> On 4 Aug 2018, at 03:09, Bruce Kellett <[email protected]> wrote: > > From: Bruno Marchal <[email protected] <mailto:[email protected]>> >>> On 3 Aug 2018, at 13:43, Bruce Kellett <[email protected] >>> <mailto:[email protected]>> wrote: >>> >>> From: Bruno Marchal <[email protected] <mailto:[email protected]>> >>>> On 2 Aug 2018, at 12:54, Bruce Kellett <[email protected] >>>> <mailto:[email protected]>> wrote: >>>>> >>>>> From: Bruno Marchal <[email protected] <mailto:[email protected]>> >>>>>>> On 1 Aug 2018, at 21:12, Brent Meeker <[email protected] >>>>>>> <mailto:[email protected]>> wrote: >>>>>>> >>>>>>> >>>>>>> Indeed. But the common-cause explanation doesn't work for all choices >>>>>>> of measurement angle. >>>>>> >>>>>> It does. Well, it does not if you assume only one Bob and Alice, but the >>>>>> whole point is that it does if you take into account all Alices and Bobs >>>>>> in the multiverse. QM explains why in all branches, Alice and Bob will >>>>>> see the violation of Bell’s inequality, and this without any physical >>>>>> instantaneous causality on a distance. The MW theory is NOT an hidden >>>>>> variable theory in the sense of EPR or Bohm. The MW theory is based on >>>>>> the first person indeterminacy, and illustrate the first person plural >>>>>> aspect (contagion of duplication). Hidden variable theory in the sense >>>>>> of de Broglie, Böhm, or Einstein incompleteness are pure 3p theories, >>>>>> not involving the role of the person in the picture. >>>>> >>>>> In that case you have a different theory, which is not quantum mechanics. >>>>> You can believe anything you like about your own private theories, but >>>>> you cannot expect others to join in. If we are talking about quantum >>>>> mechanics, then it would be polite to stick to that theory. >>>> >>>> I am talking about Quantum Mechanics without collapse. You are the one >>>> seeming to interpret ud + du as a superposition of worlds with Alice >>>> having a particle in state u (and Bob having the corresponding particle in >>>> state d) with worlds with Alice having a particle in state d (and Bob >>>> having the corresponding particle in state u). That would contradict the >>>> rotational symmetry of the singlet state. >>> >>> The rotationally symmetric singlet is ud - du. The state you mention, ud+ >>> du, is the spin zero component of the triplet, which is not rotationally >>> symmetric. >> >> I meant ud-du, which is the same state as u’d’-d’u’ up to some phase >> e^i*theta. >> >>> >>> You ask how I interpret the singlet in MWI. That is quite simple -- it is >>> the same as in a collapse theory. >> >> ? >> >>> In MWI you just retain all the branches, branches that are discarded in the >>> single world theory. In both cases, the ud - du state is rotationally >>> symmetric when prepared, but that rotational symmetry is destroyed as soon >>> as the spin component of one particle is measured in a particular direction. >> >> In the MWI it is never destroyed. It is just entangled with the memory of >> the observer (or the local environment containing the observer. > > That is a remarkably silly thing to say. The only thing in this context that > is rotationally symmetric is the singlet state itself.
It never disappear if there is no collapse. It leads to a more general singlet state. > The laboratory in which it was prepared is not rotationally symmetric; the > apparatus that prepared it is not rotationally symmetric; the technician who > operated the preparation apparatus is not rotationally symmetric; the > experimenter who measures it is not rotationally symmetric. Of course. > So as soon as the singlet interacts with any of these things -- becomes > entangled with a non-symmetric object -- then the rotational; symmetry of the > state is lost. I don’t see that. It is lost in each branch, not in the global wave. > This is just elementary physics of symmetry principles. > >> Alice (ud -du) = Alice ud - Alice du = Alice see up ud - Alice see down ud > > There, can't you see what you have just done? You have explicitly invoked a > collapse! (And there is a sill typo in the last part of the equation OK. Sorry. > -- it should read 'Alice see down du'. Alice can't see down from the ud > component!) > > But if we write this out a bit more explicitly so that the tensor product is > evident (using Dirac notation) we have: > > |Alice> (|u>|d> - |d>|u>) --> |Alice sees up>|u>|d> - |Alice sees > down>|d>|u>. Right. > > I have used the arrow (-->) to indicate that this step involves an > interaction between the singlet and Alice and her apparatus -- which > necessarily breaks the symmetry. (It is not actually an equality.) But you > have collapsed the wave function in this step, because 'Alice sees up' only > on the first half of the original wave function, so that Bob necessarily sees > only the |u>|d> portion of the original symmetric state when Alice sees up -- > he then necessarily gets the correlated (Bob sees down) result when Alice > sees up (for aligned measurement axes). Similarly, in the second part of the > equation, 'Alice sees down' collapses the wave function to the |d>|u> > component, meaning that Bob necessarily sees only |u>. But there has not been any collapse. Alice sees a collapse, and Bob sees a collapse. In case they get non correlated result, which is quite probable when they are space-like separated, they will never meet again. They found themselves in distinct branches, and each of them, when coming back will see only “their” counterpart, who have the right correlated particles. Measurement are only local interaction. They don’t magically act on anything space-like separated, but Alice will only meet a Bob who has got the time to be contaminated by her “apparent collapse”. > > This is the mistake that Price makes in his Q32 that you attached. I have > pointed this out many times, but it seems to have passed you by. Maudlin get the same conclusion for the many-mind version, and honestly, I don’t see anything wrong with their analysis. > This builds in the non-local collapse of the original singlet wave function > right at the start of your argument. ? You lost me. There is no collapse at all, ever. Only a local entanglement spreading at subliminal speed through local interaction. > You split the wave function following Alice's measurement so that Bob sees > only the correlated part So that the only Bob Alice will ever meet (by local means of course) got the correct correlated state. Same for Bob. Each of them will meet their counterparts, not the “original person”, which makes no sense in Everett (nor in Mechanism). > -- he doesn't see a non-collapse singlet state! The argument here is made for > aligned measurements, but the same argument applies to the general case of > non-aligned measurements. Tipler spells out the general case, but he makes > exactly the same mistake -- he builds in the non-local collapse without ever > being aware of what he has done -- just as you are clearly unaware of what > you have done. Where is that non local collapse? I don’t see any collapse. Alice just makes a measurement and discover in which partition of the multiverse she belongs. It is the same as in the WM-self-duplication. > > >> Bob(ud -du) = Bob ud - Bob du = Bob see down ud - Bob see up ud >> >> Alice and Bob get their opposite spin, without transmission of action faster >> than light, still less instantaneous. > > You have built in an instantaneous collapse. Get used to it!!!! Where is that collapse. I frankly don’t see it. > >> If they measure in arbitrary direction, or the one to verify Bell’s >> inequality violation, the reasoning is more long, but see Price (below) for >> a good approximation. > > As stressed. Price makes the same mistake of building in a non-local collapse > in the general case as well. You fail to show me which collapse you are talking about. You confuse the different Bobs which appear in that wave evolution. Most Bobs will never “fuse” with the “original” Bob, and will never meet the “original” Alice. But each will eventually meet their correct (for the correlation) counterparts, as the singlet state enforce. I think that the problem comes from you still seeing some collapse when they are none. > >> If in some branches there has been a FTL action, you might need to explain >> to me how that is possible, and why to postulate this. It does not follow >> from EPR which assumes definite results for a measurement, where we get only >> definite result in the memory of the observer(s). > > Trying to bring in counterfactual definiteness and the fact that this happens > only in the memory of the observers is just blowing smoke to confuse the > issue. That is a symptom that you might not try to understand what I say. > You have got it wrong, Bruno. Why not man up to the fact! > > > >>> The external magnet is not rotationally symmetric, so as soon as it >>> interacts with the singlet, the overall rotational symmetry is lost. That >>> is surely obvious. >> >> The overall rotational symmetry is lost for the individual particles, but >> not for the state Alice + two particles (even if far apart). I mean the >> state >> (Alice see up ud - Alice see down ud) >> is still rotationally in variant. > > Rubbish. You appear not to have the remotest understanding of what rotational > symmetry involves. How could the symmetry be lost? The symmetry is that ud -du = u’d-d’u’ up to a phase factor. So Alice-see-up ud -Alice see-dow du = Alice-see-up' u’d’ - Alice-see-down’ d’u’) are the same state. Of course, once she decide to measure in some direction, she will end up with the right proportion and the two description of the sate lead to the same local prediction (up or down), telling her in which part she belongs in the multiverse. But the rotational symmetry has not disappeared. It only enlarge itself, so to speak. > > >>> That is why I don't understand why you go on about infinities of Alice's >>> and Bob's who can measure in any direction continuing after the first >>> measurement interaction. >> >> It only needs to the entanglement of the observers with the particles. No >> rotational symmetry is lost, except for the first person pop of the >> observer, but that is only because of their ignorance or abstraction from >> the real quantum state. You persist talking like if some collapse did occur >> after the measurement, but that never happens. So when we get (Alice see up >> ud - Alice see down ud), that is still equal to (Alice see up u’d' - Alice >> see down u’d’), as no collapse have occurred. We keep an infinity of worlds >> where Alice found always up, but with different spin direction. If the >> choice of direction was decided or not change nothing to this: because >> (Alice see up ud - Alice see down ud) = e^i.theta (Alice see up u’d' - Alice >> see down u’d’), and the phase factor would not change the measurement that >> anyone could do in principle on the overall state (which would be >> technically difficult to here, but that is not relevant for our attempt to >> agree (or not) on the interpretation of the MW theory. > > You have used the rotational symmetry of the (|u>|d> - |d>|u>) state, but as > soon as this state interacts with the non-symmetric Alice, the overall > symmetry is lost. Alice get entangled in in the singlet symmetrical state. > Sure, Alice could have measured at any angle transverse to the direction of > motion. But the point is that she actually made a measurement at only one > (randomly chosen) angle. So the interpretation of the combined state after > entanglement with Alice and the rest is different. This is known as the > contextuality of measurement. No problem. > > > >>> The symmetry is lost, so there can only ever be four worlds: the uu, ud, >>> du, dd, worlds that I have been mentioning all along. These are the worlds >>> that survive from one measured singlet pair in MWI. Each branch of this can >>> be considered a single world, and since the branches are disjoint, the >>> relevant statistics must be separately satisfied in each such branch. >> >> That survive in the mind of Alice and Bob, when they have decided the >> direction in advance, I can agree with this, but no worlds has ever >> disappeared, and indeed, Alice could have measure u’/d’ instead of u/d, and >> that plays a role to explain the violation of Bell’s inequality in the local >> MW way, like the one by Price (which we have discussed, and eventually you >> did agree that there is no FTL, just inseparability). > > Sure, Alice and Bob measure along randomly chosen axes. This is necessary to > observe the violation of the inequalities experimentally. And the > inequalities are a consequence of the non-separability of the state -- there > is no FTL information transfer. But the measurements do collapse the state > instantaneously so that the measurement at one end influences the > probabilities of the results that can be obtained at the other end. I don’t understand. I agree that if such collapse occur there is FTL influence, even if there is still no FTL information transfer possible. But the are discussion the MW where there is no collapse at all, so I fail to see any FTL influence at all. > As I say, there is no FTL transfer of physical information. How you > interpret this instantaneous influence at spacelike separations is a personal > matter. But there can be no instantaneous signalling, so the situation > respects special relativity. So you can have no basis for complaint on that > score -- it does not violate relativistic covariance. If there is a FTL physical influence, even if there is no information transfer possible, it leads to big problems with any reality interpretation of special relativity, notably well described by Maudlin. Maudlin agrees that many-mind restore locality, and its “many-mind” theory is close to what I think Everett had in mind, and is close to what I defended already from the mechanist hypothesis. To be sure, Albert and Lower Many-Minds assumes an infinity of mind for one body, where in mechanism we got an infinity of relative body for one mind, but the key issue is that all measurement outcomes belongs to some mind. The measurement splits locally the observers, and propagate at subliminal speed. > > >>> It is not actually very difficult to understand once you have broken the >>> initial symmetry. A series of trials on such singlets will just lead to a >>> branching tree of 2^N copies of matched Alices and Bobs. It is the fact >>> that they always interact with the components of the same singlet state in >>> each trial that keeps the worlds in order. But the measurements that each >>> make are made non-locally. >> >> Well indeed, and that leads to Price “psi-3”. The measurement are local, but >> the splitting of the “universe” propagate locally in all circumstances. > > Price is an idiot. He uses collapse without being aware of the fact. You keep saying this, but I really don’t see any collapse mentioned or described in his reasoning, nor in mine. > >>> And the relative probabilities of their separate results (probabilities of >>> the 'worlds' or 'branches') depend on the non-locally set relative >>> orientation of their measurements. Bell's theorem is then just the >>> observation that the observed correlations cannot be reproduced by a local >>> hidden variables, such as would represent a 'common cause' that is carried >>> along from the point of creation of the singlet >> >> In one world. But in The MW the common cause is made in all words, and >> propagate locally to the correlated state in each branches. See the Q32 in >> Price's FAQ. We can discuss it again step by step. Bell’s theorem discard >> local hidden variable which would determine the state in each branch, or in >> the unique reality. That does not happen, as Alice and Bob have a >> trans-world identity: as long as they have not measured their spin, or got >> the spin result communicated, they exists on different world/branches >> simultaneously. May be this is what you are missing. > > Maybe I am not missing anything, and you are just talking rubbish. Of course. But that is a universal argument. It is not valid. > > >>> . Bell's theorem applies to each branch in the many-worlds superposition >>> and cannot be deflected by appeals to counterfactuals or any such >>> irrelevance. >> >> I guess you mean that in each branch the violation of Bell’s inequality >> occur. > > No, I mean what I say. Bell's theorem applies in every branch, But is a result which, if we enforce locality, can only be explained by the MW. > so local accounts are impossible in every branch. I don’t think so. It is impossible only if we abstract from the fact that Alice and Bob get all correlated result in all directions when choosing a (quantum, say) random direction. > Which means that locality is violated in any and all branches, and so in the > MWI wave function as a whole. The schroedinger equation is a local sort of diffusion process. I can emulate perfectly its solution (unless those based on a non computable parameter of course) with a classical computer, and if I interview all Bobs and Alice pairs obtained in each possible branches, they all test positively the Bell’s violation, and of course, without any action at a distance, as we see this at the outset in this scenario. Maybe that is the simplest way to see that no FTL needs to occur to get the quantum correlations. > You appear to fail to understand the way in which superpositions are handled > in ordinary quantum theory -- what happens for a typical branch happens for > the whole. That is ambiguous. Honestly you fail to convince me of any physical influence at a distance brought by Bell’s inequality violation when studied in the MW. Bell and Aspect works remain for me only decisive evidence that collapse never occurs, i.e. an evidence for Everett or some variants. Bruno > > Bruce > > >> I agree. But the reason why that occurs without any FTL is typically due to >> the trans world identity of Alice and Bob. >> >> 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] > <mailto:[email protected]>. > To post to this group, send email to [email protected] > <mailto:[email protected]>. > Visit this group at https://groups.google.com/group/everything-list > <https://groups.google.com/group/everything-list>. > For more options, visit https://groups.google.com/d/optout > <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 [email protected]. To post to this group, send email to [email protected]. 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