Re: [Fis] Szilard's Engine and Information

From: Stanley N. Salthe <[email protected]>
Date: Sat 10 Apr 2004 - 18:15:08 CEST

Shu-Kun said:

>Regarding the related entropy of mixing (Delta S), it is certain that
>the entropy of mixing is an information theoretical entropy
>because there is no heat involved. It should not be taken as a typical
>thermodynamic entropy (Delta S). Mixing of two chiral molecules
>gas R and gas L you mentioned cannot be a thermal process. Therefore,
>it is not a thermodynamic process in an heat engine. Mixing of R
>and L cannot be used to generate mechanical work. This is a fact.
>When we discuss the engine and related possibility of energy
>conservation, this fact must be kept in mind.
>
>If the mixing of gas R and gas L would create work (a kind of mechanical
>energy calculated as distance times force), one should be able to also create
>mechanical work by mixing red color and black color.

     I find this interesting in regard to the understanding ofphysical
entropy as disorder. This interpretation has been disputed because of
examples like mixtures of oil and water, which seem to spontaneously
separate, making a more orderly result than was present in the mixed state.
But Shu-Kun's posting here suggests why this understanding is specious.
What is neglected in this view is that energy-utilizing work had to be done
to mix the oil and water to begin with, in a thermal process. This process
set up a curious kind of dispersed energy gradient, which then dissipated,
producing the separation, and giving off heat again. That is to say, the
unmixing of oil and water is a kind of work (not unlike the unwinding of
many wound up rubber bands!), and, as such, would not be expected to
produce disorder. Put another way, the unmixing of oil and water is NOT
SPONTANEOUS, but is instead a massive amount of microscopic work.

Commenting upon Michel's posting, he said:

>About the thermodynamic equilibrium and the universe, in the reply of Stan
>Salthe:
>Since cosmology is far from my field, I confess to have difficulties to
>understand the properties of the system <<our universe>>, viewed from the
>thermodynamical viewpoint. Even the cooling of such an expanding system
>is not clear for me, since, despite that the expansion is (locally) currently
>observed, I do not know what will happen after some 1O^10 years or more
>(does anybody knows ?), and may be there are cycles, may be there are
>aperiodic contractions, may be there is...anything. I would like to
>hear further opinions about this.
>
Cosmologists currently view the entire Universe as expanding, and the
different models of its continuance all have it continuing to do so in one
style or other. They all view the Universe as "cooling", as we see all
local expansons do. My point, in any caase, is just that, at present, the
Universe is very far from equilibrum, and that is sufficient to explain why
there is a Second Law of thermodynamics -- given, of course, that we make
the reasonable assumption that the Universe is isolated. Indeed, the
Universe logically could not expand at accelerating rate unless it were
isolated!

STAN

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Received on Sat Apr 10 16:47:11 2004

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