New scientific discoveries can ignite curiosity, explain the unknown, and even improve the world. But what happens when a scientist comes to regret the knowledge he’s unleashed?
This is the central question of the upcoming film Oppenheimer, which recounts American scientist J. Robert Oppenheimer’s moonshot project to build an atomic bomb in a top-secret lab in the New Mexico desert—and his lifelong qualms about the nuclear age he ushered in.
Did the legendary physicist really regret his nuclear creation? The truth is as complicated as the science behind the bomb. Here’s how Oppenheimer birthed—and questioned—the atomic bomb.
From child prodigy to the Manhattan Project
Born in New York City in 1904, Julius Robert Oppenheimer was the son of German Jewish immigrants who found wealth in the textile importing trade. He graduated from Harvard University summa cum laude after just three years of study, then studied theoretical physics at both Cambridge University and the University of Göttingen in Germany, where he gained his doctorate at age 23.
The young physicist “Oppie” had soon rubbed shoulders with the greatest scientific figures of his age, and his academic work advanced quantum theory and predicted everything from the neutron to the black hole. He was a voracious learner outside of the sciences, too, learning Sanskrit, studying religion, and aligning himself with a variety of progressive causes.
After the United States joined the Allies in 1941, Oppenheimer was asked to participate in the top-secret Manhattan Project, whose aim was to develop an atomic weapon. As he endeavored to figure out what would need to happen to trigger and sustain the kind of neutron-chain reaction needed to create a nuclear explosion, Oppenheimer’s superiors were impressed by his wide-ranging knowledge, ambition, and ability to work with, and inspire, other scientists. In 1942, the U.S. Army called on Oppenheimer to head up the secret lab where the bomb would be tested.
Los Alamos and the Trinity test
As Army officials scouted appropriate places for such a lab, Oppenheimer, who loved the American Southwest and owned a ranch in New Mexico, suggested the site of the Los Alamos Ranch School, a private boys’ school near Santa Fe. Soon, he oversaw hundreds, then thousands, of workers at what became known as the Los Alamos Laboratory.
Oppenheimer didn’t just assemble a group of the most brilliant scientific minds of his time—he inspired, goaded, organized, and pushed them to perform. “He was intellectually and even physically present at each decisive step,” physicist Victor Weisskopf later recalled. That presence resulted in “a unique atmosphere of enthusiasm and challenge”—and in a chain reaction of scientific discoveries that produced the world’s first nuclear weapon.
On July 16, 1945, Oppenheimer and others gathered at the Trinity test site south of Los Alamos for the world’s first attempted nuclear blast. It was a tense moment: the scientists knew that the bomb they’d nicknamed “Gadget” would shape the future of the world.
But they also believed it might bring an end to World War II. Though the war in Europe had ended, U.S. officials feared the war’s bloodiest phase was still ahead of them: assaults against Japan itself. The hope was that the nation could force Japan to surrender instead by threatening to use the new weapon.
Conducted in secret, the test worked. As Oppenheimer later recounted in a 1965 interview, the moment had called to mind a line from the Hindu Bhagavad Gita: “Vishnu is trying to persuade the prince that he should do his duty, and to impress him, takes on his multi-armed form and says ‘Now I am become Death, the destroyer of worlds.’ I suppose we all thought that, one way or another.”
Bombing Japan—and the moral aftermath
On August 6 and August 9, 1945, the U.S. dropped two of the bombs Oppenheimer had helped develop over Hiroshima and Nagasaki. A minimum of 110,000 people are thought to have been killed in the blasts, which wiped out both cities on a scale of devastation never seen before or since.
Oppenheimer had served on the scientific committee that recommended the War Department deploy the bomb as soon as possible against Japan. Historical debates still rage about whether the government listened to scientists’ pleas that the bomb be deployed against military targets only, or even publicly tested beforehand in an attempt to force Japan’s surrender.
The night of the Hiroshima bombing, Oppenheimer was cheered by a crowd of fellow scientists at Los Alamos, and declared that his only regret was that the bomb hadn’t been finished in time to use against Germany.
But though they were thrilled by their accomplishment, the scientists were horrified at the loss of civilian lives in the attack, worrying that the future of the weapons would encourage future wars instead of deter them. A few weeks after the bombing, Oppenheimer wrote a letter to the Secretary of War warning that “the safety of this nation…cannot lie wholly or even primarily in its scientific or technical prowess. It can be based only on making future wars impossible.”
But Oppenheimer also defended the Manhattan Project and the bomb he’d been tasked with building, arguing that it had been necessary to fully understand the possibilities of nuclear science.
Opposition to the hydrogen bomb
Nonetheless, Oppenheimer spent much of his life after the war lobbying for nuclear deterrence, vocally opposing U.S. attempts to develop a more powerful hydrogen bomb after the U.S.S.R. made strides with its own bomb. Instead, said Oppenheimer, the U.S. should consider using nuclear weapons only tactically and pursue other uses of nuclear technology, like generating power, instead.
This earned him political enemies—and put him the crosshairs of the Red Scare, an American political era of anti-Communist hysteria during the Cold War. At a 1954 hearing looking into his supposed Communist sympathies, the Atomic Energy Commission revoked his security clearance. The move was only reversed in 2022, after government officials revisited Oppenheimer’s case and found the investigation had been flawed and unlawful.
“He doesn't slot into easy categories of pro-nuclear, anti-nuclear or anything like that,” historian Alex Wellerstein told PBS NewsHour. “He's a tricky figure.”
Oppenheimer never returned to government service, instead founding the World Academy of Arts and Sciences and lecturing on science and ethics until his death in 1967. Though he had helped create the “necessary” weapon that ended a war, destroyed two entire cities, and ushered in a dangerous new age, he lobbied against nuclear proliferation for the rest of his life.
“In some crude sense which no vulgarity, no humor, no overstatement can quite extinguish,” he said in 1950, “the physicists have known sin; and this is a knowledge which they cannot lose.”