The New World

On December 19, 1938, Otto Hahn wrote to Lise Meitner in Stockholm, asking her if she could propose some “fantastic explanation” for his and Fritz Strassmann’s finding of barium when bombarding uranium with neutrons. She and Otto Robert Frisch found such an explanation for what he called “nuclear fission” over the Christmas holidays, based on Gamow’s liquid-drop model of the nucleus. Bohr was astonished by this, but in 1936 he had speculated that the uranium nucleus would just explode. He, his son Erik, and his associate Léon Rosenfeld then took a ship to New York, arriving on January 16, 1939. Rosenfeld reported the discovery of fission that evening to the Princeton physics journal club. On January 26, physicists everywhere learned about this stunning discovery when Bohr and Fermi reported it at a conference in Washington, D.C. Physicists entered the New World of Nuclear Physics, taking Humanity with them.