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 Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=26818