The author, one of my Facebook friends, died almost one year ago. This is one of his best books. Amir, like the fine science writer he was, covered a diversity of topics well – including my favorite, mathematics. I enjoyed his Fermat’s Last Theorem: Unlocking the Secret of an Ancient Mathematical Problem, even though it’s a bit short and superficial – and he confused elliptic curves and elliptic functions. (A common error.) I’m looking forward to reading My Search for Ramanujan, which Amir co-authored with Ken Ono. Since Ono is a world-class expert on topics that interested Ramanujan, such as partition theory, their book should be excellent.

Like all books Amir wrote himself, *Entanglement* is at an elementary level, intended for general readers. I think it does an excellent job with the subject matter. There are, however, better books on the subject of quantum entanglement for readers who are more conversant with quantum mechanics, such as Nicolas Gisin’s Quantum Chance: Nonlocality, Teleportation and Other Quantum Marvels, which I reviewed here. Gisin led a group that performed a key experiment that verified the nonlocal character of quantum entanglement. That experiment receives a whole (short) chapter in Amir’s book. But what may be the most noteworthy aspect of the book reviewed here is that it also describes several other very important experiments on entanglement, of which I don’t know any other treatment at the elementary level. Among these is a fairly detailed treatment of “triple entanglement”. That involves three entangled particles instead of the much more usual two. It’s an important experiment, since it clearly demonstrates the inherent nonlocality of quantum entanglement, without having to rely on Bell’s Theorem.

Amir’s book starts out slowly and covers all the usual history of quantum mechanics, from Planck and Einstein onward. This includes the customary topics, such as the contributions of Bohr, Heisenberg, de Broglie, Schrödinger, von Neumann, Dirac, Bohm, and Wheeler. This early history occupies the first half of the book, so that readers who’re already familiar with the history may become impatient to get to the more recent “good stuff”.

Erwin Schrödinger discovered the phenomenon of entanglement, and considered it the most significant aspect of quantum mechanics. He wrote “Entanglement is not *one* but rather *the* characteristic trait of quantum mechanics.” Entanglement depends on another aspect of quantum mechanics, “superposition”, which had been discovered earlier. The two terms should not be confused even though they are closely related. Superposition is the strange property that one or more quantum particles may have, in which the particles can actually be in multiple potentially observable simple states at the same time. (This property is what makes quantum computers possible and interesting.) Two particles that have interacted at one point in time can be in a joint state that is a superposition of states of both particles. In this case, the particles may be “entangled”, so that a measurement of one particle will instantaneously determine what will be measured of the other particle, even if the two are millions of light-years apart when measured.

Obviously, this is quite a peculiar phenomenon, and it sorely perplexed Einstein. Nevertheless, it has been rigorously verified numerous times since the 1970s. The details of many of these experiments occupy the second half of Amir’s book. This part of the book requires much more careful reading than the first half, but it’s well worth the effort. If one has any interest in learning about recent practical aspects of quantum technology – such as quantum computing, quantum cryptography, and quantum teleportation – these are the details that one needs to develop a good understanding of. A reader can feel confident of the book’s accuracy in dealing with these topics, since the author spent quite a lot of time discussing the experiments with a number of physicists who actually performed them.