The notion of locality in (Quantum) Physics should be clearly defined

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Thread starter vanhees71
Start date Aug 6, 2023
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Entanglement Locality Quantum physics

In summary, the thread about entanglement and Bell tests has been closed prematurely. It has not been clarified what "locality" means. Locality is the property of a relativistic theory that obeys the causality principle of relativistic spacetime. Locality is implemented by construction through the demand that local observables must commute at space-like separated arguments. This means that there cannot be any nonlocal (inter)actions between distant parts of a quantum system. However, in the mostly discussed case of entangled photon pairs you can of course have entangled photon states with the corresponding Bell-inequality violating correlations between the outcomes of measurements on the single photons in the pair at far distant places.

Aug 21, 2023

#176

LittleSchwinger

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My view would be that "non-local" in particle physics either means literal action at a distance, i.e. dynamical coupling between spacelike separated degrees of freedom, or that the fields in the Lagrangian are not point functions of spacetime.

In quantum foundations and quantum information it's a synonym for nonclassical correlations, although in the latter field "nonclassical correlations" seems to me to be more common.