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Physics

Bell's Inequalities

Quick fact

John Bell derived his inequalities in 1964. Since then, numerous experiments, including Alain Aspect's 1982 tests, have consistently violated Bell inequalities, ruling out local hidden variable theories with high confidence.

Why this is interesting

Imagine two players, each in a sealed room, who must give opposite answers when asked the same question—yet they can't communicate. Quantum particles can perform this trick, but classical ones cannot. Why?