Wikipedia:Reference desk/Archives/Science/2011 May 9

= May 9 =

R constant
what is the difference between the R in chemistry and R in the physics where in chemistry its value is 8.023 and in physics its value is 2? —Preceding unsigned comment added by Awadheshian (talk • contribs) 10:31, 9 May 2011 (UTC)


 * How is R used in physics, R commonly represents Rydberg's constant. Plasmic Physics (talk) 11:04, 9 May 2011 (UTC)
 * First off, units are important! Unless you are talking about a dimensionless constant, you must give units so people know what your numbers mean, or grave consequences may result. I presume that the Chemistry term you are looking for is the gas constant for an ideal gas, although your number does not quite correspond to any of the values at that page. In physics, there is no commonly used physics constant for which a capital "R" is used (the above-mentioned Rydberg constant is used in spectroscopy and quantum mechanics, and its value is not even close to "2" in any system of measurement), but "R" is commonly used to denote the radius of an object in a given problem.- Running On Brains (talk) 11:41, 9 May 2011 (UTC)
 * The R in physics is likely the ideal gas constant $$R=1.98 cal/ mol K$$, and the R in chemistry might also be the ideal gas constant $$R=8.314 J/ mol  K$$. Dauto (talk) 13:37, 9 May 2011 (UTC)


 * It's the same R all around. R is basically the Boltzmann constant extrapolated for a mole of particles, rather than a single particle.  That is, it expresses the energy content of a mole of particles represented by a degree of temperature, depending on what your units are.  You could easily express R in units of ergs per Rankine per mole if you wanted.  The three most common sets of units for R are:
 * 8.314 J/mol•K (or .008314 kJ/mol•K)
 * 1.98 cal/mol•K (or .00198 kcal/mol•K)
 * .0821 L•atm/mol•K
 * The last one is a bit weird, since it uses a highly "non-standard" energy unit, that being the "liter atmosphere" (L•atm), however that form is highly convenient when working with the Ideal gas law, and some basic dimensional analysis will prove that the L•atm is, in fact, a unit of energy (sorta like some of the other weird energy units like the electron volt). The article gas constant lists a whole mess of possible expressions of R, based on a whole range of energy and temperature units.  The use of different values is based on the choice of units to solve the particular problem, which is mainly based on the application of R and the conventions of that application.  -- Jayron  32  14:26, 9 May 2011 (UTC)
 * The R of 8.023, is that used at the "standard temp" of 25 instead of 15 degrees celcius?. Polypipe Wrangler (talk) 20:05, 13 May 2011 (UTC)

Immunology: Neutralization technique
I'm doing some studying for an exam and I'm a bit confused about the purpose of the "nuetralization technique". My understanding is that this technique is used in an effort to figure out which antibodies are present in a sick patient's serum, thus identifying the disease-causing antigen. According to my lecture notes, a test animal is injected with a known antigen (the one potentialy making the patient sick) and antibodies from the patient; if the animal turns out fine, the test indicates that the patient is harboring the antigen in question due to the nuetralizing effect of their antibodies. If the animal ends up sick, the test indicates that the patient is infected with a different antigen. MY QUESTION: The patient is obviously sick, so wouldn't the known antigen make the animal sick regardless if the patient had antibodies against it? Thanks.161.165.196.84 (talk) 11:14, 9 May 2011 (UTC)
 * I know very little about immunology and that sounds strange to me from the start, I would not have guessed that human antigens or antibodies necessarily had the same effect on other animals. Ignoring that however, I have one idea: if you get sick, you have an antibody response but the problem is that a lot of the time it's "too little too late". However if you can get antibodies in sufficient quantities BEFORE you get sick, it will be enough to fight off the infection; that's how vaccines work right? So maybe they give the animal a big enough dose of the antibodies first then just a small amount of the antigen? Vespine (talk) 00:01, 10 May 2011 (UTC)
 * This is not a familiar term to me (or other modern readers), but is a valid technology:  Now it should be clear that passive immunization can work on an animal patient using a human serum, just as antivenom works on a human patient with an animal serum.  But the reference I found went a bit further and actually mixed the antigen and serum before injection, giving it every possible advantage.  In that paper, the goal was not actually diagnostic but scientific: the idea is, if one strain of a bacterium is used to raise an antiserum, how well does that work on another?  In this way one could start to classify the strains.
 * While I wouldn't be surprised if it's been done, diagnosis using this technique would not be very confident, because individual animals' susceptibilities to the disease will vary. Also, when going between species, you'd need to test a virus that could affect both.
 * The trace of virus in the antiserum-producing animal or human would not be that important, because the experiment was to see how fast animals succumbed to a range of large viral doses after the mixed injection. Wnt (talk) 00:16, 10 May 2011 (UTC)

Colour of plants.
If black colour is the best for absorbing light, why aren't all photosynthesising plants black instead of green. Seems like an easy adaptation to evolve. Or am I missing something? 110.174.117.185 (talk) 13:17, 9 May 2011 (UTC)


 * See Chlorophyll. Basically, evolutionary history places serious constraints on the options for biochemical machinery. SemanticMantis (talk) 13:40, 9 May 2011 (UTC)


 * Many organisms capable of photosynthesis do use a combination of different accessory pigments, which allow light of different colors to be absorbed and converted into energy to drive photosynthesis. Phycobilins, for example, are pigments seen in cyanobacteria and red algae that absorb yellow and green light.


 * There are tradeoffs inherent in expressing multiple pigments, however. Energy that is used to make accessory pigments is energy that can't be used to make chlorophyll a or to grow the plant, and there is a limit to how much protein you can cram into a leaf&mdash;more accessory pigments means less absorption of blue and red light per unit area, or a need for larger, thicker leaves.  From an evolutionary standpoint, accessory pigments can be challenging to create because they have to not just absorb light, but also efficiently transfer that energy to downstream molecules involved in photosynthesis.  In other words, green plant leaves are most likely one of the many examples of evolutionary dead ends reached because they're 'good enough', rather than the 'best'. TenOfAllTrades(talk) 13:43, 9 May 2011 (UTC)


 * So, unless I'm reading this incorrectly, there is no clear cut answer why. Its one of open questions of evolutionary biology? I mean, all of the explanations are plausible but unsupported either by evidence or very clear cut reasoning.


 * Has there been any attempts to genetically engineer plants with black chlorophyll? Is there any estimate on how much efficiency plants lose on by not being black? 110.174.117.185 (talk) 14:03, 9 May 2011 (UTC)


 * I was wondering that also. Ask yourself this, though: Could the world turning black in the spring possibly ever measure up to the world turning green as it does now? ←Baseball Bugs What's up, Doc? carrots→ 14:05, 9 May 2011 (UTC)


 * Yes, if that plant was able to feed more people than it's green cousin. Don't get me wrong, I like aesthetics as much as the next guy, but some things take precedent. 110.174.117.185 (talk) 14:14, 9 May 2011 (UTC)


 * Very poetic, but doesn't really advance the discussion. TenOfAllTrades(talk) 14:18, 9 May 2011 (UTC)


 * If we had evolved in a world of black vegetation, we would probably find black as pleasant as we actually find green. {The poster formerly known as 87.81.230.195} 90.201.110.223 (talk) 14:21, 9 May 2011 (UTC)


 * Aren't there some species of plants that are in fact pretty much black? Or am I thinking strictly of flower petals? ←Baseball Bugs What's up, Doc? carrots→ 15:10, 9 May 2011 (UTC)


 * The kelp used in sushi, such as Kombu, look black to me. Or are they just a very deep shade of green? ←Baseball Bugs What's up, Doc? carrots→ 15:14, 9 May 2011 (UTC)


 * One potentially clear cut reason is the hypothesis that chlorophyll only evolved once. I personally find TOAT's answer above very enlightening, because it points out that more pigments does not necessarily imply more plant productivity. Even if it does happen to be true that 'green plants are less efficient than a hypothetical black plant', this doesn't really say much about the prospects for such a black plant under selective pressure. Lastly, you may be interested in the endosymbiotic theory of chloroplasts, which is currently a well-regarded theory that also explains why chloroplast structure is fairly stable. SemanticMantis (talk) 15:06, 9 May 2011 (UTC)


 * But how can chlorophyll just "stop evolving"? Every living organism is constantly evolving (on grand scale, not any directly observable by humans), or am I wrong? Even if chlorophyll are a symbiont within the cell, an odd mutation of a black chlorophyll should have spread like wildfire. 110.174.117.185 (talk) 16:20, 9 May 2011 (UTC)


 * Maybe there were mutations that occasionally produced black leaves - and maybe they absorbed so much sun that it killed them. Green might be the "optimal" color? ←Baseball Bugs What's up, Doc? carrots→ 17:21, 9 May 2011 (UTC)


 * I didn't mean to imply that new forms of chlorophyll cannot evolve, or that it has somehow 'stopped' evolving. When I say it only evolved once, I mean that we think there was a single origin, as contrasted to e.g. the wing, which has developed independently several times across several lineages. SemanticMantis (talk) 17:35, 9 May 2011 (UTC)


 * First, I don't think a single "black chlorophyll" is possible, since each molecule can only absorb certain frequencies. Thus, black leaves would be the result of many chemicals, each of which absorb at different frequencies/colors.


 * Let's say that when regular green chlorophyll first started to evolve it wasn't anywhere near as optimized as it is now. Thus, it would not have worked particularly well, but still was better than nothing.  Now it works well.  OK, so now say that another light color adsorption chemical appears.  Initially, it will probably work as poorly as chlorophyll did, until optimized by evolution.  However, during the early period, the total productivity of this new photosynthetic chemical combined with the lower volumes of regular chlorophyll would mean reduced plant productivity, overall, and thus be selected against.


 * This does suggest, to me, that if we could combine different "fully optimized" photosynthesis chemicals together in one plant, via genetic engineering, then we may, indeed, get over the evolutionary hurdle and create a more productive plant. StuRat (talk) 18:21, 9 May 2011 (UTC)
 * Funny, i just recently came across this interesting article which deals with precisely this question. Vespine (talk) 23:54, 9 May 2011 (UTC)
 * This is an interesting mystery. Plants could evolve a different chlorophyll, or different accessory pigments; they can express them all at once.  A plant that switches a few molecules over to green from red or blue should absorb more energy for the same biosynthetic price.  And while evolution is often crazy, I don't believe for a minute that it is stupid.
 * I doubt this is true (it's not my expertise), but the only thing I can think of is that maybe the plant needs a complete band of separation between its pigment systems in order to avoid short circuits. I don't actually know the specifics, but I assume that chlorophyll b/photosystem II imparts more energy from blue light than chlorophyll a/photosystem I gets from red light.  So far as I know, energy collected by the most common accessory pigments turns into the lowest-energy red photon level without more energy being extracted.  Maybe if you have a green pigment, there can be a leak of electrons, and/or a Förster resonance energy transfer of excited states from one pigment to the next, and you end up losing blue electrons to green or red channels.
 * Bottom line: good research project for someone! Only when people start trying to make black plants will they know for sure why they don't usually work. Wnt (talk) 00:38, 10 May 2011 (UTC)
 * The kelp that they usually wrap sushi in looks black. Is that its normal color? ←Baseball Bugs What's up, Doc? carrots→ 00:50, 10 May 2011 (UTC)
 * It always looks green to me. A dark green, for sure, but I wouldn't describe it as particularly black.  At the article Nori, the pictures look anywhere from a greenish-brown to a lighter green.  Probably depends on the specific type, but I have never seen black.  -- Jayron  32  04:39, 10 May 2011 (UTC)
 * When alive it is more green, but it likely has more pigments than just chlorophyll. Graeme Bartlett (talk) 04:44, 10 May 2011 (UTC)

black holes sizes
if a very small black hole "evaporates" quickly even when in close proximity to other matter, and a very large black hole either evaporates very slowly or more importantly is able to grow faster than it can evaporate, then what is the size of the black hole that any BHs smaller than that will evaporate in the presence of other matter, and any HBs larger than that will pull the matter in and grow bigger? —Preceding unsigned comment added by 165.212.189.187 (talk) 14:52, 9 May 2011 (UTC)


 * This depends on the density of the ambient matter (and also on the average velocity of the surrounding matter paticles). If you have a black hole in vacuum devoid of matter, then it will absorb the electromagnetic background radiation, the neutrino background radiation, dark matter, and the gravitational background radiation. The density of all these components is well known. The rate at which the black hole absorbs each of these components is:


 * 1/4 n  4 pi R^2 = n  pi R^2


 * Here  is the average velocity of the component (e.g. c for electromagnetic and gravitational waves), and R is the Schwarzschild radius. Then you equate this to the evaporation rate of the black hole. To compute that, you determine the Hawking temperature of the black hole, and then you compute the emission rate of photons and gravitons using the usual Stephan-Boltzmann law. I think equilibrium will be reached at temperatures that are a lot lower than the rest mass of neutrinos, so you don't have to add the emission rate of neutrinos here (note that the formula for this emission rate is not the same as for photons, because neutrinos are described by the Fermi-Dirac distribution). Count Iblis (talk) 15:45, 9 May 2011 (UTC)

OK, but I did not ask about the rate of absorption/attraction I asked about the SIZE. so what is the LARGEST SIZE black hole that (if created using a hypothetical "black hole machine" on the surface of the earth) would NOT absorb the earth and surrounding matter, but instead evaporate "harmlessly"? —Preceding unsigned comment added by 165.212.189.187 (talk) 19:18, 9 May 2011 (UTC)
 * The count didn't tell you what is that size, but he did tell you how to calculate it. Dauto (talk) 22:17, 9 May 2011 (UTC)

So THAT is the evolution of the Wikipaedia reference desk???????? What is the world coming to? Even the kids who ask homework q's get better answers than that. I see the stonewalling afoot. Is the knowledge only for the entitled? That will not get us anywhere. Thanks anyway. —Preceding unsigned comment added by 98.221.254.154 (talk) 03:13, 10 May 2011 (UTC)
 * You're welcome. Dauto (talk) 04:11, 10 May 2011 (UTC)

My mother told me that asking questions is how we learn. Here, asking questions that no one can answer seems to be considered an insult. I used to get in trouble in school for makin frowning and scowling faces at my instructor, when I was the only one paying attention and the face was one of deep concentration trying to comprehend what was being taught. Seem nothing has changed. Do no fear the ambidexterous. —Preceding unsigned comment added by 98.221.254.154 (talk) 04:27, 10 May 2011 (UTC)
 * We like answering questions around here, but I don't like your attitude. You act as if you were entitled to an answer. Dauto (talk) 06:09, 10 May 2011 (UTC)

I'm sorry but I don't intend for my communication to come across any more confrontational than the "go fish" answers I preceive I get. I only mean to act as if there is an answer at all. Like Q:"what is largest mass black hole that will not "harm" the earth?" A: 200 kilograms. done I go away, (for the time being) what is so hard about that. I cannot do those fancy calculations. —Preceding unsigned comment added by 165.212.189.187 (talk) 15:48, 10 May 2011 (UTC)


 * The main problem is that you are refusing to accept that there is no simple answer. The real answer is that it depends on a lot of factors outside the black hole. Even by restricting this to the Earth, the outside factors are continually changing. So, you could get a simple answer that is incorrect and walk away, or you could get a complex answer that is correct and respond that the answer isn't simple enough and demand a simple one. In the end, it is important to understand your question so you can understand the answer. -- k a i n a w &trade; 15:53, 10 May 2011 (UTC)

how electric shock causes death?
how electric shock causes death? —Preceding unsigned comment added by 59.179.150.144 (talk) 16:02, 9 May 2011 (UTC)
 * The first thing that came to mind was Electric chair, and it has some insights. Basically a strong electrical charge can cause the heart to stop. ←Baseball Bugs What's up, Doc? carrots→ 16:10, 9 May 2011 (UTC)


 * One common way, if not the most common way, is by passing through the heart, causing ventricular fibrillation. See Electric shock and Electric shock.  Red Act (talk) 16:13, 9 May 2011 (UTC)


 * Electric shock can cause the heart to stop, effectively causing death by cardiac arrest. But it can also cause death by medical shock, which despite the identical name has nothing to do with electricity; it instead refers to grave injuries which hamper the ability of the body to move blood around efficiently.  Even if the heart is undamaged by the electricity, extensive injuries, such as really bad burns from the electricity, could cause the body to go into medical shock and cause death that way.  -- Jayron  32  16:14, 9 May 2011 (UTC)


 * It seems as if "luck" can be a factor. Lightning strike discusses ways that humans can escape serious injury. I have known people who were hit by lightning in some way or another and lived to tell about it. ←Baseball Bugs What's up, Doc? carrots→ 17:10, 9 May 2011 (UTC)


 * In addition to disrupting the heart, electricity can cause Burns (the heating of tissue) which, if severe enough, can be fatal. Buddy431 (talk) 18:38, 9 May 2011 (UTC)


 * Let's not forget the possibility of intense current passing through the brain stem, which would undoubtedly result in instant death.- Running On Brains (talk) 21:14, 9 May 2011 (UTC)
 * According to the electric chair article, they would typically give the poor schmo two jolts: one to kill the brain, and the second to kill the heart. ←Baseball Bugs What's up, Doc? carrots→ 21:41, 9 May 2011 (UTC)

Pulling animals by the tail
Is it true that a horse cannot lash out, if you pull its tail? Does it hold true with bulls? Quest09 (talk) 16:47, 9 May 2011 (UTC)
 * By "lash out", do you mean like kicking you with its hind feet? ←Baseball Bugs What's up, Doc? carrots→ 17:06, 9 May 2011 (UTC)


 * yes.
 * I googled [pulling a horse's tail] and a number of entries came up. At about 2:15 of this video, the lady combing the tail mentions the risk of being kicked; likewise early in this one, so I've got a hunch that your premise is untrue. And I certainly wouldn't try it with a bull, unless you've got a good life insurance policy to take care of your loved ones after he's done with you. ←Baseball Bugs What's up, Doc? carrots→ 17:18, 9 May 2011 (UTC)


 * But, maybe the horse cannot kick if you pull it with all your forces downwards. Another thing is pulling it horizontally....Quest09 (talk) 17:30, 9 May 2011 (UTC)
 * Think of it another way: If there were any truth to this claim, it would be well-known to all farriers. I've just spent a few minutes searching equestrian and farrier boards, revealing many stories of farriers being kicked, but no mention of kick prevention via tail pulling. SemanticMantis (talk) 18:09, 9 May 2011 (UTC)


 * I remember this as a joke on new farmhands when I was a kid. I was young, but I still found it rather stupid. Try to trick some new guy into getting kicked by a bull (or even a cow). He ends in the hospital. Everyone laughs. -- k a i n a w &trade; 18:11, 9 May 2011 (UTC)
 * HAHAHA! Hospitalising people is hilarious. --129.215.47.59 (talk) 21:23, 9 May 2011 (UTC)
 * Right. I expect even snipe hunts can be dangerous. ←Baseball Bugs What's up, Doc? carrots→ 21:39, 9 May 2011 (UTC)
 * (e/c)This question reminds me of the old wives tale of how if you pour salt (or was it sugar?) on a bird's tail, it cannot fly away. In a way that's true in that a bird that let you get that close and perform that indignity probably is in no shape to fly in any case. Likewise, a horse that let you get directly behind it to pull its tail is probably docile enough not to kick unless greatly provoked. Matt Deres (talk) 18:12, 9 May 2011 (UTC)
 * The Norwegian Blue is especially susceptible to this technique. In the videos, they said something about how to handle an uncooperative horse. A horse that's used to the touch of a particular trainer and to having its tail combed probably wouldn't kick. ←Baseball Bugs What's up, Doc? carrots→ 18:26, 9 May 2011 (UTC)

I can tell you from personal experience that you can get kicked when you pull on a horse's tail. Or a mules (slow learner) 74.162.132.254 (talk) 01:16, 10 May 2011 (UTC)

Do plants die of old age?
Do plants die of old age? —Preceding unsigned comment added by 129.215.47.59 (talk) 21:21, 9 May 2011 (UTC)


 * It depends on the plant. I recommend Bristlecone pine and Clonal colony as starting points for some insight on this question. ←Baseball Bugs What's up, Doc? carrots→ 21:38, 9 May 2011 (UTC)


 * And also Annual plant for some others. {The poster formerly known as 87.81.230.195} 90.201.110.223 (talk) 22:12, 9 May 2011 (UTC)


 * You may also be interested in senescence in general. From the article: "Death is the ultimate consequence of aging, though 'old age' is not a scientifically recognized cause of death because there is always a specific proximal cause". In plants this would be things such as plant pathogens, disturbance_(ecology) or herbivory." As an example of a very old clonal plant, I recommend Pando, who is probably at least 60,000 years old. SemanticMantis (talk) 00:15, 10 May 2011 (UTC)


 * Also, the concept of death isn't well defined in a plant. In cases where the offspring are genetic clones of the parent, do we say the parent died or just changed form (into the offspring) ? StuRat (talk) 01:57, 10 May 2011 (UTC)


 * Can a tree grow itself to death? Plasmic Physics (talk) 03:10, 10 May 2011 (UTC)


 * It can grow too large for it's environment, and die as a result. It could be struck by lightning, for example, if it grows to be the highest tree in the area.  A tree on the side of a mountain could also get too heavy for it's shallow roots to support it, and uproot itself. StuRat (talk) 09:53, 10 May 2011 (UTC)


 * I remember reading something about how a scaleing law has a detrimental effect on the transport system in a tree. Essentially the tree ends up strarving itself because of its size. Is there any truth in this? Plasmic Physics (talk) 01:40, 11 May 2011 (UTC)

Fertilizer
Why is it that human feces can be used as a fertilizer of trees bearing fruit but not of seasonal vegetables or fruits not on a tree? Albacore (talk) 22:03, 9 May 2011 (UTC)
 * Primarilly risk of contamination.  See Night_soil.
 * However, human waste, can be used if properly composted. See Humanure. APL (talk) 22:23, 9 May 2011 (UTC)
 * (EC) One reason is that fruit on trees is generally far enough away from the ground that the feces applied to the ground does not also get applied directly to the fruit either during spreading or by subsequent rain splashes. The desirable nutrients enter the tree and fruit only by being absorbed into the ground, processed by soil bacteria and fungi, and the breakdown products then being taken up by the roots, with perhaps further processing taking place within the roots, etc, before finally contributing to the fruit. Any toxins or harmful bacteria are destroyed or largely filtered out by these processes, though biomagnification of heavy metals might be a concern.
 * On lower fruit-bearers like bushes, there is more likelihood of the feces being inadvertently applied to the growing fruit, or being splashed up by rain, remaining on or entering into the fruit, and remaining a contaminant in sufficient quantity to threaten health, This is even more likely with vegetables that grow directly on or under the soil. That said, treated sewage is used as fertiliser on large ploughed crop fields (the smell is very evident at certain times of the year in my part of the English countryside), but presumably the treatment has taken care of such problems. {The poster formerly known as 87.81.230.195} 90.201.110.223 (talk) 22:36, 9 May 2011 (UTC)


 * I question the premise of your question. Untreated human feces has a strong likelihood of containing pathogens which could cause disease when food is contaminated with it, as well as parasites such as hookworm. If a fruit tree has human feces spread around, some fruit will fall on the ground and be contaminated. If this deadfall fruit is collected and sold and eaten, without high temperature cooking, outbreaks of disease are likely. The germs do not have to jump up into the air and get on the fruit. Pickers who walk across the ground, climb a ladder and pick the fruit, set a basket of fruit on the ground, stack the empty baskets one inside another, can also easily spread the germs to fruit which never fell on the ground. Animals and flies also spread pathogens from the ground to the upper reaches of a fruit tree. Edison (talk) 14:45, 10 May 2011 (UTC)


 * Can those pathogens really survive all that time between fertalising to fruit collection? Surely pathogens whose lifecycle involved a 37 C human cannot endure months in the cold with better-adapted environmental organisms? —Preceding unsigned comment added by 129.215.47.59 (talk) 20:04, 10 May 2011 (UTC)


 * Some pathogens can form spores and survive long periods of inhospitable conditions. Edison (talk) 23:04, 10 May 2011 (UTC)

Charles' Law gives different results for different temperature systems?
Why does Charles' Ideal Gas Law ($$\frac{V_i}{T_i}=\frac{V_f}{T_f}$$ not give the same results no matter whether the Kelvin scale, the Centigrade scale, or the Fahrenheit scale is used? I know that the absolute scale should be used because both Celcius and Fahrenheit can go to zero for real gases which would cause the relation to fail, but even not at 0 they are not the same, but the units for temperature should cancel, shouldn't they? I can show mathematically why this is (by using the conversions between F/C/K), but now I want to why physically this is? THanks. 72.128.95.0 (talk) 23:50, 9 May 2011 (UTC)
 * No, the units of temperature do not cancel because the relationship between kelvin and celsius is additive and not multiplicative. That is, the size of the Kelvin is exactly the same as the size of the degree Celsius, so you can't "cancel" the units through dimensional analysis.  Any non-absolute temperature scale is physically arbitrary, that is scales like Celsius and Fahrenheit are divorced from any connection to physical reality of what temperature is supposed to represent.  Temperature is a measure of the average kinetic energy of the particles of a substance; since negative kinetic energy is a meaningless concept (in order to be negative, that would mean that either the mass is negative or the velocity is an imaginary number, and neither concept has any physical meaning in the classical sense).  So any temperature scale that has negative numbers pretends that kinetic energy could be negative.  It cannot be negative.  Thus, you have to use an absolute temperature scale to make the gas laws work, restricting us in the normal sense to the Kelvin and Rankine scales.  Celsius and Fahrenheit simply don't work.  -- Jayron  32  00:00, 10 May 2011 (UTC)
 * Turns out that most physical equations won't work if you plug Celsius or Fahrenheit units. Dauto (talk) 02:35, 10 May 2011 (UTC)
 * The ONLY time they do is when the equation depends on ΔT, and then the distance between the starting and ending temperature is identical whether you use, say Celsius or Kelvin, because the size of the degrees is the same. But anything which depends on T, rather than ΔT must usually be measured in an absolute scale.  -- Jayron  32  04:35, 10 May 2011 (UTC)