J. Robert Oppenheimer is arguably the most influential physicist to have ever lived, despite never winning a Nobel Prize. His leadership in developing the atomic bomb changed the course of history, and every war and peace settlement since World War II has been affected by his work. He famously said, “Now I am become death, the destroyer of worlds” when the first atomic bomb was tested. This video is about the development of the atomic bomb, Oppenheimer’s life, and the fear of the bomb setting fire to the atmosphere and ending all life on Earth.
At 21, Oppenheimer’s frustration with experimental work and his fascination with quantum mechanics led him to attempt to poison his physics tutor, Patrick Blackett, with an apple laced with toxic chemicals. Fortunately, Blackett did not eat the apple, but the attempted poisoning was known to the Cambridge University authorities. Due to his family’s wealth, Oppenheimer was not expelled but was instead required to attend periodic counseling sessions in London.
In the summer of 1926, Oppenheimer traveled to the University of Göttingen, where he was mentored by Max Born and surrounded by other brilliant physicists. His mental health improved, and he found a community of people who shared his passion for physics. He graduated with a PhD in physics two years later. Born later wrote of Oppenheimer, “He was a man of great talent and he was conscious of his superiority in a way which was embarrassing and led to trouble.” All in all, in the two years he was at Göttingen, Oppenheimer published more than a dozen papers, many of which expanded upon the work of Werner Heisenberg, who was three years older than him. In 1927, the two eventually met and got along well, though they would later become rivals 15 years later, with Oppenheimer working for the USA and Heisenberg for Nazi Germany, both attempting to build the first nuclear bomb.
It was believed that getting significant amounts of energy out of radioactive atoms was impossible, since radioactivity was a passive process, with unstable atoms decaying at random, unpredictable times. Ernest Rutherford, Oppenheimer’s old boss from Cambridge, wrote that “anyone who expects a source of power from the transformations of these atoms is talking moonshine.” Albert Einstein also said that “there is not the slightest indication that nuclear energy will ever be obtainable.”
However, in 1932, John Cockcroft and Ernest Walton used 250,000 volts to accelerate protons into lithium nuclei, breaking them apart, although only about one in a billion protons actually hit and split a lithium nucleus. The same year, the neutron was discovered, a subatomic particle that has no electric charge and so would not be repelled from a nucleus. In 1933, Leo Szilard thought of using neutrons to split nuclei, and in 1939, Otto Hahn and Fritz Strassmann successfully split an atom of uranium by bombarding it with neutrons.
When a single atom of uranium-235 splits apart, it loses a little bit of mass, which is released as energy. With a trillion, trillion atoms in a one kilogram lump of uranium, the energy quickly adds up. In August of 1939, almost everyone was convinced that nuclear bombs were impossible, but Albert Einstein, who had only six years prior believed this, signed a letter addressed to President Franklin Roosevelt, written by Leo Szilard, warning of the possibility of nuclear weapons. The letter also pointed out that Germany had access to uranium from the mines in Czechoslovakia, which had recently been taken over by the Nazis. Roosevelt began an informal uranium committee to discuss this topic, but nothing happened for two years. In 1941, Roosevelt upgraded the informal uranium committee to the S-1 committee, which reported directly to the White House, with the explicit goal of developing an atomic bomb. In May of 1942, J. Robert Oppenheimer was hired onto the committee to be the coordinator of rapid rupture. Oppenheimer had recently completed his PhD and had become a physics professor at UC Berkeley and Caltech, where he had shown remarkable brilliance. In the 15 years after finishing his PhD, Oppenheimer made important contributions to nuclear physics, quantum field theory, and astrophysics, and had a number of Nobel Prize winning ideas. Even though he was nominated three times, he never won the Nobel Prize. On the 18th of September, 1942, General Leslie Groves was put in charge of the Manhattan Project. He ordered 1200 tons of uranium ore and the Oak Ridge site where the ore would be refined. He then chose Oppenheimer to be the science director of the soon to be established Los Alamos laboratory, despite the military’s concerns about Oppenheimer’s lack of a Nobel Prize, administrative experience, and his links to the Communist Party. However, Groves was impressed by Oppenheimer’s ambition and ability to understand problems in many fields, and thought that Oppenheimer was a “real genius”. Despite their ideological differences, Groves was convinced that Oppenheimer would be the person to build the atomic bomb before the Nazis. It was a real stroke of genius on the part of General Groves to hire Oppenheimer for the Manhattan Project, as he was not generally considered to be a genius. Oppenheimer had proposed Los Alamos, New Mexico as the location for the project due to his love for the region since his twenties. It was estimated that the project would need only 6 scientists and a few engineers and technicians, but in the end, 764 scientists worked on the project, with 302 of them based in Los Alamos. In total, the project involved over 600,000 people. On December 2nd, 1942, the first artificial nuclear reactor, Pile-1, was created at the University of Chicago. It was made up of 45 tons of uranium and uranium oxide, 330 tons of graphite blocks, and generated about half a watt of power. This showed that it was possible to make a nuclear bomb, the only difference being the number of neutrons that hit the next atom, causing it to split and release more neutrons. This number is known as the multiplication factor, K. In order to make a bomb, the scientists needed to get enough fissile material close together to create a runaway chain reaction, which is known as the critical mass. The simplest way to make a bomb was to use uranium-235, which required 52 kilograms to form a sphere with a diameter of 17 centimeters, or plutonium-239, which only required 10 kilograms to form a sphere 10 centimeters wide. Initially, the scientists worked on a bomb with a gun type design, which used conventional explosives to rapidly fire one slab of uranium-235 towards the other. However, this was not very efficient, as only a small percentage of the uranium underwent fission. To solve this, the scientists used oil from sperm whales to lubricate the barrel, as it was the only oil that worked. Additionally, the uranium had to be enriched, as only 0.7% of naturally occurring uranium is U235. The other option was to use plutonium-239, which had a much lower critical mass. He thought that the explosion might convert the nitrogen into a new form of matter, which would spread rapidly through the atmosphere, killing all living things."
In early 1941, a new element was discovered (or rather synthesized) when a neutron is absorbed by a nucleus of uranium-238, turning it into uranium-239. U239 is unstable, so it decays into Neptunium, which then becomes plutonium-239. This element is important for one main reason: it is an excellent fuel for a nuclear bomb, and has a critical mass of only about 10 kilograms. It is also cheaper to make than to separate uranium-235, and reacts too quickly to be used in a gun type device.
In order to create a bomb using plutonium, scientists had to find a way to lower the critical mass. This could be done by surrounding the sphere with a material that reflects neutrons, decreasing the amount of nuclear fuel needed to start a chain reaction. Additionally, a neutron source could be used to kick-start the chain reaction. For the first implosion bomb, scientists created a device called the urchin, which was a tiny pellet weighing just seven grams, and it would sit at the heart of the bomb. It was made of beryllium and polonium separated by a layer of nickel and gold. The idea was that when the explosives detonated, the shockwave would mix the beryllium and polonium together, and then the alpha particles from polonium would cause the beryllium to release a flood of neutrons, which would set off the nuclear chain reaction.
The test for this bomb was scheduled for the 16th of July 1945, one day before the start of the Potsdam conference, where Truman, Churchill, and Stalin would come together to plan the post-war peace. Oppenheimer was nervous, as there were so many things that could go wrong. The last test firing of the explosives without the actual plutonium core was a failure. He calmed himself by reciting a stanza from the Bhagavad Gita.
The scientists were also worried that the bomb could work too well. Around 1942, Oppenheimer discussed with Arthur Compton the possibility that a nuclear test could end the world. The worry was that the nuclear bomb would create temperatures so hot that fusion would occur, releasing energy and causing more fusion until the entirety of the Earth’s atmosphere would become a giant fusion bomb. Despite the initial suggestion that an atomic explosion in the atmosphere might be used to set off a fusion reaction, most scientists quickly realized how unlikely this scenario was and continued on with the project without taking the idea too seriously. However, the idea of a fission weapon jumpstarting a nuclear reaction would become important after the war. On August 6th, 1945, the United States dropped the first nuclear bomb, Little Boy, on Hiroshima, and three days later, an implosion-type bomb was dropped on Nagasaki. The blast from the explosion was equivalent to 15,000 tons of TNT, killing nearly 70,000 people, with another 70,000 dying in the months following from burns and radiation poisoning.
After the war, Oppenheimer became a national hero and was appointed director of the Institute of Advanced Study at Princeton and chairman of the General Advisory Committee, where he advocated for arms control. However, when the United States decided to develop the hydrogen bomb, Oppenheimer was against it on ethical grounds and the fear of starting an arms race. Despite his opposition, the first hydrogen bomb was tested in the Marshall Islands in 1952. The Soviet Union then tested the Tsar Bomba in 1961, the most powerful explosion ever detonated, which was around 2000 times more powerful than the Trinity test. This arms race was exactly what Oppenheimer had feared. In December, 1953, J. Robert Oppenheimer had his security clearance suspended due to his calls to avert a nuclear arms race. He had been surveilled while working for the Manhattan Project, and the wiretaps were often illegal and warrantless. Oppenheimer was questioned about his ties to the Communist Party, and was essentially accused of treason and espionage. His face was once again on the cover of Time magazine, and his security hearings were international news.
In 1964, German playwright Heinar Kipphardt wrote a play about Oppenheimer’s life, which Oppenheimer despised so much that he threatened to sue. He especially disliked the final scene where the character of Oppenheimer realizes the evil of his work and says, “We have been doing the work of the devil.” Oppenheimer believed it was more complicated than that.
In 1965, Oppenheimer was asked about the proposal of talks with the Soviet Union to halt the proliferation of nuclear weapons, and he responded that it should have been done the day after Trinity. Later that same year, he was diagnosed with throat cancer and passed away in 1967 at the age of 62.
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