Message-Id: <v01540b00b0584e425f61@[192.174.2.173]>
Date: Wed, 1 Oct 1997 11:29:02 -0800
To: pinhole@exploratorium.edu
From: pauld@exploratorium.edu (Paul Doherty)
Subject: Re: Matter at absolute zero
Hi Rich and Pinholers
There are some good and important physics ideas in the answers I have seen
already.
When scientists tested ideal gasses over a century ago, they found that the
volume of the ideal gas decreased when the temperature decreased. When they
extrapolated the linear decrease in volume versus temperature they found
that the volume extrapolated to 0 at -273 degrees Celcius. (By the way
scientists don't use Centigrade any more.)
((Don't worry about the volume going to zero, as the temperature decreases
the ideal gas liquifies and the volume of the liquid does not extrapolate
to zero.))
If you define a new temperature scale with its zero at this temperature,
-273 C, then the relationship between volume and temperature becomes a
direct proportion.This is why we use absolute, i.e. Kelvin, temperatures in
the ideal gas equation.
The 19'th century idea of temperature is that, for an ideal gas,
temperature is proportional to the
"Average random kinetic energy of translational motion per molecule (or atom)"
The definition of temperature does not apply to the motion of electrons
inside the atoms.
So by this definition, at absolute zero the kinetic energy of translational
motion is zero. However, in this century, quantum mechanics predicted that
as long as you knew where an object is (in a box) you could not exactly
know its speed. (Heisenberg uncertainty principle) This meant that no
object could have zero speed relative to the walls of any container because
if you knew its speed were exactly zero then you could not know where it
was. Even at absolute zero particles still have a minimum amount of motion
called zero point motion.
For Helium atoms at atmospheric pressure zero point motion is enough to
keep the helium a liquid.
ETC.
Notice that by this definition of temperature, the temperature of one atom
is not defined. For two atoms only the component of motion relative to the
center of mass counts for temperature (The "average random" part of the
definition.)