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The physicist Albert Einstein did not directly participate in the invention of the atomic bomb. But 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). 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 pacifist".

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.

This is pretty amazing. It’s a Scientific American article from October 1939, describing the splitting of the atom. It was written just after Einstein had written his famous letter to F.D.R and before the initiation of the Manhattan Project, yet it is obvious that scientists were well aware of the potential uses of atomic fission:

It may or may not be significant that, since early spring, no accounts of research on nuclear fission have been heard from Germany — not even from discoverer Hahn. It is not unlikely that the German government, spotting a potentially powerful weapon of war, has imposed military secrecy on all recent German investigations. A large concentration of isotope 235, subjected to neutron bombardment, might conceivably blow up all London or Paris.

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", although Einstein was quick to understand the concept (Clark, Spencer & Weart; Gertrud Weiss Szilard, eds., "Leo Szilard: His Version of the Facts"). 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).

In April 1940 an Einstein letter, ghost-written by Szilard, pressed Briggs Committee chairman Lyman Briggs on the need for "greater speed" (Weart & Szilard; Clark).

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").

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).

The atomic bomb related work that Einstein did was very limited and he completed it in two days during December 1941.

Vannevar Bush co-ordinating 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; G. Pascal Zachary, Endless Frontier: Vannevar Bush, Engineer of the American Century.

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).

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.

Einstein later wrote:

I have always condemned the use of the atomic bomb against Japan.

~Otto Nathan & Heinz Norden, editors, "Einstein on Peace".

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.

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

Albert Einstein
Old Grove Road
Peconic, Long Island
August 2, 1939

F.D. Roosevelt
President of the United States
White House
Washington, D.C.


Some recent work by E. Fermi and L. Szilard, which has been communicated to me in manuscript, leads me to expect that the element uranium may be turned into a new and important source of energy in the immediate future. Certain aspects of the situation which has arisen seem to call for watchfulness and if necessary, quick action on the part of the Administration. I believe therefore that it is my duty to bring to your attention the following facts and recommendations.

In the course of the last four months it has been made probable through the work of Joliot in France as well as Fermi and Szilard in America--that it may be possible to set up a nuclear chain reaction in a large mass of uranium, by which vast amounts of power and large quantities of new radium-like elements would be generated. Now it appears almost certain that this could be achieved in the immediate future.

This new phenomenon would also lead to the construction of bombs, and it is conceivable--though much less certain--that extremely powerful bombs of this 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. However, such bombs might very well prove too heavy for transportation by air.

The United States has only very poor ores of uranium in moderate quantities. There is some good ore in Canada and former Czechoslovakia, while the most important source of uranium is in the Belgian Congo.

In view of this situation you may think it desirable to have some permanent contact maintained between the Administration and the group of physicists working on chain reactions in America. One possible way of achieving this might be for you to entrust the task with a person who has your confidence and who could perhaps serve in an unofficial capacity. His task might comprise the following:

a) to approach Government Departments, keep them informed of the further development, and put forward recommendations for Government action, giving particular attention to the problem of securing a supply of uranium ore for the United States.

b) to speed up the experimental work, which is at present being carried on within the limits of the budgets of University laboratories, by providing funds, if such funds be required, through his contacts with private persons who are willing to make contributions for this cause, and perhaps also by obtaining co-operation of industrial laboratories which have necessary equipment.

I understand that Germany has actually stopped the sale of uranium from the Czechoslovakian mines which she has taken over. That she should have taken such early action might perhaps be understood on the ground that the son of the German Under-Secretary of State, von Weizsäcker, is attached to the Kaiser-Wilhelm Institute in Berlin, where some of the American work on uranium is now being repeated.

Yours very truly

Albert Einstein