Interstellar Ending & Space Travel Explained

The Interstellar ending is still debated by fans years later. Interstellar follows humanity’s effort to find a new habitable planet after Earth is ravaged by environmental catastrophe. Former NASA pilot-turned-corn farmer Cooper (Matthew McConaughey) is brought on board the mission to save humanity, but it means he will have to leave his children behind on Earth while he is gone for years. As it turns out, the mission is far more complex than initially thought, with betrayals and mistakes made. Meanwhile, the answer to humanity’s salvation is not what they expected.

Like many Christopher Nolan movies, Interstellar presents a number of complicated story ideas that may be confusing for certain moviegoers — especially after a first viewing. There are big sci-fi concepts at play, from the environments of the different planets to the way Nolan plays with time. It all builds to an ending that ties everything together but it’s not always easy to follow how it is all done. In order for some viewers to truly understand the Interstellar ending, there is some further explanation needed.

Why Humans Need To Leave Earth

Interstellar Sets Up The Final Generation Of Humans Who Can Survive On Earth

Early in the film, it’s revealed that the US government has secretly been funding a NASA project to find humankind a new home, since Earth in Interstellar‘s version of the future 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,” has 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, humanity’s understanding of distance is based on 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 Cooper reunites with Prof. Brand, NASA has already sent 13 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.

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The Plan For Survival In Interstellar

NASA Develops Two Plans To Save 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 the 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 and/or the Endurance take too long investigating potential homeworlds, NASA harvested a bank of fertilized human embryos to 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 members. In this scenario, the team settles down on the most habitable planet and raises the first generation of embryos with each subsequent generation helping to raise a new set of embryos (as well as reproduce naturally).

Later it is revealed 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.

Committing To Plan B In Interstellar

Cooper’s Sacrifice Saves Humanity

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”.

“They” In Interstellar Explained

The Helpful Advanced Beings Are Not Aliens At All

Cooper and the other Interstellar characters assume “They” are an advanced extraterrestrial (or supernatural) race who have unlocked the mysteries of dimensional manipulation. For some unknown reason, they decided to use this to help humankind escape their doomed planet. The NASA team believes the beings may be unable (or unwilling) to communicate directly with humans, specifically that “They” are fifth-dimensional, having transcended the three-dimensional ways of understanding the universe. Brand thinks “They” have laid out a series of rudimentary breadcrumbs (binary messages) and advanced technology (the wormhole) for humans to follow to save themselves from annihilation.

However, as revealed in Interstellar‘s final act, what NASA postulated was a single alien race is actually two separate but related entities:

• Future humans who have mastered the laws of the universe, allowing them to manipulate time and space.
• Cooper attempting to communicate with his daughter inside the “Tesseract”, which was built for him by the future humans.

As a result, most of the unexplained phenomena that NASA attributes to the beings are actually actions that Cooper takes in the future. When Cooper sacrifices himself to ensure Plan B, he is caught in the black hole’s gravitational pull but, instead of dying, ejects from his ship, landing inside The Tesseract (aka the wormhole’s gravitational singularity) — a place where the laws of space and time become infinite.

Knowing their own past, specifically, the events that led to their salvation (and exodus from Earth), it was humans who built the Tesseract at some point far in the future and then, using their advanced knowledge of fifth-dimensional physics, manipulated spacetime to place the machine into the past (where NASA finds it orbiting Saturn).

Since Cooper and Murph are remembered as the saviors of humanity, the fifth-dimensional humans, who can observe past, present, and future, custom-build The Tesseract for Cooper so that he can communicate with his daughter in the past and relay the data that TARS had collected inside the singularity. To that end, the Tesseract is a filter that translates the fifth dimension into three-dimensional visibility (tuned to Murph’s room), allowing Cooper to visit his daughter at any point in time (and “shake” Amelia’s hand during the initial launch).

As with most time-travel movies, people will debate whether the plot results in an unexplained paradox (how did future humans first survive to make a Tesseract – given that there would have been no Tesseract to save them), but Nolan leaves that particular detail up for post-viewing debate.