"There once was a doctor with cool white hair. He was well known because he came up with some important ideas. He didn't grow the cool hair until after he was done figuring that stuff out, but by the time everyone realized how good his ideas were, he had grown the hair, so that's how everyone pictures him. He was so good at coming up with ideas that we use his name to mean "someone who's good at thinking." Two of his biggest ideas were about how space and time work. This thing you're reading right now explains those ideas using only the ten hundred words people use the most often. The doctor figured out the first idea while he was working in an office, and he figured out the second one ten years later, while he was working at a school. That second idea was a hundred years ago this year. (He also had a few other ideas that were just as important. People have spent a lot of time trying to figure out how he was so good at thinking.)"