THE year was 1915. War and privation had come to Germany. Meanwhile, in Berlin, a solitary man struggled with the equations for a new theory of gravity.

"I have been laboring inhumanly," Albert Einstein, then 36, wrote to a friend in his native German. "I am quite overworked."

His fellow scientists, he complained in a letter contained in a newly published collection of his personal correspondence, were behaving abominably, either "trying to poke holes" in his theory or competing with him to finish it first.

At the same time, he was estranged from his two young sons, who were living in Switzerland with their mother, from whom Einstein had separated the year before. He was romancing his cousin Elsa Lowenthal, whom he would later marry, and was stressed about money. His stomach was acting up.