> On 6 Jul 2018, at 14:18, Bruce Kellett <[email protected]> wrote: > > From: Bruno Marchal <[email protected] <mailto:[email protected]>> >> On 5 Jul 2018, at 17:20, Lawrence Crowell <[email protected] >> <mailto:[email protected]>> wrote: >> >>> John Bell proved that any objective theory giving experimental predictions >>> identical to those of quantum theory is necessarily nonlocal. >> >> Assuming a unique reality. I prefer the term “inseparable”, because >> “non-locality” is often interpreted the existence of FTL influence (even if >> they cannot be used to transmit information), but such FTL influence seems >> to me suspicious. Some might disagree, but I have not yet seen a proof that >> any FTL subsists when we abandon the collapse postulate. Bell assumes that >> experiments gives univocal results. > > You might not have seen a proof that non-locality remains when we abandon the > collapse postulate, but that does not mean that no such proof can be given. > > Consider the following scenario. Alice and Bob are given a large number of > entangled pairs, which they measure when they are at large spacelike > separation. Each measurement is made at some angle, and gives a '1' for 'up' > or 'passed', and '0' for the opposite result. Both record the sequence of > such results that they obtain in their individual lab books, together with > the corresponding polarizer orientations. Their lab books then contain a > random sequence of say N, '1's and '0's. There are 2^N possible such > sequences in the many-worlds case, but since each observer keeps the same lab > book for the whole sequence, each series of measurements is necessarily made > in the same one world.
I am not sure I understand the idea of being in the same world when space-like separated. Each time one of them makes a measurement, they are localising themselves in different worlds. The pair state only entails that their measurement will fit accordingly, but Alice will meet the Bobs she is correlated with, and vice versa. It does not make sense to say that Alice will meet the original Bob, or something like that. > Basically, this is because the worlds are disjoint, and the observers and/or > lab books cannot move between worlds. Any measurement entails new differentiation. > > When Alice and Bob meet up at the end of the run of N trials, Each of Alice and Bob will meet only the Bob and Alice prescribed by the result of their measurement. You need to look at the entire wave function. > they take their lab books with them. When they meet they are clearly in the > same Everettian branch. “They” is ambiguous here. > And since their lab books cannot have jumped between branches, the sequence > of results that they each bring must also have all been recorded in this same > one branch. So when they come to use their data to calculate the correlations > between the measurements on their individual particles of the entangled > pairs, they are in exactly the same situation as they would be if they had > assumed a collapse model from the outset. It is like they find themselves in the relevant partition of the mutilverse, but as there has not been any collapse, nothing has needed to propagate after than light. The non-locality, or better inseparability, just assures that whatever differentiation will occur locally, they will have the correlated spin, but at no point are we assured that Alice meet something like the original Bob. The differentiation of the universe develops locally. Once Alice and Bob are space-light separated, they will never meet again after they made local measurement. Each will meet only the corresponding (correlated) person, but there is no reason we can identify them in any single word. > The correlations they observe are necessarily single-world correlations. That comes true after their measurement. But the world have differentiated before. > So the conditions of Bell's theorem are exactly satisfied, I don’t think so. All outcomes are realised (assuming the singlet state, and measurement in any direction). Each Bob and Alice have localised themselves in the corresponding branches, and will met only their corresponding partners, due to the local further separation obtained by their local measurement. That is inseparability. It does not require simultaneous action at a distance. > and since the correlations violate the Bell inequalities, their experiment > has demonstrated the impossibility of a local hidden variable account. I agree with this. That is indeed why a world or an entire history is more like a global “hidden variable”, making sense of those correlation in a local way, with differentiation occurring locally, but always ensuing the existence of the correlation. > They have demonstrated that the quantum correlations require non-locality, > even with Everett's many-worlds, just as Bell proved. I can be OK with this conclusion, unless you imply that in Everett there is still something travelling faster than light. > > And all this happens whether they assume many-worlds or a collapse model. The collapse, if taken in its usual non local (instantaneous) sense, that Einstein criticised already in 1927, would need to act FTL to explain the correlation. But that is not needed in Everett. The states are relative to each others, and further measurement are themselves propagating locally, ensuring than all the many Alices and Bobs will have their spins correlated, but they are no more necessarily related to the original Bob and Alice in any univocal way. Bruno PS Now I read Saibal Mitra comment. I agree with him. He recommend also looking at the entire wave function. It describes infinities of Alice and Bob, each “prisoner” of their branches. Their local possible statistics ensure the correlation of further results of measurements they could each done locally, but I don’t see how Bob or Alice could influence such result (even if not space-like separated, actually). > > 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 [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]. Visit this group at https://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
