It is not that he didn’t know his fair share of mathematics. Indeed, he had excelled at math in school and knew enough to put across his ideas. His papers were a perfect balance of physical reasoning and just enough mathematics to lay his ideas on a firm setting. But his 1907 predictions from his generalized theory had been done on a mathematical shoestring—one of his Zurich professors described the presentation of his work as “mathematically cumbersome.” Einstein disdained mathematics, which he called a “superfluous erudition,” sniping, “Since the mathematicians pounced on the relativity theory I no longer understand it myself.” But in 1911, when he looked at the ideas he had written up in his review, he realized that math could help him push them a bit further. Einstein looked at his principle of relativity and thought about light, once again. Imagine yourself riding in a spaceship far from any planets and stars. Now imagine that a ray of light from a distant star enters through a small window directly to your right, cuts across the inside of your ship, and exits through a window to your left.
