X-Message-Number: 24047
Date: Wed, 5 May 2004 08:23:11 -0400
From: Thomas Donaldson <>
Subject: CryoNet #24040 - #24046

For Mike Perry:

Believe it or not, I'm in the middle of a discussion with someone else
on neural nets versus brains versus standard computers.

If we were to try to actually build a structure with (to be simple)
1 billion nodes, each one with a connection to every one of the others,
then it should be clear that we'd run into serious practical problems.
Each node will have 1 billion - 1 connections emanating from it. Either
you make the node very large, or you try to make it very small (nano?).
If each connection has a diameter of one nanometer, then each node will 
have 1 billion such connections, which amounts to an outer area of 
(forgetting pi and the outer area of a sphere) about 1 meter. If the
processor inside that node is quite small, you'll have a difficult
design problem connecting it to those 1 billion connections. You may
as well make it 1 meter square. Basically the connections will make
the total size of the actual processors only 10^(-9) of the machine.
Then you have to organize a route through all the other connections
belonging to different nodes to each of the other nodes. Finally, for
most computations only a small subset of those connections would actually
be used. This looks to me like a very inefficient use of matter, and
one which raises lots of practical problems with its implementation.
Our totally connected machine will be roughly 1 km square, for instance,
and even to make it we'll need tunnels within it to reach all its parts.

And human brains have much more than 1 billion neurons, too.

Furthermore, as brains work they always use more than one path at a 
time. Our problem is to take this system with 1 billion nodes and have
more than one path between different neurons, without interference
between the paths. (It's important that brains are parallel machines:
if they were not, then their operation would take so long that other
creatures with parallel brains would have gobbled them up).

It's fine to consider such a machine theoretically, but fundamentally 
we can do much better by having a system able to grow new connections
when they are needed rather than carry about almost N! connections which
are all turned off.

                  Best wishes and long long life to all,

                      Thomas Donaldson

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