Einstein's letter to Roosevelt

2 August 1939 is the date borne by the most famous letter in the history of science. Addressed to the President of the United States, Franklin Delano Roosevelt, and signed by Albert Einstein, it warned that a nuclear chain reaction in uranium could be used to build “extremely powerful bombs of a new type”, and that Germany might already be working on the problem. It proposed that the American government establish permanent contact with the physicists studying the chain reaction, speed up their experiments and secure supplies of uranium ore for the United States.

The letter’s author, however, was not Einstein but the Hungarian physicist Leó Szilárd, who had conceived the idea of a nuclear chain reaction in London in 1933. Einstein, the most famous scientist in the world, lent him his name, because only that name could open the doors of the White House. The date of 2 August, as usually given in war chronologies, is the date written on the letter. It did not reach the President at that time. Sent to Szilárd, who passed it on to an intermediary, it reached Roosevelt only on 11 October 1939, when war had already been raging in Europe for five weeks.

Fear of a German bomb

In early 1939 news reached America that Otto Hahn and Fritz Strassmann in Berlin had discovered the fission of the uranium nucleus, and on 25 January physicists at Columbia became the first in the United States to confirm it experimentally. In March, at Columbia University, Szilárd with Walter Zinn and, in parallel, Enrico Fermi with Herbert Anderson showed that fission releases new neutrons capable of splitting further nuclei. A similar result was announced in Paris by the team of Frédéric Joliot-Curie. The chain reaction that Szilárd had been thinking about for six years was no longer a pipe dream. In the summer Szilárd and Fermi concluded that a self-sustaining reaction could probably be produced in a large mass of natural uranium mixed with a moderator to slow down the neutrons. Szilárd proposed carbon in the form of graphite as the moderator.

Szilárd, who had fled Berlin from the Nazis in 1933, had no illusions about what Hitler might do with such a weapon. He also knew that fission had been discovered in Germany and that outstanding physicists worked there, led by Werner Heisenberg. Worrying signals were coming from the Reich: in June 1939 the German physicist Siegfried Flügge published an article on the technical exploitation of the nuclear energy of uranium, and in August a popular version of it in the Berlin press. After the seizure of the Czech lands in March 1939, Germany took over the mines at Jáchymov (St. Joachimsthal), the only significant uranium deposits in Europe, and, according to reports reaching America, stopped the sale of the uranium mined there. Szilárd did not know that in April 1939 the first, still uncoordinated work on harnessing fission had indeed begun in Germany (the so-called Uranverein).

The largest reserves of rich uranium ore were in the Belgian Congo. Szilárd and his friend, the Hungarian physicist Eugene Wigner, therefore concluded that the first priority was to warn the Belgian government not to sell uranium to Germany. They remembered that Einstein, with whom Szilárd had spent several years in Berlin designing a refrigerator with no moving parts, was a friend of the Belgian Queen Mother Elisabeth.

Two visits to Nassau Point

Einstein was spending the summer of 1939 in a rented house at Nassau Point near Cutchogue, at the eastern end of Long Island. In mid-July (on 12 July, according to most accounts) Szilárd and Wigner drove there in Wigner’s car, since Szilárd could not drive. They lost their way for a long time, until a boy whom they asked in the street about “Professor Einstein” led them to the right house. When Szilárd explained that uranium could sustain a chain reaction, Einstein is said to have replied in German: “I never thought of that” (Daran habe ich gar nicht gedacht). He quickly grasped what was at stake, however, and agreed to help. He dictated to Wigner, in German, a letter to the Belgian Ambassador in Washington. On Wigner’s advice they also drafted a note to the State Department, so that the American authorities would know about the initiative and could object to it.

Szilárd soon found a better route. The Austrian economist Gustav Stolper put him in touch with Alexander Sachs, an economist at the Lehman Brothers bank and an unofficial adviser to Roosevelt with access to the White House. Sachs decided that the warning had to go directly to the President and agreed to deliver the letter in person, but advised that it be signed by someone better known than Szilárd. The choice was obvious.

At the end of July – according to most accounts on Sunday 30 July – Szilárd went to see Einstein again. Wigner had left for California, so the car was driven by a third Hungarian physicist, Edward Teller. “I entered history as Szilárd’s chauffeur,” he joked years later. Einstein dictated the text of the letter to the President in German. On that basis Szilárd prepared two English versions, a shorter and a longer one, and sent them to Einstein to choose from. Einstein signed both versions, dated 2 August 1939, and posted them back. Szilárd received them on 9 August.

What Einstein wrote

The letter runs to little more than a page. It opens by stating that in the previous four months the work of Joliot in France and of Fermi and Szilárd in America had made it probable that a nuclear chain reaction releasing vast amounts of energy could be set up in a large mass of uranium. “This new phenomenon would also lead to the construction of bombs, and it is conceivable – though much less certain – that extremely powerful bombs of a new type may thus be constructed.” A single bomb of this kind, Einstein went on, carried by ship and exploded in a port, might destroy the whole port together with part of the surrounding area – though such bombs might prove too heavy to be carried by aircraft. In 1939 it was believed that a bomb would require tons of uranium.

Einstein pointed out that the United States had little uranium, that the most important deposits lay in the Belgian Congo, and that there was good ore also in Canada and in the former Czechoslovakia. He proposed that the President entrust a person he trusted with keeping in touch with the physicists, keeping the government informed, securing uranium supplies and obtaining funds to speed up the experiments, which had so far been carried out on modest university budgets. The letter ended with a warning: Germany had stopped the sale of uranium from the Czechoslovak mines it had taken over, which might be explained by the fact that the son of the German State Secretary Ernst von Weizsäcker, the physicist Carl Friedrich von Weizsäcker, was working at the Kaiser Wilhelm Institute in Berlin, where American research on uranium was being repeated.

The road to the White House

On 15 August Szilárd handed Sachs both of Einstein’s letters and a memorandum of his own. Sachs, however, could not get an appointment with the President straight away. In the last weeks of August Roosevelt was occupied with the Polish–German crisis, and on 1 September Germany invaded Poland. Sachs judged that at such a moment the President would not give the letter his attention, and waited.

The meeting took place on 11 October 1939. Sachs read the President Einstein’s letter, Szilárd’s memorandum and a note of his own in the presence of the President’s secretary and aide, General Edwin Watson, and two ordnance experts, one from the Army and one from the Navy. Roosevelt listened without enthusiasm but invited Sachs to breakfast the next day. According to Sachs, on 12 October he told the President how Napoleon had sent away empty-handed the American inventor Robert Fulton, who had offered him a fleet of steamships for the invasion of England. Roosevelt is then said to have remarked: “Alex, what you are after is to see that the Nazis don’t blow us up”, and to have told Watson: “This requires action.” The story is known only from Sachs’s account and may be embellished, but its outcome is documented. On 19 October Roosevelt wrote to thank Einstein and informed him that he had set up a committee to investigate the question of uranium.

The Advisory Committee on Uranium, chaired by Lyman Briggs, director of the National Bureau of Standards, met for the first time on 21 October 1939, with Szilárd, Wigner and Teller taking part. It granted a modest $6,000 for the purchase of graphite and uranium for the experiments of Fermi and Szilárd. Over the next two years the work proceeded slowly. The military was sceptical and Briggs cautious. Einstein signed two further letters urging action, on 7 March and 25 April 1940.

The letter’s long shadow

Einstein’s letter marked the beginning of the United States government’s involvement in nuclear weapons research, but it was not what decided the building of the bomb. The breakthrough came from Britain. In March 1940 two refugees from the Reich working in Birmingham, Otto Frisch and Rudolf Peierls, calculated that a few kilograms of pure uranium-235 would be enough for a bomb. In July 1941 the British MAUD Committee concluded that a bomb could be built while the war was still going on. Its report, passed to the Americans, convinced Vannevar Bush, who directed American scientific research for military purposes. In the autumn of 1941, before the United States entered the war, Roosevelt approved an expansion of the work, and at the beginning of 1942 a programme to build the bomb. From 1942 it was run by the Army, and at its peak the Manhattan Project, under General Leslie Groves, employed more than a hundred thousand people.

Einstein took no part in it. In 1940 the Army refused him access to secret work, regarding an internationally famous pacifist as a security risk. He did not know how far the work had progressed and had no influence on the decision to use the bomb. In March 1945 Szilárd, alarmed at the prospect of the bomb being used and of an arms race with the USSR, prepared for him a fourth letter, introducing Szilárd to the President. Roosevelt died on 12 April before reading it. On 6 and 9 August 1945 atomic bombs destroyed Hiroshima and Nagasaki. Germany, whose bomb Szilárd and Einstein had feared, never built one. Until the end of the war its nuclear programme did not get beyond the stage of reactor experiments.

Einstein regretted his signature for the rest of his life. In a 1947 interview with Newsweek he said that had he known the Germans would not succeed in building an atomic bomb, he would have done nothing. In 1954 he confided to his friend, the chemist Linus Pauling, that signing the letter to Roosevelt had been the one great mistake of his life, but added that there had been a justification at the time: the danger that the Germans would build the bomb first. A week before his death, in April 1955, he signed an appeal known as the Russell–Einstein Manifesto, calling on governments to renounce war in the nuclear age. The letter of August 1939 has remained a symbol of how the policies of the Third Reich, which drove Jewish scientists out of Europe, turned against the Reich itself – and a warning that a weapon created out of fear of one enemy outlived that enemy and changed the whole post-war world.