Reply To: Counterfactual communication protocol

Lev Vaidman

Dear Travis,

I am ready for your semantics about beables.

About action at a distance. When I deal with a physical theory I assume a closed system and an external omnipotent creature which can test the theory making disturbances and observation of what is going on that system. So there is no issue of “free will”.

Nonlocality of Bohm is best manifested in its treatment of the EPR-Bohm system of two separated particles in a singlet state. If Bohmian position of the two particles in the EPR pair are in their upper half, then measuring spin of one particle will change the result of spin measurement of other particle immediately after.

In contrast, any local action in one place will cause no change in the complete local description (local density matrix) of other place. I describe it in detail in Quantum Theory and Determinism, L. Vaidman, Quantum Stud.: Math. Found. 1, 5-38 (2014) quant-ph 1405.4222.

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