Quantum physics, says physicist and writer Adam Becker, “is the most successful theory in all of science.” Its principles have led to breakthroughs in almost every field of physics and helped us develop technologies like LEDs and silicon transistors. And yet, Becker argues in his new book, What Is Real? The Unfinished Quest for the Meaning of Quantum Physics, physicists have yet to untangle exactly what quantum physics tells us about the nature of reality. The major difficulty is the measurement problem: What is really happening when a particle described by a probabilistic wavefunction locks into a single position when it’s measured?
In What Is Real? Becker traces the development of quantum physics, arguing that the standard historical narrative dismisses real concerns that early quantum skeptics raised. He makes the case that much work remains to be done to solidify our understanding and interpretation of the theory, a line of research known as quantum foundations. In the November issue of Physics Today, David Wallace calls the book “a superb contribution both to popular understanding of quantum theory and to ongoing debates among experts.”
PT: What inspired you to write a book about the past and future of quantum physics?
BECKER: I read a lot of popular science books when I was young, and most of them said very strange things about relativity and quantum mechanics that didn’t make sense to me. My confusion about relativity fell away when I actually learned the subject. But when I took courses on quantum mechanics in college, my confusion just got worse. Why do wavefunctions collapse when a measurement is made, rather than continuing to obey the Schrödinger equation? And what exactly constitutes a measurement?
Once I read up and got a handle on the various possible answers to those questions, I realized that I was left with a new question: How did quantum foundations end up this way? Why is the measurement problem dealt with only in this small corner of physics, rather than being treated as a theoretical problem of the first rank like the search for a theory of quantum gravity? I went looking for a good book about the history of quantum foundations. I couldn’t find one, so I decided I wanted to write one.
PT: What Is Real? revisits the famous debates between Albert Einstein and Niels Bohr. You argue that there’s a pervasive myth about Einstein stubbornly rejecting quantum mechanics in his old age as Bohr led the way into the future. What really happened?
BECKER: Einstein had no problem accepting quantum mechanics as true. He just didn’t think it could be the whole truth; he thought it was incomplete. That was the whole point of the Einstein-Podolsky-Rosen thought experiment, at least as Einstein saw it. Einstein’s version of EPR showed that either there was some more fundamental truth underlying quantum mechanics or there was something weirdly nonlocal going on. And that really got at Einstein’s two main concerns with quantum mechanics: realism and locality.
Einstein thought that quantum mechanics gave up on both of those ideas needlessly. There’s his “God doesn’t play dice” quote, which led a lot of people to think that Einstein’s concern was with randomness, but that wasn’t his true problem. He couldn’t stand the nonlocality and the antirealism. As for Bohr, it’s hard to be sure what he meant because he was such an opaque writer. But he definitely misinterpreted Einstein on several occasions.
PT: The book also discusses the brave physicists who did take the plunge into quantum foundations. What should readers take away regarding the contributions of David Bohm, Hugh Everett, and John Bell?
BECKER: Bohm was instrumental in reopening questions about quantum foundations after they had been laid aside by most of the physics community. In the early 1950s, he independently rediscovered the pilot-wave interpretation of quantum mechanics, which was first developed by Louis de Broglie in the late 1920s, and completed it to formulate a full-blown quantum theory of measurement. Bohm demonstrated that the predictions of the pilot-wave interpretation were identical to those of standard nonrelativistic quantum mechanics. That was widely believed to be impossible at the time, in part due to a flawed proof by John von Neumann.
Bohm’s ideas didn’t catch on, but his theory ultimately prompted Bell to investigate proofs like von Neumann’s in the mid 1960s. In doing so, Bell discovered his famous theorem about locality in quantum mechanics. It was ignored at first, then widely misunderstood.
Meanwhile, Everett was up to something completely different. When he was a grad student at Princeton in the mid 1950s, he developed an entirely original way of thinking about quantum mechanics. He called it the relative-states formulation of quantum theory, and at first it was ignored even more thoroughly than the ideas of Bohm and Bell. But over a decade later, physicist Bryce DeWitt picked up Everett’s ideas and promoted them for the rest of his life. He rebranded Everett’s interpretation the many-worlds interpretation, a name that stuck.
PT: Why do you think the physics community was so unreceptive to their ideas?
BECKER: Most physicists didn’t think there was any serious problem. Quantum physics, after all, works phenomenally well. If you could solve all these great problems without thinking too much about the conceptual difficulties at the heart of the theory—difficulties that even Einstein couldn’t solve—well, that sounds like a pretty good deal. So I think that led to a lot of apathy about quantum foundations among most physicists and a sense that things like solving the measurement problem were somehow unsuitable for real physicists to work on.
PT: What do you think is next—or should be next—for quantum physics?
BECKER: I think that whatever theory comes next—whatever solves the theoretical problems that people are currently trying to solve, like quantum gravity—will probably shed light on these foundational issues. I also think that the frustration and lack of progress in getting to that next theory have driven renewed interest in reexamining foundational issues. Now that we have long-standing open problems like moving beyond the standard model, maybe it’s time to go back to the foundations of our theories and say, “How can we solve the problems here, and are they connected to other problems we’re having?”
PT: What are you reading right now?
BECKER: I’m supposed to be reading books that I’m reviewing. But when I’m avoiding my work, I’m reading H Is for Hawk by Helen Macdonald. Next up is The Fifth Season by N. K. Jemisin. Other books I read relatively recently and enjoyed are Moonglow by Michael Chabon, Record of a Spaceborn Few by Becky Chambers, and Through Two Doors at Once by my friend Anil Ananthaswamy.
