On Thu, Dec 23, 2021 at 9:55 PM smitra <[email protected]> wrote: > On 22-12-2021 22:54, Bruce Kellett wrote: > > On Wed, Dec 22, 2021 at 10:12 PM smitra <[email protected]> wrote: > > > >> On 21-12-2021 22:48, Bruce Kellett wrote: > >>> > >>> In general, that is not true. When both Alice and Bob set their > >>> polarizers randomly while the particles are in flight, the fact that > >>> Alice might get |up> tells her nothing about what Bob will get at some > >>> randomly different polarizer orientation. You seem to be stuck with > >>> thinking in terms of parallel polarizer orientations. > >> > >> It's not true only when the polarizers are orthogonal. Whenever the > >> polarizers are not orthogonal, Alice will gain some amount of > >> information about what Bob will find given the result of her > >> measurement. For Bob, the probability of finding up or down are always > >> 1/2, but after Alice makes her measurement, the conditional probability > >> of what Bob will find, given her measurement result will not be equal to > >> 1/2 for both outcomes if her polarizer was not orthogonal to that of > >> Bob, so Alice will have gained information about Bob's > measurement result. > > > > The conditional probability you refer to is defined only non-locally. > > > > There are no nontrivial nonlocal effects in the MWI.
That is what remains to be proved. Once you specify > how Alice and Bob decide to choose their polarizers, you can analyze the > flow of information As I understand it, Deutsch and Hayden attempted this in arXiv:quant-ph/9906007. This idea has proved to be unsuccessful. One of the problems being that their construction bears little relationship to what happens in the laboratory. One can make up toy models to demonstrate almost anything. However, in order to be useful, such models must be closely tied to laboratory experience. If you do that within the MWI framework there won't > by any nonlocal effects apart from common cause effects where > information created at one spacetime point ended up travelling in two > directions via local processes and ended up creating correlations in > spacelike separated systems. > > >>>> In the MWI > >>>> there is no such mysterious gain of information due to the correlation > >>>> being caused by common cause when the entangled pair is created > >>> > >>> Rubbish. If there were a common cause, then that would have to depend > >>> on the final polarizer orientations. And those are not known at the > >>> time of creation of the entangled pair. You are, then, back with some > >>> non-local influence (or retro-causation). > >> > >> The setting of the polarizers will be the result of some physical > >> process. Whatever you specify for that process should be included in the > >> analysis of the problem. But when you do so, it's inevitable that in an > >> MWI analysis, there is not going to be any nonlocal effect other than > >> trivial common cause effects. > As I have said. That is your contention, but it has yet to be proved. The method of setting the polarizers can be included if you must, but this is ultimately irrelevant to the main issues here. It seems that you introduce it only as a distraction. > I see. So in desperation you resort to the superdeterminism escape. > > MWI is not necessary for the understanding of the correlations of > > entangled particles, as my simple example shows. In an actual > > experiment, the analysis is identical in many-worlds and collapse > > models. The additional worlds in MWI add nothing to the explanation. > > They are, therefore, otiose, and MWI can be discarded. > > > As Jesse Mazer pints out this has nothing to do with superdeterminism. > You can e.g. let Bon And Alice do additional spin measurements on other > (non-entangled) electrons and use the random results of those to > determine the orientation of their polarizers. Thing is that you need to > choose some physical process for this. There is then no appeal to the > setting of the polarizer having been pre-determined in a way to explain > the correlations, so this is not an appeal to superdeterminism. > I am not arguing for superdeterminism. It just seemed that insistence on including the method for setting polarizer angles was akin to the arguments made be advocates of superdeterminism. Collapse models invoke new, as of yet unobserved physics, at scales > where our present theories of physics are very solid. While such > collapse theories could be correct, they are not motivated by an attempt > to solve a problem, like e.g. tensions with experimental results. The > MWI, in contrast, is motivated with problems of standard QM, namely the > unphysical collapse of the wavefunction. > This discussion has nothing to do with one's philosophical preference for non-collapse over collapse models. The issue is whether or not MWI can give a local account of the Bell correlations. A simple analysis based on actual laboratory experience shows that many-worlds cannot accomplish this. Concocting artificial models is a well established path for proving anything at all. Your models must be based in laboratory experience. Jesse's computer models are totally unrealistic, and bear no relation to real experiments. Arguing for collapse models today is like what would have happened if > not Einstein but Maxwell had invited the theory of special relativity. > Some physicists might then have pushed back against that by inventing > the ether to restore the old familiar notion of absolute time. > > Also, collapse models may not even get rid of the parallel Worlds. If > the universe is infinite or is infinite in the temporal direction, then > identical copies of us will exist in an infinite number of different but > similar environments. Collapse will then happen, leading to a definite > outcomes in each sector, but you'll be split among all the different > outcomes in different sectors. The only difference with the MWI is then > that according to the MWI the split must happen, while according to > collapse interpretations, a split may happen depending on the large > scale structure of the universe. > That really is a confusion of ideas, all of which are completely speculative. I think it behooves us to keep a little more to the point. 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]. To view this discussion on the web visit https://groups.google.com/d/msgid/everything-list/CAFxXSLQz9A%3D89H8Vhp6K4xHBObH%2Bbc1Ssp1cu_xM_OUa1_uAHw%40mail.gmail.com.
