on mismatched socks, nonexistent cats, and the nature of reality
The Age of Entanglement: When Quantum Physics Was Reborn by Louisa Gilder (Vintage Books, 2008) Quantum entanglement is weird. Of all the weird aspects of quantum mechanics, it's the weirdest. The fact that what you do to one particle can affect another particle with no physical interaction between them--"spooky action at a distance," in Einstein's words--is a fact of nature, but just because something is proven by every experiment we throw at it doesn't mean we have any idea why.
In The Age of Entanglement, Gilder explores the foundations of quantum mechanics with a particular focus on how entanglement was interpreted, ignored, and accepted over the course of the twentieth century. It isn't a thorough history of quantum physics, as it's rather arbitrary about which fundamental ideas and experiments it bothers to explain, so parts might be hard to follow without some prior knowledge. (If it's a straightforward history of quantum physics you want, Quantum by Manjit Kumar (Norton, 2010) is a very good one.)
But overall, this book is a fascinating discussion of why entanglement was (and is) so distasteful to so many physicists and so exciting to others, and why many of the smartest people in the field balked at dealing with it until experimental proof gave them no choice. The concept of locality--that things are influenced only by events in their immediate surroundings--is hard to let go, yet that's exactly what entanglement requires. I particularly enjoyed how well the book demonstrates how so much of twentieth century physics was built on the influence of a very small number of individuals and the cults of personality surrounding them, as well as how the politics of WWII, the Cold War, and McCarthyism twisted around the lives of so many scientists.
Gilder's method of telling these many interconnected stories is an interesting one, and worth mentioning if only because I'm still undecided about how successful it is. As she explains in a five-page author's note at the beginning of the book, her goal is to bring to life the people involved, so she has constructed conversations that (in most cases) never happened by sampling and recontextualizing quotations from papers, letters, interviews and memories. There is no inherent dishonesty in the method; seventy pages of notes at the back of the book meticulously track the real source of every quotation. But it's more effective in some places than others, and my inner editor was itching to smooth over the uneven portions and the chapters where the obviously artificial nature of the "scenes" was distracting rather than illuminating.
There is a lot in this book, because it's a big story to tell. Most popular science books about quantum physics end with Bell's theorem as last-chapter conclusion. Gilder uses Bell and his ideas as a focal point and fills in the background from there to show how the physics establishment dealt with inconvenient but unavoidable ideas they'd been avoiding for decades, and to emphasize that this is an unfinished story. Quantum mechanics may be the most successful scientific theory we've ever come up with, but there are still a lot of unanswered questions.