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Name: Vitale
Status: N/a
Age: N/A
Location: N/A
Country: N/A
Date: Around 1993


Question:
I have heard of Absolute zero where all motion ceases. Is there a maximum temperature that objects can attain so that molecules reach a velocity approaching the speed of light?



Replies:
Temperature scales are organized to be proportional to the energy of the matter involved. Since, as particles approach the speed of light, their energy increases without bound, the maximum temperature you are interested in, is in fact infinity. Actually, for an isolated system of spins, it turns out there are some temperatures higher than infinity. Since what is really important there is particle over the temperature, called beta, that means beta values lower than zero, and therefore negative temperatures. I am not sure that anybody has ever succeeded in preparing a system in a negative-temperature state, but it would not last long.

A. Smith


I would like to expand a little. At absolute zero, all motion does not cease, at least not in a finite system. This is a quantum mechanical effect; closed systems have a zero-point motion, and are always in motion. This is easy to understand; if the system were motionless, you would be able to predict all the atomic positions and momenta simultaneously, which violates the Heisenberg Uncertainty Principle. Thus, the "perfect, motionless crystal" in the Nernst postulate (the "third law" of thermodynamics") does not actually exist; it is a mathematical abstraction used as a reference for entropy. Finally, lasers are an example of a system at infinite temperature; you have a population inversion in a finite-level system. The spin system defined by the spins of Li in LiF(s) will undergo population inversion if you just put the crystal in a magnetic field, then suddenly reverse it. So systems with (infinite temperature" are all around! In fact, I think that NMR spectroscopy works by population inversion, which is the basis of MRI imaging in medicine and chemistry.

Robert Topper



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