Re: Tegmark is too "physics-centric"

From: Kory Heath <kory.heath.domain.name.hidden>
Date: Sun, 18 Jan 2004 00:50:43 -0500

At 1/17/04, Eric Hawthorne wrote:
>Well here's the thing: The onus on you is to produce a "physical theory"
>that describes some subset of the computations of a 4D CA and which can
>explain (or posit or hypothesize if you will) properties of observers (in
>that kind of world), and properties of the space that they observe, which
>would be self-consistent and descriptive of "interesting, constrained,
>lifelike behaviour and interaction with environment and sentient
>representation of environment aspects" etc.

I'm not sure I really understand what you're asking for here. I'm applying
the very same concepts of "lifelike" and "sentient" that I apply to
configurations of matter here in our own universe. These concepts certainly
have to do with the things you mention - perception of surrounding
environment, information processing, the building of internal
representations, action within the environment, etc. All of these concepts
are essentially computational, and are highly general. They should be
applicable to substructures in any computation-universal system.

If you're asking how we would be able to recognize SASs (or even just
lifelike substructures) in a 4D cellular automata, there's clearly no
simple answer to that question. We can imagine running a giant computer
implementation of a 4D world, with lots of software tools at our disposal.
Obviously, we could examine the state of any bit in the lattice, and we
could also build higher-level pattern-matching tools that would help us to
recognize higher-level structures (like gliders, and perhaps larger
molecule-like structures). To recognize lifelike substructures in the
lattice, we would bring everything we know about computation,
self-replication, information processing, etc., to bear on the subject. We
already have some conception of what a self-replicating structure in
Conway's Life universe would look like. I don't see any reason why we
couldn't recognize such things if they arose naturally in some 4D CA that
we were studying.

I have no doubt that the problem would be difficult. I am also fully aware
that we have no precise "definition" which infallibly distinguishes all
"living" sub-structures from "non-living" ones. This is true for any
universe, including our own. We know that elephants are intelligent, but do
we really have a clear picture of what kind of sentience they possess? The
science-fiction author Stanislaw Lem suggests that alien intelligences in
our own universe might be as big as galaxies, and might look to us simply
like clouds of cosmic dust.

>My guess is that that physical theory (and that subset of computations or
>computed states) would end up being proven to
>be essentially equivalent to the physical theory of OUR universe.

We may be starting a game of what Dennett calls "burden tennis", but it
seems to me that the burden is entirely upon you to support such an
extraordinary claim. Are you suggesting that, for any CA we discover that
contains SASs, if we analyze how those SASs gain information about their
environment and how they affect it, if we analyze how their environment
must seem *to them*, we will find that it looks essentially like our own
quantum-physical, relativistic universe? I find that highly implausible, to
put it mildly.

Maybe you're simply arguing that our definitions of "life" and "sentience"
are so tied to our particular physics that we simply wouldn't find SASs
when we explore CA worlds. (Or, we'd only find them in those CA that manage
to behave very much like our own universe, with QM and GR and all the
rest.) Again, I find that highly implausible. I think our standard (fuzzy)
conceptions of life and sentience are substantially more "substrate
neutral" than that.

>You can't just say "there could be life and sentience in this (arbitrarily
>weird) set of constraints" and then not bother to
>define what you mean by life and sentience. They aren't self-explanatory
>concepts. Our definitions of them only apply
>within universes that behave at least roughly as ours does.

As I've said, my definitions of life and sentience are essentially
computational, and they're the same ones I apply to groups of molecules in
our own local universe. I think these definitions are applicable within any
universes that are computation-universal.

Of course, it should be obvious that my position rests on underlying
positions about the possibility of computational models of life,
consciousness, etc. If you don't believe, for instance, that hard-AI is
possible, even in principle, then obviously you won't accept my
conclusions, at least when it comes to intelligent SASs. But in that case,
we're really talking past each other, and we need to back up - way up. (And
frankly, I'm not interested in backing up that far.)

-- Kory
Received on Sun Jan 18 2004 - 00:55:32 PST