nonlocality

Nonlocality, in physics, refers to the phenomenon where quantum mechanics suggests that events at one location can instantaneously influence events at another, regardless of the distance separating them. This concept challenges the classical understanding of locality, which posits that influences can only propagate at or below the speed of light.12

The idea of nonlocality arose from the Einstein, Podolsky, and Rosen (EPR) paradox in 1935. They argued that if quantum mechanics were complete, it would imply that measuring a property of one particle in an entangled pair could instantly determine the corresponding property of the other particle, even if they were vastly separated. This seemed to violate the principle of locality.12

Subsequent work, notably by John Stewart Bell, demonstrated that quantum mechanics predicts violations of certain inequalities (Bell's inequalities) that would hold if local hidden variables were responsible for the correlations. Experiments have consistently shown that Bell's inequalities are violated, supporting the predictions of quantum mechanics and indicating that nonlocality is a fundamental aspect of nature. This means that entangled particles share a correlated state, and a measurement on one instantaneously affects the state of the other, a phenomenon that does not rely on any signal traveling between them.123