Page "Quantum entanglement" Paragraph 8

The EPR paper generated significant interest among physicists and inspired much discussion about the foundations of quantum mechanics ( perhaps most famously Bohm's interpretation of quantum mechanics ), but relatively little other published work.

So, despite the interest, the flaw in EPR's argument was not discovered until 1964, when John Stewart Bell demonstrated precisely how one of their key assumptions, the principle of locality, conflicted with quantum theory.

Specifically, he demonstrated an upper limit, known as Bell's inequality, regarding the strength of correlations that can be produced in any theory obeying local realism, and he showed that quantum theory predicts violations of this limit for certain entangled systems.

His inequality is experimentally testable, and there have been numerous relevant experiments, starting with the pioneering work of Freedman and Clauser in 1972 and Aspect's experiments in 1982.

They have all shown agreement with quantum mechanics rather than the principle of local realism.

However, the issue is not finally settled, for each of these experimental tests has left open at least one loophole by which it is possible to question the validity of the results.