Most of the conflict between Einstein and Oppenheimer came down to the fact that they were physicists of two different generations. Most of the innovations in the new field of quantum mechanics were made by younger scientists, and Einstein often didn’t find their ideas convincing. Younger physicists like Oppenheimer considered Einstein’s “stubborn refusal to embrace the new physics” to be a “sign that his time had passed,” as historians Kai Bird and Martin J. Sherwin noted in their biography, “American Prometheus,” which Nolan’s film is based on. When Oppenheimer met him for the first time in the late 1920s, he reportedly told his brother that Einstein was “completely cuckoo.”
Another big early difference is that Oppenheimer was the director of Los Alamos with a clear-cut role in creating the atomic bomb, whereas Einstein’s hands were largely clean. Beyond signing a letter to Roosevelt in 1939 urging him to start a nuclear program to beat the Nazis, Einstein had no involvement in the project because, as a German with left-wing views, he was denied security clearance. (He also just didn’t seem interested.) As a result, scientists at Los Alamos weren’t supposed to interact with him at all; the scene in the movie where Oppenheimer asks Einstein for help figuring out if their experiment would destroy the world was entirely fictional.
Their conversation at the end of the movie, the one that accidentally led to Lewis Strauss hating Oppenheimer for the rest of his life, was also apparently fictional. Yet despite the fact that Nolan took the biggest creative liberties with Einstein’s scenes, the friendship between the two scientists was certainly real.
