X-Message-Number: 8670
From: Thomas Donaldson <>
Subject: Re: CryoNet #8664
Date: Sun, 12 Oct 1997 21:54:10 -0700 (PDT)

To Mike Perry:

AS for Turing Machines, I've said repeatedly that they are abstract ideas and
fail to capture some very real issues in computing: such as speed and the
finitude of memory. This is not a criticism of Turing machines as such; the
point is that in some areas and for some problems they tell us nothing at
all.

The reference (which specifically sets up a neural net which cannot be 
emulated by a Turing machine) is by HT Siegelmannn, ED Sontag, in SCIENCE
(268(1995) 545-548). Naturally they give more information and references
themselves.

Given the practical problem of a Turing machine trying to emulate a human
brain (with billions of nodes in its neural net) the issue of whether or
not our brain might be such that it COULD NOT be emulated even with millions
of years of time, the question of whether or not it can be emulated by a
Turing machine for the reasons given in the article above --- seems kind of
moot. We already know we can't emulate a brain PRACTICALLY. It is a matter
of intellectual interest if we find we can't do so even abstractly. 

I subscribe to SCIENCE and I've been to Scottsdale, as you know. Somewhere
in my piles of old issues of SCIENCE there is the actual article. The most
efficient thing would be to go to a library which takes SCIENCE and look it
up. Yes, that will take time.

Furthermore, if we are to discuss computers and whether or not one might 
run us as if we were a program, I'd have to say myself that the only
practical implementation of a computer able to act like a human being would
be based on neural nets. The problem does not lie just in speed, but in
the structure of the processing done by neural nets compared to ordinary
computers run by only a few pentiums or whatnot. ("Few" here might be as
many as several thousand). Shall we consider neural nets to be computers,
or not? And if they aren't Turing machines (all it takes is for one node
to have a strength incommensurable with that of the others) then does that
mean that they must also not be computers? WHAT IS A COMPUTER?

			Best and long long life,

				Thomas Donaldson

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