X-Message-Number: 15328 Date: Fri, 12 Jan 2001 07:29:48 -0500 From: Thomas Donaldson <> Subject: to Mike Perry and others Hi again! Once more about Turing machines and brains, this time for Mike Perry again. First of all, I would consider the THEORETICAL possibility of imitating a brain with a single computer to be quite useless unless we could somehow make it a real possibility. I am quite willing to accept such a theoretical possibility, but think that it means virtually nothing. Sure, if we were Gods and could create whatever amount of matter and time we needed (and space, too) then it might have some reality, but we are not Gods and never will be. Second, the comments about polynomial growth are wrong. I must admit that my previous comment on this question wasn't at all clear to many, and therefore apologize. But here is a bit more which may clarify this issue: the exponentiality comes not from the creation of new neurons, but from the number of connections which they allow. These connections would presumably not be limited to connecting only those neurons which came from an original ancestor neurons, but involved connecting neurons which came from quite different other neurons. Remember the structure of neurons here: the neurites, branches of an axon, may extend quite far, while dendrites remain relatively close to the cell ... though far if measured by the size of the cell body. Moreover, even if an individual new connection is short, it may create a much longer connection which brings together the connections from two different neurons which themselves connect to others... and so the creation of connections over major distances in our brain. Given a set of N neurons, the number of connections between them goes up like N!. If we look at M sets of N neurons, then the total number of connections is greater than M! * N!. (Recall again that axons can go quite far. I will send in a message which completes these calculations later). This is where the exponentials come into play. As I have said repeatedly, the major problem comes from TIME. If we cannot build a human-like brain with a single computer without using up all the matter available to us, its theoretical possibility means very little. It continues to mean very little no matter how many believe in its THEORETICAL possibility. To do computing, or even exist as human beings (or their successors) we must deal with what is actually possible. In that sense we must deal with very large parallel computers which are composed of small processors, and theory about the behavior of Turing machines means nothing at all. And if in addition such machines as ourselves don't fit Turing's model AT ALL, not even in theory, then we'd do well to abandon it and try to make models which fit... nonTuring "computers", if such a notion does not offend too badly. Best and long long life for all, Thomas Donaldson Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=15328