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Re: [Phys-l] Negative kelvin temperatures

On 02/06/2007 04:34 PM, Dan Crowe wrote:
My
first reaction is that a system with population inversion is not in
thermal equilibrium, so it doesn't make sense to determine the
temperature of a system based on population inversion. I'm not even
sure that the system has a well defined temperature.

A two-state system can /always/ be described in terms of
a temperature. For three or more states, things get
much more complicated.

For a system with three or more states, it is certainly possible
for the system to have no well-defined temperature. Indeed
this is common.

However it is also possible for a system to have a
well-defined negative temperature. Pictures of the
probability-versus-energy distribution can be found
here:
http://www.av8n.com/physics/neg-temp.htm

... along with a lot more discussion.