On Tue, Oct 1, 2019 at 12:53 PM 'Brent Meeker' via Everything List < everything-list@googlegroups.com> 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 < > everything-list@googlegroups.com> 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 < >> everything-list@googlegroups.com> 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 everything-list+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/everything-list/CAFxXSLTvrjTCu0-huP7nCEQbbfo6eMZ7Tvt2mQtJwDqzVpyP_g%40mail.gmail.com.
