Words of John Stewart Bell, F.R.S., Nobel Prize nominee

( full references appear at the bottom of the page )



On the so called "no-hidden variables theorems"

1) ``Why did such serious people take so seriously axioms which now seem to arbitrary? I suspect they were misled by the use of the word ``measurement'' in contemporary theory. This word very strongly suggests the ascertaining of some preexisting property of some thing, any instrument involved playing a purely passive role. Quantum experiments are just not like that, as we learned especially from Bohr. The results have to be regarded as the joint-product of ``system'' and ``apparatus'' the complete experimental setup. But the misuse of the word ``measurement'' make it easy to forget this and then expect that the ``result of measurement'' should obey some simple logic in which the apparatus is not mentioned... ...I am convinced that the word ``measurement'' has now been so abused that the field would be significantly advanced by banning its use altogether, in favor, for example of the word ``experiment''.'' 
From ``On the Impossible Pilot Wave'' \bibitem{Bell Imposs Pilot}

2) ``An attempt will be made to clarify what von Neumann and his successors actually demonstrated.  This will cover, as well as von Neumann's treatment, the recent version of the argument by Jauch and Piron, and the stronger result consequent on the work of Gleason [and also that of Kochen and Specker]. It will be urged that these analyses leave the real question untouched.''
from ``On the problem of Hidden Variables in Quantum Mechanics''
 \bibitem{Bell Eclipse} ``On the Problem of Hidden Variables in Quantum Mechanics.''

3) ``...long may Louise deBroglie continue to inspire those who suspect that what is proved by impossibility proofs is lack of imagination''
from ``On the Impossible Pilot Wave''
\cite{Bell Imposs Pilot}




On EPR, incompleteness and all that

 \cite{Bertlemann's Socks}   ``Bertlemann's Socks and the Nature of Reality''
``It is important to note that to the limited degree to which {\em determinism} plays a role in the EPR argument, it is not assumed but {\em inferred}... ...It is remarkably difficult to get this point across, that determinism is not a {\em presupposition} of the analysis.''


Against standard quantum mechanical thinking (7 quotations)

1) ``It would seem that the theory is exclusively concerned with `results of measurement' and has nothing to say about anything else.When the `system' in question is the whole world, where is the `measurer' to be found? Inside, rather than outside, presumably. What exactly qualifies some subsystems to play this role? Was the world wave function waiting to jump for thousands of years until a single-celled living creature appeared? ... If the theory is to apply to anything but idealized laboratory operations, are we not obliged to admit that more or less ``measurement-like'' processes are going on more or less all the time more or less everywhere? Is there ever then a moment when there is no jumping and the Schroedinger equation applies?
``Quantum mechanics for Cosmologists'' \bibitem{Cosmologists}

2) ``The concept of `measurement' becomes so fuzzy on reflection that it is quite surprising to have it appearing in physical theory at the most fundamental level'' (emphasis due to Bell)
``Quantum mechanics for Cosmologists'' \cite{Cosmologists}

3) ``There is of course no sharply defined boundary between what is to be treated as microscopic and what as macroscopic, and this introduces a basic vagueness into [the usual formulation of] fundamental physical theory.''
\cite{Bell Everett} ``Measurement Theory of Everett and De Broglie's Pilot Wave''

4) ``The concept of ``observable'' lends itself to very precise mathematics when identified with ``self-adjoint operator''. But physically, it is a rather woolly concept. It is not easy to identify which physical processes are to be given the status of ``observations'' and which are to be relegated to the limbo between one observation and another.'' (emphasis due to Bell)
``The Theory of Local Beables''

5) ``The problem is this: quantum mechanics is fundamentally about `observations'. It necessarily divides the world into two parts, a part which is observed and a part which does the observing. The results depend in detail on just how this division is made, but no definite prescription for it is given. All that we have is a recipe which, because of practical human limitations, is sufficiently unambiguous for practical purposes.''
``Quantum Mechanics for Cosmologists''

6) ``...quantum mechanics... ...always refers to an outside observer... ...therefore the universe as a whole is an embarrassing concept.''
``Quantum Mechanics for Cosmologists''

7) ``I think that conventional formulations of quantum theory, and of quantum field theory in particular, are unprofessionally vague and ambiguous. Professional theoretical physicists ought to be able to do better.''
``Beables for Quantum Field Theory''



In Defense of Bohmian Mechanics 5 quotations

1) "But to admit things not visible to the gross creatures that we are is, in my opinion, to show a decent humility, and not just a lamentable addiction to metaphysics."- from
"Are there quantum jumps?"

2) ``Absurdly, such theories [as de Broglie Bohm `pilot wave' picture] are known as `hidden variable' theories. Absurdly, for there it is not in the wavefunction that one finds an image of the visible world, and the results of experiments, but in the complementary `hidden'(!) variables.''
from ``Are there quantum jumps?'' \bibitem{Bell Quantum Jumps}

3) \cite{Imposs Pilot Wave}
``On the Impossible Pilot Wave''
``It is the de Broglie Bohm variable X that shows up immediately each time. That X rather than Psi is historically called a ``hidden'' variable is a piece of historical silliness.''

4) ``The usual nomenclature 'hidden variables' is most unfortunate. Pragmatically minded people can well ask: `why bother about hidden entities that have no effect on anything?.' Of course, every time a scintillation occurs on a screen, every time an observation yields one thing rather than another, the value of a `hidden' variable is revealed. Perhaps uncontrolled variable would have been better, for these variables, by hypothesis, for the time being, cannot be manipulated by us.''
\cite[footnote 24]{Bell Experiments} "Einstein Podolsky Rosen Experiments"

5) ``When the cogency of Bohm's reasoning is admitted, a final protest is often this: it is all nonrelativistic. This is to ignore that Bohm himself, in an appendix to one of the 1952 papers, already applied his scheme to the electromagnetic field. And application to scalar fields is straightforward. However until recently, to my knowledge, no extension covering Fermi fields has been made. Such an extension will be sketched here.''
``Beables for Quantum Field Theory'' 
\bibitem{Bell In Bohm}



Actively Pro Bohmian Mechanics 5 quotations

1) \cite{Bell Imposs Pilot}  ``On the Impossible Pilot Wave''
``... in physics the only observations we must consider are position observations, if only the positions of instrument pointers. It is a great merit of the deBroglie-Bohm picture to force us to consider this fact. If you make axioms, rather than definitions and theorems, about the ``measurement'' of anything else [as traditional quantum mechanics certainly does] then you commit redundancy and risk inconsistency.''

2) \bibitem{Bell Delayed Choice}
from ``deBroglie-Bohm Delayed Choice Double Slit Experiment''
``That the guiding wave, in the general case, propagates not in ordinary three-space but in a multi-dimensional-configuration space is the origin of the notorious ``nonlocality'' of quantum mechanics. It is a merit of the deBroglie-Bohm version to bring this out so explicitly that it cannot be ignored.''

3) \cite{Bell Delayed Choice} ``deBroglie-Bohm Delayed Choice Double Slit Experiment''
[the deBroglie-Bohm version of nonrelativistic quantum mechanics] does not require, in its very formulation, a vague division of the world into ``system'' and ``apparatus'' nor of history into ``measurement'' and ``nonmeasurement.'' So it applies to the world at large, and not just to idealized laboratory procedures. Indeed the deBroglie-Bohm theory is sharp where the usual one is fuzzy, and general where the usual one is special.

4) ``Bohm's 1952 papers on quantum mechanics were for me a revelation. The elimination of indeterminism was very striking. But more important, it seemed to me, was the elimination of any need for a vague division of the world into ``system'' on the on hand, and ``apparatus'' on the other. I have always felt since that people who have not grasped the ideas of those papers ... and unfortunately they remain the majority [publ date 1984] ... are handicapped in any discussion of the meaning of quantum mechanics.''
``Beables for Quantum Field Theory'' \bibitem{Bell In Bohm}

5) ``I think that conventional formulations of quantum theory, and of quantum field theory in particular, are unprofessionally vague and ambiguous. Professional theoretical physicists ought to be able to do better. Bohm has shown us a way.''
``Beables for Quantum Field Theory'' \bibitem{Bell In Bohm}




The bell references:
\bibitem{Cosmologists} "quantum mechanics for cosmologists
Bell, J.S. p. 611 in {\em Quantum Gravity} {\bf 2} edited by by C. Isham, R. Penrose, D. Sciama, Oxford, Clarendon Press (1981). 
Reprinted in \cite[p. 117]{Speakable}.
\bibitem{Bell Imposs Pilot} "On the impossible pilot wave" Bell, J.S. {\em Foundations of Physics} {\bf 12} 989-999 1982
reprinted in \cite{Speakable} on page 159
\bibitem{Bell Delayed Choice} "deBroglie-Bohm Delayed Choice Double Slit Experiment" Bell, J.S. {\em International Journal of
Quantum Chemistry}: Quantum Chemistry Symposium 14 155-159 1980 reprinted in \cite{Speakable} p 111
\bibitem{Bell cascade photons} 
 "Atomic Cascade Photons and quantum mechanical nonlocality" Bell, J.S., {\em Comments on Atomic and
Molecular Physics} {\bf 9} pp. 121-126, 1980. Reprinted p 105 in \cite{Speakable}
\bibitem{Sleepwalkers} "Speakable and Unspeakable in Quantum Mechanics" Bell, J.S. in \cite[p 169]{Speakable}.
\bibitem{Bell In Bohm} "Beables for Quantum Field Theory
Bell, J.S. in \cite[p. 227]{Honor Bohm}. Reprinted in
\cite[p 173]{Speakable}.
\bibitem{Theory Beables} "Theory of Local Beables" Bell, J.S., TH-2053-CERN, 1975 July 28. Presented at the Sixth GIFT Seminar, Jaca, 2-7 June 1975, and reproduced in {\bf Epistemological Letters}, March 1976. May be found in \cite{Speakable} page 52.
\bibitem{Bell Six Worlds} "Six possible worlds of quantum mechanics
Bell, J.S., {\em Proceedings of the Nobel
Symposium 65: Possible Worlds in Arts and Sciences.} Stockholm, August 11-15, 1986. Reprinted in \cite[p 181]{Speakable}.
\bibitem{EPW} "EPR Correlations and EPW distributions
Bell, J.S. in {\bf New Techniques and Ideas in Quantum Measurement Theory} New York Academy of Sciences 1986. Reprinted in
\cite{Speakable} on page 196.
\bibitem{Last of Bell} "Against MeasurementBell, J.S. {\em Physics World} {\bf 3} 33 1990 This is reprinted in \cite[page 902]{Collected Works} and \cite[page 208]{New Collection}.
\bibitem{Bell Everett} "The measurement theory of Everett and de Broglie's pilot waveBell, J.S., in {\em Quantum Mechanics,
Determinism, Causality, and Particles} edited by M. Flato {\em et. al.} Dordrecht-Holland, D. Reidel, 11-17, (1976). Reprinted in \cite[p 93]{Speakable}.
\bibitem{Bell experiments} "Einstein-Podolsky-Rosen Experiments
Bell, J.S., {\em Proceedings on the Frontier
Problems in High Energy Physics}, Pisa, June 1976 pp 35-45.Reprinted in \cite[p 81]{Speakable}.
\bibitem{Determine Bell} "Introduction to the Hidden Variables Question
Bell, J.S. pp.171-181 in \cite{Enrico Fermi
School} This article is reprinted in \cite[p. 29]{Speakable}
\bibitem{Bell Eclipse} "On the Problem of Hidden Variables in Quantum Mechanics" Bell, J.S. {\em Reviews of Modern Physics}
{\bf 38} 447-452 1966 (This work is reprinted in two bibliogaphy references: page 1 of \cite{Speakable} and page 397 of \cite{Big Red}
\bibitem{Bell Quantum Jumps} "Are there Quantum Jumps?" Bell, J.S., in {\bf Schr{\"o}dinger, Centenary of a Polymath} Cambridge University Press, 1987.
\bibitem{Bertlemann's Socks} "Bertlemann's Socks and the nature of reality" Bell, J.S. {\em Journal de Physique} Colloque C2, suppl. au numero 3, Tome 42 1981 pp C2 41-61. Ref. 6 p. 139.
\bibitem{Bell Imposs Pilot} "On the impossible pilot wave" Bell, J.S. {\em Foundations of Physics} {\bf 12} 989-999 1982 reprinted in \cite{Speakable} on page 159
\bibitem{Speakable} Bell, J.S. { \bf Speakable and Unspeakable in Quantum Mechanics} Cambridge Univ. Press, Cambridge 1987.

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