A Conversation for Absolute Zero
Werner, I am the great Liar Posted Jul 21, 2007
i'm just a lay man so sorry if this is out of order, but
0K was invented by someone projecting graphs,
next will come someone who can work out this curve at the bottom more acuratley, he'll publish and wallop -500 will become the new zero all the sums will be re written and then we can start all over again.
or is that to simplistic
Agent of kaos
protogen Posted Aug 2, 2007
"Erm... *that* sounds like absolute twaddle to me. Sorry.
Given that 'absolute zero' actually means all the particles are completely stopped, there is definitely an absolute zero and given that scientists have cooled things within a few milliionths of a degree of it, I'd think they're pretty sure where it is.
Either way... isn't the temperature of a substance just the kinetic energy of its particles? In which case, plotting one against the other wouldn't make much sense...
There *has* to be a temperature which is the temperature of something which has zero energy, and that temperature, naturally, is absolute zero. I'm fairly sure about this one...
Consider The above comment for a moment:
Now look at it again but bear in mind Heisenbergs Uncertainty Principle. For those that are not familiar with this, it states (for the layman) that the more accurately you try and measure a particles velocity, the less accurately you can simultaneously measure its position and vice-versa. Therefore, we cannot be "absolutely" accurate in our measure of a particles velocity and thus it's energy. by this definition, "absolute" zero cannot exist. what we get is "approximately" zero. So therefore, if we are saying that the measure of Absolute Zero is the point at which a particle has no activity, then we cannot have a truely linear plot on a graph. Precisely as Heisenberg predicts. We can get close to linear but it is more reasonable to expect that you would never actually cross the zero point on the axis.
It is reasonable to expect chemists to use the linear plot as it will come very close to observed results and would be a reasonable approximation.
Right, thats my two-penneth worth!
reductio_ad_absurdum Posted Aug 3, 2007
Why you're wrong.
1. It is correct that due to the uncertainty principle that the product of the uncertainty in a particles momentum and its position must always be greater than Planck's constant (incidentally a truly minute quantity). The thermal energy of a particle is essentially due to its kinetic energy according to classical theory. Absolute zero is the point at which the particle would, according to this theory, be stationery. Yes, due to quantum theory we now know the particle would still be 'moving' (though movement is a somewhat notional term in quantum mechanics since the particle does not really move through space but is simultaneously in both places at once etc.) However this energy could not be extracted and thus the particle is considered to be a '0' energy (alright excepting the Casimir effect). Another point to be made is that energy really only makes sense in terms of differences (a body at an infinite distance from another is said to have 0 gravitational potential energy but this is really only a convention).
2. Assume you're correct. Say that at 0 K, a minute amount of energy is stedily removed from a particle to lower it's temperature by, say,
1000000 K per second. What precisely would be the observational difference as the particle cools that would allow us to justify this colossal rate of temperature drop? I'm sure you're not claiming that the particle would start to emit radiation at an increasingly intense rate with a tiny negative wavelength (sort of an anti-gamma ray). Or behave in the many other bizarre ways we would expect of a negative temperature particle (e.g. to take in energy from the 'warmer' empty space'). What I'm saying is, if as the 'energy' of the particle asymptotes to 0 as temperature continues on to -infinity, what quantity, other than temperature would also approach -infinity? If none, then how would we know that temperature was really still going down at such a phenomenal rate, despite apparently tiny differences in energy and behaviour? By Occam's razor surely it's simpler just to have temperature also approaching 0 as kinetic/thermal energy does.
3. Why would people keep banging on about approaching absolute zero to within mili- or micro- kelvin? What would be 'special' about this temperature if there were temperatures below it? Surely the record lowest temperature would be something like -1218.38 K or something, or possibly +12.439 K? It seems a remarkable that with an infintie -ve scale to reach, our scientists seem to just approach 0. I am aware that this third argument does not prove that -ve K is unattainable but it does provide strong evidence.
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