X-Message-Number: 15165
Date: Sat, 23 Dec 2000 07:19:19 -0500
From: Thomas Donaldson <>
Subject: reply to Mike Perry

Hi everyone!

Some short answers to statements about what I said. And I may later
expand them into longer answers, depending.

First, on the issue of whether or not we can solve the problem of
imitating ourselves on a single computer ie. turn ourselves into
Turing machines. Mike Perry believes that to be so as a theoretical
matter. I would say that, first, such an imitation of the entire
Universe requires more than the Universe itself. In that sense it
is NOT possible. Furthermore, when we look at how things work, it
looks quite impossible to make such an imitation with only one
computer because everything is working at the SAME TIME. That's
quite important, not a side issue at all. If single atomic events
must occur in some order, then the results will depend on the order
in which they occur, something quite different from those occurring
at the same time. 

A short scrutiny of quantum mechanics will tell us that individual
factors such as time may have a wide variety of choices. It is their
combination with other factors which is limited. IF we assume that
time itself comes in small unbreakable pieces, then we can imagine
how to write a program in which (say) everything gets done for one
instant, followed by the next etc etc. But so far as we now know,
time does not occur in small unbreakable pieces. So how are we to
imitate simultaneous events with a single computer? Sure, with 
that single computer we can come closer and closer, but that
some events occur simultaneously will remain important. A discrete
model of our universe will inevitably move away from the real 
one for just that reason. (And no, relativity does not change
the computer problem, though it clearly changes what happens).

Those comments provide two separate answers to the problem of
imitating the entire Universe with a single computer.

As for the theoretical possibilities, I would say that a theory
of the universe, or of computing, has severe faults if it is
one which we cannot use ourselves because it requires an even
larger universe to implement. AS for what would happen if the
notions of superuniverses become dominant, we would then have
an even worse problem: no matter what we do, we can only imitate
PART of our universe. If our part is NOT closed, then imitating
only a part will eventually fail because of input from outside;
if our part IS closed, then the superuniverses become theoretical
entities which do not influence what we can do.

In some respects I should apologize to Mike. I do not normally
save Cryonet, and used my memory of his comments to answer him.
But I do not believe my memory was so bad that my answers are
worthless, or that I misunderstood him so much that I failed to
see what he was basically driving at. Computers have proven
quite useful for many purposes, even SINGLE computers. It does
not follow that they can be used to make complete models of
the Universe.

		Best wishes and long long life to all,

			Thomas Donaldson

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