On Mon, Apr 25, 2016 at 2:58 AM, Bruce Kellett <bhkell...@optusnet.com.au> wrote:
> > > I think you may have missed a salient feature of my little story about > mismatching. The point to which I wish to draw attention is that Alice and > Bob do not know that they are in an impossible world until after they have > compared their experimental notes. In general, in order to do the matching > in a way that will preserve the quantum correlations, you have to know the > probabilities of the combined worlds in advance. But these probabilities > can be calculated only after Alice and Bob exchange notes. > What do you mean by "in advance"? There is no need to do any matching at all until you look at a patch of spacetime that is in the overlap of the future light cone of Alice's measurement and the future light cone of Bob's measurement; and at that point, of course information about what detector setting each one used can be available without violating locality. > > So you need to know the relative orientations and results in order to > calculate the probabilities required to get consistent matchings, but these > probabilities become available only after the matching is complete. In > other words, the model as proposed is incoherent. > To do the matching, you only need the statistics of the fraction of copies of Alice that used each setting, and the fraction of copies of Bob that used each setting, which were determined at the time each one made their measurement. These fractions can depend arbitrarily on what rule each one used to pick their setting--for example, Alice could have used a deterministic pseudorandom algorithm in which case all copies of Alice will have chosen the same detector setting, or she could have used some independent quantum experiment (say, one involving radioactive decay) to choose her setting randomly with whatever probabilities she wanted, like 1/19 chance of setting 1, 5/19 chance of setting 2, and 13/19 chance of setting 3, in which case those will be the fraction of copies of Alice that chose each of those settings. Regardless of what the fractions were for each of Alice and Bob individually, once you reach the first point in spacetime where the future light cones of their measurements overlap, that point *can* have access to each one's statistics without locality (though it doesn't necessarily have to, see below), and given that information it's always possible to match them in a one-to-one way that gives the correct quantum statistics. Do you disagree with this, and if so which point? > > Again, Alice and Bob might try to thwart such a scenario by careful > shielding of their apparatus and not communicating with anyone. Once more, > I don't think quantum mechanics can be stymied by silence and lead > shielding. > Well, if they have some ideal perfect shielding that perfectly prevents any information from getting to a given point in the overlap of the future light cones, then by definition the probabilities for physical events at that point in spacetime won't depend on what result each got, so there's no need to do any matching up of their measurement results at that point. Similarly, in the idealized Schroedinger's cat thought-experiment where the inside of the box is perfectly shielded from leaking any information to the outside, there is no need to match up copies of the experimenter outside with copies of the cat inside, even if the experimenter is in the future light cone of the event of the cat having been saved/killed. Only when there is some physical event C whose local probability depends on the results of both prior events A and B is there a need to do any matching--and by definition, such a physical event C must have had some nonzero probability of getting a "signal" from both measurement-events. And in the many-worlds interpretation, C would actually be receiving a cluster of copies of different possible signals whose statistics would reflect the statistics of different measurement results. > > The real problem is that any theory which enables the gathering of such > information from the results of environmental decoherence would have to > involve radically new physics, of a kind that has never been seen before. > This would have to be universal physics -- we can't just dream up an ad hoc > theory that applies only to the correlations of entangled particles! > You still haven't given a clear answer the basic question I've been persistently asking you about: do you claim there is any airtight argument, akin to Bell's theorem (or perhaps based on Bell's theorem itself), which would allow us to prove mathematically it's not *possible* to come up with a local theory of copies and matching which is "general" in the sense of reproducing the correct quantum predictions for *arbitrary* experiments? Or are you just skeptical/incredulous based on your personal intuitions about what such a theory would need to look like, without claiming it's possible to rule out absolutely in the same way Bell's theorem absolutely rules out a local realist theory (with the conditions he assumes, which include unique measurement outcomes and no 'conspiracy' in initial conditions) that reproduces the statistics of quantum experiments with entangled particles? If the latter, I wonder how you can be so confident that Mark Rubin's paper at http://arxiv.org/abs/quant-ph/0103079 doesn't qualify as just this sort of "local theory of copies and matching which generally reproduces the correct quantum predictions for arbitrary experiments", given that you said you hadn't actually read through the paper. Again, if you haven't read through it because you lack the expertise to evaluate the mathematical details, then I'm in the same boat, so I can't definitely claim it *does* given an example of a mathematical formulation of QM with the above properties, I can only note that it sure *sounds* like it from the descriptions of the model that appear in the paper. For example, from the abstract: 'Measurement-type interactions lead, not to many worlds but, rather, to many local copies of experimental systems and the observers who measure their properties. Transformations of the Heisenberg-picture operators corresponding to the properties of these systems and observers, induced by measurement interactions, "label" each copy and provide the mechanism which, e.g., ensures that each copy of one of the observers in an EPRB or GHZM experiment will only interact with the "correct" copy of the other observer(s). The conceptual problem of nonlocality is thus replaced with a conceptual problem of proliferating labels, as correlated systems and observers undergo measurement-type interactions with newly-encountered objects and instruments' Whatever the nature of this new theory, it would by in addition to quantum > mechanics, so you will not have solved the problem of non-locality in > quantum mechanics, you will have abandoned quantum mechanics in favour of > your new theory. > It wouldn't be *in addition to quantum mechanics" as a physical theory if it made identical predictions about all empirically measurable results, see my last message with the comment from Kip Thorne about the difference between physical claims and philosophical ones. And the central question I ask you to answer above does specify that I'm asking whether you can rule out the possibility of a mathematical model involving local copies and matching that gives rise to predictions about arbitrary measurable results that are identical to those of existing formulations of QM (and as I pointed out in my last message, there are already several mathematically distinct formulations of QM, like the 'Schroedinger picture' vs. the 'Heisenberg picture', that are considered different formulations of the same theory, not distinct theories). Jesse -- 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 post to this group, send email to everything-list@googlegroups.com. Visit this group at https://groups.google.com/group/everything-list. 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