J. Robert Oppenheimer's Work

J. Robert Oppenheimer in his office at IAS

When J. Robert Oppenheimer entered the world of physics in 1925, modern quantum mechanics was just beginning. He was able to use quantum mechanics for the exploration of problems that had been insoluble using the old quantum theory. For his Ph.D. thesis in 1927, he attacked the problem of the absorption of X-rays in matter. For an X-ray to be absorbed, one of the electrons in a bound state in an atom must jump out of the atom into an unbound state. Oppenheimer calculated exactly the probability that the jump will happen, overcoming some formidable difficulties that arise in the quantum description of unbound states.

In 1930, he was the first to understand the meaning of the negative-energy solutions of Dirac's wave equation for the electron. Dirac had suggested that a hole in the sea of negative-energy electrons would be observed as a proton. Oppenheimer showed that the hole must have the same mass as the electron, so it could not be a proton and must be a new particle with equal mass and opposite charge to the electron. The new particle was soon discovered and given the name positron.

In 1939, working with graduate student Hartland S. Snyder, Oppenheimer discovered a solution of Einstein's equations of general relativity describing the gravitational collapse of a massive star. This solution shows how the star can end its life as a collapsed object. Such objects were later observed and given the name "Black Holes." They are now known to play an important role in the evolution of the universe.

By all accounts, Oppenheimer's lecture style benefited from an erudite command of the English language and a dry wit. He conveyed a sense of excitement about the scientific endeavor. The late Hans Bethe wrote: "J. Robert Oppenheimer did more than any other man to make American theoretical physics great. His taste and his knowledge guided and stimulated young American physicists for two generations ... he communicated to his students. ‘What we don't understand we explain to each other,' he once said in describing the activities of the physics group at the Institute for Advanced Study. There was always a burning question which had to be discussed from all aspects, a solution to be found, to be rejected, and another solution attempted. Wherever he was, there was always life and excitement, and the expectation of excitement in physics for generations to come."

During Oppenheimer's tenure as Director of the Institute, outstanding physicists were appointed to the permanent Faculty: Abraham Pais in 1950, Freeman Dyson in 1953, C. N. Yang in 1955, Bengt Strömgren in 1957, and T. D. Lee in 1960. Yang and Lee did their 1957 Nobel Prize-winning work on parity violation while Yang was a professor and Lee a visiting Member at the Institute. By the 1960s, there were six physics professors–Pais, Yang, Lee, Dyson, Tullio Regge, and Strömgren–in the School of Mathematics. Nominally part of the School of Mathematics, physicists formed a working group within it until an independent School of Natural Sciences was established in 1966. The presence of physics, however, goes back to the Institute's first Faculty appointments of Einstein, Weyl, and von Neumann, in 1933. Einstein was a physicist and Weyl and von Neumann were mathematicians who had made major contributions to physics.

In his book, J. Robert Oppenheimer: A Life (Oxford University Press, 2006), Abraham Pais writes,

"Upon Oppenheimer's arrival, a function and quality of the Institute developed that had not been there before... It became a center for theoretical physics, in fact during the next decade the world's premier mecca for theoretical physicists, who came flocking as temporary members."

Among those drawn to the Institute were established figures such as Wolfgang Pauli and Paul Dirac, who had been there before, and Sin-Itiro Tomonaga and Hideki Yukawa. They were joined by emerging scientists such as Murray Gell-Mann, Geoffrey Chew, Francis Low and Yoichiro Nambu.