Reply To: Retrocausation vs Retrodiction

AvatarRobert Griffiths

Dear Mark,

I have discussed in considerable detail why the outcomes violating Bell’s inequality are perfectly consistent with the complete absence of superluminal influences. There is a very complete, but not all that readable, treatment in Ch. 23 of my book (chapters available at where I show by explicit calculation that nothing at all happens to particle ‘b’ when a measurement is made on particle ‘a’. And in the next Ch. 24 I make explicit use of Mermin’s example in the article you called to my attention, to show that there are no nonlocal influences (in contrast to nonlocal correlations)–when you throw out (classical) hidden variables and instead do the quantum mechanics properly. Continuing on, Mermin was the referee on my paper “Quantum Locality,” Found. Phys. 41 (2011) 705; arXiv:0908.2914, and did his very best to poke holes in the argument, but without success. In it I prove, using Hilbert subspaces and consistency conditions, a form of Einstein locality: Objective properties of isolated individual systems do not change when something is done to another non-interacting system. This last is in certain ways quite technical, whereas the Am. J. Phys. item I mentioned in replying to Ken Wharton above is more accessible, and a simpler read than Ch. 24 of my book.

Bob Griffiths

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