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 Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=15165