I feel like you missed a few points in the film . Gravity can work as shown in the film . A slow rotation of the craft can simulate earth gravity just fine . They weren ' t aliens , they were humans from the future working through the 4 th dimension time . The film revolves around a fair amount of temporal parodoxes future humans help their past selves , which only happened because their future selves saved them etc . Time dilation can absolutely happen as shown in the film , although there would be some physical damage to human bodies while descending to the more extremely dilated planets , feet aging faster than torsos and whatnot , with a degree of spaghettification . Neutron stars are just as dangerous as any other star , only much more dense . If our star suddenly became a neutron star it would behave almost exactly the same aside from perhaps a bit more radiation thrown around , it would just be smaller but retain the same mass . I ' m pretty sure that one dude was put in some form of stasis for 23 years .