In order for the black and white sections of the movie to be shot in the same quality as the rest of the film, Kodak produced a limited supply of its Double-X black and white film stock in 70mm. This film stock was chosen specifically for its heritage - it was originally sold to photographers as Super-XX during World War II and was very popular with photojournalists of the era.
Matt Damon was on a break from acting as a promise to his wife, with one condition: it would go on hold if Sir Christopher Nolan called. As luck would have it, Nolan offered Damon the role of Leslie Groves, and the break went on hold.
The Trinity detonation scene uses a combination of practical effects and digital compositing. Multiple explosions were performed practically, with a hybrid of gasoline, propane, aluminium and magnesium substances involving big miniatures. These were filmed at high speeds from multiple angles, and then layered using digital effects to create the iconic mushroom cloud.
Albert Einstein is shown walking in the woods with Kurt Gödel. The two of them did actually take long walks together, as friends at the Institute for Advanced Studies.
J. David Wargo, who studied physics at MIT, optioned the rights to American Prometheus in 2015, but the project languished in development hell for years. Wargo met with his old friend James Woods during the pandemic, and Woods set up a meeting with Charles Roven, who in turn passed on the book to Sir Christopher Nolan. Wargo and Woods are credited executive producers. What helped Nolan decide to direct the film was a book of J. Robert Oppenheimer's speeches given to him by Robert Pattinson at the wrap party of his previous film, Tenet (2020).