On 2/22/2013 12:10 PM, Bruno Marchal wrote:

On 22 Feb 2013, at 11:55, Richard Ruquist wrote:

Do you get separate universes from comp alone?

We get many separate dreams. It is an open question if some collections of sharable dreams define an unique complete physical reality.


If we consider that a 'reality' is that which is incontrovertible for some collection of intercommunicating observers the answer is obvious. Consider an observer as having a set of observables that mutually commute and are mutually consistent (form a Boolean algebra). For some arbitrarily large collection of such, communications (that carry actual signals and not just noise) will only occur between members of the collection that involve some subset of the observables of the collection. Completeness is not necessary and might even be counter-productive as the problem of solving satisfiability for an arbitrarily large collection of propositions is NP-complete. http://en.wikipedia.org/wiki/Boolean_satisfiability_problem

The laws of physics are the same for all Turing machines, as they emerge from all computations, but they still can have non isomorphic solutions.

I disagree. This claim is sound iff the laws of physics are 'the same' for all Turing machines only if one has a universal equivalence class of Turing machines and one can show that only one set of physical laws can exist.

My feeling is that an unique complete physical reality is not quite plausible.

    I agree.

I don't think this is compatible with the SWE+comp.

    I agree.

If the SWE is correct, then the SWE is an epistemological consequence of comp, including the MWI; and if QM is not correct, with comp, this could lead to multiverses but also to multi-multiverses, or multi-multiverses, etc. Even them might be only local, without any definite global physical reality.

ISTM that comp requires some form of MWI via the indeterminacy argument.

If the zero of the Riemann function corresponds to the eigenvalue of some hermitian operator, like some hope to show for solving Riemann conjecture, reality could emerge from a quantum chaos, which would implement a quantum universal dovetailing. To solve the mind body problem with this would still need to extract this from the (quantified) arithmetical hypostases. I mean this quantum chaos should be prove the "win" the "measure competition" among all universal systems.

I think that this is a quixotic request as proving the Riemann conjecture requires the inspection of all primes. This is asuper task <http://en.wikipedia.org/wiki/Supertask>...

Let us be clear. If computationalism is correct, we are really only at the very start of getting the comp physics. We have only the logic of the observable, and a tuns of open mathematical problems, which does not interest anyone, by lack of motivation on the mind-body problem. To use the comp-physics to do cosmology or particle physics is like using superstring theory to do a coffee. It is the "weakness" of comp, it leads to complex mathematics, very quickly, and cannot have direct applications (unlike most of physics).

The main non direct but important, in my sight, application is in the understanding that machine's theology is a science, indeed a branch of computer science, and so with comp (usually believed even if unconsciously) theology can be approached with the modest attitude of science. That can help the understanding that science has not decided between the two quite opposite conceptions of reality developed by Plato and Aristotle.

Comp provides a lot of jobs for the futures. Even without comp, biotechnologies will develop into theotechnologies, we might get artificial brains because some doctor might not ask you, and just consider it is the best treatment for you. We, here and now, might get consistent extensions in computers build by our descendents, etc.
It is not a luxe to dig on what that could mean.

To sum up, computationalism leads to the many separate physical universes, in any large sense of physical universes. With a too much strict definition of physical universe, it is possible that comp leads to just 0 universes. Just a web of dreams, defining no global sharable physical realities.

A problem: physicists don't try to define what is a (primary or not) physical universe.





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