This essay tries to separate fact from fiction, and without sacrificing rigour, to present the concepts in a way that is easily understood. Experimental technique in 1935 was inadequate to permit the actual performance of the experiment, but today more sophisticated procedures are commonplace, and in recent years many comparable tests have been carried out. The details have usually differed from those specified in the original EPR paper, but only for convenience. There is now little doubt what results to expect whenever this sort of experiment is performed. Although these results are highly perplexing, they are unambiguous.
Nature seems to ration strictly the information it makes available from such a particle.
Einstein knew, however, that we can produce pairs of identical particles travelling in opposite directions, which must necessarily have the same speed. Quantum theory predicted we could not, for a measurement applied to one particle must necessarily affect the value of the attribute we wish to measure for the other one. Einstein and his colleagues realised this implied that the two particles must, in some way, cooperate to conceal information from the experimenter, even when they are separated by so great a distance that no signal should be able to pass between them. The measurement we make on one of the particles must instantaneously affect the behaviour of the other. This proves, they argued, that Quantum Theory is wrong.