Interstellar follows humanity's last-ditch effort to find a new habitable planet - after Earth is ravaged by environmental catastrophe. When former NASA pilot-turned-corn farmer Cooper (Matthew McConaughey) finds the coordinates to a top secret government project, he's brought in on the secret that the government has secretly been working to send a crew through a recently discovered wormhole in the hopes that humankind can find refuge in a new galaxy. However, in order to help save the remaining people on Earth, Cooper must leave his own family behind - and journey into unknown regions of space.
Like many Christopher Nolan films, Insterstellar presents a number of complicated story ideas that may be confusing for certain moviegoers - especially after a first viewing. For that reason, we're here to help breakdown how space travel works in the movie, as well as explain Interstellar's ending. Our discussion is going to be full of SPOILERS for Interstellar, so READ NO FURTHER unless you’re all caught up. You have been warned.
MAJOR SPOILERS FOLLOW
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Human Salvation (Plans A & B) Explained
Early on in the film we learn that the US government has secretly been funding a NASA project to find humankind a new home - since Earth is being ravaged by blight (and can no longer sustain agriculture). Cooper questions how NASA intends to find a planet capable of sustaining human life since humanity is already living on borrowed time, and transport to the nearest galaxy alone would take decades. Professor Brand (Michael Caine) then reveals that an unknown civilization, which he refers to as "They" (more on them later), have strategically created a wormhole near Saturn - a wormhole that can serve as a shortcut to a distant region of space.
As explained by Romilly (David Gyasi) in his impromptu paper hole example, our understanding of distance is based in three-dimensions - whereas theoretical physics suggests that space is a place of multi-dimensional interplay.
For that reason, the wormhole essentially functions as a bridge connecting two points in space by taking advantage of imperceptible fourth dimensional space. By the time that Cooper reunites with Prof. Brand, NASA has already sent thirteen humans through the wormhole - each one on a mission to determine whether nearby planets (on the other side of the wormhole) can sustain human life.
Upon arrival at their planet, each of the astronauts was to set up a beacon - indicating that their planet was a candidate for human colonization. NASA cannot communicate directly with the astronauts, but has been able to track their beacons for nearly a decade - of which only three remain active.
As a result, it is up to Cooper and the rest of the Endurance crew to uncover the fate of the other three astronauts - and collect any subsequent data that can be used to make an informed decision regarding which planet provides the best hope for humanity.
Should the Endurance team find a habitable planet, Brand claims that NASA has two plans for humanity's survival:
- Plan A) While the Endurance team is away, Brand will continue to work on an advanced equation that, if solved, will allow humans to harness fifth-dimensional physics - specifically gravity. Should Brand succeed, NASA will be able to defy our traditional understanding of physics and launch an enormous space station (carrying the remainder of Earth's surviving population) into space. The very facility that Cooper and Murph stumble upon at the beginning of the film isn't just a NASA research station - it's a construction site for humankind's space-traveling ark.
- Plan B) Should Brand fail in his calculation and/or the Endurance take too much time investigating potential homeworlds, NASA has harvested a bank of fertilized human embryos that can be used to ensure humanity's survival - after everyone on Earth is wiped out. To ensure genetic diversity, NASA procured DNA from a wide range of sources - so that future generations would not be limited to reproduction between Endurance crew members. In this scenario, the Endurance team would settle down on the most habitable planet and raise the first generation of embryos - with each subsequent generation helping to raise a new set of embryos (as well as reproduce naturally).
Later we learn that Professor Brand never believed that Plan A was possible - stating that he solved the equation years back, but it would not save them. He only championed the idea in order to rally Earth leaders into working together - and building the necessary infrastructure to ensure that, unknown to anyone but him, Plan B would be a success. Brand reasoned that people would not have cooperated just to save humanity - they needed to believe that working together could lead to their own personal salvation.
Upon learning that Plan A was a farce, Cooper and Amelia Brand (Anne Hathaway) commit to Plan B on their third (and final) planetary option - where Amelia's astronaut lover, Wolf Edmonds, was still reporting a positive beacon. Yet, Cooper remains unconvinced that Plan A is impossible and, as they use a nearby black hole (dubbed Gargantua) to slingshot Endurance toward Edmonds' planet, Cooper sends TARS (the crew's robot helper) into the center of the black hole - in the hopes that it can translate data that might help NASA refine any missteps in Professor Brand's calculations.
Cooper also sacrifices himself to reduce weight on the Endurance, ensuring that Amelia can make it to Edmonds' planet and enact Plan B should TARS fail. However, instead of dying alone in space, Cooper is pulled inside The Tesseract - the gravitational singularity that is maintaining the wormhole - created by the aforementioned "They".
But who are these beings (the "They) that gave humanity a helping hand?