Einstein–Szilard letter

• 1. Introduction

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  On the 2nd of August 1939, Albert Einstein signed a letter he had not written. The author was Leo Szilard, a Hungarian physicist who had already been losing sleep over a discovery that most of the world had not yet grasped. The letter was addressed to President Franklin D. Roosevelt, and it carried a warning: Germany might be building an atomic bomb. What followed from that single document would reshape the history of the twentieth century. How did a letter drafted with spelling errors, typed by a stenographer who thought Szilard was a lunatic, end up triggering the most consequential weapons program in human history? And what did Einstein himself think of what he had set in motion?

• 2. The Discovery That Changed Everything

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  On the 6th of January 1939, a German scientific journal called Die Naturwissenschaften published a report by Otto Hahn and Fritz Strassmann announcing the discovery of nuclear fission in uranium. A few weeks later, on the 11th of February, the physicist Lise Meitner identified the process by name in the journal Nature. Word spread fast. Danish physicist Niels Bohr carried the news to the United States. On the 26th of January 1939, the Fifth Washington Conference on Theoretical Physics opened with Enrico Fermi, and experimental physicists quickly confirmed the results. Among the most important were Fermi himself and John R. Dunning, working at Columbia University.

  Leo Szilard had been thinking about chain reactions long before the Hahn-Strassmann paper appeared. Living in London in 1933, he had read Ernest Rutherford's dismissive remarks about generating power from Rutherford's own team's 1932 experiment splitting lithium with protons. Szilard's response was to formulate and patent the idea of a neutron-driven chain reaction. The logic was elegant: if a single fission event released more than one secondary neutron, each of those neutrons could trigger its own fission, producing an exponentially growing cascade of reactions. The problem was that Szilard had not yet been able to make it work with the light atoms he was testing.

  At Columbia University, Szilard joined Fermi to pursue the chain-reaction question using natural uranium. The physics department there was headed by George B. Pegram. An early dispute divided the two men: Fermi believed the relevant isotope was the more abundant uranium-238, while others suspected it was uranium-235, which makes up less than one percent of natural uranium. Through a series of experiments they concluded that a chain reaction in natural uranium was possible, but only if they found a suitable neutron moderator. Water slowed neutrons but tended to absorb them. Szilard proposed carbon instead. Getting enough carbon and uranium to build a reactor would require resources they did not yet have.

• 3. Three Hungarians and a Decision

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  German nuclear physicist Siegfried Flügge published two influential articles on exploiting nuclear energy in the period between June and August 1939. Szilard read them and grew alarmed. If German scientists were thinking along the same lines, the race had already begun. He discussed the danger with his fellow Hungarian Eugene Wigner, and the two men agreed that someone needed to warn the Belgians. Their reasoning was specific: the Belgian Congo was the world's best source of uranium ore, and they did not want that ore falling under German influence.

  Wigner pointed out that Albert Einstein knew the Belgian royal family personally, which made him ideally placed to carry the warning. Szilard had good reason to approach Einstein beyond his royal connections. Between 1926 and 1930, the two men had worked together to develop the Einstein refrigerator, and they knew each other well.

  On the 12th of July 1939, Szilard and Wigner drove out to Cutchogue on New York's Long Island, where Einstein was spending the summer. When they laid out the possibility of atomic bombs, Einstein's reaction was striking. He said, in German, "Daran habe ich gar nicht gedacht" - "I did not even think about that." Einstein dictated a letter in German addressed to the Belgian Ambassador to the United States. Wigner wrote it down. At Wigner's suggestion, they also prepared a letter for the State Department, giving it two weeks to raise any objection before they proceeded.

• 4. Getting the Letter to Roosevelt

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  The draft letter still needed a path to the President. A friend of Szilard's, the Austrian economist Gustav Stolper, suggested Alexander Sachs, a man with direct access to Franklin Roosevelt. Sachs told Szilard that he had already raised the uranium question with the President, but that Fermi and Pegram had reported the prospects for an atomic bomb as remote. Sachs agreed to deliver a letter, but advised that it should come from someone more prominent. Einstein, again, was the obvious name.

  Sachs and Szilard drafted the letter together and mailed it to Einstein. Then, on the 2nd of August, Szilard made a second trip to Long Island. Wigner was not available, so a third Hungarian physicist entered the story: Edward Teller, who drove Szilard out to see Einstein. After Einstein dictated the letter in German, Szilard returned to Columbia University and dictated the English version to a departmental stenographer named Janet Coatesworth. She later recalled that when Szilard mentioned extremely powerful bombs, she was sure she was working for a lunatic. The letter closing with "Yours truly, Albert Einstein" did not change her mind.

  Both the short English letter and a longer explanatory version were mailed back to Einstein for his signature. He signed and returned them, and Szilard received the letters on the 9th of August. On the 15th of August, Szilard handed Sachs the short letter, the long letter, and a separate letter of his own.

• 5. Breakfast with the President

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  Germany invaded Poland before Sachs could secure an appointment, plunging the administration into crisis. Sachs deliberately delayed until October, judging that the President would only give the letter its proper attention once the immediate emergency had passed. On the 11th of October 1939, Sachs finally sat down with Roosevelt, along with the president's secretary Brigadier General Edwin "Pa" Watson and two ordnance experts: Army Lieutenant Colonel Keith F. Adamson and Navy Commander Gilbert C. Hoover.

  Sachs read the materials aloud, including Einstein's letter and a memorandum of his own. Roosevelt was not persuaded. Sachs spent a sleepless night searching for a different approach and secured an invitation to breakfast the next morning.

  When he returned on the 12th of October, Sachs told Roosevelt a story about Napoleon. A young American inventor - Robert Fulton - had approached the French emperor during the Napoleonic wars and offered to build a fleet of steamships that could carry troops across the Channel regardless of the weather. Ships without sails struck Napoleon as impossible, and he sent Fulton away. Sachs suggested that this was Napoleon's great mistake. According to Sachs, Roosevelt called for a bottle of brandy from Napoleon's time and poured two glasses. Then the president turned to Sachs and said, "Alex, what you are after is to see that the Nazis don't blow us up?" Sachs replied, "Precisely." Roosevelt turned to Watson and declared, "Pa, this requires action!"

  This account of the breakfast meeting is preserved in Robert Jungk's history Brighter Than A Thousand Suns. Roosevelt sent Einstein a written reply, informing him that he had convened a board consisting of the head of the Bureau of Standards and representatives of the Army and Navy to investigate the uranium question.

• 6. What the Letter Set in Motion

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  Roosevelt authorized the creation of the Advisory Committee on Uranium. Its chair was Lyman James Briggs, Director of the Bureau of Standards, the institution now known as the National Institute of Standards and Technology. The committee convened for the first time on the 21st of October 1939. Also present at that first meeting were Fred L. Mohler from the Bureau of Standards, Richard B. Roberts of the Carnegie Institution of Washington, and Szilard, Teller, and Wigner. Adamson remained skeptical about the bomb's feasibility but agreed to authorize six thousand dollars to buy uranium and graphite for Szilard and Fermi's experiments.

  The Advisory Committee on Uranium was not an aggressive weapons program. It concentrated on the theoretical physics of nuclear fission rather than on building a weapon. It was superseded by the National Defense Research Committee in 1940 and then by the Office of Scientific Research and Development in 1941. The Frisch-Peierls memorandum and the British Maud Reports eventually pushed Roosevelt to authorize a full-scale secret development effort through the OSRD in January 1942. In June 1942, the Army Corps of Engineers' Manhattan District was assigned to coordinate the entire effort. That program became known as the Manhattan Project.

  Einstein played no part in it. The Army and Vannevar Bush denied him security clearance in July 1940, on the grounds that his pacifist views and public prominence made him a security risk. He was permitted to work as a consultant to the Navy's Bureau of Ordnance, but he had no knowledge of the bomb's development and no influence over the decision to use it.

• 7. Regret and Reckoning

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  Szilard drafted a fourth letter for Einstein's signature in 1945. Dated the 25th of March, it urged Roosevelt to meet with Szilard directly to discuss nuclear energy policy. The letter never reached the president. Roosevelt died on the 12th of April 1945, and with him went the last chance to redirect what the 1939 letter had started.

  According to Linus Pauling, Einstein came to regret signing the original letter. The regret was real but conditional. Einstein told Newsweek magazine in 1947 that had he known the Germans would not succeed in developing an atomic bomb, he would have done nothing. His reasoning in 1939 had been that Nazi Germany might build the bomb first. That fear, grounded in Szilard's specific intelligence about Germany stopping uranium sales from Czechoslovakian mines and about von Weizsäcker's son working at the Kaiser-Wilhelm-Institut in Berlin, was the moral center of the letter. At the time of writing, scientists estimated that a fission chain reaction would require several tons of material. Seven months later, a breakthrough in Britain showed the critical mass could be less than ten kilograms, making delivery by aircraft possible and bringing the bomb suddenly within reach. That calculation, and what followed from it, haunted Einstein for the rest of his life.