How to show the weightlessness effect is the most important and difficult part of any space-themed movie. Generally filmmakers have two conventional ways to achieve it. One is to shoot in real weightlessness - obviously, this is difficult to realize, so far, there has not been any feature film into space shooting; and the effect of weightlessness in the Earth is fleeting, so short that it can not support the actors to complete a weightless performance. However, if there is a specially designed aircraft, can be upward bulging parabolic arches (parabolic arcs) in the way of high-speed flight, the theory is that in the parabola before and after the formation of a period of time before and after the top of the state of complete weightlessness, as a perfect simulation of the situation of no gravity in space. In fact, the weightlessness scene in the film "Apollo 13" was shot this way: the crew and the actors flew in a parabolic trajectory in a NASA-provided KC-135 transporter at high altitude, experiencing weightlessness for about 23 seconds at a time, enough time for the camera to capture some of the actor's movements.
But this method of filming could not be applied to Gravity, director Cuaron's request for a few minutes of long shots of weightlessness alone was technically unattainable; not to mention that the total length of weightlessness required in the film was more than the borrowed aircraft could bear.
Another alternative is to simulate the action. The cheapest way to achieve this "look-alike" weightlessness in Earth's regular gravity is to shoot underwater, where the drag effect of the water slows down the action, allowing for levitation and flight-like movement in space. Gravity also used underwater filming, mainly for some of the actors in the capsule sliding shots of special effects reference, but the vast majority of other weightlessness scenes, are not shot in this way. First of all, underwater filming can't really show the actor's expression - the look of holding his breath and trying to open his eyes is obviously not the same as performing in a space environment; secondly, the complex light reflection refraction effect underwater also makes it impossible to wear a spacesuit underwater to simulate space operations.
"Gravity" final realization of the weightlessness effect of the technique, is the oldest entertainment craft and the most advanced combination of computer technology: the crew to find the stage version of the "War Horse" of the masters behind the scenes to large-scale marionette manipulation, control of the actor's limbs to simulate weightlessness under the action. The setup has 12 strings attached to four tethered points on the actor's body, with the other ends of the strings either manipulated by three professional puppeteers, or by a mechanical system controlled by a computer program, or a combination of the two.
Both Cuaron and star Sandra Bullock (Sa.n.dra Bullock) mentioned in interviews one of the most difficult scenes in the movie: a long shot of the heroine struggling to get back to the capsule, stripping off her spacesuit and floating curled up in the air like a baby. During the actual filming, Bullock sat on a very small bicycle base to support her body, with one leg strapped to a device to help hold it in place, while the slow movement of her limbs and the tumbling and floating of her entire body was accomplished by a puppeteer with the assistance of programmable wires and cables. The process also involves using computerized special effects to create virtual limbs to replace the actor's bound legs and to make movements that match the rest of the wire-controlled body.
This type of wire-control was also used in this movie primarily for scenes inside space capsules. For those spacewalking scenes in spacesuits, the actors don't even have to do any physical movement -- because the entire space backdrop and the suits themselves are computer-generated: the actors are only responsible for providing facial expressions, and the rest of the physical movement is done, for the most part, by computer animators.
Both the wire-controlled and computer-generated movements are a breakthrough in the film's treatment of weightlessness: since it's impossible to float in space in a "native" way, it's a matter of "absolute control" over the way in which appearances are presented to reflect gravity-free movement. The idea of gravity is a breakthrough.
This breakthrough in technological realization also informed the production of Gravity.