J. Robert Oppenheimer (born Julius Robert Oppenheimer; /ˈɒpənhaɪmər/ OP-ən-hy-mər; April 22, 1904 – February 18, 1967) was an American theoretical physicist who served as the director of the Manhattan Project's Los Alamos Laboratory during World War II. He is often called the "father of the atomic bomb" for his role in overseeing the development of the first nuclear weapons.

Born in New York City, Oppenheimer obtained a degree in chemistry from Harvard University in 1925 and a doctorate in physics from the University of Göttingen in Germany in 1927, studying under Max Born. After research at other institutions, he joined the physics faculty at the University of California, Berkeley, where he was made a full professor in 1936. Oppenheimer made significant contributions to physics in the fields of quantum mechanics and nuclear physics, including the Born–Oppenheimer approximation for molecular wave functions; work on the theory of positrons, quantum electrodynamics, and quantum field theory; and the Oppenheimer–Phillips process in nuclear fusion. With his students, he also made major contributions to astrophysics, including the theory of cosmic ray showers, and the theory of neutron stars and black holes.

In 1942, Oppenheimer was recruited to work on the Manhattan Project, and in 1943 was appointed director of the project's Los Alamos Laboratory in New Mexico, tasked with developing the first nuclear weapons. His leadership and scientific expertise were instrumental in the project's success. On July 16, 1945, he was present at the first test of the atomic bomb, Trinity. In August 1945, the weapons were used against Japan in the atomic bombings of Hiroshima and Nagasaki, to date the only use of nuclear weapons in an armed conflict.

In 1947, Oppenheimer was appointed director of the Institute for Advanced Study in Princeton, New Jersey, and chairman of the General Advisory Committee of the new United States Atomic Energy Commission (AEC). He lobbied for international control of nuclear power to avert nuclear proliferation and a nuclear arms race with the Soviet Union, and opposed the development of the hydrogen bomb, partly on ethical grounds. During the second Red Scare, these stances, together with his past associations with the Communist Party USA, led to an AEC security hearing in 1954 and the revocation of his security clearance. He continued to lecture, write, and work in physics, and in 1963 was given the Enrico Fermi Award as a gesture of political rehabilitation. In 2022, the U.S. government vacated the 1954 revocation of his security clearance.

Early life
Childhood and education
Oppenheimer was born Julius Robert Oppenheimer[note 1] into a non-observant Jewish family in New York City on April 22, 1904, to Ella (née Friedman), a painter, and Julius Seligmann Oppenheimer, a successful textile importer.[5][6] Robert had a younger brother, Frank, who also became a physicist.[7] His father was born in Hanau, when it was still part of the Hesse-Nassau province of the Kingdom of Prussia, and as a teenager made his way to the United States in 1888, without money, higher education, or even English. He was hired by a textile company and within a decade was an executive there, eventually becoming wealthy.[8] In 1912, the family moved to an apartment on Riverside Drive near West 88th Street, Hudson Heights, New York, an area known for luxurious mansions and townhouses.[6] Their art collection included works by Pablo Picasso, Édouard Vuillard, and Vincent van Gogh.[9]

Oppenheimer was initially educated at Alcuin Preparatory School. In 1911, he entered the Ethical Culture Society School,[10] founded by Felix Adler to promote training based on the Ethical Culture movement, whose motto was "Deed before Creed". Oppenheimer's father had been a member of the Society for many years, serving on its board of trustees.[11] Oppenheimer was a versatile student, interested in English and French literature, and particularly mineralogy.[12] He completed third and fourth grades in one year and skipped half of eighth grade.[10] He took private music lessons by famous French flutist Georges Barrère. During his final year of school, Oppenheimer became interested in chemistry.[13] He graduated in 1921, but his further education was delayed a year by an attack of colitis contracted while prospecting in Joachimstal during a family vacation in Czechoslovakia. He recovered in New Mexico, where he developed a love for horseback riding and the southwestern United States.[14]

Oppenheimer entered Harvard College in 1922 at age 18. He majored in chemistry; Harvard also required studies in history, literature, and philosophy or mathematics. To compensate for the delay caused by his illness, he took six courses each term instead of the usual four. He was admitted to the undergraduate honor society Phi Beta Kappa and was granted graduate standing in physics on the basis of independent study, allowing him to bypass basic courses in favor of advanced ones. He was attracted to experimental physics by a course on thermodynamics taught by Percy Bridgman. Oppenheimer graduated from Harvard in 1925 with a Bachelor of Arts, summa ♥♥♥ laude, after only three years of study.[15]

Studies in Europe
Fifteen men in suits, and one woman, pose for a group photograph
Heike Kamerlingh Onnes' Laboratory in Leiden, Netherlands, July 1927. Oppenheimer is in the middle row, second from the left.
After being accepted at Christ's College, Cambridge, in 1924, Oppenheimer wrote to Ernest Rutherford requesting permission to work at the Cavendish Laboratory, though Bridgman's letter of recommendation said that Oppenheimer's clumsiness in the laboratory suggested that theoretical, rather than experimental, physics would be his forte. Rutherford was unimpressed, but Oppenheimer went to Cambridge nonetheless;[16] J. J. Thomson ultimately accepted him on the condition that he complete a basic laboratory course.[17]

Oppenheimer was very unhappy at Cambridge and wrote to a friend: "I am having a pretty bad time. The lab work is a terrible bore, and I am so bad at it that it is impossible to feel that I am learning anything."[18] He developed an antagonistic relationship with his tutor, Patrick Blackett, a future Nobel laureate. According to Oppenheimer's friend Francis Fergusson, Oppenheimer once confessed to leaving a poisoned apple on Blackett's desk, and Oppenheimer's parents convinced the university authorities not to expel him. There are no records of either a poisoning incident or probation, but Oppenheimer had regular sessions with a psychiatrist in Harley Street, London.[19][20][21][22] Oppenheimer was a tall, thin chain smoker,[23] who often neglected to eat during periods of intense concentration. Many friends said he could be self-destructive. Fergusson once tried to distract Oppenheimer from apparent depression by telling him about his girlfriend, Frances Keeley, and how he had proposed to her. Oppenheimer did not take the news well. He jumped on Fergusson and tried to strangle him. Oppenheimer was plagued by periods of depression throughout his life,[24][25] and once told his brother, "I need physics more than friends."[26]

In 1926, Oppenheimer left Cambridge for the University of Göttingen to study under Max Born; Göttingen was one of the world's leading centers for theoretical physics. Oppenheimer made friends who went on to great success, including Werner Heisenberg, Pascual Jordan, Wolfgang Pauli, Paul Dirac, Enrico Fermi and Edward Teller. He was enthusiastic in discussions to the point of sometimes taking them over.[27]
On October 9, 1941, two months before the United States entered World War II, President Franklin D. Roosevelt approved a crash program to develop an atomic bomb. On October 21, Ernest Lawrence brought Oppenheimer into what became the Manhattan Project. Oppenheimer was assigned to take over the project's specific bomb-design research