Maybe somewhere telepaths walked the Earth, but I wasn't one of them. In the process, I began to realize that the wondrous exploits of telepaths were probably impossible--at least without outside assistance. But in the years that followed, I also slowly learned another lesson: to fathom the greatest secrets in the universe, one did not need telepathic or superhuman abilities. One just had to have an open, determined, and curious mind. In particular, in order to understand whether the fantastic devices of science fiction are possible, you have to immerse yourself in advanced physics. To understand the precise point when the possible becomes the impossible, you have to appreciate and understand the laws of physics.