X-Message-Number: 9282
From: Thomas Donaldson <>
Subject: Re: CryoNet #9268 - #9272
Date: Sat, 14 Mar 1998 01:14:18 -0800 (PST)

HI everyone!

To Mr. Metzgar: I did not get my ideas from Tipler or anyone else that I know
of, and you will not hear me if you try to read those ideas into what I say.

It is flatly false that neurons are at all simple. I should go on at this 
point in great detail, but suggest that you start your education in this 
subject by reading Dudai, THE NEUROBIOLOGY OF MEMORY, and GM Shepard,
NEUROBIOLOGY. It may also help if you did a little study of the differential
equations involved in predicting the motion of planets, an excellent and 
beautiful example of chaos in the technical sense. As for how chaos becomes
involved, it becomes involved because we could only make an accurate 
prediction of the motion of all the bodies in our Solar System if we had
completely accurate, infinite-precision arithmetic. Since we do not, our
prediction begins by being wrong to a very small extent, but that small 
extent grows with time until it swamps everything.  

Furthermore, I strongly suggest you look up the reference which Mr. Freeman
kindly put back on Cryonet. A counterexample is a counterexample; no one 
claimed that the nonTuring "computer" was better, merely that it was not
a Turing computer. (Whatever a computer is supposed to be...). So just what
does that do to the Church-Turing thesis? Perhaps it needs some emendation.

As for the illusions produced by digital pictures, so far I have not seen one
which I would mistake for reality. Let us suppose that the digital picture
was so very fine that I was not conscious of any difference with one of a
real event; nonetheless my rods and cones will respond to that difference.
What I am conscious of, and how my brain runs, are two different things; it
often happens that consciousness comes AFTER you make a response. Not long
after, but after ... several experiments show this. (To digress a bit, 
consciousness seems to work as some kind of overall guide, but most decisions
your brain makes don't even reach that level). 

The main problem with any digital imitation of the world is chaos. Technically
this means that small errors grow rather than decrease with time, and the solar
system (or weather prediction) are both good examples of this. It takes very
great computer power to make your errors small enough (remember that you are
working with a digital machine) for your prediction to remain valid for very
long. The record for the Solar System, for instance, is (last time I heard)
about 20 million years ie. we have a good idea where everything was up to
about 20 million years ago. Because of its interest, astronomers are constantly
trying to lengthen this time. Note that the Solar System has probably existed
for 4 BILLION years, and of course the problem gets increasingly harder the
more accurate you try to be. 

To apply that to brains, I think it unlikely that a digital picture will 
give such an exact representation of reality that the response of my brain,
over time, to the digital representation will not diverge more and more from
its response to a real experience. Certainly it can work for a few hours,
but we live much longer than that. I would say the same of a digital
representation of a working brain, though the problem is very much worse
than simply showing a scene. 

As for quantum mechanics, it's not at all clear to me that the notion of
"digital" retains any meaning. Sure, sometimes light will behave as particles,
but what, then, about the times it behaves as a wave? Not only that, but chaos
can exist in the quantum realm, too --- though to be fair, it did give the
original proponents of chaos some cause for thought about just how that
could happen.

Finally I don't claim this to be a complete discussion at all. But maybe
it still moves a few things. There will be a delay, but as I said, I
would like to call a time-out here until I'm in Australia and have my
own books etc to consult.   

			Best wishes and long long life to everyone,

				Thomas Donaldson

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