The Experimental Investigation of the Einstein-Podolsky-Rosen Question and Bell’s Inequality

Abstract

The argument of Einstein, Podolsky, and Rosen, in 1935, concerning the completeness of quantum mechanics and the possible existence of hidden variables/⁰ was originally couched in terms of the position and momentum coordinates of a pair of particles which could assume a continuous range of values. Subsequently, in 1951, Bohm⁽²⁾ put the argument in terms of an initially spin-0 system which dissociates into two spin-1/2 systems, the components of the spin of which could only take on discrete values. Later, in 1957, Bohm and Aharonov⁽³⁾ discussed the problem with reference to the polarization properties of the γ-ray photons resulting from the annihilation of para-positronium. Then, in 1964, Bell⁽⁴⁾ derived his inequality, which allowed a quantitative distinction to be made between the predictions of quantum mechanics and local realism, and, in 1969, Clauser et al. ⁽⁵⁾ showed how this inequality might be tested experimentally by examining the polarization properties of the two photons emitted in certain atomic cascade processes.