Interstellar Plot Summary
>! Spoilers ahead !<
Cooper is a former astronaut turned farmer on a dying planet earth that is affected by a disease called blight sometime in the distant future (technically, the movie starts out in the year 2067). Blight kills almost all the food crops except corn, but soon will also kill corn, meaning that the earth will become uninhabitable very soon.
Time is ticking, so NASA decides to launch a program to save humanity. Except the only reason it is possible to save people on earth is due to a wormhole in outer space that was placed there by (spoiler) future humans who have evolved past our current form into higher dimensional beings with greater knowledge, scientific skills, and evolutionary abilities, such as the ability to affect space and time in ways we cannot yet imagine.
The wormhole leads out of our current galaxy, the Milky Way, into other distant galaxies, like a tunnel through space. NASA has used this wormhole by sending manned probes to these galaxies to find a new home that could be habitable like earth. They then send Cooper and a crew to go find out which of the probes have reported feasible worlds and choose one to settle.
Things don’t go as planned, however when (spoiler) they discover that one of the manned expeditions reported false data, leaving them semi-stranded in space without enough fuel to get home. They choose to press forward in time to try to discover another habitable world, but don’t have enough fuel, so they launch a slingshot route around a giant black hole named Gargantua.
Gargantua will give them enough of a gravity boost to reach their destination but will have two problems: 1) The only way they can succeed is if Cooper manually detaches from the ship to allow momentum to take the ship to its course, thus stranding Cooper in the center of Gargantua. 2) The time will advance very fast for people on earth in this process because of Einstein’s theory of relativity that says the closer you are to a large gravity source like Gargantua, the slower time will go for you (thus meaning that people back on earth will advance in years ahead of Cooper), and thus Cooper may never see his daughter again if he would escape the black hole somehow.
Back on earth, Cooper’s daughter, Murph, is grown up and she discovers that (spoiler) the only way to figure out how to get humans launched into space in their space station is to solve a complex mathematical physics problem involving gravity, and the only way to get that data is from the center of the black hole (Gargantua). So Cooper hopes that once he and the robot with him are inside the black hole, he can somehow transmit that data back to earth to save them.
Back in space, light years away, Cooper and TARS (the robot) are falling helplessly into the black hole and something unexpected happens. (Spoiler) They fall into a “Tesseract” structure which looks like a library bookcase that has been unfolded into multiple dimensions. Cooper can see that this bookcase is in fact the same bookcase that exists in his daughter Murph’s room, but has multiple timelines. In this Tesseract structure, Cooper can actually access different timelines in the past, as gravity fields can apparently transcend time itself.
In the Tesseract, Cooper learns how to communicate with Murph in the past and the present (on earth) by using gravitational forces to affect both the books on her shelf and the watch hands on the watch he gave her which is on the shelf. Using this newly discovered process of communication, he manages to relay the data from the black hole that Murph needs back on earth, to solve the equation and get humanity into outer space and off the dying planet.
Now for the fun part: Cooper theoretically should have died in the black hole, but the Tesseract was a structure that future humans built to help him, so it doesn’t kill him. We don’t know exactly how it works, but it shoots him out of the black hole when he is done, and into space. He is now well over 100 years old in earth time, but he looks the same age. This is because time moved much slower for him while inside the black hole. He then drifts through space and is picked up by the space station that was launched from earth, thus reuniting him with his daughter, who is now old, because time did not move slowly for her while he was away. He then returns back to space to help re-colonize the new planet for all future humans to live on.
Now for the really fun part: The thing to realize is that none of this story makes sense if time is linear (e.g. a straight line moving forward only). This movie’s plot only works if time is not linear, but rather like a loop. (Or a mobius strip) Time can be affected by gravity, so since a lot of the events happen in and around large gravity sources like Gargantua, time doesn’t behave the way we think of it. It bends and curves, and thus, Cooper is able to take action that will affect time before his present day, which would normally be a paradox, but in this case, since time is nonlinear, it is possible. And the future humans wouldn’t have been alive to build the Tesseract without all these events, so clearly it all depends on itself, in a cyclical or roundabout way.
