Re: pinhole temperature of a vacuum

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From: Paul Doherty (pauld@exploratorium.edu)
Date: Wed Sep 20 2000 - 16:21:15 PDT 

Message-Id: <l0311071fb5eef51a6ed2@[192.174.2.173]>
Date: Wed, 20 Sep 2000 15:21:15 -0800
From: Paul Doherty <pauld@exploratorium.edu>
Subject: Re: pinhole temperature of a vacuum

Hi Marc

Temperature is not defined for 1 molecule or for 1 photon, so it is
certainly not defined for no particles i.e. a vacuum.

In the classical definition of temperature for an ideal gas, it is
the average, random, kinetic energy of translational motion per molecule.

the "average random" part means that you take a group of molecules, find
their center of mass motion, exclude that, then take the average energy of
translational motion relative to the center of mass. A single particle has
no translational motion relative to its center of mass so therefor
temperature is undefined.

According to this classical definition negative temperature has no meaning.

However there is a more modern definition of temperature in which negative
temperatures have meaning.

More on this later.

Paul D.

Paul "But it is more complicated than that!" Doherty,
Senior Staff Scientist, The Exploratorium.
pauld@exploratorium.edu, www.exo.net/~pauld

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