On 6 June 2017 at 01:46, Bruce Kellett <bhkell...@optusnet.com.au> wrote:
> On 6/06/2017 10:21 am, David Nyman wrote: > > On 6 June 2017 at 00:23, Bruce Kellett < <bhkell...@optusnet.com.au> > bhkell...@optusnet.com.au> wrote: > >> On 5/06/2017 8:42 pm, Bruno Marchal wrote: >> >> I am not alone skeptical about inferring that the violation of the Bell >>> inequalities shows action at a distance. What is wrong in Deutsch and >>> Hayden? What is wrong in Rubin (Rubin, M.A. Found Phys Lett (2001) 14: 301. >>> doi:10.1023/A:1012357515678), or in Maudlin's book? >>> >> >> They don't all necessarily make the same mistake as Price, but they all >> make equally silly mistakes, and build in the non-locality without >> realizing it. Last year I analysed the argument by Tipler >> (arxiv:quant-ph/0003146v1) in detail and showed where he made exactly this >> mistake of building the non-locality in without realizing it. > > > Bruce, I'm reading The Emergent Multiverse by David Wallace at the > moment. He's well known as a prominent theorist of MWI. I don't know > whether he falls under your definition of competence in this area, but as > far as I've understood him, he fully accepts that MWI must be consistent > with QM in all respects, including of course nonlocality. The distinction > he makes is between nonlocality and the question of whether this requires > us to think in terms of instantaneous transfer of information at > greater-than-light speed, or "action at a distance". I can't say I've been > able to get my head around his full exposition of this yet, but I'm pretty > sure he doesn't go along with your exposition of Price's seemingly faulty > version of this. > > > It is interesting that Wallace has come to this view. He, with Deutsch, > was one of those who attempted to argue that MWI restored full locality. > They also tried to derive the Born Rule from within MWI, and failed in that > too. > > I do not know the book you refer to, but if Wallace now accepts that QM > and Bell implies non-locality, then I fully agree. I have always argued, on > this list and elsewhere, that non-locality does not mean the instantaneous > transfer of physical information -- if you think about it, that would, in a > sense, be a local, albeit FTL, effect. The core of the quantum singlet > state is that it does not involve the physical positions of the particles. > It is expressed in configuration space, and the difficulties appear to > arise from interpreting configuration space as though it were the same as > ordinary 3-space. What has been said is that the singlet state is always > local in configuration space, which translates to non-locality in 3-space. > And this without some FTL information transfer. If there were FTL > information transfer, then that could be manipulated to give FTL > signalling, and there are all sorts of theorems in QM that show that FTL > signalling is not possible. > > But it seems as though Wallace is coming to see these things as do the > majority of other physicists -- non-locality is intrinsic to quantum > entanglement. > Wallace uses the term non-separability. He makes an analogy, to a certain extent, with the ontology of field theories such as electromagnetism, about which he says "The structural complexity of a given electromagnetic field is represented not in the properties of very small spacetime regions (indeed in the limit as these regions become point sized, the field's structure becomes almost trivial) but in the way in which those properties vary across spacetime. Furthermore, this general model is characteristic of pretty much any classical field theory, except that vector fields seem mathematically tame compared to the sorts of mathematical objects used to represent the field values of many classical field theories.". He gives a number of examples of these latter objects including the affine connections of General Relativity. He then goes on from this analogy to propose an ontology for quantum field theory which he calls Spacetime State Realism. I can't really attempt to elaborate on this here. Moving on this basis to the question "Does Everettian quantum mechanics display action at a distance?" he answers in the negative. He justifies this by elaborating on the observation that "In a quantum field theory, the quantum state of any region depends on the quantum state of some cross section of the past light cone of that region. Disturbances cannot propagate into that light cone." To the question "Does Everettian quantum mechanics display non-separability?" he answers in the positive. He justifies this by elaborating on the observation that "Because of entanglement, knowing the density operators of regions A and B does not suffice to fix the density operator of (the union of) A and B. Some of the properties of (the union of) A and B are genuinely non-local: they have local physical manifestations only if we arrange appropriate dynamics.". I can't do justice to his exposition of the above positions in the full text, but they seem reasonably plausible (from my admittedly very amateur perspective) on a first reading. David > > As we know, MWI hypothesises multiple outcomes for each measurement event. > So on this basis, when Alice makes a measurement there is an immediate > split into branches consistent both with the measurement she records and > with its counterfactual partner. The same considerations must apply equally > to Bob. So we now have a spectrum of available branches in which exist > potential pairings of recorded measurements that would be consistent with > QM. The question then concerns which pairings of Alice and Bob we (or they) > should expect to observe in the form of actual encounters for the purpose > of comparing notes. QM tells us that the results of any such observable > pairings must be consistent with violation of Bell's inequalities. Can we > say, in terms of the logic of MWI, why this might be so? > > > Yes. This is essentially the Tipler calculation that I have summarized > elsewhere. It is non-local, but it shows how the different branches arising > from each measurement must always match up to give the correct > correlations. Conceptually, what goes on is easier to understand if you > consider an EPR experiment at time-like separations. Then Bob can always be > in Alice's forward light cone, and there is no ambiguity as to what splits > occur, and when they occur. > > 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 post to this group, send email to everything-list@googlegroups.com. > Visit this group at https://groups.google.com/group/everything-list. > For more options, visit https://groups.google.com/d/optout. > -- 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 post to this group, send email to everything-list@googlegroups.com. Visit this group at https://groups.google.com/group/everything-list. 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