Einstein's letter to FDR regarding
the possibility of the creation of a nuclear bomb.
Scientists in the 1930s, using
machines that could break apart the nuclear cores of atoms,
confirmed Einstein's formula E=mc² . The release of energy
in a nuclear transformation was so great that it could cause
a detectable change in the mass of the nucleus. But the study
of nuclei -- in those years the fastest growing area of physics
-- had scant effect on Einstein. Nuclear physicists were gathering
into ever-larger teams of scientists and technicians, heavily
funded by governments and foundations, engaged in experiments
using massive devices. Such work was alien to Einstein's habit
of abstract thought, done alone or with a mathematical assistant.
In return, experimental nuclear physicists in the 1930s had
little need for Einstein's theories.
In August 1939 nuclear physicists came to Einstein, not
for scientific but for political help. The fission of the
uranium nucleus had recently been discovered. A long-time
friend, Leo Szilard, and other physicists realized that uranium
might be used for enormously devastating bombs. They had reason
to fear that Nazi Germany might construct such weapons. Einstein,
reacting to the danger from Hitler's aggression, had already
abandoned his strict pacifism. He now signed a letter that
was delivered to the American president, Franklin D. Roosevelt,
warning him to take action. This letter, and a second Einstein-Szilard
letter of March 1940, joined efforts by other scientists to
prod the United States government into preparing for nuclear
warfare. Einstein played no other role in the nuclear bomb
project. As a German who had supported left-wing causes, he
was denied security clearance for such sensitive work. But
during the war he did perform useful service as a consultant
for the United States Navy's Bureau of Ordnance.