Christopher Nolan's sci-fi epic Interstellar is a lot of things—action thriller, thoughtful treatise on the love between a parent and a child, and an effects-driven spectacle—but easy to understand isn't necessarily one of them, particularly in the film's final act. Astronaut Joseph Cooper (Matthew McConaughey), on a desperate mission to find a new home for humanity, plummets into a black hole and drifts beyond the event horizon, finding himself inside a tesseract where he's able to see inside his daughter's bedroom at any point in her life. He communicates with her through gravity, thus guiding her to unlock the equation that helps humanity escape Earth.
Nolan's movies give viewers a lot to think about and discuss, but Interstellar is just plain trippy—and it grows more so after Cooper is discovered floating through space by later members of the human race he's saved, brought to meet his dying daughter (who's aged at normal speed while he's been on his intergalactic travels and is thus much "older" than he is). There's plenty to unpack—more than we have the space to dive into here—and much of it is left unexplained. So what was Nolan trying to tell us?
The gist of the whole film rests on the notion that time is a circle—and the possibility of a "bootstrap paradox," a theory explained by Slate with a comparison movie fans should appreciate:
"In the first [Terminator movie], Kyle Reese is sent back in time by John Connor to protect Sarah Connor, John Connor's mother. The paradox is that Reese turns out to be the father of John Connor—by sending Reese back in time, John Connor created himself."
Back to Interstellar
: the tesseract Cooper entered was created by future humans who'd been saved by the work done by his daughter…so they gave him an opening through time and space so he could give her the knowledge she needed to finish her work. Hey, look, sometimes the explanations are just as confusing as the endings, okay?