While working at the Swiss patent office in Bern from 1902 to 1909, Albert Einstein did research and completed three major papers without close contact to scientific literature or colleagues. The first of the principal papers published in 1905 explained the photoelectric effect and formed the basis for much of quantum mechanics. His second paper of that year proposed what today is known as the special theory of relativity. The third paper of 1905 concerned statistical mechanics. Unaware of other research, Einstein calculated the average trajectory of a microscopic particle buffeted by random collisions with molecules in a fluid or gas. With the rise of fascism in Germany, where he had moved his research, Einstein moved to the United States in 1933 and abandoned his pacifist stance. He agreed that the new menace had to be put down through force of arms. In this context, he sent a letter to President Franklin D. Roosevelt that urged the United States to proceed with developing an atomic bomb before Germany did so.