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Because EPR's proposal involved properties that were not captured in the wave equation and which were local and real, it became known as a local ' hidden variables ' theory.

After the EPR paper, several scientists such as de Broglie took up interest in local hidden variables theories.

In the 1960s John Bell derived an inequality that showed a testable difference between the predictions of quantum mechanics and local hidden variables theories.

Experiments testing Bell-type inequalities in situations analogous to EPR's thought experiments have been consistent with the predictions of quantum mechanics, suggesting that local hidden variables theories can be ruled out.

Whether or not this is interpreted as evidence for nonlocality depends on one's interpretation of quantum mechanics .< ref > Berkovitz, J.

" Action at a Distance in Quantum Mechanics ", The Stanford Encyclopedia of Philosophy ( Winter 2008 Edition ), Edward N. Zalta ( ed.

), URL = < http :// plato. stanford. edu / entries / qm-action-distance />.</ ref > In the standard interpretation the wave function is still considered a complete description so the nonlocality is generally accepted, but there is still debate over what this means physically.