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Speakable and Unspeakable in Quantum Mechanics (Collected papers on quantum philosophy)

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Many people tend to treat the quantum formalism as sacred or untouchable. Not too many seem to question the relevancy of the undefined concepts of 'measurement', 'observer' and 'system' on which which QM stands. Can we really call a theory 'fundamental' when it rests upon undefined concepts? Reading this book is a pure pleasure mostly because it treats QM in a very simple and uncomplicated way. Some lines written in this book are almost poetic. This is a book for people really interested in foundations of QM and for those prepared to let go of quantum doctrines.

It is a travesty that this book is out of print. Almost unbelievable, in fact. What is Cambridge University Press thinking?

This book is not destined to become a classic-- because It IS a classic ALREADY!! It is just one that hasn't been widely recognized yet.

That's only a matter of time.

Nowadays everyone and their uncle seems to be talking about Quantum Communication this and Einstein-Podolsky-Rosen that-- and I guess with good reason, for we are now starting to see practical applications of this most esoteric of physics subfields.

However, it seems that the more non-intuitve and interesting a topic is, the more obfuscation (both intended and accidental) is written about it. (I'm not just talking about laymen and mystics, but physicists too!) Or, said another way, the more people talk, the less they really understand.

Forget all the rest of the [stuff] out there. Cut to chase. Read about the ESSENTIALS of what QUANTUM MECAHNICS really MEANS from one of the Masters of the field in about 15 short, lucid, crystal-clear essays.

There is some math here, but not much. That is the beauty and the danger of Quantum Mechanics-- because calculations are not that difficult in this field, people are lulled into thinking they really understand what it is they are calculating.

Well, most don't.

If you really want to get a grasp as to what it all MEANS-- forgetting the calculations for a moment--- you must read this book.

Feynman said that nobody really understood Quantum Mechanics. That may be so...

But John Stuart Bell came the closest.

You can't meet him at a conference anymore (he died in 1990,) but you CAN have him tutor you personally in this short, brilliant masterpiece.

It would be difficult to find a more controversial topic in the philosophy of physics than what is discussed in this book. But its implications go beyond philosophy, in that some of the ideas in the book have been used in the attempts to build a quantum computer. Since it was written at a time when quantum computation was not taken as seriously as it is now, if at all, it is not surprising that experimental backing for the content is not included in the book. That such experimental evidence is lacking in the book is also a sign that such experiments are not conclusive in the verification of what the author expounds in the book. I can only speak for myself here, but having undertaken a painstaking look at the literature on the experiments purporting to verify entanglement and the "Bell inequalities", I have yet to find one that does so in a convincing way. The mathematical formalism employed by the author in the book allows him to prove some interesting theoretical conclusions, and those who work in the field of quantum computation even more so, but real-world experiments are lagging considerably behind these purely theoretical constructions.

The reader will find good discussions of the Einstein-Podolsky-Rosen and the de Broglie-Bohm delayed-choice "thought experiments" in the book, as well as a few other interesting discussions, such as the problem of hidden variables all from a pretty much philosophical viewpoint. The author however does not hesitate to use mathematical formalism where appropriate. Some of his conclusions will depend on what philosophical "school of thought" the reader is in. For example, in his discussion on hidden variables, he refers to the work of the mathematician Andrew Gleason on the impossibility of hidden variables. However, Gleason's proof would be unacceptable to a reader from the "intuitionist" school of mathematics, since the proof is nonconstructive. The author though does give an interesting analysis of why the von Neumann proof, and others after him (due to for example Jauch, Piron, and Gleason), are of limited relevance when analyzed in depth. Hence, for those who accept non-constructivism in mathematics, the Gleason proof would still not be a refutation of the existence of hidden variables in quantum mechanics. The author analyzes the arguments of von Neumann, Jauch, Piron, and Gleason, and rejects them mostly on the grounds of their demand that dispersion-free states must have the same properties as the usual quantum-mechanical states that allow all the successful predictions of quantum mechanics. The dispersion-free states could still reproduce the measurable peculiarities of quantum mechanics when they are averaged over, the author concludes.

Along these same lines, the author also gives an interesting discussion of the argument of Einstein, Podolsky, and Rosen on the incompleteness of quantum mechanics. He formulates their requirement that quantum mechanics contain additional variables mathematically and then proceeds to show that it is incompatible with the statistical predictions of quantum mechanics. These extra variables or parameters must have a probability distribution, and it is then shown, for a pair of spin-1/2 particles in a singlet spin state, and moving in opposite directions, that these extra variable do not give the quantum mechanical expectation value for the singlet state. The author concludes that in a theory in which parameters are added to quantum mechanics to determine the results of individual measurements without changing the statistical predictions, there must be a mechanism in which the setting of one measuring device influences the reading of another instrument, no matter how remote. He concludes that instantaneous propagation would exist in such a theory, which violates Lorentz invariance. His proof is straightforward to follow, but he does use a classical (Kolmogorovian) expression for the expectation value of the two spin components. This has provoked some debate, and has brought about a notion of "contextual probability", which is a probability theory that follows more on the lines of the frequency approach of von Mises. Also, the notion of locality that the author employs has been seriously challenged by some researchers, who assert that the real notions of space and time have not been used by Bell in the proof.

Therefore it could be said without a doubt that this book will introduce the reader to the raging debate on locality and other issues in the "foundations" of quantum physics. Papers supporting Bell and those against his conclusions appear frequently on the preprint servers. Since this book is widely quoted in these papers, it should perhaps then be on the shelf of all those readers who really have a desire to understand the mysteries of quantum mechanics.

Bell dispatches a number of quantum myths, most courteously and most irrevocably--in particular, regarding what quantum experiments require us to conclude about the world. E.g. #1 indeterminism; #2 nature (Schrodinger evolution) stops and sits on her hands when a "measurement" is made; #3 Bohr got the better of Einstein. Another interesting point of Bell: Bohm = many-worlds minus absurdity. I felt the urge to stand up and cheer certain passages. Also, a nice brain-teaser on Lorentz vs. Einstein relativity.

In the early days of quantum mechanics, Einstein (who was
actually at the origin of the basic ideas of the theory)
and Bohr (one of the founders of the formalism of quantum
mechanics) had a lot of discussions: Einstein just couldn't
accept the (to "common sense") weird predictions of
quantum theory. Einstein's criticism on quantum theory
reached a top in a few papers that describe what is called
"the Einstein-Podolski-Rosen paradox". It describes long
distance correlations between measurements that seem to depend
on arbitrary decisions made by the two distant observers and
that can have no causal relationship.
Einstein's favorite view of the statistical nature of quantum
mechanical predictions was some hidden "gears and wheels"
that wasn't found out yet.
John Bell examined the question in detail and wrote a few
historical papers in which he showed that it is mathematically
impossible that the predictions of quantum mechanics follow
from hidden local "gears and wheels" in the situation
described by the EPR paradox; as such the strangeness
of the EPR paradox is underlined and can be settled by
experiment: if the "gears and wheels" exist, then the
predictions of quantum mechanics cannot be right (that is the
content of the Bell papers). Today, very sophisticated experiments indicate
that quantum mechanics is right and that the weirdness is
with us for good.
In this volume, those historical papers by Bell are reprinted
with added comments by the author. The merit is that they
have raised the issue from a conceptual debate to a scientific
question, amenable to experimental inquiery.

This book is necessary for even the casual investigator of QM philosophy. Ideas once considered heresy are largely accepted now, but there are still competing interpretations. It is by no means settled. But the author shows how to think beyond just mechanically exploring the QM equations and consider the underlying implications.

If you are interested in quantum entanglement, hidden variables and the Einstein-Podolsky-Rosenberg paradox, this is the book for you. Pretty clear, even for those with only an introduction to quantum mechanics behind their belt.

Any book that seems likely to stand as the most representative piece in one of science's greatest missteps deserves a five-star recommendation and should be widely read; this is how science progresses. Papers by E. T. Jaynes, A. F. Kracklauer, and C. S. Unnikrishnan have been published that not only seem to expose gaps in Bell's arguments, but even (in the case of Unnikrishnan) go so far as to show _how_ to get the same results as quantum mechanics but using only local information.

We may be standing on the cusp of a revolution in physics. Here are some important papers to read along with Bell, all of which are published on-line and elsewhere (get out your search engines):

C. S. Unnikrishnan: "Quantum correlations from wave-particle unity and locality: Resolution of the EPR puzzle" in the Annales de la Fondation Louis de Broglie, vol. 25 no. 3, 2000

A. F. Kracklauer: "La 'theorie' de Bell, est-elle la plus grande meprise de l'histoire de la physique?" in the same journal, vol. 25 no. 2, 2000

E. T. Jaynes: "Clearing Up Mysteries -- The Original Goal" in "Maximum Entropy and Bayesian Methods", edited by J. Skilling, Kluwer, 1989. Look also for "Probability in Quantum Theory" by the same author.

I agree with the enthusiasm shown by other reviewers (see also the 2nd. edition) for this book's treatment of interpretive issues at the foundations of quantum theory. However, chapter 9 unfortunately titled "How to teach Relativity" shows that Bell's expertise in quantum theory did not extend to special relativity, which he seriously misunderstood. Drawing on an old mistaken paper by Dewan & Beran from 1959, a thought experiment is described where two spaceships are joined by a thread and accelerate identically. Like the earlier authors, Bell wrongly believed the thread would break, showing the Lorentz contraction (again wrongly) to be a "real" effect, rather than an apparent one manifested only in another relatively moving inertial frame.
Despite the fact that, as is mentioned in the book, all his CERN colleagues contradicted him, he nevertheless included this old "chestnut" with a false interpretation that can only do harm to the general understanding of STR. It is precisely this misunderstanding that has caused so much confusion over the rotating disc problem (Ehrenfest paradox), which has generated many meaningless papers over the years - and still does !

This is some provocative work from a man who is not satisfied with the copenhagen interpretation of Quantum Mechanics.