A few days ago, I read the paper about Bohmian mechanics on the website of the Stanford Encyclopaedia of Philosophy (SEP) [1]. The last time I came across the name of David Bohm [2] was during my stay in Princeton in 2005. I was subletting a house of Princeton University and people in the neighborhood had the habit of leaving on a shelf at the laundry any book they didn’t want to carry along when they were moving out. In one of these, there was a chapter about scientists in Princeton who had been the victims of McCarthy. David Bohm was one of them.David Bohm had worked on the Manhattan project, he was assistant professor at Princeton University in 1949. After being suspected of being a communist, he was fired from Princeton and he could not find any position in any other American university. He worked in several countries -notably in Brazil- and he eventually settled in London, where he died in 1992.
The exile of David Bohm was actually twofold: not only was he persona non grata in his own country, he was also left out of the international clique of physicists who mattered. Not surprisingly is Bohmian mechanics unorthodox; it is the work of an outcast.
What I realized with the SEP article is that the Copenhagen interpretation of quantum mechanics (QM) is not all there is about QM. David Bohm proposed a causal (deterministic) interpretation of quantum mechanics, the predictions of which are identical with the orthodox QM [3]. Philosophically, however, the two theories are at odds. In Bohmian mechanics the particles have a well defined position and momentum, and the wave function acts as a potential (a so-called pilot wave) that guides the particles. Such an approach was claimed to be impossible, and proved to be so by a famous theorem due to John Steward Bell [4]. Interestingly enough, here is what Bell himself wrote in 1987 about Bohmian mechanics [1]:
But why then had Born not told me of this ‘pilot wave’? If only to point out what was wrong with it? Why did von Neumann not consider it? More extraordinarily, why did people go on producing ‘‘impossibility’’ proofs, after 1952, and as recently as 1978? ... Why is the pilot wave picture ignored in text books? Should it not be taught, not as the only way, but as an antidote to the prevailing complacency? To show us that vagueness, subjectivity, and indeterminism, are not forced on us by experimental facts, but by deliberate theoretical choice?
This is the story of David Bohm and of his unorthodox theory. Yet another sad example of organized skepticism turned de facto into dogmatic denial.
[1] http://www.science.uva.nl/~seop/entries/qm-bohm/
[2] http://en.wikipedia.org/wiki/David_Bohm
[3] D. Bohm, Phys. Rev. 85 (1952) 166-180.
[4] http://en.wikipedia.org/wiki/Bell%27s_Theorem
