Through letters, visits, and science meetings, Einstein came to know most of the major physicists of Europe (there were not many in those days). In 1912 Einstein was invited back to the Swiss Federal Institute of Technology as professor. Here he rejoined his old friend Marcel Grossmann, now professor of mathematics. With Grossmann's aid, Einstein studied the mathematical theories and techniques which he found necessary for his work toward a new theory of gravitation. Meanwhile, Einstein was being introduced to a different sort of world by another friend, Friedrich Adler: the world of the Second International and its attempt to halt the growth of international rivalries in Europe.

In 1914, the German government gave Einstein a senior research appointment in Berlin, along with a membership in the prestigious Prussian Academy of Sciences. When Einstein had left his native land as a youth, he had renounced German citizenship and all of the militarist German society. But Berlin -- with no teaching duties and a galaxy of top scientists for colleagues -- could not be resisted. It was the highest level a scientific career could ordinarily reach.

"With such fame, not much time remains for his wife," Mileva complained. "I am very starved for love." Einstein felt suffocated in the increasingly strained and gloomy relationship. He found solace in a love affair with his cousin, Elsa Löwenthal. Mileva and Albert separated in 1914, after bitter arguments, and divorced in 1919. That same year he married Elsa, and settled in with her and her two grown daughters by a previous marriage. "The Lord has put into him so much that's beautiful, and I find him wonderful," Elsa later wrote, "even though life at his side is enervating and difficult." (Click here for more on Einstein at home.)