The scientific breakthroughs that led to the creation of nuclear fission and the atomic bomb began with Albert Einstein’s theory of special relativity in 1905 and his formula E=mc² (Energy equals mass times the speed of light squared). Bringing this to fruition would require four decades of research experiments and the military impetus to create a bomb during World War II. Like most scientific breakthroughs, it was not the work of a single scientist, but a long-term effort in which scientists built upon the theories and experiments of others, including Ernest Rutherford, Lise Meitner, Otto Hahn, Niels Bohr, Frédéric Joliot, Hans von Halban, Lew Kowarski, Enrico Fermi, Ernest Lawrence and Leo Szilard. As these scientists collaborated and competed to advance nuclear physics, they thought more about the science and potential economic implications of applying atomic energy for domestic industrial uses, such as the generation of power, than the military implications of splitting the atom.
This changed when a war with Nazi Germany, which had its own atomic weapons program, seemed inevitable. On August 2, 1939, Albert Einstein, together with Leo Szilard, wrote President Franklin Roosevelt that Germany could develop an atomic bomb and that the United States must begin its own program. In 1942 this became the Manhattan Project. Under the leadership of Lieutenant General Leslie Groves and physicist J. Robert Oppenheimer, it brought together 200 of the world’s leading physicists and chemists, many of them Jewish refugees, to develop an atomic bomb in Los Alamos, NM, while nuclear reactors in Oak Ridge, TN, and Hanford, WA, created the fissionable elements Uranium 235 and Plutonium as the fuel for the atomic bombs. At a cost of $2 billion, the United States had created the first atomic weapons. Completed after Nazi Germany had surrendered, the United States dropped two atomic weapons, in a still highly debated decision, on Hiroshima and Nagasaki, leading the Japanese to surrender.