Incompleteness of Quantum Physics - Bohm's Hidden Variable Theory

Bohm's Hidden Variable Theory

Main article: de Broglie-Bohm theory

Assuming the validity of Bell's theorem, any deterministic hidden-variable theory which is consistent with quantum mechanics would have to be non-local, maintaining the existence of instantaneous or faster-than-light relations (correlations) between physically separated entities. The currently best-known hidden-variable theory, the "causal" interpretation of the physicist and philosopher David Bohm, originally published in 1952, is a non-local hidden variable theory. Bohm unknowingly rediscovered (and extended) the idea that Louis de Broglie had proposed in 1927 (and abandoned) -- hence this theory is commonly called "de Broglie-Bohm theory". Bohm posited both the quantum particle, e.g. an electron, and a hidden 'guiding wave' that governs its motion. Thus, in this theory electrons are quite clearly particles—when a double-slit experiment is performed, its trajectory goes through one slit rather than the other. Also, the slit passed through is not random but is governed by the (hidden) guiding wave, resulting in the wave pattern that is observed.

Such a view does not contradict the idea of local events that is used in both classical atomism and relativity theory as Bohm's theory (and quantum mechanics) are still locally causal (that is, information travel is still restricted to the speed of light) but allow nonlocal correlations. It points to a view of a more holistic, mutually interpenetrating and interacting world. Indeed Bohm himself stressed the holistic aspect of quantum theory in his later years, when he became interested in the ideas of Jiddu Krishnamurti.

In Bohm's interpretation, the (nonlocal) quantum potential constitutes an implicate (hidden) order, and may itself be the result of yet a further implicate order (superimplicate order). Nowadays Bohm's theory is considered to be one of many interpretations of quantum mechanics which give a realist interpretation, and not merely a positivistic one, to quantum-mechanical calculations. Some consider it the simplest theory to explain quantum phenomena. Nevertheless it is a hidden variable theory. The major reference for Bohm's theory today is his posthumous book with Basil Hiley.

A possible weakness of Bohm's theory is that some feel that it looks contrived. (Indeed, Bohm thought this of his original formulation of the theory.) It was deliberately designed to give predictions that are in all details identical to conventional quantum mechanics. Bohm's original aim was not to make a serious counterproposal but simply to demonstrate that hidden-variable theories are indeed possible. (It thus provided a supposed counterexample to the famous proof by John von Neumann that was generally believed to demonstrate that no deterministic theory reproducing the statistical predictions of quantum mechanics is possible.) Bohm said he considered his theory to be unacceptable as a physical theory due to the guiding wave's existence in an abstract multi-dimensional configuration space, rather than three-dimensional space. His hope was that the theory would lead to new insights and experiments that would lead ultimately to an acceptable one; his aim was not to set out a deterministic, mechanical viewpoint, but rather to show that it was possible to attribute properties to an underlying reality, in contrast to the conventional approach to quantum mechanics.