On Mon, Aug 19, 2019 at 6:41 PM Bruno Marchal <marc...@ulb.ac.be> wrote:
> On 19 Aug 2019, at 04:02, Bruce Kellett <bhkellet...@gmail.com> wrote: > > On Sat, Aug 17, 2019 at 11:00 PM Bruno Marchal <marc...@ulb.ac.be> wrote: > >> Brent, Bruce, >> >> On 16 Aug 2019, at 22:26, 'Brent Meeker' via Everything List < >> everything-list@googlegroups.com> 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. > 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. > 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. > 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. 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. 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. 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. > 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. This account explicitly keeps all branches of the superposition in play, even though that does not really alter anything. 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 view this discussion on the web visit https://groups.google.com/d/msgid/everything-list/CAFxXSLRfGxyn26xRJ03feO1xTrA-aHSLzsCBBVUbqotP1xeSkg%40mail.gmail.com.
