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I still don't really understand what contextuality means in reference to quantum mechanics. If someone could give a clear definition that would be great. It sounds like it means you can't always relate the state of a system to its wavefunction or something? That confuses me since it seems to violate quantum mechanics. So a clear explanation would be great.

The question is then, does any interpretation of quantum mechanics require us to accept contextuality? This paper seems to claim yes, but I don't know enough to evaluate it, so would appreciate a professional's eye: http://arxiv.com/abs/1006.0500

(This is a follow up on a previous question: What combinations of realism, non-locality, and contextuality are ruled out in quantum theory? )

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John, It's not my Answer, but this morning on arXiv I see the fairly interesting and quite closely topical arxiv.org/abs/1103.3980. Somehow this question doesn't juice me much, where your question physics.stackexchange.com/questions/7276/… did a little. –  Peter Morgan Mar 22 '11 at 13:18
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3 Answers

To understand contextuality in QM see this helpful example

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+1 cool stuff! That's really 10 minutes! :-) –  iii Mar 27 '11 at 8:56
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I think this should clear it up that quantum mechanics in it's all models or interpretations is indeed contextual. http://arxiv.org/abs/quant-ph/0406166

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+1, Hard to write something better here than the paper you cite. It seems a better starting point for discussion than arxiv.com/abs/1006.0500, which at a glance seems slightly idiosyncratic. The definition of operational equivalence in section II seems problematic, however, because of its reliance on the phrase "every possible measurement procedure", insofar as advances in Physics precisely depend on previously unconceived measurement procedures. Particularly if we devote all our effort to discriminating one preparation apparatus from another. Absolutely identical? –  Peter Morgan Mar 22 '11 at 13:51
    
Peter, I think Spekkens mentions this worry in the conclusions, although he leaves it for future work: "The question of whether an experimental test of contextuality is even possible has been the subject of some controversy, due to the finite precision of real experimental procedures. The problem...is that finite precision might imply that in practice no two experimental procedures are found to be operationally equivalent.... A possible resolution of this finite precision loophole is to further generalize the definition..." –  Jess Riedel Apr 2 at 17:54
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