After receiving near-universal critical acclaim and earning more than $700 million at the worldwide box office, there isn’t much you can do to improve Gravity in the eyes of most moviegoers. However, early in the production, the film was going in a much different direction.
In an interview with The Hollywood Reporter, director Alfonso Cuaron revealed that instead of George Clooney and Sandra Bullock starring in the movie, Angelina Jolie and Robert Downey Jr. were almost cast instead. While Jolie was replaced for scheduling reasons, Cuaron had a much more interesting reason not to bring Downey into the picture.
It became very clear that, as we started to nail the technology, or narrow the technology, that was going to be a big obstacle for his performance. I think Robert is fantastic if you give him the freedom to completely breathe and improvise and change stuff. [But] we tried one of these technologies and it was not compatible. And, after that, we [had a] week that we pretended as if nothing was happening and then we talked and said, 'This is not going to work. This is tough.'
Basically, the camera technology used to film Gravity had to be so precise, that the actors had absolutely no room to veer off the script. This means that each take had to be exactly the same as the previous one because of the timing and movements of the camera.
Obviously, that’s not Downey’s forte. He’s an actor who lives in improvisation; unfortunately, this is one of the few times when his brilliance would have hurt the movie. Clooney, on the other hand, is perhaps at his strongest when giving defined performances based on what he sees on the page.
In the end, Cuaron made the right move for this specific film, but don’t be surprised to see Downey pop up in one of his movies eventually.