J. Robert Oppenheimer

Atomic Energy Commission  -   · The government committee created after World War II to replace the Manhattan Project. The Atomic Energy Commission was charged with overseeing all atomic research and development in the United States. Oppenheimer was chairman of its General Advisory Committee for several years. The Commission later turned against him, voting to strip him of his security clearance.

Atom  -   · The building block of all matter. An atom is the smallest piece of an element that still retains all the characters of that element, and all matter is made up of atoms. An atom is made up of three main types of particles: protons (positively charged particles), electrons (negatively charged particles), and neutrons (neutrally charged particles). According to the atomic model created in the early twentieth century, the protons and neutrons are located in the center, or nucleus, of the atom, while the electrons orbit around the nucleus on a series of energy levels. The concept of an atom had existed for thousands of years, but it wasn't until the twentieth century that physicists were able to prove its existence and gain some understanding of its internal structure.

Cold War -   · The name given to the state of continuing hostility between the United States and the Soviet Union after World War II. For four decades, American foreign policy was dictated by the necessities of the Cold War, as the United States strategized about how best to defeat the Soviet Union without antagonizing it into full-fledged war. The Cold War came to a symbolic end in 1989, with the tearing down of the Berlin Wall–the divider between democratic West Germany and communist East Germany. The non-war came to a definitive end two years later when, in 1991, the Soviet Union dissolved into independent republics.

Communism  -   · The philosophy created by Karl Marx to describe a society in which all property is owned by the community rather than individuals. After the communists came to power in the Russian Revolution of 1917, communism became synonymous with Russia and the Soviet Union. In the period before World War II, communism was considered a socially acceptable liberal philosophy. But with the advent of the Cold War, communism was determined to be an evil force–and all Americans with any connections to communism were feared to be enemy agents of the Soviet Union.

Fat Man -   · One of the two bombs designed at Los Alamos. It used a sphere of plutonium as its radioactive core. The bomb mechanism used what was called the "implosion method": The plutonium was surrounded by explosives, and when the explosives fired, they set off a shock wave that compressed the plutonium into a critical mass, setting off a nuclear explosion. This is the type of bomb that was used at both Trinity and Nagasaki.

Hiroshima -   · The Japanese city that was bombed by the United States on August 6, 1945. One hundred thousand of its 300,000 residents were killed instantly, and another 100,000 would die over the next five years. Three days later, the United States dropped a second bomb over the Japanese city of Nagasaki. Five days after that, Japan surrendered.

Hydrogen Bomb  -   · Also known as the "Super," this bomb was developed after World War II and was one thousand times as powerful as the atomic bomb. It is called a hydrogen bomb because its energy comes from the fusion, or combining, of hydrogen atoms. Fusion is the same process that powers the sun.

Manhattan Project  -   · The code-name given to the atomic bomb development program during World War II. The Manhattan Project consisted of several laboratories in secret locations across the country, including the University of Chicago, Tennessee, and Los Alamos, New Mexico. Over the course of three years, the government spent over two billion dollars in pursuit of the world's first atomic bomb. Although almost every top physicist in the country was involved, the government managed to keep the program a secret from the rest of the world.

Little Boy -   ·  One of the two bombs designed at Los Alamos. It utilized two masses of Uranium 235 as its radioactive material. The bomb mechanism used what was called the "gun-assembly method": One subcritical mass of uranium was fired at another, and they combined to make a critical mass, setting off a nuclear explosion. This is the type of bomb that was dropped on Hiroshima.

Los Alamos -   · The secret lab where some of the best physicists in the world assembled to design and construct the world's first atomic bomb. The scientists lived on the isolated New Mexico compound for three years–and residents of neighboring towns never found out what went on there. Oppenheimer was the director of the lab. Thanks to his position there, the public later saw him as the man responsible for creating the bomb.

McCarthyism -   · The term describing the anti-communist hysteria that swept through Washington in the 1950s, spearheaded by the conservative senator Joseph McCarthy. McCarthy and his allies devoted themselves to rooting out communist spies from every walk of American life–their zeal often leading them to destroy people's lives with little or no evidence to back up their claims.

Nuclear Fission -   · The process by which the nucleus of an atom splits in half, releasing an enormous amount of energy. When a nucleus fissions, it also releases neutrons, which can then go on to impact and split other nuclei, creating a chain reaction. The fission of a nucleus is the process at the core of an atomic bomb. A critical mass of radioactive material is the amount required to start a chain reaction.

Quantum Physics  -   · The new system of physics created at the beginning of the twentieth century to explain the bizarre, counterintuitive behavior of light and subatomic particles. Physicists realized that activity on this small scale could not be described using physical models from the larger world, and they were forced to cobble together a new understanding of the way the basic particles of matter interact. The creation of quantum physics constituted an exciting revolution in the way people studied and applied physics, a revolution that was totally dominated by European figures such as Niels Bohr, Wolfgang Pauli, and Werner Heisenberg. The American physics community took a back seat, struggling to keep up with the newest discoveries of the European colleagues.

Trinity -   · The desolate site of the world's first atomic explosion. In a single moment, it represented the triumph of the past three years and the nuclear horrors that were to follow.

University of Göttingen -   ·  The center of the quantum physics revolution. Oppenheimer did his graduate work there in physics, studying under some of the most famous names in physics.

Haakon Chevalier  -  A professor of French Literature at University of California, Berkeley, with close ties to the Communist Party. Oppenheimer and Chevalier were close friends during Oppenheimer's time at Berkeley, a relationship that would cause great trouble for him later in life. During World War II, Chevalier tried to convince Oppenheimer to pass information about the bomb on to the Soviet Union. Oppenheimer refused, but he never fully reported the incident to the military. This gave his enemies ammunition later on and made Oppenheimer look like he was hiding things from the government.

Leslie Groves  - The brigadier general who had control over the entire Manhattan Project. Groves recruited Oppenheimer to direct the Los Alamos laboratory, even though Oppenheimer had almost no administrative experience. Although all the scientists at Los Alamos resented the military's harsh security measures, Oppenheimer and Groves maintained a solid respect for each other. Groves later testified in Oppenheimer's defense during the hearings about his security clearance.

Ernest Lawrence -  A fellow professor in the University of California, Berkeley physics lab who worked with Oppenheimer to improve the department. Lawrence is the one who first involved Oppenheimer in the Manhattan Project, by inviting him to an early meeting about the new top-secret project.

Ella Oppenheimer  -  Oppenheimer's mother. She was a stay-at-home mother and a painter. Her family had been in New York for generations.

Frank Oppenheimer  -  Oppenheimer's brother. Frank was also a physicist, although he was never as well known or as successful as his famous older brother. Frank was also a member of the Communist Party in the late 1930s, a fact that would later help make Robert Oppenheimer seem less reliable.

Julius Oppenheimer  -  Oppenheimer's father. A German immigrant who worked in his family's cloth importation business.

Kitty Oppenheimer  -  Oppenheimer's wife. They were married in 1940, after Kitty divorced her third husband. Oppenheimer's marriage to Kitty drew him even farther away from the radical politics he had been involved with before meeting her.

Jean Tatlock - A radical psychology graduate student at University of California, Berkeley. Oppenheimer fell in love with her in the late 1930s and became heavily involved with her radical friends and organizations. The love affair ended by 1940, as did Oppenheimer's interest in radical causes.

Edward Teller -  A European physicist who immigrated to the United States to escape European fascism. He worked under Oppenheimer at Los Alamos and stayed on after the war to develop a hydrogen bomb, or "Super." He turned against Oppenheimer when Oppenheimer refused to support the development of the Super. Later Teller testified against Oppenheimer in the hearings about his security clearance.