One day, would it be possible to walk through walls? To build starships that can travel faster than the speed of light? To read other people’s minds? To become invisible? To move objects with the power of our minds? To transport our bodies instantly through outer space? Since I was a child, I’ve always been fascinated by these questions. Like many physicists, when I was growing up, I was mesmerized by the possibility of time travel, ray guns, force fields, parallel universes, and the like. Magic, fantasy, science fiction was all a gigantic playground for my imagination.