X-Message-Number: 26128
Date: Tue, 3 May 2005 10:04:28 -0400
From: Thomas Donaldson <>
Subject: CryoNet #26122 - #26123

To Mike Perry:

I should go to bed soon because its getting late here. However:

1. Quantum computers are no longer Turing computers by any
   reasonable interpretation. I hope we can build useful ones,
   but that also looks like a hard problem.

2. I haven't read Deutsch on this question, but I would certainly
   agree that in some sense (very loosely speaking) we are machines,
   but not Turing machines. We're even highly parallel. It does
   not take quantum mechanics to simulate a human brain. It WILL
   take processors which can do things no present processors
   can do, like change their connections (remember those connections
   are our memories), grow new ones, and get more processors
   when needed. 

3. We will not have truly simulated a brain until our manufactured
   brain can actually deal not with a simulated world but with 
   the real world that surrounds us. Even a working Turing machine
   fails this particular test: it or the person is in a box, unable
   to see anything but the notes passed to it. The fundamental problem
   with simulating the world is that to be consistent you end up
   simulating the entire Universe, and get buried in the mapping 
   the whole world problem from the Jorge Luis Borges story ---
   though in practise our simulation is likely to fall apart 
   because of errors, not matter how much care we take. An artificial
   brain is useless unless it can deal with the real world. It's
   even useless to itself: who wants to live in a doll's house?

SO: in one way I agree with Bob Ettinger, in another way I agree
with you. Even simulating an mammal's brain raises lots of problems
which have not yet got solution and sometimes don't even have
any thought given to them at all (too many computer people think
that it's a very simple problem, and because they never try 
solving it, never learn of its subtleties). However I would still
agree with you in the sense that an artificial brain is certainly
possible. To what extent it will be superior to our present brains,
and whether we'll ever seriously WANT to build an artificial
brain, are different questions, yet again.

            Best wishes and long long life to all,

                 Thomas Donaldson

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