I watched the film in its recommended 3D version and it was enjoyable. The film belongs to the genre of disaster films where people are stranded in a remote place because of an unfortunate series of accidents. There is no place more remote than outer space and the set up for this film is when a space shuttle repair mission to the Hubble telescope is bombarded by space debris that causes havoc.
Almost the entire film takes place in space at the orbital height of the Hubble and the International Space Station and so takes place in zero gravity or, to be slightly more precise, micro-gravity. The difficult thing about filming zero gravity scenes is that there is no way to shield the effects of Earth’s gravity to make things weightless. Unlike all the other forces, gravity acts on everything all the time and there is no getting around it.
The only way out is to use the Equivalence Principle that says that the observable effects of gravity are identical to those that would be observed in an accelerating frame of reference. Hence the force we feel on the Earth due to gravity (which creates a downward acceleration of 9.8m/s2 for freely falling objects) would be indistinguishable from what we would see and feel if there were no gravity force at all but the ground beneath our feet were accelerating up at the rate of 9.8m/s2 (ignoring the small non-uniformity of the gravitational field due to the sphericity of the Earth).
So if we could be inside a container that was falling down with an acceleration of 9.8 m/s2, then the combined effect of those two frames (the downward accelerating container and the upward accelerating ground) would cancel each other out and, voila! we get zero gravity. This is how the astronauts train for zero gravity, by going to high altitudes in a jet plane that then cuts its engines and falls freely. As it falls, the astronauts inside the plane feel truly weightless.
The catch about filming zero-g scenes is that on Earth one cannot have free-fall for very long times since you soon hit the ground. This makes filming extended zero-g scenes impossible. Some space films ignore this problem altogether and have people walking around as if gravity still exists in space. Others, like 2001: A Space Odyssey, create spaceships and space stations that rotate in a way that simulates gravity by creating accelerations. Others use unseen wires and the like to make things seem to float.
One thing the film makes clear is that the shuttle orbit is quite close to the Earth since we can see the Earth dominate the sky and can make out cities and major geographical features. At the height above the Earth that the Hubble is, the force of gravity due to the Earth is still considerable, about 85% of the value on the surface of the Earth. The reason we think of it as zero-g is that the shuttle is freely falling and so we have the same cancellation effect as the one I described above. The difference is that as the shuttle falls to the Earth, it does so in a parabolic path because of its lateral speed, the way a ball behaves when it is thrown. But the shuttle is high enough and is moving fast enough that the shuttle does not hit the Earth because, due to its curvature, the surface of the Earth keeps ‘falling away’ at the same rate. That is what an orbit is. We could, in theory, put a baseball in orbit near the surface of the Earth by throwing it fast enough horizontally so that as it falls, the Earth’s curvature ‘falls’ at the same rate. The problem is that the Earth’s atmosphere would cause the ball to burn up.
A major problem with simulating zero-g is the behavior of hair and loose clothing. While rigid objects can be suspended by wires and the like and made to look as if they are freely floating, in zero-g hair and clothes would simply separate from the head and body instead of clinging to it, and that is hard to simulate. In Gravity they do an excellent job of filming extended scenes in zero-g (I don’t quite know how but I suspect with wires and CGI and camera angles) and they get around the hair-clothes problem by keeping people’s hair short and having them wear either fairly rigid spacesuits or tight clothing. Some critics have carped on some details of the film as being scientifically inaccurate but those would not be noticed by anyone. I have never been in space of course, but this film supposedly conveys quite accurately what it is like and much of it was visually beautiful.
It was an enjoyable film, keeping you in suspense. There was some maudlin religious sentimentality thrown in and but it was not too bad. Was it great? I would not say that. What it did do very well was simulate a zero-g environment and when awards season comes around, cinematography and special effects prizes seems likely.
Here’s the trailer.