Cuarón has stated that the film is not always scientifically accurate and that some liberties were needed to sustain the story. "This is not a documentary," Cuarón said. "It is a piece of fiction."
Nevertheless, the film has been praised for the realism of its premises and its overall adherence to physical principles, despite a number of inaccuracies and exaggerations.According to NASA Astronaut Michael J. Massimino, who took part in two Hubble Space Telescope (HST) Servicing Missions (STS-109 and STS-125),
"nothing was out of place, nothing was missing. There was a one-of-a-kind wirecutter we used on one of my spacewalks and sure enough they had that wirecutter in the movie."
Astronaut Buzz Aldrin called the visual effects "remarkable". He adds, "I was so extravagantly impressed by the portrayal of the reality of zero gravity. Going through the space station was done just the way that I've seen people do it in reality. The spinning is going to happen—maybe not quite that vigorous—but certainly we've been fortunate that people haven't been in those situations yet. I think it reminds us that there really are hazards in the space business, especially in activities outside the spacecraft." Garrett Reisman, a former NASA astronaut, noted that, "The pace and story was definitely engaging and I think it was the best use of the 3-D IMAX medium to date. Rather than using the medium as a gimmick, 'Gravity' uses it to depict a real environment that is completely alien to most people. But the question that most people want me to answer is, how realistic was it? The very fact that the question is being asked so earnestly is a testament to the verisimilitude of the movie. When a bad science fiction movie comes out, no one bothers to ask me if it reminded me of the real thing."
Comparison of International Space Station and Hubble Space Telescope orbits
On the other hand, astrophysicist Neil deGrasse Tyson, astronomer and skeptic Phil Plait, and veteran NASA astronaut and spacewalker Scott E. Parazynski have offered comments about some of the most "glaring" inaccuracies. Examples of such mistakes include:
The HST, which is being repaired at the beginning of the movie, has an altitude of about 559 kilometers (347 mi), and an orbital inclination of 28.5 degrees. The ISS has an altitude of around 420 kilometers (260 mi), and an orbital inclination of 51.65 degrees. With such significant differences in orbital parameters, it would be impossible to travel between them without precise preparation, planning, calculation, appropriate technology and a large amount of fuel.
When Kowalski unclips his tether and floats away to his death to save Stone from being pulled away from the ISS, several observers (including Plait and Tyson) contend that all Stone had to do was to give the tether a gentle tug, and Kowalski would have been safely pulled toward her, since the movie shows the pair having stopped and there would thus be no centrifugal force to pull Kowalski away. Others, however, such as Kevin Grazier, science adviser for the movie, and NASA engineer Robert Frost, maintain that the pair are actually still decelerating, with Stone's leg caught in the parachute cords from the Soyuz. As the cords absorb her kinetic energy, they stretch. Kowalski's interpretation of the situation is that the cords are not strong enough to absorb his kinetic energy as well as hers, and that he must therefore release the tether in order to give her a chance of stopping before the cords fail and doom both of them.
Stone was not shown to have worn a liquid-cooled ventilation garment or a diaper or even socks under the EVA suit, all of which are always put on to protect against temperature extremes of space.
Stone's tears first roll down her face in zero gravity, and later are seen floating off her face. Without sufficient force to dislodge the tears, the tears would remain on her face due to surface tension. However, the movie does correctly portray the spherical appearance of liquid drops in a micro-gravity environment.
Despite the inaccuracies in Gravity, Tyson, Plait and Parazynski have all said they enjoyed watching the film. Aldrin hoped that the film would stimulate the public to find an interest in space again, after decades of diminishing investments into advancements in the field.