Julius Robert Oppenheimer (April 22, 1904 – February 18, 1967) was an American theoretical physicist and professor of physics at the University of California, Berkeley. Along with Enrico Fermi, he is often called the "father of the atomic bomb" for his role in the Manhattan Project, the World War II project that developed the first nuclear weapons. The first atomic bomb was detonated on July 16, 1945 in the Trinity test in New Mexico; Oppenheimer remarked later that it brought to mind words from the Bhagavad Gita: "Now, I am become Death, the destroyer of worlds."

After the war he became a chief adviser to the newly created United States Atomic Energy Commission and used that position to lobby for international control of nuclear power to avert nuclear proliferation and an arms race with the Soviet Union. After provoking the ire of many politicians with his outspoken opinions during the Second Red Scare, he had his security clearance revoked in a much publicized hearing in 1954. Though stripped of his direct political influence he continued to lecture, write and work in physics. A decade later President John F. Kennedy awarded (and Lyndon B. Johnson presented) him with the Enrico Fermi Award as a gesture of political rehabilitation.

Oppenheimer's notable achievements in physics include the Born – Oppenheimer approximation for molecular wave functions, work on the theory of electrons and positrons, the Oppenheimer – Phillips process in nuclear fusion, and the first prediction of quantum tunneling. With his students he also made important contributions to the modern theory of neutron stars and black holes, as well as to quantum mechanics, quantum field theory, and the interactions of cosmic rays. As a teacher and promoter of science, he is remembered as a founding father of the American school of theoretical physics that gained world prominence in the 1930s. After World War II, he became director of the Institute for Advanced Study in Princeton.

Oppenheimer was born in New York City on April 22, 1904, to Julius S. Oppenheimer, a wealthy Jewish textile importer who had immigrated to the United States from Germany in 1888, and Ella Friedman, a painter. In 1912 the family moved to an apartment on the eleventh floor of 155 Riverside Drive, near West 88th Street, Manhattan, an area known for luxurious mansions and town houses. Their art collection included works by Pablo Picasso and Édouard Vuillard, and at least three original paintings by Vincent van Gogh. Robert had a younger brother, Frank, who also became a physicist.

Oppenheimer was initially schooled at Alcuin Preparatory School, and in 1911 entered the Ethical Culture Society School. This had been founded by Felix Adler to promote a form of ethical training based on the Ethical Culture movement, whose motto was "Deed before Creed". His father had been a member of the Society for many years, serving on its board of trustees from 1907 to 1915. Oppenheimer was a versatile scholar, interested in English and French literature, and particularly in mineralogy. He completed the third and fourth grades in one year, and skipped half the eighth grade. During his final year, he became interested in chemistry. He entered Harvard College a year late, at age 18, because he suffered an attack of colitis while prospecting in Joachimstal during a family summer vacation in Europe. To help him recover from the illness, his father enlisted the help of his English teacher Herbert Smith who took him to New Mexico, where Oppenheimer fell in love with horseback riding and the southwestern United States.

In addition to majoring in chemistry, he was also required by Harvard's rules to study history, literature, and philosophy or mathematics. He made up for his late start by taking six courses each term and was admitted to the undergraduate honor society Phi Beta Kappa. In his first year he was admitted to graduate standing in physics on the basis of independent study, which meant he was not required to take the basic classes and could enroll instead in advanced ones. A course on thermodynamics taught by Percy Bridgman attracted him to experimental physics. He graduated summa cum laude in three years.

In 1924, Oppenheimer was informed that he had been accepted into Christ's College, Cambridge. He wrote to Ernest Rutherford requesting permission to work at the Cavendish Laboratory. Bridgman provided Oppenheimer with a recommendation, which conceded that Oppenheimer's clumsiness in the laboratory made it apparent his forte was not experimental but rather theoretical physics. Rutherford was unimpressed, but Oppenheimer went to Cambridge in the hope of landing another offer. He was ultimately accepted by J.J. Thomson on condition that he complete a basic laboratory course. He developed an antagonistic relationship with his tutor, Patrick Blackett, who was only a few years his senior. While on vacation, as recalled by his friend Francis Ferguson, Oppenheimer once confessed that he had left an apple doused with noxious chemicals on Blackett's desk. While Ferguson's account is the only detailed version of this event, Oppenheimer's parents were alerted by the university authorities who considered placing him on probation, a fate prevented by his parents successfully lobbying the authorities.

A tall, thin chain smoker, who often neglected to eat during periods of intense thought and concentration, Oppenheimer was marked by many of his friends as having self - destructive tendencies. A disturbing event occurred when he took a vacation from his studies in Cambridge to meet up with his friend Francis Ferguson in Paris. During a conversation in which Oppenheimer was explaining his frustration with experimental physics, he suddenly leapt up and tried to strangle Ferguson. Although Ferguson easily fended off the attack, the episode convinced him of Oppenheimer's deep psychological troubles. Plagued throughout his life by periods of depression, Oppenheimer once told his brother, "I need physics more than friends".

In 1926 he 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 would go on to great success, including Werner Heisenberg, Pascual Jordan, Wolfgang Pauli, Paul Dirac, Enrico Fermi and Edward Teller. He was known for being too enthusiastic in discussion, sometimes to the point of taking over seminar sessions. This irritated some of Born's other students so much that Maria Goeppert presented Born with a petition signed by herself and others threatening a boycott of the class unless he made Oppenheimer quiet down. Born left it out on his desk where Oppenheimer could read it, and it was effective without a word being said.

He obtained his Doctor of Philosophy degree in March 1927 at age 23, supervised by Born. After the oral exam, James Franck, the professor administering, reportedly said, "I'm glad that's over. He was on the point of questioning me." Oppenheimer published more than a dozen papers at Göttingen, including many important contributions to the new field of quantum mechanics. He and Born published a famous paper on the Born - Oppenheimer approximation, which separates nuclear motion from electronic motion in the mathematical treatment of molecules, allowing nuclear motion to be neglected to simplify calculations. It remains his most cited work.

Oppenheimer was awarded a United States National Research Council fellowship to the California Institute of Technology (Caltech) in September 1927. Bridgman also wanted him at Harvard, so a compromise was reached whereby he split his fellowship for the 1927 – 28 academic year between Harvard in 1927 and Caltech in 1928. At Caltech he struck up a close friendship with Linus Pauling, and they planned to mount a joint attack on the nature of the chemical bond, a field in which Pauling was a pioneer, with Oppenheimer supplying the mathematics and Pauling interpreting the results. Both the collaboration and their friendship were nipped in the bud when Pauling began to suspect Oppenheimer of becoming too close to his wife, Ava Helen Pauling. Once, when Pauling was at work, Oppenheimer had arrived at their home and invited Ava Helen to join him on a tryst in Mexico, though she refused and reported the incident to her husband. The invitation, and her apparent nonchalance about it, disquieted Pauling, and he ended his relationship with Oppenheimer. Oppenheimer later invited him to become head of the Chemistry Division of the Manhattan Project, but Pauling refused, saying he was a pacifist.

In the autumn of 1928, Oppenheimer visited Paul Ehrenfest's institute at the University of Leiden, the Netherlands, where he impressed them by giving lectures in Dutch, despite having little experience with the language. There he was given the nickname of Opje, later Anglicized by his students as "Oppie". From Leiden he continued on to the ETH in Zurich to work with Wolfgang Pauli on quantum mechanics and the continuous spectrum. Oppenheimer respected and liked Pauli, who may have inspired some of Oppenheimer's own style and his critical approach to problems.

On returning to the United States, Oppenheimer accepted an associate professorship from the University of California, Berkeley, where Raymond T. Birge wanted him badly enough to offer to share him with Caltech. Before his Berkeley professorship began, Oppenheimer was diagnosed with a mild case of tuberculosis and, with his brother Frank, spent some weeks at a ranch in New Mexico, which he leased and eventually purchased. When he heard the ranch was available for lease, he exclaimed, "Hot dog!", and later called it Perro Caliente, literally "hot dog" in Spanish. Later he used to say that "physics and desert country" were his "two great loves". He recovered from the tuberculosis and returned to Berkeley, where he prospered as an adviser and collaborator to a generation of physicists who admired him for his intellectual virtuosity and broad interests. His students and colleagues saw him as mesmerizing: hypnotic in private interaction, but often frigid in more public settings. His associates fell into two camps: one that saw him as an aloof and impressive genius and aesthete, the other that saw him as a pretentious and insecure poseur. His students almost always fell into the former category, adopting his walk, speech, and other mannerisms, and even his inclination for reading entire texts in their original languages. Hans Bethe said of him:

Probably the most important ingredient he brought to his teaching was his exquisite taste. He always knew what were the important problems, as shown by his choice of subjects. He truly lived with those problems, struggling for a solution, and he communicated his concern to the group. In its heyday, there were about eight or ten graduate students in his group and about six Post - doctoral Fellows. He met this group once a day in his office, and discussed with one after another the status of the student’s research problem. He was interested in everything, and in one afternoon they might discuss quantum electrodynamics, cosmic rays, electron pair production and nuclear physics.

He worked closely with Nobel Prize winning experimental physicist Ernest O. Lawrence and his cyclotron pioneers, helping them understand the data their machines were producing at the Lawrence Berkeley National Laboratory. In 1936 Berkeley promoted him to full professor at a salary of $3,300 per annum. In return he was asked to curtail his teaching at Caltech, so a compromise was reached whereby Berkeley released him for six weeks each year, enough to teach one term at Caltech.

Oppenheimer did important research in theoretical astronomy (especially as related to general relativity and nuclear theory), nuclear physics, spectroscopy, and quantum field theory, including its extension into quantum electrodynamics. The formal mathematics of relativistic quantum mechanics also attracted his attention, although he doubted its validity. His work predicted many later finds, which include the neutron, meson and neutron star.

Initially, his major interest was the theory of the continuous spectrum and his first published paper, in 1926, concerned the quantum theory of molecular band spectra. He developed a method to carry out calculations of its transition probabilities. He calculated the photoelectric effect for hydrogen and X-rays, obtaining the absorption coefficient at the K-edge. His calculations accorded with observations of the X-ray absorption of the sun, but not hydrogen. Years later it was realized that the sun was largely composed of hydrogen and that his calculations were indeed correct.

Oppenheimer also made important contributions to the theory of cosmic ray showers and started work that eventually led to descriptions of quantum tunneling. In 1931 he co-wrote a paper on the "Relativistic Theory of the Photoelectric Effect" with his student Harvey Hall, in which, based on empirical evidence, he correctly disputed Dirac's assertion that two of the energy levels of the hydrogen atom have the same energy. Subsequently, one of his doctoral students, Willis Lamb, determined that this was a consequence of the Lamb shift, for which Lamb was awarded the Nobel Prize in Physics in 1955.

Oppenheimer worked with his first doctoral student, Melba Phillips, on calculations of artificial radioactivity under bombardment by deuterons. When Ernest Lawrence and Edwin McMillan bombarded nuclei with deuterons they found the results agreed closely with the predictions of George Gamow, but when higher energies and heavier nuclei were involved, the results did not conform to the theory. In 1935, Oppenheimer and Phillips worked out a theory now known as the Oppenheimer - Phillips process to explain the results, a theory still in use today.

As early as 1930, Oppenheimer wrote a paper essentially predicting the existence of the positron, after a paper by Paul Dirac proposed that electrons could have both a positive charge and negative energy. The paper introduced the Dirac equation, a unification of quantum mechanics, special relativity and the then new concept of electron spin, to explain the Zeeman effect. Oppenheimer, drawing on the body of experimental evidence, rejected the idea that the predicted positively charged electrons were protons. He argued that they would have to have the same mass as an electron, whereas experiments showed that protons were much heavier than electrons. Two years later, Carl David Anderson discovered the positron, for which he received the 1936 Nobel Prize in Physics.

In the late 1930s, Oppenheimer became interested in astrophysics, probably through his friendship with Richard Tolman, resulting in a series of papers. In the first of these, a 1938 paper co-written with Robert Serber entitled "On the Stability of Stellar Neutron Cores", Oppenheimer explored the properties of white dwarves. This was followed by a paper co-written with one of his students, George Volkoff, "On Massive Neutron Cores", in which they demonstrated that there was a limit, the so-called Tolman - Oppenheimer - Volkoff limit, to the mass of stars beyond which they would not remain stable as neutron stars and would undergo gravitational collapse. Finally, in 1939, Oppenheimer and another of his students, Hartland Snyder, produced a paper "On Continued Gravitational Attraction", which predicted the existence of what are today known as black holes. After the Born - Oppenheimer approximation paper, these papers remain his most cited and were key factors in the rejuvenation of astrophysical research in the United States in the 1950s, mainly by John A. Wheeler.

Oppenheimer's papers were considered difficult to understand even by the standards of the abstract topics he was expert in. He was fond of using elegant, if extremely complex, mathematical techniques to demonstrate physical principles, though he was sometimes criticized for making mathematical mistakes, presumably out of haste. "His physics was good", said his student Snyder, "but his arithmetic awful."

Oppenheimer published only five scientific papers, one of which was in biophysics, after World War II, and none after 1950. Murray Gell - Mann a later Nobelist who, as a visiting scientist, worked with him at the Institute for Advanced Study in 1951, offered this opinion:

He didn't have Sitzfleisch, 'sitting flesh,' when you sit on a chair. As far as I know, he never wrote a long paper or did a long calculation, anything of that kind. He didn't have patience for that; his own work consisted of little aperçus, but quite brilliant ones. But he inspired other people to do things, and his influence was fantastic.

Oppenheimer's diverse interests sometimes interrupted his focus on projects. In 1933, he learned Sanskrit and met the Indologist Arthur W. Ryder at Berkeley. He read the Bhagavad Gita in the original language and later he cited it as one of the books that most shaped his philosophy of life. His close confidant and colleague, Nobel Prize winner Isidor Rabi, later gave his own interpretation:

Oppenheimer was overeducated in those fields, which lie outside the scientific tradition, such as his interest in religion, in the Hindu religion in particular, which resulted in a feeling of mystery of the universe that surrounded him like a fog. He saw physics clearly, looking toward what had already been done, but at the border he tended to feel there was much more of the mysterious and novel than there actually was ... [he turned] away from the hard, crude methods of theoretical physics into a mystical realm of broad intuition.

In spite of this, observers such as Nobel Prize winning physicist Luis Alvarez have suggested that if he had lived long enough to see his predictions substantiated by experiment, Oppenheimer might have won a Nobel Prize for his work on gravitational collapse, concerning neutron stars and black holes. In retrospect, some physicists and historians consider this to be his most important contribution, though it was not taken up by other scientists in his own lifetime. When the physicist and historian Abraham Pais once asked Oppenheimer what he considered to be his most important scientific contributions, Oppenheimer cited his work on electrons and positrons, not his work on gravitational contraction. Oppenheimer was nominated for the Nobel Prize for physics three times, in 1945, 1951 and 1967, but never won.

During the 1920s, Oppenheimer remained aloof from worldly matters. He claimed that he did not read newspapers or listen to the radio, and had only learned of the Wall Street crash of 1929 some time after it occurred. He once remarked that he never cast a vote until the 1936 election. However, from 1934 on, he became increasingly concerned about politics and international affairs. In 1934, he earmarked three percent of his salary — about $100 a year — for two years to support German physicists fleeing from Nazi Germany. During the 1934 West Coast Waterfront Strike, he and some of his students, including Melba Phillips and Bob Serber, attended a longshoremen's rally. Oppenheimer repeatedly attempted to get Serber a position at Berkeley but was blocked by Birge, who felt that "one Jew in the department was enough".

Oppenheimer's mother died in 1931, and he became closer to his father who, although still living in New York, became a frequent visitor in California. When his father died in 1937 leaving $ 392,602 to be divided between Oppenheimer and his brother Frank, Oppenheimer immediately wrote out a will leaving his estate to the University of California for graduate scholarships. Like many young intellectuals in the 1930s, he was a supporter of social reforms that were later alleged to be communist ideas. He donated to many progressive efforts which were later branded as "left - wing" during the McCarthy era. The majority of his allegedly radical work consisted of hosting fund raisers for the Republican cause in the Spanish Civil War and other anti - fascist activity. He never openly joined the Communist Party, though he did pass money to liberal causes by way of acquaintances who were alleged to be Party members. In 1936, Oppenheimer became involved with Jean Tatlock, the daughter of a Berkeley literature professor and a student at Stanford University School of Medicine. The two had similar political views; she wrote for the Western Worker, a Communist Party newspaper.

Oppenheimer broke up with Tatlock in 1939. In August that year he met Katherine ("Kitty") Puening Harrison, a radical Berkeley student and former Communist Party member. Harrison had been married three times previously. Her first marriage lasted only a few months. Her second husband was Joe Dallet, an active member of the Communist party, who was killed in the Spanish Civil War. Kitty returned to the United States where she obtained a bachelor of arts degree in botany from the University of Pennsylvania. There she married Richard Harrison, a physician and medical researcher, in 1938. In June 1939 Kitty and Harrison moved to Pasadena, California, where he became chief of radiology at a local hospital and she enrolled as a graduate student at the University of California, Los Angeles. Oppenheimer and Kitty created a minor scandal by sleeping together after one of Tolman's parties. In the summer of 1940 she stayed with Oppenheimer at his ranch in New Mexico. She finally asked Harrison for a divorce when she found out she was pregnant. When he refused, she obtained an instant divorce in Reno, Nevada, and married Oppenheimer on November 1, 1940.

Their first child Peter was born in May 1941, and their second child, Katherine ("Toni"), was born in Los Alamos, New Mexico, on December 7, 1944. During his marriage, Oppenheimer continued his affair with Jean Tatlock. Later their continued contact became an issue in his security clearance hearings because of Tatlock's Communist associations. Many of Oppenheimer's closest associates were active in the Communist Party in the '30s or '40s. They included his brother Frank, Frank's wife Jackie, Kitty, Jean Tatlock, his landlady Mary Ellen Washburn, and several of his graduate students at Berkeley.

When he joined the Manhattan Project in 1942, Oppenheimer wrote on his personal security questionnaire that he [Oppenheimer] had been "a member of just about every Communist Front organization on the West Coast". Years later he claimed that he did not remember saying this, that it was not true, and that if he had said anything along those lines, it was "a half - jocular overstatement". He was a subscriber to the People's World, a Communist Party organ, and he testified in 1954, "I was associated with the Communist movement." From 1937 to 1942, in the midst of the Great Purge and Hitler - Stalin pact, Oppenheimer was a member at Berkeley of what he called a "discussion group", which was later identified by fellow members, Haakon Chevalier and Gordon Griffiths, as a "closed" (secret) unit of the Communist Party for Berkeley faculty.

The Federal Bureau of Investigation (FBI) recorded that J. Robert Oppenheimer attended a meeting in the home of self - proclaimed Communist Haakon Chevalier, that the Communist Party's California state chairman William Schneiderman, and Isaac Folkoff, West Coast liaison between the Communist Party and NKVD, attended in Fall 1940, during the Hitler - Stalin pact. Shortly thereafter, the FBI added Oppenheimer to its Custodial Detention Index, for arrest in case of national emergency, and listed him as "Nationalistic Tendency: Communist". Debates over Oppenheimer's Party membership or lack thereof have turned on very fine points; almost all historians agree he had strong socialist sympathies during this time and interacted with Party members, though there is considerable dispute over whether he was officially a member of the Party. At his 1954 security clearance hearings, he denied being a member of the Communist Party, but identified himself as a fellow traveler, which he defined as someone who agrees with many of the goals of Communism, but without being willing to blindly follow orders from any Communist party apparatus.

Throughout the development of the atomic bomb, Oppenheimer was under investigation by both the FBI and the Manhattan Project's internal security arm for his past left wing associations. He was followed by Army security agents during a trip to California in June 1943 to visit his former girlfriend, Jean Tatlock, who was suffering from depression. Oppenheimer spent the night in her apartment. Jean committed suicide on January 4, 1944, which left Oppenheimer deeply grieved. In August 1943, he volunteered to Manhattan Project security agents that George Eltenton, whom he did not know, had solicited three men at Los Alamos for nuclear secrets on behalf of the Soviet Union. When pressed on the issue in later interviews, Oppenheimer admitted that the only person who had approached him was his friend Haakon Chevalier, a Berkeley professor of French literature, who had mentioned the matter privately at a dinner at Oppenheimer's house. Groves thought Oppenheimer was too important to the project to oust him over this suspicious behavior. On July 20, 1943, he wrote to the Manhattan Engineer District:

In accordance with my verbal directions of July 15, it is desired that clearance be issued to Julius Robert Oppenheimer without delay irrespective of the information which you have concerning Mr Oppenheimer. He is absolutely essential to the project.