Carroll 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. He explains that there are multiple copies of you. And everyone else. Carroll begins with the news that physics is in a crisis. Quantum mechanics underlies all of modern physics but major gaps in the theory have been ignored since 1927. Putting his professional reputation on the line, Carroll says that crisis can now come to an end, that we just have to accept that there is more than one of us in the universe. Many of every one of us. 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, the author sets out the major objections to this notion until his case is established. The holy gr