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we can indeed interpret some of the fundamental laws of physics as if
matter were composed of elementary particles, the molecules. They suc-
ceeded. They showed that three fundamental quantities in thermodynam-
ics could be expressed in terms of molecular properties. The one is pressure.
It is interpreted as a hailstorm of molecules flying against the walls of a con-
tainer. The kinetic energy, or the speed of the molecules, would determine
temperature. And then they came to the notion of entropy, or
utropy
, as I
would say, and here a fascinating thing happened.
They could not explain utropy in purely molecular terms, and had to
make an appeal to the cognitive functions of the observer. This is the first
time when, in science, the observer enters into his descriptive system. What
was necessary in order to handle the notion of utropy, was to talk about the
distinguishability of states of affairs. I will give you an example. Take again
the two boxes which can be distinguished by their different temperatures:
one at a high temperature, the other at a low temperature. Put them
together so that they are fused. Now the hotter will become colder, and the
colder slowly warmer, and as time goes on their distinction will be lost: they
become more and more “confused.” Better, the observer becomes “con-
fused” because he will be unable to distinguish between the two contain-
ers, his confusion increasing with the increase of the utropy. Here you have
one version of the Second Law of Thermodynamics: utropy increases with
confusion. Or, as others may say: entropy increases with disorder.
Seeing the Fundamental Laws of Thermodynamics, which were originally
formulated so as to account for a macroscopic phenomenology, to have—
in turn—their foundation in a microscopic mechanics, stimulated questions
about the potential and limits of these Fundamental Laws.
I can see Clerk Maxwell sitting there, dreaming up some mischief about
how to defeat the Second Law of Thermodynamics: “Hmm, if I have two
containers at equal temperature, what must go on between them so that,
without external interference, the one gets hotter, while the other gets
colder?” Or, if you wish, letting order (discriminability) emerge from
disorder (indiscriminateness), i.e., reducing the entropy of the system.
Maxwell, indeed, came up with a charming proposal by inventing a demon
who would operate according to a well-defined rule. This demon is to guard
a small aperture in the wall separating the two containers and to watch the
molecules that come flying toward this aperture. He opens the aperture to
let a molecule pass whenever a fast one comes from the cool side or a slow
one comes from the hot side. Otherwise he keeps the aperture closed. Obvi-
ously, by this maneuver he gets the cool container cooler (for it loses all its
“hot” molecules) and the hot container hotter (for it loses all its “cool” mol-
ecules), thus apparently upsetting the Second Law of Thermodynamics. So,
Maxwell invented his famous demon, whose name is, of course, “Maxwell's
Demon,” and for quite a while it was thought he would indeed have
defeated the Second Law. (Later on, however, it was shown—but that is
quite irrelevant to my story—that indeed, the Second Law of Thermody-
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