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Volume 15: Pages 211-229, 2002

Hidden Variables: The End of the Road for Quantum Mechanics?

Dominic J. R. Vella

Trinity College, Cambridge, CB2 1TQ U.K.

Einstein's unrealized dream was a theory that could explain away the weirdness of quantum mechanics as a result of our ignorance of the world; if we knew the values of certain “hidden” variables, a deterministic theory of the small scale world might emerge. Although it is already well known that the existing formalism of quantum mechanics is extremely successful at predicting the behavior of systems on the small scale, the possibility of such a theory would clearly be a prize worth pursuing and remains an area of intense interest. Einstein's distrust of the new physics that was ushered in with the “quantum revolution” led him (along with Podolsky and Rosen) to formulate the now famous EPR (Einstein‐Podolsky‐Rosen) Gedankenexperiment to demonstrate what he saw as the absurdity that lay at its very heart. Ironically, it was Bell who, using Einstein's brainchild, apparently proved that no hidden‐variables theory in which local actions have purely local consequences is capable of producing the same predictions as quantum mechanics. Aspect's experiments ostensibly show that it is these “classical” theories that are at fault and not quantum theory, but in the last two years the conclusions from Aspect's experiments have come under increased scrutiny. Not only does it seem that the tests on Bell's “theorem” may be flawed but also that some new theories may be able to explain the results of the experiments with greater success than quantum theory itself! This essay constitutes a review of some of the most influential papers on the subject of hidden variables. It also details new work that exposes some of the flaws in Bell's original work as well as one rival to quantum mechanics that emerges once these flaws have been taken into account. Not only is the resulting theory inherently local while predicting the same correlations in the EPR experiment that quantum mechanics does but it also predicts the results of Aspect‐like experiments with significantly greater accuracy than can be achieved within the quantum‐mechanical framework.

Keywords: hidden‐variables theories, quantum mechanics, Bell's inequality

Received: March 6, 2002; Published online: December 15, 2008