The question of hidden variables in quantum mechanics and the nature of quantum entanglement has been the subject of intense debate among physicists for many years. While it is difficult to definitively prove the absence of hidden variables, several experimental and theoretical results strongly suggest that hidden variables are not required to explain quantum entanglement.
One of the most famous experiments in this regard is the Bell's theorem experiment, which was first proposed by physicist John Bell in 1964 and later conducted by physicist Alain Aspect and his colleagues in the 1980s. The Bell's theorem experiment involves entangled particles and measurements performed on them in different directions and at different angles. The results of these experiments consistently violate certain inequalities derived from the assumption of local hidden variables.
By violating these inequalities, the experiments strongly suggest that the correlations observed between entangled particles cannot be explained by pre-existing hidden variables that carry information about the particle's state from the beginning. Instead, the outcomes of the measurements appear to be intrinsically random and non-local, meaning they are not determined by local hidden variables.
Furthermore, the violation of these inequalities has been experimentally confirmed in various setups and with different types of entangled particles, providing strong evidence against the existence of hidden variables in quantum entanglement.
It is important to note that the experimental results are consistent with the predictions of quantum mechanics, which describe entanglement as a fundamental property of particles. Quantum mechanics provides a mathematical framework that successfully predicts and explains the behavior of particles in entangled states without the need for hidden variables.
While the debate is still ongoing and further research is being conducted to explore the nature of quantum entanglement, the currently available evidence suggests that hidden variables are not required to explain the phenomenon and that the particle's state is defined upon measurement rather than being predetermined from the beginning.