2017 International Workshop: Collapse of the Wave Function

Collapse. What else?

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    Nicolas Gisin

    We present the quantum measurement problem as a serious physics problem. Serious because without a resolution, quantum theory is not complete, as it does not tell how one should – in principle – perform measurements. It is physical in the sense that the solution will bring new physics, i.e. new testable predictions; hence it is not merely a matter of interpretation of a frozen formalism. I argue that the two popular ways around the measurement problem, many-worlds and Bohmian-like mechanics, do, de facto, introduce effective collapses when I” interact with the quantum system. Hence, surprisingly, in many-worlds and Bohmian mechanics, the I” plays a more active role than in alternative models, like e.g. collapse models. Finally, I argue that either there are several kinds of stuffs out there, i.e. physical dualism, some stuff that respects the superposition principle and some that doesn’t, or there are special configurations of atoms and photons for which the superposition principle breaks down. Or, and this I argue is the most promising, the dynamics has to be modified, i.e. in the form of a stochastic Schr\”odinger equation.

    Robert Griffiths

    Dear Nicolas,

    I appreciate your including some references [19] to older work on the consistent histories (CH) approach, at the beginning of your discussion of Bohmian mechanics (BM) in Sec. III. That could, unfortunately, give the reader the mistaken impression that CH has something to do with BM, whereas the two approaches are quite different. Let me suggest that you take a look at more recent stuff on CH–I think my article in [1] is reasonably short and readable–and then reconsider what you want to say in Sec. III.

    Next, relative to your claim that QM is nonlocal. We had some correspondence about that back in 2013. You (and Norsen) were helpful in convincing me that I was misrepresenting Bell’s lambda as something classical, and I corrected that in [2]. In brief, the problem with Bell’s derivation is that it ignores the fact that projectors on the relevant Hilbert subspaces do not commute.

    Finally, you prefer a stochastic dynamics. So do I. No need to modify the Schrodinger equation. Take a look at [1].

    Bob Griffiths

    [1] R. B. Griffiths, “The Consistent Histories Approach to Quantum Mechanics”, Stanford Encyclopedia of Philosophy (2014) http://plato.stanford.edu/entries/qm-consistent-histories/

    [2] R. B. Griffiths, “Nonexistence of Quantum Nonlocality” arXiv:1304.4425.

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