But while Einstein won—and would continue to win—all the logical battles, Bohr was decisively winning the propaganda war. The Copenhagen doctrine of the completeness of quantum theory and the inescapability of fundamental chance spread, enforced by Bohr and Heisenberg and the rest of the Copenhagen school. Behind the scenes, the Copenhagenists did not agree with each other, but to the world they presented a unified front. Meanwhile, Einstein and Schrödinger both rejected Bohr, but they also bickered with each other.
Here is Einstein’s own description of Copenhagen: “The theory reminds me a little of the system of delusions of an exceedingly intelligent paranoiac.” Philosopher Imre Lakatos gave this later assessment:
In the new, post-1925 quantum theory the ‘anarchist’ position became dominant and modern quantum physics, in its ‘Copenhagen interpretation’, became one of the main standard bearers of philosophical obscurantism. In the new theory Bohr’s notorious ‘complementarity principle’ enthroned [weak] inconsistency as a basic ultimate feature of nature, and merged subjectivist positivism and antilogical dialectic and even ordinary language philosophy into one unholy alliance. After 1925 Bohr and his associates introduced a new and unprecedented lowering of critical standards for scientific theories. This led to a defeat of reason within modern physics and to an anarchist cult of incomprehensible chaos.
Strong words. It is Becker’s burden, and Becker’s triumph, to show that every word is true.
The story has twists and turns: John von Neumann’s purported mathematical proof (1932) that quantum mechanics is complete and one could not add anything more to it and retain its successful predictions; the philosopher Grete Hermann’s detection in 1935 of the fatal flaw in von Neumann’s proof—and the complete disregard of her work; the elaboration of Einstein’s reasoning into the famous Einstein-Podolsky-Rosen (EPR) argument; Bohr’s incomprehensible response to EPR; Schrödinger’s reaction, including his eponymous cat. Surely, one thinks, this mess must have been cleaned up eventually! But it never was. It persists to this day. And we are only through the first third of the book.
Robert Oppenheimer is reported to have said, ‘If we cannot disprove Bohm, then we must agree to ignore him.’
The middle third of Becker’s book adopts a somber tone in the stories of three renegades who bucked the system in the 1950s and ’60s, after the Copenhagen mysticism had congealed into an icy command: shut up and calculate! Work on the foundations of quantum theory was effectively forbidden, with one’s career and future at peril. The first renegade was David Bohm, a bright and dutiful Copenhagenist until he met the aging Einstein and recanted. Bohm rediscovered the pilot wave theory that Louis de Broglie had presented at Solvay in 1927. The theory slices through the enigma—wave or particle?—like Alexander’s sword through the Gordian knot: the answer is wave and particle. The wavefunction becomes a pilot wave that guides the particles along their paths. The theory is completely deterministic—no playing dice—and recovers all the predictions of standard quantum mechanics. One would think Einstein would love the theory, but he did not. The dreaded nonlocality had not been exorcized. Indeed, it was even more striking.
Bohm’s theory put the lie to von Neumann’s impossibility proof by direct counterexample. Contra Bohr, the particles are visualizable even at microscopic scale. In short, the theory demonstrates beyond all doubt that the Copenhagen interpretation is nonsense. But Bohm’s work was ignored and effectively suppressed.
A political leftist, Bohm had refused to testify at the House Un-American Activities Committee. He was dismissed from his job at Princeton and went into exile in Brazil. His U.S. passport was revoked. He eventually found his way to Birkbeck College in London, but never received the recognition that was his due. In a notorious episode, Robert Oppenheimer is reported to have said, “If we cannot disprove Bohm, then we must agree to ignore him.”
The second renegade was a graduate student at Princeton not long after Bohm left in 1952. Also rejecting Copenhagen, Hugh Everett took Schrödinger’s evolving wavefunction and removed the collapse. He argued that rather than an incomprehensible smear resulting, as Schrödinger’s neither-alive-nor-dead cat suggested, a multiplication of worlds results. Schrödinger’s cat ends up both dead and alive, as two cats in two equally real physical worlds. Today this approach is called the many-worlds interpretation.
Everett’s thesis advisor, John Wheeler, had great enthusiasm for Everett’s innovation. But he insisted that Everett get the nod of approval from Bohr. Bohr refused, and Wheeler required Everett to bowdlerize his thesis. Everett left academia and did not look back. His work lay in obscurity.
The last and greatest renegade was John Stewart Bell. Spurred by Bohm’s papers, Bell queried whether Einstein’s dreaded spooky action at a distance could be avoided. Copenhagen and the pilot wave theory had both failed this test. Bell proved that the nonlocality is unavoidable. No local theory—the type Einstein had sought—could recover the predictions of quantum mechanics. The predictions of all possible local theories must satisfy the condition called Bell’s inequality. Quantum theory predicts that Bell’s inequality can be violated. All that was left was to ask nature herself. In a series of sophisticated experiments, the answer has been established: Bell’s inequality is violated. The world is not local. No future innovation in physics can make it local again. The spookiness that Einstein spent decades deriding is here to stay.
How did the physics community react to this epochal discovery? With a shrug of incomprehension. For decades, discussion of the foundations of quantum theory had been suppressed. Physicists were unaware of the problems and unaware of the solutions. To this day, they commonly claim that Bell’s result proves Bohm’s theory to be impossible and indeterminism to be inevitable, while Bell himself was the staunchest advocate of Bohm’s deterministic theory. Even now, the average physicist has no understanding of what Einstein argued in the EPR paper and what Bell proved.
The last third of What Is Real? could hopefully be titled “Slow Convalescence.” Gradually the worst excesses of Bohr’s influence are mitigated as Bell’s work inspires a new generation to look into foundational issues. We meet a new cast of characters, and the overall atmosphere is mildly optimistic. But there is a long way to go, and this very book could prove to be a watershed moment for the physics community if it faces up to its own past and its present. Or, following the fate of Einstein, Bohm, and Everett, Becker could just be ignored. But if you have any interest in the implications of quantum theory, or in the suppression of scientific curiosity, What is Real? is required reading. There is no more reliable, careful, and readable account of the whole history of quantum theory in all its scandalous detail.--Tim Maudlin reviewing What Is Real?: The Unfinished Quest for the Meaning of Quantum Physics by Adam Becker in Boston Review. [HT: Liam Kofi Bright]
In his review, Maudlin (recall) makes clear that he thinks that in the history of quantum mechanics epistemic considerations have been thwarted by political machinations in the physics community. I want to make an impure three-fold distinction: 1. Some of the political machinations are connected to external politics--e.g., the reception of Bohm's theory really suffered due to his leftism. 2. Some of the political machinations are internal to science--including debates over resources and, let's say, conceptual hegemony (which often creates better access to resources). For example, Bohr and his students/admirers turn out to be very good at turning conceptual hegemony into resources. 3. And some of the political machinations are connected to underlying philosophical commitments (about nature of explanation, about what counts as intelligible, action at a distance, etc.)
The problem is that 2-3 also often involve debates over what counts as proper epistemic considerations. (Let's stipulate that 1 is really unconnected to epistemic considerations.) But Maudlin, a word class philosopher of physics, is unabashed in taking sides here and suggesting that the scientific community has not merely made mistakes about philosophy (as philosophy arises in research), but also failed to make all possible epistemic progress in some sense.
It's worth noting that Maudlin here does not consider the possibility that the conceptual and theoretical confusions in the physics community (which are response of politics in all three senses) may have been fruitful to the epistemic progress physics has made. This is not my own view in this case, but that's because I don't consider myself an expert on the history and philosophy of quantum mechanics. Even so, the older I get, the more receptive I am to the idea (I associate it with Bill Wimsatt) that too much conceptual clarity can sometimes hinder progress (for example, ambiguity can be useful).
One important implication of Maudlin's analysis is that even in a field that is central to much of science, attracts widespread interest, and which is broadly international in scope, one cannot assume an efficient market in ideas in science. Regular readers know I think (recall for example) too much philosophy and science, decision-theory, and epistemology tacitly relies on such a free market in ideas in its image of science (but that's changing among students of Kevin Zolman and folks with a Ghent connection).
It is notable that Maudlin aims to end (the review of Becker) on an optimistic note about the future of quantum mechanics (and cosmology). But it is notable that he offers no ground for this optimism. For, he (Maudlin--I have not yet read Becker) never confronts what norms and institutions are responsible for the thwarting of epistemic considerations. (We do get mention of some big personalities -- Bohr, Feynman --, but that is not sufficient explanation.) I mention this because in some way the epistemic grounds of contemporary particle physics have narrowed considerably: there are a few big and very expensive particle accelerators and a few very very expensive instruments that probe space (and so back in time); access to these machines is a political (in the second sense) affair; they are controlled by committees funded by big grant agencies. And their publications are committee work (sometimes huge number of 'authors'). This is big science, big data, big statistics,* big software and big committees. It would be a miracle if politics became less under these circumstances.
Maudlin himself holds Kant and Kantian philosophy responsible for the mess in physics (and Kuhn). Really: "The hand of Kant lies behind both Bohr and Kuhn." I think it is undeniable that neo-Kantianism is important for understanding both the early debates in the reception of quantum mechanics and (mediated via Max Weber) as background to Kuhn's philosophy. Much as I like holding philosophers responsible for mucking things up in the world, but I really doubt that Kantianism is responsible for the state of affairs diagnosed by Maudlin/Becker. I do suspect that the decline of philosophical education and wider cultural literacy in the larger culture of science education impacted the decline of conceptual clarity and philosophical discussion within physics. I suspect this because we see something similar in the development of twentieth century economics (often recruited from physicists), who also show such a decline. But that's just a hypothesis.
I close with a final reflection. The peculiarity of Maudlin's larger review is that the first half of the review really vindicates let's call it the empirical basis of Kuhn's philosophy of science. (I leave aside here incommensurability.) The internal life of science is, in part, governed by politics in various senses. That was part of the scandal Kuhn caused. It does not follow it is wholly so governed, and so I am not suggesting Kuhn's whole philosophy is thereby vindicated.
*The statistics used in collecting the big data is also quite esoteric now.