Richard Rhodes — The making of the atomic bomb

Dwarkesh Patel opens by introducing Richard Rhodes, Pulitzer Prize-winning author of The Making of the Atomic Bomb and, most recently, Energy, A Human History. He starts with a current event: a new film about Oppenheimer on which Rhodes has been consulted. Rhodes is cautiously positive about the trailer. He praises the recreation of the Trinity test device, a sphere covered in cables, and the casting of an actor who shares Oppenheimer's build. Oppenheimer was about six feet tall and rail thin in structure as well as weight, and never weighed more than about 140 pounds.

Rhodes is realistic about what a film can do. So many aspects of the story exist that none could squeeze into one two-hour movie, and he thinks a multi-part series would be needed to tell much more of it. He notes that there have been some terrible depictions of Oppenheimer and of the bomb program, and hopes this one gets it right.

Patel then asks whether Oppenheimer, known as a communist sympathizer, might have leaked information to the Soviets. Rhodes sees no possibility that he shared information. His 1930s leftism was driven less by theory than by the practical work of helping Jews escape Nazi Germany, and Jean Tatlock, one of the loves of his life and a Communist Party member who was also working to extract Jews from Europe, encouraged him to attend meetings. Oppenheimer himself said he read Marx on a train between Berkeley and Washington and thought it was hooey, judging it by its logic and finding little there.

Rhodes explains the sympathy by Oppenheimer's background. He was born into considerable wealth, with impressionist paintings throughout the family's New York apartments, and his father had made a great deal of money in military uniform linings. Rhodes puts his income in the war years and before at around $100,000 a month. He lived mostly in his head until he reached Berkeley and found that prime students were living on cans of cat food because they could afford nothing else. Once he understood there was great suffering, he threw himself into it, as he did with anything that interested him.

Rhodes also offers a more specific explanation for Oppenheimer's lies to wartime security officers about who had approached him for espionage: it was primarily an effort to cover up his brother Frank's involvement. Frank and Frank's wife were party members. Rhodes does not think the brothers gave away secrets, but says Army security, had it understood Frank's role, would probably have shipped him to the Aleutians or another distant place. Oppenheimer wanted Frank nearby because he trusted him.

Asked whether the bomb might never have been built without World War II, Rhodes thinks it would have been essentially inevitable, though perhaps not as an accelerated program. The wartime push came from the belief that the Germans had already started. Fission was discovered in Berlin in 1938, nine months before the war in Europe began, and the West had no technological surveillance, only spies or moles, which it lacked. The Americans did not know where the Germans stood, but they knew the basic physics had been found there a year or more before anyone in the West began thinking about it. Without the war, that urgency would be missing.

The physics itself pointed toward a bomb. Once good physicists considered a slow neutron striking a uranium-235 nucleus, they saw a massive response. Rhodes cites Isidore Rabi's comparison to the moon striking the earth. The reaction puts out far more energy than it takes to start. The critical step was the chain reaction: a couple of neutrons emerge from one fission, hit other uranium atoms, and produce a geometric progression of 1, 2, 4, 8, 16, 32. For most of today's bombs, Rhodes says, 80 generations of fission lead to a city-busting explosion.

The Germans, fortunately for everyone else, never worked out how much material a bomb needs. They were still thinking in terms of a reactor. Rhodes recounts that when Niels Bohr escaped Denmark in 1943, he carried a rough sketch Werner Heisenberg had handed him while trying to learn what Bohr knew about American work. Shown to the Los Alamos physicists, it prompted Hans Bethe to ask whether the Germans were trying to throw a reactor down on them. Rhodes adds that a reactor can blow up, as Chernobyl showed, but that this is not a nuclear explosion on the scale of a bomb.

Rhodes contrasts this with the British calculation. Two emigre Jewish physicists in England, still technically enemy aliens and therefore excluded from top secret discussions, worked out how much pure uranium-235 a bomb would need. They arrived at one pound, which startled them. Rhodes says the real figure is about 125 pounds, but still not much material. They then estimated that a plant to separate the isotope would cost no more than a battleship, little for a country at war. Their report went up through their superiors at Manchester University.

The report stated that no physical structure came to their minds that could protect against such a bomb. Rhodes notes it dated from 1940, long before the Manhattan Project, and that its only suggested protection was a bomb of similar destructive force that could be threatened if the other side attacked. In his words, "That’s deterrence." He argues that whoever built the first bomb could theoretically prevent others from building any and dominate the world, and that Hitler doing so was horrifying. He says every country with the technological infrastructure began thinking about it once fission was announced: France, the Soviet Union, Great Britain, the United States, even Japan. His conclusion is that the bomb would have been developed, but maybe not so quickly.

Patel raises the German belief that critical mass was around 10 tons, a miscalculation. Rhodes corrects the point: that figure was for a reactor.

Patel mentions how other countries learned of the American effort. The Russians noticed that top physicists, chemists and metallurgists had stopped publishing and concluded something was going on. He then tells Rhodes, who says he was unaware, that the book has become a cult classic among people working on AI, who were the ones who first recommended it to him.

Patel gives their reasoning. Early scientific hints parallel each other: deep learning, which can teach itself any function, is like Szilárd noticing the nuclear chain reaction. AI scaling laws say that a bigger model gets much better at reasoning and predicting text, and by extrapolating the curve, two more orders of magnitude would reach something like human-level intelligence. They see many analogies in the next few years, and must feel they are at page 400 of where the Manhattan Project was. Rhodes responds only that they must later discuss unintended consequences, a subject he finds fascinating and a possible title for his next book.

Patel notes that many scientists, especially Jewish emigres, joined because they feared Hitler getting the bomb first. By 1943 and 1944 it was clear the Nazis were not close, yet he believes almost none quit. He asks why more did not conclude they were wrong and stop.

Rhodes says only one did, Joseph Rotblat, who packed up and left in May 1945 on hearing Germany was defeated. General Groves, the imperious Army Corps of Engineers general who ran the whole Manhattan Project, was upset and feared Rotblat would spill the beans, so he threatened arrest and jail. Rotblat was determined and, in Rhodes's words, was not interested in building bombs to aggrandize the national power of the United States, which Rhodes calls perfectly understandable. He then turns to why others stayed, through Victor Weisskopf, an Austrian theoretical physicist who escaped the Nazi takeover and ended up at Los Alamos. Weisskopf later wrote that they were in the midst of the darkest part of their science, working on a weapon of mass destruction, though before it had almost seemed like a spiritual quest.

Rhodes begins with how differently physics was regarded before and after the war. Louis Alvarez told him that after getting his physics PhD at Berkeley in 1937 he told people at cocktail parties his degree was in chemistry, because he did not want to have to explain what physics was. Rhodes notes there were only about 1,000 physicists in the world in 1900, many more by the mid-1930s, but the field was still arcane. Its practitioners did not feel they were doing anything mean, dirty or warlike; they were doing pure science.

Fission then arrived as public news. Rhodes stresses that people born after the war do not realize it was not a secret at first. It appeared first in a German chemistry journal, Die Naturwissenschaften, then in Nature and American journals, with headlines in the New York Times, the Los Angeles Times, the Chicago Tribune and papers around the world.

People had long thought about getting energy from the nucleus. A piece of radium glows in the dark and burns the hand without being plugged into anything, so the energy had to come from the nucleus. The nucleus is a very small part of the atom, 1/100,000th of its diameter, which someone in England likened to a fly in a cathedral. Chemical energy comes from the surrounding electron cloud, while the nucleus is the center of powerful forces. The problem was getting those forces out.

Up to 1938 the only method was bombarding nuclei with protons. Because protons and nuclei share positive charge, the protons were repelled and had to be accelerated in machines such as the cyclotron. At best this chipped off a small piece and moved an atom one step up or down the periodic table, like the transmutation of medieval alchemy, which did not yield much. Physicists therefore thought of the nucleus as a small, dense rock that had to be hammered hard.