There are few moments in cinema more embedded in cultural memory than the opening of 2001: A Space Odyssey. The scene is simple enough—the sun rises over a crescent earth—but Kubrick sets the shot to Richard Strauss’s Thus Spake Zarathustra, a bombastic and now instantly recognizable piece of music. It’s a perfect pairing of sound and image, but it almost never happened: Kubrick initially hired Alex North, a renowned film composer, to write the film’s music. Below is the opening act of the movie set to North’s score, alongside the actual scene for comparison.
So why did Kubrick end up using Strauss? The main reason is obvious: it’s way better. For a more nuanced, qualified explanation, here’s Kubrick himself answering the question for French film critic Michel Ciment:
However good our best film composers may be, they are not a Beethoven, a Mozart or a Brahms. Why use music which is less good when there is such a multitude of great orchestral music available from the past and from our own time? When you’re editing a film, it’s very helpful to be able to try out different pieces of music to see how they work with the scene. This is not at all an uncommon practice. Well, with a little more care and thought, these temporary music tracks can become the final score. When I had completed the editing of 2001: A Space Odyssey, I had laid in temporary music tracks for almost all of the music which was eventually used in the film. Then, in the normal way, I engaged the services of a distinguished film composer to write the score. Although he and I went over the picture very carefully, and he listened to these temporary tracks (Strauss, Ligeti, Khatchaturian) and agreed that they worked fine and would serve as a guide to the musical objectives of each sequence he, nevertheless, wrote and recorded a score which could not have been more alien to the music we had listened to, and much more serious than that, a score which, in my opinion, was completely inadequate for the film.