Bell’s Theorem, formulated by physicist John Bell in 1964, is a landmark result in quantum physics that shows no theory based on local hidden variables can fully explain the predictions of quantum mechanics.
Here’s what it means:
- Locality is the idea that objects are only influenced by their immediate surroundings—no instantaneous effects at a distance.
- Hidden variables refer to unknown, underlying properties that could deterministically explain quantum behavior, removing randomness.
- Many physicists once hoped that quantum uncertainty was just a sign of incomplete knowledge—a temporary limitation.
Bell showed that if such local hidden variable theories were true, then certain correlations between entangled particles would be limited—described by what’s now called Bell inequalities.
But quantum mechanics predicts stronger correlations than those allowed by any local hidden variable theory.
Experiments (notably by Alain Aspect in the 1980s and many since) have confirmed these predictions:
- Entangled particles show correlations that violate Bell inequalities,
- Indicating that either locality or realism (or both) must be abandoned.
So, Bell’s Theorem tells us:
- Nature does not follow local realism.
- Quantum entanglement involves non-local connections—changes in one particle can instantly correlate with changes in its partner, regardless of distance.
In short, Bell’s Theorem rules out a classical view of the world and reinforces the truly strange, interconnected nature of the quantum realm.