On 7/06/2017 5:51 am, Bruno Marchal wrote:
Here I found a not too bad paper on this subtle subject: https://arxiv.org/pdf/0902.3827.pdf He do the calculus that different people have done sometimes. I mainly agree with it, but read it quickly.
His notation is somewhat difficult to follow. But it is instructive that footnote 36 comments that his treatment follows that of Price in the Everett FAQ. Since that derivation has been shown to assume non-locality "by the back door", it follows that Baylock's derivation is equally flawed. Besides, Baylock does not actually derive the full result -- he omits to explicitly mention the step where Price assumes what amounts to a non-local influence. Baylock's equation 6, where he gets the 4 possible combinations of results for the two experimenters, omits to calculate the relative probabilities of these sets of results, and it is those probabilities that can only be determined non-locally.
His discussion of counterfactual definiteness, and of its violation in MWI, is also flawed. He does not demonstrate that Bell actually uses CFD -- his treatment of CFD considers separate sequences of measurements, and then compares them. His criticism is that one of the sequences was not actually performed, so it cannot be assumed to give the QM result (could violate CFD).
But that is an entirely contrived situation. If you look at the original experimental papers, what Freedman and Clauser, Clauser, and Aspect et al., actually do is measure coincidence rates at various randomly set polarizer angles. They then compare coincidence rates at different angles -- they never use results from angles that were not actually measured! So whether CFD is true or not is totally irrelevant for the experiments. They find violations of the relative coincidence rates expected if locality is assumed: CFD does not come into it; their results agree with QM at all relative angles.
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