Jim Baggott’s new book, Quantum Reality, is now out here in US, and I highly recommend it to anyone interested in the issues surrounding the interpretation of quantum mechanics. Starting next week I’ll be teaching a course on quantum mechanics for mathematicians (more about this in a few days when I have a better idea how it’s going to work). I’ll be lecturing about the formalism, and for the topic of how this connects to physical reality I’ll be referring the students to this new book (as well as Philip Ball’s Beyond Weird).
When I was first studying quantum mechanics in the early-mid 1970s, the main popular sources discussing interpretational issues were uniform triumphalist accounts of how physicists had struggled with these issues and finally ended up with the “Copenhagen interpretation” (which no one was sure exactly how to state, due to diversity of opinion among theorists and Bohr’s obscurity of expression). Everyone now says that the reigning ideology of the time was “shut up and calculate”, but that’s not exactly what I remember. The Standard Model had just appeared, offering up a huge advance and a long list of new questions with powerful methods to attack them. In this context it was was hard to justify spending time worrying about the subtleties of what Copenhagen might have gotten wrong.
In recent decades things have changed completely, with the question of what’s wrong with Copenhagen and how to do better getting a lot of attention. By now a huge and baffling literature about alternatives has accumulated, forming somewhat of a tower of Babel confronting anyone trying to learn more about the subject. Some popular accounts have dealt with this complexity by turning the subject into a morality play, with alternative interpretations portrayed as the Rebel Alliance fighting righteous battles against the Copenhagen Empire. Others accounts are pretty much propaganda for a particular alternative, be it Bohmian mechanics or a many-worlds interpretation.
Instead of something like this, Baggott provides a refreshingly sane and sensible survey of the subject, trying to get at the core of what is unsatisfying about the Copenhagen account, while explaining the high points of the many different alternatives that have been pursued. He doesn’t have an ax to grind, sees the subject more as a “Game of Theories” in which one must navigate carefully, avoiding Scylla, Charybdis, and various calls from the Sirens. One thing which is driving this whole subject is the advent of new technologies that allow the experimental study of quantum coherence and decoherence, with great attention being paid as possible quantum computing technology has become the hottest and best-funded topic around. Whatever you think about Copenhagen, what Bohr and others characterized as inaccessible to experiment is now anything but that.
While one of my least favorite aspects of discussions of this subject is the various ways the terms “real” and “reality” get used, I have realized that one has to get over that when trying to follow people’s arguments, since the terms have become standard sign-posts. What’s at issue here are fundamental questions about physical science and reality, including the question of what the words “real” and “reality” might mean. In Quantum Reality, Baggott provides a well-informed, reliable and enlightening tour of the increasingly complex and contentious terrain of arguments over what our best fundamental theory is telling us about what is physically “real”.
Update: For a much better and more detailed review of the book, Sabine Hossenfelder’s is here.