> On 5 Oct 2019, at 07:14, Bruce Kellett <[email protected]> wrote: > > On Sat, Oct 5, 2019 at 1:10 AM Bruno Marchal <[email protected] > <mailto:[email protected]>> wrote: > On 3 Oct 2019, at 13:31, Bruce Kellett <[email protected] > <mailto:[email protected]>> wrote: >> And there is no FTL action -- that would be a local hidden variable causal >> explanation, and Bell rules that out. > > This I do not understand, unless you bring t’Hooft super-determinism. In a > unique universe, the violation of BI requires that when Alice do a > measurement she influences and change the “map of the accessible reality” of > Bob. They still cannot do signalling, but, with or without hidden variables, > Alice does restrict instantaneously the state available Bob. Withe MW, as > long as the light has not entangle Bob, Bob can make a measurement entangling > him so other Alice of the multiverse. Everyone will agree with what the > singlet state predicts, and no FTL signalling, nor influence has to occur. > > You contradict yourself, Bruno. You say "when Alice do a measurement she > influences and changes the 'map of accessible reality' of Bob”.
Yes, of course, but that influence propagate at a speed slower than light, but successive entanglement “contagion”. > Then you say "Everyone will agree...no influence has to occur.” You confuse the Bobs to whom Alice can access, to the all Bobs, including those Alice will never been able to access. > > I think your complete failure to understand the non-local entangled state (Semantic play) > -- the fact that the wave function itself is non-local -- is at the root of > all your misunderstandings, and leads you into these contradictory positions. No, you are not understanding what I said. Reread the post and the full explanation. > Let us start again. Consider the entangled singlet state that we have been > talking about: >> |psi> = (|+>|-> - |->|+>)/sqrt(2). > This refers to two spacetime locations; You can’t at the start impose your own interpretation. You know that I disagree with this interpretation since the start. The singlet state refer to a continuum of relative worlds accessible to all Alice and Bobs sharing the entangled particles. > let us call them (t1,x1) and (t2,x2), where the x1 and x2 stand for > 3-vectors. The spacetime interval between these particles or events when > measured, is s^2 = (t1-t2)^2 - (x1-x2)^2. When s^2 > 0, the separation is > time-like, and when s^2 < 0, the separation is space-like (in the (+,-,-,-) > metric that I am using. When Alice makes her measurement, she gets, say, 'up’. Now, all Alice get some result, some get ‘down' to. > According to the above non-separable wave function, that means that Bob gets > only the ket |->, That is vague. It means that Alice will access to the Bobs who get that state, and never access to the Bobs who did not got it. > in the basis of Alice's measurement. Similarly if Alice gets 'down', Bob must > measure the |+> ket, in Alice's basis. By rotating these kets into his local > measurement basis, Bob gets 'up' or 'down' with the required probabilities. … relatively to their corresponding Alices, only. > > This is a what your statement "when Alice do a measurement she influences and > changes the 'map of accessible reality' of Bob" means. And I agree with this. I am not sure, because that influence never get higher than the speed of light. Bob could find a non correlated state, and that will mean that such Bob and Alice are in different worlds, and will never meet. The state just describes their possible relative states. > So (this all assumes, without loss of generality, a frame in which Alice's > measurement is first) Alice's measurement does inevitably affect the state > that Bob can measure. Which Bob? She does not affect Bob’s state “physically”, she just learn that she is in a universe in which she can access only to the Bob who will find the correlated state, and never access to the Bob who get different states. No FTL influence. If there is only one Alice and Bob, then there would be FTL influences. > The question then is, how does this effect come about? What is the mechanism? > You appear to be only able to think of some FTL influence. No. You are the one inking this. With the MW, at no moment Alice change the state of Bob. She just change her own map of histories available. She knows that she can no more met a Bob with another state than the correlated one. That is why I take Aspect experience as an evidence of the other worlds, as I do not give any sense to any FTL influence. > But that cannot work. There are a lot of problems with such an idea. Apart > from violations of special relativity, it would involve the exchange of some > particle or tachyon that conveys Alice's result and polarizer orientation to > Bob *before* he makes his measurement. Dynamics for that might be > conceivable, but there is a problem in deciding whether it is a particle or > an FTL tachyon that must be exchanged. Notice that when this information has > to be sent out from Alice's measurement, Bob still has not made his > measurement, and there is no way at the spacetime point (t1,x1) to know when > Bob will make his measurement. It could be at either space-like or time-like > separation, s^2 > 0 or s^2 < 0, and there is no way of knowing, so there can > be no suitable dynamics that will send a particle or a tachyon appropriate to > the situation (because the situation is unknown at the relevant time). I agree. No FTL, but if the collapse exist and is a physical phenomenon, that violation of Bell’s inequality make non-locality into FTL influence. That is why I reject the uniqueness of Bob and Alice. > > There is an additional dynamical problem in understanding how this particle > or tachyon conveying Alice's information is actually going to affect Bob's > state when it arrives there. If the correct statistics are to come out at the > end, it would seem that this intermediate particle must suppress that part of > Bob's state that is inconsistent with Alice's result. I leave the design of > such dynamics to you -- it is beyond me to even begin to imagine it. On top > of this, there is the problem that in some other frame, Bob's measurement is > first, so his measurement must affect the joint state in a symmetrical > way!!!!! > > I think this goes beyond impossibility to the point of absurdity. That is my point, exactly. > > So what are we left with? I think we can rule out FTL interaction, or even > sub-light speed interactions for time-like separations, because there are too > many contradictory requirements on such a particle exchange of information. > But the influence must occur, because the final correlations can only be > explained in that way. (Attempts to explain the correlations away by MWI, or > further interactions when the light cones overlap, have all failed. Nope. You have not shown this. > Mainly because there are no relevant interactions at the point of overlap of > the future light cones from the separated measurements.) > > We are left with a non-local influence, or interaction. Where by non-local, I > mean precisely that -- an action on two separated spacetime points *without* > there being any local causal contact between them, by exchange of particles > or tachyons or whatever. If there were such an exchange, impossible as it > seems, that would be a *local* explanation, because interactions via particle > exchanges are the paradigm of locality. > > I know that this is contrary to all our instincts -- we believe that there is > no "spooky action at a distance". And I know that your rejection of such > action at a distance is why you have always called references to 'non-local' > effects, FTL exchanges. I say explicitly the contrary!!!!!! I reject FTL, and do no need them, thanks to the MWI. You should reread cautiously my post, as you attribute me the very idea that I reject. > I hope it is clear that I absolutely reject that interpretation, and do not > think that any dynamical theory of such FTL exchanges could ever be made to > work. > > Non-locality is exactly what it says -- a non-local influence or interaction > between two points separated in space and time, whether by a space-like or a > time-like interval -- call it "spooky action at a distance" if you must. But > there is nothing spooky about it --no other rational explanation of the > situation is available. So, you are the one introducing the spooky action, and indeed, if there is only one couple Alice-Boob, that is the only solution, but with the MWI, we don’t need them at all, as I have explained, but seems to have misunderstood my post. > > Your further point about an infinity of different possible 'worlds' for Alice > and Bob coming from the rotational invariance of the singlet state is just a > smoke screen, having nothing to do with any rational explanation of what is > going on. … that confirms you have fail to understand my point, as this is crucial in exposing why the violation of BI implies only the necessity of many worlds or many histories to avoid FTL influence. Please reread my explanation in my previous post, as it seems to me that you have missed it. 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 view this discussion on the web visit > https://groups.google.com/d/msgid/everything-list/CAFxXSLSrtLn0CAqN4irNi1NMFgC%3DBW%3DKzpxynH35%2B%3Dyz1voX1w%40mail.gmail.com > > <https://groups.google.com/d/msgid/everything-list/CAFxXSLSrtLn0CAqN4irNi1NMFgC%3DBW%3DKzpxynH35%2B%3Dyz1voX1w%40mail.gmail.com?utm_medium=email&utm_source=footer>. -- 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 view this discussion on the web visit https://groups.google.com/d/msgid/everything-list/30B7ECBC-FF0C-4375-A92D-BFD3D748BA8A%40ulb.ac.be.
