X-Message-Number: 8626 Date: Fri, 26 Sep 1997 10:04:38 -0400 From: "John P. Pietrzak" <> Subject: My brain is practically a Turing Machine References: <> Hi again, still catching up on stuff here. Thomas Donaldson wrote: > To John Pietrzak: > > You're strictly correct that there is no such thing as a PRACTICAL > Turing machine (Turing machines are hardly practical, being > intellectual constructions only). I do hope, though, that you > understood the point I was making when I made that statement. Yes, in so far as the brain is a massively parallel computing device (which, from overwhelming evidence, appears to be the case), real-world parallel devices should have a significant advantage in simulating mental activity. > I will say the same about your ideas for using a Turing machine to > simulate a brain. Sure. But they tell us nothing about simulating a > brain on a computer in the real world. Well, I wouldn't go that far. :) The TM does for this case what it does for any other problem in which it is used; it doesn't show how to implement the solution to a particular problem, but it does _prove_ that, given the axioms are correct, the solution can be implemented in some form on a processor. This is significantly more than nothing in my book. But you've already noted this point further on in your message. > Whether or not anyone has defined one, I believe it would be useful to > consider a device which is like a Turing machine but suffers from > limits of various kinds: length of tape, speed with which it can write > or read from its tape, and so on. Such a machine might allow us to > find better bounds for the behavior of real machines at any given > time, for instance. I will call such machines "practical Turing > machines". They are yet another intellectual construction, and in the > sense of existence that an idea has existence, I guess they must > exist. Unfortunately, the problem with this sort of construction is in holding it to bounds which are appropriate to the real world. Processors have consistently gotten faster, smaller, cheaper, disk space gets larger and cheaper. New ideas (parallel processing, quantum computers, holographic storage, etc.) hold out promise of even greater increases in the _rate_ of increase. Of what value, then, would a mental model with a particular bound in one of these variables be? The new machine would hold only until it's bounds were broken, and then anything proven with it would be again subject to question. John Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=8626