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Einstein's Unfinished Revolution: The Search for What Lies Beyond the Quantum

Lee Smolin
Penguin Press
Publication Date: 
Number of Pages: 
[Reviewed by
Michael Berg
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Lee Smolin can be found all over the internet, in particular in a plethora of videos. Perhaps a good introduction to what he deals with in the book under review is the video by the same title, presented at the Perimeter Institute, where he is headquartered. Of course, the coverage in the book is far more ramified and expansive, but the lecture is representative.
Smolin’s focus in the book and talk is the foundations of quantum mechanics and the claim that there is something rotten in Denmark, in other words, with the Copenhagen interpretation of quantum mechanics as spearheaded by Niels Bohr, and, 369 miles south in Göttingen, Max Born. This all goes back to the 1920s, and the so-called Knabenphysik, with Werner Heisenberg as possibly its most prominent representative. According to Smolin, the concepts at the center of the turmoil are the principle of uncertainty of Heisenberg, Bohr’s notion of complementarity, and the non-classical statistics of Born which give rise to the probabilistic nature of the computations in QM. Of course, the agreement of QM with experimental results are stunning and largely unassailable, and Smolin certainly acknowledges this with enthusiasm, but that does not imply the theory is perfect.
This takes us to the titan of titans, Bohr’s friend and foil, Albert Einstein himself, one of the founders of quantum physics and, later, one of the most ardent opponents of the Copenhagen interpretation of QM. It is in connection with the latter that Einstein famously quipped, Raffiniert ist der Herrgott, aber boshaft ist er nicht, usually translated as “God is subtle, but He is not malicious.” Einstein objected to the fact that QM à la Copenhagen was (and is) not a realist theory: roughly speaking what this means is that the observer or measurer is necessary in all aspects of this business — remove him and there is no there there. On p. 84 of the book under review, Smolin describes it as follows: 
It was [Bohr’s] moment and he seized it, announcing the birth not just of a new physics but of a new philosophy. The moment for radical anti-realism had come … Bohr called the new philosophy complementarity [italics in the original] … Neither particles nor waves are attributes of nature. They are no more that ideas in our minds, which we impose on the natural world …
On p. 85 we read: 
Bohr’s position is anti-realist in the extreme, in that he denies that it is even possible to talk about an electron as it is in itself, outside the context of an experiment we construct. Science according to this picture is not about electrons; it is about how we talk about our interactions with them.
We find these pithy characterizations of the extreme positions of the Copenhagen interpretation of QM in Chapter 6, “The Triumph of Anti-realism,” and it is manifestly unsettling. But there is a counteroffensive about to be launched: Chapter 7 is titled, “The Challenge of Realism: de Broglie and Einstein,” and Chapter 8 is focused on David Bohm: “Bohm: Realism Tries Again.” Accordingly, we encounter, in addition to Einstein (who was in fact responsible for introducing the notion of wave/particle duality in the first place — for light particles), a courageous cadre of quantum physicists who refused to follow the Pied Piper. In point of fact, none other than Erwin Schrödinger was a non-believer, as was, to an extent, every mathematician’s favorite modern physicist, Paul Dirac. In 1935, Einstein, together with his collaborators, Boris Podolsky and Nathan Rosen, produced a famous thought-experiment which Smolin discusses very evocatively (see pp. 47–48 in the book), arguing that it fails (barely) because of its failure to take into account the QM notion of locality.
It is worth noting, for the purpose of clarification, that Smolin precedes the polemical fireworks which are featured throughout the book with a soft-ball presentation of quantum mechanics, altogether void of equations. There are no expositions of unbounded operators densely defined on a Hilbert space of states, no bras and no kets, nothing unitary except the pronouncement on p. 31 that the Schrödinger wave equation’s capacity of precisely describing the time-evolution of a quantum mechanical system is referred to as unitarity. Well, there it is, then, a reminder of how our cousins in (typically) the neighboring building speak a mathematical dialect that is rather unlike ours. C’est la vie.
The thrust of this book is to argue that QM as per the Copenhagen mainstream is an incomplete theory. There is no denying its success and its power, but there’s more to be said. Smolin argues that it is philosophically inadmissible to dance around reality by means of ploys that offend the sense of the real which is such an integral part of our perception of the world. Therefore, it is proper for science to keep seeking a realist presentation of quantum mechanics, extending what we have now, and correcting in various places. And so it is that as the book progresses, after Smolin has made his case criticizing the Copenhagen interpretation of QM, he proceeds to address what a future theory, in concert with Einstein’s dream, might look like.
But promoting his realist cause is a tricky business. He starts his twelfth chapter as follows: 
In the last few years the field of quantum foundations has undergone a lively ascension. After eight decades in the shadows it is finally possible to make a good career as a specialist in quantum foundations. That is all for the good; however, most of the progress (and most of the young people) has been on the anti-realist side of the field. 
Chapter Twelve starts the third and last part of the book; its two predecessors, closing Part Two, are titled, respectively, “Magical Realism” and “Critical Realism.” Suffice it to say that these two attempts at introducing a realist perspective into QM don’t make the cut as far as Smolin is concerned.
Regarding magical realism, the principal feature of which is the many worlds postulate due to Hugh Everett, he says on p. 146: 
It does not tell us which outcome will be observed. Contingent statements may be useful as they give us definite information about the system. But they do not give us complete information. A theory that gave us only contingent statements could not be enough for a realist. 
Regarding critical realism, the lynchpin is the notion of decoherence, which Smolin characterizes as the brainchild of a group of Oxford philosophers. To wit (p. 155): 
The idea of decoherence starts with the observation that a macroscopic system, such as a detector or an observer, is never isolated. Instead, it lives in constant interaction with its environment … This, roughly speaking, leads the detector to lose its delicate quantum properties and behave as if it were described by the laws of classical physics. 
Smolin presents a rebuttal of the decoherence stipulation originally due to Abner Shimony, for which the reader should refer to p. 158 ff.: it is somewhat intricate, and its discussion here would take too much space. Suffice it to say that critical realism won’t do either — so says Smolin — and we’re in Part Three. But he does not take us all the way home: home has not been defined yet or even identified. Here’s Smolin’s last paragraph (p. 279):
So I have no better answer than to face the blank notebook. We do have role models. Einstein did it. Bohr did it. De Broglie, Schrödinger, and Heisenberg did it, as did Bohm and Bell. They each found a path from that blank page to a foundational discovery that enlarged our understanding of how nature works. Start by writing down what you are confident we know for sure. Ask yourself which of the fundamental principles of the present canon must survive the coming revolution. That’s the first page. Then turn again to a blank page and start thinking.
I like the book, but be forewarned, it is somewhat idiosyncratic. 


Michael Berg is Professor of Mathematics at Loyola Marymount University in Los Angeles, CA.
The table of contents is not available.