Thermodynamics [was Re: photochemical advance]

From: Robert J. Bradbury (
Date: Mon Dec 10 2001 - 15:52:56 MST

On Mon, 10 Dec 2001, Dossy wrote:

> Yes, this starts to sound a lot like the "perpetual motion"
> pipe-dream, I know. Perpetual motion _may_ be a pipe-dream,
> but I don't think the concept is.

This is a *very* complex area and I don't think scientists really
understand it yet. There are conferences every few years on
the "Physics of Information Theory" and things move forward
a bit. I suspect there are only a few dozen people in the
world that understand this to any significant degree.

Leaving aside the potential vs. kinetic debate, one would
assume that "computation" ought to be doing "work" which
should require energy inputs (no perpertual motion).
Well, as Bennett has shown, this isn't really the case.
You can use the latent heat in an environment as an
energy source for computation if you are clever about
how you utilize it. What consumes the energy is the
process of erasing bits (generating entropy).

So *if* in fact you can design machines that do not
destroy information you may indeed have a "perpetual
motion" machine. It remains questionable however whether
you can get any useful work out of it because the
harvesting of the work would seem to require the
destruction of information.

So perpetual motion may be possible, its just impossible
to ever prove it...


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