X-Message-Number: 9275
From: Ettinger <>
Date: Fri, 13 Mar 1998 12:41:28 EST
Subject: Church-Turing etc

Some recent posts have renewed aspects of the old argument about simulations
or emulations, and whether we could be considered finite Turing machines; and,
in this context, whether a universal Turing machine could emulate any
computer. 

Different questions are mixed up here, including that of accuracy of
simulation--which is NOT the main issue.  

In the most extreme Artificial Intelligence view, a Turing tape machine could
emulate a person, and therefore could be a person. The extreme info folk take
it as a PREMISE (which they nevertheless call a conclusion) that only the
information matters and isomorphism is everything.  

Donaldson's recent #9272 includes a reminder that Turing machines are
SEQUENTIAL, hence not well suited for recursive functions, for which parallel
processors are much better. This helps to focus attention on the MEANING of
the Church-Turing thesis. IN WHAT SENSE can a Turing machine emulate any
computer? Only in the sense that it can, in principle, eventually arrive at
the same results, or print out the same answers. For example, it might be able
to describe your brain state at a particular moment in the future, if fed the
appropriate initial data.

The extreme info folk (apparently including David Deutsch) claim, in effect,
that not only is a copy of you also you, but a DESCRIPTION of you (or of you
and your activities) is you. Again, this is just their article of faith, based
on plausibility and perhaps preference, not a conclusion rigorously derived
from generally accepted premises.

Any substantial discussion of Church-Turing would be a long one. A great deal
has been written, e.g. by Hofstadter in his well known works. There are
subtleties and complexities that do not lend themselves to brief discussion.
Yet the bottom line, as far as I can see, is that the CT thesis, even if
correct, only guarantees that the Turing Tape can calculate any calculable
number, or collection or sequence of numbers. 

Are you just a collection of numbers, or symbols representing  numbers? Is the
map identical with the territory, for all purposes? Does a moving tape have
feeling? How do you know, since we do not yet know the physiology/anatomy of
feeling in animals?

Donaldson also included a reminder that SIMULTANEITY may play a role in the
inner life. It is not only possible, but probable, that feeling and
understanding depend on MORE THAN ONE EVENT or condition happening or existing
at the same time inside the brain--maybe something akin to a standing wave, or
an interference effect between waves. Since the Turing tape is linear
sequential, it would then be ruled out as an emulation of a person--of almost
anything physical, in fact, even a hydrogen atom (even if it could be
programmed with quantum effects).

All right, none of this has much practical importance at the moment, and I've
wasted my time again, and yours. Or maybe straightening out our mental kinks
does have a degree of importance.

Robert Ettinger
Cryonics Institute
Immortalist Society
http://www.cryonics.org

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