Book review: Spooky Action at a Distance by George Musser (Scientific American/Farrar, Strauss, and Giroux, 2016 [paperback]).
There’s an old adage that gets bandied about, often in activist and political circles: think globally but act locally. In this context, the word ‘local’ is usually referring to a certain, small geographical region (sometimes as small as a town). But what do physicists mean when they use the word? This turns out to be a trickier point than many people realize. For the sake of argument, let’s assume that the universe consists of a bunch of stuff interacting with other stuff. There are two senses in which the word ‘local’ is applied. In one sense, when we say that something is ‘localized’, we mean that it is confined to a particular region of space and time. Einstein called this aspect “separability” and it is the idea that you can pull things apart and consider each of the parts on their own, in theory. So even if they initially take up lots of space (e.g. a whale or a tree or a galaxy) the various parts have identities that do not rely on the identities of the other parts. A tree branch is always a tree branch whether or not it is attached to a tree. This is fundamentally a statement about the nature of the stuff in the universe.
The other sense in which we use the term is related to the interactions in the universe. When we say an interaction is local, we usually mean that events in one region of spacetime should not affect events in some other, spacelike separated region of spacetime. To have an effect on something, we need to cross the spatial gap (or use intermediaries) between us and whatever we wish to influence that thing. Einstein called this “local action”. This sense of the word ‘local’ is deeply tied to the concepts of determinism and causality (which are not the same thing!).
Of course, if you’re reading this review then you probably already know that the world is inherently nonlocal at the quantum level where both senses of locality appear not to hold universally. Perhaps no phenomenon captures both senses of the word better than that of entanglement. In entangled quantum states, two (or more) things can seemingly act in unison regardless of how far apart they are. This was so unsettling to Einstein that he referred to it as “spooky action at a distance.” That phrase serves as the title of George Musser‘s excellent new book (Spooky Action at a Distance, Scientific American/Farrar, Strauss, and Giroux, 2016, $16.00 [paperback]). Musser first encountered the notion of nonlocality in a bookshop in the early 1990s while in graduate school. Back then, the nonlocality of quantum mechanics was rarely discussed in polite company. Certainly most courses on the subject completely ignored this disturbing fact. Thankfully, that is changing.
I was heartened to see that Musser begins his travelogue of the world of nonlocality with a visit to Enrique “Kiko” Galvez at Colgate University. Few people have done more to bring entanglement to the masses than Galvez who is one of the pioneers of low-cost entanglement experiments for use in undergraduate laboratories. I have had the joy of visiting Galvez’s lab myself and have known him for over a decade. He is one of a handful of people (including Mark Beck, David Branning, and a few others) who have endeavored to make entanglement a regular part of the quantum mechanics curriculum so that present and future students don’t have to stumble onto the concepts, which are so fundamental to the theory, by wandering into a bookshop (or, in today’s day and age, stumbling onto something via a google search). Indeed, their work allowed me—a theorist!—to introduce a lab component into our junior/senior-level quantum mechanics course and add interesting entanglement and single-photon labs to our sophomore-level modern physics course.
Musser uses his visit to Galvez’s lab as a launch point for a grand tour of the many aspects of nonlocality that pervade physics, including those in classical physics. Indeed, not all nonlocal features of the universe are confined to the quantum realm. One of Einstein’s goals in his development of general relativity was to eliminate the apparent nonlocal ambiguities in Newtonian gravity. In Newton’s theory, gravitational influences are instantaneous—there is no mechanical intermediary between two gravitationally interacting objects. This fact led to criticisms of Newton’s theory almost immediately from the likes of his long-time foil Leibniz. Musser deftly uses historical debates such as these in order to lay the conceptual groundwork for today’s attempts to unite quantum mechanics and gravity where the weirdness of nonlocality seems to reach its pinnacle, and spacetime itself may not be fundamental.
It is in these descriptions of both historical and contemporary scientific debates, and the profiles of the people involved, that I think Musser really shines. In particular, one point that really struck me was that he does an excellent job of conveying to the reader what it is like to be a physicist. Physics, as a science, is a bit different from the other sciences in how it is practiced and physicists, as a result, are unique. We approach the world in a slightly different manner than many other scientists. That’s not to say that we are in any way superior, just that we’re different. Contrary to the stereotype portrayed in popular media (e.g. The Big Bang Theory) physicists are hard to pin down. It is notable that, unlike the chemists (who are very hierarchical), we, physicists, tend to bristle at such tendencies. Getting physicists to agree on anything is a bit like herding cats. What unites us, aside from our natural curiosity, is the way we think. We are a strange mash-up of mathematician, philosopher, engineer, logician, and wide-eyed kid. (It is perhaps worth noting that Musser has degrees in electrical engineering, mathematics, and planetary science which, to me, is the ultimate physicist. Physics, after all, is more a way of thinking than a discipline.) As I like to tell people who ask me why I am a physicist, I never really grew out of that annoying “why?” stage. Answers rarely satisfy me. Musser really captures this in a way that I haven’t seen before.
Musser, of course, has spent many years as a science writer and editor, and thus spends a good deal of his time at scientific meetings or visiting individual scientists. He mines these connections throughout the book to great advantage, guiding the reader through the most up-to-date, cutting edge research into nonlocality. But he does so in a way that is approachable to the non-specialist. In fact, I liked this book so much that I have already assigned it to a few high school students that I have recently met as “required reading for future physicists.” But the book is not just for non-specialists. It’s an enjoyable summary of an odd phenomenon that is at the heart of how the universe operates and it captures precisely why that oddness strikes a certain chord with us as humans. Nonlocality calls into question the very structure of the universe itself, both in its operation and in its fundamental constituents. As Musser says, those constituents
…exist everywhere. They may well be right in front of our eyes and have gone unnoticed all this time. We may find the most exotic phenomena in the most prosaic places.