EDGE: Did Einstein stop asking questions later in his life? Did something happen to him later in his life where he turned inward and stopped listening to other people?

OVERBYE: Einstein never stopped talking to other people and asking questions, but after a certain time he increasingly steered an independent course of thought. One turning point came in the fall of 1915 when Einstein got the final version of general relativity into shape and he used it to calculate the perihelion shift of mercury — a minute discrepancy in the planet's motion that had puzzled astronomers for decades. This was a calculation which had no fudge factors at all. It was either right or wrong, and it came out right on the nose. Einstein had developed this theory basically from pure thought and logic.

It was almost like a conversion experience. Later he said he had heart palpitations when the answer came out. And it probably made him a little too cocky about the power of pure thought. He was so impressed that he started being guided more and more by mathematical elegance, and probably less and less by experimental fact as he went on through the succeeding years searching for his so-called unified field theory and he became divorced from the main body of physics that was going on.. And of course what was going on mainly was nuclear physics, which was all quantum mechanics, and he wasn't very happy with the direction that that was going, so he basically reserved his right to step aside from it.

EDGE: If he were alive today, how would he feel about the way things are?

OVERBYE: That 's an interesting question. I think he'd be very puzzled. Today there is a candidate for a unified theory, namely string theory, and it certainly is mathematically challenging, to say the least. Would Einstein be a string theorist? Strings seem to have taken physics departments by storm and they are almost the only game in town, but Einstein had this deep-seated need to be an outsider. So I don't know.

He would be disappointed with the current vogue for multiple universes, I think, and of course that quantum mechanics is still at the center of physics. There is a small minority of physicists, I am told, who think that string theory may ultimately wind up resolving some of the paradoxes of quantum mechanics. But I think most physicists believe that the main principles of quantum mechanics are here to stay, and that general relativity won't be modified. But there certainly is a big schism in physics.

There is a saying in the newspaper business that some stories are too good to check, and the legend of the humble patent clerk who overturned the universe was certainly such a story for most of my life. Not ever having done any investigation, I didn't realize that there was a lot of mystery about Einstein. He'd been very secretive about his family life, and the secrecy had prevailed after his death. He left behind some 40,000 documents in Princeton, and they had been locked up like the Dead Sea Scrolls until the late 1980s when the Hebrew University (which owns Einstein's copyright) and the Princeton University Press began to publish them. In the course of their investigation the scholars on the Einstein Papers project found love letters that he had written to Mileva when they were both students in Zurich in the late 1890s, and the years just after the turn of the century. It was clear from these letters that Einstein had talked about the issues of relativity, and atomic theory and everything else, but especially relativity, with Mileva. There were statements in these letters such as "how happy and proud I will be when our work on the relative motion is complete." It sounded provocative to some renegade historians and they made a fuss about Mileva having been deprived of her share of credit. I walked into one of those debates by accident.

Actually if you read these letters in full and in context, that statement has more emotional content than intellectual content. He was reassuring her about the state of their relationship. At the time they were separated and their parents were both violently opposed to the union. She was Serbian, he was a Jew from southern Germany. This was just not done as far as his mother was concerned. Plus Mileva was older, and that was a no-no. So I began looking into it. I discovered that these love letters were just the tip of the iceberg. Nobody had really tried to tell the story of where general relativity had come from, and the very winding path that he had taken to it, for a popular audience.