A realist's vision of the quantum world
Kragh, Helge Stjernholm
Published in: American Scientist
Publication date: 2019
Document version Publisher's PDF, also known as Version of record
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Citation for published version (APA): Kragh, H. S. (2019). A realist's vision of the quantum world. American Scientist, 107, 374-376. https://www.americanscientist.org/article/a-realist-vision-of-the-quantum-world
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has been the most successful theory of nature, and quantum mechanics The Scientists’ Nightstand, A Realist Vision precludes the sort of realism to which American Scientist’s books of the Quantum Smolin aspires. He describes three dif- section, offers reviews, review ferent kinds of anti-realists: The radical essays, brief excerpts, and more. World anti-realists, such as Niels Bohr, who For additional books coverage, believe that the properties we ascribe please see our Science Culture Helge Kragh to atoms and elementary particles are blog channel, which explores EINSTEIN’S UNFINISHED REVOLUTION: not inherent in them but are created by how science intersects with other The Search for What Lies Beyond the our interactions with them and exist areas of knowledge, entertain- Quantum. Lee Smolin. xxix + 322 pp. only at the time of measurement; the ment, and society: Penguin Press, 2019. $28. quantum epistemologists, who believe that science is not about what is real americanscientist.org/blogs he title of Lee Smolin’s new book in nature but is only about our knowl- /science-culture. may seem a little puzzling, given edge of the world; and the operational- Tthat Albert Einstein notoriously ists, who say that quantum mechanics ALSO IN THIS ISSUE chose to disregard quantum mechanics is not about reality but is just a set of NO SHADOW OF A DOUBT: rather than suggesting an alternative procedures for interrogating atoms. The 1919 Eclipse That Confirmed to it. In 1954, a year before his death, Smolin is a highly regarded theo- Einstein’s Theory of Relativity. he wrote, “I must seem like an ostrich retical physicist, a modern natural By Daniel Kennefick. who forever buries its head in the rela- philosopher, who in previous popular EINSTEIN’S WAR: How Relativity tivistic sand in order not to face the evil books has criticized the contemporary Triumphed amid the Vicious Na- quanta.” And yet Smolin’s title is not state of fundamental physics. In his tionalism of World War I. that much off the mark, for his ambi- influential 2006 book, The Trouble with By Matthew Stanley. tious project is to formulate a theory Physics, he provocatively attacked cur- page 376 of the quantum world—indeed, of the rent developments in string theory for physical world in its entirety—that sat- betraying the traditional standards of isfies Einstein’s philosophical desid- empirical science. Now he goes deeper, erata. To do so, the theory must be re- as deep as one can go, by investigating alistic, meaning that it must describe a critically and expertly the foundation- world that is comprehensible to the hu- al issues at the heart of quantum me- man mind but exists independently of chanics. Smolin does not merely want it. In Smolin’s words, the theory must to revise quantum mechanics or offer explain that matter has “a stable set yet another interpretation of it. No, he of properties in and of itself, without wants to replace it with an ultimate regard to our perceptions and knowl- fundamental theory. Because quantum edge”; furthermore, we must be able to mechanics, according to Smolin, rules 1919 eclipse. From Einstein’s War. comprehend and describe those prop- out realism, the new theory cannot be erties, and “understand enough about quantum-mechanical in nature, and FABLES AND FUTURES: the laws of nature to explain the history yet he describes it as a completion of Biotechnology, Disability, and of our universe and predict its future.” quantum mechanics. the Stories We Tell Ourselves. That is to say, the theory Smolin seeks It is not entirely clear how Smolin By George Estreich. must realistically capture the true es- conceives the relationship between his page 379 sence of the external world, and it must alternative and what is ordinarily un- be fully comprehensible. Moreover, it derstood as quantum mechanics. Like ONLINE must be deterministic, meaning that Einstein in the 1930s, Smolin admits the future state of a system is complete- the amazing instrumental successes of Upcoming in December on our ly determined by the laws of physics quantum mechanics, which have long Science Culture blog: acting on the present state. made it a sine qua non for physicists; 2019 Holiday Gift Guide “Most scientists are realists about however, like Einstein, Smolin is uncon- Gift recommendations for the everyday objects on the human scale,” vinced that these successes imply that science bookworms on your list. Smolin explains. But on the scale of quantum mechanics is true. And truth individual atoms, quantum mechanics is what matters. The anti-realism and
374 American Scientist, Volume 107 © 2019 Sigma Xi, The Scientific Research Honor Society. Reproduction with permission only. Contact [email protected]. indeterminacy of quantum mechanics Readers should be aware that Smo- sent his own proposal of a new concep- led Einstein to reject it as an incomplete lin’s courageous attempt to establish tual foundation for physics and cosmol- description of nature. Einstein’s unfin- fundamental physics on a new founda- ogy. This he does in terms of general ished mission, alluded to in the title of tion is to some extent a personal project. principles, which have in common that Smolin’s book, was to find the missing Based as it is on full-blown realism, the they are all related to Leibniz’s principle features of nature that would make it project is of course meant to result in an of sufficient reason: the metaphysical possible to construct a true theory of objective conception of nature that can claim that for every state of affairs there atoms, and Smolin is one of the few be comprehended and evaluated by all is an explanation of why it is as it is. modern Einsteinians who have taken physicists. But it is more than that. As Impressed by Leibniz’s “shockingly up this quest for a realist “theory of ev- Smolin candidly writes in an epilogue, modern” philosophy, Smolin suggests erything.” The alternative theory that for him the book is “a kind of mental that spacetime is not a continuum but Smolin is proposing needs to reproduce therapy,” because writing it has forced consists instead of hypothetical space- all of the verified results of standard him to reexamine the foundations of time atoms, an idea that also appears quantum mechanics—just as Einstein’s quantum mechanics and develop them in some theories of quantum gravity. theory of relativity needed to reproduce into a radically new conception of the In Smolin’s view, time is the one and the verified results of Newtonian me- quantum world. Likewise, he admits only fundamental substratum of the chanics—while resting on that deeper that his historical sketch of the many world, whereas space and the laws of truth. How this correspondence might quantum controversies is biased in that nature are not fundamental in the same be established is unclear to me. Einstein’s Unfinished Revolution is an eminently readable and engaging ac- count of a most difficult subject area. In Smolin’s view, time is the one and only In plain language Smolin describes by means of analogies the problems fundamental substratum of the world, with existing quantum theory and the meanings of fundamental concepts whereas space and the laws of nature are such as space, time, and causality. Some of these analogies are illuminat- not fundamental in the same sense. ing and refreshingly novel, as when he explains the concepts of locality and nonlocality by means of an imagined he definitely sides with Einstein and sense. They are emergent. It follows couple, Anna and Beth, who are both other physicists in supporting a real- that the laws of nature evolve in time, cat lovers but who disagree on other istic approach to the quantum world. a hypothesis that in different versions issues. Nonetheless, the book is no Realism is a premise, not a conclusion has been entertained by physicists for easy read, for the simple reason that it following from arguments. quite some time. One of the radical fea- deals with topics that are far from easy Nonempirical factors cannot help tures of Smolin’s theory is that it denies to understand. Smolin takes the reader playing an important role in areas of symmetries and reversibility at the fun- on an exciting journey through a doz- foundational physics, and Smolin ac- damental level, thereby contradicting en or more interpretations of quantum knowledges that these depend in part the known laws of physics, which are mechanics, some of them more exotic on “individual taste and judgment.” In symmetric with respect to time. than others. Among the better known, a critical and informative section on the All of this is very interesting and apart from the Copenhagen Interpre- so-called Many Worlds Interpretation of provocatively innovative, but it begs tation, are pilot wave theory, Bohmian quantum mechanics (which states that the question of why we should be- mechanics, and various so-called col- every quantum event that has multiple lieve in it. Smolin apparently thinks lapse models. In spite of Smolin’s he- possible outcomes leads to the splin- that some of the consequences of his roic efforts to explain in a simple man- tering of the universe into multiple re- theory—or vision of a theory—are em- ner what it is all about, in the end the alities), Smolin makes it clear that this pirically testable, at least in principle, reader may feel that he or she has just theory is not to his taste, even though it but he does not elaborate, and he gen- reached a higher level of confusion. ostensibly belongs to the realist camp. erally pays little attention to the pos- Smolin is as much a philosopher as When Smolin dismisses the Many sibility of experimental tests. a physicist, and he is at his best when it Worlds Interpretation as “magical real- The framework of Smolin’s book comes to explaining fundamental philo- ism,” it is for another reason: because it is in part historical, insofar as he uses sophical categories relevant to quantum presents “a moral and ethical quanda- the history of quantum physics to de- theory. In contrast to most other physi- ry.” After all, if there are numerous oth- fend his cause of finding a realist un- cists who are engaged in examining er copies of ourselves, why should we derstanding of the quantum world. foundational problems, he has a solid care about starvation, climate change, Although he admits that he is not a his- grasp of the philosophical literature and and tyranny on planet Earth? torian of science and that his version of takes seriously the work of quantum Smolin’s book is structured in three quantum history is merely a collection philosophers, such as David Deutsch parts, with the first being a semi- of “creation myths,” he nonetheless and Simon Saunders, at the University historical introduction and the second a presents a fairly detailed account of the of Oxford and elsewhere. It is rare to critical account of various more or less battles that have taken place between find such an appreciation of professional realist versions of quantum mechanics. realists and anti-realists since the mid- philosophers among modern physicists. Only in the third part does Smolin pre- 1920s. This account, in which the good www.americanscientist.org © 2019 Sigma Xi, The Scientific Research Honor Society. Reproduction 2019 November–December 375 with permission only. Contact [email protected]. guys (from Einstein onward) are con- trasted with the bad guys (Niels Bohr and the “Copenhagen ideology”—the belief that reality is fundamentally intertwined with the observer), is en- tertaining, but it is also one-sided and somewhat misleading. Smolin gen- erally exaggerates the dominance of the so-called Copenhagen orthodoxy, claiming that from about 1930 to 1980 “the anti-realism of the Copenhagenists would be the only version of quantum theory taught.” In fact, most textbooks in the period were nonphilosophical, ignoring the question of realism versus anti-realism, and they did not advocate Bohr’s quantum philosophy. Unfortunately the book is filled with historical errors. Some of them are fair- ly innocent, but others are of a more serious nature. For example, Smolin states more than once that Bohr’s atom- ic theory relied on Einstein’s hypothesis of photons, which is quite wrong. The quantum jumps in Bohr’s atom gave rise to monochromatic light waves, not photons, and Bohr resisted the concept of the photon until 1925. Also, Smo- lin states that at the turn of the 20th century, belief in atoms was a minority view, when in fact it definitely was a view shared by the majority of physi- cists. Readers who care about authentic history are advised to read Smolin’s ac- count with critical eyes. Nevertheless, the historical flaws are not essential to Smolin’s overall argument and they do not seriously weaken it. To summarize, Einstein’s Unfinished Revolution is a rewarding and thought- provoking book written by an eminent physicist-philosopher, one of the few in the great tradition of Einstein and Bohr. However, Smolin’s honest search for a fully comprehensible realist theory of everything may be just a noble dream, a sketch of a future revolution that re- mains unfinished because it cannot be finished. What Smolin offers in his book is not really a theory but a vision. To borrow a phrase from Einstein (from a 1922 letter commenting on a fundamen- tal unified theory proposed by German physicist Gustav Mie), “it is a fine frame, but one cannot see how it can be filled.”
Helge Kragh is a professor emeritus at the Niels Bohr Institute, University of Copenhagen, Denmark. He is coeditor with Malcolm Longair of The Oxford Handbook of the History of Modern Cosmology (Oxford University Press, 2019) and is the author of a number of books, including Niels Bohr and the Quantum Atom (Oxford University Press, 2012).
376 American Scientist, Volume 107 © 2019 Sigma Xi, The Scientific Research Honor Society. Reproduction with permission only. Contact [email protected].