Bruno Marchal wrote:
On 29 Jun 2015, at 12:27, Bruce Kellett wrote:
This then gives the entire universe. The computation may be repeated
many times, but by the identity of indiscernibles, those repetitions
are just the same universe.
Assuming that the limit above is computable, which can hardly be the
case (unless my generalized brain is the entire universe, which I doubt,
but of course, we don't know, although the QM/MWI suggests empirically
that it is not the case).
Your generalized brain has nothing to do with it. We are talking about
computations run by the dovetailer. And yes, QM in the Everettian
interpretation does entail that the entire universe/multiverse is
computable. That is what unitary evolution means. As I said:
>> This means that physics is completely computable -- Turing emulable.
>> But that is what quantum mechanics in the Everettian interpretation
>> tells us. Unitary evolution preserves (quantum) information, and is
>> completely calculable.
>
> Which suggests that the quantum part of QM is part of the winner
> program for the measure, but this remains neutral on the hamiltonian.
That is covered in what I say below. Different O-regions can have
different Hamiltonians and different initial conditions, but all are
present, and all are completely computable and computed. The
computations may not halt, but that is not a problem when you are
computing universes of potentially infinite duration.
There will be computations that differ from the one giving this
universe to greater or lesser degrees, so these give neighbouring
universes that differ in these degrees. Actually, this is just the
level 1 multiverse of Tegmark. Given eternal inflation, there are an
infinite number of O-regions (observable universes) sharing our basic
physics. The idea is that there are only a finite number of possible
histories for these O-regions, so any history is repeated indefinitely
often. And for any history, all close and not-so-close copies are also
frequently repeated. This is just what comes out of the UD as well as
these physical theories.
More or less OK.
Computations also exist that correspond to less than complete
universes, or give inconsistent physics, or whatever. The very limited
computation that gives an individual consciousness or conscious moment
is insignificant in the bulk, and because of the problem of consistent
continuations, those "moments" have zero measure. So we do not have
the situation of "reversal", where the physics is derived from the
continuations of these moments. The physics is given by the extended
computations that create entire observable universe.
But if the physical universe run the UD, to predict (conceptually) if
this apple will fall on the ground, I must look at all computation going
through my current state (where I look at the apple still in my hands).
How would you do? That is obligatory by the (even just local) FPI.
No, that is the mistake. If the entire universe is computed infinitely
many times, then piecemeal bits where we look at computations going
through particular states become irrelevant. I do not have to extract
physics from this -- physics is already there in the master computation.
Complete, given, and ready to go. All we have to do is explore it
empirically. The little bits have zero measure relative to the whole
computation, so can safely be ignored. No more white rabbits.
Bruce
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