Summary

  • Interstellar presents complex story ideas that may be confusing for certain viewers, requiring further explanation to fully understand the ending.
  • The film revolves around humanity's effort to find a new habitable planet, with big sci-fi concepts and betrayals adding to the complexity.
  • The ending reveals that Plan A was a farce and Plan B, involving genetic diversity through embryos, becomes the only hope for humanity's survival.

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 is 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.

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Why Humans Need To Leave Earth

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

Players standing on a baseball field as a sand storm approaches in Interstellar

Early on 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 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.

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The Plan For Survival

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

Cooper's Sacrifice Saves Humanity

Brandt scared in the water planet in Interstellar.

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" Explained

The Helpful Advanced Beings Are Not Aliens At All

An object near the black hole in Interstellar

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 mankind 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, as previously mentioned, 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.

Time And Space Used Against The Mission

The First Interstellar Planet Presents The Perils Of The Time Dilation Concept

Interstellar is based on the ideas of theoretical physicist Kip Thorne - specifically the notion that while people observe the universe in three dimensions, there could be at least five dimensions. In certain theories, it is posited that certain forces (in this case gravity) bleed through dimensions - meaning that, based on Newton's Laws, what people perceive as a finite calculation could actually have infinite implications. Christopher Nolan movies often focus on time but Interstellar is the greatest example of this. Interstellar's time distillation concept is outright exemplified in the first planet that the Endurance team visits.

In general, time on humanity's side of the wormhole moves faster than time on the uncharted side. Due to proximity to gravitational anomalies from a nearby black hole (Gargantua), time on the other side is exponentially slower - relative to the distance between an object and the black hole's gravitational pull. As a result, time on Miller's planet moves significantly slower: for every hour that the team spends on the water planet, seven years pass back home - a primary reason that Cooper is motivated to get off the planet as soon as possible (even before they realize it's a death trap).

Cooper knows that three hours on the planet's surface will cost him decades with his family. As Amelia suggests, the effect of gravity from the black hole on time was to blame for the Endurance team's unfortunate visit to Miller's planet in the first place - since what they perceived as years of positive beacon readings were actually mere minutes for Miller (who was killed by a wave moments after she landed).

The concept is further hammered home when, following the mission, Amelia and Cooper reunite with Romilly, who stayed behind on the Endurance to gather data (far from Gargantua) - and, in the three hours his team was gone, has lived twenty-three full years alone without them. Similarly, the crew receives video messages from back home and Cooper's children, Tom and Murph have also aged from the beginning of Interstellar's timeline - now full-grown adults (played by Casey Affleck and Jessica Chastain, respectively).

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Time And Space As Humanity's Salvation

How Cooper Communicates With Murph

A tangible effect of gravity on spacetime is also responsible for Cooper's ability to communicate with young Murph when inside the Tesseract. Inside the machine, gravity bleeds through to other dimensions in time and space, allowing Cooper to spell out a message ("S-T-A-Y") by pushing books off of Murph's shelf - or communicate map coordinates to the past version of himself by spreading dust across the floor (in binary language).

Most importantly, the fifth-dimensional communication through gravity (made visible by three-dimensional objects back on Earth) enables Cooper to gently manipulate the hands on Murph's watch - transferring the data that TARS acquired with morse-coded watch ticks. Subsequently, translating that coded data gives Murph all the information she needs to drastically advance humanity's understanding of space and time - as well as complete Plan A.

How Did Coop Survive & What Happens To Amelia

Cooper's Bittersweet Reunion With Murph

When it comes to how Cooper survives and reunites with Murph, Nolan simply reapplies the same theory that has been present the entire film. Given that time moves slower near the gravity pull of the black hole, Cooper's ejection from the Tesseract is only seconds for him, but over half a century for the rest of humanity.

If the ratio of time on Miller's planet was 1 hour for every 7 years on Earth, the proportion would be skewed exponentially at the absolute center of the Tesseract singularity. As a result, while it appears to Earthbound humans that TARS and Cooper have been floating out in space for nearly ninety years, they were actually only out there for mere seconds as they perceived it. The disproportionate relativity allows Cooper to survive and reunite with Murph - who, living on the faster-moving side of the wormhole, is now over 100 years old.

Knowing that Cooper has nothing left to live for in a post-Earth existence (since his son Tom is presumed dead and Murph will soon join him), Murph reminds her father that, through the wormhole, Amelia is just beginning to set up Plan B on Edmonds' planet. At the same time, it is revealed that even though Edmonds' planet is actually habitable, the astronaut himself did not survive the landing - leaving Amelia alone at the colonization site.

Using a reversal of the film's primary relativity theory, Cooper hops into a ship, with the knowledge that even though nearly one hundred years have passed since the Endurance first set out, time on the other side of the wormhole is moving much slower - meaning that a second trip should allow him to reunite with Amelia on Edmonds' planet only a short time after Cooper first sacrificed himself and dropped into the singularity. The ending to Interstellar doesn't reveal if Cooper and Amelia reunite, but it certainly hints at a happy ending.

The Meaning Of Interstellar

The Repeated Quote From Prof. Brand Sums Up The Movie

Matthew McConaughey's Cooper and his daughter look up at the sky in a poster for 2014's Interstellar by Christopher Nolan

Interstellar is a film about venturing into the unknown. Much like Nolan's mind-bending sci-fi drama Inception the main takeaway from the end of Interstellar is not that Cooper and Amelia will be reunited (though it's possible that they will). Rather the ending, and Cooper's departure to find Amelia illustrates what Prof. Brand regularly suggested by way of poet Dylan Thomas:

"Do not go gentle into that good night, old age should burn and rage at close of day. Rage, rage against the dying of the light."

The movie seems to posit that humanity is at its best when people throw themselves passionately into the unknown - in search of love and discovery. In the end, that is what Cooper intends to do.

Here's a chart that explains what happened in visual terms (CLICK TO SEE FULL SIZED VERSION):

Interstellar ending spoilers poster infographic

  • Interstellar Poster Ice
    Interstellar
    Summary:
    A group of explorers make use of a newly discovered wormhole to surpass the limitations on human space travel and conquer the vast distances involved in an interstellar voyage.
    Release Date:
    2014-11-07
    Cast:
    Anne Hathaway, Matthew McConaughey, Jessica Chastain, Ellen Burstyn, Michael Caine, Bill Irwin
    Director:
    Christopher Nolan
    Rating:
    PG-13
    Writers:
    Christopher Nolan, Jonathan Nolan
    Runtime:
    2h 49m
    Genres:
    Sci-Fi, Drama, Thriller, Action, Adventure, Fantasy
    Budget:
    165 million
    Studio(s):
    Warner Bros. Pictures, Paramount Pictures
    Distributor(s):
    Paramount Pictures, Warner Bros. Pictures