Einstein's atomic bomb letter, which he called his 'one great mistake,' just sold for almost $4 million

In the summer of 1939, Albert Einstein made what he considered his 'one great mistake': signing a letter that would reach the desk of President Franklin Roosevelt and help usher in the nuclear age. Now, a copy of that letter, also signed by Einstein, has sold at a Christie's auction for $3.9 million. The original that was sent to Roosevelt is part of the Franklin D. Roosevelt Library's collection in New York.

The letter warned that Germany could develop 'extremely powerful bombs' using uranium and urged the president to 'speed up' the US's own work on the element, eventually leading to the Manhattan Project and the development of the world's first atomic bomb.

Though Einstein didn't write the letter, his worldwide esteem meant his signature added significance and credibility to the letter. The copy that sold at auction on Tuesday was the only version in private hands, according to Christie's.

Peter Klarnet, senior specialist for Americana, books, and manuscripts at Christie's, said, 'This has been described as one of the most influential letters in history,' highlighting the considerable impact of this correspondence.

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