and the

The physicist Albert Einstein did not directly participate in the invention of the atomic bomb. But as we shall see,
he was instrumental in facilitating its development.

In 1905, as part of his Special Theory of Relativity, he made the intriguing point that a large amount of energy
could be released from a small amount of matter. This was expressed by the equation E=mc2 (energy = mass
times the speed of light squared). The atomic bomb would clearly illustrate this principle.

But bombs were not what Einstein had in mind when he published this equation. Indeed, he considered himself to
be a pacifist. In 1929, he publicly declared that if a war broke out he would "unconditionally refuse to do war
service, direct or indirect... regardless of how the cause of the war should be judged." (Ronald Clark, "Einstein:
The Life and Times", pg. 428). His position would change in 1933, as the result of Adolf Hitler's ascent to power in
Germany. While still promoting peace, Einstein no longer fit his previous self-description of being an "absolute

Einstein's greatest role in the invention of the atomic bomb was signing a letter to President Franklin Roosevelt
urging that the bomb be built. The splitting of the uranium atom in Germany in December 1938 plus continued
German aggression led some physicists to fear that Germany might be working on an atomic bomb. Among those
concerned were physicists Leo Szilard and Eugene Wigner. But Szilard and Wigner had no influence with those in
power. So in July 1939 they explained the problem to someone who did: Albert Einstein. According to Szilard,
Einstein said the possibility of a chain reaction "never occurred to me", altho Einstein was quick to understand the
concept (Clark, pg. 669+; Spencer Weart & Gertrud Weiss Szilard, eds., "Leo Szilard: His Version of the Facts",
pg. 83). After consulting with Einstein, in August 1939 Szilard wrote a letter to President Roosevelt with Einstein's
signature on it. The letter was delivered to Roosevelt in October 1939 by Alexander Sachs, a friend of the
President. Germany had invaded Poland the previous month; the time was ripe for action. That October the Briggs
Committee was appointed to study uranium chain reactions.

But the Briggs Committee moved very slowly, prompting Einstein, Szilard, and Sachs to write to FDR in March
1940, pointing again to German progress in uranium research (Weart & Szilard, pg. 119+). In April 1940 an
Einstein letter, ghost-written by Szilard, pressed Briggs Committee chairman Lyman Briggs on the need for
"greater speed" (Weart & Szilard, pg. 125+; Clark, pg. 680).

Research still proceeded slowly, because the invention of the atomic bomb seemed distant and unlikely, rather
than a weapon that might be used in the current war. It was not until after the British MAUD Report was presented
to FDR in October 1941 that a more accelerated pace was taken. This British document stated that an atomic
bomb could be built and that it might be ready for use by late 1943, in time for use during the war (Richard
Rhodes, "The Making of the Atomic Bomb", pg. 377+).

Einstein biographer Ronald Clark has observed that the atomic bomb would have been invented without Einstein's
letters, but that without the early U.S. work that resulted from the letters, the a-bombs might not have been ready
in time to use during the war on Japan (Clark, pg. 682-683).

The atomic bomb related work that Einstein did was very limited and he completed it in two days during December
1941. Vannevar Bush, who was coordinating the scientific work on the a-bomb at that time, asked Einstein's
advice on a theoretical problem involved in separating fissionable material by gaseous diffusion. But Bush and
other leaders in the atomic bomb project excluded Einstein from any other a-bomb related work. Bush didn't trust
Einstein to keep the project a secret: "I am not at all sure... [Einstein] would not discuss it in a way that it should
not be discussed." (Clark, pg. 684-685; G. Pascal Zachary, "Endless Frontier: Vannevar Bush, Engineer of the
American Century", pg. 204).

As the realization of nuclear weapons grew near, Einstein looked beyond the current war to future problems that
such weapons could bring. He wrote to physicist Niels Bohr in December 1944, "when the war is over, then there
will be in all countries a pursuit of secret war preparations with technological means which will lead inevitably to
preventative wars and to destruction even more terrible than the present destruction of life." (Clark, pg. 698).

The atomic bombings of Japan occurred three months after the surrender of Germany, whose potential for
creating a Nazi a-bomb had led Einstein to push for the development of an a-bomb for the Allies. Einstein withheld
public comment on the atomic bombing of Japan until a year afterward. A short article on the front page of the New
York Times contained his view: "Prof. Albert Einstein... said that he was sure that President Roosevelt would have
forbidden the atomic bombing of Hiroshima had he been alive and that it was probably carried out to end the
Pacific war before Russia could participate." ("Einstein Deplores Use of Atom Bomb", New York Times, 8/19/46,
pg. 1). Einstein later wrote, "I have always condemned the use of the atomic bomb against Japan." (Otto Nathan &
Heinz Norden, editors, "Einstein on Peace", pg. 589).

In November 1954, five months before his death, Einstein summarized his feelings about his role in the creation of
the atomic bomb: "I made one great mistake in my life... when I signed the letter to President Roosevelt
recommending that atom bombs be made; but there was some justification - the danger that the Germans would
make them." (Clark, pg. 752).

- Doug Long


For further information:

Ronald Clark, Einstein: The Life and Times

Otto Nathan & Heinz Norden, editors, Einstein on Peace

Richard Rhodes, The Making of the Atomic Bomb

Spencer Weart & Gertrud Weiss Szilard, editors., Leo Szilard: His Version of the Facts

The American Institute of Physics' Albert Einstein web site

Albert Einstein Online - web site links


To return to the Who's Who and What'd They Do? index, click Who's Who (


To return to the Hiroshima: Was it Necessary? home page, click Home Page (