

Absolute zero and Absolute Infinity.
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
negativetemperature 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 zeropoint 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 finitelevel 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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Update: June 2012

