On Tue, Oct 1, 2019 at 12:53 PM 'Brent Meeker' via Everything List < [email protected]> wrote:
> On 9/30/2019 3:53 PM, Bruce Kellett wrote: > > On Tue, Oct 1, 2019 at 2:50 AM 'Brent Meeker' via Everything List < > [email protected]> wrote: > >> On 9/29/2019 6:53 PM, Bruce Kellett wrote: >> >> On Thu, Sep 26, 2019 at 10:32 AM 'Brent Meeker' via Everything List < >> [email protected]> wrote: >> >>> I think the alternative is something suggested by Zurek. He shows that >>> decoherence plus einselection will make the reduced density matrix strictly >>> diagonal, i.e. he solves the preferred basis and derivation of the Born >>> rule. Then he suggests, but doesn't really argue, that the universe cannot >>> have enough information to realize all the non-zero states on the diagonal >>> and so only a few can be realized and that realization is per the Born >>> rule. This is what Carroll would dismiss as a "disappearing world >>> interpretation"; but it would provide a physical principle for why worlds >>> disappear, i.e. branches of lowest probability are continually pruned. >>> >> >> I don't think this is exactly what Zurek is arguing. He mentions >> Halliwell, but is concerned more with Quantum Darwism, which is an account >> of the records left in the environment by the system, than with the effects >> of decoherence on the system itself -- as would be the case if the limits >> on environmental information set some probabilities to zero. He says: >> >> "Copying yields branches of records inscribed in subsystems of E. Initial >> superposition yields superposition of branches, so there is no literal >> collapse. However, fragments of E can reveal only one branch (and not their >> superposition). Such evidence will suggest 'quantum jump' from >> superposition to a single outcome...." >> >> So it is the fact that our access is limited to only fragments of the the >> entire environment that leads to the perception of collapse -- our >> inability to see the superposition, or to reverse the measurement. If you >> take only a portion of the complete state you certainly reduce the pure >> state to a mixture. This is not a particularly new position, being in line >> with the IGUS ideas of Gell-Mann and others. >> >> >> That seems to be the same as MWI. Our access is limited because we are in >> a relative state...so each copy me has limited access. Yet he refers to >> "the myth of multiple worlds". >> > > Our access is limited because we are finite beings, with limited > information capacity. Sure, you can imagine that the other "relative > states" exist in the same way that we do, but I would take the view that > since we cannot in principle access these other states, and they can, in > principle, have no effect on us and our physics, then they are essentially > non-existent. Or rather, their existence is a metaphysical matter, not a > subject of physics. > > There was a time when I thought that MWI might mean more than this, > because many MWI enthusiasts claim that many worlds does away with Bell > non-locality -- giving a purely local explanation for violations of the > Bell inequalities. > > > Have you read Carroll's book? I was surprised that he drew two diagrams > of a Bell experiment. In one he shows the world splitting instantaneously > (non-locally) and in the other the split propagating within the forward > light-cone. He writes that it doesn't matter which?? I have always > imagined the "split" as propagating, since the spread of decoherence must > be at the speed of light or less...which I suppose is what is meant by > "local". It is only in the future overlap of lightcones that the > non-orthogonal "worlds" (subspaces) cancel out by interference. > I haven't read Carroll's book, it isn't released in Australia until November. I would be interested to see if he has a better account of Bell non-locality than Wallace. About the spread of "splitting": decoherence is a local physical interaction -- photons interacting with walls and the like. This clearly spreads at the speed of light (or less). But splitting is not really just decoherence. The trouble with Bell non-locality is that the splitting of worlds is not a physical interaction like decoherence. Bruno and others speak about a "spread of entanglement" as being associated with the splitting. But again, entanglement is the result of physical interaction, and the interaction of looking at a pointer to see a result is not really an entanglement interaction. I think that there is a lot of loose thinking about this "splitting" process. The absence of disallowed branches (Alice and Bob both seeing spin-up with aligned polarisers) is not a matter of worlds (branches) cancelling by destructive interference, because there is no interaction -- the light carrying information from the space like separated measurements is not coherent, so it can't interfere. If it were coherent, allowing interference, then that coherence itself would indicate non-locality. > This, to my mind, was the last gasp of MWI realists -- and that hope has > been dashed. First, because Bruno has resolutely been unable to give any > such local account, even in MWI; and second, extensive searches of the MWI > literature have shown many claims, and also the same number of failed > analyses. The final straw came recently when I read David Wallace's 2012 > book, "The Emergent Multiverse". In Sections 8.5 and following of that book > he confidently proclaims that Everett banishes non-locality, but he totally > wimps out on giving any sort of an account, even a half-plausible one. > Section 8.7 is one of the most disappointing accounts of Aspect's > experiments that I have ever read. > > > I haven't read Wallace. > It is the most irritating of books because of the arrogant triumphalism regarding many worlds. > So MWI has no practical application -- it is pure metaphysics, and can be > relegated to the dustbin of history, along with celestial spheres and > phlogiston. > > > I'm not so dismissive of philosophy. I think it's role is in suggesting > ways extend or improve or replace theories. In the case of Everett's > relative state, it suggested decoherence and quantum Darwinism which I > think have gone a long way to answering the questions of preferred pointer > states and the Heisenberg cut. > I don't think these advances have come through philosophy. They have come through physics -- taking the quantum nature of the measuring apparatus and the observer seriously. Metaphysics is not physics -- if it makes a difference, it is physics. All else is padding..... Bruce -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/everything-list/CAFxXSLTvrjTCu0-huP7nCEQbbfo6eMZ7Tvt2mQtJwDqzVpyP_g%40mail.gmail.com.
