Gravity is a stunner of a movie in large measure because of what it doesn't do—it's restrained and elegant in the way that most big space epics aren't. Here's a great behind-the-scenes look at how the film makes the vacuum of space sound terrifying—even at times when sound is impossible.
The SoundWorks collection documentary features Director Alfonso Cuarón and Re-recording Mixer Skip Lievsay discussing how they attempted to stick to a realistic sonic portrayal of space. Sound in space is impossible, duh, but this fact gave the filmmakers a scientific loophole to work with for the sound. You see, when a floating astronaut's body makes contact with something in space, the impact vibrations travel through their bodies to their ears. So when, for example, Sandra Bullock is opening a huge steel hatch to an airlock, the scraping sound would travel from the hatch to her hands, through her body to her ears, so she could actually hear it.
Now, when you hear this scraping sound in the movie, the recordists didn't just hold a microphone up to a hatch because that's not what the real event would sound like in space. Instead, they used transducer mics—microphones attached to the surface of an object—that record vibrations of the solid objects rather than the vibration of air. The recording method gives the sound muffled quality more like what an astronaut might hear while floating in the great abyss.
The whole short doc is worth watching, if only to give you a sense for the huge amount of thought that went into a film that looks—and sounds—effortlessly minimal. [SoundWorks Collection]