Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10 5/3/83 based; site hou2g.UUCP Path: utzoo!watmath!clyde!burl!ulysses!mhuxr!mhuxj!houxm!hou2g!stekas From: stekas@hou2g.UUCP (J.STEKAS) Newsgroups: net.physics Subject: Re: Non-linear systems. Message-ID: <389@hou2g.UUCP> Date: Mon, 14-Jan-85 11:16:21 EST Article-I.D.: hou2g.389 Posted: Mon Jan 14 11:16:21 1985 Date-Received: Tue, 15-Jan-85 02:07:39 EST References: <209@talcott.UUCP>, <328@rlgvax.UUCP> <384@hou2g.UUCP>, <273@harvard.ARPA> Organization: AT&T Bell Labs, Holmdel NJ Lines: 26 >> The concept of "predicable, in principle" is usefull if and only if >> it has some connection with reality. > >Sorry, you're wrong. The technical term for "predictable in principle" >is computable. You mean "predictable in principle" (i.e. computable) is a useful concept even when it has NO connection with reality?! I wasn't aiming at a definition of "computability" only an understanding of the usefullness of the concept. Even so, I would think that most of modern physics is NOT computable! The point I was trying to make was that if the universe is governed by a collection of non-linear equations (of sufficient ugliness) then the question of whether the universe is predictable may moot because we might not be able to calculate with them. So we couldn't verify the correctness of our theories, or determine the future even if they were correct. Is QED a "computable" theory? QCD? General Relativity? Have we verified them to sufficient accuracy to believe them? Are they deterministic theories? Are they deterministic approximations of a non-deterministic reality? Are these questions of more concern to a physicist, philosopher, or theologian? Jim