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Sneaking a Look at God's Cards, Revised Edition: Unraveling the Mysteries of Quantum Mechanics

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This is the best book I've seen on quantum mechanics. It's probably too hard to follow without some scientific experience on the part of the reader. But it is the only book I know of (and I'm aware of most) that really covers the conceptual issues of the entire subject in an open-minded non-romantic, non-mystical and realistic way. Very refreshing. A gem.

This is a very comprehensive introduction to the foundations of quantum mechanics for the sophisticated lay person who is willing to think and work through the examples and explanations.If you do the work you will really learn something--as opposed to popularizations that only give you the feeling of understanding--usually an illusion. No math background is assumed but the less math exposure you have the harder you have to work. I have read numerous popularizations--this is one of the very best. In particular it clearly and evenhandedly addresses the alternative interpretations of the quantum formalism pointing out the various myths and popular misconceptions that one can find in both popular and technical literature, the mistakes of Popper and Pais among them. The historical progression from the first versions of the Copenhagen Interpretations up through von Neumann's theorem, and Einstein's challenges(for once Einstein is treated fairly--not as an old geezer who was stuck in the past) through Bohm's 'hidden variables' approach, to Bell's analysis of nonlocality is especially good. It is often hard to keep straight the various logical twists and turns of the competing interpretations but Ghirardi continually recaps the arguments and clarifies the the different points of view. This book is in the league with Albert's and Gibbin's introductions to the philosophy of quantum mechanics.It is often useful to have more than one such book so that when you get stuck in one maybe the other has a clearer explanation. Also you could use this book in conjunction with Prof. Leonard Susskind"s quantum mechanics for the rest of us video lectures (9) on Stanford University itunes (FREE).

The public fascination with modern physics, particularly the strange world of quantum mechanics, seems to be growing and growing. This, like most fads, has both good and bad points - the good being the public is interested in science and seems to want to learn more; the bad being, well, many pop books have arisen exploiting the public's interest in these exotic topics, some of which tend to be written on a casual level - or worse, a quack level- and can therefore be fairly misleading.

That doesn't concern us here. Enter a fairly new book on quantum mechanics geared toward the popular level (superbly translated from the Italian by Gerald Malsbary), but the difference this time is, author Giancarlo Ghirardi is not only a theoretical physicist, he is actively involved in quantum foundational questions. Indeed, Ghirardi is one of the originators of an influential interpretation (more accurately, a "rival" scheme, we'll get into that later) of QM. So here we have the rare treat of an expert in quantum foundations sharing the challenges and struggles of his craft with the public. One couldn't ask for more in this regard. Nonetheless, when I say the book is geared toward the "popular" level, readers should realize the book is demanding. While equations illustrating key points are kept to a minimum and can be ignored to get the gist of his arguments, Ghirardi is very thorough in his description of the microphysics and the epistemological interpretation problems involved, as we might expect coming from an eminent physicist with a keen interest in these areas. Lay folks expecting an easy ride, even assuming some prior familiarity with the concepts, are in for a bumpy journey. One should realize this is a serious treatment of the issues.

I mentioned Ghirardi's "rival" scheme to orthodox QM above...what is it? Briefly, in 1985/86, Ghirardi together with two other Italian physicists (A. Rimini and T. Weber) proposed a theory which introduced two new constants into the standard quantum formalism, proposing a so-called "spontaneous localization" model for fellow specialists to consider. Thus, the trio essentially introduced another "hidden-variable" theory, alongside the existing de Broglie- David Bohm "pilot wave" model. The trio's theory became known throughout the physics literature as the "GRW" model (using the initials of all three physicists). The original motivation arose out of a dissatisfaction, shared by many physicists, with the orthodox so-called "Copenhagen" interpretation...something needed to be done to get around the troublesome "split" or boundary between the quantum world of linear superpositions vs. our classical world of definite outcomes, which is what we actually observe. The standard interpretation of QM left this issue poorly-defined and not succeeding in removing the "split" (although the split was certainly flexible), and hence many physicists interested in quantum foundational problems have attempted to tackle the problem with the goal of eliminating the inherent dualism implied. In the famous words of physicist/philosopher Abner Shimony, the goal is to "close the circle". The "GRW" trio, hence, saw the current orthodox interpretation of QM as merely a set of "recipes" for describing the outcomes of experiments, rather than a truly satisfying explanation for how the objective macroscopic world we observe comes about naturally out of the QM formalism. They wanted to "close the circle".

The GRW proposal, therefore, introduced several modifications to the standard linear Schrodinger state-vector formalism with several goals in mind:
1) the "collapse" of a wavefunction was taken seriously- i.e., there is an actual act of amplification, leading to well-defined individual states- of live cats or dead cats, definite pointer states, objective macroscopic outcomes, etc.. In the GRW model, this "collapse" is configured to come naturally from the dynamics of the microscopic formalism itself. (Hence, the model belongs in a general classification to those theories which accept an "objective collapse" as a real event, which differentiates it from decoherence models...the latter seeing microscopic-type behavior still continuing into the quasi-classical realm);
2) a starting assumption was that any additional terms must nonetheless render the modification equivalent to the standard model of QM, since the latter's predictions for microscopic behavior have been proven over and over to be highly accurate. Hence, any new theory should not contradict standard QM statistical predictions, if it wanted to be taken seriously; and
3) the behavior of a macroscopic system - and this is the strong point of the GRW model - should be shown to arise naturally from its microscopic constituents, and should be consistent with what we observe in the dynamics of the classical world. The virtue of the GRW model is that it does so without any troubling superpositions of macroscopic states. By tweaking the microscopic formalism by a few terms to allow for true collapses of superposition states, subatomic processes lead nicely into what we actually observe in the macroscopic realm- i..e, definite states and well-defined outcomes. This desirable result seems to give the theory somewhat of a conceptual advantage over non-collapse theories such as environmental decoherence- the latter not providing any real explanation for how definite outcomes occur from merely a density-matrix mix. (However, perhaps quantum behavior continues forever! It must be mentioned here that with the success of recent experiments to reproduce quantum-like behavior in larger and larger macroscopic objects, the precise point where quantum behavior leaves off and macroscopic objects take on well-defined properties is still a thorny problem. Indeed, some have speculated that our perception of macroscopic objects with "definite" properties is a result of our own evolutionary development as humans learned to structure the world into familiar patterns...and hence our sense of "definite" objects may not be an objective feature of reality).

Be that as it may, the overall goal of the GRW proposal was to obtain a unified description of all physical processes - microscopic AND macroscopic.
While this is not the place to attempt a detailed explanation of the GRW proposal (not a task most of us are equipped for anyway, including me), let's quickly look at some of the logic behind it. As Ghirardi recounts it, his trio initially set about asking themselves what objectives they wanted to reach and what should be the characteristics of those objectives. As we saw above, any new model should not disagree with the well-tested predictions of the standard theory on microscopic processes, but the GRW trio also wanted to be able to reproduce the dynamic "reduction" processes at the macroscopic level. Since the existing Schrodinger formalism only describes a perfectly deterministic linear evolution, getting beyond this limited state of affairs to get to a truly-collapsed dynamic could be accomplished by looking at various ways to modify it. Somehow, abrupt non-linear stochastic processes (i.e., "collapses") should be allowed and included to alter the smooth evolution of the Schrodinger wavefunction, which would account for the definite outcomes we observe in the world around us. But what is responsible for these "stochastic" dynamics? Our illustrious trio of researchers looked- very logically - at the macroscopic world for clues. It seemed that "position" (spatial location) stood out as a true key. Since sharply-defined positions seem to be a primary characteristic of macroscopic objects, what seemed to be needed on the microscopic level was to view "position" as a truly objective feature (vs. other possible variables), and hence build a theory around position's seemingly privileged role.

Let's quickly look at how the world evolves according to the original GRW model. A quantum state of a system develops according to Schrodinger's equation. At certain randomly selected instants, however, this development is arrested and the quantum state spontaneously collapses into a well-localized state (we won't worry about later refinements here, such as collective density perhaps being a trigger). Again, a particle spontaneously undergoes localization in the sense that it experiences a "collapse" of the linear Schrodinger evolution, a spontaneous abrupt "reduction" takes place, and hence our (previously only approximate) position becomes definite. For a single particle the probability of such a spontaneous collapse is so low that, in practical terms, the predictions of the theory are the same as those of standard quantum mechanics. But for a macroscopic system- i.e., a system consisting of a very large number of particles, this spontaneous collapse becomes a rather frequent event. The definite results are due to a group dynamic of the localized particle being coupled with other particles. When particles couple together to form an object, the small probabilities of spontaneous collapse quickly add up for the system as a whole, since when one particle collapses so does every particle to which that particle is entangled. Naturally, each outcome is unique, just as in our macroscopic world, because each run of events is a unique combination and therefore each collapse-dynamic produces distinct macroscopic results. Thus, the GRW proposal can explain in a mathematically precise way why we often observe superposition interference effects when looking at isolated subatomic particles, but never observe macroscopic objects in superpositions. By appreciating the privileged role played by spatial positions and thus focusing on the possibility of true localizations, the GRW model gives us a logical picture of how the micro-world produces our everyday world of definiteness. GRW obtains an evolution for wave functions that reproduces the Schrödinger evolution on the atomic level, while avoiding most of the "embarrassment" of macroscopic superpositions, such as suggested by Schrodinger's famous Cat Paradox. (In the GRW model, these superposition effects only occur for a fraction of a split-second).

After the trio published their work, the physics community's collective curiosity was aroused and theorists immediately began analyzing it in the journals. Weaknesses were of course found (only a few are mentioned here), such as the theory's seeming tension with the theory of relativity- it seems the GRW proposal requires a preferred initial frame of reference. The theory also has an inherent irreversibility, which some physicists see as a virtue, some as a vice. Perhaps the most common objection from other physicists questions the wisdom of modifying standard QM at all- the GRW proposal, as we have said, is not just another "interpretation" - it is actually a "rival" theory which introduces modifications into the standard formalism. As such, many physicists take a rather dim view of all such "hidden-variable" theories. As theorist Anton Zeilinger comments, "suggestions to actually change quantum mechanics are not just interpretations but are really alternative theories. In view of the extremely high precision with which the standard theory has been experimentally confirmed, and in view of its superb mathematical beauty and symmetry, I consider a final success of such attempts to be extremely unlikely."

Nonetheless, Ghirardi seems to take a pragmatic view, hoping readers will not lose sight of the many worthwhile accomplishments of his approach (he obviously is appealing to his fellow peers here, in spite of the book supposedly being geared toward the public). No doubt even those who see some technical problems in the theory as currently drawn up appreciate how much of an improvement the main idea is over the orthodox interpretation with its poorly-defined "measurement" postulate. And who knows - perhaps standard quantum theory may need some such modifications in the future. Modifications happen quite often in science and one never knows if the situation concerning QM might at some point require revision.
One can do no better than to end here with an appropriate quote from the last chapter of his book: "...I do not think it proper, in the present circumstances, to attempt to endow this theory with the status of a true scientific revolution. Its real merit, in my view, is that it constitutes an explicit example of how new lines of thought can be followed in order to escape the conceptual impasse encountered by the standard theory in its treatment of macrosystems. Thanks to the new theory, it has been possible to identify some of the characteristics that any future theory of the same type would have, and we get a clearer picture of the price that has to be paid for these characteristics."
Pretty much sums it up. Five stars.

You must NOT miss this book, if you are interested in foundational issues in quantum. Some may think its exaggeration, but I call this the best book outside of John S. Bell's own classic "Speakable" text. I would rate Ghirardi's work 6 stars out of 5, if I could(!)

I was unaware until recently that such an outstanding text exists, and what a pleasant surprise to find it. "God's Cards" does a terrific job in just about every way: it offers nice historical introduction including concise summaries of positions of famous physicists (not just Bohr, Einstein, Heisenberg and Schroedinger, but others who played a role, as well). The conceptual approach is performed in a gradual and careful way, with outstanding physical examples using optics and polarization. I've simply never seen such clear physical examples of quantum mechanical concepts and these alone make the book more than worthwhile.

When the author brings the reader to topics such as Einstein Podolsky Rosen and Bell's Theorem, the reader is well-prepared to get right to the heart of the matter and Ghriardi's clear prose brings the concepts home admirably.

While these latter topics also receive very nice (but brief!) treatment in Brian Greene's well known The Fabric of the Cosmos: Space, Time, and the Texture of Reality Ghirardi offers much more detail and depth on the background issues at stake.

But Ghriardi does not content himself with giving reader's a great understanding of EPR and Bell. He then goes on to discuss experiments to test quantum predictions in comparison with Bell's inequality, additional objections and interpretations of these analyses. Every topic is addressed carefully and deliberately.

The presence of quantum computing and quantum cryptography topics are also well done.

Buy this book!

This review was posted the (principal) author of Bell's Theorem and Quantum Realism: Reassessment in Light of the Schrödinger Paradox (SpringerBriefs in Physics)

If you want a serious book on conceptual problems behind quantum mechanics theory that does not use mathematics to fool the readers about the physical and philosophical troubles bounded to this discipline, this is your book. A convincing confirmation of the reason why one of the best physicist such as Dr. Feynman thought that no one has never understood completely quantum mechanics.

Yet another book that explores the mysteries of Quantum Mechanics (Q.M.) with the aim of making them accessible to an audience beyond those with degrees in physics or some related area of study that requires taking courses in Q.M. This has been a regular topic for authors that are practicing physicists (as Ghirardi is...), historians of science, popularizers of science, and others since the acceptance of Q.M. as an integral part of modern physical theory in the 1930s. This reviewer has read a fair number of those books over the years and overall I found Ghirardi's book a worthwhile addition on the topics it covers.

The content of the book's chapters can be divided into four areas. Chapters 1-7 introduce the fundmental concepts of Q.M. and some of the intellectual challenges and debates the physicists involved in their development (mainly Bohr and Einstein) engaged in during the formulation of what came to known as the Copenhagen interpretation of Q.M. Chapters 8-10 discuss later developments centered around the Einstein-Podolski-Rosen (EPR) challenge to the Copenhagen interpretation and re-examination of Q.M.'s foundations by John Bell with the concept of nonlocality emerging as key. Chapters 11-14 explore the implications of Q.M. with a variety of illustrative discussions - quantum computing and encryption, characterization of microsystems with identical particles, and superluminal (i.e. faster than light speed) signals. Finally, Chapters 15-19 discuss some of the perplexing situations that arise when attempting to develop a consistent view of how observations in the macroscopic world based on "classical physics" can be reconciled with microsystem behaviors based on Q.M. and different approaches that have been proposed for "closing the circle" including a discussion of the one that Ghirardi and two colleagues worked on known as GRW Theory.

In style Ghirardi's book is an attempt to give a technically correct discussion using only basic high school-level mathematics in the main body of the text with the material requiring more effort on the part of the reader placed in appendices at the end of some of the chapters. He also offers further elaboration on some material in the main text in notes collected at the end of the book that are bookmarked in the text. Overall the reviewer thought the approach worked well for the content discussed in chapters 1-10, but the content in chapters 11-19 was not so well served by the approach. In general the content discussed in chapters 11-19 involved the use of more intricate constructs and covered more subtle concepts. This part of the book might have been better, if the author had reduced the scope of material he attempted to cover and provided a more leisurely expanded discussion of some subset of topics. Overall though the book was readable and the author's ehthusiasm for the material really comes through. If a reader is looking for a reasonably sophisticated discussion of the foundations of Quantum Mechanics and the perplexing issues that arise when attempting to reconcile the behavior of microsystems obeying the dictates of Q.M. with the macroscopic "real world", this is a book definitely worth considering. The book does not go into the history of the development of Q.M., but there are many good books on that topic already. Another book on Q.M. that covers much of the same material, but takes a different approach and includes more of the history is "Beyond Measure" by Jim Baggott. Yet another book that can be an interesting read is Whitaker's book "Einstein, Bohr, & the Quantum Dilemma" which gives a simplified discussion of the material Ghirardi covers in Chapters 1-10 with less technical detail. If one wants to really go into the material of Chapters 1-7 in detail with a blow by blow account of the arguments among the founders of Q.M. there is the book "Quantum Dialogue" by Mara Heller, but this is not always an easy read due to the fact that Heller is a Professor of History and Philosophy of Science and assumes the reader already has some background in the topics and in open questions related to the development of Q.M. up to 1930 (Baggott's book has most of the background necessary for Heller).