Re: "How cold is it?" -- very funny junk mail (fwd)

I made the mistake of forwarding the original post to the SM of one of my
units. I'm not sure I know more now than when I sent it to him. :-)

But, he works well with the scouts, and that is what counts.

Paul H. Brown, UC, GW District, National Capital Area Council, BSA
phbrown@capaccess.org

> > -460 / -273 (Absolute Zero)
> > * All atomic motion ceases
> > * Wisconsinites allow as to how it's getting a mite nippy

Seeing that I am a low temperature physicist, I must correct the notion that
atomic motion stops at absolute zero. The vibrational motion of atoms or
molecules in a solid is quantized which means that there are only certain
vibrational energies which are available. As the temperature drops, the
vibrational energy falls down the latter of allowed energy states and at 0
Kelvin (absolute zero) the vibrational energy is at the ground state or lowest
allowed energy state. For vibrational motion this ground state has a non-zero
energy which means that there is still vibrational motion in all solids at
absolute zero.

The more correct way of describing absolute zero is that you obtain a state of
perfect order not zero motion. Although the atoms and/or molecules are moving
at absolute zero, the motion is perfectly coordinated; that is, there is no
randomness in the motion.

The best example is liquid Helium 4 (two protons two neutrons). He4 liquifies
at 4.2 K under atmospheric pressure. Through various methods, you can cool He4
down to very low temperatures, but He4 will never soldify. It is a liquid to
absolute zero. Here, the atoms aren't even in specific lattice positions as in
a solid but are free to move throughout the liquid. What does happen is that at
2.2 Kelvin He4 goes through a transition to a new liquid state called a
superfluid where the atoms start to move in a coordinated fashion but not at
fixed lattice sites. At 2.2 Kelvin, just a handful of atoms are moving in this
way. At absolute zero, all movement of atoms in the sample of He4 is
coordinated. Because of this coordinated motion in the liquid, superfluid He4
has absolutly zero viscosity and perfect thermal conductivity. A superfluid is
perfectly analogous to a superconductor where a superconductor as perfect
electron flow and a superfluid has perfect mass flow.

Helium 3 (two protons one neutron) behaves totally differently which is a story
for a different time.

At the risk of boring you, there is another explanation why motion can never
cease at absolute zero. From quantum mechanics you can derive (not easily of
course) what's called Heisenberg's Uncertainty Principal which states that the
uncertainty in a particle's position times its uncertainty in momentum must be
greater than or equal to Planck's Constant. Planck's Constant is very small
(6.626 x 10^-27 Joule second, but is, nevertheless, finite which implies that
the uncertainty in position can never be zero (perfect rest).

Sorry for the long explanation, but the physics of matter near absolute zero is
not usually understood very well by the general public. I have always found
this stuff very interesting which is why I do what I do.

Bye.

Brian

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