Time Travel in ‘Interstellar’: Time Dilation and Causal Loops

FROM THE LECTURE SERIES: SCI-PHI—SCIENCE FICTION AS PHILOPSOPHY

By David K. Johnson, Ph.D., King’s College

Christopher Nolan’s Interstellar has possibly the best representation of time travel that is shown in any film. But, the question that arises is whether the situation experienced by the lead character could be called time travel at all. However, the film also creates a causal loop that seems self-explanatory. Read on to investigate how the film presents the idea of time travel.

Wormhole for space and time travel.
Time travel is a staple of science fiction, but it was best represented in the film Interstellar. (Image: imagophotodesign/Shutterstock)

Interstellar and Patterns in the Dust

Interstellar is set in a future where Earth has been decimated by ecological disaster. Joseph Cooper, a former NASA pilot, lives on a farm with his daughter, ‘Murph’. After a dust storm, they notice a strange pattern of dust on Murph’s bedroom floor. Murph thinks she has a ghost in her room, but Cooper realizes the pattern is due to gravitational variations emanating from her bookshelf.

Decoding the pattern leads them to a NASA installation, where they learn of NASA’s secret plan to save humanity. A wormhole that leads to a distant planetary system has appeared near Saturn. Years ago, NASA sent 12 astronauts through it to find a planet suitable for human life. Three of them—Miller, Mann, and Edmunds—have sent signals back through the wormhole that seem promising.

NASA asks Cooper to pilot the spaceship Endurance on a mission that would determine which planet is most habitable and then take 5,000 human embryos to that planet to restart the human race. Cooper and his team first explore Miller’s planet, and this is where perhaps the most scientifically accurate depiction of time travel in all of sci-fi is found.

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Gargantua and Time Dilation

image showing a black hole with its accretion disk
After traveling through a wormhole, the crew in Interstellar reach a planet circling a supermassive black hole. (Image: 42videography/Shutterstock)

Miller’s planet is orbiting a supermassive black hole called Gargantua, which is shown to warp space-time so magnificently that they can see its entire accretion disk, all at once.

The unique way it appears in the film was derived from equations that physicist Kip Thorne generated. Something else Kip Thorne figured out is that, given how close Miller’s planet is to Gargantua, for every hour spent on Miller’s planet, seven years will pass on Earth.

Cooper and his team leave the Endurance and go down to Miller’s planet in a shuttle. They find the wreckage of Miller’s ship in a large ocean, but the wreckage is still all together. This confuses them at first—after all, Miller landed on the planet years ago. But then they realize that if Miller landed 21 Earth-years ago, that would have been only three hours ago on this planet.

This is a transcript from the video series Sci-Phi: Science Fiction as Philosophy. Watch it now, on The Great Courses Plus.

Tide and Time

Then they realize another problem. An object that close to a black hole is subject to enormous tidal forces, and this means giant tidal waves. They had intended to only stay a few minutes to collect Miller’s data. But when a tidal wave nearly destroys them and floods their engine, they are stranded on the planet for a few hours. By the time they get back to the Endurance, 23 years have passed on Earth and the Endurance.

Cooper watches the messages from his family that have been building up while he was gone, and discovers that his daughter is now older than him and working for NASA. In effect, he has traveled in time.

This is actually what relativity predicts would happen if someone were to visit a planet close to a massive black hole like Gargantua. It’s all based on actual equations.

Is It Really Time Travel?

Of course, one might argue that this doesn’t really count as time travel; Cooper is just experiencing change more slowly.

A spaceman near a black hole.
The protagonist of Interstellar falls into a black hole, providing another possibility for time travel. (Image: Vadim Sadovski/ Shutterstock)

After the failure at Miller’s planet, Cooper and his team try to explore Mann’s planet—but it turns out that Mann is selfish and destructive. After Mann almost sabotages their mission, Cooper and the only other survivor, Dr. Amelia Brand, realize that their last hope is to try to reach Edmunds’s planet. They don’t have enough fuel, but they can use Gargantua’s gravitational forces to propel themselves there—but only if Cooper ejects himself.

He does, and is pulled into the black hole. Now, in reality, he’d likely be killed, stretched into spaghetti. But it’s not really known what lies beyond the event horizon of a black hole, the point at which its gravitational pull is so great that not even light can escape. So Nolan chose Cooper’s journey beyond the event horizon of Gargantua as an opportunity to take some artistic license.

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A Causal Loop

What Cooper finds beyond the event horizon is a tesseract—a 3-dimensional representation of a 4-dimensional object. In this case, it is Murph’s bedroom, at every moment of its existence, which he can view from behind her bookshelf. He slowly realizes that he can send her signals back through time—and thus he was the ‘ghost’ in her bedroom all along. It turns out that it’s Cooper sending messages to himself from the future—from inside Gargantua!

This raises a philosophical puzzle—a seeming paradox. Cooper went on the mission only because he sent Murph signals explaining how to get to the installation. But he was able to send Murph these signals only because he went on the mission. So what caused what here? This is what philosophers call a causal loop.

And it’s not the only causal loop in Interstellar. Later, the viewer learns that it was a race of 5-dimensional beings that placed the wormhole near Saturn, and that placed the tesseract inside the black hole; they wanted Cooper to be able to communicate with Murph so he could send her the information. So the 5-dimensional beings are saving the human race.

But, it turns out, the 5-dimensional beings are the human race—or, what the human race will eventually become, long after it has been saved. So, humanity still exists only because it saved itself, but it saved itself only because it still exists. It’s another causal loop.

Common Questions about Time Travel in Interstellar

Q. What secret NASA plan does the protagonist of Interstellar discover?

The protagonist in Interstellar discovers that NASA has a secret plan to save humanity by sending humans to a new planetary system that can be accessed through a mysterious wormhole.

Q. What happens when Cooper reaches Miller’s planet in Interstellar?

In Interstellar, when Cooper and his team reach Miller’s planet, they are stuck on it for a few hours after damage to their engines. When they return to their spaceship after a few hours, they find out that 23 years have elapsed on the ship and on Earth.

Q. What is the causal loop involving the protagonist in Interstellar?

The protagonist’s causal loop in Interstellar is that a future version of Cooper in a black hole creates the dust patterns that lead the past Cooper to act in a way that prompts his travel to the black hole.

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