Sean Carroll, theoretical physicist and one of this world’s most celebrated writers on science, rewrites the history of 20th century physics. Already hailed as a masterpiece, Something Deeply Hidden shows for the first time that facing up to the essential puzzle of quantum mechanics utterly transforms how we think about space and time. His reconciling of quantum mechanics with Einstein’s theory of relativity changes, well, everything. Most physicists haven’t even recognized the uncomfortable truth: physics has been in crisis since 1927. Quantum mechanics has always had obvious gaps—which have come to be simply ignored. Science popularizers keep telling us how weird it is, how impossible it is to understand. Academics discourage students from working on the "dead end" of quantum foundations. Putting his professional reputation on the line with this audacious yet entirely reasonable book, Carroll says that the crisis can now come to an end. We just have to accept that there is more than one of us in the universe. There are many, many Sean Carrolls. Many of every one of us. Copies of you are generated thousands of times per second. The Many Worlds Theory of quantum behavior says that every time there is a quantum event, a world splits off with everything in it the same, except in that other world the quantum event didn't happen. Step-by-step in Carroll's uniquely lucid way, he tackles the major objections to this otherworldly revelation until his case is inescapably established. Rarely does a book so fully reorganize how we think about our place in the universe. We are on the threshold of a new understanding—of where we are in the cosmos, and what we are made of. “A thrilling tour through what is perhaps humankind's greatest intellectual achievement—quantum mechanics. With bold clarity, Carroll deftly unmasks quantum weirdness to reveal a strange but utterly wondrous reality.”—Brian Greene, professor of physics and mathematics, director of the Columbia Center for Theoretical Physics, author of The Elegant Universe “Sean Carroll’s immensely enjoyable Something Deeply Hidden brings readers face to face with the fundamental quantum weirdness of the universe—or should I say universes? And by the end, you may catch yourself finding quantum weirdness not all that weird.”—Jordan Ellenberg, professor of mathematics, University of Wisconsin-Madison, author of How Not To Be Wrong “Sean Carroll is always lucid and funny, gratifyingly readable, while still excavating depths. He advocates an acceptance of quantum mechanics at its most minimal, its most austere – appealing to the allure of the pristine. The consequence is an annihilation of our conventional notions of reality in favor of an utterly surreal world of Many Worlds. Sean includes us in the battle between a simple reality versus a multitude of realities that feels barely on the periphery of human comprehension. He includes us in the ideas, the philosophy, and the foment of revolution. A fascinating and important book.”—Janna Levin, professor of physics & astronomy, Barnard College of Columbia University, author of Black Hole Blues “Sean Carroll beautifully clarifies the debate about the foundations of quantum mechanics, and champions the most elegant, courageous approach: the astonishing “many worlds” interpretation. His explanations of its pros and cons are clear, evenhanded, and philosophically gob smacking.”—Steven Strogatz, professor of mathematics, Cornell University, and author of Infinite Powers “Carroll gives us a front-row seat to the development of a new vision of physics: one that connects our everyday experiences to a dizzying hall-of-mirrors universe in which our very sense of self is challenged. It's a fascinating idea, and one that just might hold clues to a deeper reality.”—Katie Mack, theoretical astrophysicist, North Carolina State University, author of The End of Everything (forthcoming) “I was overwhelmed by tears of joy at seeing so many fundamental issues explained as well as they ever have been. Something Deeply Hidden is a masterpiece, which stands along with Feynman's QED as one of the two best popularizations of quantum mechanics I've ever seen. And if we classify QED as having had different goals, then it's just the best popularization of quantum mechanics I've ever seen, full stop.”—Scott Aaronson, professor of computer science at the University of Texas at Austin, and Director of UT’s Quantum Information Center “Irresistible and an absolute treat to read. While this is a book about some of the deepest current mysteries in physics, it is also a book about metaphysics as Carroll lucidly guides us on how to not only think about the true and hidden nature of reality but also how to make sense of it. I loved this book.”—Priyamvada Natarajan, theoretical astrophysicist, Yale University, author of Mapping the Heavens