What is Real? The Unfinished Quest for the Meaning of Quantum Physics 
by Adam Becker
Basic Books, 2018

Science writer Adam Becker begins his tremendously appealing new book What is Real? The Unfinished Quest for the Meaning of Quantum Physics in the only place this kind of book really can begin: with German physicist Erwin Schrödinger and a dead cat.

The feline in question, known far afield of the physics world, is Schrödinger's Cat, and it stars in a thought experiment designed to illustrate one of the most peculiar aspects of quantum physics. A cat (several physics-popularizers gratuitously refer to the animal as an “innocent” cat, although the smarter half of humanity knows this is a categorical impossibility) is placed in a box along with a small mass of radioactive material connected to a Geiger counter. If the Geiger counter detects radioactive decay, it trips a hammer that shatters a vial of poison, killing the cat. Since the radioactive decay is totally random, there's no way for an outside observer to know the state of the cat unless that outsider observer opens the box. In the world-view of quantum physics, prior to the opening of the box the cat is in a superposition, a floating cloud of possibilities that include both living and dead. Its final state is not only observed by opening the box – it's determined by opening the box.

Or so went the Copenhagen interpretation, which seemed to make alarming implications about a universe that doesn't quite exist in the traditional fixed sense of the term unless it's being watched. And flowing from that was another ramification of quantum physics, equally alarming: two quantum particles, having once interacted with each other, are entangled forever – alter the spin or position of one, and the spin or position of the other is simultaneously altered, regardless of the physical space separating the two. This flies in the face of several settled, accepted understandings of physics, including the unmovable ceiling of the speed of light – leading Albert Einstein, among others, to contend that since cause must always precede effect and things must always travel to their destinations in order to reach them, something must be rotten in the state of the quantum understanding of reality. Surely, objectors asserted, there must be some kind of hidden information tipping off the whole process. But decades of experimentation have shown that such hidden variables don't exist – and that, therefore, the fundamental bedrock of all reality is a constant, baffling fizz of not-quite-reality.

And yet, reality works. And this apparent contradiction is at the heart of Becker's book, which takes readers through all of these epic discoveries and disagreements, always with the subject's deepest questions (like the book's title) foremost in view. “If the unobservable 'metaphysical' content of our best scientific theories,” Becker asks, “ – stuff like electrons – really bear no relation to all the actual stuff in the world, then why do are scientific theories work at all?”

Books like What Is Real? live or die by the companionability of the author, and in this case Becker is a perfect choice to make sense of it all (or at least whatever sense is possible). He smoothly, easily dramatizes the great debates and the outsized personalities of quantum physics and fits it all into an enthusiastic, readable narrative, and along the way he digresses wonderfully on a wide variety of scientific phenomena. About the creation of thermite, for instance, he first warns his readers not to try this particular creation themselves (just in case the possibility of self immolation wasn't warning enough) and then describes it with a nifty brevity. “Not only is the thermite reaction amazingly intense, but it continues to run until the rust and aluminum are used up, no matter what you do to it,” he writes. “You can put it underwater, you can cover it with sand, you can even put it in the vacuum of space – it will keep burning.”

Of course Becker knows better than anybody that the question posed in the title of his book currently has no answer. Indeed, the blame for the lack of an answer can be laid squarely at the doorstep of quantum physics, which is eminently testable and predictable and confirmable but completely refuses to be comforting. But reading What is Real? will give you a toehold, at least. This is our story so far.

Steve Donoghue was a founding editor of Open Letters Monthly. His book criticism has appeared in the Boston Globe, the Wall Street Journal, and the American Conservative. He writes regularly for the National, the Washington Post, the Vineyard Gazette, and the Christian Science Monitor. His website is http://www.stevedonoghue.com.