American Scientist

COMING OF AGE WITH QUANTUM INFORMATION: Notes on a Paulian Idea. Christopher A. Fuchs. lvi + 543 pp. Cambridge University Press, 2011. $70.

In the post-Stalin Soviet Union, dissidents used underground networks to distribute censored material. This activity, which was called samizdat (which translates to “self-published”), put its practitioners at grave risk of harsh punishment. For scientists today, making public one’s philosophical ideas is not nearly so risky but nevertheless requires substantial courage. That is what Christopher A. Fuchs, a Senior Researcher at the Perimeter Institute for Theoretical Physics, in Waterloo, Canada, began to do in his correspondence with friends and colleagues in 1995, inspired by an encounter with two books that impressed him deeply: Wolfgang Pauli’s Writings on Physics and Philosophy, and K. V. Laurikainen’s Beyond the Atom: The Philosophical Thought of Wolfgang Pauli. As his correspondence about the ideas these books inspired in him grew, Fuchs began calling the collection of e-mail messages his “samizdat” and started distributing chunks of it to new correspondents. After his home in New Mexico burned down in May of 2000, he decided to begin gathering the correspondence with an eye toward publishing it on the preprint server arXiv.org, and a year later he posted more than 500 pages of messages there under the title Notes on a Paulian Idea: Foundational, Historical, Anecdotal and Forward-Looking Thoughts on the Quantum. (He used the fire as an excuse, saying, tongue in cheek, that he was taking this step as a way of backing up his hard drive.) These e-mails written between 1995 and 2001, grouped by correspondent, are now available in book form as Coming of Age with Quantum Information.

Among the “subversives” who were, knowingly or not, dragged into Fuchs’s samizdat by corresponding with him are some of the leading scientists in the field of quantum information theory—people such as Charles Bennett, Gilles Brassard, Carlton Caves, Rolf Landauer, David Mermin, Asher Peres, John Preskill, Abner Shimony, Bill Wootters and Anton Zeilinger. The conversations they had with Fuchs were often about technical aspects of their field, which aims to harness the power of quantum mechanics to create new technologies for cryptography, teleportation and computation. But above all, these incredibly interesting and often very personal letters, full of scholarship, excitement, enthusiasm and perplexity, are about a passionate young scientist’s attempts to come to grips with “the overwhelming message quantum theory is trying to tell us.”

In contrast to the Soviet dissidents, Fuchs takes a philosophical position that is, among the plethora of interpretations of quantum theory, well aligned with mainstream thought—that is to say, well aligned with the operationalist philosophy defended by Niels Bohr, Werner Heisenberg and Pauli, a view referred to as the “Copenhagen interpretation.” Indeed, Fuchs says that he is “concerned by the growing abandonment of standard (Copenhagen) quantum mechanics that I see all around me.” What makes Fuchs’s contribution unique is that he is one of the few who take the details of that philosophy very seriously and follow them to what seem to be their ultimate consequences. And those consequences, when clearly spelled out, can sound subversive indeed.

We learn in the introduction to the book that Fuchs was a nonconformist from an early age. After finding that the physics he learned in junior high school wouldn’t allow him to fulfill his television-fueled dream of flying to the stars, he decided that “Physics must be wrong!” and that he “had to become a physicist, not for the love of physics, but for the distrust of it.” He chose to attend the University of Texas at Austin, where his rebellious spirit found much to resonate with in the ideas of John Archibald Wheeler, who said, “The only law is that there is no law.” Wheeler’s influence is patent throughout the book and provides some of the most amusing and thought-provoking passages. For example, when Fuchs was corresponding with Peres in December of 1999 about the paper they were writing called “Quantum Theory Needs No ‘Interpretation,’” he remarked that

with Physics Today, our potential readership may be on the order of 50,000 people or more! You know that John Wheeler had this idea that things become more real as they become acknowledged by more and more members of the “community of communicators.” I would hate one of the things we said to become real if later we decided we didn’t like it!

Such a statement may on the surface appear to veer dangerously close to the type of mysticism found in some popular misrepresentations of quantum theory, but that’s far from being the case. This is good mysticism—akin to that of Erwin Schrödinger or Bohr, not that of What the Bleep Do We Know!? It is well-informed and often deep. And it’s unapologetic: In one passage David Mermin comments that Fuchs is

getting close to Schrödingerian mysticism. I suspect the only difference (if it is a difference) is that you say the observer is in the world while Schrödinger . . . says that the world is in the observer. Both of you say (with Pauli) that they cannot be separated.

Fuchs’s reaction dispels any doubt: “God, I loved that! Can I put it in the Samizdat??!?” He seems to have no qualms about sounding mystical; he talks to Mermin of his “religious love of the quantum and its mysteries,” and he says to his friend Greg Comer that “I think I take religious comfort in [quantum theory]. . . . I am a priest, a student of the holy scriptures.” But when Fuchs forwards to Paul Benioff one of his later letters to Comer, he is careful to say, “Don’t take the religious imagery as a serious re?ection of my views; I used it only to help drive a point home.”

It was in Pauli that Fuchs found substance for his thoughts: “With Pauli’s way of putting things, I felt I had finally latched on to the correct flavor of idea for taking Wheeler’s program forward.” The series of e-mails that are collected in this book are, in Fuchs’s words, “my best efforts to date at defining a vague thought that keeps creeping into my mind—the Paulian idea.” That idea is perhaps best expressed in a quote from Pauli that Fuchs shares with Comer:

In the new pattern of thought we do not assume any longer the detached observer, occurring in the idealizations of this classical type of theory, but an observer who by his indeterminable effects creates a new situation, theoretically described as a new state of the observed system.

Or as Fuchs himself puts it in a later message to Comer:

The world in some very real sense is a construct and creation of thinking beings simply because its properties are so severely tied to the particular questions we ask of it. But on the other hand, the world is not completely unreal as a result of this; we generally cannot control the outcomes of our measurements.

This book is above all very personal. In it the reader will find plenty of anecdotes about Fuchs’s friends, his wife and daughter, his dogs, his bad poems and his dreams, including one in which he finds a bottle of “Kant Cola” in a dark, smoky, Bohemian-type joint in Austin. He takes a sip, and “for a miraculous moment,” he says, “I understood all the intricacies of the world—I understood the necessity of quantum mechanics.” The personal stories give life to the book, as when we find out about his family’s tragic loss of their home and nearly all of their belongings to the Cerro Grande fire in New Mexico.

One should not approach this book expecting a coherent treatise—it is the furthest thing from that. But in it readers will find a delightfully poetic vision for our world. Fuchs’s message is one of hope—hope that we will soon finally get to “the bottom of things,” and that when we do, we will find that “the world is so much more than a mechanical contraption clinking along,” and that “there is room for something new under the sun.” When he writes to friends and family about losing his belongings in the fire, he says, “Now that so many of my records are gone, I hope there is a grain of truth in John Wheeler’s words. For then, the past would be every bit as open as the future.” Fuchs finds it “hard to gulp that my whole life is an illusion.” He talks about “wanting a locus for free will,” saying that “quantum mechanics . . . helps me believe we’re closer to that situation than I once thought possible.”

Fuchs can be tendentious at times. In one passage, for example, he dismisses the widely held many-worlds interpretation of quantum theory because the many-worlders “likely would have been predisposed to many-worlds even if they had known no quantum mechanics.” Writing to Peres about some of the criticism of their 1999 Physics Today article, he says,

I am not pushed to the rejection of a free-standing reality in the quantum world out of a predilection for positivism. I am pushed there because that is the overwhelming message quantum THEORY is trying to tell me.

Elsewhere, however, he gives signs that he would probably also have been predisposed to his subjectivist view even if he had known no quantum mechanics: “If [quantum] indeterminism had not been of such a variety as to allow us more free reign over our destiny or destruction,” he says, “I think I would be quite disappointed in it.” One can believe in Bayesianism—the subjective interpretation of probabilities that is favored by Fuchs—regardless of quantum mechanics. Indeed, subjective probabilities actually make more sense in a classical world. In a deterministic universe, any probabilities must be a measure of someone’s ignorance about the factual situation; in a quantum world, where probabilities seem to be determined by physical law, it is harder to defend such an interpretation.

Although some of Fuchs’s pronouncements must be taken with a grain of salt, the book is indeed a gem. But it is not easy reading. Few other than those initiated in the mathematics of quantum theory will be able to make much of all the talk of Hilbert spaces, mutually unbiased bases, density operators, trace-preserving completely positive maps and whatnot. But some of the explanations of quantum information technologies such as teleportation and cryptography will be accessible to a larger audience. And none of the technicalities are important for the understanding, or entertainment, that the book provides. Also, thanks to its nonlinear organization, readers can skip over the most opaque parts and just sample what interests them. Those interested in quantum foundations will find the book an inexhaustible source of amusing quotes and food for thought, even when—or especially when!—they disagree with the views expressed. Anyone under the impression that all questions about the foundations of quantum theory were settled long ago ought to take this unique opportunity to peek into the personal communications of some of the leaders in the field. They will find evidence that the debates about the fundamental nature of our world are very much alive—even if few have the courage, as Fuchs does, to bring them out in the open.

Eric Cavalcanti is a Research Fellow at the Centre for Quantum Dynamics at the Nathan campus of Griffith University in Queensland, Australia.