A Proposed Two Photon Correlation Experiment as a Test of Hidden Variable Theories
According to hidden variable theories of quantum mechanics the various parameters of interest (e.g.a particle’s position and momentum) are determinate but just not known to us. This is the logic of classical statistical mechanics wherein we settle for probabilities of certain configurations rather than the knowable (but unknown) complete specification of the state of the system. BELL’s theorem  renders the hidden variable idea susceptible to experimental test and several experiments in this direction have been carried out. However, according to CLAUSER and SHIMONY the experimental case for or against hidden variables is not air-tight. To quote from their paper  (which is enthusiastically recommended):
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