In quantum mechanics, the concept of hidden variables refers to theoretical properties or quantities that are assumed to exist but are not directly observable or accounted for within the standard formalism of quantum theory. These hidden variables are hypothetical entities that, if they exist, would provide a more complete description of quantum systems and potentially explain some of the observed probabilistic behavior.
The idea of hidden variables was initially proposed as a way to reconcile the indeterministic nature of quantum mechanics with the deterministic worldview of classical physics. However, in the mid-20th century, physicist John Bell formulated a series of mathematical inequalities, known as Bell's inequalities, that placed constraints on the types of hidden variables theories that could reproduce the predictions of quantum mechanics.
Bell's inequalities provide a framework for experimental tests to distinguish between hidden variables theories and the predictions of quantum mechanics. These tests typically involve measuring correlations between entangled particles in different configurations. If the results violate Bell's inequalities, it would imply that hidden variables cannot explain the observed quantum phenomena.
Several experiments have been conducted to test Bell's inequalities, and the results consistently favor the predictions of quantum mechanics over local hidden variable theories. These experiments suggest that the behavior of quantum systems cannot be explained solely by the presence of hidden variables that determine their properties in a deterministic manner.
It's important to note that the concept of hidden variables is still a subject of ongoing debate and research in the field of quantum foundations. While the prevailing view among physicists is that hidden variables are not necessary to explain quantum phenomena, there may be alternative interpretations or modifications of quantum theory that incorporate hidden variables in some form. However, no conclusive evidence has been found to support the existence of hidden variables in the context of quantum mechanics.