J. Robert Oppenheimer was an American theoretical physicist and professor of physics at the University of California, Berkeley. He is best known for his role as the scientific director of the Los Alamos Laboratory and the Manhattan Project – the effort during World War Two to develop the world’s first nuclear weapons, and is often referred to as the ‘father of the atomic bomb’.
Oppenheimer was also a vocal critic of the use of nuclear weapons and later became an advocate for nuclear disarmament. He was later stripped of his security clearance in the 1950s due to this opposition and his left-leaning political views. Despite this, he remained a respected figure in the scientific community and received numerous awards for his contributions to science.
Here we explore more about his career, role in the Manhattan Project and later advocacy for nuclear disarmament.
Early life
J. (Julius) Robert Oppenheimer was born on 22 April 1904 in New York. After joining Harvard in 1922 intending to become a chemist, he soon switched to physics. During his time there, he also excelled in Latin and Greek, published poetry and also studied Eastern philosophy.
After graduating, he spent time at Cambridge University conducting research at their Cavendish Laboratory, which gave him the opportunity to collaborate with the British scientific community and its efforts to advance atomic research.
Listen NowAfter this, Oppenheimer studied at the University of Göttingen in 1926, obtaining his PhD aged just 22. While there, Oppenheimer published many important contributions to the newly developed quantum theory – most notably a famous paper on the ‘Born-Oppenheimer approximation’, which separates nuclear motion from electronic motion in the mathematical treatment of molecules.
In 1927, he returned to Harvard as a National Research Council Fellow studying mathematical physics, and a year later, studied at the California Institute of Technology. Whilst there, he also accepted a job at the University of California, Berkeley as an assistant professor. For the next 13 years, he maintained his joint roles at the two universities, commuting between them – along with many of his associates and students who followed him.
Oppenheimer’s intelligence in this field was outstanding, and he became credited as a founding father of the American school of theoretical physics.
As well as researching a breadth of topics including astrophysics, nuclear physics, spectroscopy and quantum field theory, he made key contributions in the theory of cosmic ray showers and descriptions of quantum tunneling. He was also the first to write papers (in the 1930’s) suggesting the existence of black holes.
Albert Einstein (left) and Oppenheimer (right)
Image Credit: Public Domain, via Wikimedia Commons
The Manhattan Project
Hitler’s rise in Germany had stirred Oppenheimer’s interest in politics. In 1936 he had sided with the republic during the Spanish Civil War and became acquainted with Communist students, yet he later withdrew his associations with the Communist Party due to the suffering inflicted by Stalin on Russian scientists.
After Poland’s invasion by Nazi Germany in 1939, Albert Einstein and other prominent scientists had warned the US government of the danger threatening all of humanity if the Nazis should be the first to make a nuclear bomb, urging President Roosevelt to fund research into the development of a nuclear weapon. Subsequently Roosevelt established the Office of Scientific Research and Development to oversee the project, and Oppenheimer became heavily involved in efforts to develop an atomic bomb.
Oppenheimer began to seek a process for separating uranium-235 from natural uranium and in determining the critical mass of the material required to make such a bomb. Newly married (1940) and a year in to fatherhood (1941), Oppenheimer was appointed the scientific director of the Manhattan Project by General Leslie Groves in June 1942, in order to seek a way to harness nuclear energy for military purposes.
Three ‘secret cities’ were chosen to be part of the Manhattan Project – Oak Ridge in East Tennessee, the plateau of Los Alamos near Santa Fe in New Mexico and Hanford/Richland in Washington state.
Oppenheimer oversaw the construction and administration of the laboratories at Los Alamos, before then bringing in the best minds in physics to work on how to create an atomic bomb. Ultimately, Oppenheimer went on to manage more than 3,000 people whilst tackling the theoretical and mechanical problems that arose during the bomb’s creation (whilst also becoming a father again in 1944).
The first nuclear explosion occurred at Alamagordo air base, New Mexico on 16 July 1945, which Oppenheimer had codenamed ‘Trinity’. The blast was the equivalent to 20,000 tons of TNT and created a fireball that reached temperatures of several million degrees.
Hiroshima and Nagasaki
Less than one month after its initial successful test, on 6 August 1945, an American B-29 bomber named Enola Gay dropped the world’s first atomic bomb on the city of Hiroshima in Japan, killing an estimated 80,000 people. Tens of thousands more would later die of radiation exposure.
Just 3 days later on 9 August 1945, another atomic bomb was dropped on Nagasaki in Japan, instantly killing a further 40,000 people and many more over time. The attacks are widely believed to have played a decisive role in convincing Japan to surrender and bringing about an end to World War Two.
Oppenheimer’s work had therefore achieved what it set out to do.
Mushroom cloud after Fat Man exploded over Nagasaki on 9 August 1945
Image Credit: Public Domain, via Wikimedia Commons; History Hit
Postwar opposition to nuclear weapons
After the war ended, in 1947 Oppenheimer was appointed Chairman of the General Advisory Committee to the Atomic Energy Commission (AEC), a role he served in until 1952. Oppenheimer used this position to lobby for international control of nuclear power to avert nuclear proliferation and a nuclear arms race with the Soviet Union. In October 1949, Oppenheimer and the AEC also opposed the development of the hydrogen bomb during a government debate on the question and took opposing stances on defence-related issues.
By 1953, America was in the midst of McCarthyism and strong anticommunist feeling. During this ‘Second Red Scare’, Oppenheimer was notified of a military security report unfavourable to him, and was accused of having communist sympathies and delaying the naming of Soviet agents. These accusations combined with his opposition to the hydrogen bomb led to a government hearing that resulted in his military security clearance being taken away, ending his time at the AEC and his position as adviser to the highest echelons of the US government.
The Federation of American Scientists and nearly the entire scientific community were shocked by the AEC’s decision, and protested his trial. The case aroused widespread controversy in the world of science and Oppenheimer was made a symbol of a scientist who, while working in government and trying to resolve the moral problems that arise from scientific discovery, becomes the victim of a witch hunt. By 1963, President Johnson tried to make up for the injustice, honouring Oppenheimer with the prestigious Enrico Fermi Award by the AEC.
Between 1947-1966, Oppenheimer had also served as the Director of the Institute for Advanced Study at Princeton, discussing and conducting research on quantum and relativistic physics, as well as working out ideas on the relationship between science and society. A year after his retirement, he died of throat cancer on 18 February 1967.
On 16 December 2022, the US Secretary of Energy Jennifer Granholm finally cleared Oppenheimer of the allegations that had led to the revocation of his security clearance, citing the AEC’s ‘flawed investigation’ of his background.
