Colloquium: Bell’s theorem and locally mediated reformulations of quantum mechanics

Quantum mechanics and relativity are two of the most profound theoretical developments of the 20th century. In 1964, John Bell proposed a test for quantum mechanics that shocked the theoretical community, showing that quantum mechanics implies a violation of locality, that is, action at a distance beyond the light-speed limits of relativity. In this Colloquium this fundamental problem is reviewed in a framework wider than the usual hidden-variable formulation, indicating an allowable ``continuous action'' option in addition to the standard action-at-a-distance approaches.