Re: [Fis] FIS / introductory text / 5 April 2004

Here is my reaction to parts of Michel's text:

> Entropy and Information: two polymorphic concepts.

-snip-

>Entropy calculations are sometimes made discarding the implicit assumptions
>done for an idealized Carnot Cycle. Here come difficulties. E.g., the
>whole universe is sometimes considered as a system for which the
>the entropy is assumed to have sense. Does the equilibrium of
>such a system has sense?
     SS: I believe that it seems to make sense for cosmologists and
astrophysicists. In any case, I find that it makes sense to me, as
follows: We understand what a system being at equilibrium means. From
this we can quickly understand that the world around us is NOT at
equilibrium. From this we might infer that the Universe, in which the
world around us must be located, is either itself not at equilibrium, or we
are in a local fluctation within it. Now, from astrophysics we learn that
there is evidence that the Universe is expanding. This we know is a
condition NOT associated with equilibrium. Furthermore, the evidence is
now interpreted to show that Universal expansion is accelerating. If that
is so, then the Universe CANNOT be in equilibrium. We know as well that we
ourselves are not at equilibrium, because we need constantly renewed
sources of energy to keep functioning.
     Now, experimental observations tell us that any isolated system left
to itself diffuses and equilizes, more rapidly at first, and then more and
more slowly, approaching a condition where it does not change any more.
Its energy gradients are gradually dissipated and it goes to ever more
probable distributions of its materials. This we call the Second Law of
thermodynamics, which, in the context of radical Universal disequilibrium,
can be interpreted as the Universe's tendency to equilibrate. So, yes, the
concept of thermodynamic equilibrium does make sense in connection with the
Universe (which is far away from it).

>Does thermodynamical state functions
>make sense here? And what about "the" temperature? These latter
>variable, even when viewed as a function of coordinates and/or
>time, has sense only for a restricted number of situations.
     SS: Well, any expanding system is cooling, and so we know that the
temperature of the universe overall must be decreasing.

>These difficulties appear for many other systems. At other scales,
>they may appear for microscopic systems, and for macroscopic
>systems unrelated to thermochemistry.
>In fact, what is often implicitly postulated is that the
>thermodynamical entropy theory could work outside thermodynamics.
     SS: Yes. I have argued that disorder can occur at any scale whatever.
It can be interpreted to be the condition, at whatever scale, that best
promotes the microscopic equilibration of its constituents. So, a piece of
meat is more disrderly than the fish from which it came.

-snip-

>Although "entropy" is a well known term in information theory, and used
>coherently with the term "information" in this area, the situation
>is different in science. I do not know what is "information" in
>thermodynamics (does anybody know?).
     SS: I would venture to say (based on the Negentropy Principle of
Information) that it is the initial, boundary and initiating conditions
(the material and formal causes) that promote the production and
maintenance of energy gradients in the face of their tendency to dissipate.

STAN

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Received on Tue Apr 6 21:21:09 2004