Birth of Modern Physics
Fission is Discovered
In 1938, working at the Kaiser Wilhelm Institute in Berlin, Otto Hahn and Fritz Strassmann bombarded uranium with neutrons in an experiment studying radioactive substances. Unknowingly, they split uranium atoms. Perplexed by their findings, Hahn wrote to a former colleague, Lise Meitner, describing the experimental results. Meitner in turn discussed those results with her nephew, Otto Frisch. Together, Meitner and Frisch deduced what had really happened — atoms of uranium had been split into two nearly equal halves and, in the process, some matter had been converted to energy. Fission had been discovered.
The Einstein Letter
Several European refugees, who had fled Nazi persecution on the continent, also joined the team. Included amongst them was the Austrian, Otto Frisch, the two Danes, Niels Bohr and his son Aage, and Joseph Rotblat, a Pole. Klaus Fuchs, an outstanding theoretical physicist and native of Germany, also came to Los Alamos as part of the British Mission. He played a prominent role in the development of the implosion bomb, but repeatedly passed classified information to the Soviet Union. The man who recruited Fuchs, Rudolf Peierls, a fellow German theorist, also came to Los Alamos and eventually succeeded Chadwick as leader of the British Mission.
It became immediately obvious to physicists that if enough uranium atoms could be split, the cumulative energy released in the process would produce an explosion of unprecedented magnitude. Fearing that Germany might develop an atomic bomb, Leo Szilard, Edward Teller, and Eugene Wigner convinced Albert Einstein to alert President Roosevelt of this possibility. In a letter to Roosevelt dated August 2, 1939, drafted mostly by Szilard, Einstein made clear the dangers of a Germany armed with nuclear weapons. It stated,
"...it is conceivable — though much less certain — that extremely powerful bombs of a new type may thus be constructed. A single bomb of this type, carried by boat and exploded in a port, might very well destroy the whole port together with some of the surrounding territory."
The Manhattan Project
In response to Einstein's letter, the United States government began a modest program of nuclear research. After the Japanese attacked Pearl Harbor, President Franklin Roosevelt directed the War Department to build an atomic bomb. The Army Corps of Engineers created the Manhattan Engineering District (MED) in August 1942 for this purpose. The name Manhattan came from the first headquarters of the new Corps of Engineers District, which was located in New York City. Under the command of General Leslie R. Groves, the MED began to work procuring uranium ore, land for sites such as Oak Ridge, Hanford, and Los Alamos, and the scientific and technical labor needed to build an atomic bomb.