How Accurate is Christopher Nolan’s ‘Oppenheimer’?

The critics rave—and I don’t disagree—that the box-office blockbuster Oppenheimer is the greatest film, or at least biopic, since Lawrence of Arabia. The cinematography is grand, the acting is fine, the pace is excellent, and the story has real importance. If, considered as a meal, most movies today are a bag of skittles, Oppenheimer is a thick juicy corn-fed Iowa steak. So, if all you need to know from a film’s review is whether you should go see it, the answer, in Oppenheimer’s case, is unquestionably yes.

But is Oppenheimer accurate? That’s the question that Claire Lehmann asked me to answer for the readers of Quillette.

I have some qualifications for such a role. I hold a doctorate in Nuclear engineering, and my Ph.D advisor, Fred Ribe, was himself the student of Sam Allison, who was a member of Enrico Fermi’s Chicago pile team. Allison was thus my academic grandfather. It was he, a professor at the University of Chicago, who recommended that Fermi’s Chicago Pile-1, the world’s first critical nuclear reactor, be built under the stands of University’s Stagg Field football stadium. I share his dislike of spectator sports. During the first test of Fermi’s atomic pile in November 1942, Allison stood by with a bucket of neutron-absorbing cadmium solution to throw on the reactor to shut it down if it got out of control. In July 1945, he was the man who threw the switch that ignited the first atomic bomb test at Trinity.

Ribe was too junior to take part in the Manhattan Project, but by the 1950s he had earned his doctorate and had made his way to Los Alamos, where he was one of many scientists who signed the petition protesting the persecution of Oppenheimer. By the 1970s he had risen to lead the controlled thermonuclear fusion program at the lab, after which he semi-retired to a full professorship at the University of Washington. He was thus able to get me a Los Alamos internship while I was in graduate school at the University of Washington in the mid-1980s. In addition to learning a lot and perhaps contributing something to the development of the spherical tokamak (which is now being pursued on an entrepreneurial basis by the British Tokamak Energy company), that allowed me to experience the magic of Los Alamos for myself.

So, is Oppenheimer accurate? For the most part it is, although some important developments have been shifted around to enhance the narrative's structure. For example, when the news that nuclear fission may have been accomplished by Otto Hahn in Berlin reached America in January 1939, his experiment was immediately reproduced by Fermi’s Columbia university graduate student Herbert Anderson and then by the US Naval Observatory’s Richard Roberts, not by Lawrence at Berkeley as shown in the film. One critical point that the film does cover correctly, albeit only dwelling on it briefly, is the mathematical error that German physicist Werner Heisenberg made that prevented Nazi Germany from developing its own atomic bomb. This had to do with the question of choosing the right moderator to enable the operation of a critical nuclear reactor using natural (unenriched) uranium as fuel.

Fermi discovered that the way we initially thought nuclear fission worked was wrong. Instead of high-energy neutrons hitting nuclei like cannonballs, a better way to picture it is that neutrons move around and get pulled into nuclei by nuclear forces. As a result, this causes the nuclei to become unstable and split. Surprisingly, it's not the newly-born fast-moving neutrons from fission events that are best at causing more fissions. It's the slower, older neutrons that have lost energy through collisions with reactor materials.

Now, when a neutron collides with the nucleus of a reactor material, there's a chance it can either bounce away, wasting some energy, or get absorbed by the material. In order to sustain a chain reaction, we need to avoid too many neutrons being absorbed. To make the reactor work, no more than 50 percent of the "daughter" neutrons can be absorbed.

The best material to slow down neutrons is "light" hydrogen, like water, but unfortunately, light hydrogen also absorbs a lot of neutrons. So to use water as a moderator, the uranium fuel needs to be enriched, which wasn't available when the first nuclear reactors were designed.

On the other hand, "heavy hydrogen" (deuterium) is great at slowing down neutrons with very little absorption. Using a simple model of a reactor that mixed fuel and moderator homogenously, Heisenberg calculated that to create a critical atomic pile (a controlled nuclear reaction) with natural uranium as fuel, you would need to use deuterium-enriched "heavy water" as the moderator. The only facility in the world that could produce the necessary heavy water in quantity was the Norwegian hydroelectric power plant at Vemork. So the Nazis expropriated it. But the British found out about the plan, and following a request by Winston Churchill to Norway’s exiled King Haakon VII, the Norwegian resistance blew the plant up.

However, Fermi had a different approach. He allowed for different arrangements of fuel and moderator in his reactor model. This way, he found a configuration where ordinary, cheap graphite could do the moderating job without the need for heavy water. This led to the success of his Chicago pile and the Hanford reactor, which produced the plutonium fuel used in the Nagasaki bomb.

In summary, Fermi's innovative design avoided the need for scarce and expensive heavy water, making the nuclear reactors more practical and successful.

Thus the scene in the movie where the physicists are celebrating the news that Heisenberg had committed the German atomic bomb program to heavy water is right on target.

The movie makes only one technical mistake by focusing on a question raised at one point by Edward Teller's about whether a fission bomb might cause a chain reaction in the Earth's atmosphere. In reality, this worry was quickly dismissed once calculations showed it was impossible. Nitrogen fission would not release any energy, and nitrogen fusion would be too slow to sustain a chain reaction due to energy loss. So, there was no risk of setting the atmosphere on fire during the Trinity test.

Instead, the main concern during the test was whether the bomb would actually work. Making a nuclear bomb is tricky; it's not enough to just have a critical chain reaction or a runaway reaction. You need a reaction that multiplies so fast that it releases most of the bomb's potential energy before the explosion disrupts the process. Remarkably, they succeeded on their first attempt.

Shifting to the social aspects of the project, it's nice to see that the film doesn't try to change the historical reality of World War II America to fit today's diversity, equity, and inclusion agenda- one woman scientist is shown working as part of Oppenheimer’s team at Los Alamos. But in fact the Manhattan Project did include one such person, Leona Woods, who invented the neutron detector that allowed the power level in Fermi’s Chicago Pile-1 to be monitored and thus controlled, and who later found the solution to the absorption of neutrons by fission product xenon-131 (“xenon poisoning”) that was causing repeated shutdowns of the Hanford nuclear reactor.

Nor did the movie attempt to show the project staff being morally conflicted about the use of the bomb to end the war. In fact, very few were. As Leona Woods commented when asked about it years later,

“I certainly do recall how I felt when the atomic bombs were used. My brother-in-law was captain of the first minesweeper scheduled into Sasebo Harbor. My brother was a Marine, with a flame thrower on Okinawa. I’m sure these people would not have lasted in an invasion. It was pretty clear the war would continue, with half a million of our fighting men dead not to say how many Japanese.…I have no regrets. I think we did right, and we couldn’t have done it differently.”

Indeed, I was present at the celebration of the 40th anniversary of the dropping of the bomb on Hiroshima at the lab in August 1985. The keynote was given by Harold Agnew, the Manhattan Project physicist who flew in the chase plane at Hiroshima to photograph the bombing. His speech was entitled “That’s the way it was. No regrets.”

In fact, there was no moral alternative. The war was still raging across Asia and the Pacific costing tens of thousands of American, British, Australian, Kiwi, Filipino, Polynesian, Indonesian, Vietnamese, Indian, Chinese, and Japanese lives every day. A far more intense bloodbath would have occurred if the Allies had invaded Japan, with the supposedly more 'moderate' alternative of starving Japan into submission, which would have potentially cost millions of lives.

The film shows Oppenheimer being first welcomed warmly by President Harry Truman but then meeting contempt when he switched to affecting moral conflict over his role in the bombing. I doubt that scene is literally accurate, but it contains poetic truth. Truman was willing to take moral responsibility for both his actions and inactions. As he famously put it: “The buck stops here.”

Such decisive leadership was necessary to end the war. Truman was willing to accept responsibility. How might he have regarded those then — or now — who are not?

The weakest part of the film was the portrayal of Oppenheimer’s nemesis, Lewis Strauss. Not the performance by Robert Downey Junior, which is fine enough, but the writing, which casts Strauss as the villain in a melodrama. In fact Strauss was a complex and very accomplished person with a strong humanistic streak. He was one of the few major players to try to have the US take action to avert the Holocaust in the 1930s, and virtually alone among those near the top to advocate that the first atomic bomb used in the war not be dropped on a city, but in a demonstration to the Japanese on an uninhabited island instead. Later on he was one of the leaders pushing Eisenhower’s Atoms for Peace initiative. As noted, I think Truman was right and Strauss was wrong about the first use of the bomb, but my point is that Strauss was a much deeper person than the vicious police mind he is portrayed to be in the film.

Oppenheimer was certainly no communist spy. But he was very left-of-center, and had numerous social connections with people who, in the context of the Cold War, had to be regarded as security risks. Furthermore, his argument that if the US refrained from developing the hydrogen bomb the Soviets would hold back as well was clearly wishful thinking. In fact, the Soviets demonstrated the first practical hydrogen bomb before the United States did. In one scene of the movie, Oppenheimer corrects Strauss’ statement that Einstein is “the greatest scientist of our time.” No, says the arrogant Oppenheimer, he is “the greatest scientist of his time.” The same could be said of Oppenheimer in the 1950s. The right scientific leader for World War II — he was like a fish out of water during the Cold War. So long as the enemy was the Nazis, Oppenheimer was willing and able to go all the way. But he lacked the same moral clarity in his view of the Soviets. Strauss was a tough customer, and treated Oppenheimer brutally when he made the decision to dethrone him, but there were real policy issues at stake.

Finally, there is the magic of Los Alamos. The movie attempts to capture this with its majestic photography. It makes a fair try, but frankly you just have to be there to see it, and feel it. The desert landscape is spectacular, and while it is mostly dry, when it rains the water comes down in incredible torrents. On dry nights lightning ripping through sky can create a sight and sound show to behold, exceeded in grandeur only by that presented by the quiet stars in their multitudes when all is clear. Perhaps the movie will show you enough to induce you to make the trip yourself. If you do, be sure to go to the guest house of the old boy’s Ranch School, which is the only building in town that predates the Manhattan project, and which now serves as a museum of the project’s history.

It tells the story of a group of people, some extraordinary in certain ways, but all in a way mostly ordinary, who rose to greatness meet the challenge of their time.

But, alas, most will never make that trip. So it is good that there is now a movie worthy to tell at least part of the tale. The great deeds of little people should not be forgotten.