Planetary Radio • Aug 26, 2020

Katie Mack and The End of Everything

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Katherine Mack

Theoretical astrophysicist and professor, North Carolina State University

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Bruce Betts

Chief Scientist / LightSail Program Manager for The Planetary Society

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Mat Kaplan

Senior Communications Adviser and former Host of Planetary Radio for The Planetary Society

Known as Astrokatie to her 370 thousand Twitter followers, astrophysicist and cosmologist Katie Mack has written a funny, fantastic guide to the end of the universe. The End of Everything (Astrophysically Speaking) explores five major scenarios for the big finish of the cosmos that scientists currently consider to be possible. We’ll award a copy of Katie’s book to the winner of this week’s What’s Up space trivia contest.

The End of Everything (Astrophysically Speaking)
The End of Everything (Astrophysically Speaking) Book cover for The End of Everything (Astrophysically Speaking) by Katie Mack.
Nine Year Microwave Sky
Nine Year Microwave Sky The detailed, all-sky picture of the infant universe created from nine years of WMAP data. The image reveals 13.77 billion year old temperature fluctuations (shown as color differences) that correspond to the seeds that grew to become the galaxies.Image: NASA / WMAP Science Team

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Trivia Contest

This week's prizes:

The End of Everything (Astrophysically Speaking) by Katie Mack

This week's question:

Assuming a combined Greek and Roman pantheon mythology, within this mythology, which planet (in our solar system) is named after the earliest (oldest) god?

To submit your answer:

Complete the contest entry form at or write to us at [email protected] no later than Wednesday, September 2nd at 8am Pacific Time. Be sure to include your name and mailing address.

Last week's question:

As of August, 2020, what is our Mat Kaplan’s single credit in the Internet Movie Database (IMDB)?


The winner will be revealed next week. 

Question from the 12 August space trivia contest:

What is the wavelength of the SuperCam laser you’ve been hearing about?


The SuperCam laser operates at two wavelengths: 1064 and 532 nanometers.


Mat Kaplan: Katie Mack on our impending cosmic doom and other cheerful topics this week on Planetary Radio. Welcome. I'm Mat Kaplan of The Planetary Society with more of the human adventure across our solar system and way beyond.

Mat Kaplan: Cosmologist and science communicator Katie Mack joins us to talk about her truly delightful new book. It's called The End of Everything (Astrophysically Speaking). We'll take you through the five ways the universe and everything in it could end just possibly at any moment. Then we'll join Bruce Betts for a look at the especially crowded night sky. You might win a copy of Katie's book in the space trivia contest.

Mat Kaplan: Happy birthday, Mars Reconnaissance Orbiter. It has been 15 years since the launch of our spy in the Martian sky. To celebrate, the August 21st edition of the downlink is topped by a real stunner of an MRO image, rippled powder blue dunes on the surface of the red planet. Okay, the color was added to heighten the texture, but still.

Mat Kaplan: Perseverance and the UAE's Hope spacecraft are doing just fine. Both successfully completed small course adjustments and both are still set to arrive at Mars in February, along with China's Tianwen-1.

Mat Kaplan: Speaking of Perseverance, NASA has created a review board to analyze the agency's ambitious plan to bring bits of Mars to Earth. We now know which astronauts will be carried by the first operational mission by SpaceX's Crew Dragon vehicle. It's set to launch toward the International Space Station on October 23rd. You can visit to see their names and much, much more.

Mat Kaplan: Here's a reminder that there may still be time to sign up for the first ever Virtual Humans to Mars Summit. Details, including the agenda, speaker list, and registration info, are at

Mat Kaplan: Dr. Katie, or Katherine Mack, is a theoretical astrophysicist and cosmologist who studies everything, by which I mean the universe, from its beginning to its end. Now she's written a book about that. And Katie is an Assistant Professor of Physics at North Carolina State University where she is also a member of the Leadership in Public Science cluster. You'll find her work in Scientific American, Slate, and Sky & Telescope among other places.

Mat Kaplan: Her 370,000 Twitter followers know her as AstroKatie. I bet a few of you have joined us for this conversation Katie and I had a few days ago. Katie, what a pleasure to welcome you to Planetary Radio. Thank you for joining us and thank you for this terrific book, The End of Everything (Astrophysically Speaking). Welcome to the show.

Katie Mack: Thanks. Thanks so much for having me.

Mat Kaplan: So you want to know what I would write if I was doing a blurb for this book?

Katie Mack: Sure, yeah. Please.

Mat Kaplan: Here you go. A fascinating, delightful romp toward our ultimate doom.

Katie Mack: Awesome. I'll take it.

Mat Kaplan: I'm so glad. Do you remember the moment when it hit you that everything, I mean everything, could end at any second?

Katie Mack: Yeah. There are these times when you're studying something like astronomy, you're studying things that are far away and distant and mathematical. And so, most of the time, it feels very separate from your daily life. But there was this time when I was at this sort of Dessert Night for the undergraduate astronomy course at Caltech, and this professor was talking about the early universe and this inflation period where the universe expanded very, very rapidly for a time in the early universe. Then that inflation period stopped and the regular expansion of the universe took over from there.

Katie Mack: He was saying that we don't know why inflation happened or why it started, where it stopped, and we don't know that something like that couldn't just happen right now and just massively rip the universe apart. I was like, "Wait a minute. I'm not okay with this."

Katie Mack: I realize that some of these massively powerful processes that happen out there in the cosmos, they seem really separate from us. But because we don't know exactly how they work, we can't say for sure that something can't happen to us and actually affect us. We see violent events out there in the universe. There's nothing to say that they can't really happen here. That was a moment that really shook me because I hadn't made that connection before.

Mat Kaplan: I also love that this happened as you were sitting on the floor at your professor's feet and he had his young daughter in his lap.

Katie Mack: Yeah. He had this little three-year-old girl sitting there, totally oblivious, no idea what was happening, and her dad sitting there talking about the universe suddenly coming to an end. It was a very surreal moment.

Mat Kaplan: Of course, as you mentioned in the book, and we may get to this, it could happen and we won't even be aware of it. We'll just be gone, because our nervous systems wouldn't have time to react.

Katie Mack: Yeah, yeah. So that's one of the end of universe scenarios. I talk about vacuum decay. The main features of it are that it's unpredictable and that you wouldn't really notice it because it's so quick and you wouldn't see it coming. Yeah, I guess we can talk about that a little bit more later.

Mat Kaplan: Sure.

Katie Mack: But that kind of thing definitely gives you pause sometimes.

Mat Kaplan: What is your answer when people like me ask, "What do you do?" You talk about this fairly upfront in the book and it seems like you are between the two worlds of physics that we mostly hear about.

Katie Mack: Yeah. So I work in an area that is between astrophysics and particle physics. I do cosmology, and that's the study of the universe from beginning to end, and I'm on the theoretical side of that. But really the place I sit is I sit right between the people who come up with new theories of how physics works or how the universe works and the people who are actually out there with telescopes and experiments testing these ideas.

Katie Mack: My job is really to try to make connections between the theories and the observations or experiments to try to find out what we can do with observations or experiments that we can do now or in the future that will give us some insight into the theories that people are coming up with.

Mat Kaplan: Yeah. So really in between two different worlds. I mean the worlds of the impossibly huge and the impossibly small, but also in the theorists and the experimentalists.

Katie Mack: Yeah, yeah. It's an interesting place to be because it means that I have to really keep track of what's going on in all of those realms. So I have to take a really big picture view of not just the technological aspects and the theories, but also how everything fits together in the cosmos, because in the universe, we study the largest things, but physics is fundamentally driven by theories that govern the very small. You have to make those big connections and see how that all plays out in the cosmos itself.

Mat Kaplan: Well, this may be more work, but it doesn't sound like it's really a downside. I mean it sounds like fun. You can-

Katie Mack: Oh, it's super fun. Yeah, it's very fun, it's very creative, trying to make these new connections. The idea that I have to know about all of the things that are going on and all of the theories and stuff, that's a good thing as far as I'm concerned. It means that I can take a very broad view and I get to learn about a lot of really interesting topics and a lot of really interesting areas of physics and astronomy.

Mat Kaplan: We get to talk about cosmology now and then on Planetary Radio, even though The Planetary Society, as you might imagine, mostly pays attention to small round things, fairly insignificant probably in your view. But it's such fun to do this, and when we do ... I mean it has become obvious to me, something you point out in the book, that a lot of cosmology and popular writing about it is devoted to the beginning of the universe, what you delightfully call the infernoverse.

Katie Mack: Yeah.

Mat Kaplan: What do you think our eventual ending gets less attention, at least until your book?

Katie Mack: Well, I think there are a few reasons. One is that it's less direct, the information we get about the end of the universe. We have to extrapolate from what we know about the current universal history of the cosmos into this unknown time in the future.

Katie Mack: But when I say that this is less direct, I mean that when we work on the beginning of the universe, we really are actually looking at it. When we see into out into the distance in the cosmos, we're seeing into the past. And so, we can see the Big Bang. We can see the end stages of the Big Bang very directly just by looking far enough away. That's much more solid in terms of what we know about the beginning of the universe.

Katie Mack: I think that a lot of people think of the end of the universe as something that's just very much speculative and maybe not as important in some senses. But I think that it can be a really important exercise to go through thinking through what our theories predict about the future and how physics will change as the universe evolves. I think that's a really useful exercise as a way of thinking about what our theories mean and how to conceptualize these ideas.

Mat Kaplan: I think you make this case very, very well in the book.

Katie Mack: Thank you.

Mat Kaplan: There's a statement in here that I wonder about. You say in the book that our understanding is being advanced, thank goodness, by new technological and theoretical tools. I get the technological part. You talk about some of those. But what do you mean by theoretical tools?

Katie Mack: Well, there are a lot of insights that we can gain by examining the mathematical structures of the models that we use to talk about the universe. So there's a lot of work in areas like string theory where we're trying to find a way to reconcile quantum mechanics and gravity, which don't seem to play well together.

Katie Mack: So string theory's an attempt to bring that all together into one big theory that covers everything. That's really just theoretical tools at the moment because we don't have a way to test that stuff experimentally. We can gain insights into the structures of the theory and into possible implications just by doing the theoretical work. And so, when I say new theoretical tools, I mean new ideas, new structures, new frameworks for how physics works that can then be hopefully tested with experiments.

Mat Kaplan: With these new tools, would you say that we've made progress on both ends? I mean we seem to know more about the beginning than we do toward the ending. Is this still largely pointing outward, though, in saying here be dragons?

Katie Mack: We are making progress, I think. We're getting a lot of new data about how the universe has evolved over time, and that's super important for understanding both the beginning and the ending, so understanding where we came from, how astrophysics has changed since the early times to today.

Katie Mack: We are able to study more and more galaxies out there in the universe, which means we're getting a better mapping of the history of the expansion of the universe, the history of the buildup of structure, by which I mean galaxies and clusters of galaxies and so on, and we're getting new tools all the time. I mean between the new particle experiments where we have a ton of new experiments that are looking at various aspects of particle physics, neutrinos, how neutrino physics works, which is a whole big topic and lots of interesting mysteries in there.

Katie Mack: We're also getting new tools for studying the cosmos, and one of the biggest ones is gravitational waves where we're able to now pick up the vibrations of space itself as black holes are colliding in other galaxies. This is just a whole new window on the cosmos where we can feel the vibrations of space as these big violent events are happening. That teaches us about those events themselves, how black holes come together and things like that, but also about gravity.

Katie Mack: We're also able to learn a little bit about the structure of the universe itself by how the gravitational waves are traveling through the universe. So we do have a lot of new tools, and we're getting new insights all the time into the cosmos and the structure of physics.

Mat Kaplan: It is so thrilling to be able to talk now and then about gravitational wave astronomy, and to be around for the beginning of it as well.

Katie Mack: Yeah, yeah. It's so exciting. It's such a huge deal. We're going to have space-based gravitational wave detectors that'll tell us about supermassive black holes and how those are coming together in distant galaxies. I mean it's going to be really amazing over the next few decades as we get more of that information and we see the universe in a whole new way.

Mat Kaplan: I wish we had all the time in the universe to talk. We don't, of course, but maybe you could briefly take us through the five scenarios that are really the heart, the singularity of this book. We can do them one at a time, but I'm afraid they may have to be elevator pitch-like explanations.

Katie Mack: Sure.

Mat Kaplan: So tell us about the first one, the Big Crunch.

Katie Mack: The Big Crunch is the idea that the current expansion of the universe might reverse. Right now we know that the universe is expanding, galaxies are getting farther apart from each other in general. We didn't know for a long time if that expansion will continue forever or if the expansion would stop and turn around and everything would come crashing back together.

Katie Mack: The Big Crunch is this idea that maybe the expansion would stop and turn around and maybe everything would come back and we'd get this hot, dense state very much like the beginning of the universe. That would destroy everything in the cosmos. We think that's probably not going to happen, but for a long time it was thought to be the most likely scenario.

Mat Kaplan: Perhaps the most likely scenario, at least from my reading of the book, is this next one: heat death. I'm going to open this by ... It brought back a memory. Back in college, an engineer friend of mine and I were asked by a very good friend of ours, a very smart guy, well-educated, why the room doesn't get colder if you leave the refrigerator door open.

Katie Mack: Yeah.

Mat Kaplan: I remember feeling disappointed that he could have come so far in his education without having been taught about this. That leads us right into heat death, doesn't it?

Katie Mack: Yeah. So that connects the idea of entropy. So entropy is just disorder really. It's a way of talking about how disordered system of objects or physical things becomes.

Katie Mack: There's the second law of thermodynamics, which is a rule that seems to apply very strictly in the universe, that says the entropy increases over time, meaning that things become disordered and it means that you can't have a perfectly efficient machine. There's always going to be a little bit of loss through friction or something like that.

Katie Mack: That's why when you leave the refrigerator door open, the refrigerator is putting energy into cooling the section inside, but some of that energy is also being lost through waste heat. The sum total result of that is that the room will get hotter overall because that waste heat is building up, because there's always some kind of waste heat when you do any kind of process in physics.

Katie Mack: The heat death is the idea that as the universe evolves into the future, entropy is always increasing and there's a buildup of waste heat of the stuff in the cosmos. Now the universe is also expanding, so all of the matter and radiation and everything is being diluted out. And so, on average, the universe itself is getting colder and darker and emptier, but also everything is decaying through this process of increasing entropy. Over time, everything will be decayed away to just a tiny amount of trace leftover waste heat of the cosmos, and that'll be all that's left in the universe.

Mat Kaplan: Was I right? Is this now at least currently seen as the most likely big finish for the universe?

Katie Mack: Yeah, it seems to be the direction we're heading because we see that the universe is expanding and it's actually speeding up in its expansion. So this idea that everything will continue to get farther and farther apart seems to be borne out by the data.

Katie Mack: Our best guess as to what's making the expansion happen faster all the time is, well, there's something that's making the expansion speed up. We call it dark energy. We don't know what it is, but our best guess is that it's a cosmological constant, which is just a property of space that there's this inherent expansion built into space. It's an idea that Einstein first came up with. If that's what the dark energy is, it just leads to this cold, dark, empty universe and the heat death.

Mat Kaplan: I love that at one point, I think it's one of the footnotes, you mentioned that good old Albert, wasn't he wrong about anything? It's like-

Katie Mack: It's so frustrating.

Mat Kaplan: You do address at some length the cosmological constant, it comes up several times, and that maybe it's just a property of the universe, that maybe, like you said, we shouldn't be thinking of it as like another particle or a field. [crosstalk 00:17:44].

Katie Mack: Yeah, it seems like it's very possible, maybe even likely, that it's just something that exists in the universe, that when you have a bit of space, there's some cosmological constant associated with that bit of space, and it just expands it over time.

Katie Mack: Because the universe is expanding all the time and there's more and more space, there's then more and more of this cosmological constant, which means that the expansion continues. And so, the density of this stretchiness, if you want to call it that, stays the same. And so, that ends up accelerating the expansion of the universe.

Mat Kaplan: We won't get into it here, but you also talk about what if the cosmological constant isn't so constant?

Katie Mack: Yeah.

Mat Kaplan: But that's another good reason to read the book, everybody. It's also while you're talking about the heat death of the universe that you first mentioned the possible appearance ... In fact, not just possible, we know it happens ... of something from nothing, from what I was taught growing up was just the vacuum. In fact, you specify a sperm whale and a bowl of petunias, by the way. You're not fooling anybody here. I hope you have your towel handy.

Katie Mack: Yeah. We know that there can be random fluctuations in the universe, and this is indeed an idea that was discussed in Douglas Adams' The Hitchhiker's Guide to the Galaxy. But these random fluctuations can cause, apparently, unlikely things to happen. I do go into a bit in the book about what kinds of unlikely things we might expect to see.

Mat Kaplan: We better go on to the next way everything might end, the Big Rip.

Katie Mack: Yeah. So the Big Rip is based on the idea that maybe whatever's making the universe expand faster, dark energy, is not a cosmological constant, but something that could change over time and get, in some sense, more powerful over time. If that were to happen, it wouldn't just move galaxies apart from each other and make more empty space, it would actually also be inside galaxies, tearing the galaxies themselves apart.

Katie Mack: So you would see that the stars would be pulled away from their galaxies, planets would be pulled away from their stars, and even stars and planets would be destroyed over time. As you get closer and closer to this ultimate Big Rip event, atoms themselves will be pulled apart. Then space is torn asunder. That's the Big Rip. That's a way for the universe to end in a very violent and complete manner.

Mat Kaplan: You mentioned a paper by physicist Robert Caldwell, which you say is one of your absolute favorites of all time. The title is Phantom Energy: Dark Energy with w<−1 Causes a Cosmic Doomsday. This is what you read for fun?

Katie Mack: The great thing is that it's also what I read for work. This is part of my job is to keep track of these cosmic scenarios, and that's one of the ones that came out while I was in grad school. It's a really fun idea.

Mat Kaplan: Katie Mack has more doom, but no gloom right after this break.

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Mat Kaplan: Here's something else that's in this chapter about the Big Rip that caught me by surprise. Of course, a lot of this is wrapped up in calculating, figuring out the effect of gravity across multiple galaxies and huge regions of the universe. You say that when you're doing this, you have to take into account not just the mass of something, like the mass of a cloud of gas, but the pressure of the gas with in it. That also enters into figuring out the gravity? What's up with this?

Katie Mack: Yeah. So one of the things the Einstein's formulation of gravity, general relativity, includes is that the gravitational effect of something isn't just the mass of it, but also its pressure, also the energy of the motion of the stuff inside.

Katie Mack: When you look at gravity from Einstein's perspective, what's happening is that the mass of things or the energy density of things is changing the shape of space around them. You often picture it as a dent in space where a planet or a star is sitting, or a really deep one where there's a black hole. So you can think of space being curved around massive objects, and the amount of curvature, the effect on the shape of space is the mass and also the pressure of the object.

Mat Kaplan: Now I get it because, let's say, molecules bouncing around in a glass of water, Brownian motion, that's still energy.

Katie Mack: Yeah, it's energy.

Mat Kaplan: I mean they're observing pressure.

Katie Mack: Yeah.

Mat Kaplan: Okay. All right. Well, thank you. Next up, maybe the one that scares me the most, and it sounded like even though you ... At the end of the book, you quote from people, colleagues of yours in physics, who aren't particularly bothered by this. You seem to be. It's vacuum delay. And it's-

Katie Mack: Vacuum decay.

Mat Kaplan: Oh, sorry, vacuum decay. And I was looking right at it. What would vacuum delay be? I wonder. I hope it's delayed. It's in this chapter that you fondly look back on our existence and wish that the Large Hadron Collider hadn't destroyed the universe.

Katie Mack: Okay. The Large Hadron Collider is not powerful enough to destroy the universe. I want to make that really clear because there are a lot of people who think that it could.

Mat Kaplan: Phew.

Katie Mack: What happens with the Large Hadron Collider, how this fits into vacuum decay, is that the Large Hadron Collider gave us some new insight into how particle physics works and suggested that vacuum decay could be possible. It might have always been possible. Maybe we just wouldn't know about it if it weren't for the Large Hadron Collider. So it's really doing us a favor. It's not making this happen, but it's giving us a heads up that maybe this could happen.

Katie Mack: The way that vacuum decay works is we know because of experiments with the Large Hadron Collider that there is an energy field called the Higgs field that pervades all of space. We know that because we've detected the Higgs boson, which is a particle associated with this Higgs field. This Higgs field has something to do with how particle physics works in our universe.

Katie Mack: People often talk about the Higgs particle in connection with how particles got mass in the early universe. That's why people sometimes call it the God particle because it imbued particles in the early universe with mass in some way. But it's really the Higgs field that was associated with that.

Katie Mack: What happened was the Higgs field, this energy field through space, there's some value associated with the Higgs field, and that value changed in the early universe from one thing to another. When it changed, that changed how physics works and it allowed the particles we see in the universe now to exist and the interactions of physics to happen the way they do now. And so, it allowed for the existence of atoms and molecules and chemistry and life and all of that.

Mat Kaplan: Us.

Katie Mack: Yeah, us. So we like the Higgs field being where it's at because that allows us to exist. What the Large Hadron Collider told us is that based on its measurements of the masses of particles and things, it suggested maybe the current value of the Higgs field is not necessarily the one it's going to have all the time.

Katie Mack: It suggested that maybe the Higgs field is not entirely stable, meaning that something could happen somewhere in space. A quantum event, a quantum tunneling event, could happen to the Higgs field at one point in space, and that would change the value of the Higgs field at that point.

Katie Mack: That would create a little bubble of a region where the Higgs field has a different value, and that's really a different kind of space. It's called a true vacuum. This true vacuum bubble would then expand out of the speed of light, or roughly the speed of light, and just destroy everything in its path. If you ended up inside that bubble of true vacuum, your molecules wouldn't hold together anymore because particle physics would no longer work the way that you're used to it working. That bubble would just destroy the whole universe.

Katie Mack: The reason that it's scary to a lot of people is because it's governed by a quantum transition, a quantum tunneling event. What we know about those kinds of events, about a lot of things in quantum mechanics, is we really can't predict when it'll happen or where it'll happen. It's a random occurrence.

Katie Mack: So we can give a time scale. We can say that it's probably not going to happen any time soon. We can say that the likelihood is we would have to wait 10 to the power of 100 years for this to occur. But we can't say for certain that it won't happen soon. So that's what makes people nervous.

Katie Mack: I want to just make sure that I say don't worry about vacuum decay. We don't even know for sure if it could happen. The chance of it happening, like you're much more likely to get hit by a meteor and a lightning bolt and win the lottery all at the same time than vacuum decay occurring. So don't worry about it, but it is intriguing because it's the thing that ties into how fundamental physics works in our universe. It would be such an extreme violent event and just out of nowhere.

Mat Kaplan: I'm reassured, and I love it. We've already made one literary reference to good old Douglas Adams. You work Kurt Vonnegut in here as well because you make the comparison to Ice-Nine, that form of water that whenever it comes into contact with other water freezes well above 32 degrees Fahrenheit, and eventually the whole world is ice. It just spreads.

Katie Mack: Yeah. That's how vacuum decay would work. The little bit of space next to the bubble would be transitioned to the bubble, and that would go on indefinitely as the bubble is expanding.

Mat Kaplan: It would spread at the speed of light and, therefore, we wouldn't see it coming.

Katie Mack: Right. Yeah, yeah, because if something's coming at you at the speed of light, by the time the light from it gets to you to warn you that it's coming, it's already on top of you. So you would have no way of knowing it's about to happen. You wouldn't even know that it did happen, because let's say it actually hits you, your nerve impulses don't travel that fast. By the time the signal got to you that something had happened, you would no longer exist.

Katie Mack: So in that sense, it's very humane. You don't have to worry about it. You don't see it coming, you don't feel it. You don't notice. Then it destroys everything. So nobody's left to miss you. There's no tragic aftermath. It's just over. Everything's over.

Mat Kaplan: Ignorance is truly bliss.

Katie Mack: Mm-hmm (affirmative).

Mat Kaplan: There's a line in this chapter that also made me give a long sigh. You said, "You'll just have to trust me that if you decide to go and learn the mathematics behind all this, it gets much cooler." I feel so inadequate. It's as if you and people who know the math have special glasses that lets you see the beauty of the world and the universe far more deeply than I can without the math.

Katie Mack: Well, I definitely think that learning more about how the universe works does make it more beautiful. Understanding these mathematical structures and these physical concepts, I think, can give you a new appreciation for physics and for the world we live in. I feel very, very fortunate to have access to some of that and to be able to see the universe in that way.

Mat Kaplan: I envy you. Okay, we're in the home stretch here. We've reached the Bounce.

Katie Mack: Bouncing cosmology is a set of different ideas where the universe would go through some kind of cycle or transition where when the universe ends, it's not forever ending and everything's over, but it would start a new cycle. A new universe would be born out of the ashes of our own.

Katie Mack: So you can have a situation where there's a Big Crunch type thing that then leads to a new Big Bang or a heat death where a new Big Bang sprouts out of that. There are a few different ways. You can have collision of adjacent universes that sparks a new Big Bang.

Katie Mack: There a couple of different ways that this could happen, but bouncing cosmologies or cyclic cosmologies all have in common that the start of our universe was due to the end of a previous universe, and maybe when our universe is over, a new one will begin.

Katie Mack: A lot of people find bouncing cosmologies to be hopeful because even if our universe is totally destroyed and everything that we ever had here is gone, maybe something else will occur afterward. Some people find comfort in that.

Katie Mack: There's also an intriguing possibility in some of these scenarios that something might survive across the transition, not an object but some kind of information of some sort, maybe gravitational waves or some kind of trace, that could tell us something about the previous cycle or could carry information from our universe into the next one.

Mat Kaplan: Is it possible, if the Bounce is the correct scenario for the big finish and a new beginning, that you and I have had this conversation before eleventy billion times, or does quantum mechanics eliminate that?

Katie Mack: I think that there's no particularly good reason to believe that the next cycle would be particularly similar to ours. So I think that enough weird things could happen that you wouldn't expect a lot of similarity on that level for a future universe.

Katie Mack: There are some interesting ideas in quantum mechanics where every time a quantum event occurs, a new universe branches out. And so, there could be infinite copies of us in these parallel universes that are totally inaccessible to us through quantum mechanics.

Katie Mack: But in terms of the next cycle of our universe occurring, it's a little unlikely it would look like ours. Although, there are certain scenarios in the heat death where you can have these sudden random reoccurrences of our universe in any configuration our universe ever had. In those situations, you can have this moment repeated over and over again forever just through the random rearrangement of particles in a post-heat death universe.

Katie Mack: That's a particularly weird idea that I get into a bit in the heat death chapter. That's a very fun and mind-bending way of looking at the possible distant future of our universe.

Mat Kaplan: Mind-bending indeed, yeah. All right. Those are the big five. You can read much more about them in the book. I want to begin our close here by talking a little bit about where we're headed. I mean what are you looking forward to, and something that you mentioned in the book, another one of these new tools that is going to help us understand our place in the universe and maybe our future?

Mat Kaplan: I'm going to be moderating an event about planetary defense efforts in a few days, and you mentioned that you recently attended a session on this topic, and the Large Synoptic Survey Telescope, now known as the Vera Rubin Observatory, was brought up, because it's going to help us find these little rocks that threaten our planet, not the whole universe. But that it's going to be useful to folks like you, too.

Katie Mack: Yeah, yeah. That's going to be an amazing survey of the sky that's going to show us billions of galaxies out there in the universe. We'll be able to catalog just a huge number of galaxies and supernovae, and that's going to allow us to map out the structure of the universe as we never could before, and to learn about dark energy and dark matter and the structure of our cosmos. And so, that's going to give us some huge clues about both the history of the cosmos and the future.

Mat Kaplan: What else are you looking forward to? I mean are there other tools or are there theoretical developments that have you worked up looking forward to where they may take us?

Katie Mack: I'm really looking forward to new particle physics experiments. There was this proposed experiment, the Future Circular Collider, which would be a much larger version of the Large Hadron Collider, that could give us new insights into particle physics.

Katie Mack: I'm really excited about some of these new observatories like the Vera Rubin Observatory, space-based experiments or observations, like the James Webb Space Telescope, and some other space telescopes that are going to show us early galaxies, some of the first galaxies in the universe, and teaches about the history of our cosmos. There are a lot of ideas like that. Then gravitational waves. I'm very, very excited about what we're going to learn from gravitational waves, seeing collisions of black holes out there in distinct galaxies.

Katie Mack: On the theoretical side, I'm very interested to see where ideas around string theory and around what's called holography can take us, where we're learning about connections between different areas of physics that suggests some really strange things about how physics works.

Katie Mack: I talk about this a little bit in the book, where it's possible that space and time are not really fundamental to our universe, that our universe is really built on a different kind of mathematical structure in space and time are emergent, which means that we exist in space and time and we deal with space and time, but really what's happening is something much more abstract, much more mathematical, and we just perceive space and time being real. But they're not strictly what our universe is built out of, which is a very strange and intriguing idea.

Mat Kaplan: I love this stuff. I think you say it, space-time is not fundamental. At least you quote somebody saying that.

Katie Mack: Yeah, it's a very weird and unsettling thing to think about.

Mat Kaplan: You mused toward the end of the book about the Drake equation, that great thought experiment by Frank Drake, that we've talked about many times in the show. You're not in the business of figuring out how to detect intelligent life elsewhere in the universe, but you still find great significance in what this equation attempts to do.

Katie Mack: Yeah. So the thing about the Drake equation that I was connecting with in this book is that the Drake equation is a great way to figure out what the questions are that we need to be asking. You can write down this equation, you can put numbers into all of the terms, and you get a number out, and the number that you get out of the equation is not really telling you something new because the numbers that you put in are all very uncertain.

Katie Mack: So the number you get out is not the important thing about the Drake equation. The important thing is going through the exercise of thinking like what are the numbers I need to put in here? What are the factors that play into this question of how many alien messages can I expect on galactic voicemail?

Katie Mack: In terms of cosmology, in terms of thinking about the end of the universe, it's a similar idea. We want to know how the universe is going to end. There are a lot of things we don't know yet. By thinking about how the universe is going to end, we figure out, okay, what are the ingredients that go into this? What do we need to know to answer this question? What can trying to figure that out tell us about how physics works and how the universe works?

Mat Kaplan: So getting there is half or maybe more than half the fun.

Katie Mack: Yeah, I think so. I think that we're not going to see the end of the universe, I hope not, but we're going to learn a lot along the way. We can project our understanding into the future, and that can be a really great and fascinating exercise.

Mat Kaplan: We've reached the end, but I'm glad I've already asked you to pull out from your website this great poem that you have there, which you titled Disorientation. You very kindly agreed to read a bit of it to us. We don't have time for the whole thing, but maybe you could take on those last four stanzas?

Katie Mack: Sure, sure. I want to utterly disorient you and let you navigate back by the stars. I want you to lose yourself and find it again, not just here but everywhere in everything. I want you to believe that the universe is a vast, random, uncaring place in which our species, our world has absolutely no significance, and I want you to believe that the only response is to make our own beauty and meaning and to share it while we can.

Katie Mack: I want to make you wonder what is out there, what dreams may come in waves of radiation across the breadth of an endless expanse, what we may know given time, and what splendors might never ever reach us. I want to make it mean something to you, that you're in the cosmos, that you were of the cosmos, that you were born from stardust and to stardust you will return, that you are a way for the universe to be in awe of itself.

Mat Kaplan: What a lovely way to end a lovely conversation. Thank you so much, Katie.

Katie Mack: Thank you. It's really great to talk with you.

Mat Kaplan: That's cosmologist and science communicator Katie Mack of The End of Everything (Astrophysically Speaking) is published by Scribner. We've got a link to the book on this week's episode page at A copy just might be yours if you stick around for Bruce.

Mat Kaplan: Time for What's Up on Planetary Radio. Bruce Betts is the Chief Scientist of The Planetary Society. That means he does a whole bunch of stuff for us. I don't know if you have to be a scientist to do this, but he also runs our LightSail program. That seems more engineering to me. What do you think?

Bruce Betts: Yes, it's management. But I'm also the camera guy. We've been getting some cool pictures lately.

Mat Kaplan: Oh, yeah. How many more of those are available now? I know you've been sharing them with colleagues.

Bruce Betts: I have. We'll get more up. You should be able to find more at, at least a couple of the recent ones, if you follow the Pictures link. They're looking pretty cool, hurricanes and Bahamas and stuff.

Mat Kaplan: They're more than cool. Do check those out. I'm glad that that came up. Speaking of op, what else is there?

Bruce Betts: Oh, nice segue. Early evening, just evening in general, it's a planet party. We've got Jupiter looking super bright over in the southeast, Saturn to its lower left looking yellowish. Coming up now just an hour or so after twilight is really bright Mars, brighter than the brightest star in the sky, but still outshone by Jupiter. You'll find that in the east, to the left of Jupiter and Saturn.

Bruce Betts: Pre-dawn, also parties happening. We've got one planet, but it's really bright, and that's Venus. You can find the Pollux and Castor to the left of it, and Procyon, which is the bright star in Canis Minor, to the lower right of Venus. So all sorts of stuff to look at.

Bruce Betts: But wait, don't order yet. We can also get the moon involved. On the 28th, it will be fairly near Jupiter and, on the 5th of September, it will be very close, just a couple moon diameters or less to Mars. So a cool conjunction of the moon and Mars on the 5th.

Mat Kaplan: Nice way to celebrate the season.

Bruce Betts: We move on to this week in space history. It was this week in 1979 that Pioneer 11 became the first spacecraft to fly by Saturn.

Mat Kaplan: A real pioneer.

Bruce Betts: Oh, nice. Speaking of nice, random space fact.

Mat Kaplan: Oh, that's nice.

Bruce Betts: Per unit area, Neptune receives only one-900th the amount of sunlight received by Earth. That's why it's really cold out there.

Mat Kaplan: Cold and dark.

Bruce Betts: Cold and quite dark. I mean the sun's really bright, but still.

Mat Kaplan: Yeah, I imagine their gas bills for heating would be huge. But there's gas everywhere, so it's a thing.

Bruce Betts: Gosh, that's positive.

Mat Kaplan: All right, contest time.

Bruce Betts: We asked you what is the wavelength of the SuperCam laser on the Perseverance rover? How'd we do, Mat?

Mat Kaplan: I'm going to start with this one from Ian Jackson in Germany. "It seems to be an easy one this week. Bruce feeling guilty about the black hole question?"

Bruce Betts: Maybe.

Mat Kaplan: I'm sort of going to let [Gene Luanne 00:43:24] in Washington answer with a poem. You'll find out why I say sort of. "SuperCam can proudly tout the ability to look about, and through Raman spectroscopy discern a sample's chemistry, a neodymium YAG device this laser fires quite precise, revealing possible life in Martian dirts between 281 and 563 terahertz."

Mat Kaplan: Great work. The only problem is you asked for it in wavelength, and he gave it to us in terahertz. It's accurate, I checked it. I converted the wavelength to frequency, and it works.

Bruce Betts: One person's wavelength is another person's frequency. I've always been a wavelength fan, but people, especially these radio astronomers, they think in frequency.

Mat Kaplan: Me too because I'm a radio guy.

Bruce Betts: Oh, you are a radio guy.

Mat Kaplan: So I think frequencies. Wavelengths are just ... That's like for short wave people and I guess astronomers. But thank you, Gene. Good job. Not our winner. Here's the winner, [John Birsteaker 00:44:30]. It's my favorite kind of steak. I bet he hasn't heard that one before.

Bruce Betts: [crosstalk 00:44:33].

Mat Kaplan: In Massachusetts. First time winner. "1064 nanometers or 532 nanometers for the Raman spectroscopy work that it also does with the same laser, as we learned from the episode," he adds. John, congratulations. You have won yourself a copy of Lou Friedman's new book, Planetary Adventures: From Moscow to Mars, from Page Publishing. It was the source of all these great stories I talked with Lou about a couple of weeks ago.

Bruce Betts: Cool.

Mat Kaplan: I got more. Here's another poem from [Maureen Bends 00:45:08] in Washington. "Upon listening to the podcast, I heard men of science speak. The SuperCam laser was the topic of the week. Measurements of this and that, though nary a mention concerning leaders. The key wavelength 1064 is, of course, in nanometers." It's a good effort.

Mat Kaplan: Then not really a response to the contest, but this comment from [Povel Parsonzick 00:45:31] or [Parsfinzick 00:45:34] in Scotland. "Hi, Mat and Bruce. Hope you're as excited as I am about Perseverance landing on Mars. Just imagine what awesome new discoveries it will bring. Will it find a rubber asteroid? Because that sure would be nice to find in my mailbox." Nice, [inaudible 00:45:49]. We'll get back to them before too long, I'm sure.

Bruce Betts: If they find a rubber asteroid, I'm sure they'll try to prepare it for a sample return.

Mat Kaplan: Yeah. Well, they'll be able to squeeze it down and carry more mass back.

Bruce Betts: We'll have to take a rubber asteroid squeezer, the newest instrument for the follow-on mission.

Mat Kaplan: They should have put one on the sample target.

Bruce Betts: Moving on, so stick with me on this one. Here's your new trivia contest. Assuming a combined Greek and Roman pantheon mythology, within this mythology, which planet is named after the earliest, in other words the oldest, god? Go to In case there's any confusion, I'll stick within our solar system.

Mat Kaplan: You have until Wednesday, September 2nd, at 2:00 PM, Pacific time to get us this answer for this one. Guess what we're giving away. Now you already know. It's The End of Everything, that great book from Katie Mack. The End of Everything, (Astrophysically Speaking) is the subtitle, from Scribner. I hope you will love that book as much as I did. It was great fun, just like the conversation we had with Katie a few minutes ago.

Bruce Betts: All right, everybody. Go out there and look up the night sky and think about your favorite utensil. Thank you and good night.

Mat Kaplan: Oh, I could probably do better than this. But off the top of my head, a barbecue spatula, the ones with the really long handles so you don't get burned. [crosstalk 00:47:27].

Bruce Betts: Very practical.

Mat Kaplan: Even after all this, he is still the very practical chief scientist at The Planetary Society who comes to us every week as part of What's Up. Planetary Radio is produced by The Planetary Society in Pasadena, California, and is made possible by its universally marvelous members. Join our little cosmos at Mark Hilverda is our associate producer, Josh Doyle composed our theme, which is arranged and performed by Peter Schlosser. Ad astra.