Wikipedia:Reference desk/Archives/Science/2007 May 11

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May 11

Vascular bundles

I understood from the monocotyledon article that vascular bundles are randomly interspersed in monocotyledons and annularly arranged in dicotyledons, but how are they arranged in the stems of woody plants? Thanks, anon. —The preceding unsigned comment was added by 162.83.152.149 (talk) 01:38, 11 May 2007 (UTC).

Try vascular cambium and cork cambium as a starting point. David D. (Talk) 03:56, 11 May 2007 (UTC)

drug names

Where do drug names come from? One expects brand names to be arbitrary, but the generic names also seem to have very little in the way of etymology, as if the syllables were chosen like Bingo numbers. —Tamfang 02:04, 11 May 2007 (UTC)

See the International Nonproprietary Name page. DMacks 02:26, 11 May 2007 (UTC)

That article tells me only that an authority exists; nothing about its principles or its procedures. (Compare planetary nomenclature.) Is a name proposed by the developer, or does the developer ask the INN authority to pull some syllables out of a hat? Does the IUPAC name (which has less apparent freedom) come first, and if so does the INN tend to reflect it somehow? —Tamfang 04:46, 11 May 2007 (UTC)

It uses syllables from the "INN stems and modifiers from the WHO" document listed in the External links. That thing is almost 200 pages of fairly detailed and specific meanings for each syllable, not really amenable to a short list in the wiki article. DMacks 05:43, 11 May 2007 (UTC)

(glancing at the huge PDF) Wow, so there's more etymology than I thought. Thanks. —Tamfang 04:22, 12 May 2007 (UTC)

Bioethics and astrobiology

From what I understand, most people think it's perfectly ethical to use animals for academic purposes-- capture the animals, study their behaviour in a controlled environment, disect them, other expirements that may involved killing the animal, etc, so long as you don't cause unnecessary suffering or do really cruel things (definions of that vary greatly, but anyway). Ok what my question is, would it be the same for life on other planets? Obviously it would be okay for microbial life, and plant-like things if we find any. What about animals (or animal-like beings, aliens whatever)? On earth, we kinda think we're superior to animals, and human life much is more precious probably because of the enormous intelligence gap between us and the next most intelligent animals (apes, monkeys, dogs?). What about on other planets. Let's say we found a planet that resembles ours: millions of different species with one intelligent, dominant (perhaps civilized) one. Would we treat that one as an equall to us or just like any animal? Afterall, if aliens landed on earth and decided to study organisms, we would expect them to treat us different than the rest of the animals, right? (For example, we would be outraged if they rounded up a village of people and took them back home to study, but maybe not so much if they took a school of fish or something.) 209.53.181.150 03:17, 11 May 2007 (UTC)

I would think the same rules for deciding which animals get which protections would apply. It might be a bit more difficult to decide which alien animals are intelligent, though, if they are very different from us. For example, a creature which lives for a million years and has one thought a year might appear to us to be unintelligent. StuRat 03:31, 11 May 2007 (UTC)

"Perhaps, on alien worlds, we will be the ones bringing the anal probes." StuRat 03:31, 11 May 2007 (UTC)

Are you asking for an ethical principle or for a prediction of what's likely to happen? Either one is, I think, inappropriate here. —Tamfang 04:38, 11 May 2007 (UTC)

H Tristram Engelhardt has a book called "The Foundations of Bioethics" out there. He writes about creating a distinction between "person" and "human" for ethical purposes. He discusses criteria for persons, those who ethically cannot be experimented upon, and nonpersons, those that can. Check it out, I'll scan a few pages in for you or type in some quotes if you're interested. It's pretty heavy reading. [Mac Δαvιs] ❖ 07:19, 11 May 2007 (UTC)

Google Books has it here. --TotoBaggins 13:59, 11 May 2007 (UTC)

Nice find; I don't remember "Christian" being in it though. [Mac Δαvιs] ❖ 18:53, 11 May 2007 (UTC)

Dang, you're right, they're totally separate books. You can browse the, er, secular one here. --TotoBaggins 20:32, 11 May 2007 (UTC)

If aliens smarter than us by the same amount as we are smarter than chimps landed here and rounded us up by the village-load for dissection, our opinions on the topic would matter about as much as the opinions of the chimps matter when we do such things to them. --TotoBaggins 13:59, 11 May 2007 (UTC)

But chimps and other animals don't have opinions! That's the point, if they're not intelligents, they are not entitled to er "personness" or "personhood". 209.53.181.69 22:56, 11 May 2007 (UTC)

I think animals have opinions. For example, they tend to have opinions about which mates are, and are not, appropriate. StuRat 02:04, 12 May 2007 (UTC)

True in most cases, Stu. But bonobos couldn't give a damn. :) JackofOz 05:41, 13 May 2007 (UTC)

Even they must have some standards, if only that their mates must be warm and/or breathing. StuRat 21:58, 13 May 2007 (UTC)

That's my point. If we're as much dumber than the Martians as chimps are dumber than us, we're not going to qualify for Martianhood, which will probably mean they'll have no compunctions about doing things like this to us. --TotoBaggins 01:03, 12 May 2007 (UTC)

There is a spectrum of what is acceptable, varying with each type of creature, which is at least partly normalized by the perceived intelligence or proximity to human-ness. We have no problems destroying bacteria en-masse with bleach or penicillin as part of a routine experiment. Lab rats, which are often killed for science research, are often treated well (often subject to the institutional ethics review board). Dogs and chimps are rarely killed; and human experimental subjects are treated fairly well. Hopefully the hypothetical extra terrestrials would have a similar spectrum which does not involve sever mistreatment of humans. Nimur 07:09, 12 May 2007 (UTC)

Alzeimer's Disease

I read in an article that Insulin can spur Alzeimers Disease. What if the patient is a diabetic??? Would it effect them neurologicaly? Would it effect thier motor skills???

TamaraDissa 05:01, 11 May 2007 (UTC)

A quick google search seems to say that Alzheimer's disease causes a drop in insulin or something, I am not a medical practitioner. Splintercellguy 06:37, 11 May 2007 (UTC)

Alz has nothing to do with diabetes or pancreatic insulin. Certain brain cells apparently produce small amounts of insulin within the central nervous system and it may play a role in maintaining neurons. Alz was associated with lower CNS insulin levels in one study [1] but whether low CNS insulin levels cause Alz or are simply an effect or associated problem has not been determined. Peripheral circulating insulin levels do not seem to have much effect on the brain, and the CNS insulin does not have any known effect outside the brain. alteripse 13:47, 12 May 2007 (UTC)

EyeBrow Growth

Hypothetically speaking, If removed by using a blade, Will they grow back but to a slightly shorter length, slightly longer length, or no discernable difference in length? Its just i lost half an eyebrow in an accident and i really liked them incase you were wondering about such a bizzare question.

Thankyou. Weoyreb321 07:20, 11 May 2007 (UTC)

Assuming they were just cut, and there was no damage to the follicles, your eyebrows should grow back good as new same as before eventually. Just remember, not all follicles are growing at any given time, so it will be slightly thinner until all come back. Czmtzc 13:53, 11 May 2007 (UTC)

Note also that it's a myth that shaving causes hair to grow back coarser or thicker than it was previously. It can just seem like it since short hairs are stubby and stiff. --TotoBaggins 14:04, 11 May 2007 (UTC)

And after a while (when it returns to its normal equillibrium of hairs "wearing out" and falling out and growing back) it won't stay stubby like that. 209.53.181.69 22:59, 11 May 2007 (UTC)

Vaporisation of Sweat

I was asked an interesting question in a heating and cooling test, and I'd like to be able to either justify my answer or understand why it was wrong by the time I talk to my teacher next. If a person's body gains 300J of heat every second while running a marathon, how much sweat must be produced in order for the body to remain at a constant temperature, ignoring heat loss by means other than perspiration? The question also gives a value for the latent heat of vaporisation of sweat, although I forgot what it was. I assumed that the average body temperature is 310K (although it is probably closer to 309.6K) and that the specific heat capacity of sweat is very close to that of water. Given this, should my formula for the amount of sweat needed to absorb 300J of heat contain the energy required for the water to heat from 310K to 373K, or should it just contain the energy required to vaporise the unkown mass of sweat? Or is there something else I'm forgetting entirely? Any help in understanding this question would be appreciated :) Vvitor 08:22, 11 May 2007 (UTC)

You know how when you're running a marathon, you don't writhe in agony? That's because the sweat on your body does not get heated to 373K before it evaporates. I would guess you're expected to assume that sweat evaporates at body temperature (don't know how true this is, but it's probably pretty close). So you're presumably meant to only count the latent heat of evaporation of sweat, which is probably close to that of water, giving about 0.13g of sweat a second. However, none of this matters much, since the energy required to evaporate is so much greater than that required to heat (about 260J to heat 1g by 63K). Algebraist 11:11, 11 May 2007 (UTC)

Bah! I feel like such an idiot! That makes sense, many thanks. If you have the time, though, could you please tell me if the question was correct in listing the "specific heat of vaporisation of sweat" and if a similar formula to boiling (mass x latent heat) would be used? This concept of a latent heat of evaporation is new to me. Thanks again! Vvitor 11:37, 11 May 2007 (UTC)

According to Standard enthalpy change of vaporization (latent heat is out of fashion, it seems), the energy involved depends on temperature but the dependence is so small it's generally ignored. Thus using the standard value and the standard formula seems good enough. Algebraist 15:01, 11 May 2007 (UTC)

Well, there goes my two marks :P. Thank you once again! Vvitor 02:30, 12 May 2007 (UTC)

I would bet that ignoring other means of cooling is quite a big error. I am not sweating a lot when I sit here, but it's not like I stop eating unless I do sports. My guess is direct heat exchange from skin to air and breathing make up a good portion of the heat exchange. Yes, that wasn't the question. —The preceding unsigned comment was added by 84.187.19.133 (talk) 22:05, 12 May 2007 (UTC).

Intelligent Dinosaurs

Human beings have been around for thousands of years and we evolved to intelligent beings. Dinosaurs had been around for millions of years. Is it possible (or any evidence) that an intelligent race evolved from the dinosaurs? If so, do you think that they probably left the planet? --Juliet 13:01, 11 May 2007 (UTC)

Well, scorpions and dragonflies have been around for a longer time yet, and still they never built a decent spacecraft ;) . Seriously, being around for a longer time impoves neither intelligence nor dexterity of a species, generally speaking. As for having left the Earth - I wouldn't subscribe to that point of view, unless presented with a very, very compelling piece of evidence. Cheers, Dr_Dima.

If our current thinking is correct, it's likely that modern birds are evolved from dinosaurs. African Grey Parrots haven't left the planet yet, but once they acquire a complete, developed system of language from humans, I'd watch out...

Atlant 13:28, 11 May 2007 (UTC)

I read about intelligent dinos somewhere but I don't remember where. Does anyone have a link to it? --Juliet 13:28, 11 May 2007 (UTC)

I recall a series of science fiction books (sorry but I don't know titles or author) which imagined a world in which dinosaurs survived and developed intelligence and existed in competition with humans.

Bloodcancerguy 09:56, 14 May 2007 (UTC)

Evolution isn't teleological — it doesn't necessarily lead towards big brains at all, in fact most species do not require them and never even began to evolve them (think about how successful insects are even though they are pretty dumb). Dinosaurs evolved into thousands if not millions of species, all working within their evolutinary niches. They evolved flight, they evolved great size and small size, they evolved all manners of spikes and armor and the like. They, nor too many other species, evolved much intelligence. Most of them never bothered to evolve much of a forebrain, a necessary prerequisite. So there's no reason to think an intelligent race would have evolved from dinosaurs. Additionally any intelligent race with the abiilty for space travel would have left behind ample signs of this ability, if not in intelligently built structures, then likely in the record of their resource consumption (we'd find empty oil wells, evidence of ancient uranium mines, etc.). So no. --24.147.86.187 13:32, 11 May 2007 (UTC)

Evolution ... doesn't necessarily lead towards big brains at all. Indeed, our big brains will likely cause us to be selected against as a species. Does anyone really think humanity will fail to kill itself for as long as the scorpions and dragonflies have been around? So long as we don't do it by something like creating a laboratory black hole that doesn't immediately evaporate, I think big brains will just be an interesting evolutionary dead-end, not nearly as successful as a great set of wings or a really rad stinger. --TotoBaggins 14:17, 11 May 2007 (UTC)

I am sure we will not create a laboratory black hole, that's just something that gets in the press to try and make science more exciting. Also intelligence is selected against in terms of big brains taking lots of energy to run, but in certain circumstances can be worth the extra effort. However evolution is about filling niches, to go with the brains you'd also need the dexterity to use tools, the ability to make a range of sounds to form a complex language, all things probably necessary for intelligence to thrive. And why is space travel the definition of intelligence?Cyta 07:24, 14 May 2007 (UTC)

Even so, 24, wouldn't all of that evidence rotted or decayed away? Also, I thought that Velociraptors and other types of raptors were intelligent? Isn't possible that they could have evolved into something greater?

Sure, and maybe they still will, if the aforementioned grey parrots ever get their act together, but there is no evidence that dinosaurs lived in cities or had nuclear reactors or aircraft carriers or even manhole covers. All of these things would be preserved at least as well as simple bones. FWIW, here's a paleontologist's *very* speculative view of what an intelligent saurian might look like: Troodon#The "Dinosauroid" --TotoBaggins 14:31, 11 May 2007 (UTC)

I think you're right that the most intelligent dinosaurs were Deinonychus and its relatives (judging from brain and body masses).

An interesting thought experiment: What would a fossilized car look like? The steel would oxidize, but the glass would probably only lose its organic components (AFAIK car windows are made of layers of glass and some synthetic material between them). Would the platinum catalyst survive?

I think from an intelligent species with an industrial civilization one would expect to find at least some durable metal alloys.

A thought about intelligence: Intelligence is hard to define. If you come up with a rigorous definition of intelligence - or if you say that IQ tests measure intelligence - most people will probably disagree and say that your definition does not include all aspects of intelligence. So to a certain degree we don't even know what we are talking about. What would constitute a "superhuman" intelligence?

That Dinosauroid looks like an alien that everyone describes as one should look like. Perhaps all aliens that are visiting/probing humans are Dinosauroids! --Juliet 14:36, 11 May 2007 (UTC)

Even if the dinos had an incredibly advanced civilization, more advanced than our own, all evidence would have been wiped out millions of years ago when Xenu dropped H-bombs all over the earth. Don't you guys pay any attention to L. Ron Hubbard? Someguy1221 16:04, 11 May 2007 (UTC)

There's an interesting New Scientist article, Imagine Earth Without People, which discusses how long it would take for all traces of a post-industrial civilisation to disappear; there's some quite interesting prospects: core samples from the ocean would show layers of heavy metal pollution and higher-than-normal levels of long-lasting radioactive isotopes, there would large concentrations of glass and decaying organic matter concentrated around old landfills, and there most likely would be a strange order to the fossils, indicating organised burial. None of these have be identified so far in prehistoric animals (for example, dinosaur fossils appear to be completely random and no-one has ever found any signs of dinosaur-caused pollution, although there is that mysterious iridium layer...). I particularly like the idea of herds of feral poodles roaming the plains, but sadly this particular theory is debunked. Laïka 22:05, 11 May 2007 (UTC)

Proof: [2] Capuchin 22:41, 11 May 2007 (UTC)

The most intelligent dinosaurs were, probably, dromaeosaurids, Compsognathus, Coelophysis and other quick and small theropods with large brains and eyes. In any case, they lacked our extremely sophisticated hands, brain-to-size ratio and, obviously, it's so improbable it's impossible they developed any kind of technology. --Taraborn 12:08, 13 May 2007 (UTC)

But they didn't need to go into space, or build cities, they already had everything they wanted. (unsigned comment)

Had there been technological dinos, I would expect that we would find obvious evidence in the form of mine tailings, and likely also there would be very little coal or oil left in the present day. --BenBurch 20:25, 13 May 2007 (UTC)

Kidney donor?

Is it legal in Canada or other countries for a person to sell their kidney to somebody who needs it? Kidney_transplantation didn't have much.--Sonjaaa 13:39, 11 May 2007 (UTC)

In the UK the Human Tissue Act (and specifically this section) makes it an offence to "[offer] to supply any controlled material for reward", as this man just found out. — Matt Eason ^{(Talk • Contribs)} 14:31, 11 May 2007 (UTC)

It's not legal in the US either, although there are some doctors who want it to be in order to prevent a black market developing. You might find this article in the New York Times interesting. --TotoBaggins 14:33, 11 May 2007 (UTC)

In the US, selling of your (or anyone else's) organs is illegal, as TotoBaggins noted, per the Uniform Anatomical Gift Act. It does appear to be legal in Iran, according to the Transplant#Compensated_donation article (with sources, even). -- MarcoTolo 20:09, 11 May 2007 (UTC)

artificial symbiosis

how can we induce artificial symbiotic relationship between two microorganisms,knowing their genome.can you please tell me the actual sceintific process. —The preceding unsigned comment was added by 220.225.77.230 (talk) 14:39, 11 May 2007 (UTC).

I'm sorry, but what kind of symbiosis are you referring to? There are quite a few different ways for organisms to be in symbiosis. Have you looked at its article by chance? Someguy1221 15:59, 11 May 2007 (UTC)

Well, you could knock out the ability of one microorganism to make an amino acid, say Alanine. In another organism you knock out the ability to make a different amino acid say Lysine. Now neither of the organisms can survive independently with out a source of the protein that it is unable to synthesize itself, but together they could live symbiotically off of each other. --Czmtzc 19:45, 11 May 2007 (UTC)

I will give you a million dollars if you can get two bacterial colonies to sign a trade agreement ;-) Someguy1221 20:49, 11 May 2007 (UTC)

Body acts as a wireless radio antenna

I've got a little shower radio whose coated wire antenna snapped off a while ago. Now when I turn it on the output is mostly noise, but when I put my hand within about four inches of it the signal becomes crystal-clear - I don't even have to be touching the metal where the antenna snapped. Why? — Matt Eason ^{(Talk • Contribs)} 14:59, 11 May 2007 (UTC)

I guess (emphasis on "guess") that your hand and some conducting parts inside the radio form a capacitor which allows the high-frequency current to flow without you touching the radio. Then your body works as an antenna. Cheers, Dr_Dima.

Your body definitely interacts with and somewhat channels EM radiation. I don't know if there's a very simple mechanism for explaining what you observed, though. -- mattb 15:59, 11 May 2007 (UTC)

You're probably affecting the ground plane the antenna uses. Single wire antenna's (like car antenna's) use the earths or the hood as a ground plane. This essentially acts a mirror and for analysis purposes turns the antenna into a diploe. By putting your hand that close, you move the plane for the stub of antenna that was left when the wire broke off. This can affect gain and directionality of the antenna and improve ir diminish the reception depending on a number of factors that would probably be not worth modeling. Our article on this, Image antenna is somewhat lacking. --Tbeatty 03:45, 12 May 2007 (UTC)

Compact fluorescent lamps

According to compact fluorescent lamp, the length of their life is dependent upon, among other factors, "frequency of cycling on and off". I am trying to find out just how significant this is. I know it is significant in old style fluorescent tubes that use a starter. Does this mean I should leave, say, a CFL in a hallway on for most of the evening to maximize its life? Obviously I don't want to leave it on for too long, otherwise I don't save any energy.--Shantavira 15:23, 11 May 2007 (UTC)

No, you shouldn't leave it on. here is the best source I can find on this. --Allen 15:58, 11 May 2007 (UTC)

"...so if you turn your fluorescent lamp off and on more frequently than every 5 seconds, you will use more power than normal." Very interesting. A myth exploded. Thank you.--Shantavira 18:06, 11 May 2007 (UTC)

Gaslighting

What is the evolutionary purpose behind gaslighting? I just got gaslighted at work (very successfully, btw), and after reading the article, I recall several times I have gaslighted friends or have been the victum of gaslighting, in particuar I've always felt a *strong* compelling desire to gaslight people. Is there some reason we seek to test/improve our ablity to manipulate others, or is it perhaps a way of putting someone in a position of uncertanity? XM 15:42, 11 May 2007 (UTC)

I would differentiate between cases where the perpetrator admits to the deception ("I was just playing with you"), which seems to be a type of joke, versus cases where no admission ever comes, which seems to be more a type of abuse aimed at increasing the perps power relative to the victim, by making the victim unsure of himself/herself. StuRat 18:36, 11 May 2007 (UTC)

I'm not sure there is a "evolutionary purpose" to this sort of very high-level psychological behavior (that is, I doubt it is selected for or against with any specificity, and I'd be dubious that there is any genetic specificity for it). As for why people would want to do it, it is probably just the old, basic desire for power over others. We like to feel powerful, and quite often at the expense of others. --24.147.86.187 00:12, 12 May 2007 (UTC)

Eggplant IQ

I heard a rumor that the eggplant has an IQ of 3, and since I am a vegetarian that really freaks me out. What is the real IQ of an eggplant? —The preceding unsigned comment was added by 66.92.72.238 (talk) 18:22, 11 May 2007 (UTC).

Eggplants do not have IQs - as they would not be able to take an IQ test to obtain a score. --Ali 18:27, 11 May 2007 (UTC)

Yes, it is most likely just a rumor. Once I asked from a professor studying the human brain what the meaning of the IQ associated to plants, animals, computers is (as found on some nice graphics in some newspapers). He replied that it is all nonsense. The IQ is calculated specifically based on the average human intelligence, so not only is it impossible to calculate on, for example, animals; it gets very inaccurate in the case of outstandingly intelligent/unintelligent people. --V. Szabolcs 18:41, 11 May 2007 (UTC)

I suppose it means that plants are, actually alive and actually do have some small bit of intelligence. Vegetarians seem to treat them as almost, unalive. They seem to treat eating live plants as different from dead animals, yet eating animals is barbaric and plants is intelligent. [Mac Δαvιs] ❖ 18:51, 11 May 2007 (UTC)

You know you have to kill the animal, right? They don't come dead. --User:bmk

they do now, unless you are a farmer/butcher.

I take it that was sarcasm. Plants do some things, like repositioning themselves in the sunlight, that, in animals, is often accomplished by intelligence (a cat finding a sunny patch to warm up, fur example). However, in plants, this type of thing is accomplished by different mechanism. StuRat 19:57, 11 May 2007 (UTC)

Plant behaviour follows similar basic mechanisms to animals with respect to interacting with the environment, sense, signal, respond. These mechanisms do not require intelligence although intelligence might improve the response. David D. (Talk) 20:16, 11 May 2007 (UTC)

In any case, an eggplant is certainly less "intelligent" than a gnat, and I am sure few of us weep after swatting. At some point everyone has to draw the line between the animals they care about and the ones they don't. Vegetarians often set that bar a bit lower than others (saying that fish, cattle, pigs, and fowl count as "non-expendable" whereas omnivore humans generally think they are) but at some point there's a bar nonetheless. Lowering that bar to the level of plants would be somewhat insane, in my opinion. --24.147.86.187 00:16, 12 May 2007 (UTC)

See breatharianism for the limit. Rmhermen 02:53, 12 May 2007 (UTC)

You may find Plant perception (physiology) interesting. Personally, I think that just because we can't understand plants' equivalent of a CNS, doesn't mean that they don't have one. Aaadddaaammm 03:28, 13 May 2007 (UTC)

Yes, plants have positive IQ and therefore are intelligent. Rocks too, that's where the comparison between an idiot and a rock's intelligence comes from. So never eat plants nor rocks, because they have intelligence. My God. --Taraborn 19:41, 14 May 2007 (UTC)

Soap Bubbles

Can anybody tell me the effect of water temperature on soap bubble forming? As surface tension is a function of temperature and the higher the temperature the lower the surface tension. So, are the soap bubbles less stablized in hot water as the surface tension is lower? —The preceding unsigned comment was added by Lucia12321 (talk • contribs) 18:35, 11 May 2007 (UTC).

Another factor is that soap bubbles tend to evaporate and pop rapidly in dry air, and temperature affects humidity. I'm not sure what the net effect is, however. StuRat 18:40, 11 May 2007 (UTC)

Astronomy : Black dwarf stars

It seems from information already in Wikipedia that white dwarfs take an exceptionally long time to cool into hypothetical black dwarfs. They cool more slowly as time progresses, and the coolest known white dwarfs are about 3900 K. It also seems that not enough time has passed for any stars in the universe to have cooled enough to become black dwarfs. Therefore my question is: Exactly how many Gyr will it take for a white dwarf currently at 3900 K to reach thermal equilibrium with the space in which it sits (presumably single digits of K), and become a black dwarf? I know this can vary with the mass and elemental content, so if necessary just assume common values.

This is not homework, just personal curiosity. 70.171.11.122 21:32, 11 May 2007 (UTC)

According to NASA it takes tens to hundreds of billions of years. Someguy1221 21:40, 11 May 2007 (UTC)

I believe there was a mistaken assumption in your question, however, that temps must fall to below 10°K for it to stop emitting light. I believe dwarf stars will stop emitting significant amounts of light at much higher temps than that. StuRat 21:49, 11 May 2007 (UTC)

I would probably say a few hundred K, I mean, the stuff around you is only glowing significantly in the infra-red. You have to heat a metal bar significantly above room temperature for it to start emitting enough light for it to be visible. Stars will be similar. Richard B 23:04, 11 May 2007 (UTC)

I wonder if it might be different though for something a million times the density of water. Someguy1221 23:53, 11 May 2007 (UTC)

Not really; see blackbody radiation. When you're not talking about special things like synchrotron radiation or LED light, but just "glowing" from disorganized matter, you and a white dwarf and a charcoal briquette are about the same. Even black holes can be assigned a temperature, although that has not been experimentally verified. --Tardis 01:16, 12 May 2007 (UTC)

Oh, dear. our black dwarf article uses the term "significant radiation'.Significant is a qualitatitave term that is subject to arbitary interpretation. Pick a definition (in degrees K) for significant, and we can then calculate a time in the future at which the black dwarf will be indetectable. -Arch dude 01:53, 12 May 2007 (UTC)

Hi, I tried to be specific in my original question, but it seems that people are confused over when a star becomes a black dwarf. That's why I originally asked how long it will take for a cooling white dwarf to reach thermal equilibirum with the interstellar medium, which is very specific. It seems at this point nobody has an exact answer, the "tens to hundreds" of billions of years is what I found myself, I wanted something more specific than that. 128.227.68.119 13:04, 15 May 2007 (UTC)

Shouldn't it take infinite time to reach thermal equilibrium, being an asymptotic process and all? Especially since the background is a moving target, what with the continuing cosmological redshift of the photons in it... --Tardis 20:09, 15 May 2007 (UTC)

Homogeneous and Heterogeneous

I have 9 items that deals with which one is which is homogeneous or heterogeneous.

• a)freshed-squeezed orange juice
• b)white vinegar
• c)red wine
• d)an antique bronze dagger
• e)a stainless steel knife
• f)an old lead water pipe
• g)humid air
• h)a cloud
• i)a dirty puddle

By the way, it's not homework.

"Deals with" what? Your question is not entirely clear. However, our articles on Homogeneity and Heterogeneous may help. Rockpocket 23:53, 11 May 2007 (UTC)

"Homogeneous" is one of those words I love so much for its multitude of meanings... Even within single disciplines folks can't settle on just one meaning (like its multiple meanings just in the context of differential equations). Anyway, back to your question... You're going to have to define what you mean by homogeneity more explicitly for your question to be answerable, and if you do this you will have answered your own question. -- mattb 00:17, 12 May 2007 (UTC)

Don't forget Phase (matter). TenOfAllTrades(talk) 00:28, 12 May 2007 (UTC)

What fun. I can construct a total of 18 defensible arguments, one for each substance that it is homogeneous, and one for each substance that it is heterogeneous. in each case, it's a matter of scale. -Arch dude 01:38, 12 May 2007 (UTC)

This is one place to start learning: Mixture deals with the chemistry definition for homogeneity and heterogeneity. Nimur 19:29, 12 May 2007 (UTC)

I think Arch dude is correct; this will depend on how homogeneous you set your threshold at. The best formal definition that I can think is that you determine homogeneity for a particular property (such as density); then take several random samples of finite size; then measure the absolute variance of that quantitative measurement. If the mixture is homogeneous then the variance must be less than some pre-decided threshold. Nimur 19:45, 12 May 2007 (UTC)

solutions and not solutions

Hi there, I have 9 items that deals with which one is solutions and which are not solutions.

• a)milk
• b)apple juice
• c)the gas in a helium-filled balloon
• d)pop
• e)pure water
• f)smoked-filled air
• g)silt-filled water
• h)rainwater
• i)14K gold in jewellery

—The preceding unsigned comment was added by 76.64.137.23 (talk) 23:49, 11 May 2007 (UTC).

See solution and then determine which fits (i.e. it has to be one material with another fully dissolved in it). Rockpocket 23:53, 11 May 2007 (UTC)

It doesn't have to be dissolved in a liquid. It usually refers to something dissolved in liquid, but it truly anything dissolved in anything. Someguy1221 23:57, 11 May 2007 (UTC)

This one is a bit easier. Just find a formal definition of solution and guage each item against the definition. -Arch dude 01:43, 12 May 2007 (UTC)

remember there is also a difference between compounds and solutions.