A physicist's efforts to understand the enigma that is quantum mechanics. "One of the finest books I have read on quantum mechanics: lucid and careful, but also entertaining, honest, and generous."—Phillip Ball, author of Beyond Weird Astrophysicist George Greenstein has been both fascinated and confused by quantum mechanics for his entire career. In this book, he describes, engagingly and accessibly, his efforts to understand the enigma that is quantum mechanics. Even now, many years after the creation of quantum mechanics, physicists continue to argue about it. The fastest route to the insight into the ultimate nature of reality revealed by quantum mechanics, Greenstein writes, is through Bell's Theorem, which concerns reality at the quantum level. Bell's 1964 discovery drives Greenstein's quest. Greenstein recounts a scientific odyssey that begins with Einstein, continues with Bell, and culminates with today's push to develop an industry of quantum machines. Along the way, he discusses spin, entanglement, experimental metaphysics, and quantum teleportation, often with easy-to-grasp analogies. Quantum mechanics is one of the glories of our age. The theory lies at the heart of modern society. Quantum mechanics is one of our most valuable forecasters—a “great predictor.” It has immeasurably altered our conception of the natural world. Its philosophical implications are earthshaking.