> >Cars are optimised.
>
> In no sense. They get substantially better every year even after you
> discount for technological improvement. In what sense could they possibly be
> optimal at any point?
(Fairly optimal.) In the sense that it would be *much* easier to
build something on four wheels that moves by itself than it is to
build a vehicle that can compete on the open market today. The
context was this: Carl said that a simple self-replicator would
contain about the same amount of information as a car. So some
kind of analogy-inference might be made if we know how difficult is
it to design a car. Well, how difficult is it? Many highly skilled
people have been busy for many decades designing cars, so it seems
very hard. But this would be to overlook the fact that the
self-replicators we are trying to build need not be optimised in the
sense that cars need to be, if they are to be acceptable to car
designers. The relevant analogy (a weak one, to be sure) is rather to
steerable automobiles on four wheels or something like that; not to
car that could be sold today.
> >> >To build an optimised nano
> >> >self-reproducing device would be much harder than simply to make
> >> >something useful that can replicate. For example, a universal Turing
> >> >machine has been constructed in Conway's Life world. The entity is
> >> >very big and it was hard, but nothing near a thousands of genius-year
> >> >task, to do it.
> >>
> >> Nobody has presented a self-replicating Life system. All Conway did was
> >> produce a feasibility proof, so you know it *can* be done. Actually
> >> designing such a system is still considered not yet possible.
> >
> >Really? I thought I've heard that the Universal Turing machine was
> >actually designed, with streams of gliders serving as tape etc. But I
> >may be wrong, in which case I'm glad you pointed it out. Do you have
> >any references?
>
> "The Recursive Universe" by William Poundstone. It has a good layman's
> description of Conway's proof, and some guesstimates of what it would take to
> actually make a self-replicating Life computer (conclusion: no time soon).
I don't have that book handy, but now I'm beginning to suspect that
what Poundstond makes guesstimates about is constructing such a
gadget in the real world. What we were talking about was Conway's
universal Turing machine in the Life world (a mathematical model).
I think Carl Feynman said that he was aquainted with Conway's proof
and thought that going to the detailed design was only a matter of
filling in some details. (Did you really think that I believed that
somebody had built a Life world replicator in the real world out of
cogwheels or whatever?)
Nicholas Bostrom
London School of Economics
Department of Philosphy, Logic and Scientifc Method
email: n.bostrom@lse.ac.uk
homepage: http://www.hedweb.com/nickb