Gerhard Groessing
16.12.2000
In a festive lecture at the University of Vienna in 1987, on the occasion of Erwin Schrödinger’s 100th birthday, the famous physicist John Bell complained about the «scandal» (literally) that the so-called «deBroglie-Bohm interpretation» (BBI) of quantum theory was not taught at the universities and treated on an equal footing with the predominant «Copenhagen interpretation». On the contrary, over decades, and up to the present day, the BBI has almost always been marginalized or grossly misrepresented by leading quantum physicists.
Actually, John Bell devoted practically all of his papers on quantum theory to the implications around the BBI, as can easily be seen from the collection of said papers in his book on «Speakable and Unspeakable in Quantum Mechanics». Now, in November 2000, a symposium was held at the University of Vienna on the occasion of the 10th anniversary of Bell’s death. Physicists were invited to talk at this symposium who only recently had published utterly wrong «arguments» calling for the dismissal of the BBI. However, not a single exponent of the BBI was to give a talk, although the symposium was performed in the name of John Bell. Thus, the scandal is being prolonged.
Moreover, the series of (often provably intentional) misrepresentations of the BBI is continued in articles celebrating «100 years of quantum theory».
Perhaps one can best explain the story by starting out with a reference to the famous article by Einstein, Podolsky, and Rosen (EPR) published in 1935. Two topics can be considered as the central ones in their paper:
1) the notion of a «reality»:
EPR denote an event as an «element of reality» if it can be predicted with certainty: if, for example, a coin shows «1» on one side, and «head» on the other, one can after tossing the coin, and with the result that «1» is visible, predict with certainty that the lower, «invisible» side would exhibit «head»; i.e., also the unobserved «head» is considered an «element of reality»;
2) a purely quantum-mechanical effect, which today is termed «nonlocality»:
in a metaphorical transposition one could say that if «1» was measured at one location, then practically without delay, «head» would be implied at some other location, which could in principle be arbitrarily far away.
(However, the effect is even more spectacularly non-classical if more than just two possible outcomes are involved.)
Now, the central mathematical formulation of quantum theory is given by the so-called Schrödinger equation, which had been postulated by its creator to describe quantum mechanical states («wave functions») via complex numbers. Complex numbers are mathematical tools which allow to «translate» two equations using the (more common) real numbers into one single, more compact (and thus also more abstract) equation. However, after Louis de Broglie in the 1920ies, David Bohm in the 1950ies was strongly fascinated by the following fact: the (complex-valued) Schrödinger equation may not be interpretable in a concrete kind of imaging («Anschaulichkeit»), but if it is decomposed into its two equivalent (real-valued) equations, both of them make sense! Bohm published his theory of «hidden variables», which he recognized as explaining the physically existing, ontological background of these equations, believing that now physicists would happily devote their attention to them in order to arrive at a more profound theory. Central to the approach via «hidden variables» in the BBI is the assumption of the existence of some kind of «aether» filling the quantum vacuum and being causally responsible for the (now experimentally confirmed) nonlocal correlations.
However, historically it was the so-called «Copenhagen interpretation» that has become the dominant one: with it, one denies any interest in what may lie «behind» the observed quantum phenomena. Instead, one is content with the perfectly working formalism, which alone suffices to continue the success story of ever more refined technological applications. However, there’s a price for this: the notion of «reality» is being so radically questioned that much space is opened for wild mystifications. (Compare, e.g., an article by Mara Beller in «Physics Today» 9/1998, intended as a contribution on the so-called «science wars» dispute. The gist of her article is given by examples showing how it is often mystical and/or cryptic statements by famous quantum physicists which had been taken up and proliferated by «postmodern» theorists in the arts and social sciences.)
In any case, the BBI (via thoroughly documented lobbying) has been marginalized over decades, and also grossly misrepresented when it was mentioned (even by most famous physicists). The «materialist» Bohm was politically prosecuted (without justification) during the McCarthy era, and defenders of the BBI until recently were denied public recognition (not to speak of substantial grant money).
[Concerning Bohm’s tragic life as a scientist, see F.D. Peat, «Infinite Potential. The Life and Times of David Bohm», Addison-Wesley 1997; extensive historical material on the hegemony of the «Copenhagen» people or on the suppression of the BBI can be found in M. Beller, «Quantum Dialogue» (U of Chicago Press 1999), or, respectively, in J.T. Cushing, «Quantum Mechanics. Historical Contingency and the Copenhagen Hegemony» (U of Chicago Press 1994).
The widely-practiced ignorance of the scientific community towards Bohm and the BBI even constitutes the material for a new novel by Rebecca Goldstein: «Properties of Light. A Novel of Love, Betrayal and Quantum Physics» (Houghton Mifflin 2000; see the review in the NYT Book Review of 17 September 2000.)]
If at physics conferences eventually a controversy on the BBI does emerge, one often gets to hear the standard beginning of a sentence like this: «Yes, but quantum theory says that….», thereby automatically implying that «quantum theory» was synonymous with the orthodox (mostly Copenhagen) interpretations – a classical rhetorical means to exert power, but not to have an honest scientific controversy.
The latter hardly ever takes place. Rather, one often revels in an «anti-materialism» and couples this to some mysterious questioning of our notion of «reality» altogether. Unfortunately, also Anton Zeilinger, one of the organizers of the Bell symposium in Vienna, belongs to this group of mystifiers. His world-famous experiments on «beaming» (or better: «quantum teleportation»), and others (in my view even more important ones), are, of course, not to be questioned at all in this context. However, this has only very little to do with the private, highly speculative «philosophical» positions, which are being massively transmitted via the media along with the «serious» results. No wonder that also the BBI is vehemently opposed when adopting such «mysterious» world views.
But things hardly were different here in earlier days.
Just to give one example: Zeilinger’s predecessor, Peter Weinzierl, had strongly criticized an article on the BBI by D.Z. Albert in «Spektrum der Wissenschaften», i.e., the German version of «Scientific American». In a letter to the editors (published in the edition of June 1995), Weinzierl had written: «In my view, there has hardly been a theory so unequivocally refuted than Bohm’s, which is thus only of historical interest. … Albert, however, makes the impression as if this theory was still in the center of controversies among physicists, which is certainly not true for 90 percent of them.» Fortunately, the editors of the «Spektrum» were attentive enough to give the following polite answer to the former head of the Institute for Experimental Physics at the University of Vienna: «Contrary to a widely-held opinion, Bell’s inequalities do not mean a refutation of Bohm’s quantum theory. They exclude any type of local theory, i.e., any theory that would explain typical quantum correlations as pseudo-effects or that would reduce them to classical and local actions. Bohm’s theory is not one of them: it is an explicitly non-local theory» […which had originally inspired Bell to derive his inequality in the first place, one could add!]
Similar misrepresentations and wrong imputations were always published, from the 50ies through the 90ies, but what about most recent times? Well, in a recent preprint by D. Deutsch, A. Ekert und R. Lupacchini we read about the path of a photon through an «interferometer» (similar to a double slit), about which the BBI has proven that said path is causally explainable, but still provides the correct quantum-mechanical interference effects: «Any explanation which assumes that the photon takes exactly one path through the interferometer leads to the conclusion that the two detectors should on average each fire on half the occasions when the experiment is performed. But experiment shows otherwise!» [i.e., shows interference effects] (web-source: math.HO/9911150, 19 Nov. 1999) By the way, one of the authors, A. Ekert, gave a talk at the above-mentioned Bell conference in Vienna.
Another example? In the 11 August 2000 issue of «Science», D. Kleppner und R. Jackiw of MIT published a review article on «One Hundred Years of Quantum Physics». They discuss Bell’s inequalities and briefly mention the possibility of «hidden variables». However, according to the authors, the corresponding experiments had shown the following: «Their collective data came down decisively against the possibility of hidden variables. For most scientists this resolved any doubt about the validity of quantum mechanics» (Reading such sentences, in «Science», in the year 2000, almost takes my breath away!).
By the way, one of the authors, R. Jackiw, gave a talk at the above-mentioned Bell conference in Vienna.
The title of the Vienna conference was «Quantum [Un]speakables», thereby referring to John Bell’s book «Speakable and Unspeakable in Quantum Mechanics» (Cambridge University Press, 1987), where all his papers on quantum theory (as well as on relativity and the physics of the «aether») are collected. At least 80 percent of the articles deal explicitly with the BBI, and implicitly all of them. Since the conference was devoted to the person and (quantum) works of Bell on the occasion of the 10th anniversary of his death, the policy of whom to invite (and whom not) only clearly documents the ignorance and (practically cynical) power politics within the «physics community», against which John Bell fought throughout his life.
Let me end this sad story (which nevertheless has to be told, particularly to the younger generations of physicists!) with a quotation from another celebratory review. In the February 2001 issue of «Scientific American», Max Tegmark and John Archibald Wheeler published an article entitled «100 years of the Quantum». (An extended version of the article can be found on the web: quant-ph/0101077.) Now, at least Wheeler is somebody who is very familiar with the controversy around the BBI because he always has been an explicit opponent of Bohm’s and others’ «hidden variable» theories. Still, I wonder what drives him (and also other leading physicists on similar occasions) to produce the following lie (!) in a widely publicized article:
«Could the apparent quantum randomness be replaced by some kind of unknown quantity carried out inside particles, so-called “hidden variables”?» [Remark: This is a blunt misrepresentation. Firstly, it is not the quantum randomness which lies at the heart of the BBI concerns. Secondly, and most importantly, the essence of the BBI lies in the contextuality of the situation involving the whole apparatus, such that looking just «inside particles» is the contrary of what the Bohm approach does. GG; Tegmark and Wheeler continue:]
«CERN theorist John Bell showed that in this case, quantities that could be measured in certain difficult experiments would inevitably disagree with standard quantum predictions. After many years, technology allowed researchers to conduct these experiments and eliminate hidden variables as a possibility.»
Well, what to say…?