"The classic sci-fi novels of H.G. Wells, Robert Heinlein, and Arthur C. Clarke, along with hundreds of sci-fi movies and TV shows, have explored an array of exotic, at times mind-bending themes, among them the existence of intelligent aliens, time travel, and parallel universes. One often asked question is whether such things are scientifically plausible. In this volume, modern physicists and other scientists weigh in and try to answer that question"--.