J. Robert Oppenheimer (born Julius Robert Oppenheimer; April 22, 1904 – February 18, 1967) was an American scientist who studied how the universe works. He led the Los Alamos Laboratory during World War II as part of the Manhattan Project, which developed the first nuclear weapons. He is often called the "father of the atomic bomb" because he oversaw this work.

Oppenheimer was born in New York City. He earned a degree in chemistry from Harvard University in 1925 and a doctorate in physics from the University of Göttingen in Germany in 1927. He studied under Max Born, a well-known physicist. Later, he joined the physics department at the University of California, Berkeley, where he became a full professor in 1936.

Oppenheimer made important discoveries in physics, including the Born–Oppenheimer approximation, which helps explain how molecules behave. He also worked on theories related to particles called positrons, quantum electrodynamics, and quantum field theory. He contributed to the Oppenheimer–Phillips process, which explains how atoms fuse. With his students, he studied astrophysics, including how cosmic rays interact with the atmosphere and the formation of neutron stars and black holes.

In 1941, Oppenheimer learned about nuclear weapon design from Australian physicist Mark Oliphant. In 1942, he was asked to join the Manhattan Project. In 1943, he became the director of the Los Alamos Laboratory in New Mexico, where he led efforts to create the first nuclear weapons. His leadership helped the project succeed. On July 16, 1945, he watched the first test of an atomic bomb, called Trinity. In August 1945, the weapons were used in Japan during the bombings of Hiroshima and Nagasaki, the only times nuclear weapons have been used in war.

In 1947, Oppenheimer became director of the Institute for Advanced Study in Princeton, New Jersey, and chairman of the United States Atomic Energy Commission’s General Advisory Committee. He supported international control of nuclear weapons to prevent an arms race with the Soviet Union. He later opposed the development of the hydrogen bomb, partly because of ethical concerns. During the Second Red Scare, his views and past connections to the Communist Party USA led to a security hearing in 1954, where his security clearance was removed. He continued teaching and writing about physics, and in 1963, he received the Enrico Fermi Award for his work in theoretical physics. In 2022, the 1954 decision was overturned.

Early life

Julius Robert Oppenheimer was born on April 22, 1904, in New York City to Ella (née Friedman), a painter, and Julius Seligmann Oppenheimer, a successful textile importer. He had a younger brother named Frank, who also became a physicist. Oppenheimer’s father was born in Hanau, which was part of the Hesse-Nassau province of the Kingdom of Prussia. As a teenager, he moved to the United States in 1888 without money, higher education, or English. He worked for a textile company and later became wealthy. In 1912, the family moved to an apartment on Riverside Drive near West 88th Street in New York. Their home included art by Pablo Picasso, Édouard Vuillard, and Vincent van Gogh.

Oppenheimer was first educated at Alcuin Preparatory School. In 1911, he joined the Ethical Culture Society School, which was founded by Felix Adler to teach values based on the Ethical movement, with the motto "Deed before Creed." His father had been a member of the society for many years and served on its board of trustees. Oppenheimer was a talented student who studied English and French literature, as well as mineralogy. He completed third and fourth grades in one year and skipped half of eighth grade. He took private music lessons from a famous French flutist named Georges Barrère. During his final year of school, he became interested in chemistry. He graduated in 1921 but delayed his education for a year after contracting colitis during a family vacation in Czechoslovakia. He recovered in New Mexico, where he developed a love for horseback riding and the southwestern United States.

In 1922, at age 18, Oppenheimer entered Harvard College. He studied chemistry, and Harvard required courses in history, literature, and philosophy or mathematics. To make up for the time lost due to his illness, he took six courses each term instead of the usual four. He joined the undergraduate honor society Phi Beta Kappa and earned graduate standing in physics through independent study, allowing him to skip basic courses. He became interested in experimental physics after taking a thermodynamics course taught by Percy Bridgman. Oppenheimer graduated from Harvard in 1925 with a Bachelor of Arts degree, summa cum laude, after studying for only three years.

In 1924, Oppenheimer was accepted to Christ’s College at the University of Cambridge. He wrote to Ernest Rutherford, asking to work at the Cavendish Laboratory, but a letter of recommendation from Bridgman suggested Oppenheimer might be better suited for theoretical physics. Rutherford was unimpressed, but Oppenheimer went to Cambridge anyway. J. J. Thomson accepted him on the condition that he complete a basic laboratory course.

Oppenheimer struggled 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." He had a difficult relationship with his tutor, Patrick Blackett, a future Nobel laureate. A friend, Francis Fergusson, claimed Oppenheimer once left a poisoned apple on Blackett’s desk, but there is no record of this incident or any punishment. Oppenheimer saw a psychiatrist in London and, according to his grandson, the poison apple story is unproven. Oppenheimer was tall, thin, and smoked heavily. He often skipped meals during intense work periods. Friends said he could be self-destructive. Fergusson once tried to distract him from depression by talking about his girlfriend, and Oppenheimer reacted violently. Oppenheimer struggled with depression throughout his life and once told his brother, "I need physics more than friends."

In 1926, Oppenheimer left Cambridge to study at the University of Göttingen under Max Born, a leading physicist. Göttingen was a major center for theoretical physics. He became friends with future scientists like Werner Heisenberg, Pascual Jordan, Wolfgang Pauli, Paul Dirac, Enrico Fermi, and Edward Teller. He was very enthusiastic in discussions, sometimes dominating them. Maria Goeppert, a classmate, presented Born with a petition signed by others demanding Oppenheimer be quieter. Born placed it on his desk, and it worked without further action.

Oppenheimer earned his Doctor of Philosophy degree in March 1927 at age 23, supervised by Born. After his oral exam, James Franck, the professor who administered it, reportedly said, "I'm glad that's over. He was on the point of questioning me." Oppenheimer published over a dozen papers in Europe, including important contributions to quantum mechanics. He and Born co-authored a famous paper on the Born–Oppenheimer approximation, which simplifies calculations in molecular physics by separating nuclear motion from electronic motion. This work remains his most cited contribution.

Early career

In September 1927, Oppenheimer received a fellowship from the United States National Research Council to study at the California Institute of Technology (Caltech). At the same time, physicist Percy Bridgman wanted Oppenheimer to join Harvard University. To resolve this, a plan was made for Oppenheimer to split his fellowship: he studied at Harvard in 1927 and at Caltech in 1928. At Caltech, Oppenheimer became close friends with Linus Pauling. They planned to work together on the nature of the chemical bond, a topic Pauling was already studying. Oppenheimer would provide mathematical ideas, and Pauling would explain the results. Their partnership and friendship ended when Oppenheimer invited Pauling’s wife, Ava Helen Pauling, to join him on a trip to Mexico. Later, Oppenheimer invited Pauling to lead the Chemistry Division of the Manhattan Project, but Pauling refused because he believed in peace.

In the fall of 1928, Oppenheimer visited the University of Leiden in the Netherlands, where he gave lectures in Dutch, even though he had little experience with the language. He impressed people there and was nicknamed "Opje," which his students later changed to "Oppie." From Leiden, he traveled to the Swiss Federal Institute of Technology in Zurich to work with Wolfgang Pauli on quantum mechanics and the continuous spectrum. Oppenheimer respected Pauli and may have followed his way of thinking and problem-solving.

When Oppenheimer returned to the United States, he accepted a job as an associate professor at the University of California, Berkeley. Raymond Thayer Birge wanted Oppenheimer to join Berkeley so badly that he was willing to share him with Caltech. Before starting his job at Berkeley, Oppenheimer was diagnosed with a mild case of tuberculosis. He spent time at a ranch in New Mexico with his brother Frank. He called the ranch "Perro Caliente," which means "hot dog" in Spanish. He later said that physics and the desert were his two greatest loves. After recovering from tuberculosis, Oppenheimer returned to Berkeley, where he helped many young physicists and was admired for his intelligence and wide range of interests. Some people thought he was impressive and distant, while others believed he was overly confident and lacked self-assurance. Most of his students admired him and imitated his style, including how he walked, spoke, and even read texts in their original languages.

At Berkeley, Oppenheimer worked closely with Nobel Prize-winning physicist Ernest Lawrence and his team, helping them understand data from their machines at the Radiation Laboratory, which later became the Lawrence Berkeley National Laboratory. In 1936, Berkeley promoted Oppenheimer to full professor with an annual salary of $3,300 (about $77,000 in 2025). In exchange, Oppenheimer agreed to teach at Caltech for six weeks each year.

Oppenheimer tried many times to get Robert Serber a job at Berkeley but was stopped by Birge, who believed "one Jew in the department was enough."

Oppenheimer did important research in astrophysics, nuclear physics, spectroscopy, and quantum field theory, including its development into quantum electrodynamics. His most important work involved predicting the existence of neutron stars, which were not discovered until 1967.

His early research focused on the theory of the continuous spectrum. His first published paper, in 1926, discussed the quantum theory of molecular band spectra. He created a method to calculate transition probabilities in these spectra. He also calculated the photoelectric effect for hydrogen and X-rays, finding the absorption coefficient at the K-edge. His calculations matched observations of the Sun’s X-ray absorption but not helium. Later, it was discovered that the Sun is mostly made of hydrogen, confirming his calculations.

Oppenheimer made important contributions to the theory of cosmic ray showers and the problem of field electron emission. This work helped develop the concept of quantum tunneling. In 1931, he co-wrote a paper with his student Harvey Hall titled "Relativistic Theory of the Photoelectric Effect." Based on evidence, they corrected Paul Dirac’s claim that two energy levels of the hydrogen atom had the same energy. Later, his student Willis Lamb found this was due to the Lamb shift, for which Lamb won the Nobel Prize in Physics in 1955.

With Melba Phillips, his first graduate student, Oppenheimer studied artificial radioactivity caused by deuterons. When Ernest Lawrence and Edwin McMillan bombarded nuclei with deuterons, their results matched George Gamow’s predictions for lighter nuclei but not for heavier ones. In 1935, Oppenheimer and Phillips developed a theory, now called the Oppenheimer–Phillips process, to explain these results. This theory is still used today.

As early as 1930, Oppenheimer wrote a paper that predicted the existence of the positron. This came after Paul Dirac proposed that electrons could have positive and negative energy. Dirac’s work led to the Dirac equation, which combined quantum mechanics, special relativity, and electron spin to explain the Zeeman effect. Oppenheimer disagreed with Dirac’s idea that positively charged electrons were protons, arguing that protons were much heavier than electrons. In 1936, Carl David Anderson discovered the positron, for which he won the Nobel Prize in Physics.

In the late 1930s, Oppenheimer became interested in astrophysics, likely through his friendship with Richard Tolman. He wrote several papers on the topic. His first, "On the Stability of Stellar Neutron Cores" (1938), co-written with Serber, studied white dwarfs. Later, with student George Volkoff, he wrote "On Massive Neutron Cores," showing that there is a limit to the mass of neutron stars, now called the Tolman–Oppenheimer–Volkoff limit. In 1939, Oppenheimer and student Hartland Snyder published "On Continued Gravitational Contraction," predicting what would later be called black holes. These papers, along with the Born–Oppenheimer approximation, remain his most cited works and helped revive astrophysical research in the United States in the 1950s, especially through John A. Wheeler.

Oppenheimer’s papers were known for being difficult to understand, even within his field. He used elegant but complex mathematical methods to explain physical principles. However, he sometimes made mathematical errors, possibly due to rushing.

Private and political life

Oppenheimer's mother passed away in 1931. After this, he became closer to his father, who lived in New York but often visited California. When his father died in 1937, he left $392,602 (equivalent to $8.6 million in 2024) to be split between Oppenheimer and his brother Frank. Oppenheimer quickly wrote a will giving his share of the money to the University of California to help fund graduate scholarships.

During the 1920s, Oppenheimer did not pay much attention to world events. He said he did not read newspapers or magazines and only found out about the Wall Street crash of 1929 while walking with Ernest Lawrence six months after it happened. He claimed he did not vote in any election until the 1936 presidential election. Starting in 1934, he became more interested in politics and international issues. In 1934, he set aside 3% of his yearly salary—about $100 (equivalent to $2,400 in 2025)—for two years to support German scientists fleeing Nazi Germany. During the 1934 West Coast Waterfront Strike, he and some students, including Melba Phillips and Serber, attended a rally for longshoremen.

After the Spanish Civil War began in 1936, Oppenheimer helped raise money for the Spanish Republican cause. In 1939, he joined the American Committee for Democracy and Intellectual Freedom, which worked to stop the persecution of Jewish scientists in Nazi Germany. This group was later labeled a communist front by others.

Many of Oppenheimer's close friends were part of the Communist Party in the 1930s or 1940s, including his brother Frank, Frank's wife Jackie, Kitty, Jean Tatlock, his landlady Mary Ellen Washburn, and several of his students at Berkeley. Whether Oppenheimer was a member of the Communist Party has been debated. Some sources say he never officially joined, while others claim he was secretly a member in the late 1930s. From 1937 to 1942, he was part of a "discussion group" at Berkeley, which some members later said was a secret unit of the Communist Party for university faculty.

The Federal Bureau of Investigation (FBI) created a file on Oppenheimer in March 1941. It noted that he attended a meeting in December 1940 at the home of Haakon Chevalier, where the Communist Party's California state secretary, William Schneiderman, and treasurer, Isaac Folkoff, were also present. The FBI also recorded that Oppenheimer was on the executive committee of the American Civil Liberties Union, which it considered a communist front. Soon after, the FBI added Oppenheimer to its Custodial Detention Index, which listed people who might be arrested during a national emergency.

When Oppenheimer joined the Manhattan Project in 1942, he wrote on a security form that he had been "a member of just about every Communist Front organization on the West Coast." Years later, he said he did not remember writing this and claimed it was not true. He added that if he had written anything similar, it was "a half-jocular overstatement." He subscribed to People's World, a Communist Party newspaper, and in 1954, he said, "I was associated with the communist movement."

In 1953, Oppenheimer helped organize a conference on "Science and Freedom" for the Congress for Cultural Freedom, an anti-communist group. During his 1954 security hearing, he denied being a Communist Party member but called himself a "fellow traveler," meaning he supported some communist goals but did not follow orders from the party. A biographer later said Oppenheimer was a committed supporter of the Communist Party, spending time and money on its activities.

In 1936, Oppenheimer became involved with Jean Tatlock, the daughter of a Berkeley literature professor and a student at Stanford University. She wrote for the Western Worker, a Communist Party newspaper. Their relationship ended in 1939. That same year, he met Katherine ("Kitty") Puening, a former Communist Party member. Kitty had been married twice before marrying Oppenheimer in 1940. They had two children: Peter, born in 1941, and Katherine ("Toni"), born in 1944. During his marriage, Oppenheimer had an affair with Tatlock, which later became an issue during his security hearings because of her Communist Party ties.

Throughout the development of the atomic bomb, Oppenheimer was investigated by the FBI and the Manhattan Project's security team for his past left-wing connections. In 1943, he visited Tatlock in California, where she was struggling with depression. He stayed overnight at her apartment. Tatlock died by suicide in 1944, deeply affecting Oppenheimer.

At Los Alamos, Oppenheimer had an emotional relationship with Ruth Tolman, the wife of his friend Richard Tolman. The affair ended when Oppenheimer moved east to become director of the Institute for Advanced Study. After Richard Tolman's death in 1948, Oppenheimer and Ruth reconnected occasionally until her death in 1957. Their letters showed a close and affectionate relationship, with Oppenheimer calling her "My Love."

In the spring of 1929, Oppenheimer worked very hard on a difficult physics problem but hid his effort by appearing relaxed. He was calculating how light from stars interacts with their surfaces, a key part of understanding stars. He rarely talked about this work and seemed more interested in literature, especially Hindu texts and esoteric Western writers. A colleague once said Oppenheimer treated physics as a hobby and psychoanalysis as his main job.

Oppenheimer's varied interests sometimes distracted him from science. He liked challenges and found much of his scientific work easy, so he turned to mystical and complex subjects. After attending Harvard, he studied Hindu texts in English translations and learned Sanskrit at Berkeley in 1933. He eventually read works like the Bhagavad Gita and Meghaduta in the original Sanskrit and deeply considered their meanings. He later said the Gita was one of the most important books to him.

Manhattan Project

In September 1941, Australian physicist Mark Oliphant told Oppenheimer about the United Kingdom’s atomic bomb program and a report called the MAUD report during a visit to the University of California, Berkeley. On October 9, 1941, two months before the United States joined World War II, President Franklin D. Roosevelt approved an urgent plan to create an atomic bomb. On October 21, Ernest Lawrence introduced Oppenheimer to the Manhattan Project. Oppenheimer was later assigned by Arthur Compton to lead bomb-design research at the Metallurgical Laboratory. On May 18, 1942, Gregory Breit left the project due to security concerns and doubts about its success. Soon after, Arthur Compton asked Oppenheimer to take over Breit’s work on fast neutron calculations. Oppenheimer worked hard on this task and was given the title “Coordinator of Rapid Rupture.” “Rapid rupture” is a term that describes how fast neutrons spread in an atomic bomb. One of his first actions was to organize a summer school in Berkeley for scientists to study atomic bomb theory. European scientists and Oppenheimer’s students, including Serber, Emil Konopinski, Felix Bloch, Hans Bethe, and Edward Teller, worked together to calculate the steps needed to build the bomb.

In June 1942, the U.S. Army created the Manhattan Engineer District to manage its role in the atomic bomb project, shifting responsibility from the Office of Scientific Research and Development to the military. In September, Brigadier General Leslie R. Groves Jr. was chosen to lead the Manhattan Project. By October 12, 1942, Groves and Oppenheimer agreed that a secret, centralized research lab in a remote area was needed for security and teamwork.

Groves chose Oppenheimer to lead the project’s secret weapons lab, though the exact time of this decision is unclear. On October 15, 1942, after a meeting in Chicago, Groves invited Oppenheimer to join him, James C. Marshall, and Kenneth Nichols on a train ride to New York. After dinner, they discussed the project. When Oppenheimer left the train, none of the three men could think of another scientist who could lead the project. Soon after, Oppenheimer was named head of the Los Alamos Laboratory.

This decision surprised many because Oppenheimer had left-wing political views and no experience leading large projects. Groves worried that Oppenheimer’s lack of a Nobel Prize might make it hard for him to earn respect from scientists. However, Groves was impressed by Oppenheimer’s deep understanding of the project’s practical needs and his wide knowledge. As a military engineer, Groves knew this would be important for a project involving physics, chemistry, metallurgy, and engineering. Groves also noticed Oppenheimer’s strong drive, which he believed would help complete the project. Oppenheimer’s past associations were not ignored, but in July 1943, Groves ordered that Oppenheimer receive a security clearance immediately, regardless of concerns about his background. Rabi called Oppenheimer’s appointment “a real stroke of genius” by General Groves, who was not usually seen as a genius.

Oppenheimer chose New Mexico, near his ranch, for the lab’s location. On November 16, 1942, he, Groves, and others visited a possible site. Oppenheimer worried the area might feel too small and feared flooding. He then suggested a flat area near Santa Fe, New Mexico, where a private school, the Los Alamos Ranch School, was located. Engineers worried about the poor road and water supply but found the site otherwise ideal. The Los Alamos Laboratory was built on the school’s grounds, using some of its buildings and adding new ones quickly. At the lab, Oppenheimer gathered top scientists, whom he called the “luminaries.”

Los Alamos was originally planned as a military lab, and scientists were to be commissioned into the Army. Oppenheimer even ordered a lieutenant colonel’s uniform and took an Army physical test, which he failed. Army doctors said he was too thin, diagnosed his cough as tuberculosis, and noted his chronic back pain. The plan to commission scientists failed when Rabi and Robert Bacher objected. James B. Conant, Groves, and Oppenheimer created a compromise: the University of California would operate the lab under contract with the War Department. Oppenheimer greatly underestimated the project’s size: Los Alamos grew from a few hundred people in 1943 to over 6,000 by 1945.

Scientists were paid the same as they were before. However, Oppenheimer, who had worked at a state university, initially earned less than some of his colleagues. Groves decided to increase his salary to match others, without asking him.

At first, Oppenheimer struggled to organize large groups, but he quickly learned how to manage big projects after moving to Los Alamos. He was known for his deep understanding of the project’s science and for helping scientists and the military work together. Victor Weisskopf wrote:

At this time, scientists were worried that Germany’s nuclear program might be ahead of the Manhattan Project. In a letter dated May 25, 1943, Oppenheimer responded to Fermi’s idea of using radioactive materials to poison German food supplies. Oppenheimer asked Fermi if he could produce enough strontium without revealing the plan. Oppenheimer wrote, “I think we should not attempt a plan unless we can poison food sufficient to kill a half a million men.”

In 1943, scientists focused on creating a plutonium gun-type fission weapon called “Thin Man.” Early research used very pure plutonium-239 made in a cyclotron, but only small amounts could be produced. When Los Alamos received the first sample of plutonium from the X-10 Graphite Reactor in April 1944, a problem was found: reactor-made plutonium had more plutonium-240 than cyclotron-made plutonium, making it unsuitable for a gun-type weapon.

In July 1944, Oppenheimer stopped using the Thin Man design and switched to an implosion-type weapon. A smaller version of Thin Man became Little Boy. Using chemical explosives, a sub-critical sphere of fissile material could be compressed into a smaller, denser form. The material needed to move only short distances, allowing the critical mass to be assembled quickly. In August 1944, Oppenheimer reorganized Los Alamos to focus on implosion. He concentrated efforts on the gun-type device, but with a simpler design that only needed highly enriched uranium, in one group. This device became Little Boy in February 1945. After much research, the more complex implosion design, called the “Christy gadget,” was completed.

Postwar activities

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After the bombings of Hiroshima and Nagasaki, the public learned about the Manhattan Project. Oppenheimer, now famous as the "father of the atomic bomb," became a national leader for science, showing a new kind of power based on science and technology. He appeared on the covers of Life and Time magazines. Nuclear physics gained importance as countries recognized the power and influence atomic weapons could bring. Like many scientists of his time, Oppenheimer believed that only an international group, such as the newly formed United Nations, could prevent a nuclear arms race by creating rules to stop it.

In November 1945, Oppenheimer left Los Alamos to return to Caltech, but he soon realized he no longer wanted to teach. In 1947, he accepted a job offer from Lewis Strauss to become the director of the Institute for Advanced Study in Princeton, New Jersey. This meant moving back east and leaving Ruth Tolman, the wife of his friend Richard Tolman, with whom he had started a relationship after leaving Los Alamos. The job paid $20,000 a year, plus free housing in the director’s house, a 17th-century manor with a cook and groundskeeper, surrounded by 265 acres of woodlands. He collected European furniture and art, including works by Cézanne, Derain, Despiau, de Vlaminck, Picasso, Rembrandt, Renoir, Van Gogh, and Vuillard.

Oppenheimer brought together experts from many fields to answer important questions of the time. He supported the research of scientists like Freeman Dyson and the team of Chen Ning Yang and Tsung-Dao Lee, who later won a Nobel Prize for their discovery about the behavior of particles. He also invited scholars from the humanities, such as T. S. Eliot and George F. Kennan, to join the institute. Some members of the math department were unhappy, as they wanted the institute to focus only on science. Abraham Pais noted that Oppenheimer believed one of his challenges was failing to unite scientists from different areas.

At conferences in New York in 1947, 1948, and 1949, physicists returned to theoretical research after wartime work. Oppenheimer guided efforts to solve a major problem in quantum electrodynamics: confusing and seemingly nonsensical equations. Scientists like Julian Schwinger, Richard Feynman, and Shin'ichiro Tomonaga developed methods called renormalization. Freeman Dyson showed their methods gave similar results. Oppenheimer also helped address questions about mesons and their role in nuclear forces. His questions led to Robert Marshak’s idea that there are two types of mesons, pions and muons, which helped Cecil Frank Powell win a Nobel Prize for discovering pions.

Oppenheimer remained director of the institute until 1966, when he left due to poor health. As of 2023, he is still the longest-serving director of the institute.

As a member of a board advising President Truman, Oppenheimer influenced the 1946 Acheson–Lilienthal Report. This report proposed creating an international group to control all nuclear materials and use them for peaceful energy. Bernard Baruch translated this idea into the Baruch Plan for the United Nations, which included rules for inspecting the Soviet Union’s uranium resources. The Soviets rejected the plan, seeing it as an attempt to keep the United States’ nuclear advantage. Oppenheimer realized an arms race between the United States and the Soviet Union was unavoidable.

After the Atomic Energy Commission (AEC) was created in 1947 to manage nuclear research and weapons, Oppenheimer became chairman of its General Advisory Committee (GAC). From this role, he advised on nuclear issues, including funding, lab construction, and international policy, though his advice was not always followed. He pushed for arms control and support for scientific research, trying to avoid a nuclear arms race.

In August 1949, the Soviet Union tested its first atomic bomb earlier than expected, sparking debate in the U.S. about developing a more powerful hydrogen bomb, called "the Super." Oppenheimer had known about the possibility of such a weapon since the Manhattan Project but had limited research on it during the war. After the war, he argued against developing the Super, citing lack of need and the risk of massive civilian deaths.

In October 1949, Oppenheimer and the GAC recommended against building the Super. They worried about the ethical and practical challenges, as no working design for a hydrogen bomb existed at the time. They also believed the U.S. could retaliate with atomic weapons if the Soviet Union developed a hydrogen bomb. Oppenheimer and others were concerned about using nuclear reactors for materials needed for the Super instead of atomic bombs.

Most members of the AEC agreed with the GAC’s recommendation, but supporters of the hydrogen bomb lobbied the White House. On January 31, 1950, President Truman decided to proceed with the project. Oppenheimer and others, like James B. Conant, felt discouraged and considered leaving the GAC but stayed on.

In 1951, Edward Teller and Stanislaw Ulam developed the Teller–Ulam design for a hydrogen bomb, which seemed technically possible. Oppenheimer officially supported the weapon’s development but continued to question its testing or use. He later said:

Final years

Science has become very specialized, with experts spending many years studying different areas. These fields now use unique vocabulary, skills, and knowledge that are far removed from the shared understanding of even the most advanced societies. Scientists working at the edges of these fields are far from the practical origins of their work, which were once closely tied to what we now call art.

Starting in 1954, Oppenheimer lived on the island of Saint John in the U.S. Virgin Islands for several months each year. In 1957, he bought land on Gibney Beach and built a simple home on the shore. He spent time sailing with his daughter, Toni, and wife, Kitty.

After losing his security clearance, Oppenheimer gave a public lecture titled "Prospects in the Arts and Sciences" for Columbia University's radio show Man's Right to Knowledge. He shared his views on the role of science in the modern world. He had been chosen for the final lecture in the series two years before the security hearing, and the university insisted he remain part of the program despite the controversy.

In February 1955, the president of the University of Washington, Henry Schmitz, canceled an invitation for Oppenheimer to give lectures there. Students were upset, and 1,200 signed a protest petition. Schmitz was burned in effigy during protests. At the same time, the state of Washington banned the Communist Party and required government workers to take loyalty oaths. A colleague of Oppenheimer’s, Edwin Uehling, argued against Schmitz’s decision, and the university overturned it by a vote of 56 to 40. Oppenheimer briefly visited Seattle during a trip to Oregon but did not give lectures there. Instead, he gave two lectures on "The Constitution of Matter" at Oregon State University.

Oppenheimer grew worried about the dangers of scientific inventions to humanity. He worked with Albert Einstein, Bertrand Russell, Joseph Rotblat, and others to create the World Academy of Art and Science in 1960. After his public controversy, he did not sign major protests against nuclear weapons, such as the Russell–Einstein Manifesto of 1955, nor did he attend the first Pugwash Conferences on Science and World Affairs in 1957.

In speeches and writings, Oppenheimer emphasized the challenges of controlling knowledge in a world where political concerns often limited scientific freedom. He gave the Reith Lectures on the BBC in 1953, which were later published as Science and the Common Understanding.

In 1955, Oppenheimer published The Open Mind, a book of eight lectures he had given since 1946 about nuclear weapons and popular culture. He opposed the use of nuclear weapons for political pressure, stating that "the purposes of this country in foreign policy cannot be achieved through coercion."

In 1957, Harvard University’s philosophy and psychology departments invited Oppenheimer to give the William James Lectures. Some Harvard alumni, including Archibald Roosevelt, protested the decision. About 1,200 people attended his six lectures, "The Hope of Order," in Sanders Theatre. In 1962, he gave the Whidden Lectures at McMaster University, which were published in 1964 as The Flying Trapeze: Three Crises for Physicists.

Without political influence, Oppenheimer continued to lecture, write, and study physics. He traveled to Europe and Japan, speaking about the history of science, its role in society, and the nature of the universe. During a 1960 lecture tour in Japan, he was warmly received, though he did not visit Hiroshima or Nagasaki. In 1963, he spoke about the importance of studying science history at the dedication of the Niels Bohr Library and Archives.

Oppenheimer visited academic institutions until his later years. He remained a controversial figure among students, faculty, and communities. In 1955, he became the first visiting fellow at the Phillips Exeter Academy in New Hampshire.

In 1957, France honored Oppenheimer with the Legion of Honor. In 1962, he was elected a Foreign Member of the Royal Society in Britain.

In 1959, Senator John F. Kennedy helped stop Lewis Strauss, Oppenheimer’s main opponent during his security hearing, from becoming Secretary of Commerce. In 1962, as president, Kennedy invited Oppenheimer to a ceremony honoring 49 Nobel Prize winners. At the event, AEC chairman Glenn Seaborg asked Oppenheimer if he wanted another security hearing. Oppenheimer declined.

In 1963, the AEC’s General Advisory Committee chose Oppenheimer to receive the Enrico Fermi Award, created by Congress in 1954. President Kennedy had planned to present the award but was assassinated before doing so. His successor, President Lyndon Johnson, gave the award in December 1963, praising Oppenheimer’s work in physics and leadership during critical years. Oppenheimer thanked Johnson, saying it took "charity and courage" to make the award.

Kennedy’s wife, Jackie, attended the ceremony to tell Oppenheimer how much her husband had wanted him to receive the medal. Also present were Edward Teller, who had supported the award, and Henry D. Smyth, who had opposed Oppenheimer’s security risk designation in 1954.

Despite the award, some members of Congress still opposed Oppenheimer. Senator Bourke Hickenlooper protested his selection shortly after Kennedy’s death, and some Republican lawmakers boycotted the ceremony.

The award symbolized Oppenheimer’s rehabilitation, though he still lacked a security clearance and could not influence official policy. The award included a $50,000 tax-free stipend.

Death

In late 1965, Oppenheimer was found to have throat cancer, which may have been caused by smoking cigarettes for most of his life. After surgery that did not provide clear results, he received radiation treatment and chemotherapy in late 1966, but these treatments did not help. On February 18, 1967, he passed away at his home in Princeton at the age of 62. A memorial service was held one week later at Alexander Hall on the Princeton University campus. About 600 people attended, including scientists, political figures, and military leaders such as Bethe, Groves, Kennan, Lilienthal, Rabi, Smyth, and Wigner. His brother Frank and the rest of his family were present, along with historian Arthur M. Schlesinger Jr., novelist John O'Hara, and George Balanchine, the director of the New York City Ballet. Bethe, Kennan, and Smyth gave short speeches honoring Oppenheimer. His body was burned, and his ashes were placed in an urn. His wife, Kitty, later scattered the ashes into the ocean near the Saint John beach house.

In October 1972, Kitty died from an infection in her intestines that was made worse by a blood clot in her lungs. She was 62 years old. After her death, their son Peter inherited Oppenheimer’s ranch in New Mexico, and their daughter Katherine "Toni" Oppenheimer Silber inherited the beach property on Saint John. Toni’s two marriages ended in divorce. In 1969, she worked as a translator at the United Nations, but she could not get permission to hold the job because of past issues involving her father. She moved to the family beach house on Saint John and took her own life by hanging there in 1977. She left the property to the people of Saint John. The house was built too close to the ocean and was destroyed by a storm. As of 2007, the Virgin Islands Government operated a Community Center near the site.

Legacy

In 1954, Oppenheimer lost his political influence, which made many people think about the mistakes scientists might make when they believe they can control how their research is used. It also showed the difficult choices scientists face about morality in the nuclear age. The hearings that led to this decision were driven by politics and personal conflicts. Some people in the nuclear weapons community strongly feared the Soviet Union and believed that having the most powerful weapons was the best way to protect the United States. Others thought building the hydrogen bomb would not help Western security and that using such weapons on civilians would be a form of mass killing. They instead supported using smaller nuclear weapons, stronger regular military forces, and agreements to control weapons. The group that supported powerful weapons had more political influence, and Oppenheimer became their target.

Instead of always opposing the accusations of being a communist that happened in the late 1940s and early 1950s, Oppenheimer testified against former colleagues and students before and during his hearing. One example was when he gave harmful testimony about his former student Bernard Peters, which was shared with the press. Historians believe this was an attempt by Oppenheimer to gain favor with government officials and possibly to avoid attention on his own past ties to left-wing groups and those of his brother. However, this became a problem later when it became clear that Oppenheimer had doubted Peters’s loyalty and had made a mistake by recommending him for the Manhattan Project.

Popular stories about Oppenheimer often show his security issues as a conflict between right-wing military leaders (like Teller) and left-wing intellectuals (like Oppenheimer) about the morality of weapons of mass destruction. Many historians and biographers see Oppenheimer’s life as a tragedy. McGeorge Bundy, a national security advisor and academic who worked with Oppenheimer, wrote that Oppenheimer’s story was sad because of the mix of charm and arrogance, intelligence and blindness, awareness and insensitivity, and daring and fatalism in his character. These traits hurt him during the hearings.

The question of scientists’ responsibility to humanity inspired Bertolt Brecht’s play Life of Galileo (1955), influenced Friedrich Dürrenmatt’s The Physicists, and formed the basis of John Adams’s 2005 opera Doctor Atomic, which portrays Oppenheimer as a modern-day Faust. Heinar Kipphardt’s play In the Matter of J. Robert Oppenheimer was first shown on German television and later performed in Berlin and Munich in 1964. A 1967 Finnish film, Oppenheimerin tapaus, was based on the same play. Oppenheimer disagreed with some parts of the play and threatened to sue Kipphardt for inaccuracies. The play was later performed in New York in 1968, with Joseph Wiseman playing Oppenheimer. A New York Times critic called the play “angry” and “partisan,” saying it supported Oppenheimer but showed him as a “tragic fool and genius.” Oppenheimer was not happy with this portrayal.

Oppenheimer is the subject of many books, including American Prometheus (2005) by Kai Bird and Martin J. Sherwin, which won the 2006 Pulitzer Prize for Biography or Autobiography. A 1980 BBC TV series, Oppenheimer, starring Sam Waterston, won three BAFTA Television Awards. A 1980 documentary, The Day After Trinity, was nominated for an Academy Award and received a Peabody Award. His life is also explored in Tom Morton-Smith’s 2015 play Oppenheimer and the 1989 film Fat Man and Little Boy, where he was played by Dwight Schultz. In 1989, David Strathairn played Oppenheimer in the TV film Day One. In the 2023 film Oppenheimer, directed by Christopher Nolan and based on American Prometheus, Cillian Murphy portrays Oppenheimer. The film won the Academy Award for Best Picture, and Murphy won for Best Actor.

In 2004, a centennial conference about Oppenheimer’s legacy was held at the University of California, Berkeley, along with a digital exhibition on his life. The conference’s findings were published in 2005 as Reappraising Oppenheimer: Centennial Studies and Reflections. His personal papers are kept in the Library of Congress.

As a scientist, Oppenheimer was remembered by students and colleagues as a brilliant researcher and inspiring teacher who helped establish modern theoretical physics in the United States. Hans Bethe said Oppenheimer was responsible for raising American theoretical physics from a less prominent part of European science to a world leader. However, his quick changes in focus meant he never worked long enough on any one topic to win the Nobel Prize. His work on black hole theory might have earned him the prize if he had lived long enough to see it fully developed. An asteroid, 67085 Oppenheimer, was named in his honor on January 4, 2000, and a lunar crater, Oppenheimer, was named in 1970.

As a military and public policy advisor, Oppenheimer helped shift science and the military toward technocracy, which is the use of experts in decision-making. During World War II, scientists became deeply involved in military research for the first time because of the threat of fascism. They worked on important tools like radar, the proximity fuze, and operations research. Oppenheimer, as a smart and cultured physicist who became a skilled military organizer, showed that scientists could have practical roles, not just theoretical ones.

Two days before the Trinity test, Oppenheimer shared his hopes and fears by quoting a line from Bhartṛhari’s Śatakatraya.

Publications

• Oppenheimer, J. Robert (1954). Science and the Common Understanding. New York: Simon and Schuster. OCLC 34304713.
• Oppenheimer, J. Robert (1955). The Open Mind. New York: Simon and Schuster. OCLC 297109.
• Oppenheimer, J. Robert (1964). The Flying Trapeze: Three Crises for Physicists. London: Oxford University Press. OCLC 592102.
• Oppenheimer, J. Robert and Rabi, I.I (1969). Oppenheimer. New York: Scribner. OCLC 2729. (Published after his death).
• Oppenheimer, J. Robert, Smith, Alice Kimball, and Weiner, Charles (1980). Robert Oppenheimer, Letters and Recollections. Cambridge, Massachusetts: Harvard University Press. ISBN 978-0-674-77605-0. OCLC 5946652. (Published after his death).
• Oppenheimer, J. Robert, Metropolis, N., Rota, Gian-Carlo, and Sharp, D. H. (1984). Uncommon Sense. Cambridge, Massachusetts: Birkhäuser Boston. ISBN 978-0-8176-3165-9. OCLC 10458715. (Published after his death).
• Oppenheimer, J. Robert (1989). Atom and Void: Essays on Science and Community. Princeton, New Jersey: Princeton University Press. ISBN 978-0-691-08547-0. OCLC 19981106. (Published after his death).