Bruno, I think it is clear that you have no coherent local causal many-worlds account of the EPR correlations. If you did have one, you would have produced it by now. Instead you keep changing the subject and propounding irrelevant truisms as if they were great insights.
So be it. I must admit that I am somewhat disappointed by this. Many people casually claim that many-worlds solves the problem of non-locality, but few even attempt to explain how this works. I thought that you might be able to shed some light on the matter. If you could have done so, it would have given some reason for taking the many-worlds ontology more seriously. As it stands, there would appear to be no reason for believing in the real existence of the other worlds. One can then follow Zurek and use the Everett insights into the primacy of unitary evolution of the wave function, and the quantum basis for the classical world, to investigate how the preferred basis is found (einselection); to investigate the origin of probabilities and the Born rule (envariance); and to explain how the objective classical world emerges from this unitary quantum substrate (quantum Darwinism). As Zurek points out, once you can do this, the real existence of these other worlds becomes irrelevant to physics, and one can safely abandon them as superfluous mathematical superstructure. It seems that the last hope of finding a use for these other worlds as a substitute for non-locality is now dead, and we are left with physics as it always was -- a single classical world emerging from a quantum substrate. There are many who will see this development as a relief from metaphysical nonsense. Bruce On Tue, Aug 20, 2019 at 8:34 PM Bruno Marchal <[email protected]> wrote: > On 20 Aug 2019, at 08:24, Bruce Kellett <[email protected]> wrote: > > On Mon, Aug 19, 2019 at 6:41 PM Bruno Marchal <[email protected]> wrote: > >> On 19 Aug 2019, at 04:02, Bruce Kellett <[email protected]> wrote: >> >> On Sat, Aug 17, 2019 at 11:00 PM Bruno Marchal <[email protected]> wrote: >> >>> Brent, Bruce, >>> >>> On 16 Aug 2019, at 22:26, 'Brent Meeker' via Everything List < >>> [email protected]> wrote: >>> >>> I think you can interpret it as decoherence spreads at light speed from >>> Alice's measurement event and decoheres Bob's system when it comes within >>> the future light cone of Alice's measurement....and vice versa, which is >>> why it needs to assume MWI to maintain symmetry between Alice and Bob. >>> >>> >>> That is my understanding. That explains entirely, it seems to me, the >>> violation of Bell’s inequality in a local, but multi-versal type of >>> reality. When Alice and Bob separates, they simply never meet again, but >>> both can meet their correlated counterparts. Each Alice and each Bob can >>> meet only their correlates, that they enforce by decoherence, at a speed >>> lower than light. >>> >>> >>> But as Bruce says, it's a kind of magic as stated. To not be magic >>> there must be some physical interactions communicating Alice's result to >>> Bob's system: Photons would the obvious candidate, but how exactly do they >>> interact with Bob and his system to make them orthogonal to one of Alice's >>> results and not the other? >>> >>> >>> The state is ud - du, for d = down and u = up, with the usual sqrt(2) = >>> 1. >>> >>> The idea is that when Alice see her photon being u, she knows that >>> whatever she will be interact with will be consistent wit her photon being >>> u and with bob photon being d, including the bob she could ever manifest >>> herself relatively. >>> >> >> That is exactly the magic that needs to be explained. >> >> >> I don’t see this. ud - du predicts this, by the quantum formalism. >> > > Yes. And that is the standard non-local argument. Don't forget that, as > Maudlin points out, the quantum wave function is, itself, a non-local > object. > > > I can hardly imagine a notion more local than a wave. > > But, yes, if a wave describe an amplitude of probability concerning a > single particle, then, if that wave collapse, it can only do this in a > highly non-local way. That was the reason why Einstein criticise Bohr’s QM, > notably in 1927 at the Solvay Congress in Brussels, and which lead to EPR. > > I think Maudlin said that the quantum wave is a non-local object in the > context of the “one-world” assumption. In my edition of his book on > non-separability he explains this is no more true in the non-collapse > theory (but you said he changes his mind on this?). > > > > > > > >> And reciprocally with Bob. It is just that when Alice see u, it means >>> that her accessible histories will all be consistent with u for her photon >>> and d for bob’s photon. If Bob sees u to, that will be the same: he knows >>> that he will meet Alice having seen d. Both possibilities will exist. The >>> Alices seeing u will access a world with Bob seeing d. The Alice seeing d, >>> will access a world with Bob seeing u. The same for Bob. Both Alices and >>> Bobs observations will spread toward each other at the speed of light, or >>> slower, and no physical influence exist at all. They both only localise >>> themselves in the multiverse, at different possible cosmic branches. >>> >> >> What makes a history "accessible"? You have offered only magic to rule >> out histories that violate the basic conservation rules. >> >> >> I don’t see this at all. (I assume QM here, not mechanism). >> > > I don't know how I can make you understand that just multiplying the > number of "worlds", and appealing to some obscure notion of "histories", > does nothing towards providing a coherent local causal account of the > observed correlations. > > > It is not the multiplication of worlds per se which solves the problem, it > is the fact that the "multiplication of worlds” is itself a local > phenomenon. When Alice measures her particle, and Bob measure his particle, > they both “multiply” their accessible worlds, in which both will met > eventually their correlated counterparts, whatever the results their could > be said to have obtained initially (if we could give some sense for this). > > > > > > >> The magic comes only from the idea that there is one Alice and one Bob, >>> which would make this reasoning obviously invalid, or introduce faster than >>> light physical influence. >>> >> >> The argument does not depend on any "one world" assumption. The problem >> is clearly present even in the Everettian setting, when there are copies of >> Alice and Bob who see each result. These always exist, since both up and >> down results are always possible for any measurement on the separated >> singlet particles. >> >> >> I don’t see this. Alice and Bob have prepared the particle together (or >> by some entanglement swapping technic), the state ud-du require the >> correlations, in all base. Once separated, they can only access to their >> correlate parts, which requires the “creation” of “new” Bob and Alice. >> > > Any copies of Alice and Bob that there might be are created at the time > they make their measurements and observe (record) their results. This > happens at space-like separations, so any correlations are necessarily > non-local in origin. All else is magic or mysticism. > > > The splitting or differentiation of the “world” is a local phenomenon. > > FTL action at a distance seems more magic to me than a local > differentiation of histories. > > > > > > >> It is up to you, if you think that some FTL influence occur, to explain >> why and how. >> > > Don't try and divert attention from your own failings by claiming that it > is all my responsibility. This is about you, and your failure to provide > the advertised local causal account through many worlds, that is at issue. > > > The wave propagate locally. Everything is local at all “space-time” > situation. You continue to talk like if the wave collapsed when we do > measurement, but that does not occur once we abandon the idea that any > collapse ever occur. > > > > > > A quantum state does not describe a world, but is only an indexical map, >>> for a subject, of the histories that he/she can access to. ud-du means >>> only, to Alice and Bob, that they will always means their corresponding >>> correlated counterpart, whatever they found. >>> >> >> Given the miracle that occurs at this step in your account. >> >> Which miracle? I just use the fact that once a superposition is there, it >> never collapse. It is the collapse which would be magical. >> > > Collapse is irrelevant. > > > I don’t see this. If the wave collapse, it has to be non-local. Without > collapse, the multiplication of worlds is a local phenomenon spreading at > the speed of the possible local interaction with the environment. > > > > > > This is just another of your diversionary tactics. You claim that there is > "some collapse" if you have no answer to the points being made. I have not > made any collapse assumption; all along I have been working in a > many-worlds setting. I maintain that this does not result in a local > account. You claim different, so prove it by providing this local account. > > > > My feeling is that you interpret the multiplication of worlds like if that > was an instantaneous process, but it is a local one: like a front wave made > of many single waves. The singlet sate is for personal use only: it says to > Bob and to Alice which types of Alice and Bob they can meet in their > future. In a sense, once separated, the “original” will never meet again: > only their counterparts in the relevant histories with a measure given from > the state. > > > > > > Even if we give sense to “they both find u”, each of us will meet they >>> counterparts, which they can interact with when meeting again, having >>> found d. >>> >> >> You are not convincing anyone other than yourself here, Bruno. >> >> >> I don’t think so. I am not sure if you are not the only one, perhaps with >> one other, who believes that the violation of Bell’s inequality entails >> physical action at a distance (which have no meaning for me in a >> relativistic context). >> > > Don't change the subject, and ascribe to me views that I have never held > and have never advocated. There is no FTL physical action. The > no-signalling theorems guarantee this. > > > Existence of FTL is weaker than No-signalling, but with some amount of > physical realism, it is about the same. > > If you agree that there is no FTL when there is no collapse, then again, I > am no more sure we disagree on anything here. > > > > > >> Both EPR and Bell assumes that "Alice and Bob” are well defined and keep >> their identity throughout the experience, which indeed would require some >> FTL influence, but I don’t see that FTL when we keep all branch of the >> superposition into account. >> > > Your conclusion does not follow from your premises. I have given a clear > account of how Alice and Bob can maintain their identities, even though > they split according to the results obtained, and still meet to exchange > data and calculate non-local correlations, even though there are no > physical FTL effects. > > > In absence of collapse. > > > This account explicitly keeps all branches of the superposition in play, > even though that does not really alter anything. > > > If there is a collapse, it has to be non local, as Einstein understood > very early. Only differentiation of worlds at lower speed of light can > maintain the localness of the actions together with maintaining the quantum > statistics right in the mind of all Alices and Bobs. > > Bruno > -- 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]. 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