Theoretical physicist J. Robert Oppenheimer was a pioneer in the field of quantum mechanics , the study of the energy of atomic particles. His research on protons and their relation to electrons led directly to the discovery of a new particle, the positron. His later work shed light on deuterons, the nuclei of heavy hydrogen atoms. He was a charismatic teacher and effective administrator who directed the laboratory at Los Alamos, New Mexico, where the atomic bomb was developed during World War II. In the postwar years, however, Oppenheimer staunchly opposed the proliferation of nuclear weapons. This stance brought him before Congress during the McCarthy era and cost him his security clearance as a government consultant.

Julius Robert Oppenheimer was born in New York City on April 22, 1904, to a wealthy and cultured family. His father, Julius Oppenheimer, who emigrated from Germany as a young man, had a successful business...