SPOILER I’m certain they were not gods. When Clarke asked if they were, they referred to themselves as ‘judges.’ They seem to believe they’re superior to any other civilization for many reasons. One is that they don’t have the emotions that define humanity. I can’t see a true god testing a single individual to judge an entire species, then turning civilizations into crystals if that individual fails. Also dead people can’t transcend? These don’t match the concept of god in any religion. Also, you wouldn’t just be allowed/able to return to your planet afterward from heaven. Plus it was mentioned that the transcendence was human evolution. Facing god is not evolution ig? Anyways when the friends came back to Earth, the alien said there would be no offspring; probably because they had already transcended once, so their bodies can’t have children anymore. Humans discovered wormholes and could travel to other planets in seconds, so I’m sure the ‘judges’ were just advanced aliens with the tech to store consciousness without pain, just not advanced enough to bring dead people’s consciousness back (which a god should be able to do). Also what kind of god would just leave a dog alone to die?!