What was the experiment that turned Dr. Manhattan into a nuclear weapon? It was never discussed or shown in the movie or comic was it? Or did I miss something?
Indeed it was! Jon Osterman is a nuclear physicist who is caught in an intrinsic field generator in 1959. It effectively tore him apart at an atomic level and, when his atoms reconfigured themselves, Doctor Manhattan was born.
The similarities between Dr Manhattan’s origin and Firestorm’s are striking IMO in light of recent developments in Doomsday Clock.