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From: ethan@utastro.UUCP (Ethan Vishniac)
Newsgroups: net.origins
Subject: Re: Second Law
Message-ID: <113@utastro.UUCP>
Date: Mon, 20-May-85 15:44:50 EDT
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Posted: Mon May 20 15:44:50 1985
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> Someone used the Second Law of Thermodynamics as an argument for creationism.
> In a philosophy course I attended here at Hopkins, the idea was presented
> that the Second Law isn't a law, but an observation.  Entropy may follow a
> jagged sort of curve, increasing sometimes, decreasing other times (on a
> _very_ large time scale.)
> 
> Any comments from those in the know?  I don't know that much about physics.
> 
> 				Rob St. Amant
You've got it right.  The second law is a statement about probable states.
If a system has enough time to reach equilibrium then the chances are
overwhelming that it will be in certain states, and not in others.  The
statement that entropy shouldn't decrease is a probabilistic one, not
an absolute statement.  Given enough time a system in equilibrium will
sample *all* accessible states.  Some large number of them will appear
indistinguishable on a macroscopic scale.  This means that the odds will
favor a system occupying this macroscopic state at any one time.  It is
not a guarantee.  A good example is the distribution of air in a room.
There are many many microscopic states which correspond to an even distribution
of air.  There are very few that correspond to "all the air in the upper left
corner of the room".  Therefore, if we check the air in a room we expect
to find it evenly distributed.

"Don't argue with a fool.      Ethan Vishniac
 Borrow his money."            {charm,ut-sally,ut-ngp,noao}!utastro!ethan
                               Department of Astronomy
                               University of Texas