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From: djsalomon@watdaisy.UUCP (Daniel J. Salomon)
Newsgroups: net.physics
Subject: Re: predicting the universe with computers
Message-ID: <6861@watdaisy.UUCP>
Date: Fri, 18-Jan-85 12:33:12 EST
Article-I.D.: watdaisy.6861
Posted: Fri Jan 18 12:33:12 1985
Date-Received: Fri, 18-Jan-85 15:06:51 EST
References: <1027@sunybcs.UUCP> <215@looking.UUCP>
Organization: U of Waterloo, Ontario
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> No computer, now matter how powerful, can predict its OWN future, let
> alone that of the universe.   Or do I have to prove to you that no
> computer can predict whether an arbitrary algorithm will halt in a
> limitless universe?
> 
> So the universe is definitely not predictable from within.  Whether it
> is FIXED or not is another matter, of course.
> -- 
> Brad Templeton, Looking Glass Software Ltd. - Waterloo, Ontario 519/884-7473

     The halting problem states that no Turing machine can be built
that decides whether some other arbitrary Turing machine will halt.
But there is no rule against predicting what a Turing machine will do
for the next little while.  The halting problem is more of a comment on
the inadequacy of our logic systems along the lines of Russell's
Paradox, than it is a statement about the universe.

     Turing machines also have the property that they have an infinite
tape.  This is the practical problem that one encounters when trying to
build a halt detector.  But it has not been shown that the universe is
infinite.  In fact I believe that Einstein proved that the universe is
finite.