quantum nonlocality

Quantum nonlocality is the established fact that the correlations between entangled particles cannot be explained by any theory in which influences travel only locally and outcomes are fixed in advance. It is not a vague feeling that 'everything is connected'; it is the sharp, experimentally demonstrated conclusion that the world violates Bell's inequalities. Whatever picture of reality we settle on, it must be one in which distant parts are linked more tightly than local, classical physics permits.

It is essential to be careful about what nonlocality does and does not mean. It does not mean you can send a message, push a button, or transfer energy faster than light. The outcome you see on your side of an entangled pair is, by itself, completely random and cannot be controlled, so there is no way to encode information in it. Relativity's prohibition on faster-than-light signalling stays perfectly intact.

What nonlocality rules out is a specific and once-cherished worldview: that the universe is made of separate parts, each with its own self-contained reality, influenced only by their immediate surroundings. Bell's theorem and the experiments confirming it tell us we cannot keep both locality and definite pre-existing values. Nonlocality is the name for that lesson — a structural feature of how quantum correlations defy a tidy, part-by-part account, without ever letting us break the cosmic speed limit.