After his ambitious film Tenet, Christopher Nolan decided to explore real history with Oppenheimer, a film based on the book American Prometheus, by Kai Bird and Martin J. Sherwin, which narrates the life of J. Robert Oppenheimer, the "father of the atomic bomb", a weapon that changed the fate of the planet. One of the aspects that has attracted the most attention is that the director assures that he did not use computer-generated effects (CGI) to recreate the first nuclear explosion, and now he went further in an interview with Collider, saying that the film has "zero CGI".
Indeed, Nolan's preference for the latter is in all of his films, even those where CGI is is unavoidable. In the Batman trilogy, for example, there was an impressive use of miniatures and real sets, to the point that in Batman: The Dark Knight, he blew up a building for the scene in which the Joker blows up a hospital.
In fact, it was in a recent interview with Collider Editor-in-Chief Steve Weintraub that Christopher Nolan stated that Oppenheimer has "zero CGI shots". The filmmaker had already said that he wanted to recreate the Trinity Test in a practical way, but now he claims that the entire film is only in this way.
Practical special effects are those that are created with real elements; if an iconic building needs to be blown up, it is blown up, or a miniature (better known as a giant) is created and filled with explosives; or if a very dangerous stunt scene is required, stuntmen perform it at risk to their lives. Computer effects make the job easier, but in many cases, perhaps in most cases, they are not as realistic as the practical effects.