X-Message-Number: 11577 From: Thomas Donaldson <> Subject: To Mike Perry: why computability is not the same as unreachable worlds Date: Mon, 19 Apr 1999 23:37:03 +1000 (EST) To Mike Perry: While I agree with the arguments about "computable functions" it's not clear at all that they work the same in the case of possible worlds. Be warned, however, that when we speak of real worlds rather than mathematical entities I become very much a constructivist. It is easy enough to postulate (say) an arbitrary endless decimal number, but unless you have some means to produce the integers contained in it, you are postulating far too much for the real world. Yes, in one sense we might have a world produced by a number of infinite length: if we can compute each integer in that number then in a sense we can characterize that world. The computation rule, of course, would have to be one we can do, even if it takes increasing time for each integer. I am happy to put up with nonconstructivist arguments when we do theoretical math. They bring with them lots of other problems, but also have some convenience, too. You takes your choice. But when we talk about the REAL world we are not just doing theory. We want to live and act in that world. Best and long long life, Thomas Donaldson Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=11577