Abstract: 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 criticised 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 also
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-publicised 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 … ?
Gerhard Grössing