'Interstellar': Time Dilation And Wormholes Explained

Summary

Podcast Summary

Podcast: Short Wave (NPR)
Episode: "Interstellar: Time Dilation And Wormholes Explained"
Date: September 9, 2025
Hosts: Emily Kwong & Regina Barber
Guest: Dr. Erin MacDonald (Astrophysicist, Scientific Advisor for Star Trek)

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Overview of the Episode

This episode takes a deep dive into the science behind Christopher Nolan’s film Interstellar, focusing on its portrayal of concepts like spacetime, wormholes, time dilation, and black holes. Hosts Emily Kwong and Regina Barber are joined by astrophysicist Dr. Erin MacDonald, who helps disentangle the film’s fact from fiction while highlighting notable scientific achievements and missteps. The conversation covers the film’s realism, the real-world physics it drew from, and its impact on science communication.

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Key Discussion Points & Insights

1. Environmental Catastrophe and Science Fiction Set-up

• [04:15–05:49] The film’s opening, depicting a worldwide crop blight and dust bowl, is lauded for its realism and subtle (perhaps too subtle) reference to climate change.
• Emily notes the use of actual Dust Bowl survivor footage for realism.
  • "They're showing what the Dust bowl of the 30s might have been like..." (Emily, 04:32)

2. Realism in Scientific Advisory & Black Hole Depiction

• [01:17–02:21] The role of physicist Kip Thorne as scientific consultant is spotlighted.
  • Regina highlights Thorne’s gravity research and how even her physics students were obsessed with the movie’s accuracy.
• [12:07–12:33] The film’s rendering of black holes, especially “Gargantua,” is celebrated for its accuracy.
  • "It was basically the most accurate black hole depicted by Hollywood in its time." (Emily, 12:07)
  • Dr. MacDonald emphasizes how the look aligns with real black hole images received after the film’s release.
    • "You can actually kind of see how the Interstellar black hole...would look the same, which is really, really cool." (Erin, 12:25)

3. Explaining Spacetime and Wormholes

• [06:16–08:16] Erin breaks down the concept of spacetime (four dimensions) and the visualization of wormholes.
  • The classic "folding paper" analogy from the film is discussed, emphasizing why a wormhole would look spherical in three dimensions, not just like a “hole” or “tunnel.”
    • "It's...really hard for us to conceptualize...but it would look something spherical, basically. And that's how they portrayed it in the film. Brilliantly." (Erin, 08:09)
• The concept of gravitational lensing is praised in the film’s visual effects.

4. Time Dilation: The Science Behind “One Hour = Seven Years”

• [09:15–11:15] The mechanics of time dilation, as shown in the infamous “Miller’s planet” sequence, are dissected.
  • Erin clarifies that time dilation is due to gravitational effects (general relativity), not just planetary conditions.
    • "Gravitational time dilation is...the most practical application of general relativity we have right now. Our GPS system uses this..." (Erin, 09:37)
  • GPS satellites experience time at a different rate than people on Earth due to varying depths in the planet’s gravity well.

5. Special vs. General Relativity

• [11:15–11:51] Time dilation via high speeds vs. high gravity is explained.
  • Special relativity (high speed): "as you're moving really fast...you're experiencing it [time] differently...That's special relativity."
  • General relativity (gravity/mass): "has to do with gravity and mass and the distortion of space."
  • Erin admits the movie blurs this distinction:
    • "I never understood the difference. Got it." (Emily, 11:47)
    • "Neither did the movie." (Erin, 11:51)

6. The “Spaghettification" Conundrum

• [12:56–13:42] In the final act, the film’s protagonist survives entering a black hole, defying the science of “spaghettification” (being stretched by gravity).
  • "Spaghettification should have happened...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." (Erin, 13:09)

7. Science Communication & Trust in Scientists

• [13:47–14:59] Erin shares a “hot take” on the film’s legacy in science communication.
  • "People were curious about relativity...they had never understood before. [But] it made people distrust scientists more..." (Erin, 13:59)
  • The portrayal of scientists as duplicitous is criticized, with only a few exceptions (notably Murph).

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Memorable Quotes

• On the value of the film’s science:

  • "Like the most accurate depiction of a black hole in Hollywood history. That was in this film."
    — Regina Barber, 02:20

• On spacetime:

  • "We live in a four dimensional universe of space and time...we also move forward in time at 1 second per second..."
    — Erin MacDonald, 06:26

• On time dilation’s real-world application:

  • "Our GPS system uses this idea of time dilation... GPS satellites experience time slightly faster than we do, but it's like fractions of a nanosecond."
    — Erin MacDonald, 09:37

• On the film’s impact on trust in scientists:

  • "Where the film fails epically...I think it made people distrust scientists more. And that's because the scientists in the film...was duplicitous or had some weird motivation."
    — Erin MacDonald, 13:59

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Notable Timestamps

• 01:05 — Introduction of Dr. Erin MacDonald
• 06:26 — Erin explains spacetime and wormholes
• 09:37 — Time dilation explained via GPS analogy
• 12:07 — Discussion of Gargantua’s visual accuracy
• 13:09 — Erin evaluates the scientific accuracy of “spaghettification”
• 13:59 — Erin critiques the film’s portrayal of scientists

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Conclusion

The hosts and their guest strike a balance between playful fan discourse and serious science. Interstellar is lauded for getting many physics concepts right, thanks to real scientific consultation, but also critiqued for missed opportunities in accuracy and science communication, especially regarding representation of scientists. The episode supplies both fans and newcomers to the science behind Interstellar a welcoming, accessible entry point into complex theories, while inviting reflection on media portrayals of science.

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Transcript

[A]

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[B]

Edu this episode contains spoilers to Interstellar, a film that came out over a decade ago. You've been warned.

[C]

You're listening to shortwave from npr.

[B]

Hey, short wavers. Regina Barber here and Emily Kuang.

[C]

And about a month ago, I asked Gina what I thought was an innocent question. Simply, have you seen Interstellar?

[D]

We must confront the reality of interstellar travel. Martha.

[B]

The movie about a dying Earth and NASA's plan to find humanity a new home in another galaxy. This Christopher Nolan movie has haunted the astrophysics field for the past decade.

[C]

Yeah. Yeah.

[D]

The tiniest synopsis I can give of Interstellar is that Christopher Nolan learned about relativity.

[C]

That is Erin MacDonald. She's an astrophysicist who has studied spacetime and how it bends. Now, Erin is the official scientific advisor for the Star Trek franchise.

[B]

Dream job.

[C]

So she knows a thing or two about movie representations of physics.

[D]

Yeah.

[C]

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.

[B]

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.

[C]

And here I am begging you to rewatch it. Lucky you. It's 2 hours and 49 minutes.

[B]

It's so long. I do like the beginning.

[C]

Go back to bed, man. I thought you were the ghost.

[D]

No.

[B]

Okay, this is going to come back. Emily, pay attention. This is a bookshelf.

[C]

It's covered with dust. That's concerning to me.

[B]

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.

[C]

Oh, cool.

[B]

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.

[C]

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.

[B]

And I'm Regina Barber. You're listening to Shortwave, the science podcast from npr.

[A]

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[B]

Okay, so this movie Interstellar starts with a blight killing all the crops. So the human race is eventually gonna die on Earth because we don't have anything more to eat. Em, did you like when this movie started basically with this environmental take?

[C]

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 building 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. I guess. I can't describe it. It was just constant, just that steady blow of dirt.

[D]

Wow.

[B]

Wow. I got a feeling it was that too. And Aaron, how did you feel about this as somebody who really knows a lot about the physics in this movie, but it starts with this really bleak farming crisis. Farming crisis?

[D]

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.

[B]

Wow.

[D]

I guess for me, like I really appreciated what it show 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, you know, because I think it was. Yeah, it was very kind of shied away from it. That's true.

[B]

And then so 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.

[C]

Gina and I turned to each other feelings. They got rid of the moon landing and it all, and they. And they did it without even blinking, those teachers.

[D]

That was not good.

[B]

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 this ship through a wormhole.

[C]

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?

[D]

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 1 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.

[B]

But they're the same. Like, not the same thing, but they are like part of something of a whole.

[D]

Exactly. Yep.

[B]

But when we start thinking about this wormhole 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, like, great scene in the movie which explains why this wormhole looks spherical. Dr. Romilly, he draws two X's on a piece of paper and he connects them with a line.

[C]

So a wormhole bends space like this so you can take a shortcut through a higher dimension.

[B]

So he folds the paper in half and he lines up the X's so they're right on top of each other. And then he punches the X's with his pen, creating a hole.

[C]

What's a circle in three dimensions?

[D]

Sphere.

[C]

Exactly. Spherical hole. But who put it there? Do you think a wormhole could exist in real life?

[D]

Mathematically, they could exist. I would argue that we just don't have any mechanism for how they would form.

[B]

And then why was it so great? Wonderfully done in the film.

[D]

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 tunnels that you're able to travel through. But it would look something spherical, basically. And. 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.

[C]

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. And how does that relate to gravity.

[B]

And our own planet?

[C]

Yeah.

[D]

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.

[C]

Is that because the gravity is pulling stronger on us?

[D]

Yes.

[C]

So it's slowing things down.

[B]

We're in. We're in the. We're in the bent part more.

[D]

Oh, yeah.

[B]

Of space time. So it's.

[D]

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. That does make a lot of difference. What they do such a good job of 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 dilation. It's the black hole that it's orbiting.

[C]

Black hole pulling on the planet makes this time slow. They make it seem like the planet itself is doing that.

[B]

No, see, the planet's in the bendy part, too. Oh, the stretchy part.

[D]

It's so close to the black hole. Yeah.

[B]

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?

[D]

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. Um, 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.

[C]

I never understood the difference. Got it.

[D]

Neither did the movie.

[C]

Before we go, we just gotta 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.

[D]

Beautiful.

[C]

It was beautiful, yes.

[D]

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 you zoomed back enough, it would look the same, which is really, really cool.

[C]

Wow. What an accomplishment for the scientists.

[D]

Yes. The story aspect of him falling into the black hole, which really is like the wormhole, or they connect him to the wormhole, like, it becomes a wormhole. The way I kind of read it is that he entered a higher dimension through the black hole.

[C]

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?

[D]

You're absolutely right. Spaghettification 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 going to reach a point where your feet are experiencing higher gravity than your head, and 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.

[B]

And it was love.

[C]

It was.

[D]

Love.

[B]

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?

[D]

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. Big were 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 science, 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.

[C]

Yeah.

[B]

Just got chills. Yeah, you're right.

[C]

But Murph is not duplicitous.

[B]

She's the only one she does light.

[C]

Her brother's corn on.

[B]

But again, though, she does. Oh, my God, she is duplicitous, too.

[D]

Like everyone is. They're all kind of out for their own agenda.

[B]

You're right.

[D]

No one was just in the science for the sake of the science. Except for maybe the Romilly. Yeah, Romilly.

[C]

Wow. This is true. Aaron, you know what? You know what? We have to write Christopher Nolan a letter. He's got to be a little more thoughtful.

[B]

Let's hope he listens.

[C]

Yeah.

[B]

Aaron, 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. It was a pleasure coming to talk to us.

[D]

Yeah. Thank you. I really appreciate it. It was fun.

[C]

This episode was produced by Rachel Carlson, it was edited by our showrunner, Rebecca Ramirez, and fact checked by Tyler Jones. Jimmy Keeley was the audio engineer, Beth.

[B]

Donovan is our senior director, and Colin Campbell is our senior vice president of podcasting strategy. I'm Regina Barber.

[C]

And I'm Emily Kwong. Thanks for listening to shore wave from NPR.

[A]

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