On Thu, Apr 21, 2016 at 11:25 PM, Bruce Kellett <bhkell...@optusnet.com.au> wrote:
> On 22/04/2016 12:53 pm, Jesse Mazer wrote: > > On Thu, Apr 21, 2016 at 9:49 PM, Bruce Kellett <bhkell...@optusnet.com.au> > wrote: > >> >> >> The point here is that some combinations of results are forbidden. How >> can this happen? >> > > By the appropriate matching rules for locally-generated copies in > different locations, as in my toy model. There's no reason you can't have > something similar in a more general model, which I think is exactly what > people like Rubin are presenting. > > > The best I can make of this is that you have some theory that is not > quantum mechanics. Quantum mechanics does not give any such "matching rules" > It's important to distinguish between theories of physics and the mathematical models used to express them--a physical theory is defined entirely by the predictions about observable outcomes, not any elements of the model that are not directly measurable even in principle. For example, curved spacetime is not essential to general relativity as a theory, though it is a feature of the most commonly-used mathematical model (there is an alternate formulation that only uses flat spacetime, but has a field defined on this spacetime which varies the length of rulers and the ticking rate of clocks at different points in the spacetime, and physicists would still call this 'general relativity'). Likewise, a state vector in Hilbert space is not essential to quantum mechanics as a theory. And if one *could* come up with a model involving "matching rules" that would be equivalent in its predictions about observable measurement results as the existing mathematical models, this would merely be a new mathematical model for the same physical theory. If you disagree with any of this, please explain your disagreement. And if you don't disagree that physics theories are defined solely in terms of their predictions about measurement results, but you think there is something intrinsically impossible about the idea that a mathematical model involving "matching rules" could reproduce these predictions, please explain the argument, because it clearly can't just be Bell's theorem. > nor does it give any dynamics whereby such matching could be effected. So > you no longer have an interpretation of quantum mechanics, you have a > different theory. It remains for you to develop this in a way that is > convincing. > But I am not claiming I can definitely present such a model--though as I said, my *impression* is that Rubin's paper seems to be doing that--I'm just disputing the idea that you can state with certainty that no such model is possible, such that you are confident that Rubin's paper can't contain an example without actually needing to read and understand it in detail. > Following back the train of information exchange between the participants, >> and accepting that worlds, once decohered, cannot suddenly disappear, it >> becomes apparent that the zero probability branches cannot arise because >> they are forbidden at the stage when A and B are still at spacelike >> separations. So they are forbidden non-locally. >> > > But that clearly isn't true in my model, so there's no reason to think it > *must* be true in more general models that reproduce arbitrary quantum > measurements. In my model *and* in more general models of the sort that > people like Rubin seem to be proposing, until matching between Alice and > Bob has happened there *are* no "branches" containing facts about both of > their results, only a set of local branches for one region and a different > unrelated set of branches for another region. And once the two sets of > branches can interact, they can be matched up in a way that creates zero > probability of matching up a version of Alice who got + at zero degrees and > a version of Bob who got + at zero degrees. > > > But your model only reproduces the quantum correlations because you have > put them in by hand. That is not a viable model of physics. > I didn't claim it was, I only claimed it demonstrated that Bell's theorem does not present any fundamental obstacle to coming up with such a model. Remember, Bell's theorem too deals only with the predicted quantum correlations in specific experiments, and the proof doesn't depend at all on what mathematical theory was used to derive those predicted correlations. You claim that there are no branches containing facts about both A and B > until this matching takes place. The rules for this matching presumably say > that one must not match incompatible results. How is the matching done: > does one pick one result, and search about for a match that does not > violate the quantum statistics? You will have a problem if the basic > experiment on each entangled pair is done at a recorded time. Both branches > carry this timing information, so you can only match pairs that have the > same time stamp. This means that for aligned magnets, you will have to > discard 50% of the possible matches -- giving worlds that simply vanish for > no coherent internal reason. > You don't have to discard any individual copies of Bob or individual copies of Alice, if that's what you mean--I already gave a numerical example showing the matching could be done in a one-to-one way between the independently-generated copies of each, so that however many copies of Alice got a message like "Bob used detector setting 2 and got result +", the same number of copies of Bob would have in fact used detector setting 2 and got result +. Do you disagree that this sort of one-to-one matching between copies of each experimenter that were independently generated at a spacelike separation can always generated the correct statistics for pairs of matched results? And of course, once you generate a given set of matches, there is no need to later throw away some of those matched pairs either--if you think there would be a need to do that, please explain. > Frankly, such matching is absurd, no physical law acts in this way. > > I don't think "absurd" is an objection many physicist would find meaningful, assuming a model was mathematically well-defined and didn't obviously lead to predictions that conflicted with observations. And the fact that no prior physics model has worked this way doesn't seem like a physically meaningful objection either, after all many successful new mathematical models in physics have had features that no previous one had (like Einstein's model where gravity was modeled in terms of geodesics in a curved manifold). Jesse -- You received this message because you are subscribed to the Google Groups "Everything List" group. 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