Short Wave - How Will the Universe End?

Episode Date: August 13, 2024

Today, we're bringing you the final installment of our space summer series ... with the end ... of EVERYTHING. Will the universe end in a huge cosmic unraveling? A slow and lonely dissolution? Or a quantum-level transition that breaks the laws of physics? Theoretical astrophysicist Katie Mack breaks down three possible scenarios for how the universe as we know it will finally come to an end. To celebrate the end of our Space Camp series, we also made a QUIZ! Check it out at npr.org/spacecamp.Questions? Comments? Existential dread or excitement? Email us at [e-mail] — we'd love to hear from you!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

You're listening to Shortwave from NPR. Hey, Shortwaivers, it's Emily Kwong and Regina Barber. And today we're bringing you the final installment of our space camp series. We're going to end it with the end of everything. That's right. We're speculating about how the universe as we know it will finally come to a close. But this is Shortwave. So we're speculating supported by science.

Yes. And by our spectacular scientist, Katie Mac. I really studied kind of the big questions. You know, the beginning of the universe, the end of the universe, what the universe is made of, how it works, all of the kind of questions about the nature of the cosmos, how it's changing over time, and, you know, our whole cosmic story. Casual. Katie is a theoretical astrophysicist at the Perimeter Institute for Theoretical Physics. And most importantly, for our purposes today, she's also written a book. It's called The End of Everything, astrophysically speaking.

You know, in a sense, I'm a little bit worried that people are going to be like, oh, there's enough terrible stuff happening. But what I've heard from people is that the book is actually kind of a nice escape from the day-to-day terribleness and stress and worries that everybody's going through. I mean, this makes sense to me. Why I think about the doom and gloom of today when we can think about the doom and gloom trillions of years into the future? Totally. I mean, it helps my anxiety. And it also doesn't hurt that all these different scenarios have pretty incredible names. Based on name alone, I think the big rip is pretty good.

So today on the show, we're going back to the beginning of Shortwave to discuss the end of the universe. As Katie Mack and our former host, Maddie Safaya, break down some of the possible ways everything will come to an end. I'm Emily Kwong. I'm Regina Barber, and you're listening to Shortwave, the science podcast from NPR. So before we get into it, we need to talk about something that will definitely play a role in the end of the universe, dark energy. See, our universe is expanding, spread and on out. And that expansion is speeding up. Scientists think that's due to something called dark energy, but they don't really know what dark energy is. And there's nothing in normal physics that'll do that. Like regular matter won't do that. You know, it has to be something weird and whatever it is.

We call it dark energy, but we do not know what dark energy is made of. We don't know how it got here, you know, why it exists. It might be just a property of space, something called a cosmological constant, that space just has this kind of inherent stretchiness in it. Right. But it may be something different that changes over time and could get very extreme in the far future and lead to the big rip. Yeah. Depending what dark energy is really kind of dictates potentially the end of the universe. So how long do you think that'll take you to figure out, Katie, like 10 or 15 years?

I'm personally not working on dark energy myself. I see. Really passing the buck, Katie. Really passing. Yeah. It's a very hard thing to study, okay? Because all it does is make the universe expand faster. Okay, okay.

So are you ready to start talking about the end of the universe, the different situerneros? As you will? Okay. All right. So let's start with heat death. Our universe is expanding and that expansion is accelerating due to dark energy. And in the heat death scenario, our universe kind of continues to expand and expand and expand, right? Yeah. Yeah. What happens is that everything gets farther apart from everything else. You have fewer of these galaxy interactions, so you make fewer stars. And eventually each galaxy gets more and more isolated. So we would get to a point, you know, in only about 100 billion years, we'll get to this point where we can't see other galaxies in the sky anymore because they'll be so far away and their light will be stretched out so much that we won't be able to see them. And so the universe will just get a lot darker.

And then, you know, the stars in our galaxy will be dying out. So our galaxy will kind of fade away. And then, you know, even black holes will start to evaporate because that's something that can happen to a black hole is that it, It can lose its mass through this process called hawking evaporation. So black holes will start disappearing and then matter decays. And then eventually you end up with a universe that's just cold, dark, and empty. And all that's left is kind of a traced amount of waste heat from the processes of the universe.

So that's called the heat death. Cold, dark, and empty, you know? Mm-hmm. That actually just sounds right. But really, like, that is considered to be one of the more likely ends. Yeah, that's kind of what happens if you just extrapolate from what we know about the universe's evolution today and assume that dark energy is this cosmological constant, this just property of space, that it has this expansion built in. It takes a ridiculous number of trillions and trillions of years, but you end up with basically an empty universe. Yeah.

All right. So if dark energy acts a little differently, then we potentially get to a different end game. The big rip, right? You describe it as an unraveling, and this happens considerably faster than heat death, right? Yeah, yeah. So the idea behind the big rip is if dark energy is something else, if it's a particular kind of stuff we call phantom dark energy, where instead of just being a property of space, it actually is something that grows in its intensity over time. So it's something that there's more and more of it, you know, in each little space of space over time. then it can be something that doesn't just move galaxies apart from each other and isolate them, but actually tears the galaxies themselves apart. So what it would do is it would pull the stars away from our galaxy. So we'd see the Milky Way kind of dissipating.

And then it would pull planets away from their stars, and then it would start to actually rip apart stars and planets, and then atoms and molecules and eventually rip apart space itself. then that's the big rip. Wow. I can't believe that one's your favorite, Katie. No, no. You asked about my favorite in terms of the name,

and it's definitely my favorite in terms of the name. My favorite one is the next one, which we'll get to, I assume. But, no, the big rip is, it's one of the most terrifying ones because you would see it coming. You know, you would know that this was happening, and you would know that there's, you can't hide. Because you would see these things being kind of, of unraveled out there in space. And then you would know that there's nothing you can do. You can't

hide from space itself, right? The dark energy would be inside your own space, your own body, and it would be starting to kind of pull you apart. It's a terrifying prospect. Wow. I just want to quote, you can't hide from space, Katie, back. That's my God. You just can't. You just can't. Okay. Yeah. Okay. So last up is the end of the universe situation called vacuum decay. And Katie, this ending is very metal. Like, it is very intense. Yeah, so the idea behind vacuum decay is sort of that there's an instability built into how physics works in our universe. So, you know, we have laws of physics. We have the way that electrons move around in atoms and stuff like that. There are relationships

between particles and forces that make our universe work the way it does, make atoms work, make, you know, chemistry and biology and planets. and everything possible. And there's a possibility that there's an instability built into that where, you know, something could change in the universe, specifically in something we call the Higgs field, which is this energy field that sort of pervades all of space, that would rewrite the laws of physics where that happens. So somewhere in the universe, there would be this weird little quantum transition in the Higgs field,

and that would create a bubble of a new kind of space where the laws of physics are different inside that bubble. And that bubble would expand. through the universe at about the speed of light. And then anything that ends up, you know, being engulfed by this bubble would be in a kind of space where the laws of physics are different. So atoms can't hold together anymore. And everything would be just totally destroyed. And it's my favorite of these scenarios because it's just so out of left field, you know?

Right. Yeah. Like, oh, the universe is expanding, whatever. This is just like, no, physics breaks somewhere and creates a bubble of death. And that bubble of death expands out of the speed of light. You don't see it coming. And it just destroys everything. That's kind of merciful. I mean, it's, yeah, it's very humane. Like, there's nobody left to miss you. There's no tragic aftermath. And then it's done. Yeah. I like it because it's like, I've ordered that. I like, here are all these scenarios based on things we can observe. But what if physics was just broken and everything was wiped out all at once? Come on. But I love it. Okay. So wild. Yeah. I do think one of, in let me know if this is wrong, but like one of the things about this that I find particularly unsettling is that this could happen just like whenever. Is that fair? Yeah. Well, so it's a quantum transition. It's a quantum tunneling event. And one thing we know about quantum mechanics is it really breaks our

ability to predict things precisely. So we can give probabilities about when it might happen. But we can't say exactly when it will happen, if it even will. And people write me, email saying that they're freaked out about this idea. So I always want to make sure that I put in caveats like the chance is so small, you know, you're more likely to be, you know, hit by a meteor and a lightning bolt at the same time while winning the lottery. Like it's, you know, it's really small chances. Right. So, Katie, bigger question here, which is hard to do since it's already pretty big question you're talking about. But why study this? You know what I mean? Like, why spend resources trying to figure out the end of our universe that's, you know, so far in the future that humans won't

have existed for billions of years. You know what I mean? Right. Yeah, I mean, I think that the main reason is just curiosity. You know, we want to know how the universe works, and we want to know where we came from, and we want to know where we're going. And so when we think about the far future

and we extrapolate our current cosmic evolution into the future, it's a way that we can kind of examine our theories of physics and kind of push things to their theoretical breaking point. can give us new insights into how physics works. That's kind of just built into human nature, that we want to understand things. We want to figure out how we fit into everything. What does it all mean? And I wanted to write something that would give people access to that and give people some way to step into that.

To learn more about the possible endings to our universe, you can check out Katie Mac's book. It's called End of Everything, Astrophysically Speaking. And Emily, that concludes our 10-week journey. through space time and the outer reaches of the universe. We did it. We did it. We're back on Earth. Thank you all so much for listening.

If you missed any of our space camp episodes, you can find them plus extra content, like photos and physics explanations on NPR.org slash space camp. Wait, also, keep listening to this. You can test your knowledge of stars, space, and all things universe on that same page, NPR.org slash space camp. If you pass the test, you will be rewarded with your very own shortwave space camp badge. Limited edition. The original version of this episode was produced by Rebecca Ramirez, edited by Viet Le and fact-checked by Burley McCoy. Hannah Chin, Emily, and I did the space camp version. Julia Carney is our space camp project manager.

Beth Donovan is our senior director and Colin Campbell is our senior vice president of podcasting strategy. Special thanks to our friends at the U.S. Space and Rocket Center home of space camp. You're listening to Shortwave from NPR.