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From: gwyn@brl-tgr.ARPA (Doug Gwyn )
Newsgroups: net.physics
Subject: Re: Re: why FTL is illegal (wrt: free will).
Message-ID: <7007@brl-tgr.ARPA>
Date: Fri, 4-Jan-85 17:05:09 EST
Article-I.D.: brl-tgr.7007
Posted: Fri Jan  4 17:05:09 1985
Date-Received: Mon, 7-Jan-85 02:27:16 EST
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Organization: Ballistic Research Lab
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> ... I thought that even the simplest Newtonian models
> of the universe result in intrinsically INSOLUBLE differential equations
> (like the three-body problem). 
> 
> Doesn't this mean that prediction is impossible, even in a vanilla
> Newtonian universe with more than two objects? 

The "three-body problem" is NOT insoluble; it just has no simple
closed-form solution.  Given enough computing resources, one can
compute the motion of three gravitating bodies to any desired
degree of accuracy.

In practice, of course, one does NOT try to calculate even the
classical motion of individual gas molecules; the amount of
computation is just too burdensome.  Instead, one sacrifices
some degree of absolute detailed accuracy in exchange for
statistical knowledge.  That doesn't make things IN PRINCIPLE
nondeterministic.  The question becomes, how detailed do you
want your predictions?

Quantum considerations are of an ENTIRELY DIFFERENT type.  According
to conventional quantum theory, the evolution of a physical system
proceeds according to INHERENTLY PROBABILISTIC laws; there are no
underlying deterministic mechanisms at work.  This notion is quite
unsettling to one brought up in the Renaissance tradition.