Re: the ultimate refrigerator

Robin Hanson (hanson@econ.Berkeley.EDU)
Tue, 06 Jan 1998 11:34:12 -0800

>> ... there is no particular advantage to erasing bits at lower
>> temperatures. If it were otherwise you could make a perpetual motion
machine:
>> erase bits (= replace unknown bits with known bits) at low temps and then
>> reverse the operation (replace known bits with unknown bits) at high temps.
>> By the "costs less energy" intution this cycle would create available
energy.
>
>Isn't that exactly what a heat engine does, when you think of it in
>information theoretic terms?

Yes.

>I don't see how you can say there is no advantage to erasing bits at lower
>temperatures, since your free energy is limitied, and at lower
>temperatures the same amount of free energy allows you to erase more bits.
>The trick is to obtain a low temperature without spending energy on active
>cooling, and that's what a black hole allows you to do.

Whatever you could do by erasing bits at low temperature you could do by
erasing bits at high temperature, and using a heat engine to move free
energy from the low temp source to the high temp source. (Free energy is
defined as F = E - TS, and so how much you have depends on the temp.)

>Perhaps what
>you're saying is that it wouldn't help to cool your computer to 0.1K if
>the best heat sink you have access to has a temperature of 3K. I certainly
>agree with this.

We agree here.

Robin Hanson
hanson@econ.berkeley.edu http://hanson.berkeley.edu/
RWJF Health Policy Scholar, Sch. of Public Health 510-643-1884
140 Warren Hall, UC Berkeley, CA 94720-7360 FAX: 510-643-8614