X-Message-Number: 26818
Date: Tue, 16 Aug 2005 09:23:48 -0400
From: Thomas Donaldson <>
Subject: to Yvan Bozzonetti

For Yvan, umpteenth time:

I have no fundamental objection to making a device which acts like our
brain. However this does not mean that I will accept any proposed
device as one which acts like our brain. 

I've raised these points before, without getting much answers, and
I will raise them again: 
1. We cannot imitate a parallel machine with any smaller assemblage
   of processors which may try to imitate subsets of the processors
   of the parallel machine. The original processors in these subsets
   can genuinely act at the same time, not at different times no
   matter how small. Fundamentally, a parallel machine with N
   processors cannot be accurately simulated by any other machine
   with M < N processors.
2. Our neurons grow new connections with one another as part of 
   learning. Sometimes our brain even produces new neurons for the
   same purpose. Various people on Cryonet (and elsewhere) have
   proposed that new connections might be formed instead by light
   beams between "neurons" or other nonbiological means. If nothing
   else, such a method will involve a lot of complexity to actually
   implement --- at least as much as we have with brains. Growth
   of new connections looks much simpler if we have millions of
   neurons.
3. Before we think about making our brains faster, it would be useful
   to think just what use we would make of such speed. (This is not
   an argument about making fast machines). It's important that
   electrical currents play a role inside neurons; if we really needed
   lots of speed, a path to evolving such speed is open to us.
   It's not enough here to think of occasions in which processing
   speed would be useful. If we use it for 1% of our time, and carry
   around all the machinery needed for it for the remaining 99% of
   our time, then that looks like it will make our design inefficient.
   Moreover, how fast we can physically move becomes important here
   too: if we can work out what to do in a microsecond, but take 
   a whole minute to do it, we're inefficient in another way.

Just some comments on the project of building a "human brain".

          Best wishes and long long life for all,

               Thomas Donaldson

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