TheEinstein–Szilard letter was a letter written byLeo Szilard and signed byAlbert Einstein on August 2, 1939, that was sent toPresident of the United StatesFranklin D. Roosevelt. Written by Szilard in consultation with fellowHungarian physicistsEdward Teller andEugene Wigner, the letter warned thatGermany might developatomic bombs and suggested that the United States start its own nuclear program. It prompted action by Roosevelt, which eventually resulted in theManhattan Project, the development of the first atomic bombs, and theuse of these bombs on the cities of Hiroshima and Nagasaki.
Otto Hahn andFritz Strassmann reported thediscovery of nuclear fission in uranium in the January 6, 1939, issue ofDie Naturwissenschaften, andLise Meitner identified it asnuclear fission in the February 11, 1939 issue ofNature. This generated intense interest among physicists. Danish physicistNiels Bohr brought the news to the United States, and the U.S. opened the FifthWashington Conference on Theoretical Physics withEnrico Fermi on January 26, 1939. The results were quickly corroborated by experimental physicists, most notably Fermi andJohn R. Dunning atColumbia University.[1]
Hungarian physicistLeo Szilard realized that theneutron-driven fission of heavy atoms could be used to create anuclear chain reaction which could yield vast amounts of energy for electric power generation or atomic bombs. He had first formulated and patented such an idea while he lived in London in 1933 after readingErnest Rutherford's disparaging remarks about generating power from his team's 1932 experiment usingprotons to splitlithium. However, Szilard had not been able to achieve a neutron-driven chain reaction with neutron-rich light atoms. In theory, if the number of secondary neutrons produced in a neutron-driven chain reaction was greater than one, then each such reaction could trigger multiple additional reactions, producing an exponentially increasing number of reactions.[2][3]
Szilard collaborated with Fermi to build a nuclear reactor from natural uranium at Columbia University, whereGeorge B. Pegram headed the physics department. There was disagreement about whether fission was produced byuranium-235, which made up less than one percent of natural uranium, or the more abundanturanium-238isotope, as Fermi maintained. Fermi and Szilard conducted a series of experiments and concluded that a chain reaction in natural uranium could be possible if they could find a suitableneutron moderator. They found that the hydrogen atoms in water slowed neutrons but tended tocapture them. Szilard then suggested using carbon as a moderator. They then needed large quantities of carbon and uranium to create a reactor. Szilard was convinced that they would succeed if they could get the materials.[4]
Szilard was concerned that German scientists might also attempt this experiment. German nuclear physicistSiegfried Flügge published two influential articles on the exploitation of nuclear energy in June-August 1939.[5][6] After discussing this prospect with fellow Hungarian physicistEugene Wigner, they decided that they should warn the Belgians, as theBelgian Congo was the best source of uranium ore. Wigner suggested thatAlbert Einstein might be a suitable person to do this, as he knew theBelgian royal family.[7] Szilard knew Einstein well; between 1926 and 1930, he had worked with Einstein to develop theEinstein refrigerator.[8][9]
On July 12, 1939, Szilard and Wigner drove in Wigner's car toCutchogue on New York'sLong Island, where Einstein was staying.[10] When they explained the possibility of atomic bombs, Einstein replied:"Daran habe ich gar nicht gedacht" ("I did not even think about that").[11] Einstein dictated a letter in German to the Belgian Ambassador to the United States. Wigner wrote it down, and Einstein agreed and signed it. At Wigner's suggestion, they also prepared a letter for theState Department explaining what they were doing and why, giving it two weeks to respond if it had any objections.[10]
This still left the problem of getting government support for uranium research. Another friend of Szilard's, the Austrian economistGustav Stolper, suggested approachingAlexander Sachs, who had access toPresidentFranklin D. Roosevelt. Sachs told Szilard that he had already spoken to the President about uranium, but thatFermi andPegram had reported that the prospects for building an atomic bomb were remote. He told Szilard that he would deliver the letter, but suggested that it come from someone more prestigious. For Szilard, Einstein was again the obvious choice.[7] Sachs and Szilard drafted a letter riddled with spelling errors and mailed it to Einstein.[12]
Szilard also set out himself for Long Island again on August 2. Wigner was unavailable, so this time Szilard co-opted another Hungarian physicist,Edward Teller, to do the driving. After receiving the draft, Einstein dictated the letter first in German. On returning to Columbia University, Szilard dictated the letter in English to a young departmentalstenographer, Janet Coatesworth. She later recalled that when Szilard mentioned extremely powerful bombs, she "was sure she was working for a nut".[13] Ending the letter with "Yours truly, Albert Einstein" did nothing to alter this impression. Both the English letter and a longer explanatory letter were then posted to Einstein for him to sign.[13]
The letter dated August 2 and addressed to President Roosevelt warned:[14]
In the course of the last four months it has been made probable – through the work ofJoliot in France as well as Fermi and Szilard in America – that it may become 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 ofbombs, 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 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 to be too heavy for transportation by air.
It also specifically warned about Germany:[14]
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 theKaiser-Wilhelm-Institut in Berlin where some of the American work on uranium is now being repeated.
At the time of the letter, the estimated material necessary for a fission chain reaction was several tons. Seven months later abreakthrough in Britain would estimate the necessarycritical mass to be less than 10 kilograms, making delivery of a bomb by air a possibility.[15]
The Einstein–Szilard letter was signed by Einstein and posted back to Szilard, who received it on August 9.[13] Szilard gave both the short and long letters, along with a letter of his own, to Sachs on August 15. Sachs asked theWhite House staff for an appointment to see President Roosevelt, but before one could be set up, the administration became embroiled in a crisis due toGermany'sinvasion of Poland, which startedWorld War II.[16]
Sachs delayed his appointment until October so that the president would give the letter due attention, securing an appointment on October 11. On that date he met with the president, the president's secretary,Brigadier GeneralEdwin "Pa" Watson, and two ordnance experts, ArmyLieutenant Colonel Keith F. Adamson and NavyCommander Gilbert C. Hoover.
Sachs's own accounts of his meetings with Roosevelt are recounted inBrighter Than A Thousand Suns, Robert Jungk's seminal history of the development of atomic science.[17]
By this account, Sachs presented the Einstein-Szilard letter and accompanying materials, including a memorandum of his own. He read the materials aloud to Roosevelt, but the president was not persuaded that the U.S. government should get involved. Sachs managed to get an invitation to breakfast the next morning, and spent a sleepless night trying to conceive how he might persuade the president to support the plan.[18]
When he returned to the White House the next day, October 12th, Sachs said, he told the president the following story:
During the Napoleonic wars a young American inventor came to the French emperor and offered to build a fleet of steamships with the help of which Napoleon could, in spite of the uncertain weather, land in England. Ships without sails? This seemed to the great Corsican so impossible that he sent [Robert]Fulton away .... Had Napoleon shown more imagination and humility at that time, the history of the nineteenth century would have taken a different course.[19]
According to Sachs, after considering the implication of this tale, FDR called for an aide to bring a bottle of brandy from Napoleon's time, which he poured into two glasses for himself and Sachs.
Then the president remarked, "Alex, what you are after is to see that the Nazis don't blow us up?" Sachs replied, "Precisely." Roosevelt turned to his attache, General Ewin "Pa" Watson, and declared, "Pa, this requires action!"[20][21]
Roosevelt sent a reply thanking Einstein, and informing him:[22]
I found this data of such import that I have convened a Board consisting of the head of theBureau of Standards and a chosen representative of the Army and Navy to thoroughly investigate the possibilities of your suggestion regarding the element of uranium.
Einstein sent two more letters to Roosevelt, on March 7, 1940, and April 25, 1940, calling for action onnuclear research. Szilard drafted a fourth letter for Einstein's signature that urged the President to meet with Szilard to discuss policy on nuclear energy. Dated March 25, 1945, it did not reach Roosevelt before his death on April 12, 1945.[14]
Roosevelt decided that the letter required action, and authorized the creation of theAdvisory Committee on Uranium. The committee was chaired byLyman James Briggs, the Director of the Bureau of Standards (currently theNational Institute of Standards and Technology), with Adamson and Hoover as its other members. It convened for the first time on October 21. The meeting was also attended by Fred L. Mohler from the Bureau of Standards, Richard B. Roberts of theCarnegie Institution of Washington, and Szilard, Teller and Wigner. Adamson was skeptical about the prospect of building an atomic bomb, but was willing to authorize $6,000 ($100,000 in current USD) for the purchase ofuranium andgraphite for Szilard and Fermi's experiment.[23]
The Advisory Committee on Uranium (ACU) was the beginning of the US government's effort to develop an atomic bomb, but it did not vigorously pursue the development of a weapon, instead focusing on the theoretical physics concerning practical development of nuclear fission. The ACU was superseded by theNational Defense Research Committee in 1940,[24] and then theOffice of Scientific Research and Development (OSRD) in 1941.[25] TheFrisch–Peierls memorandum and the BritishMaud Reports eventually prompted Roosevelt to authorize the OSRD's secret full-scale development effort in January 1942.[26] The work of coordinating funding, material, personnel, security, and the primarily civilian research of the OSRD (specifically, theS-1 Executive Committee) was assigned to theUnited States Army Corps of Engineers'sManhattan District in June 1942, which then directed the all-out bomb development program known as theManhattan Project.[27]
Einstein did not work on the Manhattan Project. The Army andVannevar Bush denied him the work clearance needed in July 1940, saying hispacifist leanings and celebrity status made him a security risk.[28] At least one source states that Einstein did clandestinely contribute some equations to the Manhattan Project.[29] Einstein was allowed to work as a consultant to theUnited States Navy'sBureau of Ordnance.[30][31] He had no knowledge of the atomic bomb's development, and no influence on the decision of any being used.[14][28]
According toLinus Pauling, Einstein later regretted signing the letter because it led to the development and use of the atomic bomb in combat, adding that Einstein had justified his decision because of the greater danger that Nazi Germany would develop the bomb first.[32] In 1947 Einstein toldNewsweek magazine that "had I known that the Germans would not succeed in developing an atomic bomb, I would have done nothing."[28][33]
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