the ultimate refrigerator

John K Clark (
Sun, 14 Dec 1997 21:19:04 -0800 (PST)


On Sun, 14 Dec 1997 Wei Dai <> Wrote:

>Black holes emit Hawking radiation at a temperature of
>T=h*c^3/(16*pi*G*M). With the mass of the sun, the temperature of a
>black hole would be about 10^-8 K.

I think Laser cooling would be much more practical, temperatures about that
low have already been reached with it, it's how a Bose Einstein condensate
was made a few years ago. It's not easy and has only been done over a small
area, but with Quantum Dot Lasers in the wings that will certainly improve.

The idea is to tune a Laser beam to a frequency slightly below the quantum
absorption frequency of an atom, if the atom is motionless or moving away
from the Laser it will not be able to absorb a photon from the Laser, but if
the atom is moving toward the Laser the frequency of the photon that the atom
sees will be shifted slightly higher due to the Doppler effect. The photon is
now right at the quantum absorption frequency, the atom will swallow it whole
including the momentum of the photon, this will slow the atom down.

Yes, now that the atom is excited and no longer in its ground state
eventually the atom will re emit the photon, but the direction is random,
it's just as likely to cool the atom further as heat it, so this has no net
effect on the cooling process. If you have 6 such Laser beams one for,
forward, backward, right, left, up, down, you can cool things to very close
to absolute zero.

John K Clark

Version: 2.6.i