> On 16 Jul 2018, at 14:15, Bruce Kellett <[email protected]> wrote: > > From: Bruno Marchal <[email protected] <mailto:[email protected]>> >> >>> On 16 Jul 2018, at 03:57, Bruce Kellett <[email protected] >>> <mailto:[email protected]>> wrote: >>> >>> Other directions are irrelevant to the measurement. The state is not in a >>> superposition of eigenvectors of every possible orientation. >> >> After the measurement is done, and this makes sense only with orthogonal >> measurement from Alice and Bob parts, if not, as I say above, the notion of >> belonging to the same world makes no sense. You tall like if a measurement >> determine which world they are both in, which is true only for particular >> case, when they made the measurement of the spin or polarisation in >> correspond direction. > > This is simply wrong. The state is a superposition of up and down for both > observers, regardless of whether their measurements are along the same axis > or not. The measurement does determine the world in which they will find > themselves when they meet. Just think through the significance of the facts > that they record their measurements in their lab books as they go along; they > are in the same world when they meet; and they can't jump between worlds at > any point. The logical conclusion of this is that the correlated Alice/Bob > pair are always in the same world -- they can't be in any other world because > world-hopping is not allowed. When you can get this point, all the mystery of > EPR correlations vanishes -- they are still non-local, but that is just a > consequence of the non-separability of the singlet state. > > All your worries about FTL are irrelevant -- as I have pointed out many > times. It is all a lot simpler than you seem to want to make it. > > > .......... > >>> And then each tracks along a particular branching tree as recorded by the >>> sequence of up/down results recorded in their lab books. There is >>> absolutely no ambiguity here because neither Alice nor Bob can switch >>> between branches -- they must always be in the same branch. >> >> But when non orthogonal measurement are done, this makes no sense. > > It is the only thing that does make any sense. If you can't track back > through the history of your sequences of branches -- by referring to your lab > book if necessary -- then Everettian branching worlds make no sense. And it > does not matter whether the measurements are orthogonal or not -- they always > end up with Alice and Bob meeting in one world with sequences of measurements > made in that world. Once you can grasp this, Bruno, you might gain some > insight into both Everett and EPR. > > > > >> >> I did. I referred also to Pirce FAQ for a good approximation. > > The Price account assumes non-locality -- as I have pointed out on many > occasions. > >> You are the one invoking the FTL, so I think you are the one who should >> explain where that comes from, and how to test it experimentally. Aspect >> experience test non-locality or inseparability, not FTL. > > You keep accusing me of invoking FTL. I have never done any such thing. All I > have talked about is the non-separability of the state and the fact that the > spin measurements are made non-locally. If you invoke FTL then you are > invoking a non-local hidden variable. I see no need to do this, and never > have done. Stop reading things into my arguments that are not there. > > > > >>> There are not an infinity of worlds, there are only 2^N of them. Of course >>> the correlations come out right for every Alice/Bob pair when they meet. >>> But you have not explained this locally. >> >> That is exactly what the wave explains, when you dismiss all collapse. The >> wave evolves purely locally in the phase space, which is the real >> “mutiversal” reality (up to some gauge nuances). > > The wave function, as Maudlin explains, is itself non-local. So you have not > magically restored locality by invoking the wave function. The wave function > for this state is non-separable = non-local. > > > > > > >>>>> In fact, the multi-branching tree forms a giant superposition, and we >>>>> have just singled out one component of this superposition. There is >>>>> nothing at all mysterious in this -- it is what physicists do all the >>>>> time when they perform calculations in momentum space -- on just one >>>>> component of the superposition that makes up a wave packet. >>>> >>>> That makes sense. >>> >>> That is what I have been saying all along, and this is what removes your >>> worry about 'collapse models' -- they are just a branch from the >>> many-worlds superposition. >> >> >> I don’t see how you would do that when Alice and Bob makes non orthogonal >> measurements. > > You don't understand the underlying quantum mechanics in that case. > > > > >>> The "giant superposition", in so far as it exists, has been spirited away >>> by just looking at a single branch. There is nothing the "giant >>> superposition" can add to the conclusions obtained from just one branch. >> >> ? It changes the result of further possible measurement, notably involving >> Alice and Bob possible amnesia, in theory. Collapse has to be non local to >> make sense, as Eistein made already clear in 1927. It is just worst with the >> singlet state, but here too, avoiding a collapse avoid the need of FTL. > > Avoiding the collapse does not change one thing in relation to the > understanding of EPR correlations, as my analysis of the superposition of the > 2^N copies of Bob and Alice in terms of a single branch within this > superposition shows. Collapse models do nothing more than pick out one > branch in the Everettian tree. Nothing magical about it. We do this all the > time when we disregard the other worlds in everyday life. > > >>>> I don’t see at all why and how any FTL would be needed once we agree that >>>> both the evolution and the tensor product are linear. >>> >>> Stop worrying about FTL. There is no physical FTL mechanism >> >> Then; like last time, se agree on everything! > > I would like to think that this were the case, but you keep coming up with > irrelevancies that contradict the straightforward account of these phenomena. > If you forget about the metaphysics and just concentrate on Alice and Bob > making real measurements and recording them in their lab books, then all > these superfluities vanish. There are no counterfactuals, no worries with > other unobserved worlds, and Bell's theorem goes through exactly as he > intended. Many-worlds does not invalidate Bell's argument. In fact, > deflecting Bell's theorem would do no more than allow for the possibility of > a local hidden variable account. That alone does not prove that many-worlds > is local -- that would still have to be established by developing such a > local hidden variable theory. No one has to date developed such a theory. But > since Bell's theorem has not been deflected, we do not have to worry about > such contingencies.
So we really agree. You have been probably misguided when trying to defend John Clark who claimed that there are still FTL influence in Everett, when the Bell’s inequality relations implies FTL only when we assume unique outcomes of the experiences (i.e. some collapse, or Bohm’s type of hidden variable). No need of patronizing remark either, especially when rephrasing what I was just saying. If you agree that there is no FTL in the many-worlds, we do agree, that was the point I was making to J. Clark. Not sure why you defended it, especially that you have shown implicitly that you have no problem with the step 3 of the Universal Dovetailer Paradox. You might eventually understand that with mechanism, Everett’s task is still incomplete, as we need to justify the wave from all computations, as seen from some self-referential modes (fortunately and constantly implied by incompleteness). Bruno > > 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.
