Space and Time
3
Hadron Collider at the European Center for Particle Physics (CERN) in Geneva, Switzerland. The existence of such a special speed, a cosmic speed limit, is a strange concept. As we will discover later in this book, linking this special speed with the speed of light turns out to be something of a red herring. It has a much deeper role to play in Einstein’s universe, and there is a good reason why light travels at the speed it does. We will get to that later on. For now, suffice to say that when objects approach the special speed, strange things happen. How else could an object be prevented from accelerating beyond that speed? It’s as though there were a universal law of physics that prevented your car going faster than seventy miles per hour, no matter how large the engine. Unlike a speed restriction, however, this law is not something that needs to be enforced by some kind of ethereal police force. The very fabric of space and time is constructed in such a way that it is absolutely impossible to break the law, and this turns out to be extremely fortunate, for otherwise there would be unpleasant consequences. Later, we shall see that if it were possible to exceed the speed of light, we could construct time machines capable of transporting us backward through history to any point in the past. We could imagine journeying back to a time before we were born and, by accident or design, preventing our parents from ever meeting. This makes for excellent science fiction, but it is no way to build a universe, and indeed Einstein found that the universe is not built like this. Space and time are delicately interwoven in a way that prevents such paradoxes from occurring. However, there is a price to pay: We must jettison our deeply held notions of space and time. Einstein’s universe is one