In making “Oppenheimer,” which opens in theatres this weekend, the director Christopher Nolan relied on a Pulitzer Prize-winning 2005 biography of the father of the atomic bomb, “American Prometheus,” by Kai Bird and the late Martin J. Sherwin. Bird is credited as a writer of Nolan’s movie, and he spoke with David Remnick about Oppenheimer’s life story—in particular, about the ambivalence that the scientist felt, and expressed publicly, about the use of the bomb, which led to a McCarthyist show trial that destroyed his career and reputation. “He’s very complicated and he’s highly intelligent, so he’s capable of understanding and holding in his head contradictory ideas,” Bird says. On the one hand, “He feared that if [the bomb] was not used, or the war ended without the use of this weapon, the next war was going to be fought by two nuclear-armed adversaries and it would be Armageddon.” On the other hand, after Hiroshima, Oppenheimer used his status as a celebrity scientist to educate the public about the dangers of nuclear warfare, a move that landed him in the crosshairs of federal officials. “What happened to him in 1954 sent a message to several generations of scientists, here in America but [also] abroad, that scientists should keep in their narrow lane. They shouldn’t become public intellectuals. And if they dared to do this, they could be tarred and feathered,” Bird notes. “The same thing that happened to Oppenheimer in a sense happened to Tony Fauci.”