Re: Tegmark is too "physics-centric"

From: Kory Heath <>
Date: Sat, 17 Jan 2004 22:23:14 -0500

At 1/17/04, Hal Finney wrote:
>By natural I mean that we could have simple laws of physics and initial
>conditions in which the creatures evolve over a long period of time,
>as we have seen in our universe.

It is very likely that even Conway's Life universe has this feature. Its
rules are absurdly simple, and we know that it can contain self-replicating
structures, which would be capable of mutation, and therefore evolution. We
can specify very simple initial conditions from which self-replicating
structures would be overwhelmingly likely to appear, as long as the lattice
is big enough. (The binary digits of many easily-computable real numbers
would work.) Moving from this 2D world, in which each cell can be pictured
as a square with 4 orthogonal neighbors, we can consider 3D CA in which
each cell is a cube with 6 orthogonal neighbors. There are rule sets and
initial conditions for this lattice structure that are just as simple as
Conway's life, which can similarly contain evolving self-replicating
structures. We can go further and envision a 4D CA in which each cell is a
hypercube with 8 orthogonal neighbors. Without a doubt, there are absurdly
simple rulesets for this lattice structure which are computation universal,
support stable structures like gliders, and support self-replicating
structures which would grow and evolve.

>Universes of the natural type would seem likely to have higher measure,
>because they are inherently simpler to specify.

If that's true, then the CA universes described above should have very high
measure, because they are extremely simple to specify.

>Tegmark goes into some detail on the
>problems with other than 3+1 dimensional space.

Once again, I don't see how these problems apply to 4D CA. His arguments
are extremely physics-centric ones having to do with what happens when you
tweak quantum-mechanical or string-theory models of our particular universe.

-- Kory
Received on Sat Jan 17 2004 - 22:24:44 PST

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