Re: Is the universe computable

From: Stephen Paul King <>
Date: Tue, 27 Jan 2004 17:12:13 -0500

Dear Kory and Hal,

    Kory's idea strongly reminds me of the basic idea explored by John
Cramer in his "Interactional" interpretation in that it takes into account
both past and future states. Please see:

    One thing you might wish to bear in mind is that David Deutsch has
pointed out that Cramer's idea is equivalent to the Many worlds
interpretation, but I can not find the exact quote at this time. ;-)

    The main problem that I have with any CA based model is that it
explicity requires some from of absolute synchronicity of the shift
functions of the cells. I see this as a disallowance of CA based models to
guide us into our questions about the appearence of a "flow of time", it
assumes a form of Newton's "Absolute time" from the onset!
    In addition, it has been pointed out be several CA experts that CAs are
equivalent to universal Turing Machines and if UTMs are incapable of
deriving QM and its phenomena then neither can CAs.

Kindest regards,


----- Original Message -----
From: "Hal Finney" <>
To: <>
Sent: Tuesday, January 27, 2004 1:33 PM
Subject: Re: Is the universe computable

> Kory Heath writes:
> > Forget about our own (potentially non-computable) universe for a second.
> > Surely you agree that we can imagine some large-but-finite 3+1D CA (it
> > doesn't have to be anything like our own universe) in which the state of
> > each bit is dependent on the states of neighboring bits one tick in the
> > "future" as well as one tick in the "past". Surely you agree that we
> > search through all the possible 4D cube bit-strings, discarding those
> > don't follow our rule. (This would take a Vast amount of computation,
> > that's irrelevant to the particular questions I'm interested in.) Some
> > the 4D cubes that we're left with will (assuming we've chosen a good
> > for our CA) contain patterns that look all the world like SASs, moving
> > through their world, reacting to their environment, having a sense of
> > passing time, etc.
> That is indeed a fascinating thought experiment, and I agree with
> everything up to the last part. Are you sure that a CA whose state
> depends on the future as well as the past can have self aware subsystems?
> This seems different enough from our own physics that I'm not sure that we
> can assume that it will work like that. I'm not saying it can't happen,
> but I'm curious to see evidence that it can.
> Our own universe's microphysics appears to be basically reversible, and
> I remember that Wolfram's book had some CAs, I think universal ones,
> which could be expressed in reversible terms. A reversible CA is one
> where the present state can be deduced either from the future or the
> past.
> But I think you're talking about something stronger and stranger, where
> you'd need to know both the future and the past in order to compute
> the present. This puts your questions about "when" the consciousness
> exists in a much sharper light. (I do have answers to those questions
> which I have somewhat explained in recent postings.)
> One way to approach an answer to the question is to ask, is there such
> a CA in which a universal computer can be constructed? That would be
> evidence for at least a major prerequisite for conscious observations.
> Do you have any examples like this?
> Hal Finney
Received on Tue Jan 27 2004 - 17:47:13 PST

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