon outwards - hence there are TWO tidal bulges - one that is strongest when the moon is overhead - and the other that's strongest when the moon is directly below your feet. The daily rotation of the earth places the moon overhead and beneath the ground roughly twice per day - so the high tides are roughly 12 hours apart. In fact - because the entire earth-moon system rotates around it's center once a month, that means that there is actually one extra pair of tides every lunar month - so the interval isn't quite 12 hours. To throw some more complexity into the mix - the sun's gravity also produces tides - although not so strongly as the moon. So you get smaller solar tides added to the lunar ones. The combination of the two means that the strongest tides are when the sun and moon are close together in the sky at midday - or close together underground at midnight.
None of that explanation requires reference to general relativity - but doubtless there are TINY, MINISCULE effects due to relativity - which would be much too small to measure against the other properties of the ocean that can cause the tidal changes to be either more or less than you'd expect (eg the shape of the coastline - or the slight changes in the temperature of the water between summer and winter).
Hence the best answer to your question is a resounding "No" - although some pedants might like to say otherwise. To the pedants...please don't let pedantry get in the way of a clear and useful answer to a simple question.
Actually, the question was "Does the theory of general relativity explain ocean tides?" not "Is Newtonian physics good enough to explain ocean tides.". Anyway, it's all good. :) 12.10.248.51 (talk) 20:18, 29 October 2008 (UTC)[reply]
I don't understand your centrifugal-force explanation of the tide on the far side, and I think it's incorrect. The tide on the far side happens for the same reason as the tide on the near side: because things nearer the Moon are pulled more strongly. The water nearest the Moon gets pulled more than the Earth, so it separates slightly from the Earth; the water farthest from the Moon gets pulled less than the Earth, so it separates slightly from the Earth.
I'd never argue that general relativity is needed to explain the tides, but I might argue that the "philosophical framework" of general relativity is better for understanding the tides. In general relativity the gross acceleration of gravity is fictitious, just like the centrifugal force. When you're weightless, you're weightless; a gravitational acceleration you can't feel doesn't exist. The real gravitational field, i.e. what's left when you subtract out the fictitious part, turns out to be exactly the tidal force. (Not quite true, but close enough. I don't want to be pedantic...) The tidal force tries to "spaghettify" you, by stretching you parallel to the direction of the gravitating body and squeezing you in the perpendicular directions. So in general relativity it's very simple: the Earth is in freefall, and there's a tidal-force contribution from the Moon and another from the Sun. They both spaghettify the water, which is why they cause two high tides on opposite sides of the Earth and a ring of low tides in between. (Or would, anyway, if not for all the confounding factors mentioned in the tide article.) -- BenRG (talk) 23:36, 29 October 2008 (UTC)[reply]
The viscosity of sea water affects tides. It slows down the flow of sea water into the high tide regions on both sides of the earth. This makes high tides lower and low tides higher. Also, land masses deflect tidal current, causing variations in tidal height and timing. See "Tide" in Wikipedia.
Glassmaking kiln explosions?
Hi - I'm writing a scene where I need a disastrous explosion of a kiln in a sixteenth century glassmaking workshop - was such a thing possible? - if so, how?
The glassmakers of Wimpole Street were the best in the business - they've been commissioned to make an enormous glass snowglobe for a rich nobleman - it's a wedding present for his new wife who comes from Sweden and misses the snow terribly. It's 3 gallons of water enclosed in a two foot sphere of inch-thick glass - soon to be engraved with the nobleman's vows to his new wife (just as soon as they get that Swedish translator in). It's held in an delicate, ornately carved wooden frame that's perfectly weighted so the enormous globe is easy to turn over to make the snow fall. The glass blowers have been struggling to make it for months - there have been many attempts and many failures. It's the hardest thing they've ever had to produce. But finally they have something so perfectly round and amazingly clear that nobody has seen the likes of it before. They fill it up with water and fake snow (maybe some kind of wax-based concoction) and their top glass-guy is melting a small disk of glass into the very top to invisibly block the hole that they used to fill it through. His apprentice looks on at the most impressive object they've ever made - realising that he'll never again be in the presence of something so beautiful - despite it's deceptive simplicity. The glass plug is in place and is cooling off nicely when the klutzy apprentice rests his hand atop the globe. It's still pretty hot and he recoils in pain...trips and falls against the ornately carved (but flimsy) wooden frame. The frame snaps and the globe rolls slowly and ponderously towards the furnace while everyone looks on in horror - they don't have time to make another before the wedding day. They are all frozen to the spot as the globe wobbles on the edge of the kiln...then falls in. It doesn't break - the glass is too thick. But it's too hot inside the kiln and the globe is FAR too heavy to lift out with the tools they have. Try as they may, they can't get it back out again. The glass on the outside won't get hot enough to melt because the water inside is absorbing the heat and keeping it under 100 degC...until the water boils...then KABOOOOOOM!!!!! Glass, fake snow, steam and white-hot coals from the kiln go everywhere - most of the building is levelled by the explosion. The only person to survive (inevitably) is the klutzy apprentice who "learns a valuable lesson".
The big problem with that is that snowglobes weren't invented until the 1800's sometime...so no good for you. But maybe you can come up with something similar? SteveBaker (talk) 20:29, 29 October 2008 (UTC)[reply]
The glass makers may have used Sulphur (or brimstone) as pigmentation in the glass. To form a glass you need to rapidly quench a melt. So the Sulphur will need to be heated to above its melting point. Since Sulphur burns easily in air, it will have to be sealed in a container with the other glass constituents to prevent exposure to air. The vapour pressure of Sulphur is very high and so it is quite likely the container would explode! Since molten Sulphur is extremely flammable there will be quite an explosion and resulting fire. Jdrewitt (talk) 21:39, 29 October 2008 (UTC)[reply]
But sulphur boils at 444 degC - but glass doesn't melt until 1500 degC. How are you going to get even liquid sulphur into the liquid glass if it boils before you can get it in there? As our article Glass_production#Colors says - the Sulphur is added in the form of "iron polysulphides". It can't just be pure sulphur...no way! iron sulphides melt at temperatures similar to the glass - so they aren't going to do anything exciting in the kiln. SteveBaker (talk) 03:06, 30 October 2008 (UTC)[reply]
Sorry but you are incorrect. I have made plenty of chalcogenide glasses using pure elemental sulphur. I have also had a few ampoules explode! The fact that Sulphur boils at 444 degC is irrelevant, since once it has been melted it will react with the other glass constituents. These don't necessarily have to be in the liquid-state. Also, you mention "glass" melts at 1500 degC. This is a complete fallacy. It depends what glass composition you are talking about! Many glasses have melting temperatures much much lower than the temperature you are talking about. Jdrewitt (talk) 13:39, 30 October 2008 (UTC)[reply]
Just to clarify, the glass constituents, including elemental Sulphur are sealed in a container and heated, this could be done through a series of furnaces at different temperatures so to gradually raise the temperature. However, since the vapour pressure of Sulphur is very high, the pressure is too much and the container explodes, exposing the molten Sulphur to air, and any the other constituents. The Sulphur immediately ignites and destroys the glass workshop. Jdrewitt (talk) 08:02, 31 October 2008 (UTC)[reply]
Oh man, I'm already picking apart Steve's sphere explosion theory on his talk page. Do I have to go after this one too? Sigh. What size pressure vessel and how much elemental sulphur are they using? What other components are in the sealed vessel? When will people learn the simple answer - snow-globe technology was developed by the Picts and suppressed by the Knights Templar until Charles Dickens rediscovered it when he found The Pickwick Papers in a Welsh barrow. Franamax (talk) 09:23, 31 October 2008 (UTC)[reply]
Sorry but I'm not sure whether you're being flippant or serious. Which part of the theory do you disagree with. I don't expect you would need too much elemental sulphur to produce some nice colours. But it would need to be heated in a vessel since otherwise it would just react with the air. Other glass constituents? Well that depends what they are making but lets just go for a silica based glass but this is really not very important since its the vapour pressure of sulphur which will produce the explosion. I have made some sulphide glasses up to 3 g sealed in ampoules. If these are heated too quickly, the vapour pressure of the sulphur causes the ampoules to explode, violently. I have witnessed this and was glad I had appropriate shielding in place. Scaling this to an industrial scale and can easily envisage a large scale explosion. Jdrewitt (talk) 10:15, 31 October 2008 (UTC)[reply]
I'm being both flippant and serious, as usual. We're talking 160 lb. or so of glass, so it's going to be a lot of sulphur anyway. This glass needs to be extracted as a melt though, and shaped into a globe, right? - so it has to be an openable container at the very least. But why would you use a sealed container anyway - unless you knew you had to contain vapour pressure during the melt process, in which case you would use a freakin' big cast iron lid, because you already knew what happened when you did it with 3g of sulphur? Questions along that line is where I would start, then I would look at the vapour containment efficiency of the openable container to estimate at what point it would start venting gas. Then I'd go back to what you already said about how as the sulphur vapourized, it would begin reacting with the other solid components, and I would wonder about why the Renaissance glassmakers would be trying to use elemental sulphur instead of compounds with a better melt compatibility. I don't doubt what you're saying about vapour pressure of heated sulphur though, nor its reactivity - just trying to figure out how the glassmakers got killed. Franamax (talk) 10:35, 31 October 2008 (UTC)[reply]
Where does it say the glass makers are trying to make a globe? That was just SteveBaker's suggestion - which by the way I'm not very impressed with (but I think my impression is tainted by the fact that he told everyone that you can't make glass using elemental sulphur when you/I clearly can!) But anyway, I was thinking along the lines that they just want to make some coloured glass for some reason - any reason, the OP didn't specify. So they would heat up the consituents in their container to the melting point of Sulphur. When I speak of vapour pressure, I mean at its melting point. Sulphur has a very high vapour pressure at its melting point, see the article on Vapor_pressure to see what I mean. I'll try and find an article that actually states the vapour pressure of Sulphur. So anyway, the majority of Sulphur is still molten and will react with the other constituents while still molten. The reason I thought they might use elemental Sulphur is purely because I think it would be readily available. Jdrewitt (talk) 10:53, 31 October 2008 (UTC)[reply]
Oh yes, and the reason you need to contain the glass constituents is to prevent the sulphur reacting with the air. It would just burn if left in the open. Jdrewitt (talk) 11:05, 31 October 2008 (UTC)[reply]
(e/c) You're indented under the snow-globe, so I thought it was the same story :) There's still the issue of the need for an openable container, if they wanted to shape the glass - so what is the failure mode of the container? Now using elemental sulphur is a possibility, but wouldn't they then throw the sulphur into the melt at full temp? Some (or most) would burn off, but the molten part could be mixed in. Or heat the sulphur to molten in a container that could off-gas, then add the molten sulphur to the melt? But to get a uniform mix in the melt, seems to me it would be more practical to use a compound with a higher melt point, so as to be more compatible with the process. These are practical people after all. I'll go with your story, you just need to flesh it out a bit :) Personally, I think the easiest way to go is that rain built up on the roof, which collapsed and dumped cold water into the kiln - if we're talking 1500 C, that should make a nice mess. Franamax (talk) 11:24, 31 October 2008 (UTC)[reply]
And wouldn't you heap the other components on top of the sulphur to prevent it being exposed to air? And maybe heap some lime on top, or ash, or whatever will segregate from the melt, either top or bottom, to prevent air exposure during the melting process? Franamax (talk) 11:24, 31 October 2008 (UTC)[reply]
Many of your points are valid but I really don't care enough to make any further comment :) It's not my story after all, I agree it needs fleshing out but the OP can do that themself! I have provided a possible cause of an explosion in a glass making workshop and am not saying its the best explanation but it is possible nonetheless. Your water explanation would indeed be disastrous also. Jdrewitt (talk) 13:15, 31 October 2008 (UTC) P.S. I have adjusted the indentation of these posts.[reply]
Well, we've killed these people three different ways now, I guess that's enough - and the OP is happy. Another RefDesk question successfully beaten unto death! :) Franamax (talk) 13:37, 31 October 2008 (UTC)[reply]
See "Shattered" by Dick Francis [11] for a hint about what unannealed glass can do. An explosion involves potential energy suddenly released. Edison (talk) 04:31, 30 October 2008 (UTC)[reply]
I agree annealed glass can be very dangerous, but the OP is asking for an accident inside the kiln, which will be before the glass has been made. Maybe there is a chance that something could go wrong in the annealing kiln though, maybe if it is heated too quickly or something? Jdrewitt (talk) 10:21, 31 October 2008 (UTC)[reply]
Wouldn't a glassmaking workshop have a large supply of coal on hand? Perhaps they get careless with it, and somehow their coal store fills with explosive coal dust? This seems like rather a stretch. APL (talk) 05:14, 30 October 2008 (UTC)[reply]
Not sure about exploding, but you might be interested to know that in 1291 the city of Venice forced their famous glassmakers to move their workshops to the island of Murano because they feared the dangers of fire in their mostly wooden city.
All great stuff - I'm extremely grateful for the detail everyone - Steve Baker's story's fantastic - I might try a variation on that - not a snowglobe, but another waterfilled glass sphere - I love the sulphur and rain ideas too - will keep them for future use - thanks, all Adambrowne666 (talk) 11:39, 31 October 2008 (UTC)[reply]
If you're seriously going to go with it - you should probably take a spin over to my talk: page where User:Franamax and I were engaging in some side-discussions on the subject. It's certain that I didn't do any kind of math (bad, bad, bad!) in proposing the idea - and I got a lot wrong that Franamax can help to correct. A two foot sphere would contain around 20 gallons of water - not three - so we might want to go with a smaller sphere in order to give it a chance to explode before they can put out the fire in the kiln. Franamax has some convincing math that shows the kinds of pressure it would take to rupture a 1" thick sphere - and in retrospect, that may be WAY too thick. But I'm convinced that some variation on the numbers would correctly produce the kind of situation you need...at least to the degree necessary to convince 99% of the readers of your work! The business of snow globes not being invented for another 200 years is actually a nice thing you could weave into the story. These guys invented the snow globe - but the explosion resulting from the disaster kills all but the young apprentice - so the idea for making such things (along with the not-inconsiderable technology needed to make one this big) would have been lost in the explosion...not to be re-invented for another 200 years. So it's at least a consistent story - if not historically accurate. SteveBaker (talk) 18:45, 31 October 2008 (UTC)[reply]
Maximum visual acuity
In conventional optometry you increase visual acuity by correcting the curvature of the cornea, or by using glasses to bend the light in a similar manner. The upper limit on the visual acuity provided by these methods seems to be the exactness of the lens and the precision of the prescription, but I am wondering whether there is an upper-bound imposed by the density of receptors on the retina. Ignoring changes in the shape of the eye and assuming a perfect lens, what is the limit of human visual acuity? PlasticupT/C22:21, 29 October 2008 (UTC)[reply]
We have around 120 million 'rod' cells (and a lot fewer cones) so we can resolve brightness (but not color) at roughly 11,000 x 11,000 pixels - that's pretty amazingly good (consider that we think a 10 megapixel camera is pretty nifty - but we have two 120 megapixel devices in our heads!) - but we can actually do even better than that. The eyeball never stays precisely still - it's always moving around a teeny-tiny bit. This means that each of those 120 million detectors is able to sweep over a small area around the point it's nominally aimed at. By noticing how the brightness changes over time as the eyeball wobbles, we can get even more precision. The precise resolution is hard to deduce since it depends on complicated aspects of how the data is compressed and encoded in the layers of cells behind the retina and down the optic nerve. However, within a roughly 50x50 degree region that we can take in with a single glance - so we can resolve better than 16 arc-seconds when the lens is good. Color resolution is not so good - 4.5 million cone cells. But they are more concentrated in the center of the retina - perhaps 2,000x2,000 pixels. A pretty standard 4 Megapixel camera can do color about as well as we can - but our huge lead in brightness precision wipes that out in terms of image sharpness. SteveBaker (talk) 02:29, 1 November 2008 (UTC)[reply]
Proving that the moon exists to doubters
Is there a simple experiment that can be carried out at home, requiring no complex/expensive scientific equipment, that can conclusively prove that the moon, our moon, is in fact a genuine, bona-fide moon (in the 'celestial body' sense) - and not a man-made construct, floating above us, at most a couple of hundred miles away? --Kurt Shaped Box (talk) 22:34, 29 October 2008 (UTC)[reply]
Proof is a mathematical concept, there is no such thing in science. All you can do is collect evidence to support or oppose a theory. You then pick the theory that is most likely given the evidence. The fact that there is documented evidence of the moon existing before we developed the technology to create anything that would look like that is pretty conclusive. If anyone truly believes that the moon isn't real then they are basing their belief on something other than reason so no reasoned argument will ever persuade them. --Tango (talk) 23:15, 29 October 2008 (UTC)[reply]
If the moon were only a couple of hundred miles above the Earth, what are the chances that it would pass over your house every night? If you ever take a vacation you will notice that the moon is visible from all over the planet, and must therefore be very far away. PlasticupT/C23:19, 29 October 2008 (UTC)[reply]
That logic only works if you assume the Earth is large and round. ;-) But yeah, the fact the moon looks the same from two widely seperated vantage points is an argument for it being a great distance away. Dragons flight (talk) 23:26, 29 October 2008 (UTC)[reply]
The fact that it can be seen simultaneously by people in different places would take care of that objection -- and incidentally also provides a proof that the Earth is not flat, because which way up you see the Moon depends on your latitude. However, this really falls outside of the category of household experiments, because it requires long-distance communications. --Anonymous, 05:52 UTC, October 30, 2008.
I was going to give the parallax answer, but Theresa beat me to it. On the other hand, you don't even need that measurement to determine that the Moon is very far from the Earth. The equipment-free solution is to go outside and look up at the Moon. Wait five minutes, and look up at the Moon again. Notice how it's in the same place relative to the background stars? Any small body in low Earth orbit would have swept across the entire sky in that time. (For comparison, the International Space Station, orbiting at an altitude of rougly 400 km, completes one orbit of the Earth about every ninety minutes. Most folks would notice pretty readily if the Moon rose and set eight times over the course of a single evening.)
For more precision, one could use a camera to take pictures of the Moon on consecutive evenings. Measuring the movement of the Moon between images against the background stars would allow you to calculate its orbital period, and from that its altitude.
That only proves that the fusion reactors and anti-grav drives on the lunar station are able to keep it moving in such a way that it looks like it is far away. Dragons flight (talk) 23:59, 29 October 2008 (UTC)[reply]
My point, which obviously escaped you, is that if someone is already engaging in fantastical thinking to disbelieve in the moon then they are likely to invoke similar nonsense to counter any proof one might offer. Dragons flight (talk) 00:07, 30 October 2008 (UTC)[reply]
Probably the easiest proof that the Moon is large and far away is that the apparent size does not change over the course of the night. If the Moon is only 500 miles up and 4.3 miles across, then (assuming the Earth is 8000 miles in diameter) the apparent size should be about five times larger when the Moon's overhead than when it's on the horizon. Incidentally, this works regardless of if the Earth is flat or round, and doesn't require that either Einstein's or Newton's law of gravity be correct. --Carnildo (talk) 23:46, 29 October 2008 (UTC)[reply]
Tides. It takes a monumental amount of force to move a bajillion tons of water 10' vertically upwards. If the moon isn't really a chunk of matter 1/6th the size of the earth - then how do the tides happen precisely in sync with that white circle up there in the sky? So - no fancy hardware. A measuring stick - a beach and someone to watch where the "moon" is in the sky when the tide is at it's highest. QED. SteveBaker (talk) 02:44, 30 October 2008 (UTC)[reply]
1/6?! It's over 1/4 of the Earth's size by diameter, and under 1/80 by mass. --Anonymous, 05:53 UTC, October 30, 2008.
If the Moon's orbiting the Earth once per month at an altitude of 500 miles, you can't assume that gravity is behaving according to Newton, so the tides aren't proof of anything. --Carnildo (talk) 08:25, 30 October 2008 (UTC)[reply]
Occam's razor doesn't tell you to ignore evidence. In this case the evidence is overwhelming. Let me cut and paste:
“
THE MOON: RIDICULOUS LIBERAL MYTH
It amazes me that so many allegedly "educated" people have fallen so quickly and so hard for a fraudulent fabrication of such laughable proportions. The very idea that a gigantic ball of rock happens to orbit our planet, showing itself in neat, four-week cycles -- with the same side facing us all the time -- is ludicrous. Furthermore, it is an insult to common sense and a damnable affront to intellectual honesty and integrity. That people actually believe it is evidence that the liberals have wrested the last vestiges of control of our public school system from decent, God-fearing Americans (as if any further evidence was needed! Daddy's Roommate? God Almighty!)
Documentaries such as Enemy of the State have accurately portrayed the elaborate, byzantine network of surveillance satellites that the liberals have sent into space to spy on law-abiding Americans. Equipped with technology developed by Handgun Control, Inc., these satellites have the ability to detect firearms from hundreds of kilometers up. That's right, neighbors .. the next time you're out in the backyard exercising your Second Amendment rights, the liberals will see it! These satellites are sensitive enough to tell the difference between a Colt .45 and a .38 Special! And when they detect you with a firearm, their computers cross-reference the address to figure out your name, and then an enormous database housed at Berkeley is updated with information about you.
Of course, this all works fine during the day, but what about at night? Even the liberals can't control the rotation of the Earth to prevent nightfall from setting in (only Joshua was able to ask for that particular favor!) That's where the "moon" comes in. Powered by nuclear reactors, the "moon" is nothing more than an enormous balloon, emitting trillions of candlepower of gun-revealing light. Piloted by key members of the liberal community, the "moon" is strategically moved across the country, pointing out those who dare to make use of their God-given rights at night!
Yes, I know this probably sounds paranoid and preposterous, but consider this. Despite what the revisionist historians tell you, there is no mention of the "moon" anywhere in literature or historical documents -- anywhere -- before 1950. That is when it was initially launched. When President Josef Kennedy, at the State of the Union address, proclaimed "We choose to go to the moon", he may as well have said "We choose to go to the weather balloon." The subsequent faking of a "moon" landing on national TV was the first step in a long history of the erosion of our constitutional rights by leftists in this country. No longer can we hide from our government when the sun goes down.
Wow - so "The moving Moon went up the sky, And no where did abide: Softly she was going up, And a star or two beside." (Samuel Taylor Coleridge, The Rime of the Ancient Mariner) must refer to the launching of the "moon" - and since it's claimed (in those Liberal "public schools") that Coleridge died 120 years before the "moon" was launched in 1950 - we have proof that the school system is covering up for "big government". Since he's also claiming that one or two of the stars were launched on the same day - we have to wonder what other things are being looked at?! But "When I consider thy heavens, the work of thy fingers, the 'moon and the stars, which thou hast ordained..." comes from Psalm 8:3-4. This means that they even rewrote bits of the Bible! Is there no depths to which they will not sink? If we can't trust the bible then maybe the Theory of Evolution is true too! Where does the rabbit hole end? SteveBaker (talk) 18:27, 31 October 2008 (UTC)[reply]
October 30
Venus and Jupiter's true color
This is siad to be Venus true color is it close to white with faint yellow. If I was orbiting Jupiter will the planet look like a pearl, always playing with color. Seen from Saturn's low magnitude will Saturn still be around blueish silver if I was orbiting planet. If I was far away from the planet, it will look darker, if I was clser to planet, it looks brighter. if I was orbit one foot away from Uranus, it's methane gas will still give glows of violet color since it's magnitude is 5. For Neptune, it would be essentially dim, since the magnitude is 8, I beleive I will still see a dark indigo color when I am orbiting the planet since it have little light far away, for Pluto, and it's other dwarfs, the surface will look black, even if I stad on it--Freewayguy00:27, 30 October 2008 (UTC)[reply]
We discussed this stuff in some detail in your earlier question about Uranus's color. But what you are saying here is bogus. The 'magnitude' of an object depends on it's size as well as it's brightness. When you are up close to it - the size is irrelevant - so comparing the magnitude of these objects and using that to estimate surface brightness is pretty much meaningless. To do this right - compare the albedo divided square of the range of each of the objects from the sun. Do the comparison with the same numbers calculated for the Earth and you'll have a better idea of relative brightnesses from close to the planet. Both sets of data are available in the standardized info-boxes in the articles about each planet. SteveBaker (talk) 04:18, 30 October 2008 (UTC)[reply]
I don't think that you would see Pluto as black when you are on the surface, in the same way that the moon does not look black from earth, but a moon rock does when you have it on earth, and on the moon surface it looks bright grey. Pluto seems to be mostly an apricot colour. The light at Pluto may not be as dark as you think, instead it would be like an incandescent bulb, dim but still good enough to see colour. For Venus you are right it look white, you can see it with your own eyes. Graeme Bartlett (talk) 06:25, 30 October 2008 (UTC)[reply]
I've been to the moon-rock 'vault' at the NASA space center in Houston (it's open to visitors most days). You can see the actual moon rocks (LOTS of them!) in normal room lighting - and there is even one moon rock there that you can actually touch (although the surface of it is so covered with grease and dead human skin cells...I'm not sure you are actually getting in contact with it)! Those rocks are emphatically NOT black - they are mid-grey with very little color to them. So they match more or less what the moon looks like in the sky - with an albedo of 0.1 or so.
But here is the problem (and we talked about it before when the same OP asked about the color of Uranus): Human vision is a crappy way to measure brightness and color. We have eyes that adapt to the dark and to the very bright. So when you see Venus in a dark sky, it looks impossibly bright. But your dark-adapted eyes have shut down all of your color sensors and really wound up the "brightness" controls. So you can really only see in black and white and the fairly dim dot that is Venus is overloading the few 'pixels' in your retina because it's soaked in rhodopsin and the iris is wide open. This means that the light-sensitive cells that Venus impacts simply report "Ouch! Too bright!" and not much else. The atmosphere here on Earth is also scattering blue light due to the Raleigh and Mei scattering mechanisms...that leaches blue out of the image and further distorts any chance of getting good color information from distant objects. (Especially Venus which is only ever visible near the horizon where the atmospheric color distortions are greatest). Hence, Venus LOOKS white to the naked eye - an slightly yellowish in a telescope. When we fly a spacecraft up next to it or use the Hubble telescope - we don't have any of those annoying human visual wierdnesses - and the planet looks yellow.
So our OP asks "What color is it "really"?" - is it white or yellow?
Well, that's an utterly meaningless question. Humans can't even see yellow light properly - we don't have sensors for yellow light. We only notice it at all because it slightly stimulates our red and green sensors and we've decided to label that "red-and-green-together" sensation using the word "Yellow". However, small amounts of pure red and pure green light (such as you'd see in a photo of Venus on your computer screen) also appear "Yellow" - but for different reasons. If you stare for 30 seconds at a picture of the US (or British) flag - then look quickly over at a sheet of white paper, the paper "looks" like it has an orange and cyan flag hovering over it because our eyes have color-adapted to the strong reds and blues in the flag and take a few seconds to recover. So in orbit about Venus, our eyes would adapt to the colors and start to wash them out. So what we see and how the universe truly is are very different things - photos (either on photographic prints, or in CMYK magazine prints or RGB computer screens) have nothing like the range of colors that the planet actually has or that our eyes could potentially resolve (you simply cannot reproduce a really strong "cherry red" on a TV or computer screen for example). When NASA design a space probe - they need to capture specific data to determine chemical compositions, etc. So they may well decide to use a true yellow filter on their camera (so it really can tell the difference between a mixture or red and green light - which would appear dark - versus true yellow light - which would pass through the filter and look bright). So even the photo we took with a satellite is hopelessly "wrong" compared to what we'd see with our own eyes or with a more traditional RGB camera. Then it would depend on whether we needed to be dark-adapted to see it (in which case it would all be pretty much monochromatic) - or whether our eyes were overloaded by the brightness (in which case everything pretty much looks white). Hence it doesn't make a whole lot of sense to be asking about the "real" color of objects in space - where the lighting is so very different from here on Earth where our vision system evolved.
If you have two cars - an orange one and blue one. Park them out in the street. In daylight - they look orange and blue. At night (in the dark) they look light blue-ish grey and dark blue-ish grey. At night under sodium street lights - they look orange and black. At night under moonlight they look orange and blue again. If you have a weak-green sensor because you are mildly color-blind then the orange car looks red. If you have cataract surgery and lose the filtering ability of your corneas - then if the paint used on the orange car happens to be strongly reflective of UV for some reason and the blue car not so much so - and they both look to be different shades of blue in strong sunlight - but revert to orange and blue on cloudy days. If you stand 20 miles away from the cars and look at them through binoculars with the sun behind your back, the blue car looks darker than it did before and the orange car looks more pale - perhaps, almost yellow-ish. If you do the same thing with the sun in front of you then the blue car still looks darker but the orange car still looks even more intensely orange. What color are the cars "really"? Well, it's a meaningless question. By convention, we humans say that they are orange and blue because we have decided that normal daylight vision is what we're going to use to label the colors...but in space, there is no "normal daylight" - so that labelling scheme fails.
Hence questions about the "real" colors of planets are not ones we could (or should) answer - it falls into the realms of predictions and speculations. We should leave it up to the astronomers to create spectrograms of the light and print graphs in journals...or we should send a poet/artist along in a capsule to write movingly about the things he/she sees there and paint pictures that speak to us of the color impressions that person got.
Good answer, but a major mistake in there. We don't have red, green, and blue sensors in our eyes. The wavelength response of the three cone types is something like what's shown in this picture. The L (long wavelength) cone's peak sensitivity is actually in the yellow-green range, and it's as sensitive to blue-cyan frequencies as it is to red. But when reproducing colors we want to be able to stimulate the S, M, and L cones as independently as possible, and red (which stimulates L much more than M) is better for that than yellow (which stimulates L and M about equally). Blue stimulates S almost exclusively, and green preferentially stimulates M. Thus monochromatic red, green, and blue are useful for reproducing color. They're not good for capturing color, though. Monochromatic red, green, and blue filters throw away most of the spectral information that you need to determine the correct cone stimulus levels in the first place. To capture the perceived color reliably you need to use filters that match the cone response curves. Once you have the SML stimulus information you can derive from it the RGB intensities that will most accurately reproduce that stimulus. Of course, there are tons of details. The curves are somewhat different on different parts of the retina. Real cameras don't use the right curves. The eye compensates for ambient lighting so that white objects still look white even when illuminated by colored light, but this process doesn't work when you're viewing the photographs later in different lighting conditions. No set of three primaries can reproduce all SML stimulus triples, and on top of that the primaries used on typical computer monitors are highly suboptimal.
But the number one problem with making true-color astronomical images is not the difficulty, it's the pointlessness of it. There's nothing magical about human color vision. The particular cone types we evolved served us well in the environment we evolved in (I think the red-yellow-green distinction helps in finding ripe fruit). They're meaningless on Mars. True-color images aren't interesting to look at, and they aren't any more true to life than false-color images. Compare this false-color image and this "true-color" image. (I put "true-color" in quotes because the filters they used don't match the human cones, so the color calibration involves a certain amount of guesswork.) Our eyes don't do a good job of seeing what's interesting in these exotic environments, and it's ridiculous to copy their limitations in our technology when we can do better. That's what technology is for. -- BenRG (talk) 00:11, 31 October 2008 (UTC)[reply]
I would argue that "true color" images are "More true to life" than the false color ones. Imagine I sent my handy digital camera to Mars, snapped it a few pictures and brought it back to Earth. When I reviewed the images, the colors on the screen that I observed with my eyes would at least roughly match the colors I would have observed had I gone to Mars myself instead of sending my camera.
I completely grant that true color images are not nearly as scientifically useful. And perhaps even not worth the money required to capture accurately. But it's disingenuous to claim that there isn't an element of truth in true color images that a false color image lacks. There is a very real, common desire to know what faraway places would be like "if I were there". To satisfy this (rather unscientific) desire you need to know what things look like to human vision under natural lighting. (And perhaps what they would look like under what us earthlings would consider a white flashlight.) APL (talk) 18:41, 31 October 2008 (UTC)[reply]
Yeah, you're right. I suppose the images could even have scientific value as a preview of what future Mars colonists would see out their windows every day. I don't know whether your digital camera would reproduce the Martian colors accurately; I think they're calibrated for typical Terran lighting conditions. NASA's true-color images were made very carefully if this page is to be believed—they took all the data they had available (six frequencies), guessed the rest of the visible spectrum by cubic interpolation, then derived the XYZ coordinates from that and converted to sRGB or something closely resembling it. Reading that gives me more confidence in the accuracy of the colors. Some of the other descriptions I'd read gave the impression that they just took the blue, green, and infrared data and stuck it in the blue, green, and red channels and called it true color. -- BenRG (talk) 22:50, 31 October 2008 (UTC)[reply]
Jupiter's Great Red Spot On Earth
I've searched a lot of places but can't find anything that helps me answer...
Say that our planet was an Earth-sized Jupiter. (I.E. we're Jupiter, but not Jupiter-sized.) How big would The Great Red Spot be on here? -WarthogDemon01:16, 30 October 2008 (UTC)[reply]
Let's do a little math. According to our article on Jupiter, the great red spot varries in size, covering an area of 24–40,000 km × 12–14,000 km. Using the formula for the area of an ellipse (pi*a*b) we get an area of 9.04x109 - 1.7x1010 km2. The surface area of Jupiter, according to the article is 6.21796×1010 km2. Thus, at the smaller end of the scale, the red spot covers 14-27% of its surface. Given that Earth's land is about 29.2% of its surface, the great red spot would cover somewhere between 1/2 and all of the Earth's land area. As a further reference point, the Atlantic Ocean is 22% of Earth's surface area, which falls in the mid-point of the estimated sizes of the Great Red Spot. Thus, if transcribed onto Earth, it would be roughly the size of the Atlantic Ocean.
Someone can check my math on this, but it seems about right... --Jayron32.talk.contribs02:07, 30 October 2008 (UTC)[reply]
Something must have gone wrong with the maths there. The Red Spot can't cover anywhere near 27% of Jupiter's surface, the picture on the Jupiter article shows that it covers a much smaller proportion (less than 5% I would argue by looking at the picture). According to Jupiter, the radius of the planet is 11 times larger than the radius of earth. From Atmosphere of Jupiter, the Red Spot's "dimensions are 24–40,000 km west–to–east and 12–14,000 km south–to–north." Divide them by 11 and you have the approximate equivalent. - Akamad (talk) 02:13, 30 October 2008 (UTC)[reply]
I double checked the maths, and the calculations are correct. There must be a problem with the numbers I used then; either the dimmensions of the Great Spot are too large, or the surface area given is too small. And divide by 11 wont work. If jupiter is 11 times larger, than its surface area is 112 times larger, so we would need to divide by 121. Dividing by 121 gives an Earth-scaled area of the great red spot as: 7.47x107 - 1.40x108 km2. Since Earth's surface area is given as: 5.10x108 in our article on Earth, that gives us an overall ratio of 14.6% - 27.4%, or the same thing I got by calculating it the other way. --Jayron32.talk.contribs02:30, 30 October 2008 (UTC)[reply]
Sorry I meant divide the 24 - 40000 km by 11 and divide the 12 - 14000 km by 11 too. So you are dividing the area by 121. I think the problem in the maths was that you used 24000 km and 12000 km in the Pi*A*B equation. The numbers used should be half that (12000 and 6000) since the equation refers to the distance from the middle. See http://www.math.hmc.edu/funfacts/ffiles/10006.3.shtml. - Akamad (talk) 02:36, 30 October 2008 (UTC)[reply]
(I wrote this during and edit conflicted with above. We had the same thought at the same time) I assumed that a and b in the ellipse area equation were the major and minor DIAMETERS of the ellipse. Its not. Its the major and minor RADII of the ellipse. My answers were thus off by a factor of 4. Thus, the actual % area is 3.65% - 6.85%. Since the surface area of the earth is 5.10x108 km2, that gives us an "Earth-scaled" size of 18,615,000 - 34,935,000 km2. North America covers an area of 24,709,000 km2 , which falls dead in the middle of this range. Thus, the Great Red Spot is roughly the size of North America, scaled to Earth's dimmensions. --Jayron32.talk.contribs02:39, 30 October 2008 (UTC)[reply]
OK - move aside - let a professional through here. OMFG! This answer is a train wreck!
Great_Red_Spot#Great_Red_Spot says "Its dimensions are 24–40,000 km west–to–east and 12–14,000 km south–to–north." - so diameters - not radii. Jupiter has a radius of 71,500 km. Earth has a radius of 6,380 km - so to convert dimensions on Jupiter to "Earth scale" you've gotta multiply by 6380/71500 which is 0.09 - or for mental arithmetic: Divide Jupiter-linear-dimensions by 11 to get Earth-linear-dimensions. So an "Earth scale" spot is 2,200 to 3,600km by 1100km to 1300km. Since there are big error bars in the original data for the spot size - let's cheat and pretend it's a rectangle of the smaller size...that way we avoid all of the ikky ellipse math stuff. So the area is roughly 2200x1100 = 2.4 million square kilometers.
Now - for comparisons: According to List_of_continents#Area_and_population, North America covers 24 million square kilometers - so I don't know how you arrived at "the size of North America"...that's wrong by a factor of 10! (Which is bloody obvious if you compare a picture of Jupiter and Earth scaled to similar sizes!)....so a third the size of Australia...or Texas plus Alaska...or somewhere between Sudan and Algeria...the drainage area of the Black Sea...I dunno.
The image (at right) was made by taking two NASA photos - one of Earth, the other of Jupiter. I resized the two images to be identical in size - then overlaid one onto the other. Finally I erased all of Jupiter EXCEPT the red spot. So - here is an image of what the OP is imagining. Notice in the top of the image we have Africa. The red spot looks to be maybe four times the area of Madagascar - which is half a million square kilometers - so two million seems about right (although it's a pretty fuzzy "spot" - so there is plenty of room for error)...anyway - it's NOTHING LIKE the size of North America.
The original question described a counterfactual situation ("we're Jupiter, but not Jupiter-sized"). In answering, we have to figure out what exactly that means. To me the obvious interpretation is that the relevant linear dimensions are reduced in the same proportion, as if making a scale model. That's what Steve did. The initial derailment that started the train wreck earlier was to try working with areas, which of course vary as the square of the linear dimensions. --Anonymous, 06:00:00 UTC, October 30.00000 :-), 2008.
Yes - it's a very common error to assume that since "A is 1/11th the diameter of B" that "The area of A is 1/11th of B" (when in fact it's the SQUARE of the linear dimensions - so A is 1/121th the area of B) and that "The volume of A is 1/11th of B" (when it's really the CUBE of the linear dimensions - so A is 1/1331th the volume of B). If I had $1 for every time I'd seen that mistake made I'd have...well, actually, maybe just enough for lunch today. The trouble is that the word "size" is vague - so you hear things like "Jupiter is 11 times bigger than the Earth" and "Jupiter is 1300 times bigger than the Earth" - both of which are true in some fuzzy-thinking way. That's why I was so careful to say "Divide Jupiter-linear-dimensions by 11 to get Earth-linear-dimensions." in my answer. SteveBaker (talk) 13:12, 30 October 2008 (UTC)[reply]
The trouble is, physics isn't scale-invariant, so it's really hopeless to conceive of an "Earth-sized Jupiter". The physics that formed and sustains the Red Spot, whatever it is, wouldn't form a scale-model Red Spot on an Earth-sized planet. I don't think an Earth-sized gas "giant" can exist in any case since it wouldn't have enough self-gravity to hold it together. So the only way to understand this question is as a visualization aid: to get a feel for the size of the Red Spot, scale it down to something more familiar. Personally, though, I find these comparisons singularly unhelpful. (As the saying goes, there is so much sand in Northern Africa that if it were spread out it would completely cover the Sahara desert.) -- BenRG (talk) 12:58, 30 October 2008 (UTC)[reply]
Yeah, I was curious about a size comparison. I understand how a Great Red Spot couldn't exist on Earth. (Though hurricane speeds can get pretty close to the same wind speeds.) And plus, if I put my question further and said what if we had the Great Red Spot composed of the same materials, it wouldn't last long: hydrogen-rich storm in an oxygen-rich atmosphere? Nope, nope, nope. :) -WarthogDemon16:46, 30 October 2008 (UTC)[reply]
That's true - but sometimes it helps people to bring vast or tiny things to "human scales" in order to think about them. Saying that the spot is "big" isn't helpful - and saying that it's 40,000 km across when Jupiter itself is the largest planet in the solar system doesn't give you a feeling for it either. But knowing that (compared to the size of the planet) it's like a third the size of Australia really gives you the strong idea that this is a really big thing. On the other hand - compared to the size of the planet - it's not that much bigger than the "great white spots" we get a couple of dozen times a year here on Earth. (We call them hurricanes and cyclones). Those can be up to 1000km in diameter - which (proportionate to the size of the planet) is only about half the size of the Great Red Spot. What's different about our hurricanes is that they can't sustain themselves over land - so they inevitably fizzle out after a week or two. Jupiter has no land masses - so there is really nothing to stop the spot from staying pretty much together for (at least) hundreds of years - we don't know whether it's truly a permanent feature. The Great Dark Spot on Neptunes southern hemisphere was a similar kind of storm - and it fizzled out sometime between 1989 and 1994, to be replaced by another one in Neptune's northern hemisphere. Saturn has shown similar features (eg Dragon Storm (astronomy)). SteveBaker (talk) 13:12, 30 October 2008 (UTC)[reply]
Well, that probably depends on the size of the alien more than the size of the planet. People have occasionally speculated that the Giant Red Spot IS an alien! But since Jupiter has no solid surface - anything living there must live in a gaseous environment - so it has to complete it's entire life-cycle flying or floating or something. The most likely form of such creatures would be massive solar-powered gas-bags floating around - and they could easily need to be very large indeed. So perhaps the spot doesn't seem all that big to them after all. SteveBaker (talk) 00:39, 31 October 2008 (UTC)[reply]
LANDFILLS - why are garbage cells covered with a layer of soil?
Having read the landfill page, I see that individual cells are covered with a layer of soil or in some cases another material. Innumerable other google-found webpages explaining landfills mention the same process. However, I can find no direct explanation as to WHY this is done?
Thank you.
To trap all that rubbish in a contained way. It will reduce smell, reduce vermin and scavengers, stop plastic bags blowing in the wind, and speed decay. Graeme Bartlett (talk) 06:08, 30 October 2008 (UTC)[reply]
To close the top is sometimes done to prevent rain water going in. The water will be contaminated and has a chance to reach ground water. Other possibility is air thight closing to collect the natural gas from decomposition within the landfill. You also get rid of the smell and the animals lifing in an open landfill (rats seagulls).--Stone (talk) 11:15, 30 October 2008 (UTC)[reply]
Also, gas (methane) from the landfill is sometimes collected for use as a fuel...the soil helps to trap this in. The main reason is to keep smells and litter in and vermin outGaryReggae (talk) 12:59, 30 October 2008 (UTC)[reply]
I'm the original poster, and I wanted to say thank you. :-)
The decomposing organic matter produces methane, and if the landfill is not adequately vented by perforated pipes driven through it or other means, the methane can work its way through the ground and come out in people's basements. Sealing the top of the landfill might increase the likelihood of this. Edison (talk) 19:14, 30 October 2008 (UTC)[reply]
Careful Steve! When the landfill is ultimately covered and landscaped, then yes grass can grow (although you want to be careful with trees due to the roots). But just covering each cell with soil is done at the end of each day as the landfill develops, for all the reasons given above. You're likely to be putting another layer of rubbish on top of that soil tomorrow, so there's no time for grass yet! 79.66.32.150 (talk) 21:12, 30 October 2008 (UTC)[reply]
This one has me stump
How the hell do you even go about solving problems like this. By the way I have not looked at the answer.
Ah! I think I got it. It's a trick question. There is a measuring device. It is called the water or the water level. Using the water level as a measuring device, measure out half the volume of water in the cylinder. 122.107.157.9 (talk) 11:07, 30 October 2008 (UTC)[reply]
Did you understand what Dmcq was saying? You still need to know a way to measure exactly half. You can't just eyeball it from the glass when it's level. If you don't get it, read his statement more carefully and think Nil Einne (talk) 12:31, 30 October 2008 (UTC)[reply]
As you very slowly pour the water out, there will come a point when the surface of the water just touches the bottom of the glass (and also just the lip of the glass on the opposite side) - at that moment - it's exactly half-full....like this:
That's one way to solve it. Another would be to completely fill the glass, and then get an identical glass and pour the water from the full one to the empty one until they both have equal amounts. --Russoc4 (talk) 19:59, 30 October 2008 (UTC)[reply]
Or you could get REALLY crazy. You could put the glass into a larger sealed container whose overall volume would allow the evaporation of the water to proceed until the vapor pressure of the water and partial pressure of the water vapor in the larger container were in equilibrium. Per the ideal gas law, you would only need to know the initial amount of water in the container you started with, and as long as you maintain a constant temperature, you make the volume larger container such a size as to allow exactly 1/2 of the original volume of water to evaporate. Its a whole bunch of algebra, but its certainly doable... --Jayron32.talk.contribs20:13, 30 October 2008 (UTC)[reply]
There's not much to measure really. Just maintain a constant temperature, and the ratio of the size of the larger, air-tight container should be some ratio of the size of the smaller, water filled cylander. This ratio is dependent ONLY on temperature and nothing else, so as long as you maintain a constant temperature, there is some ratio of large box/smaller cylander which will cause exactly 1/2 of the water to evaporate. You don't even need to know the volume of the smaller cylander; you just need to build a box that has a volume that is some number of times larger than that cylander. Here, let me work it out for you. At, say, 25oC, the vapor pressure of water, using this site: [13] to calculate, is 0.0312 atm. Now, once the partial pressure water vapor in the air is equal to this pressure, the water stops evaporating. So, lets assume, to make the calculations easier, that our cylander is 1 liter. So, we want 500 mL of water to evaporate. The density of water being 1 g/mL that makes this water have a mass of 500 grams. Divide by the molar mass of water (18 grams/mole) to give us 500/18 = 27.8 moles of water vapor. Now, by the ideal gas law, PV=nRT or for our purposes V=nRT/P, where V is the volume of the box we need, n=27.8 (moles of water vapor), R = .08206 L*atm/mol*K (the Gas constant), T = 298 K (25oC), and P = .0312 atm. Solve and you get V = 21789 liters. Now, the ratio of the amount of water to the size of the box should be constant, since less water would need a proprotionally smaller box, while all the other numbers remain constant. So as long as the box is exactly 21789 times the size of the cylinder of water, and assuming of course the air in the box was fully dry (leave a dessicant in there for a few days, then remove it right before putting the cyilnder in it), once the system equilibrates, the cylinder will be EXACTLY 1/2 empty. Oh, and for our 1-liter example, it IS a pretty big box. There are 1000 liters in a cubic meter, so the box is 21.789 cubic meters, or if a perfect cube would be 2.79 meters to a side, or about the size of the average bathroom. To answer your question, the ONLY measurement you need to make is the temperature. The ratio of the volumes is ONLY depedndent on this number. Once you know that ratio of volumes, you can simply create a box that is that much bigger than the cylinder. I never said it was an EASY solution, from a practical standpoint, but who cares about being practical. Plus, unlike the "tip the glass to the diagonal" solution, this one doesn't have the pesky meniscus problem. --Jayron32.talk.contribs02:43, 31 October 2008 (UTC)[reply]
All of these ideas (apart from my 'tip the glass' suggestion) fail miserably because the problem states that you don't have a measuring device of any kind. If you are going to argue that getting the temperature just right in a particularly-dimensioned box doesn't constitute using "a measuring device" then I might as well say "I'll just take a second glass of exactly half the height of the original but of the same diameter, fill it to the brim and carefully pour the contents into the first glass" - which is vastly easier and gets you to the correct answer much more realistically. But I'd argue that the terms of the question say you have a glass - and water - and absolutely nothing else of known dimensions or other definite properties - since anything like that confers the ability to measure. If you're allowed to invent your own devices to help - then there are easier and more direct ways. SteveBaker (talk) 18:17, 31 October 2008 (UTC)[reply]
Oh, you are entirely right. I was just having fun coming up with the most rediculous and esoteric way to remove half of the water from the glass. Your method of using the diagonal of the glass is, of course, the only scrupulously correct way. My solution had an air of Rube Goldberg to it, and I was just goofing. --Jayron32.talk.contribs19:02, 31 October 2008 (UTC)[reply]
There is a tradition at some US college or other that every year the following question is always asked on their 1st year general science term paper: "Given an accurate barometer, how do you determine the height of a tall building?" - the "correct" answer is obvious - but there has come a tradition of awarding extra marks for "other" answers. So, for example, one may climb to the top of the building, drop the accurate barometer over the edge and count the number of seconds for it to hit the ground - and thus determine the height. Or one could tie the barometer onto a length of string and use it as a pendulum - and by accurately timing a large number of swings, determine the variation in the force of gravity at the top and bottom of the building - and thereby determine it's height. However, the neatest solution is that you take the barometer to the custodian and say "I'll give you this beautiful (and highly accurate) barometer, if you'll tell me the height of the building". SteveBaker (talk) 02:07, 1 November 2008 (UTC)[reply]
I added a subject header to your post. You may want to take time to read the guidelines if you want to receive a better response. You also should sign your post Nil Einne (talk) 12:31, 30 October 2008 (UTC)[reply]
There are three basic types of rock:
"Sedimentary" rocks (like sandstone and chalk) form as layers of mud and other 'stuff' accumulate at the bottoms of lakes and oceans ("sediments"). Over millions of years, enough layers build up that the weight of all of that stuff pressing down on the lower layers compresses them into rocks. Since the sands and other silts that make up sedimentary rocks came from older rocks that had been eroded by wind, rain, rivers, etc - it's often the case that pebbles and other small bits of other rocks get mixed up into the sedimentary rocks.
"Igneous" (volcanic) rocks form when lava or ash comes out of a volcano. As it cools, it turns into various kinds of rock. Sometimes, small bits of other rocks that got crushed up by the volcano end up mixed into the igneous rock.
"Metamorphic" rocks are formed when igneous or sedimentary rocks are crushed under yet more pressure from rocks in layers above them changes their form or composition (they change...or "metamorphose"). Some of the chemicals in a rock may get washed away by water flowing through them - and some rocks may have small voids and bubbles filled in by stuff deposited by flowing water. Some rocks get heated up by lava or by being so far underground - those undergo all sorts of chemical changes.
See also Rock cycle for more info. Rocks are mostly various forms of silica and other silicon-containing compounds, though there are some other components that make for some sharp differences. The relative amounts of silica to other components will determine the differences between the rocks. --Jayron32.talk.contribs13:04, 30 October 2008 (UTC)[reply]
Some rocks contain metals, either in a pure form like gold or in combination with oxygen or other substances like hematite(which contains iron), and these are called Ore. Edison (talk) 19:12, 30 October 2008 (UTC)[reply]
Mathematics
A delivery boy collected 5.35 pesos part in 5 centavo coins, 8 part in centavo coins. If the number of 5 centavo coins were 7 more than one-half the no. of 10 centavo coins, how many 5 centavo coins?
There is a mathematics reference desk located at Wikipedia:Reference desk/Mathematics, but if you post the question there you are going to get the same response I am going to tell you. Wikipedia is not here to do your homework for you. If you need help finding information, we can point you towards articles (like Currency of Mexico, which contains info on pesos and centavos. But seriously, you can push the buttons on your calculator by yourself... --Jayron32.talk.contribs15:37, 30 October 2008 (UTC)[reply]
There is a standard method for this kind of question. Assign letters to all your unknowns (number of each type of coin) and then rewrite the problem as equations. You can then solve those equations to get the answer. --Tango (talk) 16:29, 30 October 2008 (UTC)[reply]
There is probably something wrong in the way you have rewritten/translated your problem, or else there is something wrong in the problem itself. As written, it's not solvable. The first sentence mentions five-centavo coins and centavo coins (i.e. one-centavo coins). The second sentence mentions ten-centavo coins and five-centavo coins. So you say you have three unknowns, but as far as I can see, you have only provided information for writing two equations. You need as many equations as you have unknowns. Also, the meaning of the first sentence is not clear. I don't understand what you mean by "8 part in centavo coins". However, if the first sentence should be "A delivery boy collected 5.35 pesos, partly in five-centavo coins, partly in ten-centavo coins", the problem can be solved as Tango suggested, by letting x be the number of five centavo coins, and y be the number of ten-centavo coins. I'll help you along by showing how you make the second sentence into an equation:
If the number of five-centavo coins were 7 more than one-half the number of ten-centavo coins
Just substitute x and y for the number of five- and ten-centavo coins:
If x were 7 more than one-half of y
Then replace the remaining words with numbers and the mathematical operators (= + - * / etc) that have the same meaning as the words:
x = 7 + 0.5 * y
Do the same thing with the first piece of information. Now you have two equations with two unknowns. Solve these, then you know the value of x and y. The answer to the question, "how many 5 centavo coins?", is the value of x. --NorwegianBluetalk22:44, 30 October 2008 (UTC)[reply]
My question is why women who are menstruating easily get or feel electrocuted once they simply touch a door knob or any thing that is made of metal?
That sounds unlikely to me. I can't see any reason for it. The chance of getting static shocks depends on what you're wearing (particularly your shoes), what kind of floor you walk on and also the weather (dry air doesn't conduct as well as humid air, so you can build up a charge easier). I can't see why it would depend on whether or not your menstruating. I guess it's possible that some women like to wear big fluffy jumpers when menstruating and that's what causes it, but that's about it. --Tango (talk) 18:22, 30 October 2008 (UTC)[reply]
It may be possible menstruating women are more sensitive to the sort of thing for some reason. But I agree with you it seems unlikely and there's no evidence so far to suggest otherwise. Nil Einne (talk) 12:46, 31 October 2008 (UTC)[reply]
Pay attention to the pi-bonding and the location of the hydrogen atoms in 3D space, and what effect that has on the strength of the C-H bond. Remember that an acid is any substance that easily loses an H+ ion, and that will be directly related to the strength of that C-H bond (i.e. the weaker the bond, the better acid it is). Another factor is the relative stability of the resulting carboanion (i.e. if you lose an H+ as an acid, you will leave behind a C- ion; and the pi-molecular orbitals in the triple bond system has an effect on the stability of that carboanion. --Jayron32.talk.contribs18:19, 30 October 2008 (UTC)[reply]
This page here: [14] also contains lots of good info on the reactivity of alkynes (the class of compounds that acetylene is the smallest member). Read closely the section titled "Acidity of Terminal Alkynes". --Jayron32.talk.contribs18:23, 30 October 2008 (UTC)[reply]
An sp hybridized carbon also has a higher electronegativity than sp2 and sp3, making the resulting carbanion relatively stable. --Russoc4 (talk) 20:01, 30 October 2008 (UTC)[reply]
"three-day malaria": would it call brain damage?
Hello. I'm playing Merlie Ryan in an adaptation of Carson McCuller's Ballad of the Sad Cafe. Merlie is known as "Crazy Merlie", and is generally the village idiot. In the book, it says he has the "three-day malaria", which means for two days he's dull and cross, then on the third day he livens up and has an idea or two, mostly foolish.
The entry for malaria says it can cause brain damage if you get it when you're young, so I'm assuming that's why he's foolish. But the play lasts for about 8 years. Could he have malaria the whole time? I thought you'd get better or get dead. And is it right that it might have caused some sort of cognitive problem? In the play he seems to be uninhibited, as if his sense of social appropriateness is missing. Might that come from the disease?
Slightly rambling question there, but I'd be grateful for any light anyone can shed on the effects of the disease.
(ec) Well, "three-day malaria" is "tertian malaria", which is that caused by Plasmodium vivax. The three-day cycle corresponds to the release of the merozoites from the liver and their invasion of red blood cells. Vivax malaria is not as bad as other forms of malaria, and is seldom fatal. The usual treatment is with chloroquine, which was developed in the 1930s -and was acknowledged as first line therapy since 1946 - I'm not cure if The Ballad of the Sad Cafe is explicitly set after this. But chloroquine alone doesn't cure the disease; to wipe out the liver infection primaquine is necessary, and this became available in the late 1940s, and wouldn't be widely available until after that, and so probably wouldn't figure in "Sad Cafe" published in 1951. So Merlie definitely would be expected to suffer from a chronic form of malaria that would last years and years. I don't think Merlie's foolishness is necessarily attributable to his malaria, though. But in answer to your specific question, absolutely he could have malaria the whole time. But no, people with malaria are not noted for being socially inappropriate in the way that, say, drunks, are. The brain damage in those who have it seems to result in cognitive difficulties: trouble in memory, in concentration, and learning. You could play Merlie as not caring much about social niceties because of his preoccupation with his own suffering; you could play him as unable to concentrate, with a short attention span; you could play him as mentally "slow". BTW, today we think of malaria as a disease of travellers, because it's been eradicated in the U.S. now, but in Merlie's time could certainly have been acquired here. - Nunh-huh21:28, 30 October 2008 (UTC)[reply]
Thanks for the prompt replies! We have set it finishing in 1945, so none of the treatments mentioned would be available to him. And it's useful to know that he could have suffered for the whole time without actually dying. "Unable to concentrate" seems to match most with my impressions of the character, but it's the way she links the three-day cycle of the disease with his activity and behaviour that confuses me - two days cross and dull, then livens up on the third to have a few foolish ideas. I thought at first this was a poetic way of saying he had some form of bipolar condition, but given that three-day malaria is a genuine thing, this seems less likely. Maybe having a fever involves less time shivering in bed than it does in my imagination, or maybe it's feverish in the sense of a feverish imagination.
78.86.213.238 (talk) 22:45, 30 October 2008 (UTC)[reply]
Well, it would certainly be fever in the sense of increased body temperature, but not all fevers involve shivering in bed or cold sweats. In 1945, he would probably have been taking quinine, which is not terribly effective (especially as it had to be made from cinchona bark rather than synthesized in 1945) but would have given some relief. - Nunh-huh01:14, 31 October 2008 (UTC)[reply]
I caught a weasel in my house!
Well, its either a weasel or a ferrit (I thought it was a rat at first when I found it rummaging in my upturned kitchen bin and I was going to brain it with a claw hammer). The RSPCA man can't come to pick it up until tomorrow. I've put it in a cat carrier with some straw and given it water but what do I feed it? Sunflower seeds? Nuts? Hay? Carrots? They're similar to rabbits and other small rodents aren't they? --84.64.99.103 (talk) 21:54, 30 October 2008 (UTC)[reply]
It could also be a Stoat. You might not want to keep a ferret in the house - they REALLY, REALLY STINK! Anyway - it won't die if it goes without food for 24 hours - and you know it just ate when you caught it. You aren't doing it any favors by getting it used to getting free handouts from humans - so you should probably avoid giving it anything at all. So long as it has water and fresh air - it'll be fine. SteveBaker (talk) 00:28, 31 October 2008 (UTC)[reply]
Depending on where you live, it could also be a fisher cat or any other of a number of mustelids. Still, they are pretty much requisite carnivors, like a cat, so if you threw some hambuger or something in there, it should be fine. Cat food would probably work too... --Jayron32.talk.contribs02:23, 31 October 2008 (UTC)[reply]
Why not just let it go in the local woods where it can find its own food? I mean, unless it's injured I'd think the reason to call the RSPCA would be to catch it, which you took care of on your own, so why not release it on your own as well? --Shaggorama (talk) 05:58, 31 October 2008 (UTC)[reply]
Sorry, I should've made it clear. I'm quite sure that it's someone's pet. It's very tame. Either that or it's ill and weak (looks okay though). I fed it some beef last night and I gave it some cat food this morning. The guy is coming by to pick it up later. —Preceding unsigned comment added by 90.241.161.187 (talk) 11:54, 31 October 2008 (UTC)[reply]
I realize you boys are fisher-ing for laughs here, but if your dad told you were funny, he must'a lied. Frankly, you otter be ashamed at your stoatally stinky puns, but I'll stop badgering you now that I've skunked you. Matt Deres (talk) 14:05, 1 November 2008 (UTC)[reply]
I don't know exactly, but my initial guess is that ibuprofen might induce higher concentrations of the enzyme that metabolizes atenolol, therefore reducing the effectiveness of atenolol, assuming the parent compound is the active one. --Russoc4 (talk) 00:07, 31 October 2008 (UTC)[reply]
I'm pretty sure that atenolol is renally cleared, so that's not it. Also, ibuprofen reduces GFR (at moderate concentrations), which would be expected to reduce renal clearance (and increase atenolol concentration, all other things being equal). My guess is that the renal effects of ibuprofen would generally raise blood pressure, and that would counterbalance atenolol's effect. If there's a more direct mechanism, that would be interesting. --Scray (talk) 02:24, 31 October 2008 (UTC)[reply]
I had a further look around and found somewhere that it's an antagonistic effect due to NSAID-induced inhibition of renal prostaglandins, sodium and fluid retention. Thanks. —Cyclonenim (talk · contribs · email) 10:31, 31 October 2008 (UTC)[reply]
Yes, ibuprofen and other NSAIDs block prostanglandin synthesis, including PGE2. By the way, you know that beta-blockers are no longer recommended as treatment for hypertension? Axl ¤ [Talk]11:13, 31 October 2008 (UTC)[reply]
The problem was initially flagged by this classic paper in the Lancet. Beta-blockers will reduce blood pressure equally well, but they do not prevent the undesirable outcome: stroke, as effectively. There have been several other papers showing similar findings. Here is the Cochrane review. The NICE guideline states "the cost-effect analysis... [supports] the clinical data in that beta-blockers are the class of drug least favoured, and CCBs and thiazide-type diuretics appear the most cost-effective choices in most scenarios". Beta-blockers are now fourth-line treatment. Axl ¤ [Talk]11:37, 31 October 2008 (UTC)[reply]
preventing liver spots?
i'm 23 and my hands look fine, but I wouldn't like to have liver spots all over them when I'm 76. Do you think I can do anything (daily) or avoid doing something so I won't get them eventually?
My textbook says concentration of pure solids and liquids is taken as unity.But no explanation is given as to why.Can some1 please why is it taken so?
"Concentration" in what sort of units? If you are asking about %, it should make some sense that a pure sample of some chemical X is "100% X" based on the standard meaning of percent ("X is what fraction of the whole?"). But for concentrations that aren't just "fractional of the whole", it's clearly a false statement: 1 g of water is 1/18 mole and has a volume of 1 mL, so it most certainly does not have a molarity of 1 mol/mL. DMacks (talk) 23:58, 30 October 2008 (UTC)[reply]
It is because 1 part in 1 is that pure substance. And 0 parts in 1 of anything else. In reality what you may call pure sugar for example will have air between the crystals, and the density of the bulk material may be below that of a pure uniform crystal. They would be saying the concentration of H2O in water is 1 and the concentration of NaCl (or anything else) in pure water is 0. Graeme Bartlett (talk) 00:03, 31 October 2008 (UTC)[reply]
Actually, the above is not really the reason. It sounds good, but it doesn't get to the heart of the problem. The one could certainly calculate the "concentration" of a pure solid. It would merely be the density (grams/liter) divided by the molar mass (grams/mol). You would get mol/liter, which is of course concentration. After all, we can and do use concentrations of pure gases, and their calculation can be done essentially the same way. The same problems where a pure gas concentration is used as calculated, the pure solid concentration is treated as unity. This is not the same thing as being equal to one, but we'll get to that in a minute. The question is "Why do you need to know the concentration?". For the problems I am guessing you are doing, you are probably working in kinetics and equilibrium, that is the problems are largely dependent on the rate of reaction. The rate of a chemical reaction is dependent on the number of collisions occuring between the reactants. In gases and aqueous solutions, the reactants are spread out over a large space, so how often they colide is a direct function of how close together they are packed. If you double the number of molecules of a gas or an aqueous solution in a given space, the number of collisions doubles as well, because the molecules are forced closer together. Thus, changes in amounts effect changes in rate. Now, here's the thing with pure solids and pure liquids. They are condensed phases, which means that the molecules are already touching essentially. If you, say, double the number of molecules of a pure liquid, you don't effect the rate at which those molecules collide since those molecules can't be forced closer together. Thus, for questions that involve rates of reaction, the amounts of condensed phases don't affect the rate of the reaction. In our calculations, we ignore these amounts because they don't change the outcome. Ignoring them is the same as multiplying by 1 (since multiplying by 1 doesn't do anything at all). So we say that we treat them as "unity", but we could just as easily say we ignore them all together, because they don't affect the outcome. When you do an equilibrium calculation, well, the equilibrium is just a situation where the rates of the forward and reverse reactions are equal. Since equilibrium is determined by rate, and solids and liquids don't effect rate anyways, we can ignore these here too... --Jayron32.talk.contribs02:18, 31 October 2008 (UTC)[reply]
Having been a chemistry teacher for 10 years, I think I am fairly qualified to make these assumptions. The only type of situations where one finds the statement "treat the concentrations of solids and liquids as unity" is in the kinteics and equilibrium chapters of your standard general chemistry textbook. Its the particular phrasing he used, and that he mentioned that it came from his textbook that cued me in on the kinds of problems he was working out. Trust me on this, he's working out rate law and equilibrium problems. --Jayron32.talk.contribs03:26, 31 October 2008 (UTC)[reply]
Yup. The real problem is when they think that context doesn't matter, which is why I led with that caveat. Otherwise they get into my chemistry class and tell me "the concentration of water is 1" or "solvents don't have a concentration themselves" because that's what they were told, not knowing what the heck it actually means:( DMacks (talk) 04:04, 31 October 2008 (UTC)[reply]
When working with reaction rate and equilibrium-type problems, you're not actually using the concentration of the substance, you are using the Activity (chemistry). This isn't an absolute measure, it's a dimensionless relative measure. Usually, the reference concentration is taken to be 1 mol/L, so that the activities match exactly with the concentration. However, this is not always the case, and very concentrated solutions can have activities which differ numerically from their molar concentration. In the case of solids, the activity doesn't change when increasing the amount of undissolved material. Thus the activities are constant, and are effectively rolled into the rate constant or equilibrium constant. The same thing happens with rates and equilibria in aqueous solution: the amount of water in most solutions is near constant (~55 M), and varies very little from one aqueous reaction to another, and is defined as unity. If you happened to be working in a solution where the concentration of water was significantly different from a normal aqueous solution (e.g. in a highly concentrated alcohol in water mix) you would have to explicitly account for the water concentration, and would have to use rate and equilibrium constants which account for this. -- 128.104.112.72 (talk) 15:51, 31 October 2008 (UTC)[reply]
October 31
Why is space so big?
I mean, isnt the distance just....overwhelming? You cant wrap your mind around it! Just think about how big a light year is. The distance that light travels in a freakin' year, that's what! That's 11,600,000 miles in just one minute! ....Wow Wow Wow...When we say that something is millions of light years away, I just...can't comprehend it.--Sunburned Baby (talk) 02:56, 31 October 2008 (UTC)[reply]
Space is so big because its been around for a long time. If we consider that the availible evidence tells us that the universe is expanding, and since we know about how fast it IS expanding and about how long it has been expanding, we get an estimate for how big the whole thing is. And the answer is REALLY FREAKING HUGE. No shit. I used to teach an Earth Science class, and for the astronomy unit, I would take the kids out to the football field to map out the solar system. If you put the sun at one goal (endzone or soccer goal, its about the same size) and put pluto/neptune at the other goal/endzone, then on that scale the sun is the size of a Quarter coin, and the earth is about the size of a speck of sand. And that's ONLY our solar system, which if scaled to such a size so that the galaxy could fit on a football field, the entire solar system would be a speck of sand. And if we put our galaxy on a football field scaled to teh size of our local group of galaxies, it would be a speck of sand, and so on and so on. Feeling insiginficant yet? --Jayron32.talk.contribs03:14, 31 October 2008 (UTC)[reply]
I never know whether saying "the volume of the observable universe is around 3×1080 cubic meters" makes the size seem more or less comprehendable. At least I can actually consider how immense that is, rather than saying "larger than I can imagine", but then I have troubles imagining 1080. DMacks (talk) 04:11, 31 October 2008 (UTC)[reply]
Often when one gets a question like this it makes sense to invoke the anthropic principle and assert that if it weren't just so then life as we know it wouldn't be here to observe it. However I'm not sure if that is the case here. What if instead of being 3×108 m/s, the speed of light were only 3×104 m/s ? The visible universe would be 1/10000 the diameter it is now, but would it really matter? We'd expect our new universe to have room for ~1 galaxy, but who needs the other galaxies anyway? Satellite communication might suck, and microchips wouldn't be as speedy, but does life as we know it really require such a large c?
As far as I can tell, the answer would appear to be no. Are there any really fundemental downsides to envisioning a universe with a much slower speed of light (and hence a universe that grows much more slowly)? Dragons flight (talk) 04:28, 31 October 2008 (UTC)[reply]
The point is that the processes that created our galaxy require a universe with more than just our galaxy. Our galaxy exists only because the processes that create galaxies require a universe which is pretty much exactly the size it is now, with a fundamental speed of light equal to exactly what it does in our universe. If the laws were not so, the conditions would not exist to create the Universe as it is, with us studying it. Its not just about whether or not we could survive in a 1-galaxy universe with a slower speed of light; we could, its that such a universe could not have come into being in such a manner as to create the necessary conditions for life to exist. The Anthropic Principle is a bit of a tautology, but a useful one. --Jayron32.talk.contribs04:45, 31 October 2008 (UTC)[reply]
That's merely an assertion, not an explanation. What about the big bang and structure formation requires lots of space? Galaxies nucleate from primordial density fluctuations that would presumably still exist. The necessary mass only comes from a sphere ~10 times wider than the ultimate disk of the galaxy itself. I don't see any reason all that other distant mass is actually necessary to forming a galaxy. As best I can tell, the dynamics of galaxy formation don't require the universe to be huge. Dragons flight (talk) 05:06, 31 October 2008 (UTC)[reply]
Having a small speed of light would also affect speed of gravity, and a galaxy may not form as big as we know it. Then you may find a lack of heavy elements needed to make planets and humans. We also need plenty of space to make a cold background in the sky, so that solar energy can drive life on earth. Graeme Bartlett (talk) 05:36, 31 October 2008 (UTC)[reply]
Look man, space is big. Really big. You just won't believe how vastly hugely mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist, but that's just peanuts to space. Listen: When confronted by the sheer enormity of space, better minds than the ones responsible for this reference desk have faltered. Some invite you to consider for a moment a peanut in Reading and a small walnut in Johannesburg, and other dizzying concepts. The simple truth is that interstellar distances will not fit into the human imagination. :) --Shaggorama (talk) 05:51, 31 October 2008 (UTC)[reply]
I can easily envision space being much much much bigger say a googleplex times as wide or maybe another power or two than that. Why is it so small relative to us? Perhaps it just couldn't be any smaller. Dmcq (talk) 09:06, 31 October 2008 (UTC)[reply]
Big can be looked at in other ways too: which is more, stars in the Milky Way or cells in a single human brain? stars in the Universe or bacteria in the oceans? Franamax (talk) 09:33, 31 October 2008 (UTC)[reply]
My very quick research shows there are about 2-4 times as many stars in our galaxy as there are neurons in the human brain (I don't know about other cells). I have no idea how many bacteria there are in the oceans, though... --Tango (talk) 17:22, 31 October 2008 (UTC)[reply]
You need to be careful when considering what would happen if a physical constant were different. All the constants are interrelated, so if you're changing the speed of light you're going to have to change some others as well. What would happen will depend on which ones you change and in what way. There is a way of doing it (I don't remember the details) that results in pretty much no observable change at all because it results in atoms being 10,000 times smaller, and therefore everything else is 10,000 times smaller (that doesn't follow exactly, but I think the conclusion is still correct) so the time it takes for light to get from A to B is unchanged since A and B are just closer together. --Tango (talk) 10:43, 31 October 2008 (UTC)[reply]
"Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist, but that's just peanuts to space." - Douglas Adams88.211.96.3 (talk) 11:25, 31 October 2008 (UTC)[reply]
Which seems fairly complete. In the absence of faster-than-light technology, which seems unlikely to say the least, humans are just not really going to get very far as a species in space. Look upon "we'll colonize space!" proposals with a gimlet eye unless someone suggests a really plausible explanation of how we'd get significant numbers of people (e.g. significant breeding populations) anywhere useful within the lifetimes of those traveling. --98.217.8.46 (talk) 13:26, 31 October 2008 (UTC)[reply]
I believe the trick is NOT to try to do it in the lifetimes of the people inside. We need huge, landscaped, spinning (for artificial gravity) mini-worlds made from hollowed out objects from the 'belt - each with LARGE populations (thousands of people at a minimum). Power will have to be from fusion sources to keep the fuel supply compact enough - and the progress from one star to the next has to be expected to take thousands of years. It seems inevitable that such habitats will be needed in the future - and once there are enough of them in solar-orbit - it's only a matter of time until one of them takes on the trip. If you are living your life in such a place anyway - it may not make much difference to you whether you are orbiting the sun - or heading off to Alpha Centauri with no hope of arriving during your lifetime.
An alternative (which is perhaps more likely to be of interest and I'm fairly sure will happen in the next 100 years) is the "scan your brain - produce an exact software simulation of it - then die". "You" will continue to exist with all of your thoughts and memories intact inside a computer somewhere - presumably with some kind of robotic body with robotic senses. You feel like you are still "you" and your family and friends can easily tell it's still you - and you behave pretty much like any other human - albeit in that robotic body. Now we can do a couple of interesting things:
Shoot a small, unmanned probe to the next star. It's small - it gets there in 100 years and proceeds to drop off some handy robots. When it arrives, we transmit a colony of humans by radio or laser communications to the probe and thence to the robots. Elapsed journey time is at the speed of light - but to the traveller it would seem instantaneous. When you arrive, you live out your life in a robotic body - and if you want to return - you simply transmit yourself back again as another radio signal and you're home again in the blink of an eye. The travel time is still at the speed of light - so it's gonna take 4 years to go and 4 years to come back from Alpha Centauri - but 8 or 9 years away is not so terrible if you don't have to endure the journey.
Using a very small probe - shoot a computer and a robot body to the nearest star. But have the computer's clock rate be adjustable. When there is nothing much happening, it executes one instruction every second - when there is an emergency - or at the start and end of the journey - it runs at a few teraflops. Your brain can 'fast-forwards' through the boring parts and consume almost no energy - and zero other resources. When you arrive, you ramp the clock up to full speed and download yourself into the robotic body to do whatever exploration you fancy. Sure - it takes hundreds of years to get there and to get back again - but you won't die of old age and you won't get bored.
Once you can 'fast forward' your life through the boring bits and have your thoughts and memories transmitted and reconstructed at the speed of light - you can live as long as you want to - and there are a LOT of interesting possibilities.
A wonderful Star Trek-like solution, but the humans you imagine have little to do with any humans I have ever seen. Make a big dome, put a few thousand humans inside it, wait a few weeks and they'll be in a state of civil war, disrepair, disaster. I don't see us getting off this planet in any major way. The human race will, at some point, go extinct—of that there cannot be any question. Once you accept that it just becomes a question of when and where. --98.217.8.46 (talk) 21:12, 31 October 2008 (UTC)[reply]
There are plenty of remote groups of humans with populations under 1000 who manage just fine. The Pitcairn Islands had a rough start - but they survived and thrive today with almost no contact with the outside world and only just barely enough genetic diversity to keep going. I don't see the need for passimism in that regard. As for the "humanity" of the humans I imagine - well, I think what matters is our intellects - and what I suggest would preserve that in the purest way possible. You might think we couldn't survive that - yet wikipedians talk via the clunkiest links - form friendships - and seem in every way "human" - even though we rarely meet face to face. If my brain was merely simulated on a big computer - I don't see how you could possibly tell. SteveBaker (talk) 01:48, 1 November 2008 (UTC)[reply]
In special relativity, light are waves, and the inertia of objects increase as the velocity of objects increase toward the speed of light. sound are also waves, so do the inertia of objects increase as their velocity increases towards the speed of sound? —Preceding unsigned comment added by Superwj5 (talk • contribs) 12:14, 31 October 2008 (UTC)[reply]
Short answer, no. You get interesting aerodynamic effects as you approach and pass the speed of sound (sonic booms, etc), but nothing relativistic. While light and sound are both waves, they are very different things - sound is compression waves in a medium (air, usually), light doesn't have a medium, it's just self-propagating electric and magnetic fields. Light is a fundamental feature of the universe, sound is just a consequence of vibrations in matter. --Tango (talk) 13:19, 31 October 2008 (UTC)[reply]
Bosenova
Does anybody even have any evidence what Bosenovae really are? Or at least some possibilities and guesses? I think they might have entered an unknown interaction and changed into sparticles, bosinos or dark matter or perhaps the magnetic field stuck some of the atoms into their Schwarchild radius in quantum gravity and Hawking radiated into other stuff? Do you have any idea what it is? —Preceding unsigned comment added by Superwj5 (talk • contribs) 12:22, 31 October 2008 (UTC)[reply]
Apart from what the Bosenova article says, no people don't know exactly. But you'll find proposed theories on it if you search arxiv.org and scholar.google.com. For instance, Phys. Rev. Lett. 89, 180403 (2002) Mean-Field Theory of Feshbach-Resonant Interactions in 85Rb Condensates implies 'rogue dissociation. For a definition, see arXiv:physics/0607075v1 but simply put the atoms in the bose einstein condensate spontaneously turns into molecules, which are then repelled. This process is more likely at certain densities than others. EverGreg (talk) 14:34, 31 October 2008 (UTC)[reply]
The basic principle will work - you throw something out the back you'll get an equal and opposite reaction pushing the rocket forwards. However, resistance from the water would make an underwater rocket extremely inefficient, probably to the point of being useless. The same is true of air, to a lesser extent, rockets are significantly more efficient in a vacuum than in the atmosphere. That's one of the reasons for taking off vertically and then going sideways to enter orbit, rather than taking off diagonally to start with - you spend less time in the atmosphere. Propulsion underwater usually involves taking in water from the front and expelling it out the back (eg. using a propeller), that turns out to be far more efficient that expelling rocket exhaust out the back. --Tango (talk) 16:37, 31 October 2008 (UTC)[reply]
Yeah, what are you guys talking about? Rockets work just fine under water. They just don't move as fast. Missiles are routinely launched from submarines underwater, and you can fire a fireworks rocket or Estes model rocket into a swimming pool and observe that it still works. ~Amatulić (talk) 21:01, 31 October 2008 (UTC)[reply]
Sure - the distinguishing difference between a rocket and a jet is that a rocket contains it's own oxidizer. Hence it likely burns just fine underwater. Gasses still shoot out of the back pretty quickly - and Newton's laws guarantee that if something shoots out of the back - it WILL go forwards. The only question is thrust-versus-drag ratios that will affect your accelleration and top speed underwater. SteveBaker (talk) 01:37, 1 November 2008 (UTC)[reply]
How to select motor rating for pure electric vehicle
(moved from Village pump).
If i want to replace a 150cc IC engine base two wheeler with an electric vehicle run by a direct drive motor what rating of motor will i have to use??? Is there a direct relation between cc and kW of the machine??? Any help please??? —Preceding unsigned comment added by LifestyleBangalore (talk • contribs) 16:38, 31 October 2008 (UTC)[reply]
Try to find an equivalent horsepower or kW rating. The cc number for an engine tells you very little about the power it can produce these days. It's a bit more complex than that though - electric motors have spectacular low-end torque - so you can get really great 0-60 times with a fairly wimpy little motor - but then find that your top speed sucks. That may not matter if you do lots of in-town driving and very little freeway - but it's easy to be fooled by those kinds of numbers. Also, without a gearbox, you need a very flat torque curve across the entire RPM range - electric motors are pretty good at that - but some are much better than others. SteveBaker (talk) 18:03, 31 October 2008 (UTC)[reply]
They're usually referred to as "Office Partitions". A google search will get you loads of suppliers sites, and an image search lets you see the variety on offer. Fribbler (talk) 18:26, 31 October 2008 (UTC)[reply]
Not all open office dividers are "cubicles". My office is a donut design. The elevators, plumbing, and main cabling are in the middle. Offices are around the outside windows. They are divided using full-height walls and doors that appear to be real fixed walls. The advantage is that the maintenance people can move walls around to enlarge or divide offices as needed. -- kainaw™21:11, 31 October 2008 (UTC)[reply]
"Oh look, see, its not a square office, so your not a mindless paper-pushing drone like those people who have to work in cubicles. See, you mean something as an individual cuz you work in a round building!". Industrial psychology writ large... --Jayron32.talk.contribs02:35, 1 November 2008 (UTC)[reply]
In sci-fi, whenever there is an EMP everyone runs around frantically turning everything off. Does that actually help? If so, how? My understanding of the relevant physics suggests it wouldn't (and the unreliable sources I've found via google tend to agree), does anyone know for sure? --Tango (talk) 22:15, 31 October 2008 (UTC)[reply]
That makes as much sense as space ships executing banked turns in weightless vacuum, or having high-current power lines running behind display panels so they emit showers of sparks when something bad happens.
No, turning things off after an EMP event accomplishes nothing. It may help to power-off stuff before the pulse. In my industry, we can incorporate nuclear event detectors that cause critical equipment to switch off automatically, to protect them from EMP, and the equipment itself is designed to be "hardened" against such events in the first place. ~Amatulić (talk)
Sorry, I should have said "whenever there is *going to be* an EMP", obviously turning things off after they've been fried isn't going to help. --Tango (talk) 22:48, 31 October 2008 (UTC)[reply]
I think the OP is asking, "does EMP only affect things that are turned on in the first place". I mean, does turning things off change anything if they are not hardened to EMP in the first place? --98.217.8.46 (talk) 22:51, 31 October 2008 (UTC)[reply]
There is absolutely no doubt that EMP is "real". In the early 1960s, computers used clunky 'Ferrite core memory' technology. You could literally see the individual bits as little grey donuts threaded on wires. One interesting thing about core memory is that it's magnetic - and if you turn your computer off and back on again, it doesn't wipe the memory as happens with "DRAM" technology. As core memory became obsolete, the very last application of it was in military aircraft that were designed to deploy nuclear payloads. After they dropped "the bomb" - and turned around to get the heck out of there - the aircraft stood a chance of catching the EMP from it's own weapon. Hence they used core storage in their flight computers - so that the computer could be turned off and rebooted without losing a beat.
What an EMP does is to induce voltages in metal objects in its path. If you are close enough - and the geometry of the metal is just right - that voltage may be large enough to disrupt or destroy the circuit. Whether turning it off helps has to depend on an awful lot of things. Let's imagine some delicate piece of electronics with two LONG wires going off to a switch and a battery. If the wires lie in one pattern then the voltage will be induced between the battery/switch and the electronics - and both ends of the wire that contact the electronics could be at the same voltage - the electronics themselves might be small enough to to pick up any significant voltage at all. In that case, the electronics are probably undamaged. If we imagine another situation where two wires lead out of the electronics in opposite directions then the induced voltage could be large and fry the electronics instantly. If the switch happens to be up close to the electronics - and breaks the physical connection between the long wires and the electronics - then sure - turning it off beforehand ought to reduce the risk...but it's certainly not going to ensure it'll be undamaged. Turning the switch off AFTER the pulse has passed is obviously pointless though.
So - if you know an EMP is coming - I guess you should turn off anything you can get to in time - there is no guarantee it'll help - but then there is no guarantee that an EMP will destroy everything electronic/electrical anyway.
So the key thing is not so much to have things switched off as to have them unplugged (or otherwise isolated from the long wires), so if you have a laptop running off its battery, it's not going to matter whether it's on or off? --Tango (talk) 01:54, 1 November 2008 (UTC)[reply]
Yes exactly. Most things plugged into the power grid will likely be fried - an EMP crossing those mile-long power lines (or even the shorter ones that go into your house) induces one heck of a voltage. The longer the conductor, the more voltage induced for a given EMP. I think the "magic number" is 30 inches (76 cm) for nuke-level EMPs to damage sensitive electronics. Not sure what era's electronics that was for though. ArakunemTalk14:47, 1 November 2008 (UTC)[reply]
Age of Aneurysms?
I'd like a little more information about aneurysms that I couldn't find in the article. First, what ages can get them? Can you even have them from birth? I know the article did mention men have a higher risk than young women, but would it still be reasonable for a teenage girl to have an aneurysm? Also, if they burst, does it always lead to death? Thanks for the help! 71.13.209.44 (talk) 22:40, 31 October 2008 (UTC)[reply]
Aneurysms can be present from any age, as far as I'm aware. I read a case study of a 1-month year old male who had one, so it is possible, but the risk increases significantly with age and aneurysms in paediatric patients are rare. If you're asking about teenage girls having aneurysms, and you are that teenage girl, I strongly suggest you seek the help of a doctor. It is possible for a teenage girl to have an aneurysm, but again, it'd be rare at such a young age. If an aneursym ruptures, a lot of factors can determine the outcome. Where was the aneurysm? Aneurysms in the brain feature high mortality rates, same with the aorta (this one in particular is incredibly high without prompt medical treatment). However, they do not always lead to death —Cyclonenim (talk · contribs · email) 23:15, 31 October 2008 (UTC)[reply]
I'm wondering if chimpanzees and apes/gorillas have menstrual periods like humans, or if they have an egg already ready and waiting, and if that is the case, do the females go into "heat" like cats and dogs?Cindycat (talk) 00:47, 1 November 2008 (UTC)[reply]
Its a good question. We have three articles on Chimps: Chimpanzee, which covers the genus Pan in general, and the two species of chimpanzee: the Common Chimpanzee and the Bonobo or pygmy chimpanzee. Chimpanzee females of both species exhibit what is called "genital swelling", an engorgement of the vulva, which is an indication of being ready to mate. Common Chimpanzees only exhibit this during fertile periods, while the Bonobo female is pretty much in a state of constant sexual readiness, regardless of fertility. However, our articles coverage on Chimpanzee sexual physiology is lacking, and I am not much of a zoologist, so I will have to defer to a more expert person beyond that. As far as Great Apes beyond the Chimps, well, 3 genus (Chimp, Gorilla, and Orangutan), 6 species, and about a dozen or so subspecies of Great Ape, and our articles there don't expand much on this either. --Jayron32.talk.contribs02:30, 1 November 2008 (UTC)[reply]
When was the speed of sound broken (by man made object)
Can anyone give me suggestions or give me tips and things to look out for? I am building a ROV with a constraint of using these materials provided to me:
2 24" PVC pipes
10 L-joints
10 T-joints
3 motor mounts
The tethered ROV will be dropped and launched in a 50x25m pool. The ROV will pick up a metallic object using an electromagnet and will drop it on a target elsewhere in the pool. --hello, i'm a member | talk to me!04:15, 1 November 2008 (UTC)[reply]
Mechanical Puzzle
This has been bugging me. Say we have two identical cylinders A and B, with their axes parallel and set up to spin freely. Then gear them together so that B always spins through three times the angle A does. Procure a long strip of stretchy material (rubber band or something) and attach one end to A. Wrap it around A repeatedly, keeping a bit of tension so it doesn't slip off, and when you get to the end stretch it out and attached the loose end to B. Now, spin B to wind the rubber band off of A. Once it's wrapped around B, it will be three times as stretched out as it was when it was wrapped around A. So, if you let go, will it unwind? If so, with how much force? Black Carrot (talk) 07:39, 1 November 2008 (UTC)[reply]
Yes, it'll unwind with the same force as it was wound up. Just put on wheels, a seat steering and brake and you've got yourself a green vehicle for when fuel prices go up again :) Dmcq (talk) 10:23, 1 November 2008 (UTC)[reply]
I have a friend who is keen to keep her old black-and-white television through the digital switchover as the licence is so much cheaper. Of course this tv doesn't have a scart socket, but apparently all she needs is a (Freeview) set-top box with an RF output rather than (or as well as) the usual scart. The official site lists several models of box that have this, but a couple of hours of searching brings up few on-line suppliers that have any of them in their catalogue, and none of those actually have any of those models in stock. Does anyone know for sure that these boxes are actually available? Or does anyone know of a gizmo that can convert the scart signal to RF for the aerial socket on the back of the television?--Shantavira|feed me14:05, 1 November 2008 (UTC)[reply]
