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The Age of Entanglement: When Quantum Physics Was Reborn

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Louisa Gilder's new book is about abstract science and the very real people who clash (and collaborate) over its truth and meaning. *The Age of Entanglement* is an old story with a new perspective, a dramatic new telling -- and a new ending. An ending that shows Einstein was right and launches quantum physics toward its next great chapter.

All the old characters are here -- Bohr, Heisenberg, Schrödinger (who coined the word "entanglement"), Pauli, Born, Dirac, de Broglie, and of course Einstein, who thought "spooky action at a distance" was implausible yet found Bohr's entire quantum mechanical philosophy even less convincing. Unlike other tellings, however, Gilder vividly deploys their actual words from speeches, papers, letters, and memoirs to recreate the intense conversations and rancorous debates that toppled the Newtonian world. Our new understanding of entanglement, moreover, changes the very nature of the old quantum debates. Gilder's description of Schrödinger's epiphany that led to his wave equation is almost euphorically exciting and inspiring.

Despite the quantum revolution, big questions remained, questions that only Einstein, Schrödinger and few others had the courage to raise. And now enters the new cast -- Robert Oppenheimer, John von Neumann, David Bohm, Richard Feynman, and the particle smashing Irishman John Bell, who from the early 1960s through his untimely death in 1990 showed entanglement was real. Bell is perhaps the most-important-little-known physicist, and Gilder brings the late CERN engineer-theorist to life just as his work has become the most-cited in all of physics and is breaking out across the scientific and technological frontiers.

From Vienna, Solvay, and Copenhagen to Rio, Princeton, Berkeley, Geneva, and back to Vienna, the reader is there for Bell's intuitive breakthrough that brought the 1935 Einstein-Podolsky-Rosen paper out of laughable obscurity back to forefront of the debate (EPR argued that quantum mechanics was incomplete). And you are in the basement room where the experimentalists John Clauser and Dick Holt constructed the awkward tubular photon-counter that first proved the entanglement that years later multi-kilometer fiber-optic rings around Geneva would show with even greater precision.

Waves or particles, statistics or reality, mind or matter, information or physics, these are some of the biggest questions we know. This is the mystery of the entanglement that, although still not fully understood, is even now spawning new technologies like quantum cryptography and quantum computing and which, as you will find at the end of Gilder's great book, somehow connects the universe across the generations.

-Bret Swanson

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Here is Gilder (on page 242) recounting a typically rich offering from the understated but always logical John Bell:

Bell looked at Jauch as if he wasn't quite certain the other hadn't been making a joke. "I have a question about complementarity," he said, in the voice of one who is changing the topic slightly. "Because it seems to me that Bohr used the word with the reverse of its usual meaning." He grinned, tipping he head to the side. "Consider, for example, the elephant. From the front she is head, trunk, and two legs. From the back she is bottom, tail, and two legs. From the sides she is otherwise, and from the top and bottom different again. These various views are complementary in the usual sense of the word. The supplement one another, they are consistent with one another, and they are all entailed by the unifying concept `elephant.'" Bell's hands gestured to suggest this. His eyebrows then lowered. "But Bohr, Bohr wouldn't -- it's my impression that to suppose Bohr used the word in this ordinary way would have been regarded by him as missing his point and trivializing his thought. He seems to insist rather that we must use in our analysis elements which contradict one another, which do not add up to, or derive from, a whole. By `complementary' he meant, it seems to me, the reverse: contradictariness."

This book is a laudable effort at a popular account of one of the most remarkable and counterintuitive discoveries in modern science, the existence of entanglement. Gilder covers the development of quantum mechanics, the considerable disputes over its foundations and consequences, and the eventual discovery of non-locality and entanglement. A number of important figures, notably Bohr, Einstein, and Schrodinger figure prominently. Gilder focuses also on a number of lesser known figures, notably the theoretician David Bohm and several experimental physicists, and above all, the important theoretician JS Bell. Gilder develops her narrative with an unconventional and largely successful device. She reconstructs important events and particularly important conversations in an effort to present the history accurately and give it an accessible quality.

Gilder's story is essentially the difficulty of coming to terms of some of the counter-intuitive implications of quantum theory. She presents Einstein and some others, notably Louis DeBroglie and Schrodinger, as drawing attention to some of the challenges to conventional thinking inherent in quantum mechanics. In her reconstruction, efforts to draw attention to these problems were repulsed by the fuzzy orthodoxy of the doctrine of complementarity emanating from Bohr. Eventually, individuals like Bell would question this orthodoxy and produce theoretical treatments that expanded the truly strange implications of quantum mechanics and suggest possible experiments. In an irony that Gilder doesn't expand upon, Einstein's doubts eventually gave rise to research that confirmed the counter-intuitive properties that Einstein felt were likely to undermine quantum mechanics. Much of this is quite well done and this book is generally written well.

Gilder has, however, bitten off more than she can chew. A large fraction of the book is an abbreviated history of the emergence of quantum theory. While generally solid, this is not crucial for the main story. At the same time, her description of quantum phenomena and entanglement would have benefited from more extensive description. The same is true for her description of the experiments that demonstrated entanglement and its features. Gilder would have done better to provide more detail on the basic features of quantum mechanics and entanglement and then proceed to the history of entanglement. She is also somewhat superficial on some important issues, such as the role of Von Neumann's non hidden variables argument.

Gilder also presents the story as one of generational conflict and change, and to a considerable extent, this is correct. But what would have happened if WWII hadn't occurred and interrupted the normal activities of many physicists? It seems likely that physicists would have had to confront the problems at the root of quantum mechanics much earlier.

Kudos to Louisa Gilder for tackling an important topic in such a creative and wonderful manner. The author has done what very few seem capable of doing - making quantum physics understandable and enjoyable for the non-scientist and layperson. There are quite a few books that attempt to tackle the subject of entanglement, but Gilder's book stands above the pack. It's a tour de force. She does a terrific job of presenting the dynamics of scientific discovery with extraordinary flair. It is as if the reader is a fly on the wall during the many important discoveries and debates that have fueled the accumulation of scientific knowledge. Many of the great minds that have contributed to the advance of quantum physics over the past century come to life in Gilder's book. We see the humanness that exists along side the genius. There is a wonderful complexity to scientific discovery that is not well appreciated by the masses. Gilder's book illuminates that complexity in splendid fashion. This book is a treasure. I congratulate the author on her fine accomplishment, and enthusiastically encourage readers to purchase a copy of The Age of Entanglement. It's the kind of book that is difficult to put down and you don't want to end. Five stars for the book and one more star for the incredible effort that it took to produce it.

I thoughly enjoyed reading the carefully referenced "dialogs/conversations" Miss Gilder weaved together to create a novel like experience. I hope that people are not turned off by the "quantum physics" in the title. Miss Gilder does a wonderful job of following the ideas of quantum physics from it's beginnings with it's many false starts, to current understanding (or puzzled understanding- can this really be?)
I felt as though I was a fly on the wall, as the well-known, and not so well known, scientists had discussions, reasoned out ideas, lost some, regained others, and puzzled thier way though the seemingly impossible complex possiblities. She caught "science" as it realy happens. False leads, promising ideas that could not be tested, experiments with unexpected results, and personality conflicts between scientists. All the human elements that are lost in many nonfiction accounts of modern science. People tend to think of "science" as being a series of linear discoveries, when in reality the "connect the dots" is sometimes quite random, and connections come from unexpectted places/people.
Louisa Gilder's book is one such unexpected welcome find.
She not your usual science writter. Enjoy.

In 1989, the year before he died, John Bell gave the "speech of his career" to his fellow physicists, taking issue with the standard interpretation of quantum physics: "It would seem that the theory is exclusively concerned about 'results of measurement' and has nothing to say about anything else. What exactly qualifies some physical systems to play the role of 'measurer'? Was the wavefunction of the world waiting to jump for thousands of millions of years until a single-celled living creature appeared? Or did it have to wait a little longer, for some better qualified system...with a Ph.D.? If the theory is to apply to anything but highly 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?"

In The Age of Entanglement, Louisa Gilder presents us with quantum physics not as a textbook abstraction, but as a vigorous debate among brilliant men and women trying to make sense of the most baffling of mysteries. Gilder has performed a great service by assembling a vast collection of letters, conversations, speeches and anecdotes to tell this story in a fascinating way. Over many years of contentious theorizing and difficult experimentation, physicists came to grips with the implications of quantum mechanics: either little things are not fully real until they are observed by big things like us (the view attacked by Bell); or maybe they are real in some mysterious way, entangled in a hidden web of nonlocal connections. Quantum physics challenges the traditional scientific view of a world consisting of separate, independently existing objects exerting forces on one another from point to point to point in space.

I suggest that readers without a lot of familiarity with quantum physics have handy a book which explains the physics a little more clearly, such as Rosenblum and Kuttner's Quantum Enigma. The strength of Gilder's book is less in its explanations than its storytelling. For that, it is a great read.

Louisa Gilder's book "The Age of Entanglement" is a rather unique and thoroughly engrossing book which tells the story of quantum mechanics and especially the bizarre quantum phenomenon called entanglement through a unique device- recreations of conversations between famous physicists. Although Gilder does take considerable liberty in fictionalizing the conversations, they are based on real events and for the most part the device works. Gilder is especially skilled at describing the fascinating experiments done by recent physicists which validated entanglement. This part is usually not found in other treatments of the history of physics. Having said that, the book is more a work of popular history than popular science, and I thought that Gilder should have taken more pains to clearly describe the science behind the spooky phenomena.

Gilder's research seems quite exhaustive and well-referenced, which was why the following observation jumped out of the pages and bothered me even more.

On pg. 189, Gilder describes a paragraph from a very controversial and largely discredited book by Jerrold and Leona Schecter. The book which created a furor extensively quotes a Soviet KGB agent named Pavel Sudoplatov who claimed that, among others, Niels Bohr, Enrico Fermi and Robert Oppenheimer were working for the Soviet Union and that Oppenheimer knew that Klaus Fuchs was a Soviet spy (who knew!). No evidence for these fantastic allegations has ever turned up. In spite of this, Gilder refers to the book and essentially quotes a Soviet handler named Merkulov who says that a KGB agent in California named Grigory Kheifets thought that Oppenheimer was willing to transmit secret information to the Soviets. Gilder says nothing more after this and moves on to a different topic.

Now take a look at the footnotes on pg. 190-191 of Kai Bird and Martin Sherwin's authoritative biography of Oppenheimer ("American Prometheus"). B & S also quote exactly the same paragraph, but then emphatically add how there is not a shred of evidence to support what was said and how the whole thing was probably fabricated by Merkulov to save Kheifets's life (since Kheifets had otherwise turned up empty-handed on potential recruits).

If you want to obtain even more authoritative information on this topic, I would recommend the recent book "Spies" by Haynes, Klehr and Vassiliev. The book has a detailed chapter which discusses the Merkulov and Kheifets letter procured by the Schecters and cited by Gilder. The chapter clearly says that absolutely no corroboration of the contents of this letter has been found in Kheifets's own testimony after he returned to the Soviet Union or in the Venona transcripts. You would think that material of such importance would at the very least be corroborated by Kheifets himself. A source as valuable as Oppenheimer would also most certainly be mentioned in other communications. But no such evidence exists. The authors also point out other multiple glaring inconsistencies and fabrications in the documents cited in the Schecter volume. The book quite clearly says that as of 2008, there is absolutely no ambiguity or the slightest hint that Oppenheimer was willing to transmit secrets to the Soviets; the authors emphatically end the chapter saying that the case is closed.

What is troubling is that Gilder quotes the paragraph and simply ends it there, leaving the question of Oppenheimer's loyalty dangling and tantalizingly open-ended. She does not quote the clear conclusion drawn by B & S, Haynes, Klehr, Vassiliev and others that there is no evidence to support this insinuation. She also must surely be aware of several other general works on Oppenheimer and the Manhattan Project, none of which give any credence to such allegations.

You would expect more from an otherwise meticulous author like Gilder. I have no idea why she entertains the canard about Oppenheimer. But in an interview with her which I saw, she said that she was first fascinated by Oppenheimer (as most people were and still are) but was then repulsed by his treatment of his student David Bohm who dominates the second half of her book. Bohm was a great physicist and philosopher (his still-in-print textbook on quantum theory is unmatched for its logical and clear exposition), a dedicated left-wing thinker who was Oppenheimer's student at Berkeley in the 1930s. After the War, he was suspected of being a communist and stripped of his faculty position at Princeton which was then very much an establishment institution. After this unfortunate incident, Bohm lived a peripatetic life in Brazil and Israel before settling down at Birkbeck College in England. Oppenheimer essentially distanced himself from Bohm after the war, had no trouble detailing Bohm's left-wing associations to security agents and generally did not try to save Bohm from McCarthy's onslaught.

This is well-known; Robert Oppenheimer was a complex and flawed character. But did Gilder's personal views of Oppenheimer in the context of Bohm taint her attitude toward him and cause her to casually toss out a tantalizing allegation which she must have known is not substantiated? I sure hope not. I think it would be great if Gilder would retract this material in a forthcoming edition of this otherwise fine book.

Age of Entanglement is really two books in one, and what you think of it might depend on which piece you are interested in.

The book is a superb history of the development of quantum mechanics from around the beginning of the 20th century. The author tells a fascinating tale of how the most brilliant minds in physics developed and criticized quantum theory. Nonscientists should especially appreciate the thorough description of how the ideas developed via theoretical debate and devising empirical tests of the various theories. As a history of science, the book is excellent.

For anyone interested in learning about quantum theory, however, the book might be a disappointment. Descriptions of the theory are jargon-laden and not particularly illuminating. Moreover, they are embedded in longer passages about the personalities involved in the debate (including details that are often trivial and unnecessary) and surrounding circumstances such as the effect of the rise of Hitler in Germany and the HUAC in post-War America. Although those passages are usually quite interesting, the theory itself is often difficult to follow as a result and there are clearer descriptions of quantum physics elsewhere.

If you are not very familiar with quantum physics, you can still read this book as an excellent history of the development of scientific ideas without trying to understand all of the nuance behind those ideas.

After reading Louisa Gilder's new book I was at a loss for words; how does one write anything (of merit) about the subject of Quantum Mechanics while also earning the title of 'page turner' ? Initially I was unsure about how much interest the book would hold for me: as an undergraduate in Astrophysics I've had wavefunctions and uncertainty relations hammered into me until they weren't funny (if they ever were). This book however takes a totally different tack, doing away with anything text-book and yet still retaining real integrity to the subject of quantum theory. The book is not about Quantum theory in the strictest sense; it is a completely original, beautifully narrated chronology of the developments in Quantum Mechanics and the people involved (from the earliest foundations to quantum computation). Aside from the various interpretations and formulations of Quantum Mechanics that the book historicizes, it also gives an overall sense of just how different the earlier time periods (1900-1940) of Physics were and the uniqueness of the 'quantum club' of Bohr, Einstein, Pauli &c &c. The reason why this book is such a pleasure to read is due to the formidable lengths that Gilder has gone to, in order to select from the vast amount of literature and commentary, the best and most poignant discourse on the subject. The fact that the best and most poignant remarks made were deeply philosophical, controversial, and ultimately revolutionary in the field of science, is (I think) what motivated the book's writing.

Gilder deserves a great deal of credit for crafting a wonderfully original, thought-provoking and enjoyable book on the subject of Quantum Mechanics.

As a physicist, I found the first half of this book, describing the Bohr-Einstein years, fairly interesting. It vividly dramatizes the controversies of the day, and provides a good antidote to the oversimplified textbook-style history of physics.

The second half of the book was, in my opinion, far less interesting. It's bloated with dull anecdotes that should have been more selectively edited. Gilder sets up a dramatic climax in which hidden variable theories are tested experimentally and found to be incorrect, just as everyone had expected. Not very dramatic.

I definitely would not recommend this book to anyone who is not a physicist. Gilder simply doesn't explain the physics clearly enough to make it intelligible to the general reader. She uses vague analogies, like explaining entanglement in terms of a tiger pacing back and forth in front of a mirror. The lack of illustrations make it impossible to understand what she's depicting in many cases. Various people have done nice short, nontechnical explanations of topics like the EPR paradox. I suspect that a non-physicist would get through all 400 pages of Gilder's book without as clear an idea of the physics as they could get from one of these shorter explanations.

I have some concerns about the book's accuracy that go beyond the issue of dramatizing the story using fictionalized dialogs. On p. 147, Gilder describes events that took place in September 1933: "A few weeks later, Ehrenfest walked into the waiting room of the Professor Watering Instituut in Amsterdam, where his fifteen-year-old son Wassiljii, who had Down syndrome, was cared for. Hitler has just passed a law 'for the prevention of genetically impaired progeny,' starting the organized sterilization of people who were not likely to produce the 'master race.' Soon the Hitler-ordered 'mercy deaths' of disabled children would begin, the job done by doctors, in their offices." She then goes on to describe how Ehrenfest shot Wassiljii and then himself. She seems to be intent on leaving the reader with the very strong impression that Ehrenfest's actions were the result of Nazi persecution. (In addition to his son's disability, Ehrenfest was a Jew.) But Amsterdam wasn't taken by the Nazis until 1940. The eugenics law had been passed only two months before Ehrenfest's suicide, and would have only applied within Germany. The Nazi murders of the disabled didn't occur until 1939.

The book has been knitted together from a large number of original articles. The notes alone take almost 60 pages at the end of the book. The plot largely concerns with key contributors to our understanding of one of the most profound paradoxes of quantum physics, and the author is clearly passionate about the human drama involved in making science.

However, when it comes to explaining the quantum physics itself, the author's passion seems to diminish. Let me quote the definition of one of the most central concepts to the book taken from page 300: "Bell's inequality, stated roughly, is that a local hidden-variables explanation of entanglement requires certain kinds of outcomes to occur more often than they actually do". The brevity of explanation left me wondering about the depth of the issues at stake.

The book is likely to be well received by those who already have a solid understanding of the quantum physics and would like to get better acquainted with the history of events covering the period between 1909 and 2006.