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The Quantum Challenge, Second Edition: Modern Research on the Foundations of Quantum Mechanics by George Greenstein, Arthur G. Zajonc (Physics and Astronomy: Jones and Bartlett Publishers) is an engaging and thorough treatment of the extraordinary phenomena of quantum mechanics, and of the enormous challenge they present to our conception of the physical world. Traditionally, the thrill of grappling with such issues is reserved for practicing scientists, while physical science, mathematics, and engineering students are often isolated from these inspiring questions. This book was written to remove this isolation.

George Greenstein and Arthur G. Zajonc present the puzzles of quantum mechanics using vivid references to contemporary experiments. The authors focus on the most striking and conceptually significant quantum phenomena, together with a clear theoretical treatment of each. The depth and extent of the challenge of quantum mechanics become increasingly compelling as they move from the simplest experiments involving single photons or particles, to the famous Einstein-Podolsky-Rosen effect and Bell's Theorem, and then to macroscopic quantum phenomena.

New to this Edition

• Dramatic new experiments that illustrate new challenges of quantum theory

• A new chapter on the exciting new field of quantum information and computation

• An annotated bibliography of experiments accessible to the undergraduate laboratory

What Reviewers Said about the First Edition:

"This book is a real gem. In the prologue, the authors claim that they want to bring the deep mysteries and wonderful beauty of quantum mechanics to a large audience. In my opinion, they have succeeded masterfully . . . If you can, buy the hardbound copy: this book will be valuable for a long time." Erik Deumens, International Journal of Quantum Chemistry vol 69, 689, 1998.

.. the great intellectual honesty of the authors, who never hide the difficulties [of quantum mechanics] but also never overstate them, will be of great help to young readers. More knowledgeable readers will also learn a lot." Philippe Grangier, Nature vol 392, 672, 1998.

This is the only pedagogical book I have seen that tries to explain the issues in interpreting Quantum Mechanics without trying to sell the reader on a philosophical direction first. The authors just try to explain the implications and rationale behind QM as it is today, without promoting a "new direction". I think this is extremely useful - even if you want to go somewhere else, it helps to know where you are, to start.

There is a lot of discussion of the relevant experiments and the issues they settle (and raise). This is rather grounding. This is the best book available, by far, on experimental results of the quantum measurement problem. It is one of the few books that are beyond popular accounts, which generally do not have the depth necessary to understand the measurement problem, and - on the other hand - very technical quantum optics volumes. I give it my highest recommendation for anyone with some science background to become acquainted with the quantum measurement problem in detail. It is a triumph and comprehensive in its coverage and reference to quantum measurement experiments.

The reader will need a good undergraduate-level capability in mathematics and previous exposure to quantum physics, in order to make real progress with this book. I think this is unavoidable, as QM is inherently mathematical. Given this background, the reader should find this book clear and well filled-out. 

Excerpt: Since its inception in the early decades of the twentieth century, quantum mechanics has joined Einstein's theory of relativity and Darwin's theory of evolution as a dominating scientific presence. There is hardly a single facet of physical science that it has not transformed beyond recognition. Nevertheless, the theory has steadfastly resisted interpretation. It gives a detailed set of instructions for calculating submicroscopic processes, while at the same time failing to provide the usual comprehensive picture of how these processes take place.

Indeed, it seems possible that such a picture may never be reached. Quantum mechanics seems to teach, for example, that a particle can pass through two different slits at the same time to produce an interference pat-tern. It teaches that measurements can never be perfectly accurate, but rather are beset by a fundamental uncertainty. It teaches that the very concepts of cause and effect must be rethought. What can we make of these lessons?

The battle over the interpretation of quantum mechanics raged until the early 1930s. The inventors of the theory, well realizing the magnitude of the dilemma, devoted considerable energy to its mysteries. Two gigantic figures presided over this debate.

Niels Bohr, on the one hand, originated the so-called Copenhagen interpretation, according to which all hope of attaining a unified picture of objective reality must be abandoned. Quantum theory, he held, would provide predictions concerning the results of measurements—but, unlike all previous theories, it was incapable of providing a full account of "how nature did it." Indeed, Bohr argued that the very desire to seek such a complete account was misguided and naive. All human understanding takes place in terms of the classical concepts fashioned from direct experience, he maintained. But the quantum world is demonstrably nonclassical. Therefore the quantum universe cannot be understood in the old sense of the term—not even in principle.

Albert Einstein, on the other hand, never abandoned his dissatisfaction with quantum mechanics. In his famous dictum that "God does not play dice with the universe," he expressed his opposition to the probabilistic nature of the theory. In 1949, responding to the accolades lavished in honor of his seventieth birthday, he emphasized that the theory had relinquished precisely

what has always been the goal of science: "the complete description of any (individual) real situation (as it supposedly exists irrespective of any act of observation or substantiation)."  He emphasized that for centuries science had viewed its aim as the discovery of the real. This entailed creating new concepts to correspond with that reality, and so scientific ideas such as force, energy and momentum were hammered out over decades of struggle and debate. They corresponded to important features of the physical world, and so could be used productively to understand it. Yet the Copenhagen interpretation insisted that this tradition, which defined the very nature of the scientific enterprise, had now to be abandoned.

This debate never reached a satisfactory conclusion. Rather, with a few signal exceptions, it was simply relegated to the back burner. After the 1930s there followed a long period in which most physicists turned their attention elsewhere, and progress in understanding the foundations of quantum mechanics attracted only the attention of the relatively small number of people who continued to seek an understanding of these matters. During this period, the wonderful difficulties of quantum mechanics were largely trivialized, swept aside as unimportant philosophical distractions by the bulk of the physics community. This did not mean, however, that these issues of interpretation had been solved. Indeed, the interpretation of quantum theory remained as unclear as ever: in his book The Character of Physical Law, Richard Feynman unabashedly declared that "nobody understands quantum mechanics."

Recently, however, renewed efforts to explore these puzzles have gained momentum—and hence our decision to organize a meeting. A complex skein of developments, ranging across fields as diverse as physics, mathematics and philosophy, has led to this development; but in this history two important advances stand out. The first was a theorem published in 1964 by John Bell, which shed an extraordinary new light on quantum theory. Bell's Theorem showed that questions pertaining to the foundations of quantum mechanics were not purely matters of interpretation and philosophical argument. Rather, they actually had physical implications. One consequence was that experiments could be performed that would shed light on these questions, experiments that ultimately were carried out. Bell, in fact, played a central role in our conference's discussions; tragically, he was to die unexpectedly a mere few months after returning home from the conference.

The second great advance has been the enormous technological strides that have occurred in recent years. These now permit us to perform single-quantum experiments of every type. Until recently, the manipulation of individual particles had been little more than a theorist's dream. Experimenters commonly dealt with millions to trillions of particles at the very least. But now our latest techniques bring to the lab methods that permit us to manipulate and measure individual atoms, individual electrons, individual photons. Using such methods, experiments have recently been performed that the founders of quantum theory only dreamed about.

In our roundtable discussions these beautiful experiments surfaced again and again, transforming what for decades had been an abstract discussion into the stuff of everyday life. In this book we will describe many of them in detail—they show quantum effects with a vengeance. 

But they do not solve the problems that so perplexed the creators of quantum theory. Indeed, in our view, modern research has only made the theory's paradoxical nature more evident. Our thesis in this book is that the quantum universe forces upon us a radical revision in our conception of the physical world, a revision that has by no means been achieved. Our aim is not to accomplish this task, for we have no idea how this could be done. Rather, our aim is to make as vivid as possible the difficulties of interpretation posed by quantum mechanics.

In the past, books dealing with these issues have been constrained by two complementary difficulties. At the instructional level, the theoretical apparatus of quantum theory is complex and unfamiliar; textbooks are therefore forced to concentrate heavily on the technical aspects of the theory. Most texts, if they discuss issues of interpretation at all, do so only briefly. At the popular level, in contrast, considerable attention is often devoted to these questions; but owing to their nontechnical nature, such presentations are necessarily limited in the understanding they can convey.

The Quantum Challenge is explicitly intended to fill the gap between these two approaches. We believe that the material can be presented with reasonable rigor and intellectual honesty in a presentation accessible to undergraduate physical science, mathematics and engineering students. In particular, neither a presentation of Hilbert space nor of quantum electrodynamics is required for this purpose. Rather, we concentrate on developing insight by means of simple calculations using only nonrelativistic quantum mechanics. A unique feature of our presentation is that we have taken care to present conceptual issues in an experimental context, in which the difficulties of interpretation are dramatized by means of reference to actual con-temporary experiments.

In addressing our intended audience, our aim has been purely pedagogical. The goal has been to reach as many readers as possible. We have there-fore rigorously adopted the policy of introducing a topic only to the extent that it illustrates one or another of the overarching themes of quantum theory: squeezed states as exemplars of the uncertainty principle, quantum beats as exemplars of complementarity. In contrast, we have made no attempt to survey the field in its entirety and we have found ourselves forced to pass over in silence much fine work and many wonderful subjects. We have also paid only brief attention to a variety of alternative interpretations of quantum theory, and of entirely new theories that have been proposed to take its place. Brevity, we are convinced, is a great virtue.

We also hold it to be a virtue that a book speak the language of its intended readers. In this case our readers are scientists, engineers and mathematicians; and we suspect that most hold a view of the nature of physical reality shaped by their ordinary daily experience. It will become evident as this book proceeds, however, that the challenges to our understanding posed by quantum theory extend all the way to our conceptions of the nature of physical reality, and of the proper function of science itself. The research we describe has made abundantly clear that the conventional view is entirely inadequate. While a full discussion of these issues would carry us far beyond the scope of this book, we should alert the reader to the fact that modern research on the foundations of quantum mechanics has generated an extensive philosophical literature, as people struggle to find a way of thinking that can do justice to the remarkable situation that research has revealed.

No longer does it make sense to ignore the more bizarre phenomena of quantum physics. Atom-by-atom, instant-by-instant, we can probe them with fascinating results. As a consequence, contemporary research has moved far beyond the original concerns of quantum theory's founders, into such issues as quantum beats and quantum non-demolition measurements, quantum non-locality and quantum erasers. A burgeoning new mood is on the rise, in which the contradictory features of quantum phenomena are enjoyed in their own right. Seen in this light, the mysteries of quantum mechanics can enchant us, as they encourage us to ask ever-deeper questions. Perhaps by thinking long enough about these effects we will come to a new way of seeing, to a new idea that will allow us to understand the quantum world after all.

In every textbook we know, quantum mechanics has been largely sanitized of these beautiful enticements and their implications. This book is intended to complement these accounts with a broader range of considerations. With even a modest mastery of the technical side of quantum mechanics, many of its mysteries can be appreciated. Each new problem delights, through the confusion it sows in our otherwise straightforward mechanical picture of the world. We hope that every reader finds, as we do, that the puzzles of quantum theory are plums to be savored, and returned to again and again; and we write this book in the hope that our readers will join in the burgeoning discussion of these wonderful mysteries. The enjoyments they offer are both lasting and profound.

The Historical Development of Quantum Theory by Jagdisn Mehra and Helmut Rechenberg (Springer Verlag) Quantum Theory, together with the principles of special and general relativity, constitute a scientific revolution that has profoundly influenced the way in which we think about the universe and the fundamental forces that govern it. The Historical Development of Quantum Theory is a definitive historical study of that scientific work and the human struggles that accompanied it from the beginning. Drawing upon such materials as the resources of the Archives for the History of Quantum Physics, the Niels Bohr Archives, and the archives and scientific correspondence of the principal quantum physicists, as well as Jagdish Mehra's personal discussions over many years with most of the architects of quantum theory, the authors have written a rigorous scientific history of quantum theory in a deeply human context. This multivolume work presents a rich account of an intellectual triumph: a unique analysis of the creative scientific process. The Historical Development of Quantum Theory is science, history, and biography, all wrapped in the story of a great human enterprise. Its lessons will be an aid to those working in the sciences and humanities alike. Full review pending.

This is robust writing: some 1500 pages for volume 6 (part 2) which I had in my hands. But that's definitively the most complete and thoughtful account of the history of Quantum Mechanics I've read. The authors have read an impressive amount of original papers (their list takes some 200 pages) and are able to give us a fair summary of their results: what motivated them, how problems where treated and where these papers succeeded or failed. A small part of the book is devoted to the life of scientists involved in this adventure. The price of the book, unfortunately, makes it available mainly to institutions and libraries.

Quantum Non-Locality and Relativity: Metaphysical Intimations of Modern Physics by Tim Maudlin (Blackwell) Modern physics was born from two great revolutions: relativity and quantum theory. Relativity imposed a locality constraint on physical theories: since nothing can go faster than light, very distant events cannot influence one another. Only in the last few decades has it become clear that quantum theory violates this constraint. The work of J. S. Bell has demonstrated that no local theory can return the predictions of quantum theory. Thus it would seem that the central pillars of modern physics are contradictory. Quantum Non-Locality and Relativity examines the nature and possible resolution of this conflict. Beginning with accurate but non-technical presentations of Bell's work and of Special Relativity, there follows a close examination of different interpretations of relativity and of the sort of locality each demands. The story continues with a brief discussion of the General Theory of Relativity. This second edition also includes a new author's preface and an additional appendix.
It's no coincidence that those writing the clearest books in the philosophy of physics are also those doing the best work in the field. Maudlin's book is a perfect example of this. It is also remarkably self-sufficient, providing a review of special relativity, and a brief and lucid presentation of the foundations of quantum mechanics in the appendix. As a result, it should be readable by anyone with a high school education. Those already familiar with the physics and/or the issues may want to skip parts, though I should note that I found a couple hidden gems regarding things I was unfamiliar with or mistaken about even in the introductory sections.

The bulk of the book examines whether and to what extent quantum mechanics entails four superluminal phenomena often taken to be ruled out by relativity: superluminal matter transport, superluminal signaling, superluminal causation and superluminal information transfer. Maudlin convincingly argues that only the latter two of these are entailed by quantum phenomena. The book ends with an critical examination of the various theories put forward to circumvent these difficulties, and provides a brief discussion of how these issues hold up when we move to General Relativity and Quantum Field Theory.

Quantum Theory and the Flight From Realism: Philosophical Responses to Quantum Mechanics by Christopher Norris (Routledge) (HARDCOVER) is a critical introduction to the long-standing debate concerning the conceptual foundations of quantum mechanics, and the problems it has posed for physicists and philosophers from Einstein to the present. Quantum theory has been a major influence on postmodernism, and presents significant challenges for realists. Clarifying these debates for the non-specialist, Christopher Norris examines the premises of orthodox quantum theory and its impact on various philosophical developments. He subjects a wide range of opponents and supporters of realism to a high and equal level of scrutiny. Combining rigor and intellectual generosity, he draws out the merits and weaknesses from opposing arguments.

In a sequence of closely argued chapters, Norris examines the premises of orthodox quantum theory, as formulated most influentially by Bohr and Heisenberg, and its impact on various later philosophical developments. These include various proposals advanced by W V Quine, Thomas Kuhn, Michael Dummett, Bas van Fraassen, and Hilary Putnam. In each case, Norris argues, these thinkers have been influenced by the orthodox construal of quantum mechanics as requiring a drastic revision of principles that had hitherto defined the very nature of scientific method, causal explanation, and rational enquiry.

Putting the case for a realist approach that adheres to well‑tried scientific principles of causal reasoning and inference to the best explanation, Norris clarifies these debates for a non‑specialist readership and for students of philosophy, the history of science, and related disciplines. Quantum Theory and the Flight From Realism shows very strikingly how work of this kind can contribute to a better understanding of issues in the scientific domain.

 

Author introduction: In this book I examine various aspects of the near century‑long debate concerning the conceptual foundations of quantum mechanics (QM) and the problems it has posed for physicists and philosophers from Einstein to the present. They include the issue of wave particle dualism; the uncertainty attaching to measurements of particle location or momentum; the (supposedly) observer‑induced `collapse of the wave‑packet'; and the evidence of remote superluminal (i.e. faster‑than‑light) interaction between widely separated particles. I also show in some detail how the orthodox `Copenhagen' interpretation of QM has influenced current anti­realist or ontological relativist approaches to philosophy of science, among them the arguments advanced by thinkers such as Michael Dummett, Thomas Kuhn and WV Quine. Moreover, there are clear signs that some philosophers ‑ including Hilary Putnam ‑have retreated from a realist position very largely in response

to just these problems with the interpretation of quantum mechanics. So it is important to grasp exactly how the problems arose and exactly why ‑ on what scientific or philosophical grounds ‑ any alternative (realist) construal should have been so often and routinely ruled out as a matter of orthodox QM wisdom.

Perhaps a few personal reminiscences would not be out of place at this point. Eight years ago I moved from the Department of English to the Department of Philosophy in Cardiff, having previously published several books on literary theory that might be construed ‑ so it struck me now ‑ as going along with the emergent trend towards anti‑realism and cultural relativism in various quarters of `advanced' theoretical debate. What brought this home with particular force was the advent of a new postmodernist fashion which seemed to count reality a world well lost for the sake of pursuing its own favoured kinds of hyperreal fantasy projection. The results were evident

not only in literary studies ‑ a fairly safe zone for such ideas ‑ but also in other disciplines which had likewise taken the post modern‑textualist turn, among them history, sociology, political theory, and even philosophy of science. So it seemed important to challenge this burgeoning academic trend,

especially with regard to its impact on sociology of knowledge and `sciencestudies' where cultural relativism had by now established a strong disciplinary hold.

I offer the above brief remarks by way of explaining why an erstwhile literary theorist should have switched to the history and philosophy of science and then, yet more improbably, to conceptual problems in the foundations of quantum theory. For this has been among the most fertile sources for people in the (erstwhile) humanistic disciplines who wish to give `scientific' credence to their claim that realism is a thoroughly outmoded doctrine which no self-respecting physicist would nowadays endorse. Then there is the range of often far‑fetched speculative `solutions' that QM theorists have produced in response to what they take as the resultant crisis now afflicting all forms of `classical'‑realist or causal‑explanatory thought. The so‑called `many‑worlds' and `many‑minds' interpretations are among the most widely known since no doubt the most appealing in their sheer ontological extravagance and range of suggestive science‑fiction possibility. Elsewhere there is the vague notion that since quantum mechanics is deeply mysterious therefore it must be somehow connected with other such likewise mysterious matters as the nature of consciousness or the possibility of human freewill as against the claims of old‑style scientific determinism. Thus one often finds it said that present‑day science has abandoned any notion of an objective or mind independent `reality' and at last come around to an outlook of full‑fledged postmodernist scepticism with regard to such values as truth, objectivity, and method. This thesis can be made to look all the more plausible by citing authorities like Bohr, whose statements often invite such a reading on account of their highly paradoxical quality and fondness for all sorts of far-reaching speculative claims. Indeed a good many fashionable forms of anti‑realist and cultural‑relativist doctrine take for granted this idea that their position finds support from the latest findings of theoretical physics. Typical of these is Jean‑Frangois Lyotard's strangely placid assurance that `postmodern' science has nothing to do with truth‑even truth at the end of enquiry‑but everything to do with uncertainty, undecidability, chaos, paralogistic reasoning, the limits of precise measurement, and the observer‑dependent nature of (so‑called) physical `reality'.

So it seemed worthwhile ‑ even a matter of some urgency ‑ to examine the source of these ideas and determine how far they had taken hold through a failure (or refusal) to acknowledge the existence of alternative accounts. More constructively, my book presents various arguments in favour of one such alternative, the `hidden‑variables' theory developed since the early 1950s by David Bohm and consistently neglected or marginalized by proponents of the Copenhagen doctrine. This is a version of the pilot‑wave hypothesis, first put forward by Louis de Broglie, according to which the particle is `guided' by a wave whose probability amplitudes are exactly in accordance with the well­supported QM predictions and measured results. Where it challenges the orthodox theory is in Bohm's realist premise that the particle does have precise simultaneous values of position and momentum, and furthermore that these pertain to its objective state at any given time, whatever the restrictions imposed upon our knowledge by the limits of achievable precision

in measurement. On this basis, I suggest, one can begin to sort out the various deep‑laid philosophic confusions ‑especially that between ontological and epistemological issues‑which characterize Niels Bohr's writings on the topic, and which can still be seen in a great many present‑day treatments of QM theory. Very often these involve paradoxical claims about the `unreality' of time, not only within quantum physics and cosmology (e.g. John Wheeler's speculations about observer‑induced retroactive causality over billions of lightyears' distance), but also in the thinking of anti‑realist philosophers ‑ such as Michael Dummett ‑who deny the existence of verification‑transcendent truths with respect to past events other than those (very few) for which we possess adequate documentary warrant. Anti‑realism is nowadays a widespread trend among thinkers of various persuasions, from its sophisticated (Dummett‑type) logico­semantic form to Putnam's more pragmatic `internal realist' or framework‑relativist version, and ‑ at the farthest extreme ‑ postmodernist ideas about the eclipse of reality and the obsolescence of truth. What these otherwise diverse approaches all have in common, I argue, is a notion of quantum mechanics as having destroyed the case for scientific realism or created such problems with it as to require a radical redefinition of what `realism' entails, whether in the subatomic or the macrophysical domain. And this despite the well‑known paradox of Schrodinger's Cat, which amounts to a reductio ad absurdum of that doctrine when extended to the realm of macrophysical objects and events.

These confusions took hold at an early stage in the history of quantum physics (more specifically, in the well‑known series of debates between Einstein and Bohr), and cannot be resolved ‑only deepened or pushed to one side‑by adopting the orthodox instrumentalist line. They emerge most clearly in subsequent discussions of the 1935 Einstein­-Podolsky‑Rosen (EPR) paper, which laid down criteria for a realist interpretation compatible with the known laws of physics, among them those of relativity theory. The EPR argument in turn gave rise to J.S. Bell's equally famous theorem to the effect that any such interpretation ‑ one that entailed the existence of `hidden variables' would also entail some highly problematic consequences, including (what Einstein refused to accept) nonlocal effects of quantum `entanglement' at arbitrary space‑time distances. However, as I argue, Bohm's theory is able to accommodate this problem while also maintaining a realist ontology and producing results in accordance with the well‑established QM observational results and predictions. Moreover, it avoids the kinds of extravagant conjecture ‑ such as the `many­worlds' interpretation currently championed by David Deutsch ‑ which take orthodox QM as their basis for proposing a massive (scarcely thinkable) revision to our grasp of what constitutes a `realist' worldview. In Chapters 4 and 5 I take issue with the premises and the logic of Deutsch's argument, while remarking on the way that it unwittingly repeats whole chapters from the history of pre‑Kantian speculative metaphysics.

According to Deutsch, the many‑worlds (or multiverse) theory is the sole plausible, i.e. physically and logically consistent solution to the various well known QM paradoxes of wave‑particle dualism, remote simultaneous interaction, the observer‑induced `collapse of the wave‑packet', and so forth. According to this hypothesis we must assume that all possible outcomes are realized in every such momentary `collapse' since the observer splits off into so many parallel, coexisting, but epistemically non‑interaccessible `worlds' whose subsequent branchings constitute the lifeline ‑ or experiential world series ‑ for each of those endlessly proliferating centres of consciousness. Deutsch concedes that his multiverse theory is highly counter‑intuitive but none the less takes it to be borne out beyond question by the huge observational‑predictive success of QM and the conceptual dilemmas that supposedly arise with alternative (single‑universe) accounts. Moreover, he claims that this theory resolves a range of long‑standing and hitherto intractable philosophic problems, among them the mind‑body dualism, the various traditional paradoxes of time, and the freewill versus determinism issue.

I suggest, on the contrary, that Deutsch's argument involves a largely unwitting transposition of speculative themes from the history of rationalist metaphysics into the framework of present‑day quantum debate, often with bizarre or philosophically dubious results. Moreover, it discounts at least one highly promising alternative, i.e. Bohm's `hidden variables' theory, which offers a realist interpretation perfectly consistent with the full range of QM predictive­observational data. I then consider various possible reasons for the resistance to Bohm's theory among proponents of the 'orthodox' (Copenhagen) version and also for the strong anti‑realist, at times irrationalist, bias that has characterized much of this debate since Bohr's well‑known series of exchanges with Einstein. Chapter 5 concludes by pointing out some relevant contrasts between Deutsch's ontologically extravagant use of the many‑worlds hypothesis (one that bears a close though unacknowledged kinship to the thought of speculative metaphysicians from Leibniz to David Lewis) and those realist modes of counterfactual reasoning ‑e.g. in Kripke and the early Putnam ‑which deploy similar resources to very different causalexplanatory ends.

In more general terms, my book makes the case for an alethic (objective, truth‑based and verification‑transcendent) conception of realism, as opposed to the epistemic conception which on principle denies the possibility of truths beyond reach of our present‑best knowledge, evidence, or powers of observation. This latter viewpoint has dominated much of the debate about quantum mechanics, not only among orthodox theorists but also among those ‑including, arguably, the EPR authors‑who have sought to defend a realist interpretation. Indeed, it was just this ambiguity in the EPR paper that gave a hold for the apparently decisive counter‑arguments mounted by Bohr and his followers. I show how the orthodox (instrumentalist) stance gave way to a strain of dogmatic thinking which on the one hand refused to admit any question of the reality 'behind' or 'beyond' QM appearances, while on the other it effectively raised this refusal to the status of a full‑scale metaphysical creed with distinct irrationalist leanings. In short, the philosophy of quantum mechanics has remained in a state of Kuhian `crisis' for the past six decades and more compared with the theory's remarkable success in matters of applied technological progress and predictive‑observational warrant. If anything, the situation is now more confused ‑as a result of Bell's theorem and its subsequent experimental proof ‑ than when Planck and Einstein first proposed the quantum hypothesis in response to various anomalies encountered with phenomena such as black‑body radiation and wave‑particle dualism.

However, this gives all the more reason to think that the orthodox theory is indeed 'incomplete' in some crucial respect, and that Bell was justified despite his own results ‑ in holding out for a possible realist solution along the lines suggested by Einstein and Bohm. Such an argument will gain additional weight if one accepts the `classically' well established principles of causal reasoning and inference to the best (most adequate) explanation. To interpret QM‑on the orthodox account ‑as having somehow undermined those principles can scarcely be warranted given its conspicuous failure to resolve the kinds of problem pointed out by physicists, like Einstein and Schrodinger, who had themselves made decisive contributions to the theory at an early stage, but who later became deeply dissatisfied with the Copenhagen version. Still less can philosophers be justified when they invoke these unresolved problems in support of a programmatic anti‑realism extending far beyond the specialized domain of quantum‑theoretical debate. Thus it is preposterous in the strict sense of that term ‑ an inversion of the rational order of priorities ‑ when thinkers claim to draw far‑reaching ontological or epistemological lessons from a field of thought so rife with paradox and lacking (as yet) any adequate grasp of its own operative concepts. At any rate, there is something awry about a theory that has exerted such widespread influence while effectively raising incomprehension to a high point of orthodox principle. My book seeks to clarify these issues for the benefit of philosophers with a interest in theoretical physics and for physicists willing to consider philosophical questions that are often ignored or declared off-bounds in standard treatments of the topic.

Three Roads to Quantum Gravity by Lee Smolin (Basic Books) From one of the World's most distinguished scientsits, an elegant and concise presentation of the controversial ideas behind quantum gravity.

The Holy Grail of modern physics is the search for a theory of "quantum gravity." It is a search for a view of the universe that unites two seemingly opposing pillars of modern science: Einstein's theory of general relativity, which deals with large-scale phenomena (planets, solar systems and galaxies), and quantum theory, which deals with the world of the very small (molecules, atoms, electrons). In Three Roads to Quantum Gravity, cosmologist and science writer Lee Smolin provides the first concise and accessible overview of current attempts to reconcile these two theories in a final "theory of everything." Other books and articles have painted an incomplete picture by exposing only one of the different approaches, including string theory and loop quantum gravity. Here is the closest anyone has ever come to devising a completely new theory of space, time, and the universe to replace the Newtonian ideas that were the foundation of all science until the beginning of the twentieth century.

Quantum Theory and the Flight From Realism: Philosophical Responses to Quantum Mechanics by Christopher Norris (Routledge) is a critical introduction to the long-standing debate concerning the conceptual foundations of quantum mechanics, and the problems it has posed for physicists and philosophers from Einstein to the present. Quantum theory has been a major influence on postmodernism, and presents significant challenges for realists. Clarifying these debates for the non-specialist, Christopher Norris examines the premises of orthodox quantum theory and its impact on various philosophical developments. He subjects a wide range of opponents and supporters of realism to a high and equal level of scrutiny. Combining rigor and intellectual generosity, he draws out the merits and weaknesses from opposing arguments.

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