X-Message-Number: 14966 Date: Mon, 20 Nov 2000 07:17:50 -0500 From: Thomas Donaldson <> Subject: where's the proof? Yet More: So far no one has actually produced a proof or a reference to a proof that a system like a brain could be imitated by a computer (+ of course necessary peripherals). Since our brains do both more and less than just calculations, no proof that Turing machines can do any arbitrary CALCULATION shows that Turing machines can imitate brains. (It's hard for some to see this, but at the lowest level we are not calculating anything ... calculations require some set of symbols, and those symbols sit on top of other kinds of thinking which are not symbolic in any sense. In fact, that nonsymbolic thinking actually produces symbolic thinking (cf Wittgenstein's later works, among other things)). Such a proof may exist somewhere in the literature. I am only speaking here of those who have discussed this question on Cryonet. As for Turing machines, the simplest major problem is that human beings and other animals with brains must NECESSARILY do everything in real time, in the real universe. The universe does not obligingly slow down if you think slowly. The possibility of creating some other computer world in which everything goes slowly enough that a single slow computer could imitate a brain simply fails to deal with the real world. But even if we ignore this issue of timing (an important one, possibly ignored in Turing's time because the need for computation requiring parallel computers did not stand out as much as it does now), there are other features of brains which still require to be imitated by "standard computers". Brains aren't just arbitrary neural nets; they have a structure, with features which allow many changes in their connectivity and actual production of new neurons. Both of these features makes it much harder to work out just how it might fit into a Turing machine, even one which had a required time limit. So far no one has actually produced either a direct proof, or a reference to such a proof, that brains can be considered to work like Turing machines ... again, to repeat, even an extension of the notion of Turing machine which involves use of TIME as an important feature. If no one does this, then it really doesn't matter: producing a version of a Turing machine which imitates a real brain still remains undone, no matter what people are saying on Cryonet. Best wishes and long long life, Thomas Donaldson Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=14966