The EPR paradox and the problem of hidden variables

Patrick Suppes

Jorma Jormakka

The hidden variable solution to the EPR paradox proposes that correlation of measurements of entangled particles is due to variables that get decided when the entangled particles get created. It is shown that the correlation of spin measurements in Bell's form of the EPR paradox can be explained as deriving from spin of the entangled particles in the x-direction. This spin parameter is not hidden as it is included in the standard quantum mechanical formulation.

Cyrus D. Cantrell, Marlan O. Scully

Peter Mittelstaedt

The EPR experiment is analysed in terms of ordinary quantum mechanics and shown to be compatible with the orthodox interpretation of this theory. There is no need to refer to Bohrs resolution of the EPR paradox, nor is it necessary to assume any further unusual properties of the quantum physical reality. In particular, it is shown that the EPR experiment does not contradict the fact that incommensurable properties cannot be objectivized simultaneously in a quantum mechanical system, and that the measuring process can be understood in terms of quantum theory as an interaction of the measuring apparatus and the object system. From these results it follows that there is no reason to search for modifications of the quantum theory which might be more convenient for a realistic interpretation of the EPR experiment. Furthermore, the EPR experiment cannot be used as a motivation for introducing hidden variables into the quantum theory. Experimental investigations which try to test quantum mechanics in respect to the possibility of introducing local hidden variables can therefore not be justified by the EPR paradox.

Philippe H. Eberhard

M. A. B. Whitaker, Ishwar S Singh

The authors discuss a number of papers which claim that the EPR 'paradox' may be resolved using density-matrix methods. They first show that it is only inside the Copenhagen interpretation that the EPR experiment has any appearance of paradox; inside an ensemble interpretation, or hidden-variable theory, it may be analysed in a straightforward way. They then show that these 'resolutions' are implicitly using an ensemble interpretation.