On 6 June 2017 at 00:23, Bruce Kellett <bhkell...@optusnet.com.au> wrote:
> On 5/06/2017 8:42 pm, Bruno Marchal wrote: > >> On 05 Jun 2017, at 05:52, Bruce Kellett wrote: >> >>> On 5/06/2017 12:19 pm, Bruce Kellett wrote: >>> >>>> On 4/06/2017 10:05 pm, Bruno Marchal wrote: >>>> >>>>> On 02 Jun 2017, at 03:01, Bruce Kellett wrote: >>>>> >>>>> Your claim appears to be that Bell's theorem is not valid in MWI. >>>>>> >>>>> >>>>> Bell's theorem is valid. His inequality does not even assume QM, but >>>>> just locality. >>>>> >>>> >>>> I agree, but that is not what you were implying above. It seems that >>>> now you agree that the Bell inequalities assume only locality. >>>> >>> >> And a mono-universe, or a conservation of identity of Alice and Bob from >> the beginning to the end of the experience. But that is no more the case in >> the MWI. Everett explains already this when he introduces what will be >> called decoherence. Decpherence is local. >> > > Believe it or not, those things are not relevant to the derivation of > Bell's results. Besides, you simply contradict yourself -- you said exactly > the opposite a line or two ago. > > But these inequalities are violated by experiment. >>>> >>> >> Yes. >> >> That can only mean that the assumption of locality was wrong -- whatever >>>> interpretation of QM you adopt. >>>> >>> >> It means that locality and mono-universe cannot be maintained at once. >> But non-locality is not proved, unless you believe that Alice and Bob >> remains the same unique person all along, which is necessarlly not the case >> in the MWI of the EPR-Bell situation. >> > > They split, but they retain identity in each branch. > > I think that this important part of recent exchanges might have got lost >>> in the welter of to-and-fro. >>> >>> Bruno accepts: >>> >>> 1. Bell's theorem (and the associated inequalities) are valid in MWI. >>> 2. Bell's theorem assumes only locality (not even QM -- it is valid in >>> classical physics also). >>> >> >> Locality, and identity preservation (or mono-universe, or counterfactual >> definiteness: all go away with Everett). >> > > No, they do not. And these are not essential for Bell's derivation anyway. > > 3. The Aspect et al., and subsequent, experiments demonstrate that the >>> Bell inequalities are violated. >>> >> >> Yes, but only from the points of view of one branch. But when we look how >> the singlet state is handled in the MWI, the correlation are apparent, but >> the results obtained by space-separated person does not need to be >> correlated, in some absolute sense, they need to be correlated with anyone >> interacting with both of them later, so that in all branches, it will look >> like if there has been an action at a distance, but all influence and >> information flows, and splitting, go at a speed lower than light. >> > > It might have escaped your attention, but Alice and Bob need not be > spacelike separated when they do their measurements on the spin singlet. > For example, Bob could be at all times in Alice's forward light cone, so > they are always in the same world -- as Alice splits with her measurement, > Bob splits along with her, so that when he does his measurement he is in > the same world as Alice with her result as recorded in her lab book. > > A lot of your prevarications over EPR stem from a failure to realize that > spacelike separations are not essential -- the proof is valid for *any* > separation. Usually, spacelike is assumed only to assure the independence > of the measurements made by Alice and Bob. But as long as they are truly > independent, they can be at any separation. > > It seems to follow with the force of simple logic that: >>> >>> 4. Experiment shows that QM is non-local, even in MWI. >>> >>> Bruno appears to reject this conclusion. I conclude that Bruno's >>> position is incoherent. >>> >> >> I will again ask you to tell me what is wrong with Michael Clive Price >> explanation ... except that the web page is not available. >> > > I have been through this before. I looked at Price again this morning and > was frankly appalled at the stupidity of what I saw. Let me summarize > briefly what he did. He has a very cumbersome notation, but I will attempt > to simplify as far as is possible. I will use '+' and '-' as spin states, > rather than his 'left', 'right'. > > He write the initial wave function as for the case when you and I agree in > advance to have aligned polarizers: > > |psi_1> = }me, electrons,you> = |me>(|+-> - |-+>)|you> > = |me, +,-,you> - |me,-,+,you> > > He says that at this point no measurements have been made, and neither > observer is split. But his fundamental mistake is already present. > > A little test for you: what is wrong with the above set of equations from > a no-collapse pov? > > skipping some tedium, he then gets > > |psi_3> = |me[+],+,-,you[-]> - |me[-],-,+,you[+]> > > where the notation me[+] etc means I have measured '+', you[-] means you > have measured '-'. > > He then claims that the QM results of perfect anticorrelation in the case > of parallel polarizers has been recovered without any non-local interaction! > > Spoiler -- in order to write the final line for |psi_1> he has already > assumed collapse, when I measure '+', you are presented *only* with '-', so > of course you get the right result -- he has built that non-locality in > from the start. > > He then considers the case of polarizers initially set at right angles, > but he makes exactly the same mistake so I will not go through that case > here. > > > 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. 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? David > I recently re-posted here a summary of these discussions from last year. A > similar analysis that I posted here last year of the papers by Rubin found > similar mistakes. > > It seems obvious that both Bell and EPR assumes the identity of the >> observers, who prepare the singlet state and measure the correlation, but >> this is simply made false in the MWI. >> > > The trouble here is that you have simply presented an argument from > authority, and have used some less than fully competent authorities. > > I suggest you look at the recent review of Bell non-locality that I > mentioned before.: Brunner et al., (arxiv:1303.2849). I attach the > important sections from this paper here for your convenience. > I particularly draw your attention to the footnote on page 2 of my excerpt: > "It is relatively frequent to see a paper claiming to "disprove" Bell's > theorem or that a mistake in the derivation of Bell inequalities has been > found. However, once one accepts the above definition of the independence > of the measurements, it is a quite trivial mathematical theorem that this > definition is incompatible with certain quantum predictions. Such papers > are thus either using (possibly unaware) a different definition of locality > or they are erroneous." > > I must admit that I prefer the opinion of competent physicists such as the > author of this review over flaky derivations such as those by Price, > Tipler, Rubin, and those who follow them > > 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. 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