Einstein was born in 1879 in the German city of Ulm. He had been no infant prodigy; indeed, he was so late in learning to speak that his parents feared he was a dullard. In school, though his teachers saw no special talent in him, the signs were already there. He taught himself calculus, for example, and his teachers seemed a little afraid of him because he asked questions they could not answer. At the age of 16, he asked himself whether a light wave would seem stationary if one ran abreast of it. From that innocent question would arise, ten years later, his theory of relativity.

　　The intensity and depth of his concentration were fantastic. When battling a recalcitrant problem, he worried it as an animal worries its prey. Often, when we found ourselves up against a seemingly insuperable difficulty, he would stand up, put his pipe on the table, and say in his quaint English, “I will a little tink” (he could not pronounce “th”). Then he would pace up and down, twirling a lock of his long, graying hair around his fore-finger.

　　A dreamy, faraway and yet inward look would come over his face. There was no appearance of concentration, no furrowing of the brow -- only a placid inner communion. The minutes would pass, and then suddenly Einstein would stop pacing as his face relaxed into a gentle smile. He had found the solution to the problem. Sometimes it was so simple that Infeld and I could have kicked ourselves for not having thought of it. But the magic had been performed invisibly in the depths of Einstein’s mind, by a process we could not fathom.

　　He was one of the greatest scientists the world has ever known, yet if I had to convey the essence of 变态烈焰sf Einstein in a single word, I would choose simplicity. Perhaps an anecdote will help. Once, caught in a downpour, he took off his hat and held it under his coat. Asked why, he explained, with admirable logic, that the rain would damage the hat, but his hair would be none the worse for its wetting. This knack for going instinctively to the heart of a matter was the secret of his major scientific discoveries -- this and his extraordinary feeling for beauty.

　　Among the extraordinary things he produced in that memorable year were his theory of relativity, with its famous offshoot, E=mc (energy equals mass times the speed of light squared), and his quantum theory of light. These two theories were not only revolutionary, but seemingly contradictory: The former was intimately linked to the theory that light consists of waves, while the latter said it consists somehow of particles. Yet this unknown young man boldly proposed both at once—and he was right in both cases, though how he could have been is far too complex a story to tell here.

　　It was this very Mozartean simplicity that most characterized Einstein’s methods. His 1905 theory of relativity, for example, was built on just two simple assumptions. One is the so-called principle of relativity, which means, roughly speaking, that we cannot tell whether we are at rest or moving smoothly. The other assumption is that the speed of light is the same no matter what the speed of the object that produces it. You can see how reasonable this is if you think of agitating a stick in a lake to create waves. Whether you wiggle the stick from a stationary pier, or from a rushing speedboat, the waves, once generated, are on their own, and their speed has nothing to do with that of the stick..

　　When his wife died he was deeply shaken, but insisted that now more than ever was the time to be working hard. I remember going to his house to work with him during that sad time. His face was haggard and grief-lined, but he put forth a great effort to concentrate. To help him, I steered the discussion away from routine matters into more difficult theoretical problems, and Einstein gradually became absorbed in the discussion. We kept at it for some two hours, and at the end his eyes were no longer sad. As I left, he thanked me with moving sincerity. “It was a fun,” he said. He had had a moment of surcease from grief, and then groping words expressed a deep emotion.

　　Einstein was a accomplished amateur musician. We used to play duets, he on the violin, I at the piano. One day he surprised me by saying Mozart was the greatest composer of all. Beethoven “created” his music, but the music of Mozart was of such purity and beauty one felt he had merely “found” it -- that it had always existed as part of the inner beauty of the Universe, waiting to be revealed.

　　Collaborating with Einstein was an unforgettable experience. In 1937, the Polish physicist Leopold Infeld and I asked if we could work with him. He was pleased with the proposal, since he had an idea about gravitation waiting to be worked out in detail. Thus we got to know not merely the man and the friend, but also the professional.