On What Is Real?

This is one of those books I feel I can only talk about with people as crazy as I am. In spite of the madness of its contents, it’s serious, learned, and thoughtful. Becker opens with the Copenhagen Interpretation of quantum mechanics, which holds that quantum objects — electrons, photons, and so on — don’t exist in any given location until they’re observed; before that, there’s only a wave function giving the probability of an object being somewhere, not the object itself. And yet the interpretation also claims these quantum objects are the very stuff that makes up classical objects, everything from a hydrogen molecule to the Sun, and many of its adherents go further and argue that quantum objects don’t really exist at all, that they’re merely mathematical abstractions. How odd — how can a classical object be made of what doesn’t exist? And it’s unclear where the dividing line between quantum and classical even falls.

What does all this mean for us, and what does it mean to measure something? From the start, something didn’t sit right. There’s the measurement problem: if wave-function collapse can only happen through observation, then the line between quantum and macroscopic objects is being crossed. And the properties of quantum objects seem to require nonlocality — where Newtonian mechanics is like a billiard table, objects bouncing off one another and not moving unless made to, quantum mechanics violates that, with particles modified from great distances, farther than light speed should allow. None of this fits what we know about the universe, but Bohr and his followers insisted quantum theory was complete, right up until the day they all died.

Becker’s book is really about the life cycle of the Copenhagen Interpretation, especially the challenges to it. It remains the dominant theory, he tells us near the end, but it’s far from the only one: the first real challenge came from Einstein himself, and we now have pilot-wave theory, the many-worlds interpretation, and others, while spontaneous-collapse theory poses a challenge to quantum theory as a whole. What makes the book so interesting is Becker’s argument that the Copenhagen Interpretation’s dominance isn’t really due to “science” as traditionally construed. It emerged while logical positivism was in vogue and spoke to that philosophical moment; David Bohm was ostracized for his politics, spent years exiled in Brazil, and was pushed out by Bohr’s circle; Hugh Everett treated his own advances as a kind of game and much preferred a high-paying job in the Cold War military-industrial complex; and John Stewart Bell serves as a kind of unsung hero, the one who really poked holes in von Neumann’s theorem, whose work, in Becker’s telling, broke the dam and let theoretical pluralism into quantum mechanics. It’s hard to avoid the impression that Bohr is the villain of the story. He was wickedly smart and apparently charismatic, and his students worshipped him — they seem to have thought he could do no wrong — but he was also self-protective, a bit narrow-minded, and painfully obtuse, and his students went on to gatekeep the field in the next generation, to the detriment of physics as a whole. Becker elegantly shows how social, political, and philosophical concerns shaped quantum theory as much as intellect did.

Even so, it’s a wonder the Copenhagen Interpretation remains dominant. Becker argues it’s simply because it works — and here the philosophers of physics are at odds with the physicists. Sure, it functions well mathematically and gets the job done, but it’s also an incoherent theory that may be preventing the paradigm shift the rest of the field needs to click into place; it works for now, but there may be more effective, efficient ways forward if only we could think about it differently. Fascinating stuff, and some of it blew my mind. I’m so glad I read it.