TED Talks Daily - A cosmologist's guide to the end of the universe | Katie Mack and Debbie Millman

Episode Date: July 25, 2026

How does studying the end of time change your perspective of life on Earth? Cosmologist and TED Fellow Katie Mack joins designer and podcaster Debbie Millman to talk about the story of the cosmos — from the Big Bang's ancient light still glowing across the universe to the five ways it might all come to an end — plus what aerobatic flying taught her about staying present. Hosted on Acast. See acast.com/privacy for more information.

You're listening to TED Talks Daily, where we bring you new ideas to spark your curiosity every day. I'm your host, Elise Hugh. Cosmologist and TED fellow Katie Mack spends her days thinking about things that are almost impossible for the human mind to comprehend. Dark matter, black holes, the Big Bang, even the possible end of the universe. I can't conceptualize these scales really any more than anyone else can. But the work itself is very tied to our humanity because these are just things that come out of our imaginations that are tested with the data

and we are constantly making choices and constantly trying to better understand the universe we live in. In this conversation with Debbie Millman, host of Ted's Design Matters podcast, Katie shares more about the strange and beautiful creativity behind theoretical physics, the childhood curiosity that first pulled her toward the cosmos and what it means to study a universe that is so much bigger and longer lasting than we can possibly imagine.

When you read a story, you want to know the beginning, the middle, and the end. I feel like it's really part of how we fit into this cosmos. Even though Katie's work can make humanity seem very, very small, this conversation is grounding, reminding us that meaning doesn't have to come from lasting forever, and maybe it's all about how we learn to be present and pay attention to the strange, temporary moment we're in. It's coming up right after a short break.

And now our TED Conversation of the day. Katie. Yes. Hi. Hi. I understand that you earned your private pilot license during the pandemic and are now doing aerobatic training.

I've heard of acrobatic training, but never aerobatic training. Tell us what that is. Yeah, so aerobatics is. is flying the airplane in unusual ways. So things like loops and spins and rolls and really learning how to control the airplane at all areas of the envelope,

really beyond the normal straight and level flying. And it's super fun because it's like creating your own roller coaster in the sky. And it's not scary? It can be scary sometimes. So you're a daredevil? No. I enjoy it because it, It's challenging, it's interesting, it's a different perspective,

and it's a way to learn enough about how the plane behaves to be safer when you're trying to just fly a strain level. Sometimes things happen, and you need to learn how to recover. So I do it because it's a challenge because I enjoy it. I'm not an adrenaline junkie in any way, but it's just something that I feel like it can make you a better pilot, and it's just a different way of seeing the world. Has flying given you a different perspective on your work as a cosmologist?

I think what it has done is it's allowed me to have a space where I don't think about work, actually. It's when you are fully, fully absorbed in something and fully focused, you get into this zone where nothing else can touch you. And when you're flying, you have to be focused. You can't think about other things because things will go very badly. if you take your focus away from what you're doing. And so I really enjoy that opportunity to just be in the moment, be in the plane, have that different view of the world.

And I enjoy the extra challenge of trying to do something else. Your grandfather worked on the Apollo 11 mission. Yes. And I believed he saved the lives of the Apollo 11 astronauts. Can you share some of that story with us? Yeah, so my grandfather was a meteorologist in the Navy, and he worked on things like creating satellite views of the weather with these new rockets that they just developed,

and he was asked to help with the Apollo 11 mission, and his job was to figure out if the weather conditions at the splash down site when the capsule came back, we're going to be okay, right? Because you don't want to come into a storm when the capsule's coming in on the parachutes. And he was checking all the usual charts, and it looked fine,

but he knew there was a secret satellite that was a weather satellite, but it was a secret because it could also be used for spying, and he had been in the Navy. And he wanted to make sure that there was nothing in the splashdown area that was going to be a problem. So he went over to his connections through the Navy

and checked on that satellite, and it turned out that the splashdown zone that they designated had a storm coming, something called Screaming Eagle Thunderclouds, something really bad that was... Does not sound good. No, no. And apparently it was bad enough

that it could have just ripped the parachutes right off the capsule as it was coming in. And so he managed to convince NASA to move the splashdown site just 72 hours before the splash down, and he couldn't tell them why. Because NASA is a civilian agency, they couldn't know about these secret satellites. And so he had to just...

just used the weight of his expertise and his reputation to tell them, you have to move the splash down. I cannot tell you why. Here's an alternative. And so they moved it a few hundred kilometers in some direction, and it was fine. So basically it was a trust me, I've got this. Yeah, but they did say we are also going to send some planes to the original site, and if it's fine there, you're in trouble.

So they did send the planes. There was a storm, but the astronauts were fine. You said you were a curious child drawn to the night sky before you even knew the word cosmology. Were you influenced by your grandfather's work? I was definitely influenced by him as a scientist. So I knew him, I didn't know him through his Apollo 11 work because that was actually classified until I was sort of an adolescent. But I knew him through just his expertise about the weather. I knew him through, he was a volunteer at the Monterey Bay.

aquarium. So he knew everything about the sea animals. And I just love to see him talk about the things he was excited about. And he had gone to Caltech as a student to learn about meteorology. And so I knew a little bit about Caltech and about the, you know, all the nerdy people there doing fun, exciting science. And so he was definitely an influence in getting me excited about science. Katie, you've written about how you were just 10 years old, 10 years old when you read Steve. even Hawking's book, A Brief History of Time. I had to read that book really, really slowly to grasp what he was writing, and I did that when I was 30.

Yeah, yeah. How did you first hear about the book when you were 10 years old, and what provoked you to pick it up and start reading it? I think that I, you know, I had exposure to a lot of different kinds of science through just my family. I think my family picked up on the fact that I was curious. I was always a tinkerer. I was taking things apart and putting them back together,

sometimes correctly. And they knew that I was trying to understand everything. And so I had subscriptions to children's magazines about science and stuff like that. And my mom is a big science fiction fan. And so I was reading her science fiction stuff. And every once in a while there would be like a public talk about science somewhere in our area. We lived in the L.A. area. And so she'd take me to talks by scientists.

And so I think I just kind of accumulated some of those books. And when I read Hawking's book, I didn't understand very much of it as a 10-year-old. What kept you reading it then? I just wanted to know. I really wanted to try to understand this stuff. And I thought, you know, if I keep studying, I'll get this and I'll maybe be able to work in this area. I didn't know before I read that book that you could be a cosmologist. You know, I saw that Stephen Hawking is called a cosmologist.

I was like, you know, what is that? What is that work? And I thought, well, that's what I want to do. I want to study the universe. I want to study the Big Bang and black holes and space time. I thought that sounded really cool. You attended Caltech for your undergrad education and graduated with a degree in physics.

And you said that theoretical physics is not just a discipline of equations, but of imagination. Yeah, yeah. How so? You know, theoretical physics in general is the attempt to create kind of a mathematical cartoon of the world. So, you know, we have certain observations, we get data, and we try to find a way to connect that data to whatever the input was. And so we build sort of mathematical machine as a way to figure out how that all fits together. And you have to be creative. You have to,

you know, think about, like, what are the possibilities here? What are the things, you know, what kinds of symmetries can I find in this system, you know, how are these things similar to these other things. So it's very creative, it's very interactive. You know, there's the theoretical physics community is extremely collaborative. You know, everybody's gathered around chalkboards arguing about equations and, you know, going to conferences all the time giving talks, you know, we don't, we don't sit in isolation, you know, just writing down equations by ourselves. It's, it's always a conversation. And it's always, it's, it's very much a creative, imaginative kind of work. You went on to Princeton University for your PhD, where your doctor,

research focused on early universe cosmology, cosmic inflation, and dark matter. And you've written about how much of cosmology is trying to tell a story from the faintest traces of light. Katie, how are you able to decipher those earliest traces? And what are some of the most important things you've learned about that light? Yeah, so I think in that, in that I must have been talking about the cosmic microwave background, which is light that's all around us in the universe. If you tune a microwave receiver, so microwaves are just a kind of light, a kind of electromagnetic radiation. And if you tune your receiver to the right frequencies, you can see this background of just a glow all around you everywhere in space. And that's the light from the big bang.

And the way that we know that what that is is that we can look at the spectrum of that light, how much energy is at different frequencies. And we can see that the spectrum is exactly the same spectrum you get when something is glowing because it's hot. Like if you take a poker and you stick it in the fire, it glows red, and that has a certain spectrum, a certain distribution of light.

And it's just anything you heat up that glows, it glows because it's hot. It's because of the way the particles are moving around and creating light. And this background light has exactly the same spectrum and it's everywhere in space. And so what it is is, is if you look far enough away,

in any direction, you're looking so far away that the light has taken a really long time to get to you. You know, light takes some time to travel, so, you know, even in this room, you know, you're maybe six feet away from me. It takes about six nanoseconds for the light to get from you to me. So you're six nanoseconds in the past to me. And you are to me. And you, and I am to you. But if I look far enough out in the cosmos, I can look billions of years in the past. And I'm seeing directly that the past. And if you look so far away that you're looking 13. billion years ago, you're looking at the time when the whole universe was glowing with heat because it was in this hot, dense phase of the very early universe.

And so you see that glow very directly in the cosmic microwave background. And that's something that we can study. We can study that glow because we're looking directly at the very, very early universe. It's incredible. Given that light travels, the light that is being picked up in this background, where is that going? It's just diffusing through space. So it's going in every direction.

So it's just continually moving. Yeah, yeah. So if you turn on a light bulb, the light moves out in every direction and the light from the time the whole universe was glowing with heat, you know, that light was just moving in every direction. Eventually the universe cooled down

and the light kept traveling in every direction. And the places we see it at the sort of edges of our vision in the universe, that light is also going away from us, but the part that's going toward us, we see, and we see that background radiation. Voyager is not even one full light day away from Earth, but it's going to be another 40,000 years

before it encounters another celestial body. Cosmology often deals with scales that defy comprehension. How do you hold on, to the human scale with this sort of infinite, what seems like it's infinite. I mean, I can't conceptualize these scales really any more than anyone else can. You know, we talk about, you know, billions of light years and all this stuff. And I just have to write down the number and trust it.

I don't have a sense, you know, I can't hold in my head this notion of, you know, that much space or that much time. So for me, you know, there's a kind of, you know, sort of a ruler in my mind of, you know, million, billion, trillion, and I don't have a sense for how far apart those are. I just know that these are the scales that I'm working with. And then I think about on the human scale, you know, what I can do as a scientist to try to understand it. But, you know, in my work, even individual galaxies are not that important.

Let alone us. Yeah, I mean, professionally, all the human stuff is kind of lost in the weeds. But the work itself is very human because we're all working together and we're all having this continual conversation. And the mathematical models we're building are very much tied to our humanity because these are just things that come out of our imaginations that are tested with the data. And we are constantly making choices and constantly,

trying to better understand the universe we live in. What provoked you to choose a field that is primarily about how we end? So I am really interested in the whole story of the universe. So I've done a lot of work about the beginning of the universe, and I've worked on how the universe evolves over time, how the first stars formed, how the dark matter, this invisible stuff that holds galaxies,

together how that's evolved over time and brought galaxies into existence. And at some point I started getting really curious about the end as well. And I just, you know, we know the universe is evolving and changing and we know that it's not going to be the same forever. It's going to be different. And it's, we know that there was, it was different in the beginning and it's changing and it's going to be real different in the future. And so I'm really curious what that ending looks like.

And so that's why I wrote a book about the end of the universe, just because I wanted to talk about, you know, what are the possibilities? What are we thinking about how the universe will end? And, like, what is that whole story? You know, when you read a story, you want to know the beginning, the middle, and the end. And, you know, I feel like it's really part of how we fit into this cosmos. Your book is titled The End of Everything.

And in it, you explore five possible endings for the cosmos. The Big Crunch, Heat Death, the Beads. big rip, vacuum decay, and bounce. Were there others that you left out, or is this the only five options? So I focus on sort of five categories of endings that are things that are actually talked about in the physics literature. So all of these are possibilities that physicists have put together models. We've worked out what the physics would be in each of these scenarios.

there are ways to tweak each of these where they're going to be a little bit different. But basically, you know, in terms of the whole cosmos, there are only a finite number of ways that it can be destroyed. Like it can collapse, it can keep going. You can have these weird transitions where there's basically a bubble of a new kind of space that spreads through the universe and destroys everything.

And then there's like cyclic models. And there are a lot of different ways where the universe can end and start again or the beginning of our universe can be the end of a previous universe and there are a few of those that I talk about in the book as well. Yeah, that to me, fills the most hopeful. You've said that writing this book

changed your relationship to time. Yeah. In what way? You know, talking about the very, very distant future of the universe, you really think about this kind of deep time idea and how, you know, the bit of time we live in is so small. And the bit of time humanity has existed in is so small. And there was time before us, and there's going to be so much time after us.

And it made me think a lot about not just time, but like how our impact on the world. You know, we are really unimportant in the universe. Just to say, like, humanity is completely, insignificant in the cosmos in every possible way you could imagine. Optimistic morning, folks. I mean, but, you know, I mean, we are, it's impressive that we know so much, but even though we are so insignificant. But, you know, it made me think about like, you know,

everything is going to end at some point, and there's not going to be some, you know, final thing that makes it all worthwhile, right? At some point, everything will be destroyed. It kind of won't have mattered that we were here. So when we think of it, about how to find meaning and purpose, it's, you know, it has to be something that's self-contained, you know, something that exists in the universe now. And what is, you know, how do we find meaning in the moment? How do we find meaning that doesn't depend on it all being wrapped up with a tidy

bow, you know, at some future point? And that really made me think differently about what's important in my life, what to be upset about or not upset about. Because, you know, we are just temporary and we were doing the best we can while we're here. Katie, in addition to your work in theoretical astrophysics, cosmology, writing, and arrow acrobatics, you're also a poet. I've done a little bit of poetry, yeah. I'm wondering if it's possible. I know we talked a little bit about this ahead of time, but my Ted friends and I asked if you would read one of your poems today on the TED next stage, and you agreed. How lucky are we?

So can you tell us a little bit about what you're going to share with us today? So I've written a few things here and there. I've done a lot of science writing. I've written a few poems, and at some point I was contacted by a sort of graphic design company saying that they were putting together a sort of reel of their work, and they wanted a poem,

they wanted to have a poem to go along with it, Could I write a poem about something sciencey, and then they would illustrate it? They were called Finger Industries now. They're called Ouch, Ouch, Health. And so I wrote this poem for their sort of demo reel. Cool. Wonderful. Would it be okay for you to stand?

Sure, sure. Excellent. Thank you. Okay. So the poem is called Constructs. What do you see when you look at the world? This infinite variety of objects, colors, textures, weights, flavors.

What makes each person, animal, object, unique, special? There are around 90 chemical elements naturally found on this planet. But each one, hydrogen, oxygen, or carbon, is just a construct. A tiny, shivering mass of the same protons, neutrons, and electrons found in any other. Same ingredients, different recipe. We are not essentially our constituent parts. We are the knowledge that unites them.

Katie Mac. Thank you so much. That was Katie Mac in conversation with Debbie Millman at TED Next 2025. If you're curious about Ted's curation, visit ted.com slash curation guidelines. And that's it for today. Ted Talks Daily is a podcast from TED.

This episode was fact-checked by the TED Research Team and produced and edited by our team, Martha Estefanos, Oliver Friedman, Lucy Little, Emma Tobner, and Tonzika Sunglar Nivon. Additional support from Daniela Ballerazo, Christopher Faisi Bogan, Valentina Bohanini,

Ban Ban-Chang, Brian Green, and Lainey lot. Learn more at Podcasts. TED.com. I am Elise Hu. I'll be back tomorrow with a fresh idea for your feet. Thanks for listening.