I agree with Hal. CA models doesn't explain quantum non-locality. More deeply perhaps is the fact that from Kochen Specker theorem there is no boolean map on quantum reality, but a CA model always has a boolean map.
When Hal says: >As far as the claim that we already know the algorithm that runs our >universe, and it is the UD: I think this is amusing but ultimately >misleading. It's true that a dovetailer which runs all programs will >indeed run our own universe's program (assuming it has one), but I think >it is a misuse of terminology to say that the UD is the algorithm that >is running our universe. I agree. Note that my arguments (uda, auda, etc.) shows only that IF I am Turing emulable THEN the structure of the multiverse emerges from all computations at once, as seen and anticipated by internal observers, i.e. from the first plural person point of view of consistent machines. The UD is not the explanation, it is the problem! In fact with comp no classical program can explain, per se, the universe. And even if a "quantum machine" can explain the universe, with comp we have to explain how that quantum machine arise, in our mind, by relative averaging on all computationnal histories. Zuse's thesis is without doubt a step in the comp direction, but without distinguishing different sort of internal points of view Zuse cannot foreseen the quantum dreamlike feature of "everything", still less the physico/psycho reversal. Bruno Hal Finney wrote: >Juergen Schmidhuber writes: >> I welcome feedback on a little web page on Zuse's 1967 thesis >> (which states that the universe is being computed on a cellular automaton): >> >> http://www.idsia.ch/~juergen/digitalphysics.html > >That's very interesting; I was not aware of Zuse. Unfortunately I >don't know German so I can't read his paper. > >Regarding the question of the compatibility of CA models with relativity >and QM, Wolfram looks into this in some detail. He essentially abandons >a simple CA model in favor of a more complex network of interacting >nodes, which has some features similar to the Lorentz transformation of >relativity. Then to address the EPR style long-distance correlations of >QM, he proposes that while the network is mostly local, it has occasional >nodes which get stretched apart and are connected to distant nodes. >These are rare but allow for the type of information flow necessary to >reproduce long-distance QM correlations. All in all it is a pretty ad >hoc and unconvincing model. > >I tried to read the t'Hooft paper referenced here but it was over my >head. It also struck me though as not really addressing the discrepancy >between long-distance correlations and local CA models. It seems very >much an open and difficult question to me to show how a local CA model >can reproduce relativity and QM. > >One issue which CA models tend to ignore is the MWI. Most CA models >are built as hidden variable theories which define a single universe. >Some multiverse models have that structure as well. But it seems to me >that this is an entirely unnecessary restriction. If a CA can model >a universe, it can model a multiverse, and likewise with any other >computing model like TMs. > >The MWI is fully deterministic, which may make it a more attractive >target for modelling with a deterministic computational theory than >attempting to reproduce the statistical phenomena of QM, essentially >via hidden variables. Any hidden variable theory, CA based or not, >has two strikes against it from the beginning due to the the many well >known difficulties of Bell inequalities and EPR correlations. > >Regarding entropy, it is pointed out that entropy does not grow in a >CA model. Wolfram discusses this as well. While entropy technically >does not grow, you can get phenomena that look very much like entropy >growth in a CA model. Eventually you will get a Poincare recurrence >if the universe is finite. But if you start in a sufficiently simple >state, there are many CA models which will mimic entropy growth into a >more complex state. And this may be close enough to explain our universe. > >Alternatively, of course the MWI as a deterministic theory also does >not have entropy growth. As mentioned above, computational models of >our universe might well do better to aim towards an MWI world. > >As far as the claim that we already know the algorithm that runs our >universe, and it is the UD: I think this is amusing but ultimately >misleading. It's true that a dovetailer which runs all programs will >indeed run our own universe's program (assuming it has one), but I think >it is a misuse of terminology to say that the UD is the algorithm that >is running our universe. I would reserve that phrase to refer to the >specific program that generates our universe and no others. It will be a >tremendous accomplishment of physics and philosophy when that program is >discovered, but it is misleading to give the impression that we already >know what it is. > >I think a better terminology here would be something like, we don't >need to know the specific program that describes our universe in order >to imagine how to program a computer that would in fact generate our >experiences, at least in theory. And then go on and explain about >running all programs at once, etc. > >Hal Finney > >