EinsteinEverything you need to know about Albert Einstein.

The Roosevelt Letter

Einstein's most consequential signature was on a letter he didn't write, warning of a weapon he never worked on. The documented story of August 1939 — plus the other letters that define his archive.

The letter he didn’t write

In the summer of 1939, the Hungarian physicist Leo Szilard — who had conceived the nuclear chain reaction in 1933 — was alarmed by two developments: Otto Hahn and Fritz Strassmann’s discovery of nuclear fission (published January 1939, interpreted by Lise Meitner and Otto Frisch), and Germany’s seizure of Czechoslovakian uranium mines. Szilard concluded that Nazi Germany might build an atomic bomb, and that only the United States could be warned in time. He needed a name the President would heed.

With Eugene Wigner’s help, Szilard drafted a letter. Edward Teller drove Szilard to Einstein’s summer house on Long Island. Einstein — a committed pacifist who had never worked on nuclear weapons — read the draft, agreed to sign, and added his own dictation. The letter, dated 2 August 1939, warned President Franklin D. Roosevelt that “it may become possible to set up a nuclear chain reaction in a large mass of uranium” and that “extremely powerful bombs of a new type may thus be constructed.”

The delivery was slow: the economist Alexander Sachs finally carried it to Roosevelt on 11 October 1939. Roosevelt’s response was cautious but real — he authorized the Advisory Committee on Uranium, the small bureaucratic seed from which the Manhattan Project would grow three years later.

What it did — and didn’t — do

The letter’s role is documented and specific: it helped move the US government from inaction to the first official uranium committee. It did not design a bomb, propose the Manhattan Project, or involve Einstein in weapons work. Einstein’s part ended with the signature. He was subsequently denied security clearance and played no role in the Manhattan Project — the Army’s decision, documented in the record, kept the world’s most famous physicist away from the world’s most secret physics.

Years later, Einstein described the signature as a mistake. The best-documented form of that regret is secondhand: Linus Pauling recalled Einstein telling him, “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.” (See Sayings — this page repeats the methodology note: it is Pauling’s recollection of a 1954 conversation, not a signed statement.)

The myth to discard: Einstein did not “invent the atomic bomb.” He signed a warning letter, drafted by Szilard, about a German program — and spent the war excluded from the American one. (Tested in Reception.)

The other letters that matter

Einstein was a compulsive, brilliant correspondent — the Collected Papers run to many volumes of letters. A few stand out:

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