He explored electron capture and exchange processes, as well as electron-atom collision processes. In 1930 he presented a cogent symmetry argument that was later recognized to be tantamount to the prediction of the positive electron, or positron. He studied the production of cosmic-ray showers. He explored various problems in quantum electrodynamics, as well as the properties and role of the meson in nuclear forces. He helped develop the so-called Oppenheimer-Phillips interpretation of deuteronnuclear reactions, which eventually led to great insight into the structure of the nucleus. In all of these theoretical investigations—and many more could be cited— Oppenheimer displayed his genius in implementing Wolfgang Pauli's conviction that a physicist should concern himself first and foremost with those problems on the very frontiers of current knowledge.

To the general public, Oppenheimer, as a scientist, is best known for his role in directing the development of the atomic bomb at Los Alamos, the laboratory high on a New Mexican mesa at a site he chose. Many of America's foremost physicists were persuaded to come with their families to this isolated laboratory to beat the Germans in the development of the most awesome weapon of destruction in human history. When all of the huge and unique problems were solved, and the test bomb was exploded on July 16, 1945, in the desert near Alamogordo, N. Mex., Oppenheimer was deeply shaken. He thought of the words from the Bhagavad-Gita: "If the radiance of a thousands suns/ Were to burst into the sky/That would be like/The splendor of the Mighty One…./Iam become Death, the shatterer of worlds." Not much later Hiroshima and Nagasaki were obliterated.

Oppenheimer was a complex man, one who could inspire distrust as well as utter devotion, and one who could commit indiscretions as well as be a scientist of faultless integrity. After the war, his early left-wing sympathies, inflated by Senator Joseph McCarthy and his coterie of witch-hunters, made Oppenheimer the defendant in perhaps the most celebrated trial since the time of Galileo. In spite of the fact that Oppenheimer's past associations had aroused no undue concern earlier—he had received the coveted Presidential Medal of Merit in 1946 and had been serving on the highest policy-making committees—his security clearance was revoked, deeply shocking the vast majority of his fellow scientists. Not until 1961, when President John F. Kennedy made the decision to give the Fermi Award to Oppenheimer (it was actually presented in 1963 by President Lyndon B. Johnson), was a significant attempt made to publicly clear Oppenheimer's name. In the interim, Oppenheimer had been serving as the director of the Institute for Advanced Study in Princeton, giving his splendid administrative and technical talents to the young group of highly gifted physicists who had gathered there.

Oppenheimer will remain a subject of study, discussion, controversy, and admiration for years to come. His profound concern for uniting the intellectual community, and humanity in general, is evident from the vast number of lectures and articles he devoted to the subject. He died of cancer in Princeton on Feb. 18, 1967.