Hidden-variable theory

Summary

A hidden-variable theory is a model of quantum systems with a more detailed physical state, the hidden variable. Each preparation of a system produces such a hidden variable, which carries more information than the quantum state. The quantum probabilities arise from averaging over the hidden variable with a probability distribution fixed by the preparation. No-go theorems, such as Bell's theorem and the Kochen–Specker theorem, show which kinds of hidden-variable theories cannot reproduce quantum mechanics. De Broglie–Bohm theory is a hidden-variable theory that does reproduce it, at the price of nonlocality.