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November 20

Could gold jewelry, such as a necklace, have toxic amounts of mercury or other heavy metals on

its surface? I know someone who has jewelry from Pakistan. She has a visible ring of excema around her neck where a necklace would be. The excema seems to have spread from there down her back. ThanksRich (talk) 06:27, 20 November 2007 (UTC)

Well, mercury is sometimes used in the processing and extraction of gold - and it's possible that her supposedly gold jewellery is really made of something else with a gold coating - so it's certainly possible that there are other heavy metals present. Eczema isn't a symptom of mercury poisoning - but we aren't allowed to give medical advice here - it would certainly be wise to seek the services of a doctor. SteveBaker (talk) 06:39, 20 November 2007 (UTC)

This is not medical advice just jewellery facts. Nickel is very commonly used in cheaper gold jewellery as an alloy to reduce the cost. A significant number of people suffer local allergic reactions from nickel in such jewellery. Try 'nickel allergy' on google and you will be surprised. Richard Avery (talk) 09:29, 20 November 2007 (UTC)

Is Universe expanding or deflating?

If either is the case, how sure are we? -- Taku (talk) 07:23, 20 November 2007 (UTC)

Expanding. We're very sure because distant galaxies appear to be moving away fro Earth (their light is red shifted) extremely quickly, and not only that, the speed they appear to be receding at is proportional to their distance from us. See Hubble's law. I know of no way to explain this relationship between distance and speed other than with an expanding universe. --Bowlhover (talk) 08:44, 20 November 2007 (UTC)

We're absolutely certain it's expanding - you can look out at distant galaxies and see that the light from them is redder than it should be - and that's a sure sign that the universe is expanding. The 'big bang' theory for the origins of the universe is firmly established - and what happens to something after it goes "BANG!" is that debris gets flung out in all directions...and that's essentially what we have. Since the 1930's, until just recently - it hadn't been clear whether the expansion was fast enough to avoid a gradual slowing of the rate of expansion - followed by a reversal, a collapse and then a 'big crunch' at the end. However, it turns out that we're actually in the puzzling position of finding that the rate of expansion is actually gradually increasing - this is quite surprising and I don't think we have a firm grasp of why that is yet. It's almost like there is some kind of anti-gravity that's only stronger than regular gravity over very long distances. SteveBaker (talk) 21:27, 20 November 2007 (UTC)

Thanks for the answers. Can I ask then: is that the case that the Universe has been expansing so far (accepting the Big Bang) but might the process be reversed in the future? If the rate of the expansion is accelerating (e.g., due to the known value on the cosmological constant?), the idea of the continuously expanding universe is counterintuitive. -- Taku (talk) 23:02, 20 November 2007 (UTC)

Well, this was a question that was in doubt until maybe ten years ago - before that, it was considered that if there was too little mass in the universe then there wouldn't be enough gravity to prevent the universe from expanding forever (as the universe expands, so the attraction between the galaxies would get weaker as the distance between them increases) - if there was too much mass then the gravity would be strong enough that the expansion would gradually slow down, then stop, then reverse - falling faster and faster together until there would be a "big crunch". What we found in 1998 was neither of these things. The universe is not just expanding - the rate of expansion is actually increasing. So for sure we're not going to have a 'big crunch' with everything collapsing back together again. The consensus of opinion right now (I believe) is that the ultimate fate of the universe is what is currently being called "the big rip" - in which space gets stretched out so such a high degree that eventually, all matter will get pulled to shreds - the atoms themselves getting ripped to fundamental particles. Another similar theory is called the big freeze.

I don't find an expanding universe counter-intuitive - what I find counter-intuitive is that the rate of expansion is increasing. Cosmologists don't seem to have a good explanation. They talk about dark matter and dark energy somehow being the cause - but since we don't have a clue what these 'dark' things are, this explanation is little better than "I have no idea". Anyway, I recommend our article Ultimate fate of the universe which is quite approachable by the layperson. SteveBaker (talk) 00:11, 21 November 2007 (UTC)

There's no consensus that there will be a big rip; in fact it's not considered an especially likely possibility. For the big rip to happen, the cosmological "constant" would have to increase with time (which it might). A big crunch also remains possible if it decreases instead. If it's really constant, the ultimate fate of the universe is roughly de Sitter space, which wouldn't seem much different from now except that you couldn't see any other galaxies. (But eventually heat death sets in -- this is the big freeze scenario.) -- BenRG (talk) 12:30, 22 November 2007 (UTC)

There's another possibility. We are in a big crunch. As we fall together, we're speeding up. Furthermore, as we fall we come apart (expand).

Sure. If you drop a system, the part of the sysytem nearest Earth will get a stronger gravitational pull than the parts of the system furthest away. I'm sure you can see how, over time, and especially if the system is falling 'end over end', the system can be seen to expand.

The Cosmos has also clumped up. Wmap and other observations have shown the early Cosmos was almost completely smoothly spread out. Since then we've clumped up, and clumping up is a feature of a vortex. When you stir your cofee, where do the bubbles go? When you put a tablespoonful of sand in a bucket of water and stir, where does the sand go? To the center, of course. I don't know anywhere else but a vortex, or whirlpool, to look for clumping up.

If the Cosmos is a Whirlpool, maybe shaped just like the Whirlpool galaxy, or our own Milky-Way, then probably therew's also a Black Hole there too, at the center of the Universe.

Could be...

How sharp is that knife?

Is there an official standard (ASTM or similar) for measuring how sharp a knife is? --67.185.172.158 (talk) 08:50, 20 November 2007 (UTC)

I found a link to an abstract of an article (Engineering Fracture Mechanics. Volume 74, Issue 14, September 2007, Pages 2205-2224.) that says "To date, there is no standard definition, measurement or protocol to quantify blade sharpness." I'm as surprised as you are. I googled on [scalpel "sharpness" standard], thinking that if anybody would care that much it would be surgeons. --Milkbreath (talk) 12:21, 20 November 2007 (UTC)

What do the brackets do in the search query?--droptone (talk) 12:34, 20 November 2007 (UTC)

Good question. Let's see.... Nothing. Whew! What's the approved way of reporting a search string to include double quotes? --Milkbreath (talk) 13:28, 20 November 2007 (UTC)

I suggest italicizing the "search string". — Lomn 13:48, 20 November 2007 (UTC)

I would write: I googled on "scalpel", "sharpness", and "standard". Of course, the double quotes in the particular example had no effect anyway, as they did not enclose a phrase. --Anon, 05:10 UTC, November 21.

Au contraire, mon frere, if you don't use the quotes on the single word "sharpness" you get hits on "sharp", "sharps", etc. Google didn't used to do that in the beginning, but now it does. --Milkbreath (talk) 11:10, 21 November 2007 (UTC)

Take a look at the Obsidian article, which has a reference for how sharp a blade can be, at least for Obsidian blades. --Mikenorton (talk) 17:10, 20 November 2007 (UTC)

17th century Japanese samurai sword makers had a standard - the number of body-thicknesses it would cut through in one swing...determined experimentally of course! A good sword might be rated as "5 bodies". (See Tameshigiri) This is perhaps not what you were looking for though! SteveBaker (talk) 21:16, 20 November 2007 (UTC)

A problem with such a rating system is that the act of cutting blunts the knife - so once a knife had been rated, it would no longer be as sharp as it was. I am also reminded of the episode in the Crusades, when Richard the Lionheart and Paladin compared swords. Richard's was sharp enough to cut through an iron bar, while Paladin could cut through a silk cushion, and therefore won!. —Preceding unsigned comment added by DuncanHill (talk • contribs) 21:26, 20 November 2007 (UTC)

Take a look at ISO 8442.5. --80.229.152.246 (talk) 23:57, 20 November 2007 (UTC)

ISO 8442.5 sharpness and knife durability system has been in use ( prior to standardisation) since the late 1960's primarily in the UK. CATRA who pioneeered the system, manufacture a machine that is used widely throughout the World for the measurement of sharpness of knives and blades ranging from utility razor blades to large industrial cutters. They also make another sharpness and edge life durability system for more delicate blades such as surgeons scalpels and shaving razor blades. see [1] for further details — Preceding unsigned comment added by 91.85.162.215 (talk) 18:03, 31 July 2008‎

Growing up in zero-g

It must have been asked before but: Is it possible and what are the problems for a child to be conceived, born and to grow to adulthood in a zero-g, weightless environment? Let's say have a litlle family on the ISS for example. Would he survive, what imperative measures should be taken for his survival, what consequences would it have on his appearence? Keria (talk) 13:45, 20 November 2007 (UTC)

This (referenced in sex in space) has some speculations, but of course there's no direct evidence as yet. Algebraist 14:06, 20 November 2007 (UTC)

• Extended time in low gravity has various harmful effects on the body, such as blood concentrating in the upper body, muscular weakness, and bone density loss. Our space medicine article is sadly inadequate, but it's a big concern for *-onauts. Presumably it would be much more severe for a person who had never been in Earth-normal gravity; it's possible that person could not safely go to the Earth at all. --Sean 14:29, 20 November 2007 (UTC)

Even with rigourous exercise courses, people who have been in space for just one year come back pretty much as invalids for many months afterwards and can take years to fully recover. It's really hard to believe that a child would survive for very long - let alone grow to adulthood without problems. You can't have a 3 week old baby doing crunches with bungee cords tied to them for resistance - and bone density loss is bad enough for someone who is not trying to double in size after one year and double again within two. It's really hard to imagine how this could work. If we're going to be spending any amount of time in space, we need spinning spacecraft - and that means big spacecraft (in order to minimise weird coriolis and tidal effects) - and that means a strong spacecraft (the classic donut-shaped spinning space stations from the movie 2001 would be really tough to construct because all of that 1g donut would have to be supported like a suspension bridge here on earth) - and that means a heavy spacecraft - which makes it HIDEOUSLY expensive to launch. We need to get out space elevator working first. Sadly, I don't think this is happening any time soon. SteveBaker (talk) 21:08, 20 November 2007 (UTC)

People coming back from long duration spaceflight aren't 'invalids for many months' by any stretch of the imagination. But your point about people having trouble adjusting to 1 g after months in space is valid. Experiments of this sort using animals could be performed currently, and would probably yield very interesting results, though I don't know what they might be. anonymous6494 02:49, 21 November 2007 (UTC)

According to this abstract, no mammals have been born in weightlessness so far. There have been studies with pregnant rats like this one, however. Icek (talk) 09:08, 21 November 2007 (UTC)

Sound from Jupiter

The Jupiter article says:

In 1955, Bernard Burke and Kenneth Franklin detected bursts of radio signals coming from Jupiter at 22.2 MHz

• Decametric radio bursts (with a wavelength of tens of meters) vary with the rotation of Jupiter, and are influenced by interaction of Io with Jupiter's magnetic field.
• Decimetric radio emission (with wavelengths measured in centimeters) was first observed by Frank Drake and Hein Hvatum in 1959.

Does that mean it can be listened to? If so where can I find a recording? Keria (talk) 13:49, 20 November 2007 (UTC)

You can indeed listen to Jupiter. A Google search for Jupiter sounds will get you a multitude of hits.

• This page from NASA has a number of sound samples as well as a whole bunch of other information about where the signals come from.
• Radio JOVE is a NASA-sponsored educational project that records and studies astronomical radio sources, including Jupiter.
• Radio-Jupiter Central is for the advanced amateur. It has sound samples, and also describes the equipment that you will need if you want to receive Jupiter signals directly.

Hope that helps. TenOfAllTrades(talk) 14:15, 20 November 2007 (UTC)

Crack, pop, whizzz! Thank you very much TenOffAllTrades it helped a great deal. Keria (talk) 15:36, 20 November 2007 (UTC)

Aww, and here I was hoping it would be "Drops of Jupiter" on repeat. :( shoy (^words _words) 17:20, 20 November 2007 (UTC)

Note that this electromagnetic radiation can't actually be heard unassisted by the human ear because they aren't "sound". Your ear picks up mechanical pressure disturbances in the range of about 20-22,000 Hz, which we usually call sound. Radio waves are more akin to light than sound, and even if they were pressure disturbances (which don't travel too well in a vacuum), they are too high a frequency for you to hear. The sound you're actually hearing in these samples is a radio's "interpretation" of the electromagnetic signals into audible output. - Katavothron (talk) 18:11, 20 November 2007 (UTC)

And of course there are a nearly infinite number of ways of 'interpreting' radio waves as sound - so what one person did to the radio to get audio may not be the same as what someone else did. SteveBaker (talk) 20:58, 20 November 2007 (UTC)

Quite right. I'm inclined to think of a listening radio's rendering of such astronomical signals as an "artistic interpretation" more than anything else. That's not to say that no useful data can be extracted from the sounds that the radio interprets, but for serious study it's probably most useful to look at the raw signals received. - Katavothron (talk) 21:47, 20 November 2007 (UTC)

So they didn't just scale up the signal a thousand to a million times (from 22MHz to 20-22,000Hz)? Keria (talk) 08:20, 21 November 2007 (UTC)

How do you "scale" a signal? You could massively downsample it, yielding audio that contains low harmonics of the RF signal, which is one possible route for making sound. You could play it back at a much lower rate, letting you hear the events over a significantly longer period of time than they actually occurred. Short wave radios actually perform some demodulation of the signal they receive, typically assuming an AM scheme. That's why we said that what you hear is just an interpretation of the signal, and there are many ways of interpreting it. You can't actually hear the signal as it is received by the radio, so the radio does some modifications to yield something that is audible. - Katavothron (talk) 19:53, 21 November 2007 (UTC)

physiology

how is human gastro intestinal tract moves? —Preceding unsigned comment added by 59.92.102.100 (talk) 14:26, 20 November 2007 (UTC)

Peristalsis. --Sean 14:32, 20 November 2007 (UTC)

Can nanomachines potentially cure RNA viruses?

I heard nanomachines can be used in medicine. Are there any thought experiments on using them to cure RNA viruses? 64.236.121.129 (talk) 14:32, 20 November 2007 (UTC)

Today? No, we're not that advanced yet. Someday? Absolutely. It would just have to mimic the portions of the human immune system that normally deal with these problems. In theory, anything that can be done naturally could be duplicated with nanotechnology. The toughest problems would be dealing with the mutations that are common in RNA viruses, not accidentally attacking other things, such as the host or its symbiotic bacteria, keeping the host's immune system from attacking the nanomachines, and keeping the nanomachines from being toxic in some way. Still, this technology is probably a long way off, a couple of decades at least. -- HiEv 15:28, 20 November 2007 (UTC)

There are of course problems relating to such technological advances. Lanfear's Bane | t 16:46, 20 November 2007 (UTC)

I wondered if someone was going to bring that up... shoy (^words _words) 17:21, 20 November 2007 (UTC)

We're really too far away to tell. Generally, when a technologist predicts something will be here in 5 years or less, they are about right. When they say "two decades" they really mean "I have no clue if this is even a practical possibility, much less when we'll have one to play with". Somewhere between 5 and 20 years is a region where we're pretty sure something can be done - but we don't know exactly when. Nanotechnology (as in little autonomous robots) is in the "eh - maybe twenty years" class. We don't know if they will remain stable under chemical attack or survive the rigors of brownian motion even - and we really have no clue how we'd actually build one. Speculating on what such a machine might or might not be capable of is kinda crazy at this point. SteveBaker (talk) 20:29, 20 November 2007 (UTC)

interaction of infrared with skin

can an infrared beam give unique signature when reflecting from skin or flesh. also can an IR penetrate in flesh and reflect from bones? Neel shah556 (talk) 14:33, 20 November 2007 (UTC)

In IR photography with Kodak HIE, it is common to see the blood vessels under the skin. Apparently, there are biometric systems using this phenomenon. I've never noticed bones being visible in IR photography. -- Coneslayer (talk) 15:11, 20 November 2007 (UTC)

For a little context, see previous related questions from the OP, leading to this line of discussion. I would be surprised if infrared photography could reveal bones, as water absorbs radiation in most of the IR range very readily (in something on the order of thousandths of an inch.) In fact, the above article says "These wavelengths also penetrate a few millimeters into skin and give a milky look to portraits". Are there any places where bones come within a few millimeters of the skin? If so, you might get an image of them at that point. jeffjon (talk) 19:26, 20 November 2007 (UTC)

I used to design simulations of InfraRed cameras for military flight simulators - so I've spent altogether too much time worrying about these things! What you see depends strongly on where you are in the IR section of the spectrum. In the medium wave ("mid range") IR part of the spectrum, what you see is pretty much dominated by radiation from warm objects - not so much IR light reflected from them. That's why you can see veins and such - they are generally a little warmer than the surrounding flesh so they give off more IR light. But IR light doesn't penetrate skin very well, so you can't see deep into the body - probably why you don't see any bones. You won't see much by reflected light either because IR reflectivity isn't all that large or variable. However long-wave or "far" IR is getting up into the realms of microwaves and shortwave radio (it's a kinda fuzzy boundary) - which includes stuff like millimeter band radar that does refract through things like bones quite well but is hard to bring to a focus to make a decent image. However, you don't want to be irradiating people with microwaves at short range - and at longer distances, long wave IR gets blocked by water vapor in the air so there isn't much to see except at a few very specific frequencies. Short-wave or "near" IR is almost in the visible band - and (predictably) behaves a lot like ordinary red light. SteveBaker (talk) 20:24, 20 November 2007 (UTC)

If you had a gallon of pure white blood cells would it look white?

If not, what would it look like? 64.236.121.129 (talk) 15:41, 20 November 2007 (UTC)

A buffy coat is nearly all white blood cells (spinning down blood in a tube separates the red blood cells from white blood cells - the layer of white blood cells is called the buffy coat). It has that name because it is buff in color, which is kind of a whitish tan. I suspect a gallon of WBCs would retain that color. --Joelmills (talk) 17:43, 20 November 2007 (UTC)

I'm sure this is related to the fact that we call "brown people" "black", and "flesh people" "white". White and black chess pieces were probably not always actually black and white (probably made from wood and what not). Rfwoolf (talk) 18:53, 20 November 2007 (UTC)

Can radar detect organic flying creatures?

Birds and stuff? Or maybe a human skydiver? If not, is it possible to detect them through other means? 64.236.121.129 (talk) 15:58, 20 November 2007 (UTC)

Yup, according to radar "Clutter refers to actual radio frequency (RF) echoes returned from targets which are by definition uninteresting to the radar operators in general. Such targets mostly include natural objects such as ground, sea, precipitation (such as rain, snow or hail), sand storms, animals (especially birds), atmospheric turbulence, and other atmospheric effects, such as ionosphere reflections and meteor trails. Clutter may also be returned from man-made objects such as buildings and, intentionally, by radar countermeasures such as chaff." -- MacAddct  1984 ^{(talk • contribs)} 16:02, 20 November 2007 (UTC)

(After edit conflict) Yes, flocks of birds and swarms of insects are routinely seen on weather radar. -- Coneslayer (talk) 16:05, 20 November 2007 (UTC)

I see. Hmm, so we can detect them, but they are usually ignored. Can't this be exploited to make a weapon? Maybe a small ornithopter strapped with explosives? 64.236.121.129 (talk) 16:09, 20 November 2007 (UTC)

Or how about a full-sized plane whose radar cross-section is as small as a bird? I can assure you that military exploitation of radar limitations is not a new idea. -- Coneslayer (talk) 16:17, 20 November 2007 (UTC)

In theory, perhaps, but it's difficult to envision a scenario in which that would be preferable to a cruise missile or a helicopter or something else that already uses ground clutter to avoid radar. Additionally, I would expect that trained radar operators wouldn't have much trouble distinguishing the flight characteristics of organics from artificial sources. — Lomn 16:22, 20 November 2007 (UTC)

Ever see an ornithopter in the sky? Looks almost exactly like a bird. 64.236.121.129 (talk) 16:29, 20 November 2007 (UTC)

How much explosive material can they carry, while remaining capable of flight and still looking like a bird on radar? -- Coneslayer (talk) 16:50, 20 November 2007 (UTC)

Dono. Depends on how well you make it. 64.236.121.129 (talk) 16:56, 20 November 2007 (UTC)

I don't think it's so much a question of "looks" as "behaves". Birds aren't likely to fly attack vectors. While you could conceivably stretch the imitation to full-out flock behavior by the birdbombs, you're back to the question of why you'd spend the effort when other weapon systems fill the role. Here's a thought, though -- a recon ornithopter might be an interesting prospect. I'm pretty sure the military is mostly looking at fixed-wing designs for man-portable aerial recon, though -- probably due to power efficiency. — Lomn 19:01, 20 November 2007 (UTC)

Yet the ornithopter article suggests that flapping-wing designs are highly efficient compared to fixed-wing designs. Maybe the lack of popularity of ornithopters has more to do with the cyclic motion in the fuselage/body, and the higher stress loads? jeffjon (talk) 19:30, 20 November 2007 (UTC)

That's right. A flapping-wing design is more efficient. Btw, Lomn, you would spend the effort if it worked better. Which it potentially can, depending on what it is capable of, and what it can do. If it has the manuverability of a humming bird, I think that's a serious advantage. The lack of popularity I think has more to do with technological complexity. Using crappy gears and motors isn't how birds or insects flap their wings. 64.236.121.129 (talk) 19:58, 20 November 2007 (UTC)

Good point, I hadn't noticed the efficiency section. Given that, technological complexity is probably the correct reason, which would suggest that research will move in the ornithopter direction sooner or later. — Lomn 20:10, 20 November 2007 (UTC)

Unfortunately, the efficiency section is not very accurate. Ornithocopters are not efficient for high-speed flight, as the wing-section required for lift is miniscule already. At supersonic speeds, I believe flight would be impossible for an ornithocopter. Current aircraft are more efficient for their mass and speed than birds are. Comfort has nothing to do with why we don't build ornithocopters, otherwise why wouldn't our reconnaissance drones have flapping wings? It is in fact a "failing" of biology to evolve a species to occupy a high-speed, high-mass, high-altitude niche, because to do so would require some kind of rotary muscle that does not exist in any animal we know of. The phenomenon is similar to why our ships use propellers instead of flippers. In this case, engineering firmly wins out, as many sea animals can compete with the weight and speed of our ships. SamuelRiv (talk) 18:30, 21 November 2007 (UTC)

I don't think anyone is claiming an ornithopter can move at supersonic speed, nor is it supposed to. It's efficient at the speed it moves at, that's all that matters. Our recon drones don't have flapping wings because the technological complexity of such a system is great, and we can't properly emulate flapping wings that well yet. We still use rather primitive technology compared to how complex animals are. If we can emulate muscles, and ligaments, then we are on the right track. Malamockq (talk) 00:49, 26 November 2007 (UTC)

Why do cows moo?

Why? 64.236.121.129 (talk) 16:20, 20 November 2007 (UTC)

According to a 2002 book ([2]), "the social contexts in which [moos] are used have not been studied critically. Sancho 16:37, 20 November 2007 (UTC)

Communication between cattle does not seem to be particularly sophisticated. Cows moo primarily to announce their presence. A louder moo means they are objecting to something, often discomfort. AFAIK that's about it. See animal communication for a more general discussion.--Shantavira|^{feed me} 18:19, 20 November 2007 (UTC)

From having walked by and through fields at night with (nice) dogs, I can say they do make noise in order to sound the alarm when intruders walk in their pasture (I don't think they were greeting me). Keria (talk) 20:52, 20 November 2007 (UTC)

Why hasn't the Polar Bear been reclassified as a subspecies of brown bear?

The Grizzly–polar bear hybrid is a fertile offspring of a grizzly (subspecies of brown bear), and a polar bear. That would make it a sub species of brown bear. It even says so here, http://en.wikipedia.org/wiki/Polar_bear#Speciation So why is it still classified as a seperate species of bear? Shouldn't this have been corrected by now? 64.236.121.129 (talk) 16:38, 20 November 2007 (UTC)

The following is a quote directly from the section of the article that you referenced in your question:

But neither species can survive long in the other's niche, and with distinctly different morphology, metabolism, social and feeding behaviors, and other phenotypic characters, the two bears are generally classified as separate species.

Sancho 16:45, 20 November 2007 (UTC)

See also Species problem. The definition you offer (species are capable of producing fertile offspring) is not the only definition used. The definition of a species is a matter of controversy. -- Coneslayer (talk) 16:49, 20 November 2007 (UTC)

Hmm, interesting. I'm not sure allowing for social behaviors and things is a good idea though for classification of species. The scientific classification system is based on common ancestry.64.236.121.129 (talk) 16:59, 20 November 2007 (UTC)

Yes, the classification system uses common ancestry to define the relatedness of organisms, however, there is no clear-cut definition of when two organisms are different species. Often, morphology, ethology and physiology are also used, because they can affect mating populations, for example, mate selection, or even capability of producing offspring. (For example, chihuahua and mastiffs would likely be considered a different species since mating would probably be a physical impossibility without human intervention). -- JSBillings 18:56, 20 November 2007 (UTC)

The thing is, some subspecies of living beings (which are scientifically accepted) fit that criteria anyway 64.236.121.129 (talk) 20:03, 20 November 2007 (UTC)

This is another one of those things like "Is Pluto a Planet?" - in terms of scientific value, the debate has zero relevence. It's just a matter of what words we choose to use. What matters here is what the genetics of Brown and Polar bears have in common - or not. Whether we call them the same species or not is entirely irrelevent. Continually renaming plants and animals to fit the whim of some classification nut simply causes more confusion in the formal naming of species and makes otherwise useful text books become useless prematurely. It's just not worth the hassle to rename either or both kinds of bear. Their relative similarity is well understood by those who care. SteveBaker (talk) 19:48, 20 November 2007 (UTC)

That sounds more like your own personal opinion. It just seems like you could say that about anything. Anything is a matter of what words we choose to fit them. 64.236.121.129 (talk) 20:05, 20 November 2007 (UTC)

No - not at all. It is a fact that iron is a metal. That fact is true because the word "metal" has a fairly precise definition - and the fact is testable. Knowing that it's a metal tells me things I may not have known before - that iron is likely to be shiney, that it conducts heat well, that it's ductile.

But the term "species" doesn't have a clear black and white definition - it is NOT the case that "If two animals can interbreed successfully then they are defined to be of the same species" or "If two animals have more than 92% of their DNA in common then they are of the same species" - there is absolutely no hard-and-fast rule you can point to. It's a vague and fuzzy term. You can say that brown and polar bears share such and such percentage of genes or that they have similar or dissimilar habits in dietary matters or that they can interbreed - those are facts...but our classification words (like "species", "family" and "genus") are like "planet" - they are arbitary cutoffs within a continuous function with poorly defined boundaries.

Arguing whether two kinds of bear are or are not close enough in objective criteria to fall within the span of this fuzzy term is not an argument about bears - it's an argument about the meaning of "species" - and that's linguistics. Once you've decided on an answer, you know NOT ONE SINGLE THING about brown and polar bears that you didn't know at the outset. If you decide that they are indeed of the same species - you can't actually use that information to tell you whether these bears have similar diets or similar lifespans or anything that you didn't know before. That's not to say that the word "species" isn't useful - it's great for expressing larger, more obvious gaps - if you asked whether a polar bear and a giraffe were different species - we could immediately say "yes" - and if you asked whether my wife and I are from different species, we could certainly say "no". But if you ask whether a Cocker spaniel is a different species from a German Shepherd - we should have the guts to say "it really doesn't matter - it's entirely an arbitary thing" because knowing whether they are or are not considered to be of the same species conveys absolutely no useful information.

It really doesn't matter - it's a pointless and annoying debate - you might just as well flip a coin to decide.

SteveBaker (talk) 22:32, 20 November 2007 (UTC)

Sure, you know useful information if they are classified as the same species. You know they can breed with each other, and produce fertile offspring. If they are the same species, they should do that. I see what you are getting at though, but I'm not sure the analogy to the definition of a planet is comparable. Malamockq (talk) 05:15, 21 November 2007 (UTC)

Actually, this is not so black-and-white. What does "can breed" mean? Many human couples, even male/female ones, even of the proper age, fail to conceive, and not for lack of trying. Are they different species? Breeding success is always a probability. And as for even trying: Some animals of the same species will not breed in captivity, while some of different species will only if artificially brought into close contact. --Stephan Schulz (talk) 12:44, 21 November 2007 (UTC)

Yep - exactly. Lions and tigers can interbreed too (See: Liger and Tigon) - are they the same species? SteveBaker (talk) 21:06, 21 November 2007 (UTC)

No, they are not the same species because their offspring is infertile. At least the males are. But I already said that. Produce fertile offpsring, I said that was one of the criteria for being the same species. The fact that they can produce offspring shows that they are very closely related and had a common ancestor not long ago. Being the same species, can tell a lot. I don't agree with your comparison to pluto. It's completely different. Malamockq (talk) 00:40, 26 November 2007 (UTC)

I could easily argue that the definition of a metal is far too imprecise to be worthwhile: for a start, what about metalloids? Knowing whether an element is a metal doesn't tell you anything specific about its chemical or physical properties. Since the vast majority of elements are metals, and there are few enough elements for people to be familiar with most of them, it isn't really necessary to classify them in this way. However, there are so many different 'types' of living things that it is very useful to have some way of classifying them, and this is obviously going to be arbitrary to some extent. 130.88.79.77 (talk) 14:13, 22 November 2007 (UTC)

The biggest problem with invoking the strict "Can interbreed" definition of "species" is that out there in the real world, you can have four slightly different kinds of animals: A,B,C and D such that A can breed with B and B can breed with C - but A cannot breed with C. So under the "can breed with" definition, A is the same species as B and B is the same species as C - but A is not the same species as C! Worse still, you'll find that bot A and C can breed with D! So now you have a wonderfully circular collection of interbreeders and a definition for 'species' that requires that you redefine the common English phrase "is the same as" in a horrifyingly new and alarming way! Worse still, you may well find that a MALE 'A' can breed with a FEMALE 'C' but a FEMALE 'A' has no luck with a MALE 'C'. Now where is your definition? Males A's are the same species as C but females A's aren't? If you're going to use the word 'species' at all, then you have to admit that it's a loose approximation - and therefore you can't answer the question "Are brown and polar bears the same species". SteveBaker (talk) 21:19, 21 November 2007 (UTC)

...unless of course you use another definition, that e.g. includes morphological differences, ecological niche, or regional distribution. You may not be able to clearly assign each individuum, but you can distinguish both species.--Stephan Schulz (talk) 21:47, 21 November 2007 (UTC)

Certainly you COULD come up with a clear definition of the word 'species'. But the fact is that there is no such standard definition - so the word still means very little. The "Can interbreed with" rule is the one that's most often quoted - but it's not a hard and fast rule - nor can it be (as earlier arguments clearly demonstrate). SteveBaker (talk) 07:03, 22 November 2007 (UTC)

The one I'm more familiar with is "can and do interbreed if given a reasonable chance" (i.e. overlapping ranges, but not e.g. artificial insemination) with quite a bit of handwaving for historical precedence (e.g. dogs). --Stephan Schulz (talk) 09:58, 22 November 2007 (UTC)

Extinction

What problems are caused from a species going extinct? The ones I know are species naturally producing chemicals that are useful and can't be easily synthesized, and that one species going extinct could cause another one to die out (that one's recursive, but it still works, so long as there is another reason). Both of these would apply to plants more than animals, yet people seem to care more about protecting animals than plants. Why is that? Is this more of a humanities desk question? — Daniel 17:03, 20 November 2007 (UTC)

Lots of people care about protecting plants. Deforestation is a big issue. If you mean, people care more about the killing of animals than plants, then that just has to do with personal opinions and psychology. There is no universal law that says killing anything is wrong, it's just how we as a people decide for ourselves what is right or wrong. Some people only care about humans, and don't care about other animals. Some people draw the line at complex animals, but don't care about bugs or other lifeforms as much. No one is truly right or wrong in this way of thinking. Just a point of view. 64.236.121.129 (talk) 17:08, 20 November 2007 (UTC)

The organisations who do the publicity (because governments don't seem to care very much) know that people are not going to radically change their habits in order to save a freshwater snail. Polar bears and elephants however, make excellent publicity. Plants are even less impressive to most people. Heck, if some species of fern dies off, hardly anyone will notice...but if there are no cuddlywuddly white bears left - then that makes an impact. We love to anthropomorphise and while we can identify with a meercat - we can't with a snail. Sadly, this is human nature. Fortunately, in order to save the high-profile animals, we pretty much have to save the entire ecological pyramid on which they are perched - so in the end, so long as people do the right thing, the reason is less important.

The things we mostly lose when some species disappears is it's DNA. Often that can be saved and stored with the idea that at some time in the future we could use cloning techniques to bring the species back again. That might work for one species - but when an entire ecosystem vanishes - you'd have an impossible job restoring it all. The interesting pharmacological stuff could be recovered by cloneing a long-gone species, growing a few individuals and testing them for useful chemicals. The nasty problem of one species vanishing is that (as you say) whatever ate it will also die - but also whatever it ate may have a population boom and choke out a whole bunch of other species. These kinds of domino effects could reach a catastrophy point (in the mathematical sense) where the entire ecosystem goes into runaway boom/bust cycles leaving very little biodiversity at the end. With so little diversity, the world becomes very vulnerable to one disease sweeping through the population. The world will doubtless continue - but it may be a world which is exceedingly harmful to humans. Think about things like algal 'blooms' (Red tides for example, which release nasty neurotoxins into the ocean). A sufficiently monsterous one of those - which could perhaps be due to the extinction of some teeny-tiny shrimp that eats them or something - could quite easily kill off all of the marine life that humans eat across the entire planet. This would be devastating to human populations all over the world. The interconnectedness of all of the species on the planet make the present high rate of extinctions cause hard-to-predict (and therefore potentially dangerous) results. SteveBaker (talk) 19:40, 20 November 2007 (UTC)

One species going extinct usually isn't a huge problem for us, but when a large number of species become extinct, say by global warming or deforestation, you might be looking at entire ecosystems collapsing, and since we humans also rely on nature and the environment for food, shelter, medicine, etc, a large number of ecosystems becoming extinct can become a huge problem for us. Just think of all the nessecities nature provides; if a lot of those became extinct, we could run into some big problems. An extremely large ecosystem with a species going extinct may be slow to affect the whole ecosystem, but eventually the results could be worse than if a smaller self-dependant ecosystem had a key species becoming extinct. Of course ecosystems also rely on each other, so if enough of them collapsed, we might eventually go down with them. The most likely source of massive ecosystem collapse in the future would likely be globalwarmingsealevelrisedeforestationdesertificationexpandingofcitiesoveruseofresourcesetc. If the fossil fuels are depleted in a few decades though, the long-term effects will probably not extend for as many millenia as if we found a larger fossil fuel resource. I'm not an expert on this stuff, though. Hope this helps. Thanks. ~AH1^(TCU) 00:58, 21 November 2007 (UTC)

Being sliced

A common trope in action films is that during a dramatic fight, one combatant will rush past the other with a sword, or shoot a laser through the enemy. The enemy will laugh, apparently unhurt (although the sword is usually covered in blood), shrug this off... then fall apart a couple of seconds later (off the top of my head, I think this happens in Kill Bill, Underworld, Resident Evil and Cube, not to mention countless anime). How much of this is true; I can't imagine that being sliced would be painless, no matter how quick and sharp the blow, but could someone function for a few seconds cut in half provided that the halves stayed together? Laïka 18:42, 20 November 2007 (UTC)

I really, really don't think so. It's conceivable that some supervillains are just immune to pain and will laugh their evil laugh even a moment after being sliced in half. However, according to current knowledge it is not actually possible to go on functioning normally right up the point where one falls apart into pieces; lots of problems will be happening to your body right from the point where you get hit. So for the time being, this kind of thing lies strictly in the realm of fiction. I also recommend against doing any experiments to test this. ;P - green_meklar 20:04, 20 November 2007 (UTC)

If you think how much force is needed to cut meat even with a very sharp knife, and even more force to cut bone, a lot of force is going to be applied to the victim and they will be knocked about or over. Also don't expect that any nerves will function across the cut, so the distal part of the body will go limp and paralyzed. Graeme Bartlett (talk) 20:20, 20 November 2007 (UTC)

Even in the presense of massive blood loss, it takes time for the brain to die, so for cuts that are not directly thru the head, yes the person might continue functioning for "seconds". Also, from personal experience, I know that very sharp cuts can be virtually painless initially (until oxygen exposure starts killing cells). I don't think it is humanly (or physically) possible to cut a person in half with anything near the cleanness of the movie images, but if you could make that magic cut, I suspect that the unaware reaction is a plausible result. Dragons flight (talk) 20:38, 20 November 2007 (UTC)

In response to an earlier question, I just discovered that Japanese samurai swords were rated for sharpness according to the number of human bodies (typically cadavers) they could slice through with a single stroke. A good sword had a rating of 5 bodies. So, yeah - amazingly, I think we have to admit that such a sharp cut is possible. I agree that you'd have a few seconds of life left - but what bothers me about those movies is that the top and bottom halves of the body stay together so well - I don't think that is possible given the kinetic energy of a fast swinging sword. SteveBaker (talk) 21:53, 20 November 2007 (UTC)

The sharper a sword is, the less energy it delivers to its target. A sharp sword can easily make a cut without the user having to use too much force. --Bowlhover (talk) 06:13, 21 November 2007 (UTC)

In principle, I don't see that it's much different from the magician's trick of pulling a tablecloth out from under a setting without disturbing that setting -- that is, possible, but highly unlikely if you look at random tablecloth yanks. — Lomn 23:04, 20 November 2007 (UTC)

Hey Steve - do you know of any swords that are sharp enough to perform the much-seen-in-anime longitudinal 'top of head to crotch' bisection with a single stroke? --Kurt Shaped Box (talk) 23:25, 20 November 2007 (UTC)

I'm no expert - I've just been reading around articles about Japanese swords today. The various articles we have (most notably Tameshigiri) suggest that a diagonal slice starting at the shoulder and emerging on the opposite hip (cutting the victim completely in half) was the easiest and most common Japanese Katana stroke. Certainly the best swords were more than capable of getting all the way through a body with one of those strokes (which is utterly amazing). Going vertically through that heavy bones in the skull sounds tougher - so I don't know. I don't think it's obviously impossible - but it's not likely to be the kind of stroke a genuine Katana swordsman would routinely use. SteveBaker (talk) 23:48, 20 November 2007 (UTC)

Mass graves at various European battle grounds also show that this was the preferred method of killing an opponent in the West as well. (My source comes from a book on European sword technique in the middle ages, which I’m having trouble finding on Amazon at the moment.) I wonder why this is apparently one of the preferred methods of killing with a sword? --S.dedalus (talk) 07:34, 21 November 2007 (UTC)

I practice kendo and iaido, and in both we do something called tenouchi, which is a wringing of the hands as you make contact with the body of the opponent. The idea is to stiffen the sword to be able to cut through bone, and this type of cut is indeed practiced in iai from the top of the head to the crotch. Apparently it gets much easier once the initial break through the skull is made. Also remember that you get a hell of a lot of leverage through your extended arms and the blade as you make a cut, and you have the momentum of your body weight that transfers to the sword through your footwork. SamuelRiv (talk) 00:55, 21 November 2007 (UTC)

So, what's the accepted wisdom when it comes to the spine? Are you supposed to cut directly down through it - or is the idea to slice slightly to the left/right of the column itself? Top of skull -> base of spine, straight through is a *lot* of bone to cleave... --Kurt Shaped Box (talk) 08:40, 21 November 2007 (UTC)

• I remember reading a William Gibson book at some point where a guy had a garrote-type device with a weight on the end where the wire was "only one molecule thick" or some such thing. He would swing it through people and they wouldn't notice for a moment, then fall apart. I remember being nonplussed that it would damage the victim at all. Surely the severed bonds would just reattach? Also perhaps relevant is the urban legend about the invisible jet of steam that can cut you in half: Cecil Adams takes the case. --Sean 02:33, 21 November 2007 (UTC)

The device you're referring to is a monomolecular wire, and it only exists in fiction. -- HiEv 11:26, 21 November 2007 (UTC)

• Related scenario: Darth Maul is cut in half in The Phantom Menace and emits a groan and facial expression change, falls in one piece into the reactor shaft behind him, then separates about halfway down. Also, Sean, we have an article about that: monomolecular wire. -Wooty [Woot?] [Spam! Spam! Wonderful spam!] 05:33, 21 November 2007 (UTC)

Regarding the pain factor: I got bit on my face by a dog once. There were several cuts and I ended up with 36 stitches on the outside of my face, and a few more stitches on the inside of my face in the deeper cuts. Still, I didn't feel any pain until much later. The only way I knew I was cut was from the look on everyone else's face, and when I touched my face my hand came away bloody. Not a pleasant experience, but it helps answer your question. I've heard of people even getting shot before and not realizing it until later, so it might be possible to be sliced up painlessly. -- HiEv 11:26, 21 November 2007 (UTC)

Re:spine-cutting, the practice is not to actually cut the spine in both kendo and iaido shomen, since the skull is cut with the last sixth of the blade only. The sternum seems to be the only main bone to cut through after the skull. Also keep in mind that there are a variety of other cuts that avoid the bone, and indeed pre-WWII Japanese police and military practiced these cuts extensively (the shoulder-to-hip being the most common, I think, but armpit-to-throat, hip-to-hip, slashes through the eyes and stabs to the throat and heart are also practiced). I'm no expert so this last statement should not be taken to heart, but the shomen head-to-groin cut seems to often be more of a technique to train precision and swordsmanship than actual combat. This of course, like everything, comes with many exceptions. SamuelRiv (talk) 15:10, 21 November 2007 (UTC)

As a point of reference, it's been said that when people were executed by decapitation (as with a Guillotine), their dis-embodied heads were able to function for a short time afterwards (a few seconds). Supposedly, there have been instances where convicted criminals have agreed to blink repeatedly after execution, with someone counting the time. [3] Compare this to the "chicken with its head cut off" [4]. -- 20:23, 21 November 2007 (UTC) —Preceding unsigned comment added by 128.104.112.120 (talk)

Since this IS Wikipedia, and it's a matter of tradition, one cannot help but follow that reply with a link to Mike the Headless Chicken. SteveBaker (talk) 20:56, 21 November 2007 (UTC)

A recent issue of New Scientist had a feature on death. The phrase "then, after the standard 10 seconds, you loose consciousness" turned up several times. It appeared in decapitation, heart failure, exposure to vacuum, blood loss. Apparently 10 seconds is how much (more or less) useful consciousness you've got after your brain stops getting blood/oxygen. You miss out on the 10 seconds in situations like "head first into the pavement at terminal velocity" and "bullet to an important part of the brain". --Psud (talk) 12:19, 22 November 2007 (UTC)

molecular weight help

help, I was given this equation about chemistry. Here, I'll show you how it looks like:

A + B -> C + D

I was given the molecular weight for both a, and d; the grams for a and b. I'm supposed to figure out the molecular weight for d. What do I do-I've been trying lots of ways, but I don't know which way is right. —Preceding unsigned comment added by 142.132.6.16 (talk) 19:16, 20 November 2007 (UTC)

Could you clarify this question? You said you were "given the molecular weight for […] d" and you are "supposed to figure out the molecular weight for d." Perhaps the molecular weight, chemical equation, and/or conservation of mass pages would be helpful? DMacks (talk) 19:21, 20 November 2007 (UTC)

Oh, sorry. I fixed it. I wasn't given the MW for d. :D

Terribly sorry, could you restate what you've been given? It still isn't that clear. If you could also list some of your thoughts on how to approach the problem, it will make it easier to know how to help you approach it in a way that makes sense to you. Skittle (talk) 20:20, 20 November 2007 (UTC)

whole breast tumour samples

"fewer [than expected] natural killer cells found in cancer component of whole breast tumour samples" - what's a "whole breast tumour sample"? Do they actually mean a whole breast? Like it's been amputated in its entirety and cut into sections? Methods section isn't part of the paper and I don't have access to it. --Seans Potato Business 19:48, 20 November 2007 (UTC)

It could just refer to the "whole tumor" [whole (breast tumor)]. If you're talking about the same paper that I just read, I agree that it's ambiguous (they change the specific wording several times). You could always email them and request clarification. Someguy1221 (talk) 20:13, 20 November 2007 (UTC)

Density of nerves as the body grows

If a human rapidly gains weight and the surface area of their skin increases do the nerves spread further and further apart, thereby making the skin less sensitive?

24.117.4.88 (talk) 20:00, 20 November 2007 (UTC)MLOvan

Good Viruses?

Just like there are beneficial and non-beneficial bacteria for human beings, are there viruses that human beings need/benefit from? --WonderFran (talk) 20:12, 20 November 2007 (UTC)

Complicated question. Firstly, the reason bacteria can be beneficial at all is that their proliferation in the human body only requires the availability of something they can consume. This allows for bacteria that consume material we wouldn't ordinarily digest at all, and many of these turn out to be either beneficial or entirely inconsequential. Viruses, on the other hand, operate by hijacking living cells and basically turning them into virus factories. They don't consume "unconsumables" or generate anything to benefit us (viruses only use human cells to make other viruses, so no side benefits). However, there are viruses that attack bacteria (bacteriophage), and these can benefit humans by attacking harmful bacteria (see Phage therapy). Additionally, gene therapy often involves using a viral vector to introduce a (hopefully) beneficial new gene into human cells. These vectors are usually something of a "neutered" virus that can't actually hijack human cells to benefit their own replication. Someguy1221 (talk) 20:27, 20 November 2007 (UTC)

• And scientists are also looking into manipulating viruses so they will attack and kill cancer cells which would be quite beneficial for some... - Mgm|^(talk) 20:43, 20 November 2007 (UTC)
• The previous answers looked to the future, but don't forget the past! Snorting a powdered scab that you picked off of someone with a cowpox lesion was the original smallpox vaccine, and the smallpox vaccine that eventually eradicated that disease in the wild was also virus-based. --Sean 02:48, 21 November 2007 (UTC)

Human society is the wild? o_O Someguy1221 (talk) 08:52, 21 November 2007 (UTC)

You don't know the phrase, "extinct in the wild"? Lol. That's a common phrase used in science. Geeze man. No offense, but that is basic knowledge. 64.236.121.129 (talk) 14:52, 26 November 2007 (UTC)

• I just meant smallpox doesn't exist in nature anymore, just in some hopefully-but-probably-not-well-guarded freezers here and there. --Sean 14:44, 22 November 2007 (UTC)

On the same note see Inoculation. Keria (talk) 08:50, 21 November 2007 (UTC)

• The Adeno-associated virus is somewhat neutral and could be used to create viral vectors. Keria (talk) 08:55, 21 November 2007 (UTC)

  Also, the Serotype 2 and cancer section in that article makes a rather interesting and relevant claim. It's not as surprising as it might sound at first — there'd certainly be an evolutionary advantage to a virus that actually helped its host stay alive and healthy while still managing to replicate itself. AAV is a clever little thing anyway, lying dormant and essentially harmless in cells until they are infected by another virus, and then hitching a ride on the other virus's replication machinery. In fact, I wouldn't be at all surprised if it even actually managed to slow down the replication of those other viruses as a side effect. —Ilmari Karonen (talk) 16:35, 22 November 2007 (UTC)

• HERVs make a significant showing on the human genome, so I suppose you could say that viruses have added DNA to humans, but I cannot say if this was good or bad. Graeme Bartlett (talk) 20:56, 21 November 2007 (UTC)

Amoeba have more DNA than a human?

Is the reason for this because of redundant information? 64.236.121.129 (talk) 20:14, 20 November 2007 (UTC)

I would guess it is because ameobas have need of a greater variety of proteins and such. Many micro-organisms tolerate a much greater variety of living environments and a wider range of food sources than people. In a nebulously defined way, you could easily say that an ameoba is more "complex" than a comparable human cell, since individual human cells are quite limited in what they can accomplish and tolerate. Dragons flight (talk) 20:27, 20 November 2007 (UTC)

• What a cell can accomplish function-wise is more a result of specialization than anything to do with its DNA. But yes, toleration of a larger variety of environments could be one reason. I'm actually sceptical. Human cells contain A LOT of DNA --that's why it took so long to have it sequenced. DNA or RNA sequences of smaller less complicated organisms and viruses where sequenced a lot earlier and somehow I don't think amoeba DNA is more complex than that of Arabidopsis or Drosophila (fruit fly). - Mgm|^(talk) 20:41, 20 November 2007 (UTC)
  • FYI, ameobas have a genome with ~100 times as many base pairs as people. [5] They are substantially more complicated then mere flies. Dragons flight (talk) 22:56, 20 November 2007 (UTC)

There's a term for this. See C-value paradox. 128.163.224.222 (talk) 21:07, 20 November 2007 (UTC)

One thing that has always bothered me about ameobas is that they reproduce by splitting in two. This means that - in effect (a) they live forever and (b) they are all clones of each other. I presume this makes it harder for them to evolve because all change has to come from random mutations and transcription errors - and no change comes from some happy coincidence of genes obtained from a mommy amoeba and a daddy amoeba who "loved each other very much". Which in turn leads me to suppose that in order to be adaptable to a reasonably wide range of conditions, they need a lot of DNA which is pre-programmed for all kinds of tricky situations that the species has lived through in the past. But I don't know enough to know whether this is a reasonable supposition...can anyone comment usefully? SteveBaker (talk) 16:07, 21 November 2007 (UTC)

This is true of any asexually reproducing organism, as I'm sure you're well aware. Asexually reproducing organisms generally benefit from relatively rapid lifespans (from birth to giving birth, in whatever methods this might entail). So you put an amoeba in an environment, and you'll very quickly (relatively) get lots of amoebas with lots of mutations. I'm not sure your "pre-programmed for all kinds of tricky situations that the species has lived through in the past" actually works; Sexual reproduction doesn't increase the rate of mutation, but merely produces semirandom combinations of available alleles for each gene, thus increasing diversity of traits. If these amoeba are used to their environment's regularly changing in a drastic manner, entire phenotypical subsets of their population would be regularly outcompeted, and I'm not sure asexual reproduction would give them anything of a leg up in that situation. As a point of fact that disagrees with my assessment, rotifers reproduce sexually only when under environmental stress, though that is possibly only because their sexually created eggs are more survivable than asexually created rotifer-babies. Someguy1221 (talk) 16:28, 21 November 2007 (UTC)

As an organism that eats by phagocytosis, it is possible that it occassionally incorporates DNA from bacteria it eats. Dragons flight (talk) 19:57, 21 November 2007 (UTC)

Also, think of the proposed hypotheses so far for junk DNA. Amoeba have more need of mutations than we do, so they need more "raw material" to mutate. It's not so much as their complexity, but the fact that if you have more DNA, you get a higher rate of mutation as well as a bigger "shield" for your existing genes against things like free radicals or radiation. (Effect: more mutations spawning new genes, less mutations affecting existing genes.) Amoebas live in much more volatile environments, do they not? Elle _{vécut heureuse} ^{à jamais} (Be eudaimonic!) 03:10, 23 November 2007 (UTC)

Anyone know what this is?

Does anyone know what this creature is called?unkown animal Thanks! Robert Beck (talk) 22:39, 20 November 2007 (UTC)

Dunno. It might be a kind of slipper lobster. --Milkbreath (talk) 00:11, 21 November 2007 (UTC)

Looks like it might be Parribacus antarcticus, do an image search to see more. 70.171.229.76 (talk) 01:37, 21 November 2007 (UTC)

November 21

Sociology

Is there report on Bangladeshi-Canadian community in Canada? —Preceding unsigned comment added by 76.64.133.44 (talk) 03:08, 21 November 2007 (UTC)

What sort of report are you looking for? Perhaps you should ask your question on the Humanities reference desk. (EhJJ) 14:27, 21 November 2007 (UTC)

Take a look at Demography of Canada, Ethnic groups in Canada and Canadians of Asian ancestry. Gandalf61 (talk) 14:44, 21 November 2007 (UTC)

Psychology

What would be a good hypothesis when it comes to Antisocial personality disorder? —Preceding unsigned comment added by 76.64.133.44 (talk) 03:16, 21 November 2007 (UTC)

Have you looked at Antisocial personality disorder, by any chance? Someguy1221 (talk) 03:21, 21 November 2007 (UTC)

information technology in 21st century

REMOVED.

Do your own homework. The reference desk will not give you answers for your homework, although we will try to help you out if there is a specific part of your homework you do not understand. Make an effort to show that you have tried solving it first.

Do not crosspost. Post your question at one section of the reference desk only. Lanfear's Bane | t 10:56, 21 November 2007 (UTC)

Arsenic Level in Diet

What types of food, particulary fish, can cause an abnormally high arsenic level? 71.218.1.121 (talk) 05:00, 21 November 2007 (UTC)

Any food that's been grown in the presence of Arsenic contaminated groundwater. Toward the bottom of the article, the only food mentioned is rice. Presumably any other plant watered with arsenic contaminated groundwater would cause the same poisoning, as well as any animals that eat those plants. Indeed, fish living in contaminated water also have high arsenic levels [6]. So it's not so much related to particular types of food, but any food grown with contaminated water. Someguy1221 (talk) 05:21, 21 November 2007 (UTC)

Mushroms are particularly good at concentrating toxins. Otherwise perfectly edible mushrooms can turn poisonous in the presence of contaminated water. --Milkbreath (talk) 13:43, 21 November 2007 (UTC)

Prawns contain arsenic. My nutrition book says that arsenic is an essential element in human nutrition. Graeme Bartlett (talk) 20:25, 22 November 2007 (UTC)

Fertilization

About how soon after ejaculation does the physical penetration of the spem into the egg happen? I've noticed runoff within minutes so I figure the timeframe is rather short, but we're arguing about the exact time frame. Kuronue | Talk 05:50, 21 November 2007 (UTC)

Runoff? :)!?! It's not minutes, it's from several hours up to three days. - Nunh-huh 07:06, 21 November 2007 (UTC)

On that note, I see that Human fertilization is sorely lacking. Oh well. Someguy1221 (talk) 07:08, 21 November 2007 (UTC)

There is some debate about whether it's as long as "three days" - and some debate about whether it's as short as "several hours" - but it's certainly more than a few minutes! The various prescription 'morning after pills' (eg RU486) that are available in some countries to prevent pregnancy AFTER unprotected sex can be taken a day or two after intercourse and still have a good 80% to 90% chance to prevent fertilisation. They aren't approved for use after 72 hours though - so three days is the probably the outside limit. (They also have all sorts of nasty side-effects - so don't even think about relying on them routinely!) SteveBaker (talk) 15:50, 21 November 2007 (UTC)

RU486 (like most other emergency contraceptives) apparently prevents implantation, not fertilization. -Arch dude (talk) 17:37, 21 November 2007 (UTC)

I thought it was implantation that takes hours to days? It takes hours for them to physically swim up to the egg itself? Kuronue | Talk 18:24, 21 November 2007 (UTC)

Yeah, it's a long path to a small cell. The sperm starts at the bottom of the uterus and typically meet the ovum in the Fallopian tube. It's a large trip in microspic scale. 200.255.9.38 (talk) 14:41, 22 November 2007 (UTC)

Please don't confuse RU-486, an abortion medication, with emergency contraception, which is contraception. Plan B and similar emergency contraception pills are NOT abortion pills, at least by the conventional definition of pregnancy and therefore abortion. Plan B works mostly by preventing ovulation. It used to be believed that it also significantly decreased the chances of implantation, but recent research has called that into question. RU-486, on the other hand, will destroy a pregnancy that has already started, meaning ovulation, fertilization, and implantation have already happened. moink (talk) 00:42, 22 November 2007 (UTC)

Facultative Aerobes

Is there such thing as facultative aerobes? Could somone say so and, if so, direct me a source of informatio (I've already looked in wikipedia, unsuccessfully). Thnx BeefJeaunt (talk) 06:26, 21 November 2007 (UTC)

Do you mean Facultative anaerobes? Aerobic organism gives nice rundown of the terminology used to describe differing tolerances for oxygen, excluding anaerobes themselves. Someguy1221 (talk) 06:41, 21 November 2007 (UTC)

Organisms can be placed into three categories, depending on their tolerance or need of oxygen.

1. Obligatory aerobes require oxygen and will die without it (includes humans)
2. Obligatory anaerobes require the absence of oxygen as they will die from oxygen's toxic effects.
3. Facultative anaerobes can live with oxygen (not poisonous to them) but also without oxygen (they do not need it to live). They could also be called "facultative aerobes", as this is essentially the same thing (can live in oxygen but will survive without it).

Sometimes, I believe the term "facultative aerobes" refers to organisms, such as humans, that require oxygen but can live without it for a short period of time (in humans, we need oxygen to break down glucose to produce carbon dioxide, but can also break it down to lactate when oxygen is not available). Not sure about this last part. (EhJJ) 14:40, 21 November 2007 (UTC)

Humans are not facultative aerobes. Humans are obligate aerobes, though such a term is rarely applied to large animals. The fact that our cellular metabolism retains anaerobic pathways doesn't negate the fact that without oxygen, we're dead. - Nunh-huh 03:40, 22 November 2007 (UTC)

Airplane movement

Suppose a plane fly from La Paz, Bolivia to New York, USA or maybe between two cities that locate on the same longitude but far away north and south. Does the plane need to slightly move to the east (as to chase the movement of the earth to the east)? Thanks for the answer. roscoe_x (talk) 13:15, 21 November 2007 (UTC)

The plane moves through a medium, air, that in general moves with the rotation of the Earth. It has to account for variations in wind speed, but the effects of rotation are already taken care of in the flight path. Now, the Coriolis effect during takeoff and landing is another story, as an aircraft will have additional eastward velocity when dropping from high altitude to low, as the air's linear velocity is generally larger at higher altitudes ($v=r\omega$). SamuelRiv (talk) 14:58, 21 November 2007 (UTC)

Do this experiment: Put your feet together and jump as high as you can. Let's suppose you were off the ground for 1 second. During that one second, the earths surface rotated maybe 400 meters (depending on your latitude). Did you find yourself landing 400 meters from where you started? Is there a 400 meter per second wind blowing right now? You lived to tell the tale, so I guess not. It's basically the same thing for the plane. When the plane, the earth and the air are all moving at the same 400 m/s speed, there is really no way to tell that you are moving at all. However, the effect you are thinking about is called 'The Coriolis effect' and it is really there as you suspected.

As I indicated the speed at which the ground is moving due to the rotation of the planet varies depending on your latitude. At the equator it's 463 meters per second. At the poles, it's zero. So if you fly due north from the equator, the rate that the surface of the earth is moving beneath you gradually reduces - so you are moving sideways at 463m/s at the equator - and if you flew north all the way to the north pole, the ground would not be moving at all due to rotation. Somehow you had to lose that sideways speed along the way - and that would mean flying at a slight angle to your planned course in order to counteract Coriolis 'forces'.

However, aircraft don't fly in a vacuum - if an air stream is blowing from the equator towards the North pole, then it too affected by the Coriolis 'force' and starts off moving with the planet at 463 m/s - and has to gradually slow down to zero by the time it reaches the pole. This results in Northerly and Southerly winds tending to veer off to the side as they shed this lateral motion. That results in a bunch of complicated swirling wind currents and such - that'll tend to blow your aircraft off course.

But that's no different in principle to winds caused by weather events. The net result of all of this is that while theoretically a pilot would have to take account of Coriolis, in practice, the effect seems to him just like various winds blowing him around - and whilst those are driven (at least in part) by Coriolis - other effects such as heating of air over land and cooling over ocean has a much bigger effect. So you plan your course to take account of the prevailing winds and counteracting Coriolis is just a small part of what you end up doing in fighting the prevailing winds.

Note that driving your car north/south also causes a Coriolis force to be applied to it - but again, it's too small to be noticable.

SteveBaker (talk) 15:35, 21 November 2007 (UTC)

Just a clarification, the Coriolis force acts on air moving in any direction. In the Northern hemisphere, this results in the air taking a right hand turn from the direction it would have followed if the Coriolis force was not acting (ie. air following an eastward pressure gradient will get forced south, air following a northward pressure gradient will get forced east, air following a southward pressure gradient will get forced west, and air following a westward pressure gradient will get forced north). Sancho 16:03, 21 November 2007 (UTC)

Steve, that's the best and clearest way of explaining the Coriolis effect that I've ever read. Much more intuitive (to me, at least) than the ways it's explained in our article on the topic, not to mention countless Physics textbooks. jeffjon (talk) 16:21, 21 November 2007 (UTC)

You absolutely do have to account for the Coriolis effect when you are making large changes in altitude, however, which was my original point. It is the same effect that makes Foucault's pendulum precess, and the British were certainly hit by surprise during the Great War in the Battle of the Falkland Islands when their naval shells weren't hitting on target due to the effect. SamuelRiv (talk) 17:09, 21 November 2007 (UTC)

Good explanation about the nature and magnitude of Coriolis effects, Steve. I once calculated that the Coriolis effect on a French high-speed train at full speed is equivalent to the force of a crosswind of 10 km/h or 6 mph. Enough to detect if you wanted, but not enough to be important. --Anonymous, 18:34 UTC, November 21, 2007.

Wow! That's a lot! Hmmm - I think it's too much. Excuse me while I crunch some numbers: So it's 10,000 km from equator to pole (easy to remember - ten million meters - that was the original definition of a meter) - and over that distance you have to shed 460m/s - so on average (because it's not a linear rate of loss with latitude) for every kilometer you drive north you need to shed 0.046 m/s of lateral speed. So if you drive a car at 100kph (about 60mph) you need to shed 4.6 m/s of lateral speed every hour - that's 0.0013 m/s² or about one ten thousandth of a g! A TGV goes something like 200mph? That's still nothing like the force exerted by a 10kph wind...not even close. Did I make a horrible boo-boo? SteveBaker (talk) 20:48, 21 November 2007 (UTC)

Might the discrepancy be that you're going for a full-trip average, while Anon was calculating the peak momentary Coriolis acceleration? Or maybe acceleration at a France-specific latitude? jeffjon (talk) 20:55, 21 November 2007 (UTC)

Yes, I mentioned France because that established the latitude. Steve's rough method gives an estimate of 1/2,500 gee, while the actual Coriolis acceleration at the relevant latitude is about 1/1,000 gee.

Modeling one car of the train as a flat plate positioned vertically and lengthwise along the track, I calculated the drag force of a 10 km/h crosswind as around 300 N, giving the correct acceleration since the car weighs around 30,000 kg.

--Anon, 00:21 UTC, Nov. 22.

Oh - of course! I was forgetting that to accellerate something as heavy as a train with even a fairly tiny accelleration requires an immense amount of force - hence the higher-than-gut-feel wind speed required. Thanks - there had to be something I was overlooking! SteveBaker (talk) 06:46, 22 November 2007 (UTC)

So you mean actually in real-life plane this Coriolis effect was negligible? Based on your experiment, what about if I'm in equator and I'm not jumping but I'm using certain device that let me go straight 1-km up 90 degrees and go back down 90 degrees. And let see I'm in the air for 1 minute. Am I going to land in the same place or 27600m (460m/sx60s) to the west of my position before? roscoe_x (talk) 13:48, 22 November 2007 (UTC)

If your 460m/s speed around the equator is stopped, yes. The same would go if it just made you hover, and it has nothing to do with the Coriolis effect. If not, the Coriolis effect will make you seem to move less than one six thousanth that speed (the radius of the earth is over 6000km). It would move you around half a meter. Compare that to how much wind would move you. — Daniel 02:33, 23 November 2007 (UTC)

Hypochondria

What would you call a person who is excessively worried about somebody else's (e.g. their child's) health? Exohypochondriac? Any ideas? — Kpalion^(talk) 16:29, 21 November 2007 (UTC)

Hypochondria is actually quite a broad term, and could well include morbid feelings about one's family. I'm mot aware of a more specific term, but you might well do better to ask on the Language desk.--Shantavira|^{feed me} 18:30, 21 November 2007 (UTC)

You might want to have a look at Munchausen syndrome, Fabricated or Induced Illness, Factitious disorder, Anxiety and Psychosomatic illness. Keria (talk) 18:54, 21 November 2007 (UTC)

You might also look at codependency. 70.171.229.76 (talk) 23:31, 21 November 2007 (UTC)

Overconcern? bibliomaniac15 05:48, 22 November 2007 (UTC)

Parenthood. -- Kesh (talk) 14:35, 22 November 2007 (UTC)

collagen/gelatin

I'm trying to understand what exactly makes gelatin so much better at forming gels and adhesives that hydrolysates of other proteins. I know that it has an unusual amino acid composition (high in Gly, Pro, Hyp, ...) but it is not clear to me that this explains its properties. ike9898 (talk) 17:34, 21 November 2007 (UTC)

I'm new to this as an area of research, so no fun equations for you, but generally such action occurs due to cross-links that links each protein chain to each other, forming a very tough but flexible substance in the end. I suspect water catalyzes this by some hydrolysis reaction, but I don't know. This is the same process that occurs in most polymers that gives them a stiff flexibility. I'm no chemist, so I don't know if this is the specific case for gelatin. SamuelRiv (talk) 18:15, 21 November 2007 (UTC)

I don't think any covalent crosslinks are formed. ike9898 (talk) 19:54, 21 November 2007 (UTC)

Crosslinks don't have to be covalent - sometimes they can just be polarized and that will work too for a polymer. You can also have weird cases like polyethylene where the polymer chain makes nonpolar branches that get physically entangled with those of other chains, making a less elastic and more breakable polymer. SamuelRiv (talk) 23:03, 21 November 2007 (UTC)

What is coulombic interaction energy?

What is coulombic interaction energy? Is coulombic interaction energy the same as lattice energy/enthalpy? Thanks in advance. AshLin (talk) 17:45, 21 November 2007 (UTC)

Yes indeed - it is effectively the same as lattice energy. Enthalpy is a bit different as it depends on the excitation of states (that is, the internal energy of each "atom" (a general term) independent of Coulomb energy). See the article on lattice energy for a formal definition: basically, you calculate the coulomb interaction energy between each atom, and sum it all up to get the lattice energy. Note that since atomic orbitals are not fixed, there is some polarization between atoms that changes the interaction energy a little bit (see Van der Waals force, but for an ionic compound this is not very significant. SamuelRiv (talk) 17:59, 21 November 2007 (UTC)

Does lava/magma conduct electricity?

Would molten rock conduct electricity in the same way water does? --86.142.170.168 (talk) 21:19, 21 November 2007 (UTC)

Water is actually an excellent insulator. It's impurities in the water that let it conduct. Lava is also a good insulator. This link gives its conductivity as "10x10-9 mho/m (basalt) at 300 K in the dark". Compare that with copper at 59.6 × 10+6 and deionized water at 5.5 × 10-6. --Milkbreath (talk) 22:30, 21 November 2007 (UTC)

If you like equations, and I hope you do, Electrical conduction has some great ones. Conductors work by having room for charge carriers (like electrons or salt ions) to move around relatively freely. Metals are great conductors because they have lots of free energy states, so electrons travel by making jumps to nearby energy states around other atoms. Water doesn't have this property unless, like Milkbreath said, you add some kind of polar or ionic molecule to it that will dissolve (water dissolves a lot of stuff), and so when you run electric current through it those molecules will propagate the current by aligning or moving their positive ends with the current and negative ends against it, making a current appear out the other side! Quiz: which conducts electricity better, salt water or fresh water? SamuelRiv (talk) 22:58, 21 November 2007 (UTC)

Salt water - that's why you should never take an electric fire into the sea. DuncanHill (talk) 05:52, 22 November 2007 (UTC)

Does the "300K" mean 300 Kelvin? That's what I call a warm rock, not lava/magma... --antilived^{T | C | G} 06:47, 22 November 2007 (UTC)

I was just about the raise the same point. Melting the rock would allow for ions (charged particles) to travel (more) freely from place to place; the resistance would be appreciably lower than that of solid rock. One sees this effect in the industrial production of sodium metal by the electrolysis of sodium chloride (table salt) in a Downs' cell. Solid, room-temperature sodium chloride is an extremely poor conductor. In contrast, molten sodium chloride will pass a significant current, as the individual sodium and chloride ions (Na⁺ and Cl^-) are free to move.

I would expect a similar behaviour from molten rock; magmas will be molten solutions of an assortment of ionic chemical species. Compared to any sort of reasonably pure water, it will be a pretty good conductor, though not quite as good as a pure metal. TenOfAllTrades(talk) 07:07, 22 November 2007 (UTC)

The electrical conductivities of magmas have been measured under lab conditions, and it seems that sodium is the main charge carrying phase in silicate liquids [7]. It is also clear that melting increases the conductivity [8] but I'm a bit short on actual numbers. Geophysicists need to know this in order to interpret MT (magnetotellurics) and other electromagnetic data.--Mikenorton (talk) 14:25, 22 November 2007 (UTC)

I found a few references to values of about 1 S.m^-1 (1 Siemen = 1 mho) for a partially molten rock, matching observed values beneath mid-oceanic ridges[9] (Note: the values on the diagram are actually resistivities but as the one is the inverse of the other, for values near 1 it's all much the same) where we know that there should be magma chambers.--Mikenorton (talk) 17:16, 22 November 2007 (UTC)

Outdoor warm-weather ice-skating rinks

How do these work? There are at least two in downtown Los Angeles, is it a big giant freezer unit under there? Any links to info on the tech or the companies who run them would be welcome. Donald Hosek (talk) 22:10, 21 November 2007 (UTC)

There are artificial ice rinks with a surface made of high density plastic. Several companies come up on google if you search.--TrogWoolley (talk) 22:42, 21 November 2007 (UTC)

For how they work, see ice rink: "This consists of a bed of sand, or occasionally a slab of concrete, through (or on top of) which pipes run. The pipes carry a chilled fluid (usually either a salt brine or water with antifreeze) which can lower the temperature of the slab so that water placed atop it will freeze."--Shantavira|^{feed me} 08:36, 22 November 2007 (UTC)

To follow up, does anyone know whether it's plastic or ice at the outdoor skating rinks in Pershing Square (Los Angeles) and Santa Monica? The latter, I can stop by over lunch on Monday and ask, but downtown is a bit more of a trick to get to. Donald Hosek (talk) 18:59, 22 November 2007 (UTC)

Regaining consciousness

What is happening as one regains consciousness? Regaining consciousness after fainting, I start off with blurred vision and confused about my circumstances. It's like not all my mind is functional, and what parts are that are there are trying hard to figure out what's going on. It's like I've no sense of the past, but only the present until the rest of my brain comes back online. (this is not a medical question - I fainted because I had a catheter inserted, which I think is a perfectly satisfactory response to such an ordeal! I do not need to see a doctor. I'm just wondering about the human brain seeming to switch on slowly) --Seans Potato Business 23:46, 21 November 2007 (UTC)

I recall speaking with an anaesthesiologist who told me the following tidbit: as people are anaesthetized, they are usually asked to count to ten. While most people remember counting up to (around) 4, they actually typically count to (around) 7. Sorry this doesn't answer your question, but I couldn't help sharing this second-hand anecdote. (EhJJ) 01:14, 22 November 2007 (UTC)

IANAMD, but I believe fainting (or loss of consciousness) is often due to quick change in blood pressure. So I assume the recovery is due to your body regulating your blood pressure back to normal levels. -- MacAddct  1984 ^{(talk • contribs)} 03:36, 22 November 2007 (UTC)

Technically, it all has to do with the reticular activating system. There are several reasons why you might lose consciousness (i.e. being knocked in the head, stress, drugs, sleep...) The one main common factor is inhibition/reduction in activity of the reticular activating system. When you are gaining consciousness, your are becoming more and more aware of all stimuli inputs into your brain. The reticular activating system has a "late, slow, excitatory" effect on the entire brain which results in increased level of consciousness. When sleeping, fainting, or under general anesthesia it's function is inhibited and the brain moves into a state of synchronization (as determined by an EEG) in which "consciousness" is lost. Now that I have said all that, you should note how you think about consciousness now. You only know it subjectively. There is a scientific reason and explanation for consciousness, and most of the concrete knowledge there came from the study of implications of the EEG signal and the reticular activating system. Mrdeath5493 (talk) 07:07, 22 November 2007 (UTC)

Hi Sean, IAAMD, and I can tell you that, firstly, fainting is what happens when your brain does not get enough blood to it (for a stack of reasons, including medical procedure anxiety! Believe me, I've seen it plenty) - lack of bloods inhibits the RAS (aforementioned by the deadly pharmacist) and off you go. The reason for the amnesia and the visual disturbance is also because of the lack of blood and oxygen and its effects on the other parts of the brain responsible for these things. The slow return to function occurs becuase the brain needs to have its normal physiological environment restored, and that requires delivering enough O2, electrolytes, sugar and removing metabolic wastes accumulated during the lack of perfusion that caused the faint. It's not like flicking a switch off and on, its more like cleaning up after a party - it takes a little while for things to come good! Cheers! Mattopaedia (talk) 03:33, 23 November 2007 (UTC)

particle - antiparticle pairs

a T.A. of mine told our physics class that particle-antiparticle pairs can be produced spontaneously even in the "vacuum of space", which got me thinking if this is bs or not. he said they usually anhilliate each other shortly thereafter unless one of them is sucked into a black hole or something. anywho, how can these pairs be produced spontaneously unless there's energy to make them? if they don't require energy then that contradicts thermodynamics since they hav a mass (and velocity) and so would add to the total energy of the universe. if they do require energy then how is it spontaneous, as we could expect them to appear where the necessary amount of energy exists? —Preceding unsigned comment added by 67.70.31.61 (talk) 23:57, 21 November 2007 (UTC)

You answered your self, they can occur naturally where the energy require exists and indeed this is how they are made manually as well see Antiparticle--Dacium (talk) 01:26, 22 November 2007 (UTC)

If I recall correctly, they can skirt around thermodynamics because they destroy themselves within a given amount of time, something to do with the uncertainty principle. At least, I'm pretty sure that's what they told me at some point when I was in college. See virtual particle, or the small bit on conservation and uncertainty at virtual pair. --24.147.86.187 (talk) 01:33, 22 November 2007 (UTC)

So far this is mostly accurate. See Pair production for the full story. Note that virtual particles are usually referring to the exchange particles of the fundamental forces, which have slightly different properties than their real counterparts. Pair-produced particles are entirely real, however. SamuelRiv (talk) 02:28, 22 November 2007 (UTC)

Hmm. I didn't think they always self destroyed... don't pairs around the edge of a black hole which don't self destroy have something to do with Hawking Radiation? So that's not quite the correct skirt round... --BozMo talk 14:18, 22 November 2007 (UTC)

Okay, to clarify, pair production occurs by energy in = energy out, so an amount of energy is absorbed to produce a positron-electron pair. They don't have to annhilate in certain reference frames, that is, in the reference frame where you have a high-energy particle that slows down as it creates a pair. They do have to annhilate if you see a pair produced out of nothing, as in a vacuum fluctuation or a higher-order interaction effect (electrons scatter by a virtual photon that can create a particle-antiparticle pair that annhilate and recreate the photon that finally interacts with the other electron, for example. See Feynman diagram for a picture). In the case of Hawking radiation, a particle-antiparticle pair is created in a vacuum, one particle gets sucked into a black hole and the other escapes. Does this violate conservation of energy? No, because the vacuum fluctuation that created the particles was in effect a defect in space that "borrowed" energy from the black hole's mass-energy (or gravitational energy). When a particle escapes, the energy goes with it, so the black hole loses mass. Again, this depends on your reference frame (this part I'm not fully sure on - I don't do GR), so from inside a black hole you wouldn't see any Hawking radiation because the energy from that perspective doesn't exist to create it.

Side note - it's easy to understand how energy is "relative". Think of it as if I'm moving quickly past you - I obviously have energy relative to you, because I'm moving. However, if you are moving at the same speed next to me, then I have no extra energy from your perspective since I'm not moving any faster. It's the same principle here, except using General relativity instead of Galilean relativity. SamuelRiv (talk) 15:00, 22 November 2007 (UTC)

November 22

Cooling down -- drink or pour?

I do not seek medical advice, and neither is this a homework question. I have seen people pouring liquid over their heads (presumably in order to cool down). The question is: if it was a very warm day at 30 C, and I had 1 liter of water at, say, 2 deg C; would it be more cooling for me to drink it, or (bearing in mind most heat is generated/lost in the head/brain) for me to pour it over my head( slowly) —Preceding unsigned comment added by 79.76.162.232 (talk) 02:09, 22 November 2007 (UTC)

By drinking it the heat of your body goes into heating up the water, thus cooling you somewhat. By pouring over your head the heat of your body (and the air) go into heating the water. By pouring it over your head you also get the benefit of evaporative cooling which will be much more significant than the cooling you get from just heating the water up. So pour over your head..... unless you are dehydrated, then you should drink.Shniken1 (talk) 02:19, 22 November 2007 (UTC)

But it will also constrict you blood vessels so less heat can be transferred away from your skin, therefore leaving you hotter in the long run. --antilived^{T | C | G} 04:20, 22 November 2007 (UTC)

Also, not much of the water you pour over your head gets evaporated: most of it lands on the ground, whereas all that you drink gets warmed to body temperature. Dribbling water slowly over your head or body might be more helpful than pouring it all at once, but of course that keeps your hands busy while you're presuambly trying to do something else.

Another point is that if you get dehydrated enough, you'll stop sweating, leading to more overheating and possible heat stroke, which can kill you. Drinking the water will prevent that -- unless you drink so much that you suffer water intoxication (hyperhydration), which can also kill you. Giving specific guidelines, of course, would be medical advice. --Anonymous, 05:25 UTC, November 22.

We've had similar questions in the past, such as why it is that dousing yourself in cold water after an intense workout only cools you down for a short period. As explained above, the chief culprit is vasoconstriction. What you need to decide with your bottle in hand is first, do you really need to cool down or do you need to hydrate, and second, how cold is that bottle of water? If the water is as cold as you mention, I would rinse the stuff in my mouth and spit it out. Some of the (now warmed) water would get swallowed to help hydration and the mouth can deal with temperature changes better than, say, your scalp, when it comes to simply cooling. Matt Deres (talk) 17:46, 23 November 2007 (UTC)

• A subjective, originally-researched answer: I'm a marathon runner in the southern USA, where it gets quite warm, and I have found that pouring some ambient-temperature water on my head (which is covered by a hat made of technical fabric) has a *much* greater subjective cooling effect than just drinking it. --Sean 22:01, 23 November 2007 (UTC)

physics

ships r made of iron and other heavy metals so why is it that when a ship is anchored it doesnt sink? —Preceding unsigned comment added by 59.95.15.157 (talk) 03:53, 22 November 2007 (UTC)

Yes, ships are often made of materials that are heavier than water. However, much of their volume is lighter than water, since they contain air. The weight of the ship is less than the weight of water contained in volume equal to the volume displaced by the ship, allowing for buoyancy. If you fill a boat/ship with water, it will sink. moink (talk) 04:04, 22 November 2007 (UTC)

(ec)

First off, it's not the case that lightweight things automatically float and heavy things automatically sink.

If you had a ten pound piece of wood, it would float, and if you had a metal coin that weighed two ounces, it would sink.

Try this: find a metal can, such as soup or canned vegetables come in. Remove the top completely. Fill it with water, and put it in a sink or bathtub full of water. It will sink, as you expect: the steel that the can is made of is "heavier" (or as we'll see, denser) than water, so it sinks.

But then: pick the can back up and empty half the water out, so that it's now half full of water. Put it back in the sink or bathtub, right-side up. It will float! Even though it's still "heavier" than water, and even though it's half full of water! How does this work?

The answer is, you've just made a crude steel-hulled boat. The only reason I had you leave it half-full of water was so that it would stay upright, instead of tipping over, filling all the way up with water, and sinking. But it's still pretty tippy -- water is a lousy ballast; the boat has a terrible righting moment. (There's a reason you don't want your real boat half-full of water!)

So now, try one more experiment. Empty all the water out of the can, and put some coins in the bottom. For a 15 oz. can, I find that using fifty U.S. pennies works well. (Your mileage may vary, depending on the size of can you use and the coins you have available where you live.) With the coins in the bottom, the can floats even better! But this seems really strange, because the coins are heavier than the water was. Or are they? The same volume of coin metal is heavier than the same volume of water, but the volume of the coins is a lot less. So actually the fifty coins in the bottom of the can weigh less than the half-can's worth of water.

So what we're finding out here is that it's not so much how heavy something is, but rather how dense it is, that matters when we're deciding whether it will float in water. It turns out, the rule is simple: if it's denser than water, it sinks, and if it's less dense than water it floats. That's why, everything else being equal, metal sinks and wood floats.

But, when you make a boat out of metal, the boat is obviously not solid metal. (Otherwise it would sink like, well, a stone.) The inside of the boat is full of air, and it's the overall density of the boat+air system that matters. If the boat plus the air inside weighs less than the same volume of water would, its overall density ends up being less than water, and it floats. And if the boat is heavier at the bottom, it will float well, and stay upright, and not tend to tip over. (It turns out that real boats usually have something heavy -- extra metal, or rocks -- down in their keel, as ballast, so that they work this way, just like our can with coins in the bottom. You can read more about this at center of buoyancy.) —Steve Summit (talk) 04:40, 22 November 2007 (UTC)

Take a hypothetical. What if you have bucket of water in a vacuum/airless room. Then you put the empty metal can on the water. Will the can sink? Since there's no air, we don't count the air mass and volume into the density calculation, right? And since the can itself, without air, is greater than that of water, the can should sink, right?199.76.152.229 (talk) 03:23, 24 November 2007 (UTC)

No, It would float even more. It would not have the mass of the air, but it would now it would contain a certain volume of empty space. Empty space is even lighter than air. 72.10.110.107 (talk) 17:05, 26 November 2007 (UTC)

Steve - that was a really good answer! DuncanHill (talk) 06:13, 22 November 2007 (UTC)

(Thanks! —scs 00:20, 24 November 2007 (UTC))

Because math is good, I'd like to add that Archimedes's Principle is that the weight of water displaced is equal to the weight of the object displacing it. So if I have a 2000-ton ship, it will displace 2000 tons of water, which is about 2000m^3 in volume. But suppose the ship has a total volume of 5000m^3 -- then it will float, and the water line will only come as far as about 2/5 of the side if it's a barge-like ship. SamuelRiv (talk) 11:56, 22 November 2007 (UTC)

Zoom lenses

Why do some zoom lenses have a constant f-number? As focal length increases, the entrance pupil must also increase to maintain the same f-number. Since this is the case, do such lenses actually have an enterance pupil that physically expands when the lens is zoomed? If the entrance pupil can expand, why not keep it at its largest, so that, a lens that is a, say, 70-210mm f/4 (at 210mm, the pupil is 52.5mm) is a 70-210mm f/1.3-f/4 (52.5mm constant pupil diameter), so that the lens is faster at its wider end? 70.156.49.65 (talk) 04:03, 22 November 2007 (UTC)

I don't think the pupil changes size, I have a 70-210mm f/4-5.6 (NOT constant aperture) and if I set it on say f/11 at 70mm (supposed pupil size = 6.4mm), the aperture size doesn't change as I zoom, finally becoming f/16 at 210mm (supposed pupil size = 13mm), but it still doesn't solve why the effective aperture changes when the pupil size doesn't. --antilived^{T | C | G} 07:04, 22 November 2007 (UTC)

over working the kidneys

In the past I used to eat a lot of salads but when my schedule kept me from sitting down to eat I followed the great idea of adding water and pureeing my salads to consume as a drink. Now I do the same with yogurt, fruits and vegetables to the point that I must be drinking at least a gallon ever two hours. Can I hurt my kidneys by drinking so much liquid or does it make them work even better? 71.100.5.134 (talk) 08:19, 22 November 2007 (UTC)

• You should probably ask your doctor, but since that would equate to nearly 12 litres in a working day alone, I'd expect it to be unhealthy. You only need around 2-3 litres to stay hydrated and drinking too much can indeed have an adverse effect on your health, especially if you do it in such short periods. - 131.211.161.119 (talk) 09:00, 22 November 2007 (UTC)

If you have a schedule that prevents you from sitting down to eat you need, seriously, to address your life style. Fact - People do die from drinking excess liquids, usually water. Richard Avery (talk) 10:54, 22 November 2007 (UTC)

Well usually it is alcohol :D, but yes water intoxication is possible Shniken1 (talk) 12:32, 22 November 2007 (UTC)

A gallon every 2 hours, that's about 4.5Litres right? So in a day? That's 18L in an 8 hour work day, or if you're talking about your waking hours it's more like 36L! Wow, that's dedication! Water intoxication occurs when the amount of fluid you ingest causes electrolyte washout to such an extent that cell membrane physiology becomes irreparably disturbed and cell death follows. To get it just from drinking you need to drink plain water only, and lots of it. You're also consuming a lot of electrolytes in the puree so that would go a long way to helping you maintain electrolytic homeostasis. Normal kidneys should be able to excrete at least half to 2/3 of that water volume, but you'll also have water loss through perspiration, respiration etc. You're probably peeing like a racehorse and/or sweating like a pig to compensate. If you weren't, you'd probably be rather oedematous by now. The figure of 2-3L of water being required per day is a figure arrived at by looking at the metabolic requirements of a sedentary 70kg man. So if you're very physically active your water requirements will be much higher. Plenty of people don't find time to sit and eat regularly - ask any mother! And while it would be nice to say society is to blame for your salad smoothies and resultant concerns, getting the world to slow down really needs to be addressed in other venues. But the important point is:

• • See your doctor if you're worried. A simple blood test will priovide all the answers to your concerns.

Cheers! Mattopaedia (talk) 03:11, 23 November 2007 (UTC)

Anti-aliasing in human vision

Are there aliasing effects in human vision and what plays the role of the anti-aliasing? Keria (talk) 09:56, 22 November 2007 (UTC)

Correct me if I'm wrong but I always thought our retina is like film, with all the receptors are pretty much randomly distributed at a very high resolution, so that it's pretty much unnecessary. I still see aliasing outside my fovea though, so I guess the resolution outside the fovea is low enough to be able to see aliasing. --antilived^{T | C | G} 10:08, 22 November 2007 (UTC)

I associate aliasing with geometric optics, but the fovea operates pretty close to the diffraction limit. I think the blurring you get from diffraction will have about the same effect as oversampling in 3D graphics. -- BenRG (talk) 12:04, 22 November 2007 (UTC)

There are distortions that occur in human vision that are caused by a lack of spatial (an optical illusion book has tons of these, or even looking through a fine-grained mesh can cause a similar effect) and temporal (a propeller blade that appears to spin backwards) resolution. It's not quite as simple as this, because illusions can occur either as a true aliasing effect in the eye, as a pre-processing effect in the thalamus, as a processing and integration effect in the occipital lobe, or even as a post-processing effect in the rest of the brain as images are linked with memories and higher judgement. All of these areas can cause illusions as all of them also serve to resolve possible illusions in vision, which is itself technically an optical illusion. So I'd say one of the clearest examples of "anti-aliasing" would be our pattern-matching, which fails when we see a triangle when shown three circles with wedges cut out of them. SamuelRiv (talk) 12:08, 22 November 2007 (UTC)

I don't think I've ever seen an optical illusion resulting from spatial or temporal aliasing in the visual system, except perhaps outside the fovea. Looking through a fine-grained mesh can make a moiré pattern, but that's a result of "sampling" by the mesh. I see nothing in the wagon-wheel effect article to suggest that it's ever caused by temporal aliasing in the visual system. The "discrete-frame theory" sounds unlikely to me. The circles-with-wedges illusion has nothing to do with aliasing, not that it isn't interesting in its own right. -- BenRG (talk) 12:08, 23 November 2007 (UTC)

Anti-aliasing is something that is only necessary when you scale an image down, and the eye doesn't do anything like that, so there is no anti-aliasing in human vision. Also, human vision is mostly analog, so our eyes don't really use image sampling, which is what causes spatial aliasing, therefore I'm pretty sure human vision can't cause spatial aliasing. Looking through a real fine-grained mesh (not one on TV) will not produce a Moiré pattern unless there are two imperfectly overlapping meshes, though you may see a pattern anyways if the holes in the mesh are not completely flat and regular. In either case that pattern is not an optical illusion or a product of aliasing, it's simply a varying pattern of blocked and unblocked light. Also, we generally only see temporal aliasing aliasing due to a flickering light source, such as from a TV or a fluorescent lamp, which causes a sampling effect. So, aliasing generally isn't a problem caused by human vision. -- HiEv 15:13, 22 November 2007 (UTC)

You can see what is called the wagon-wheel effect without a flickering (stroboscopic) light source, however there are various explanations why this effect can occur (see here). -- HiEv 15:28, 22 November 2007 (UTC)

Anti-aliasing is not only necessary for downscaling images. It's necessary (or at any rate useful) any time you sample a signal, whether or not that signal was reconstituted from higher-frequency samples. I suppose one could argue that the laws of physics are discrete, and every sampling is a downscaling. -- BenRG (talk) 12:08, 23 November 2007 (UTC)

String theory and the shape of the Universe

String theory seems to imply a particular shape of the Universe. Therefore, could it be that local geometry of the Universe is 3-dimensional (in an Euclidean, spherical or hyperbolic form) but the global geometry of the Universe is quadridimensional?

In such a scenario, the Universe would be a kind of anomalous sphere: just like in our Earth, in such an Universe, one could go westward and return to the starting point from the East; one could go northward and return to the starting point from the South; BUT, differently from Earth, one could also go upwards into space and, after eons of travelling, one would return to the starting point from beneath. In other words, the universe would be a simply connected sphere folded on itself in such a way that each point is in contact with its antipodal point. Is this view consistent with string theory? Is this even plausible? -- Danilot (talk) 10:43, 22 November 2007 (UTC)

It sounds like you're describing a 3-sphere, which has been a popular choice of topology for the universe since the earliest days of modern cosmology. I don't understand what you mean by quadridimensional; the space you're describing has a local dimension of 3 and a global dimension of 3. Also, I don't think this has anything to do with string theory, which doesn't to my knowledge predict the shape of the universe. -- BenRG (talk) 11:57, 22 November 2007 (UTC)

You might be interested in shape of the universe. Someguy1221 (talk) 16:34, 22 November 2007 (UTC)

piezoelectricity

I would like to build a rudimental piezoelectricity sensor (generator) for highschool project. I intend to apply pressure on a sample of Rochelle salt (which I have) and show the resulting current generation using a voltmeter. Is this going to work? Can somebody show me a simple diagram of how to apply the wires which would conduct the current? What is the best metal to use for these conductors? Thanks, Curious Student —Preceding unsigned comment added by 67.189.247.193 (talk) 11:15, 22 November 2007 (UTC)

The short answer is, it depends. The current produced will be transient—just a little blip of current when pressure is applied or released, after which the potential across the crystal will be back at equilibrium. The current is likely to be fairly small for reasonable pressures and crystal sizes. I don't know if you'll be able to see a small, short-lived current, and I suspect that it will be difficult for you to measure with any accuracy (unless you've got some specialized instruments).

I wonder if some sort of rudimentary electrometer might not be a better bet for you—squeeze some charges out of the crystal and into gold-leaf electroscope for your demonstration. (Caveat—I haven't tried this stuff, and can't tell you if it will work.) TenOfAllTrades(talk) 14:48, 22 November 2007 (UTC)

Incidentally, you might find something useful in our articles on piezoelectricity and piezoelectric sensors. TenOfAllTrades(talk) 14:51, 22 November 2007 (UTC)

You could use a gas ignition lighter that makes a spark. You would then just have to wire to the outlet. Beware the voltage is high on the order of several thousand volts, so you will need some special kind of voltmeter, such as TenOfAllTrades electrometer. Graeme Bartlett (talk) 20:31, 22 November 2007 (UTC)

It's the mechanics of the ignitor that result in the high voltage. Absent the over-center mechanism that delivers the sudden impact to the piezo portion, they can produce low voltages quite nicely.

Atlant (talk) 16:06, 26 November 2007 (UTC)

In the classroom, measure voltage, not current. Just get a cheap piezo buzzer (about $2.00USD), remove the piezo element, and place it under stress to produce the voltage, which you can measure with a voltmeter. An actual generator must be a dynamic system, so you will need an oscilloscope to show the varying voltage. Alternatively, you could use the piezo as a microphone and rectify the AC voltage via a full-wave bridge to charge a capacitor, and measure the (relatively small) current as you discharge the capacitor through a resistor. -Arch dude (talk) 05:20, 23 November 2007 (UTC)

Burglar alarm glass breakage detectors are usually piezoelectric as well; you might want to investigate one of those as a "prototype" for your project. If you mention what you're doing, an alarm installer might give you one for free. Old, inexpensive phonographs also used piezo pickups. Interestingly enough, certain ceramic capacitors are also piezoelectric, leading to undesireable microphonic effects when they are used in certain electronic circuits.

Atlant (talk) 16:01, 26 November 2007 (UTC)

Glassware for baking

There is a kind of bowl made of glass that you can put into the oven or into a microwave, primarily for baking vegetable-based food. These are made of a special kind of glass as far as I know. What's the name of them? Is there an article about them? If no, what property of the glass makes them usable in an oven? I'm not interested in how they are created, but the resulting physical properties. Thanks, – b_jonas 19:01, 22 November 2007 (UTC)

I believe you are talking about Pyrex, which is made of soda-lime glass, but originally was constructed of borosilicate glass. --80.229.152.246 (talk) 19:37, 22 November 2007 (UTC)

Glass recyclers consider it to be ceramic material. They hate to find pieces of it in recycled glass containers because it screws up their process: when "regular" glass is melted this ceramic material is still solid. When pouring the glass melt in whatever shape this endproduct has to be rejected because of the ceramic shards enclosed in it. VanBurenen (talk) 22:12, 22 November 2007 (UTC)

Why should Pyrex be primarily for vegetables? --Seans Potato Business 00:13, 23 November 2007 (UTC)

Because in the regular oven, I can use metallic containers, and I rarely use the microwave for baking meat or cookies. Rice or green peas, however, can be cooked just fine in the microwave. – b_jonas 10:07, 23 November 2007 (UTC)

It could also be because acidic vegetables (? Well, acidic fruits, maybe) may pick up flavors from some reactive metals. --Mdwyer (talk) 17:22, 23 November 2007 (UTC)

Besides Pyrex, you can use ceramic, glass-ceramic, and silicone cookware in microwave ovens. See Cookware#Non-metallic cookware. -- HiEv 19:34, 23 November 2007 (UTC)

November 23

Apoptosis

If a man goes fishing, we can say "the man has started to fish", if a cell begins the process of apoptosis, what single word (of the same root) is used in the sentence "the cell is has started to ..."? --Seans Potato Business 00:10, 23 November 2007 (UTC)

In your fish sentence you are using the word as a verb. Apoptosis is a noun, so wouldn't be conjugated. The only sentence I can think of is the same as yours: "As the cell dies, it begins has begun the process of apoptosis." Jeffpw (talk) 00:17, 23 November 2007 (UTC)

Apoptosize is a verb form, so you could say "The cell has started to apoptosize." bibliomaniac15 01:04, 23 November 2007 (UTC)

Or Apoptosise... —Preceding unsigned comment added by Shniken1 (talk • contribs) 01:15, 23 November 2007 (UTC)

In the texts I've read, apoptosis is used as a verb, so we say "the cell has started to undergo apoptosis". Looking at root words, though, we also use the word ptosis, specifically in relation to things like eyelids, the liver, etcetera, and we commonly will make a comment during examination of a patient such as "he had a ptosed liver", to say the lower border of the liver is lower than expected in the abdomen (for a number of possible reasons) --- so, then the answer could also be "apoptose". To me, to "apoptosize", as suggested by Bibliomaniac15, or "apoptosise", for those of us who prefer the Queen's English, would be to cause another cell to undergo apoptosis, rather then a cell undergoing apoptosis itself. Mattopaedia (talk) 02:41, 23 November 2007 (UTC)

That sentence uses it as a noun. Using it as a verb would be "the cell has started to apoptosis". — Daniel 02:57, 23 November 2007 (UTC)

Fair enough. I'm a doctor, not a linguist. I was thinking it might have been a noun and a verb at the same time, but thought that was a bit odd, so left it like that. Mattopaedia (talk) 03:53, 23 November 2007 (UTC)

Linguistically, what you're looking for is the infinitive form of the verb: to run, to swim, to play, et cetera. "to undergo apoptosis" is not using apoptisis as a verb; "to undergo" is the verb and apoptosis is the direct object, which is (in this case) a noun. "Apoptosize" would be a verb (assuming it's a word). Kuronue | Talk 21:14, 23 November 2007 (UTC)

But that's the question, isn't it? "Apoptosize" is, at best, a nonce word: it is certainly not in common use, and would not be used in any even minimally formal document. "Apoptosis" is the noun; "apoptotic" is the adjective, and there is no accepted verb form. - Nunh-huh 21:32, 23 November 2007 (UTC)

Funny, I've always use "Apoptose" as the verb. I have no idea if this is at all correct though. Someguy1221 (talk) 21:54, 23 November 2007 (UTC)

To determine whether it is correct or not, consult a dictionary. I already have. - Nunh-huh 22:12, 23 November 2007 (UTC)

I do hear apoptose, although it's probably a word made by extension (e.g. endocytosis-endocytose). However, I'd probably go with constructing the sentence to use either the noun or adjective form. -- Flyguy649 ^talk 22:15, 23 November 2007 (UTC)

The OED doesn't acknowledge apoptosize or apoptose as words. Speaking from experience, I occasionally see apoptose in scientific presentations. It's a nonce word or neologism, and I'd tend to shy away from it in formal writing. (Apoptosize is definitely not used. Anywhere.) A PubMed search finds about a hundred uses of apoptose in paper titles or abstracts, so at least some authors have been able to sneak it past the blue pencils. TenOfAllTrades(talk) 23:42, 23 November 2007 (UTC)

The part of the OED that covers the letter A was last updated around 1970, except for selected important words in the online edition, so that's not a good reference for new words. But none of the online dictionaries indexed by www.onelook.com has "apoptose" or "apoptosise"/"apoptosize" either. I think "apoptose" is definitely the natural form, though. Several other medical nouns in -osis often form verbs in -ose, like "diagnose", "sclerose", and "thrombose". --Anonymous, 01:32 UTC, November 24, 2007.

For what it's worth, the online version of the OED includes references as recent as 2004 for apoptosis and 2002 for apoptotic; it's safe to say that they're making an honest effort to stay on top of these new words—but I would agree that they're not the be-all and end-all for new terms. TenOfAllTrades(talk) 18:26, 24 November 2007 (UTC)

As it happens, I was using "apoptose" when my spellchecker rejected it, the first event in a short series that lead to my original post. Since it clearly should be a verb, I move that we resolve to use it as we see fit, since after all, what makes a word (a word) is how many people use it and understand the meaning behind it. I have a dream, that some day, every process will have a verb form... --Seans Potato Business 19:07, 24 November 2007 (UTC)

Michael Faraday established that magnetism could affect rays of light?

Hi, Michael_Faraday established that magnetism could affect rays of light? What? I thought light is not affected by magnetism. Please explain.

Thanks --InverseSubstance (talk) 02:42, 23 November 2007 (UTC)

Good question! This is what our article on Faraday says - "In 1845, he discovered the phenomenon that he named diamagnetism, and what is now called the Faraday effect: The plane of polarization of linearly polarized light propagated through a material medium can be rotated by the application of an external magnetic field aligned in the propagation direction. He wrote in his notebook, "I have at last succeeded in illuminating a magnetic curve or line of force and in magnetising a ray of light". This established that magnetic force and light were related"

Read the linked articles (showing up in blue), hopefully they will explain better than I can. DuncanHill (talk) 02:49, 23 November 2007 (UTC)

Thanks! Thats amazing. This might be a good time to ask another question I've been curious about. Light waves are usually depicted as a series of - well - light waves. If a light wave is the product of a quantum jump from a higher electron orbital to a lower electron orbital, then how many cycles are there in a light wave train? User:InverseSubstance —Preceding comment was added at 03:24, 23 November 2007 (UTC)

Well, the difference in energy of states in the quantum leap determines the energy of the photon, or $E=h\nu$, where $\nu$ is the frequency of the photon in cycles/sec and h is Planck's constant. Just multiply the cycle frequency by the number of seconds you're generating the wave packet for and boom, you have the number of cycles. The result doesn't have much meaning, however, as quantum mechanics describes a wave packet that has an infinite number of cycles that decay to zero exponentially as it propagates away, so you can think of our calculation as more of the average total number of cycles in a series of wave packets generated with certain frequency over a length of time. SamuelRiv (talk) 03:40, 23 November 2007 (UTC)

Ok - that's interesting. So when an atom absorbs a Photon, the entire wave packet is absorbed, including the entire exponentially decaying amplitudes, right?

I'm also curious about how a light wave can interfere with itself in the Double_slit experiment. The probabilistic Wave_packet can describe it, but not explain it. And I imagine that string theory also does not explain self-interference; it only describes its probability, right? --InverseSubstance (talk) 04:12, 23 November 2007 (UTC)

Classical wave theories of light are sufficient to explain the interference pattern (but not the lack thereof) in the double slit experiment. Basically, two waves diffracting at two narrow slits will interfere in an alternating constructive and destructive way (there are many diagrams of this in double slit experiment.) Light interferes with itself as a wave, but there is also light-to-light scattering (Delbruck scattering) which occurs when a virtual particle is exchanged between photons, similar to how electrons scatter off each other by exchanging a virtual photon. This is a nonclassical effect, but it has nothing to do with the double-slit experiment. SamuelRiv (talk) 05:21, 23 November 2007 (UTC) Addendum: none of this has anything to do with string theory, and string theory explains nothing about light. The best theory we have for light is Quantum electrodynamics (QED). SamuelRiv (talk) 05:30, 23 November 2007 (UTC)

String theory does actually have an explanation for diffraction (not that I can remember it). String theory generally has an explanation for everything, and generally these explanations produce no predictions divergent from quantum, and thus they are indistinguishable from quantum. String theory is in general not worth thinking about, except as an exercise of silliness and ammusing thoughts. Someguy1221 (talk) 05:59, 23 November 2007 (UTC)

An electron in a higher orbital has got a certain lifetime, the average time it needs to fall back to a lower orbital. This lifetime also determines the "number of significant cycles" and hence the coherence length - and, as can be calculated with the Fourier transform, the width of the spectral line (the spectral line is narrower if the lifetime is longer). If the atom is not undisturbed during this lifetime of the electron in the higher orbital, e.g. if it collides with other atoms, then the lifetime gets shorter and the spectral line gets broader - see also spectral line. Icek (talk) 10:48, 23 November 2007 (UTC)

I have long been in awe of Faraday, a man who probably could not have passed freshman high school algebra, showing the relationship betwen electricity and magnetism by discovering induction and transformer action, then discovering the relationship between magnetism and light (magnetism can rotate the plane of polarization of light), and in the end attempting (unsuccessfully) to find a relationship between electricity or magnetism and gravity. He was as tireless an experimentor as Einstein was a theorist. Edison (talk) 05:27, 25 November 2007 (UTC)

Spacetime and FTL

Given that:

• space and time are only two different aspects of spacetime;
• FTL travel is not a possibility which can be ruled out;
• and all matter is essentially composed of photons and leptons;

Is it plausible that photons (which are light themselves) or leptons, do accelerate above the speed of light, but that we cannot detect this phenomenon because the surpassing of this "threshold" transforms them into time? This might be a fallacy, but it seems quite logical to think that there exists a "phase change" which works like this: time <=== photons/leptons ===> matter. Remember there are special quantum effects which allow for a violation of the law of conservation of energy, maybe accelerating above the speed of light would be such a singularity. Is this idea really a fallacy or is it plausible? —Preceding unsigned comment added by Danilot (talk • contribs) 12:04, 23 November 2007 (UTC)

Okay, let's start with your givens, all of which are wrong:

• space and time are fundamentally different in our theory of general relativity, which uses Minkowski space in which a "length" is defined as $s^{2}=c^{2}t^{2}-x^{2}-y^{2}-z^{2}$, which shows that our time t is a separate type of coordinate than our space x,y,z. We find velocity (the time derivative) is then $v\cdot r/t=c^{2}$ which sets a fundamental limit on velocity through space (remember $v=\Delta r/\Delta t$) of c, the speed of light.
• Therefore FTL travel is ruled out in space, but we can still acheive it with a warp drive which bends space itself, or a wormhole which topologically tunnels through space.
• Your link to all matter being composed of leptons and photons is only valid for the very early universe, does not describe matter (only leptons exist in matter, photons "do not", and leptons are not as significant in matter as baryons).

And then your conclusions are also mistaken. Massless particles by definition must travel at the speed of light, and massive particles (like leptons and baryons (matter)) must appear to us to travel slower than the speed of light in vacuum in accordance with quantum mechanics, namely the uncertainty principle. What you are describing is called a tachyon, which travels faster than light by definition (but appear to us to be travelling slower than light, since they are travelling backwards in time. There is a model of antimatter that describes them as tachyons, but I believe there is solid evidence against this description. Anyway, it is a fundamental principle that particles travelling faster than light can never reach light speed, so they can never slow down to become slower than light, and vice-versa, so it does not represent a possibility for FTL travel. Finally, the Law of Conservation of Energy may be locally violated, but not globally violated, so it is always true. SamuelRiv (talk) 13:53, 23 November 2007 (UTC)

I'd like to correct one of those statements:

• Therefore FTL travel is ruled out in space, but we can still acheive it with a warp drive which bends space itself, or a wormhole which topologically tunnels through space.

We can't achieve FTL travel with warp drives or wormholes - current science doesn't say that they are practically possible - we have no idea how we could even theoretically make space warp or tunnel without playing around with black holes and other things that we really have no way to do. At best we can say that perhaps they aren't ruled out as utterly impossible. But with everything we actually know FTL travel is ruled out. Tachyons are not science - we havn't observed them and none of our laws either require or predict their existance - they are purely hypothetical. Annoying though the universal speed limit is, it looks certain that we're stuck with it. SteveBaker (talk) 17:13, 23 November 2007 (UTC)

Here's where I add the usual things I like to say about this: First, if a particle could "move" faster than c it wouldn't really be like motion at all, because in one inertial reference frame it would exist at infinitely many points in space but only one point in time (the opposite of the case of motion). For other reference frames, it would be moving the opposite direction! Second, the limitation of relative speed doesn't actually limit your ability to reach faraway destinations. For example, if you had a rocket that could sustain a 1 g acceleration indefinitely, you could reach any point in the galaxy in a matter of years[10] (of your own proper time, of course), even though the points are hundreds of thousands of light-years apart. You can think of this as being due to length contraction, which causes your destination to appear closer to you as you move toward it, hence easier to reach. —Keenan Pepper 06:05, 24 November 2007 (UTC)

And better yet, by the time you get back all of your favorite shows will be out on DVD! ;-) Someguy1221 (talk) 06:34, 24 November 2007 (UTC)

No, by that time most of the videos that you remember will have been destroyed during the second coming of Jesus.

To respond to Steve, I am well aware that there is no currently existing way to build a "warp drive", but I'm sure you are aware of the hypothetical solutions to the hypothetical problems with these topological types of propulsion. There is no hard evidence for any of it, so it's pretty much assumed that it's all science fiction, at least for now. And as for the tachyon nature of antimatter, I'm not in particle research, so I can't comment on the current state of it, but in general quantum field theory certainly holds this tachyon formulation in high regard (see Feynman diagram). SamuelRiv (talk) 06:50, 24 November 2007 (UTC)

Shared blood system

Ok it is stretching it but for the sake of fiction: how realistic would it be (if possible at all) to artificially link two normally constituted persons so that they share the same cardiovascular (bi-cardiovascular?) or blood circulatory system (the blood would go through both persons to do a full circulation)? In the some order of ideas let's imagine a situation where someone is really messed up under the neck and the only way to save him/her would be to tap the head's blood system into the jugular veins of the healthy person. How would the heart cope with the extra strain and how much is the blood compatibility an issue? Is it completely irrealistic or merely highly implausible? Keria (talk) 15:48, 23 November 2007 (UTC) p.s. this question is dedicated to Zaphod Beeblebrox :p

Check out Conjoined_twins#Types_of_conjoined_twins, as thoracopagus twins have a high mortality rate. However, if one twin is parasitic, as an attached head would be, it shouldn't be too much extra strain. SamuelRiv (talk) 16:50, 23 November 2007 (UTC)

A fat person's heart and lungs can keep a large amount of extra tissue supplied with blood and oxygen for years, so supplying an attached head wouldn't be an issue that way. However, establishing the connection would obviously involve major surgery, and there'd be major stress on the artery and vein that were "tapped", as the load on it above and below the junction would be different. Still, in principle the surgical hazards and techniques shouldn't be much different than with an artery bypass.

A severed head might have blood-supply problems in the area of the cut, because some small areas were previously supplied by vessels branching from below the cut, so there could be a risk of gangrene. However, similar issues must arise with amputations generally, so I guess that also ought to be manageable.

The whole-body thing that's also asked about seems much more problematic. --Anonymous, 22:54 UTC, November 24, 2007.

definition of latitude

On the surface of an elliptical body, the line through the center of mass and the line of local gravity coincide only at the equator and the poles. So, which one defines latitude? —Tamfang (talk) 19:58, 23 November 2007 (UTC)

You may want to check out types of latitude. In short, you don't have just one measure of latitude. And, since real celestial objects don't have a perfectly elliptical shape, you may also consider gravitatorial deviations of the plumb line (the so called astronomical latitude). Pallida  Mors 20:09, 23 November 2007 (UTC)

To be a bit more specific, you have (at least):

• The geodetic or geographic latitude, (which you may consider the "main" latitude), given by the angle formed between the vertical line normal to the ellipse, and the equatorial plane. As far as I know, this accounts for the "local gravity" reference you gave.
• The geocentric latitude, which is given by the angle between the equatorial plane and a (straight) line joining the local point and the center of the ellipse (the line through the center of mass you metioned in your question.

You have other latitudes explained in the article. Most of them refer to projection topics. Pallida  Mors 20:48, 23 November 2007 (UTC)

November 24

Supercavitation

Hey I was reading a question on the science desk about the fastest way to move through water, and someone mentioned Supercavitation. I was wondering could Supercavitation be used on a plane or rocket to create a vacum throgh the air allowing it to move much faster?67.127.235.74 (talk) 00:03, 24 November 2007 (UTC)

No. The phenomenon of supercavitation depends on the fact that there is a phase boundary between liquid and gas. There can be no such phase boundary between gas and vacuum. Icek (talk) 01:48, 24 November 2007 (UTC)

IUDs and large penises

Are IUDs safe and reliable if the male has a large penis? —Preceding unsigned comment added by 189.15.179.115 (talk) 00:38, 24 November 2007 (UTC)

I would think (but IANAD) that they're just as safe and reliable as with small penises. IUDs, as their name implies, are placed inside the uterus, which is separated from the vagina by the narrow cervix. In normal women who aren't pregnant, the opening of the cervix (the external os) is tiny, maybe a few millimeters wide at most. Obviously the penis is much wider than that, so it never penetrates the cervix during intercourse. —Keenan Pepper 01:35, 24 November 2007 (UTC)

Well, not always entirely inside the uterus. The IUD article has a comment in the "Side effects and complications" section that appears to be the same information as in this ref of the article. Therein is a FAQ item:

10 Q: Should an IUD be removed if a woman's sexual partner complains about the IUD string?

A: Not necessarily. The couple may need reassurance and an explanation of what the string is. If this is not satisfactory, the end of the string can be tucked behind the cervix. If this too is not satisfactory, the string can be cut flush with the cervix. (This should be noted in the woman's record.) Such short strings will mean that the woman will not be able to check the strings and a provider will need narrow forceps to grasp the strings when removing the IUD. The woman should be given the choice of what she wants done, including whether the IUD should be removed.

Anyone know of a free diagram of a uterus with an IUD in it? Would be a good addition to our article. DMacks (talk) 19:35, 24 November 2007 (UTC)

Is suicide unique to our species?

Is there evidence that giving up on life and exiting it purposefully exists beyond our species? Sappysap (talk) 01:09, 24 November 2007 (UTC)

That depends on your definition of "purpose". Icek (talk) 01:49, 24 November 2007 (UTC)

This [11] is a nice short summary of the conventional scientific answer: No. Though you will find tons of anecdotal accounts of animals "pining away", refusing sustenance, or giving up "the will to live" after the death of their master, mate, or companion. Possibly of interest, it often seems in my experience that many of these accounts center around animals in captivity. Take that as you will. Azi Like a Fox (talk) 03:03, 24 November 2007 (UTC)

When a honeybee stings a mammal, the barbed stinger tears loose from the bee’s abdomen, leading to the bee’s death within minutes. Thus, a purposeful act of violence by the bee results in its own death as a side effect. This is comparable to a suicide bomber, whose purposeful act of violence results in the death of the bomber as a side effect. It could be argued that there’s a difference between stinging bees and suicide bombers in that there is no evidence that bees are aware that they will die if they sting. However, many if not most suicide bombers are also unaware that they will indeed completely die if they set off the bomb, instead believing that they will merely go to an afterworld. MrRedact (talk) 04:32, 24 November 2007 (UTC)

That is a very elegant answer, MrRedact. A necessary task is a necessary task. No debate over inference need apply. Death, over an impending and certain jeopardy of livelihood, is the only answer for any organism in extreme peril. Sappysap (talk) 09:36, 24 November 2007 (UTC)

Would you count programmed cell death as suicide? Elle _{vécut heureuse} ^{à jamais} (Be eudaimonic!) 04:58, 24 November 2007 (UTC)

Animal suicide is not such an outlandish idea. If resources were scarce, the suicide of a parent could make sense in a selfish gene strategy (consider the classic "you'd be better off without me" suicide note).As MrRedact says, some hive animals, certain ants and bees, will have members that will go out on what are essentially "suicide missions". Although the goal isn't to die per se, death is an inevitable consequence of its actions. In the case of hive animals, its unlikely the thing even has a "choice" - they are genetically hardwired to go on a suicide mission in response to the appropriate cue. The complex genetic relationships between the Queen and her hive means that this actually makes a lot of sense in terms of selfish gene theory, even though it appears very unselfish on the face of it. The excellent book, The Selfish Gene explains in more detail. See also here for previous discussion on the same question. Rockpocket 09:56, 24 November 2007 (UTC)

Surely the concept of suicide requires some ability to understand the act of self-killing. The idea that a bee, for example, gives up its life in some 'heroic' way is rather anthropomorphising the bee somewhat. Does the bee take a concious decision to attack? I think it is governed by genetically installed reaction behaviour that gives it no choice in its response. This is far from anticipating the results of its actions - which is perhaps an essential part of the concept of suicide. Richard Avery (talk) 16:24, 24 November 2007 (UTC)

But do brainwashed suicide bombers have a choice too? Elle _{vécut heureuse} ^{à jamais} (Be eudaimonic!) 18:47, 24 November 2007 (UTC)

They're irrelevant except as an analogy; the question is about suicide in other species. Richard has the right idea. For it to be possible in the terms we were asked about, the species involved would have to be one with the capacity to understand the concept of one's own death and to plan future actions. The more intelligent non-human species, like chimps and dolphins, might well be able of doing this; insects and lower animals generally are irrelevant. --Anonymous, 23:00 UTC, November 24, 2007.

Our concept of "suicide" as a result of a conscious decision is obviously unique to humans. As you say, to contemplate one's own death requires before choosing to kill oneself requires a level of self awareness beyond even non-human primates. You have to understand what "living" is before you can understand what "dying" means. However more abstract interpretations of "exiting life purposefully" is relevant to other species, especially when robust innate behaviour removes the concept of "choice" from the equation. Whether that qualifies as suicide is a matter of interpretation. Rockpocket 09:14, 25 November 2007 (UTC)

• I think the honeybee counts as a solid answer, but please oh please, if someone asks you about animals who commit suicide, don't ever propagate the myth about lemmings dropping to their death off cliffs. That is simply an inaccurate urban legend as confirmed by snopes.com - Mgm|^(talk) 10:37, 25 November 2007 (UTC)

Genetic possibilty of genius IQ

I am adopted and just discovered that my real father was a mathematical genius. I am not saying that I am a genius but I was in gifted/advanced classes for most of my life and read through books voraciously. Otherwise, I am a normal girl with normal wants/needs. However, I would sometimes freak out my friends for knowing more about a subject than necessary, etc. Is it possible that somehow that this could be genetic? --WonderFran (talk) 02:02, 24 November 2007 (UTC)

Yes, intellectual potential is partially determined by genetics. See genetics of intelligence and related articles. Dragons flight (talk) 02:18, 24 November 2007 (UTC)

One should be careful to read too much of a direct correlation between any given behavior and one's apparent genetic heirs. Genetics are complicated and the only direct relationships one have between genes and behavior are for extremely rare things (usually disorders)—the relationship between genetics and IQ is at this point known only in a purely statistical terms. To claim that your aptitude in school or love of learning is "only" the result of a genetic quirk both devalues your own effort but also the efforts of those around you—in reality, all things genetic require development to even become recognizable as traits, and we are not simply reflections of our genes. --24.147.86.187 (talk) 07:57, 24 November 2007 (UTC)

You might want to take note of the twin studies, which compared traits of identical and fraternal twins that were separated at birth. Identical twins showed more similarity than fraternal twins in a variety of areas, with IQ being at an intermediate level of genetic influence. So, IQ is a product of both genetics and environment. -- HiEv 16:45, 24 November 2007 (UTC)

I completely understand your point of view however, I grew up on the projects and anyone who has can contest the difficulty of achieving academically....not to dismiss the few who have.....--24.151.103.18 (talk) 08:05, 24 November 2007 (UTC)

Antisocial personality disorder

How many famous people have this disorder? —Preceding unsigned comment added by 76.64.130.224 (talk) 02:45, 24 November 2007 (UTC)

See antisocial personality disorder#prevalence. Fame is relative and somewhat subjective, so I don't see how it can be included in the calculation.--Shantavira|^{feed me} 08:25, 24 November 2007 (UTC)

BOOLEAN OPERATORS

boolean operators —Preceding unsigned comment added by 75.26.161.182 (talk) 03:38, 24 November 2007 (UTC)

Boolean operators. Someguy1221 (talk) 04:08, 24 November 2007 (UTC)

Pluto

Why didn't Voyager 2 pass Pluto? 124.176.190.64 (talk) 04:33, 24 November 2007 (UTC)

Presumably because the planets weren't lined up nicely enough for it. Someguy1221 (talk) 04:54, 24 November 2007 (UTC)

The orbit of Pluto is way out of alignment with the orbits of the planets, so although Voyager passed beyond the orbit of Pluto, it would have been far far away at the time.--Shantavira|^{feed me} 08:33, 24 November 2007 (UTC)

This answer confuses two issues. It's true that all the other planets orbit in something close to the same plane while Pluto's orbit is somewhat inclined, but it's not inclined so much that it would be unreachable. The problem is that, at the time of the Voyager probes, it was in a different part of its orbit.

The whole Voyager 2 mission was only possible because the four gas giant planets were in roughly the same direction from the Sun at that time, a rare occurrence. See Planetary Grand Tour. As it says in that article, it would have been possible to reach Pluto by directing the probe appropriately on leaving Saturn -- but then the probe would not have passed Uranus or Neptune.

The thing is that when you want to use the gravity of planet A to direct the probe onward to planet B, this fixes the course that your probe must take near planet A, and it probably won't be the same course you'd route it on if you were only interested in A. NASA was under such budget constraints at the time that they decided it was more important for the Voyagers to be well placed to visit Jupiter and Saturn than it was to pick up all three of the other planets. Only after Voyager I had succesfully visited Saturn, taking the pressure off Voyager II, was the latter probe placed on a course that would allow it to continue with the Grand Tour after Saturn. (Sorry, no cite, but that's what I remember reading.) Without a third probe, there was no way to reach Pluto as well.

--Anonymous, 12:40 UTC, November 24, 2007.

Pluto orbits the sun once in every 248 years (and at a very odd angle to that of all of the major planets). Voyager is heading away from the sun at about 35,000mph and Pluto is only 1500 miles across. The odds of it happening to be in the right place for the trajectory of the spacecraft to intercept it is quite remote unless the mission planners specifically designed things to come out that way. When they designed the route of the spacecraft they had specific things they wanted to survey - they must have had to make all sorts of compromises in order to manage the various gravity slingshot manouvers they did. Evidently they simply couldn't figure a way to get over to Pluto along the way. SteveBaker (talk) 21:56, 24 November 2007 (UTC)

See my answer above. They did figure out a way, but had other priorities. --Anon, 23:02 UTC, Nov. 24.

Path integrals and lightcones

As far as I know, in the the path integral formulation of quantum mechanics, one has to include faster-than-light paths. How would the predictions of quantum mechanics change if one would exclude faster-than=light paths? —Preceding unsigned comment added by 193.171.121.30 (talk) 09:11, 24 November 2007 (UTC)

I'm not sure if FTL paths are necessarily included when Quantum field theory is formulated in Minkowski space, but either way an exclusion of that sort would simply be a change in the geometry of one's space, which is suggested in the article to not have serious or significant consequences to the accuracy of the theory. SamuelRiv (talk) 17:24, 24 November 2007 (UTC)

Orbitofrontal cortex and ventromedial prefrontal cortex

Is the orbitofrontal cortex the same as the ventromedial prefrontal cortex? Or is it a part of the ventromedial cortex??? Lova Falk (talk) 10:33, 24 November 2007 (UTC)

I'm not sure, but they seem to correspond in location and function (see ventromedial prefrontal cortex): both process risk and judgement. SamuelRiv (talk) 13:13, 24 November 2007 (UTC)

Another question on the prefrontal cortex

In picture A one can see the vl-PFC (yellow) and the dl-PFC (blue). But what would be the name of the grey area between these two? Lova Falk (talk) 11:00, 24 November 2007 (UTC)

The mIPFC, medial inferior prefrontal cortex, i would imagine. It's been a while since neuroanatomy. SamuelRiv (talk) 12:50, 24 November 2007 (UTC)

But the medial prefrontal cortex (for some reason called MFd) is the reddish/brownish part of the picture. Would the medial inferior prefrontal cortex be in a complete different place? Lova Falk (talk) 14:13, 24 November 2007 (UTC)

Sorry, I meant medial lateral prefrontal cortex. I really don't know for sure though. Google suggests that this is a legitimate name for that region, but it doesn't look like it's used much in the literature. SamuelRiv (talk) 17:21, 24 November 2007 (UTC)

Symmetry of animals

Why are most of the biological organisms in animalia kingdom symmetric externally, though they are highly asymmetric internally? I was wondering why nature might have chosen the symmetric structure and what great benefits this symmetry brings to animals? This is not the case with plants, though their leaves and flowers also tend to be highly symmetric about at least one plane. I have never seen any asymmetric animal or plant leaf or flower, so to say. DSachan (talk) 19:28, 24 November 2007 (UTC)

I've always wondered about this, too. Here's an article I just found that might be helpful:[12]. 128.163.224.198 (talk) 20:15, 24 November 2007 (UTC)

Thanks for the link. But the article only discusses about what is responsible for the structuring of organs internally the way they are. It does not say anything about that skin deep super symmetry that exists everywhere and it also does not mention anything about why it might be so or the advantages and disadvantages of it. Though one thing I got to know from the article is that it is a pestering problem for scientists today and they are trying to speculate about the evolutionary benefits of skin deep symmetry and then asymmetry there onwards. Any other thoughts on the issue are welcome. DSachan (talk) 20:30, 24 November 2007 (UTC)

One explanation is that the macroscopic external world tends, on average, to be symmetric in the sense that there is no particular advantage to looking or turning left instead of right or vice versa. In fact, it is advantageous for many species to be able to see and turn equally well in either direction, since if they showed a preference for one direction over the other, other species (such as their predators) could evolve to take advantage of this. The easiest way to achieve this ambidexterity is to make the animal's body plan bilaterally symmetric; this also has the advantage of simplifying the ontogeny of the animal, since the development of both of its sides can be controlled by the same genes.

Another, related reason is that many methods of locomotion employed by animals, such as swimming, walking or flying, work best with pairs of symmetric limbs. A fish with bigger fins on one side than the other would tend to swim in circles, a human or any other land-dwelling animal with longer legs on one side than the other would have difficulty running straight ahead, and a bird with one wing bigger than the other could scarcely even take off.

As for why animals don't tend to be more symmetric, this is also explainable by environmental factors: on Earth, gravity breaks up-down symmetry, leading to most animals having distinctive bottom and top sides, while the need to move rapidly tends to create a need for a specialized front and rear end. It's worth noting that quite a few marine species, such as starfish and jellyfish are, in fact, radially symmetric without a distictive front end — but few if any of these are species whose survival strategies would involve rapid movement. —Ilmari Karonen (talk) 20:26, 24 November 2007 (UTC)

Someday I'd like to run artificial life in a universe of higher dimension, and see what kinds of symmetry are favored in the critters there! —Tamfang (talk) 20:36, 24 November 2007 (UTC)

Ilmari Karonen, your logic of locomotion is working fine with the animals, but what about leaves and flowers? I see only ontogenical argument of yours working there. Will this be the only reason in leaves and flowers? and that means to say, nature is also fed up with having a large number of genes required to express the characteristics of biological organisms and it wants to get rid of as many as it can.

The other point is that there are some features even in us which I see having no advantages of them being symmetrically located. For example, the navel (belly button) is also symmetric about the sagittal plane in the middle of our belly. Does this point in our belly tend to be the point making the umbilical cord shortest in length in the early stages of our life? If this is not so, what else is the reason? DSachan (talk) 20:52, 24 November 2007 (UTC)

For plants, I suspect it may indeed be just a case of symmetric leaves being simpler to produce than asymmetric ones. A leaf essentially starts with a stem and then fans out — it's probably simplest to have it fan out equally in both directions. Also note that asymmetric leaves would tend to droop due to gravity pulling the heavier side down, which might be suboptimal for catching sunlight, at least when the sun is high in the sky. As for the navel, I'd guess its location along the body's certerline may be just an accident of evolution — although it's worth noting that mammalian embryos start out highly symmetrical (spherical, in fact) and then gradually develop various asymmetric features as they mature. Since the umbilical cord forms very early during embryogenesis, at the time when the embryo just begins to acquire a distinct head-tail axis, it makes sense for it to be aligned symmetrically; at that stage, everything in the embryo is still symmetric. —Ilmari Karonen (talk) 22:38, 24 November 2007 (UTC)

I read somewhere (I forget where - sorry) that one possible reason for symmetry is that it requires less DNA to code for it - and less DNA means less to go wrong and less 'stuff' to carry around in your cells. SteveBaker (talk) 21:42, 24 November 2007 (UTC)

Plus, it's 'easier' to evolve. Plant evolves leaf. Plant's descendants have simple mutation to carry out 'reading' of leaf code twice. Plant has two symmetrical leaves. Skittle (talk) 23:36, 25 November 2007 (UTC)

Another possibility is that the symmetry seen around us can be traced back to fundamental mathematical symmetries. The golden ratio and the Fibonacci series are good examples of this. It could also reflect the underlying symmetry of the materials from which we are made, and the biochemistry. Build things up in a symmetric way, and the result will be symmetric. Redundancy, as well (only need instructions for one half of the object). Evolutionary history as well - many of our bodily structures still reflect our evolutionary history. We've inherited the symmetry in those early forms of life. Carcharoth (talk) 22:05, 24 November 2007 (UTC)

Lunar warfare

I've been thinking about what warfare would be like if it took place on the Moon in the near future. While science fiction is in love with laser weapons, it seems the worlds military are rather more conservative, in that they're very happy to go to war with weapons several decades old, but that they know work. My thoughts are below: my question is to ask y'all if I'm on the right track about the science:

• Conventional guns work pretty well. Bullets fly on shallower trajectories and (lacking air turbulence) don't need to be spin stabilised (so barrels are unrifiled). With a decent scope a sniper could be a threat at 10 miles away. Moondust and propellant residue must be cleaned from a gun's action with a can of compressed gas. For hand-held guns recoil is more of an issue that on Earth (because the firer has less weight with which to counteract it by leaning into the shot) so muzzle breaks are found on most guns. The big problem with guns is dumping excess heat. Single-shot and semi-auto guns have black radiative fins to try to dump heat, while automatic weapons must have cooling systems (which work by using the excess heat to warm dry ice, which sublimates and is then vented)

• Conventional unguided rockets work well. They don't need fins for stabilisation (again due to the lack of atmosphere), an have an effective range several times that of comparably sized terrestrial equivalents. Guided missiles must use high-performance motors (e.g sodium azide cells) to adjust their course midflight.

• a Lunar Positioning System (LPS) can be erected much like GPS. Reasonable advances in portable electronics and antennas mean that a system with fewer satellites (in wider orbits) will be sufficient.

• The weapons of artillery pieces and tanks work well (although the vehicles that propel them are obviously different). As with firearms, cooling is a major issue. When integrated with a LPS and an electronic battlefield system they can attack targets well over the horizon.

• No equivalent to close air support is possible. Tactical support of land forces is supplied by artillery or ground-to-ground rockets. Strategic bombing is achieved either by long range g2g missiles or missiles fired from orbital weapons platforms.

• With no cover, no weather, limited opportunities for camouflage, and the extreme ranges at which simple weapons are effective, everyone on the battlefield is very vulnerable. Humans, who are yet more vulnerable in pressurised suits and vehicles, are largely absent from the battlefield; most combatants are semi-autonomous robot vehicles.

Neglecting obvious speculation about energy weapons (which I appreciate would be more effective in a vacuum) does this seem, erm, airtight? 86.131.206.94 (talk) 20:20, 24 November 2007 (UTC)

Instead of weather you get the long lunar night, which may be lit by earthlight, or only starlight on the backside of the moon. Things could very cold when not lit by the sun for weeks. Another factor is the extreme vulnerability of people to puncture wounds in their air containment. Something more like a shotgun may be able to cripple dozens of unprotected people. Graeme Bartlett (talk) 20:34, 24 November 2007 (UTC)

Don't forget that conventional guns usually need air to fire properly, as they propel by a rapidly-expanding gas. New propellants or rail guns are probably a better option. SamuelRiv (talk) 20:55, 24 November 2007 (UTC)

Any recoil vector not tangential to the surface would make the firer jump or fly up, which could be a big factor for artillery. A tank firing a sabot could put the penetrator into low orbit, so it would need to be careful about trajectory and try to figure out where not to be when it comes back around if it screws that up. The same goes for any weapon firing a projectile that goes faster than about 5,500 ft/s. Runaway missiles and stray shots would be raining down all over the moon for days or weeks after a battle, going as fast as they were when fired. Barrels would still be rifled, as the stabilization helps overcome perturbations caused by asymmetry in the gas blowby at the muzzle, which will envelope the projectile quite a ways downrange. Anything like aircraft would only be needed for emergency reconnaissance, as ballistic weapons could hit anything anywhere. Nukes could be used with impunity over the horizon, as all personnel would already be suited or indoors anyhow, and no blast would be felt. --Milkbreath (talk) 21:19, 24 November 2007 (UTC)

I don't believe that's true. Conventional guns turn solid propellant into gas (during its explosion) and that's what pushes the bullet out. Gas from the atmosphere just gets in the bullet's way. -- Finlay McWalter | Talk 21:02, 24 November 2007 (UTC)

I'm not sure that there would be little opportunity for camouflage. The lunar surface isn't particularly flat in most places, so (depending on time of day) there may be lots of shadows to play with and lots of structures to hide behind (erosion is very slow on the Moon...). As well, the surface colour and texture is fairly uniform compared to Earth (just a couple of different broad classes of rock, dusted over in many places with regolith) makes supplying camo uniforms easy (none of this mucking about with separate desert/jungle/winter/city uniforms). Of course, waste heat from warm bodies and equipment will be a dead giveaway on any sort of infrared imaging during the chilly lunar night.... TenOfAllTrades(talk) 21:21, 24 November 2007 (UTC)

Yeah - you don't need air to fire a gun. The oxidizer is mixed into the propellant.

• Conventional guns work pretty well. True.

For hand-held guns recoil is more of an issue that on Earth (because the firer has less weight with which to counteract it by leaning into the shot) so muzzle breaks are found on most guns. - Not true. Every action has an equal and opposite reaction. F=ma - the mass of the bullet (NOT WEIGHT) times it's accelleration produces a force that is absorbed by your body - so your accelleration (the 'recoil') is the mass of the bullet times the accelleration of the bullet divided by your body mass. Hence the recoil will be identical to what it was on earth. Actually rather less because you're wearing that huge chunky space-suit.

The big problem with guns is dumping excess heat. Single-shot and semi-auto guns have black radiative fins to try to dump heat, while automatic weapons must have cooling systems (which work by using the excess heat to warm dry ice, which sublimates and is then vented) - Maybe that's a problem...it's hard to know. I doubt dry ice solutions would be practical though.

• Conventional unguided rockets work well. They don't need fins for stabilisation (again due to the lack of atmosphere), an have an effective range several times that of comparably sized terrestrial equivalents. Guided missiles must use high-performance motors (e.g sodium azide cells) to adjust their course midflight. - The inability to use fins for stabilisation would be a major problem - but you shouldn't be thinking of long, thin missiles - they can be any old shape. Probably gyroscopic stabilisation will suffice.
• a Lunar Positioning System (LPS) can be erected much like GPS. Reasonable advances in portable electronics and antennas mean that a system with fewer satellites (in wider orbits) will be sufficient. - Probably.
• The weapons of artillery pieces and tanks work well (although the vehicles that propel them are obviously different). As with firearms, cooling is a major issue. When integrated with a LPS and an electronic battlefield system they can attack targets well over the horizon. - There is no problem (in principle) with making over-the-horizon weapons here on earth either. But you have to consider the problems of locating your target and that they can sense your incoming weaponry with sufficient time to get out of the way. Hence you need guided weapons...which in turn brings a whole other slew of problems.
• No equivalent to close air support is possible. Tactical support of land forces is supplied by artillery or ground-to-ground rockets. Strategic bombing is achieved either by long range g2g missiles or missiles fired from orbital weapons platforms. - See below.

I don't think you are thinking far enough 'outside the box'. Because there is no atmosphere, you can in principle orbit at very low altitudes - just above the tallest mountains would be just fine. Orbital speeds can be pretty amazingly high with no air resistance or aerodynamic forces - and a weapon in polar orbit can be arranged to cover the entire moon over enough orbits. Also, you don't need to burn fuel to stay up there. So injecting an enormous cloud of low-yield rocket/bomb/satellite things up there - with primitive guidance, a camera and a small rocket to nudge them out of orbit would produce a lethal combination. They could act as their own surveillance - when they spot a likely target, they call someone who is nice and safe a long way off who decides kill/no-kill - and the next available satellite nudges itself out of orbit and comes screaming in for the kill. The speeds would be amazingly high - you probably wouldn't even need explosives. You'd be able to nominate a target to hit from the ground and just have the next available unit drop out of orbit to take it out. With weapons like that, you'd obsolete almost all of the other things you've come up with. However, with both sides taking the same approach, there simply won't be any targets to hit.

The bigger question is why there are targets out there anyway? You won't have huge civilian cities - and with no 'nuclear winter' concerns, why not just nuke the mines, factories and launch facilities out of existance? (In fact - forget the mines and factories - just take out their launch facilities and their mines and factories are irrelevent. I can't see the need for humans and tanks and stuff to be there at all.

SteveBaker (talk) 21:30, 24 November 2007 (UTC)

• Hold on there. It's true that without air resistance an orbit at very low altitude is possible, but it won't necessarily be stable. The Moon's gravitational field has irregularities and the Earth causes sizable perturbations. Your orbiting weapons would need fuel for stationkeeping, although I don't know how soon. Also, from a position close to the ground, they could only strike targets along a narrow path on each orbit... so you'd need an awful lot of them to be able to cover a reasonable amount of the Moon's surface. --Anon, 23:17 UTC, November 24, 2007, Earth.

That's true - but it's likely to be a pretty tiny amount. You only have to account for gravitational variation - a very gentle adjustment is all that's likely to be required. The craft need some kind of motor to nudge themselves out of orbit anyway - so I doubt that's a huge deal - a hydrazine thruster would probably suffice. As for the number you'd need - that would depend on how urgently you need to hit your target. A polar orbit would take half of a lunar month (14 days) to cover the entire surface - but the orbital speed would be something like a kilometer per second - taking about two hours to complete an orbit - with the orbits being about 80km apart at the equator - it doesn't take much of an orbital 'nudge' at 1km/sec to deflect your orbit by 80km. So if you had 14 of these satellites you could hit any target within a day of deciding to do so. If you had 150 of them, then you have to plan your attacks a couple of hours ahead of time. With 3000 of them you can hit any target within 5 minutes - which is pretty good by military planning times. I envisage these things as being cheap - highly networked (so you can't take out a command unit or disrupt their communications because they can pass messages over very short range radio from one satellite to the next) - and with each one carrying a camera (which they'd need for station-keeping and targetting) - you have constant surveillance of the entire moon. You'd launch them from orbit and since they're cheap you'd have a heck of a lot of them. With the kinetic energy from travelling at 1km/sec, something about the size of a football is all you'd need to vaporize your target. I had in mind satellites like the size and complexity of a cellphone - with the same communications ability and a similar kind of camera - plus a few ounces of hydrazine fuel and gyroscopic stabilisation. Cost in bulk could be thousands of dollars each - so a few million dollars (about the cost of one tank and about a lot less than the cost to get one infantryman to the moon) would allow you to bring down huge destruction on anything on the surface of the moon within a few minutes. SteveBaker (talk) 17:33, 25 November 2007 (UTC)

(edit conflict) Okay, my bad, according to MythBusters_(season_4)#Guns_Fired_Underwater, oxygen is not needed with modern guns. The ignition of gunpowder and primer does not require oxygen. I guess enough gas is produced to accelerate the bullets effectively: Smokeless powder converts almost everything to gas, but gunpowder only gets about 40% yield. There also should not be any leakage of gas behind the bullet, though maybe some is there as the cartridge is loaded... if this is the case, you'll want to manufacture some new guns and bullets that are optimized to this change in environment. Heat buildup is a big problem, as that's normally dealt with by air cooling (yes, in the end almost everything here is air-cooled). Any type of radiative cooling would kill any hope of camouflage, but I don't see any other solution besides dumping excess heat into some type of electromagnetic radiation. SamuelRiv (talk) 21:45, 24 November 2007 (UTC)

You could drive a big spike into the lunar soil and use that as a heat sink. If you find somewhere in permenant shadow, it'll be pretty amazingly cold. If you have cheap access to water (unlikely), you could build a cooling jacket that oozed water to the surface. It would boil off in the vacuum taking substantial amounts of heat with it. But I very much doubt that conventional projectile weapons are the way to go. Infantry on the ground would be horribly vulnerable - even a blast of low speed buckshot would penetrate a spacesuit. Firing a bazillion small ballbearings on a ballistic trajectory (with no air resistance to slow them down) would take out large formations of infantrymen very easily indeed. Ergo there won't be large formations of infantrymen. The lack of air resistance (and hence the absence of terminal velocities) means that if you are killable by high speed metal - you're dead. So you have to be moving fast or buried underground or very expendable. With no reason not to use nuclear weapons (no civilians, no wind-born fallout, no nuclear winter issues - and if your technology is good enough to get you to the moon in the first place, then it's good enough to build nukes with), being buried a little way underground won't help you - so you'd have to be in a gigantic bunker - very tough to construct in a lunar environment. Moving fast is possible - but moving fast in a nice, predictable, straight line is death - so you need to be accellerating unpredictably. For that you need something with no humans inside. Since you can use insanely low altitude orbits to stay airborn without using fuel, you probably want very manouverable, very low altitude satellites. Being very numerous is another way to be safe - so (as I said before) a vast number of very low altitude orbiting bombs can take out anything that moves on the surface.

But still - why fight on the moon to start with? If there are any people there at all then clobbering their supply lines from Earth is the simplest solution. Those supply craft will be big, sluggish and predictable. Fire a cloud of ball bearings at a few hundred mph in the direction of a resupply craft and they are without food and water within a month. Do it two or three times in a row and they are dead.

SteveBaker (talk) 22:16, 24 November 2007 (UTC)

a cardiac procedure called mase

What is a cardiac procedure called mase? —Preceding unsigned comment added by 67.177.212.215 (talk) 18:50, 24 November 2007 (UTC)

There's nothing in the book of medical abbreviations on my desk. Could it be something done with a maser? —Tamfang (talk) 20:32, 24 November 2007 (UTC)

MACE appears to stand for "major adverse cardiac events", which includes infarctions and other (dunno what) bad heart happenings. [13]. But that's not a procedure. -- Finlay McWalter | Talk 20:34, 24 November 2007 (UTC)

See Maze procedure. --Arcadian (talk) 23:09, 24 November 2007 (UTC)

Artificial gravity

If a spaceship, which is not near any object large enough to cause significant gravity, would generate its own gravity by rotating around its own axis, what would happen? If someone standing on the edge would climb up all the way to the centre, and then keep on climbing further, would they start falling down, but actually not back where they started, but in the same direction that they had been climbing? And where is "down" exactly when it is towards an entire area, not towards a single point? Is it towards the point on the surface that is nearest to your current location? Does that mean that if someone were to jump up on a rotating spaceship, they would land on a different spot than they originally jumped from? JIP | Talk 20:38, 24 November 2007 (UTC)

If you can, watch the movie 2001: A Space Odyssey (film) - it does a great job of showing what spin-gravity would be like. But let's imagine a vast spacecraft that's a cylinder spinning around it's long axis. You'd build the 'decks' of the craft as concentric cylinders inside the craft. The decks closest to the outside of the craft would have the strongest gravity - those closest to the central axis would have less gravity - and at the very center of the craft, you'd be in zero g. If there were windows on the curved outside surface of the cylinder, they would be in the floor of the strongest-gravity deck. If you imagine a ladder running "up" from one of the outer decks, up through the center of the ship and through to the opposite side, then someone starting out to climb the ladder up from the outermost deck would feel strong gravity at first, then slightly less and less still until reaching the center of the spaceship where there is no gravity. If you continued 'climbing' the ladder through the zero g region, you'd start to feel like you were hanging upside down and the direction that was "up" is now "down"...and as you climbed further "down" the ladder, you'd find the gravity getting stronger and stronger until you reached the outermost deck - 180 degrees around the other side of the ship from where you started.

If the spacecraft was small enough with no internal decks - then yes, as you say - you could jump upwards gently and land back where you started from - but a really big jump would take you sailing up into less and less gravity - floating gently across the middle of the ship - then (alarmingly) plummeting head-down towards the opposite side of the ship with increasing accelleration until you whacked your head on the floor on the opposite side.

However, everything I've said has missed one important thing. Coriolis forces. Since you are moving sideways at a fairly large speed on the outer surface of the ship, as you go upwards, you'd find yourself not going in a straight line because the space craft is spinning beneath you. One of the problems with producing a spin-stabilised craft "for real" is that these coriolis forces might make it's occupants have all sorts of puke-making feelings from being pushed sideways everytime they stood up too quickly - or that different gravity between their heads and their feet would cause severe disorientation. Hence spin-stabilised craft have to be big enough to where coriolis forces are sufficiently negligable to not cause problems.

SteveBaker (talk) 20:58, 24 November 2007 (UTC)

(edit conflict) The acceleration you feel due to gravity on Earth is a pretty constant 9.8m/s/s. In a spinning spaceship, acceleration looks like $a=r\omega ^{2}$, where r is the radius and ω is the angular velocity, which is constant throughout. So as you go farther from the axis, as you noted, gravity feels stronger. So you could conceivably jump and get stuck in the middle of the ship or fall towards the other side, but the effect would be gradual, not sudden. Now if you jump and fall back to the same side, you may see yourself drift a bit due to the z-terms of the Coriolis effect. There shouldn't be any force from the air as it will reach an equilibrium position inside the ship--the acceleration is always outwards and constant at each point. SamuelRiv (talk) 21:09, 24 November 2007 (UTC)

Consider also what an outside observer sees. You jump off the rim – that is, you push yourself inward by a kick against the wall, as in a swimming pool – and proceed in a straight line. Your vector is the lateral velocity of the rim at that moment plus whatever impulse your legs can impart; so to reach the axis you need to jump at an angle to negate the rotation. You "land" when you collide again with the rim; where you land depends in part on how far the rim has turned during your jump, and thus on the speed of your jump. —Tamfang (talk) 22:13, 24 November 2007 (UTC)

It's only the friction between your feet and the deck - plus any air resistance from the air inside the ship that keeps you going around in a circle as you stand "still" on the deck. In true high-school physics style, let's neglect the air resistance. Let's suppose you can jump high enough to sail across the ship and land on the other side. Let's suppose you try to jump straight upwards through the exact center of the ship. The moment you leave the floor, there are no more forces acting on you. (Remember, this isn't "real" gravity - this is just a spinning cylinder in zero g). With no forces acting on it, your body travels in a straight line - at a constant velocity. So your velocity vector is the sum of a vector that is acting tangential to the floor at the moment your feet left the ground (friction) with a inward radial vector due to the force your legs applied in the jump. Let's call the lateral vector 'F' (friction) and the vertical vector 'J' (jump). From your perspective, you would have been trying to jump "stright up" towards the center of the spacecraft - but find that you miss that point by some amount that depends on the size of the spacecraft and the amount of spin it has (this is the Coriolis effect). In ADDITION, the spacecaft is rotating so that the point you were aiming for on the opposite wall has moved by some amount by the time you get there.

Suppose your spacecraft is spinning clockwise from the perspective of our outside observer. If you aim your jump at a point exactly 180 degrees away from your start point then the coriolis effect (the addition of the small 'F' vector to your 'J' vector) forces you to land at a point a little anticlockwise of where you aimed - BUT while you were in the air, the rotation of the craft moved your aim point clockwise as you were in motion so you land even further anticlockwise of your aim point than you expect.

This means that the slower you jump, the bigger 'F' is compared to 'J' - the bigger the coriolis effect - and the further anticlockwise of your aim point you land.

But we just said that from the moment your feet leave the floor, there is no more gravity (there never was any gravity - it just felt like there was) - so how does this feel so natural? When you are standing still, the 'F' vector is pointing slightly outside the craft (it's a tangent to the curved deck), your inertia wants to put you outside the spaceship - but the deck is forcing you inwards all the time. That force feels just like gravity...well, almost.

What's going to be weird for the occupants is small vertical jumps. In a small vertical jump the coriolis effect and the rotation of the craft are more or less equal - so the point where you land is almost exactly where you jumped from - just like if you jump straight up here on earth.

The 'F' vector is tangential to the floor when you jump and the 'J' vector is tiny by comparison - so the combined vector points to a place on the deck only a little clockwise from you. More or less exactly where the deck plate you were standing on rotated to while you were in the air. However, if that distance is a significant fraction of the circumpherence of the craft - you'll be landing with your body at an angle to the deck. If the craft rotateds at 10 degrees per second and you spend a second in the air during your jump - then when you land, your body is leaning 10 degrees to the local "vertical" and you'll probably fall over when you hit the deck. So only small jumps feel natural - just like gravity providing the ship is huge and rotating slowly. If it's smaller and still trying to produce one g of similated gravity - then these peculiar coriolis-related matters will become very disturbing. Walking and bending down, picking things up and tossing them to your fellow astronauts will all feel ever so slightly 'off' from what you are used to on earth. If the space ship is too small, it's likely that nausia and other problems would be common.

SteveBaker (talk) 17:16, 25 November 2007 (UTC)

It's not a your mum joke, promise.

What is the relationship between gravitational and inertial mass? Why are they the same? Do they have the same cause? Please answer ungriftingly! Samuel P. Lemminghornsworth —Preceding unsigned comment added by 217.43.117.20 (talk) 23:07, 24 November 2007 (UTC)

Until someone who understands this turns up, you could do worse than read Mass#Inertial and gravitational mass. Algebraist 01:53, 25 November 2007 (UTC)

Inertial mass is the mass related to F=ma, one of Newton's laws. Gravitational mass is the mass related to F_g=mg or F_g=Gm₁m₂/r². Their equivalence was well known to Newton, but not understood by him. Einstein solved the problem by showing (in General relativity) that acceleration and gravitation are essentially the same thing. Someguy1221 (talk) 02:48, 25 November 2007 (UTC)

Actually, he didn't "show" they are the same thing, but rather assumed it. General relativity doesn't provide any compelling explanation for why it must be true (other than that GR works). We certainly have examples of forces (e.g. electromagnetism) where the ability to create force is determined by something (charge) that is different from the resistance to acceleration (inertial mass). There is no fundemental reason why one couldn't construct a GR-like theory in which something other than intertial mass appeared in relavant spots of the stress-energy tensor that determined the shape of space time. Dragons flight (talk) 03:14, 25 November 2007 (UTC)

General relativity works from the premise that accelleration and gravitation are indistinguishable (that's the thing that started Einstein off on his quest to establish it) - one consequence of which is that inertial mass and gravitational mass MUST be the same. If they were not, general relativity wouldn't work because you'd be able to tell whether you were out in deep space with a rocket motor pushing you along with a 1g accelleration or sitting still on the launch pad here on earth. The problem here is to ask whether general relativity is true BECAUSE of some amazing coincidence between the two interpretations of mass - or whether the two meanings of mass are the same BECAUSE general relativity is true. Asking WHY a fundamental law is true is an unanswerable question. It's more philosophy than science! SteveBaker (talk) 10:10, 25 November 2007 (UTC)

What is the best way to self-study string theory?

Are there free online text books, etc? -- Taku (talk) 23:20, 24 November 2007 (UTC)

It really would depend on your level of knowledge to begin with. Are you a serious student of theoretical physics? Or are you an interested amateur? If the latter, you can't go too wrong by reading the popularized books first. --24.147.86.187 (talk) 23:42, 24 November 2007 (UTC)

My background is mathematics, so I'm basically interested in how math is used in physics. (For example, I vaguely know the use of functional analysis in quantum physics.) Since popular books tend to have almost no math, I was wondering if there is a textbook or something comparable on string theory (because academic papers are way beyond my knowledge.) -- Taku (talk) 08:58, 25 November 2007 (UTC)

November 25

Can chiropractors prescribe scheduled medicines?

Like pain killers? Biochemza, 00:07, 25 November 2007 (UTC)

Not in the UK, unless they are also one of the following :-

"NHS prescriptions are most commonly written by your GP for you to take to your community pharmacist (chemist) to collect.

From 1 May 2006, qualified Nurse Independent Prescribers (formerly known as Extended Formulary Nurse Prescribers) are able to prescribe any licensed medicine for any medical condition within their competence, including some controlled drugs.

Doctors working in NHS hospitals also write NHS prescriptions. In most cases, you will be asked to take your prescription to the hospital pharmacy to pick up your medicine. Sometimes you will be asked to take your prescription to your local chemist - usually when the hospital pharmacy cannot supply your medicine.

An NHS dentist can also provide you with an NHS prescription if you need treatment for a dental or oral condition.

Supplementary Prescribers are pharmacists, chiropodists, podiatrists, physiotherapists and radiographers who have undergone specialist training. They may prescribe any NHS medicine provided it is in partnership with an independent prescriber who gives the initial diagnosis and starts the treatment. The Supplementary Prescriber then monitors the patient and prescribes further supplies of medication when necessary." - Source is http://www.nhsdirect.nhs.uk/articles/article.aspx?articleId=1629 Exxolon (talk) 00:24, 25 November 2007 (UTC)

In the U.S., all States currently exclude prescribing drugs from chiropractic practice [14]. There have been lawsuits from chiropractors seeking to change this; none have been successful. - Nunh-huh 03:31, 25 November 2007 (UTC)

That's probably because many chiropractors are homeopaths. -- JSBillings 17:23, 25 November 2007 (UTC)

Illegal Plant - USA

What plants are illegal to own/possess in the US? --WonderFran (talk) 00:22, 25 November 2007 (UTC)

A number are on the Controlled Substances Act schedule list, which depending on their "schedule" gives them various degrees of legality. Marijuana, psilocybin mushrooms, and peyote are always illegal (under US federal law). Without a prescription, opium poppies and coca leaves are illegal. Those are the ones that jump out immediately to me. --24.147.86.187 (talk) 00:43, 25 November 2007 (UTC)

Note that in some local jurisdictions there are plants that are illegal because of the threat they pose to the ecosystem and/or invasive. See, for example, the Illinois Exotic Weed Act, which bans a number of plants from the state of Illinois. To compile all of those would be a very long list and require a lot of digging into state and probably local laws. --24.147.86.187 (talk) 00:51, 25 November 2007 (UTC)

(Edit conflict) Certain plants are also considered noxious weeds and are illegal to possess on the basis that various governments (local, state, or federal) are trying to stamp out those plants. We used to use a particular weed in our fish pond as an oxygenator, but the fish loved to eat it as well; we can't get that weed any more as it is now illegal in New Hampshire.

Atlant (talk) 00:52, 25 November 2007 (UTC)

• Nuclear plants, unless you have the proper permits, which can be quite a headache to acquire. --Sean 01:17, 25 November 2007 (UTC)

Does my sun conure have another name?

My sun conure is named Sally. She responds and comes over to me when I call her by name. It's pretty clear that she knows that this is the 'human speak' call I use to refer to her in particular as an individual. Do sun conures also have names in their own 'parrot speak'? It would seem obvious that she does not sit and think of herself as "Sally the Sun Conure" - how would a bird which can speak only a few words of English be expected to know what name humans have given to her entire species? —Preceding unsigned comment added by 84.66.52.166 (talk) 00:25, 25 November 2007 (UTC)

My brother used to do research trying to decipher parrot-speak. He said that in groups of parrots (in some species) a single member could alter its song to more closely match that of another individual parrot, and in this manner would attract the attention of that parrot. Not a "name" per se, but certainly some species have ways of calling to a specific individual. Someguy1221 (talk) 02:42, 25 November 2007 (UTC)

Avian_intelligence#Language. This article is beautiful. SamuelRiv (talk) 03:18, 25 November 2007 (UTC)

Hmmm. I wonder if that goes some way to explain why many species of parrot mimic human sounds in the first place? I know from my experience with budgerigars that they (the males in particular) will often weave the various human words and phrases that they've learned together into a 'song'. --Kurt Shaped Box (talk) 12:57, 25 November 2007 (UTC)

I don't think names are things that animals naturally deal with. It seems that dogs, cats and parrots (at least) can be trained to recognise some specific sound as being 'theirs' but whether they even think of it as a 'name' is hard to say. Whether your Sun Conure is recognising "Sally" as her name - or whether it is the intonation of your voice for the entire senntence "Sally come here" that works is anyone's guess. Our Cocker Spaniel dog would get very excited when we said the word "Walkies!" because he loved going for walks. He would actually run off and find his leash and bring it to us when we said "Walkies!". My wife contended that he understood the word - but I convinced her not because I could say "Tomato Sandwiches!" in the exact same tone of voice and cause the dog to rush off and fetch the walkies apparatus. Furthermore, if I used the word "Walkies" in a completely neutral tone of voice in the middle of another sentence, the dog didn't recognise it at all. I eventually discovered that if I mimed saying "Walkies!" without making a single sound, the dog would respond. Dogs (and probably parrots too) are sensitive to a wider range of human expression (including body language, voice intonation, maybe even pheremones) than we are conscious of delivering to them. It's easy to assume they detect one kind of communication (words for example) when in fact it's something completely different.

• Inserting a response to this point: what that this means is that the dog isn't correctly discriminating which aspects of your pronunciation are phonemic and which aren't. It's like the way some speakers of other languages can't tell the difference between the English words "ship" and "sheep", or "fat" and "vat"; and speakers of English have to learn that in Chinese the same word pronounced in a different tone becomes an unrelated word, or that in Hindi the aspirated K in English "kin" is a different consonant than the unaspirated K in English "skin". This sort of thing doesn't prove that the dog doesn't have the concepts you're using when you talk to it, only that it has trouble with human-accented pronunciation. (Of course this also doesn't mean that it does have those concepts; I'm only talking about what is evidence for what.) --Anonymous, 22:08 UTC, November 25, 2007.

The only case I'm aware of where animals have invented names themselves is in whale song - where I believe researchers have noted specific phrases in their song that are used by many members of a pod but only when one specific individual is present or being searched for. That suggests that whales have names...although there are perhaps other interpretations.

I bet that if you start calling your bird by a different name every day - but call her with the same tone of voice and body language - then you'll get exactly the same result you get when you call her "Sally". It's an easy experiment to try. Start off with names that are similar ("Betty" - has a similar number of syllables) and then try wilder combinations.

SteveBaker (talk) 10:01, 25 November 2007 (UTC)

Another thing to consider is whether your bird takes your calling of her name to be a signal that you (the large beastie that provides her with her only regular form of social contact) are ready to 'interact' with her, feed her some tasty fruit (or nuts, or whatever snacks you give her) and perhaps preen her itchy head feathers. --Kurt Shaped Box (talk) 12:57, 25 November 2007 (UTC)

Yep - exactly. The parrot translation of the word "Sally" could easily be "Hi! It's me!" or something like that. Have you ever seen the British TV comedy "Coupling"? There is a great episode ("The Girl with Two Breasts") in which one of the characters, Jeff, is chatting with a woman in a bar who doesn't speak English. The first half of the show has Jeff speaking English and her speaking Hebrew (I think). They both think they are managing to understand what's going on and they are getting on just fine but - in the second half of the show they replay the exact same scene but with him speaking Italian and her speaking English so you can hear the conversation from her point of view. The degree of misunderstanding is of course SPECTACULAR - and somehow he mistakenly assumes that the Hebrew word for "breast" is the girls' name...um...I guess you need to have seen the show! But if that level of miscommunication is even plausible between two humans (and it does seem pretty plausible) - then on an interspecies basis, anything is possible! SteveBaker (talk) 16:31, 25 November 2007 (UTC)

Identify this plant

I bought a plant, but it had no tag saying what the species was, so I was hoping for an answer. I took a photograph of the plant, and uploaded it here.

It was purchased at a home depot store in the Twin Cities, Minnesota for 15USD, and only came with one tag, which says "Tropical in Winter G/S". —Zachary ^talk 03:58, 25 November 2007 (UTC)

It looks likely to be Dracaena Marginata. Take a look at Google images: here and the Wikipedia article here -- dharma —Preceding unsigned comment added by 24.86.250.218 (talk) 04:21, 25 November 2007 (UTC)

Yes, it sure is of Dracaena genus (which is a common houseplant), but it could either be Dracaena Marginata as was pointed earlier or it could also be Dracaena Cincta. These two species are known for their distinct pinkish edge in the leaves which is evident from the picture you have provided. Hope it helped. DSachan (talk) 04:39, 25 November 2007 (UTC)

Good point - the Wikipedia article mentions that D. marginata is often confused with D. cincta or D. concinna. -- dharma —Preceding unsigned comment added by 24.86.250.218 (talk) 05:33, 25 November 2007 (UTC)

Another identification, please

My mom found this weird looking caterpillar at home, so I took a snap, when I blew some air on to it, it curled up a bit and showed me these faux eyes that it has got, and I admit, it scared me a bit. Is this going to be a moth or a butterfly when it undergoes metamorphosis ?

Thanks for the help in advance :) SiegerKranzMeer 08:13, 25 November 2007 (UTC)

It looks a lot like some sort of hawk-moth caterpillar, especially with the faux eyes that you mention. Richard Avery (talk) 08:55, 25 November 2007 (UTC)

Oh dear, this is very difficult one. First of all, are you sure that this is a caterpillar? It could be some weird worm also. But it sure looks like a caterpillar seeing its segmented body and structure. The problem is there are about 180000 species in this lepidoptera order (which is huge) and all of them form caterpillar. So, it is obviously a tough task to pick out one of them. Furthermore, some organisms of order hymenoptera also produce larvae which look very similar to caterpillars produced by lepidopterans and hymenoptera is another big order. But here also, I can be sure that it is of lepidoptera order only because these caterpillar tend to have shorter abdominal length in contrast to the hymenoptera larvae which have longer abdominal length to generally accomodate more prolegs. So their body tends to have more segments. In this picture I can see only about 8 segments, which is quite common in lepidopteran caterpillars. This creature showed you its eyes because it always does so to frighten away or trick its predators but in your case, its predator happened to be a human, so this trick didn't work. :) Now if you have a garden around your home, the possibility could be that it may be a caterpillar of geometer moth, but that also you can tell by the way it was moving. If you noticed how many prolegs it had, things would be a bit easier. If it had only one pair of abdominal proleg, it could be the caterpillar of Geometer moth, which makes a very large family and are fairly abundant in gardens. If it had 5 pairs of prolegs, it could be caterpillar of hawk moth also. Butterfly caterpillars generally tend to be shorter, hairy and more vividly colored. But having said that, I must admit that this could be anything ranging from being a worm, some skipper's larva, some weird moth's caterpillar or even a caterpillar of a beautiful butterfly. I pointed out the difficuly in the beginning. Biological world can always be bizarre and astonishing. It always has surprises for you in its store. So, don't take my suggestions as final. DSachan (talk) 09:26, 25 November 2007 (UTC)

Thank you Richard and, DSachan: for taking the time out to write such a long but detailed explanation. :) 123.176.43.125 (talk) 11:42, 25 November 2007 (UTC)

I'm hopeless at these 'please identify this insect' questions, but there is one part of your question I can help on. Will it become a moth or a butterfly? Our article on Moth says "The division of Lepidopterans into moths and butterflies is a popular taxonomy, not a scientific one" - in other words these words "moth" and "butterfly" are not meaningful in a scientific sense. Basically, we humans have decided that "pretty" lepidoptera are butterflies and "ugly" ones are moths - but since this is in the eye of the beholder - it doesn't really fit the underlying science so until someone can nail it down exactly what species this is, we have no way to guess based on some general characteristic of "moth" catapillars that might differ from "butterfly" catapillars.

Also, in general, please - when you ask us to ID plants or animals tell us where in the world you found it! Knowing which region of which country it comes from narrows down the search to much smaller number and perhaps directs us to online resources specific to that area. Having some idea of the local habitat (woodland, grassy plains, farmland, urban, etc) also provides a little more information.

SteveBaker (talk) 16:13, 25 November 2007 (UTC)

Will keep that in mind (about the 'giving the location' part) This one was taken at hyderabad, India. And I did not know that the distinction between moths and butterflies was a man-made one. Thank you for clearing that up. SiegerKranzMeer 21:33, 25 November 2007 (UTC)

Ammonium chloride

In the article entitled Ammonium chloride shouldn't the following sentence, "Ammonium salts are irritantt to the gastric mucosa and may reduce nausea and vomiting." read "Ammonium salts are an irritant to the gastric mucosa and may induce nausea and vomiting." ${\aleph _{0}}^{\aleph _{0}}$ _{(talk) (email)} 08:33, 25 November 2007 (UTC)

Yes it should, according to this classic text. Rockpocket 09:00, 25 November 2007 (UTC)

Thanks. Corrected. ${\aleph _{0}}^{\aleph _{0}}$ _{(talk) (email)} 09:21, 25 November 2007 (UTC)

Lysogeny

At lysogeny, the article includes mention of herpes, on the basis of its genomic integration, yet HIV is not considered lysogenic. Either herpes is not lysogenic because the term 'lysogenic' refers to bacteria-infecting viruses or else HIV is lysogenic... right? --Seans Potato Business 15:48, 25 November 2007 (UTC)

I'm not sure but I think the term lysogeny could mean two things: One is like you said, genomic integration of phage DNA to bacterial DNA (a definition I suspect doesn't apply to HSV or HIV because the viruses attack human cells, not bacteria). Two, it refers to the latent state of the virus, where the virus stays dormant inside the host's cell for some time. (Which would apply to both HSV and HIV) 128.163.224.198 (talk) 19:31, 25 November 2007 (UTC)

In the context of viruses that infect bacteria, see this textbook. I would not use the term "lysogeny" with viruses that infect eukaryotic cells....I'd use the term "latent infection". --JWSchmidt (talk) 03:37, 26 November 2007 (UTC)

Respiratory Acidosis

In chronic respiratory acidosis, what is the purpose of HCO3- (bicarbonate), if it can't actually buffer the H+ (the elevated pCO2, resulting in the cause of the acidosis, would prevent buffering?). The system wouldn't be able to compensate for a failure of itself would it? (hope it makes sense)

I'm not sure at all, but my initial guess would be that it comes from the reaction CO2 + H2O -> H2CO3, carbonic acid, which HCO3- salts would buffer. Respiratory_acidosis#Mechanism seems to confirm this to some extent. SamuelRiv (talk) 19:43, 25 November 2007 (UTC)

Rodents

What is the differences between a Gerbil, Hamster and a Guinea Pig?

XX##XX —Preceding unsigned comment added by 196.208.75.208 (talk) 17:09, 25 November 2007 (UTC)

I've wikified the different animals in your question. The quick answer is their original native habitat, both the gerbil and hamster are from europe and asia, and the guinea pig is from south america. -- JSBillings 17:20, 25 November 2007 (UTC)

Guinea pigs are huge - 8" long - about the size of a large, domesticated rabbit. Hamsters and Gerbils are both just a couple of inches long - the same size as a mouse. Gerbils are distinctive because of their large hind legs and feet. All three are rodents and they all eat similar things and make good pets. Hamsters are loners - they don't very much like the company of other hamsters - which means you can have just one of them without causing them stress - they live in tunnels and are naturally nocturnal, They adapt well to those crasy cages with the maze of twisty tubes (which are quite amusing but a pain to clean out a couple of times a week). They can be grumpy (and may bite) if you try to interact with them during the day. Guinea pigs (being large) need lots of space to roam around in - so you're going to need a large (possibly outdoor) enclosure for them. You can keep guinea pigs and rabbits together - they get along quite well and eat similar foods. SteveBaker (talk) 18:19, 25 November 2007 (UTC)

I recommend looking at the articles on them in Wikipedia, perhaps by following the links JSBillings gave you. Steve's guide is pretty good, but there are different species of hamster (Syrian hamster, Russian dwarf hamster, Chinese hamster, etc). A russian dwarf is about the same size or smaller than a mouse, but a syrian hamster is rather bigger (unless you've got huge mice!), and dwarf hamsters are frequently kept with each other. A grown gerbil is also rather bigger than a mouse, but these things vary. Anyway, read the articles and look at the pictures. Skittle (talk) 22:59, 25 November 2007 (UTC)

Tornado's

Most likely locations for tornadoes to occur.

Why is it that there is no tornado's in South Africa?

Antoinette —Preceding unsigned comment added by 196.208.75.208 (talk) 17:14, 25 November 2007 (UTC)

Actually, South Africa is one of the most likely places for a tornado to occur. Sancho 18:12, 25 November 2007 (UTC)

Dust devils are a common sight on the Karoo. Rockpocket 20:06, 25 November 2007 (UTC)

Stars on moon

Can you see stars when your on the surface of the moon? I seem to remember from somewhere that you cannot, but why would that be? Is the Earth so bright that it outbrightens (new word) all of them, just as the Sun does here? Imaninjapirate^{talk to me} 18:25, 25 November 2007 (UTC)

It depends on the direction you look and if you're in lunar day - see this. See also examination of Apollo moon photos#There are no stars in any of the photos. -- Finlay McWalter | Talk 18:33, 25 November 2007 (UTC)

I don't like the first answer in the first source you attached. In lunar day, the sun is indeed very bright and the moon surface reflects a significant amount of that light. However, the light is not diffused into the atmosphere, so conceivably you should be able to look straight up while shielding the light from the surface, the Earth, and the sun, and see plenty of stars, even in the daytime. SamuelRiv (talk) 19:47, 25 November 2007 (UTC)

Yes - you can see LOTS of stars from the moon - more so than here on earth because (a) there is no atmosphere to get in the way and (b) at night there is no light pollution. From the side of the moon nearest the earth, the earth is a very bright object that might make nearby stars a little hard to see - but on the other side of the moon it should be no problem at all. During the two-week-long night, on the far side of the moon from the earth, the view of the stars would be absolutely unparalleled. The reason you think there might not be stars is probably because of the annoying conspiracy theorists who claimed that the lack of stars in photographs taken during the Apollo landings was proof that the missions had never taken place and that the photos were faked. In truth, the reason there were no obvious stars in the photos (actually, you can see some) was because the brighter objects in the foreground (the astronauts, lander and lunar surface) were being lit by EXTREMELY bright sunlight (brighter than on earth because of no atmosphere) - and the camera's lens had to be stopped down to prevent it from over-exposing the film and washing out the whole image to a white blur. When you do that, dimmer objects like stars get dimmed down to almost nothing. SteveBaker (talk) 19:50, 25 November 2007 (UTC)

It's possible to see stars on the Moon even when the Sun and the Earth are above the horizon. The sky will be pitch black because there is no diffraction of light, so as long as empty sky fills your field of view and you cannot see the Sun, Moon, or surface objects, night vision will set in and stars will become visible.

An astronaut enjoying the heavens in daytime must of course avoid looking at the lunar surface without going indoors and allowing his eyes to adjust to highler light levels. --Bowlhover (talk) 21:33, 25 November 2007 (UTC)

November 26

Fire Accelerants

Are there any fire accelerants that aren't immediately lethal when consumed in considerable quantities? I know drinking a cup of gasoline will be unpleasant, but is there something that doesn't kill you, unless you then swallow a match or something... 74.230.231.13 (talk) 00:04, 26 November 2007 (UTC)

It depends on your definition of fire accelerant. From the article, "an accelerant is any substance or mixture that "accelerates" the development of fire", I think bottles of pure oxygen will accelerate a fire very quickly, but won't immediately kill you. --antilived^{T | C | G} 02:12, 26 November 2007 (UTC)

Define "considerable" - almost anything will kill you if consumed in high enough quantities. Many spirits are flammable, as demonstrated by party tricks such as flaming sambuca; and I expect something like an overproof rum would serve as an accelerant - according to our article, a mix of water & ethanol with over about 50% ethanol is flammable, so a spirit which is in the 60-70% ABV range should go up easily enough (although it's drinkability is another matter...) -- AJR | Talk 02:14, 26 November 2007 (UTC)

Balancing a chemical equation with silver nitrate copper and water

Alright I have this problem. I disolved .0185 moles of silver nitrate into a unkown amount of water to form a solution. I then dissolved 2.81 grams of copper oixide water into the solution until there was 1.25 grams left. I need to write the chemical equation for it if the copper is suppose to be +2 and +1 in charge. Does anyone know how to do that? —Preceding unsigned comment added by 70.249.230.252 (talk) 00:26, 26 November 2007 (UTC)

It sounds like homework or schoolwork help. The question also seems to have a typo ("2.81 grams ... until there was 1.25 grams left"). Just try writing out your reaction equation: the question is asking to use two forms: cupric and cuprous oxide, which are CuO and Cu₂O, respectively. SamuelRiv (talk) 02:03, 26 November 2007 (UTC)

Kinetic energy released by expansion of space

If space is expanding everywhere then the space in which all solid bodies exist must be expanding. As it expands the bodies themselves do not because the atoms that make up the body are attracted to each other and the nuclear forces keep the particles at a constant distance.

But this must mean that the atoms, if effect, move downhill a to keep that constant distance and, as such, there is a conversion of potential energy to kinetic energy.

Has anyone calculated the rate of kinetic energy being imparted to the earth as a result of the expansion of space?

Also, where does this energy come from? Or is this question completely off base?

Doug Moffat

209.5.192.16 (talk) 00:34, 26 November 2007 (UTC)

Energy doesn't come from anything. It cannot be created or destroyed but can only change energy types of change into matter. I'm not sure what you mean when you say there is a conversion of potential energy to kinetic due to space expanding. I'm not sure if that actually occurs, because space expanding has little effect on the bodies occupying that space, it just causes the bodies to move away from each other, yet still retain there current position in space. Space (which is not matter) is expanding and doesn't really effect the matter. —Preceding unsigned comment added by 70.249.230.252 (talk) 00:55, 26 November 2007 (UTC)

No, the point is a fair one. Anon is basically saying that if we take two massive bodies stuck to each other by gravity, inflation will try to pull them apart. If it succeeds, then you suddenly have gravitational potential energy that can be exploited if you stopped inflation for a second. Unfortunately, stopping inflation is the only scenario in which that energy can be exploited, so the end effect is just an effectively lower force between objects, if I'm reading this right. That is part of the reason we need dark matter: we find that certain clusters are not being pulled apart like they should be, so obviously the gravity in the cluster is higher than that due to visible mass. SamuelRiv (talk) 02:37, 26 November 2007 (UTC)

Space is only expanding between galaxies that are far apart and have very little gravitational influence on each other. Where matter exists, space does not expand (I think). Although your point is still valid (I think) because there would still be some gravitation force between them however small. Does the energy come from vacuum energy? Shniken1 (talk) 06:07, 26 November 2007 (UTC)

Two Point Function

I was reading this book awhile ago and it talked about something called the two point function. It was caused by two flucuations in a vacumm in space diverging until they became so close that their energy density matrices became infinite. Thus causing for the equation having to be renormalized, and this somehow caused an expansion in space-time. Does anyone know what I'm talking about or does this sound like nonsense? —Preceding unsigned comment added by 70.249.230.252 (talk) 01:01, 26 November 2007 (UTC)

Could it be Zero-point energy, and the related cosmological constant problem it apparently poses? -- Finlay McWalter | Talk 02:16, 26 November 2007 (UTC)

My bet is that it's the vacuum fluctuations of Edward Tyron that describes how the universe may have been created out of nothing. There is an excellent nontechnical overview of this here [15]. It could also be bubble nucleation of a false vacuum, which is another common pre-inflationary scenario. SamuelRiv (talk) 02:26, 26 November 2007 (UTC)

Query related to Urine

Is there any harm (or what are the results), if a girl drinks a man urine mistakenly / willingly.