Short Wave - 'Interstellar': Time Dilation And Wormholes Explained

Episode Date: September 9, 2025

Christopher Nolan’s Interstellar was a phenomenon in 2014. Set in the future, Earth has been struck by a global crop blight. Former NASA pilot Cooper (Matthew McConaughey) is pulled into a NASA mission to transport the human race to a new planet, via wormhole. Back on Earth, Cooper’s daughter, Murph (Jessica Chastain), attempts to complete an equation that will allow this mass-transport of humanity from Earth. Many scientists praised the film, particularly for its depiction of black holes. In this episode co-hosts Regina G. Barber and Emily Kwong talk about Interstellar with Star Trek scientific advisor and astrophysicist Erin Macdonald. They walk through wormholes, black holes and all the ways space-time stretches in the film. Interested in more on the science behind science fiction? Email us your question at [e-mail] – we may feature it in an upcoming episode!Listen to every episode of Short Wave sponsor-free and support our work at NPR by signing up for Short Wave+ at plus.npr.org/shortwave.See pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences.NPR Privacy Policy

This episode contains spoilers to Interstellar, a film that came out over a decade ago. You've been warned. You're listening to Shortwave, from NPR. Hey, Short Wavers, Regina Barber here. And Emily Kwong, and about a month ago, I asked Gina what I thought was an innocent question. Simply, have you seen Interstellar? We must confront the reality of interstellar travel. The movie about a dying Earth and NASA's plan to find humanity in New York.

home in another galaxy. This Christopher Nolan movie has haunted the astrophysics field for the past decade. Yeah. The tiniest synopsis I can give of Interstellar is that Christopher Nolan learned about relativity. That is Aaron McDonald. She's an astrophysicist who has studied space time and how it bends. Now, Aaron is the official scientific advisor for the Star Trek franchise. Dream job. So she knows a thing or two about movie representations of physics. Yeah. And Gina, until recently, I had no idea this was a Christopher Nolan movie and that he and his brother, Jonathan Nolan, consulted with astrophysicist

Kip Thorne, who was an executive producer on the movie. Yeah, Kip Thorne, like, he's a big deal in the field. He contributed to the LIGO detector, which led to the first detection of gravitational waves. And when I taught physics at the college level, like all of my students begged me to watch this movie. And here I am begging you to rewatch it. Lucky you.

It's two hours and 49 minutes. It's so long. I do like the beginning. Go back to bed there. I thought you were the ghost. Okay, this is going to come back. Emily, pay attention. This is a bookshelf.

It's covered with dust. That's concerning to me. It's disgusting. I do actually really like the beginning. The ending I didn't enjoy as much. I like the ending. But I really could respect the science in it. Like the most accurate depiction of a black hole in Hollywood history that was in this film.

Oh, cool. And the time dilation, you know, the idea that time can slow down and speed up depending on how space is stretched or squeezed. Like the idea that time slows down near a black hole. That was pretty accurate. Today on the show, science fact, not fiction. We go through the real physics in the film Interstellar. Specifically how the stretchiness of space time can make astronauts age differently and what gravity has to do with it all. I'm Emily Kwong.

And I'm Regina Barber. You're listening to Shortwave, the science podcast. from NPR. Okay, so this movie, Interstellar, starts with a blight killing all the crops. So the human race is eventually going to die on Earth because we don't have anything more to eat. M, did you like when this movie, like, started basically with, like, this environmental take? I mean, they're doing two things really well.

They're showing what the dust bowl of the 30s might have been like through, you know, the soil erosion and the big. storms, like whipping through the buildings and making all the plates dirty. And I learned this later, the footage of everyone except the main character was from a Ken Burns PBS documentary. Those are actual Dust Bowl survivors. Wow. I guess I can't describe it. It was just constant, just that steady blow of dirt. Wow. Wow. I got a feeling it was that too. And Aaron, how did you feel about this as somebody who, you know, really knows a lot about the physics in this in this movie, but it starts with this, like, really, you know, bleak farming crisis.

Farming crisis, yeah. Yeah, I mean, my father's a meteorologist and a environmentalist. And so, like, I've always grown up with conversations about climate change and global warming. Wow. I guess for me, like, I really appreciated how it showed what our future could look like, and it did feel really real. I wish it had been more explicit about being climate change and less about, like, a blight, you know, because I think it was, yeah, it was very kind of shied away from it.

That's true. And then so we, in the beginning of the movie, we think NASA is not there. People don't believe in the moon landing. And then- We were shocked by that. Gina and I turned to each other. They got rid of the moon landing and it all, and they did it without even blinking, those teachers.

That was not great. Oh my gosh. No. Okay. Okay. So we find out that NASA is indeed not dead. And that Matthew McConaughey's character is going to pilot the ship through a wormhole.

That's near Saturn. That's been placed there by some aliens. And they start talking about this thing called space time. What is space time? Right. Space time as a concept really is just our universe. We live in a four-dimensional universe of space and time. We have three dimensions of space. We can move forward, back, left, right, up and down. And we have control over that. And then we also move. forward in time at one second per second and we don't have any control over. No. But that's like literally how our universe is structured.

And so when we talk about space time, we're just talking about our universe, our space and our time that we're all experiencing. But they're the same, like not the same thing, but they are like part of something of a whole. Exactly. Yep. But when we start thinking about this warm hole in interstellar, they have this great, analogy, and we're looking at this wormhole, and theoretically one side is a black hole and one side

is a white hole, and there's this great scene in the movie which explains why this wormhole looks spherical. Dr. Romilly, he draws two Xs on a piece of paper and he connects them with a line. So a wormhole bends space like this, so you can take a short part through a higher dimension. So he folds the paper in half and he lines up the X's so they're right. right on top of each other, and then he punches the exes with his pen, creating a hole. What's a circle in three dimensions? Exactly. Spherical hole.

But who put it there? Do you think a wormhole could exist in real life? Mathematically, they could exist. I would argue that we just don't have any mechanism for how they would form. And then why was it so great? Wonderfully done in the film. What was so great in the film that they're visualizing, because we always think of it being like a hole or a funnel, you know, that we're looking at.

But it's not. It's we're in three dimensions of space, you know. And so you have to take that funnel and then extend it in all directions, which is really hard for us to conceptualize, because of the way we try to describe space time by using that sheet and picturing wormholes or black holes as funnels and tunnel. that you're able to travel through, but it would look spherical, basically. And that's how they portrayed it in the film brilliantly, and even them going into it and just seeing what we call gravitational lensing

where the light behind the wormhole is getting bent around and warped and distorted from this gravitational object from this wormhole was fantastic. Yeah. Aaron, the other thing we really want to ask you about is the time dilation part of the movie. specifically when the team visits the planet next to a black hole, Miller's planet, and time is such that every hour on Miller's planet equals seven years on Earth, why would being on a different planet change time itself? And how does that relate to gravity?

And our own planet. Yes. Yeah. So gravitational time dilation is what we call it. And it is a real thing. It's actually the most practical application of general relativity we have right now. our GPS system uses this idea of time dilation. So we are on Earth's surface.

We are deeper in Earth's gravity well than GPS satellites. And so GPS satellites experience time slightly faster than we do, but it's like fractions of a nanosecond. Is that because the gravity is pulling stronger on us? Yes. So it's slowing things down? We're in the, we're in the bent part more. Oh. Yeah, exactly.

Of space time. So it's, again, it's like fractions. of a nanosecond, but it matters enough for GPS precision if I'm on one side of the street or another. That does make a lot of difference. What they do such a good job in the film, I think, is just showing how it works. And they do it right. Where I do think it gets a little confusing is it's like the planet itself isn't the source of this time violation. It's the black hole that it's orbiting. That it's next to. Oh, yeah. Black hole pulling on the plane. planet makes this time slow. They make it seem like the planet itself is doing that. No, see,

the planet's in the bendy part too. Oh. The stretchy part. It's so close to the black hole. Yeah, in the sheet or really like fabric analogy, you know, this planet is like a bowling ball on that fabric. And it's so heavy that's bending space time. And that's going to slow down time, right? It's going to dilate it. And there is another way to dilate time, right? Yeah. So another way that we can talk about time dilation. is through traveling at great speeds. And again, space and time are intertwined. And so as you're moving really fast,

it kind of is like shrinking together. And so you're experiencing it differently than people who are not moving at those speeds. But that is what we call special relativity. So special relativity has to do with moving fast. General relativity has to do with gravity and mass and the distortion of space time. I never understood the difference.

Yeah. Got it. Neither did the movie. Before we go, we just got to talk about that black hole, gargantua. I know, I've read enough to know that it was basically the most accurate black hole depicted by Hollywood in its time. Beautiful. It was beautiful. Yes.

We have since then actually imaged black holes and their event horizons, both in our own galaxy, and in M87, which is another galaxy. And we were able to kind of see this fuzzy ring. And you can actually kind of see how the interstellar black hole, like if he zoomed back enough, it would look the same, which is really, really cool. Wow. What an accomplishment for the scientists.

Yes. The story aspect of him falling into the black hole, which really is like the wormhole or they connect. him to the wormhole. It becomes a warm hole. The way I kind of read it is that he entered a higher dimension through the black hole. But then the spaghettification happens where Matthew McConaughey is supposed to get stretched. And wouldn't that kill him?

Why does he not die? And what do you think of the spaghettification part of the movie? You're absolutely right. Spaghettiation should have happened. That is a technical scientific term for when you are falling into that gravity well, that steep, steep, heavy, heavy bowling ball that's pulling down the trampoline, eventually you're going to reach a point where your feet are experiencing higher gravity than your head and that you're going to get stretched apart, much like his ship got torn apart,

but then also he should have been torn apart, and he wasn't, and it was weird. And then he was able to experience all time and space in his daughter's bedroom. Yes, and it was love. It was love. So, Erin, do you think this film did a good job with science communication as like something to kind of help people understand what accurate science fiction is? I have a hot take on this. And I think the film succeeded from a science communication standpoint in that people were curious about relativity. They were curious about astrophysics. They were curious about these things that they had never understood before.

I think where the film fails epically. And I only think this now. I love this. 10 years later, after it came out in our current climate, I think it made people distrust scientists more. I think it made people distrust scientists more. And that's because the scientists in the film, everyone who was purely a scientist was duplicitous

or had some weird motivation. You're right. Oh, yeah. Just got chills. You're right. But Murph is not duplicitous. She's the only one. She does light her brother's corner.

But again, that was like, Oh my gosh, she is duplicitous too. Like everyone is, they're all kind of out for their own agenda. You're right. No one was just in the science for the sake of the science, except for maybe the guy who was left behind. Romilly. Wow. This is true.

Aaron, you know what? You know what? We have to write Christopher Nolitt a letter. I'm so sorry. Let's hope he listens. Yeah. Erin, Emily, thank you so much. I'm so glad we all watched this movie again and we got a chance to talk about it.

Thank you so much for coming to talk to us. Thank you. I really appreciate it. It was fun. This episode was produced by Rachel Carlson. It was edited by our showrunner, Rebecca Ramirez, and fact-checked by Tyler Jones. Jimmy Keely was the audio engineer. Beth Donovan is our senior director and Colin Campbell is our senior vice president of podcasting strategy. I'm Regina Barber. And I'm Emily Kwong. Thanks for listening to Shorewave from NPR.