There’s a gutting scene midway through Oppenheimer that finds Cillian Murphy’s J. Robert Oppenheimer at one of his lowest moments. Despite the scientist’s service to his country, he’s being accused of harboring treasonous sympathies; an unofficial trial with a foregone conclusion is dragging him through the mud. Outside his home in Princeton, he encounters a colleague: Albert Einstein (Tom Conti), who doesn’t seem to get why his fellow physicist is lying down and taking it. 

If this is the reward the American government gives Oppenheimer after the years he spent developing the nuclear bomb that ended World War II, Einstein tells him in the film, Oppenheimer should simply “turn his back” on America. (It’s what Einstein was forced to do to his homeland of Germany, after all—and for understandable reasons, he would never trust governments or politicians.) What the essentially stateless Einstein doesn’t understand is that for New York City–born Oppenheimer, this simply isn’t an option. “Damnit,” he replies, “I happen to love this country.”

Like many of the details in Christopher Nolan’s script, both lines of dialogue come straight from Oppenheimer’s source material, Kai Bird and Martin Sherwin’s biography American Prometheus. (Though Oppenheimer’s memorable reply is actually lifted from a different exchange.) The scene is a neat illustration of how these two scientific giants both mirrored and opposed one another. Einstein only has a handful of scenes in Oppenheimer, but each of them packs a similar punch—particularly another (fictionalized) meeting that the film keeps coming back to, revealing its full significance only in the movie’s final moments.

It shouldn’t be surprising to learn that the man whose name has become synonymous with “genius” is only a supporting character in Nolan’s film. Though it was Einstein’s letter to President Roosevelt that convinced FDR to begin a nuclear weapons program, Einstein was not involved in the Manhattan Project. (The government deemed him a security risk due to his left-leaning politics—though it cleared Oppenheimer, despite his various ties to Communists and Communist sympathizers.) 

And though he and Oppenheimer both lived and worked in Princeton, New Jersey after the war—specifically at the Institute for Advanced Study, where Oppenheimer served as director from 1947 to 1966—they were not particularly close friends. (Though they’re in the same town, the Institute is not affiliated with Princeton University.) While they had known each other for years before he came to the Institute and he respected Einstein—who wouldn’t?—Oppenheimer thought of his predecessor “as a living patron saint of physics, not a working scientist,” Bird and Sherwin write. “In the last years of Einstein’s life, the last twenty-five years, his tradition in a certain sense failed him,” Oppenheimer would write in 1965, in a  lecture later published in the New York Review of Books. 

The older physicist was skeptical of quantum theory, which Oppenheimer would advance, and didn’t believe black holes could possibly exist. As shown in Oppenheimer, the younger physicist helped to prove they do. (In a paper published the same day Hitler invaded Poland!) Though Oppenheimer thought he was essentially old-fashioned, “Einstein eventually acquired a grudging respect for the new director” of the Institute, write Bird and Sherwin, “whom he described as ‘an unusually capable man of many-sided education.’ But what he admired about Oppenheimer was the man, not his physics.” 

That said, the biographers indicate Einstein and Oppenheimer did still enjoy each others’ company. They relay a charming anecdote about the two that didn’t make it into Oppenheimer but would’ve been a gas to see. In 1948, they write, “knowing Einstein’s love of classical music, and knowing that his radio could not receive New York broadcasts of concerts from Carnegie Hall, Oppenheimer arranged to have an antenna installed on the roof of Einstein’s modest home at 112 Mercer Street. This was done without Einstein’s knowledge—and then on his birthday, Robert showed up on his doorstep with a new radio and suggested that they listen to a scheduled concert. Einstein was delighted.” 

Years later, when Oppenheimer was targeted for his past Communist ties and stripped of his security clearance, Einstein was firmly on his colleague’s side—even if he didn’t understand Oppenheimer’s response. “The trouble with Oppenheimer is that he loves a woman who doesn't love him—the United States government,” he told a friend, per Bird and Sherwin. “The problem was simple: All Oppenheimer needed to do was to go to Washington, tell the officials that they were fools, and go home.” Einstein was (ahem) smart enough to keep those views private. Publicly, he expressed his support in a more palatable manner: “I admire him not only as a scientist but also as a great human being,” he told the press. 

Later, Oppenheimer would return the favor: “Einstein is also, and I think rightly, known as a man of very great good will and humanity,” he said in that 1965 lecture. “Indeed, if I had to think of a single word for his attitude towards human problems, I would pick the Sanskrit word Ahinsa, not to hurt, harmlessness.”

In the film, at least, the admiration goes both ways. Early on, Murphy’s Oppenheimer asks Conti’s Einstein to review a troubling set of calculations as the Manhattan Project gets underway. According to Edward Teller (Benny Safdie), setting off a nuclear explosion might cause a chain reaction that would ignite the atmosphere, destroying the Earth and everything on it. Einstein advises Oppenheimer to have another physicist, Hans Bethe (Gustaf Skarsgård), run the calculations again—revealing that while such an outcome is possible, it has a near-zero chance of actually happening. And near-zero winds up being good enough for them.

The scene, Nolan admits, is an invention. In reality, Oppenheimer did fear causing a chain reaction—but he sought counsel from Arthur Compton, a Nobel Prize winner who directed the Manhattan Project’s University of Chicago outpost, instead of the man behind the theory of relativity. “I shifted that to Einstein,” Nolan told The New York Times, because “Einstein is the personality people know in the audience.” 

Einstein’s status as a popular icon is likely also why Nolan uses an imagined conversation between Einstein and Oppenheimer as a recurring device in the film, one that eventually reveals Oppenheimer’s crushing thesis statement. We see their exchange from a few different perspectives throughout the movie, including that of Robert Downey Jr.’s Lewis Strauss, who inadvertently catalyzes the encounter. 

Strauss, who’s trying to woo Oppenheimer to run the Institute, spots Einstein outside the building where they’re meeting and offers to introduce Oppenheimer to him. Strauss doesn’t know that the men are already acquainted—and Oppenheimer adds insult to injury by sauntering up to Einstein, then saying something to him Strauss can’t hear. It’s the first in a series of humiliations that will spur Strauss to seek vengeance; the administrator is convinced Oppenheimer has done something to poison Einstein against him. 

In reality, Oppenheimer and Einstein don’t even mention Strauss, though we learn what the two talked about only in Oppenheimer’s final moments. Their conversation is a meditation on the consequences of achievement—how governments can use and discard scientists with impunity, then welcome them back into the fold after the metaphorical dust has settled if they so choose. When a future administration decides to give Oppenheimer a medal, Einstein tells him, “just remember, it won’t be for you.” 

It’s also a callback to that fictionalized pre–Manhattan Project meeting. Oppenheimer asks Einstein if he recalls when they worried a chain reaction from the bomb might destroy the world; Einstein remembers. “I believe we did,” Oppenheimer replies. Though the exchange came from Nolan’s imagination, it really ends the movie with a bang.

This article has been updated.