(bright music) - Welcome, everyone, to "Conversations at the Perimeter." Lauren and I are thrilled that our guest is Katie Mack, who is known as AstroKatie to her hundreds of thousands of followers on Twitter. - Katie is a professor of physics and, of course, a well-known science communicator, and in June, she's going to join us here at the Perimeter Institute for Theoretical Physics as the Hawking Chair in Cosmology and Science Communication.
- As you'll hear, it's pretty amazing that she holds the Hawking Chair because her whole exploration into science started in childhood when she picked up Stephen Hawking's "Brief History of Time." - Yeah, and she had some pretty interesting interactions with him throughout her career as she tells us.
- And she also tells us about her book, "The End of Everything: Astrophysically Speaking," which, I have to say, this conversation is the most enjoyable talk I've ever had about the end of the universe. - I agree. Let's step inside the Perimeter. - Katie Mack, thank you for joining us. - Thank you for having me. - It's great to have you here. Tell us why you're here now and why you're gonna be here again soon.
- Right now, I'm officially a visiting fellow, but I'm coming to join the Perimeter Institute on a full-time basis starting in June. - Yay! We're very happy about that. - Thank you. Yes, I'm very excited about it as well. I've been having a bunch of meetings with people and sort of sorting out details of the role, but yeah, it's gonna be great. - And what is this full-time role gonna look like here at Perimeter?
- It's called the Hawking Chair in Cosmology and Science Communication, and it's a position that is gonna be joint between cosmology research, carrying on my research program, and doing public engagement work and communication and working with the amazing outreach team here at Perimeter to bring physics to the public. - We're sitting here in the Stephen Hawking Centre at Perimeter Institute. You're going to be the Hawking Chair.
What's it like to have a position that's named after someone that you've not only sort of looked up to, I almost said idolized, but also you've worked with? Can you tell us about what it means for you to have this title? - Stephen Hawking was the first person I ever knew of who was called a cosmologist.
When I was a little kid, I read "A Brief History of Time," and I was just amazed at all these ideas about the Big Bang and black holes and space-time and all of that, and so I looked at Stephen Hawking and his job was called cosmologist, so I was like, "Okay, I'm gonna be a cosmologist. "That's what I wanna do." - What age was this where you decided- - I think I was probably 10. (laughs) I was pretty young. - And here you are, a cosmologist.
- And I am a cosmologist, and I've encountered Stephen Hawking a couple of times in my career. The first time I met him, I was like 14 years old. He gave a talk at Caltech before I was even an undergrad there, 'cause I lived in Southern California, and so I went and watched his talk, and afterward did a little fangirl moment, said hi to him and said I was an admirer of his work, and he said, "Thank you very much," which was very exciting for me.
But then when I was in grad school, I spent at year at Cambridge University working with people doing a research kind of thing, and I ended giving a talk there where Stephen Hawking came to my talk, and that was- - No pressure, no pressure. - Yeah, that was one of the most harrowing academic experiences I've had. (laughs) It's one thing to give a talk in front of your sort of childhood idol about a topic that he sort of pioneered.
I was talking about primordial black holes, which is something he worked on very extensively, but it's another when he's heckling. (laughs) So what happened was I went to give this talk, I was setting up for the talk, and all of these eminent professors were already sitting down, and I was nervous 'cause I thought he could show up, but he hadn't yet, and I was like, "Okay."
And then hear this like beep, beep, beep as his wheelchair is coming in, and so he's set up in the front of the room, so I'm like, "Okay, I have to do this thing," and so I get started with the talk and I introduce myself, I put up my title slide, I say I'm gonna talk about primordial black holes, and I hear "thank you," and I look at Hawking. I'm like, "Okay," and I kinda laugh. - You heard it in that iconic voice that everyone knows.
- Yeah, and I kind of think maybe it's a joke because I'm talking about primordial black holes and he worked on those. I don't know, but everybody kind of chuckled, and then I moved on, and then I continue the talk, and at some point, I hear "no," and I'm like, "What?" And I look at him, and he's just eating his lunch. The carer who's there feeding him was just kinda looking blankly at me.
Nobody is giving me any kind of clue what's going on here, and I can't ask him to repeat himself because at that point he was using this machine that took like two minutes per word. - He was just using a cheek muscle to- - Yeah, this little thing that looks at the cheek. He'd sorta wink to choose words.
And so I just kind of paused and then carried on, and then throughout the talk, at various times, I'd hear something like "yes" or "I don't know" or "I don't think so" and I had to just keep going, and every time I would sort of respectfully pause and then move on. - But you did hear Stephen Hawking say "I don't know" in a talk you were giving. That's gotta be something. - That is true. Yeah, yeah. It was a number of different little phrases.
But then eventually the talk finishes, he goes off somewhere else. He didn't answer or ask any questions, and then I asked the organizer, "What was going on with Stephen Hawking? "What was he doing?" And he was like, "Oh, the little sensor "that senses his cheek movement,
"it malfunctions when he's eating." (laughs) So because he was chewing, it was just going through the quick-select menu of phrases: yes, no, maybe, I don't know, I don't think so, just the things that are easy to get to, and you can't turn it off because then he wouldn't have any way of speaking, so he just has these outbursts, and nobody told me. I had no idea that was gonna happen. I don't know if it was like a hazing thing. (laughs) I was just a grad student. I didn't know what was going on.
- Do you know what he eventually thought of the talk? - I don't know what he thought of the talk. I did talk to him once more about my research at a dinner thing, and he didn't really say much. He was very careful with his words. He didn't go off on tangents. He didn't say things unless he had a really good reason to, so we didn't end up having a real conversation, although I was in the same research group sort of broadly as him, so I was around the stuff he was doing.
I wasn't working directly with him, but it was neat to be able to meet and interact with your sort of childhood hero. - And be heckled by him. - And be heckled by him. I mean, it made a great story, being able to survive that and just carry on. - Just go back a little bit. Stephen Hawking was a cosmologist. You saw him when you were young. You said, "I wanna be a cosmologist." What's a cosmologist?
- So a cosmologist is somebody who studies the universe sort of as a whole or the fundamental physics of the universe. So I often explain it as the universe from the largest to the smallest scales from beginning to end, anything to do with the bigger picture of how the universe works. So cosmologists study things like the Big Bang or the future of the universe.
They study what the universe is made of, how it works physically, what the laws are that govern the cosmos, and so I've worked in various areas around there. I've worked in the early universe and what happened at the Big Bang, that kind of question. I work on dark matter, which is one of the most important components of the universe, but we don't know what it is, and I've also thought a lot about the end of the universe and just various aspects of, how does it work, what's really going on?
- So nothing much then, just everything, just the whole universe. - Yeah, I was gonna say, just hearing your description, it seems just like such a broad field. I mean, you can study the past, the present, the future, the big and the small. At any point in your career, how do you choose where to focus your attention? - I've been very fortunate in my career that I've had a lot of freedom to study what I'm interested in and to just kind of follow my curiosity.
I've had research fellowships where I'm not tied to a particular project, but I get to present here's what I wanna work on, and then I work on that thing.
So I've just kind of looked at, what's the interesting question, where can I be really creative about this, so things like talking to the theorists about what the new sort of physical model is they're thinking about, what's the big theory that everybody's excited about, and then talking to the observers about the new telescopes that they're gonna build like, what is this new radio telescope gonna see about the first galaxies in the universe, and then trying to find ways to bring those together,
trying to find out, what can those telescopes tell us about those theories, and what kinds of experiments do we need to test those theories, and that kind of intermediate stage where you get to learn about every aspect of these questions and try and find new creative ways to bring them together.
So that's kind of the area I like to work in, but in terms of topic, it's anything from black holes to early galaxies to cosmic strings to dark matter to microscopic black holes that might have started in the early universe, all kinds of stuff like that because there's some interesting creative way I can approach the question. - What's the interesting problem you're grappling with now, and what's your creative approach to it? - I'm particularly interested in dark matter.
So we know that most of the matter in the universe, most of the stuff that has mass in the universe is totally invisible. We can't see it with ordinary light. It doesn't seem to reflect or emit light or absorb light, so it's hard to look at directly, but we can see that it's there based on how it affects things that are lit up in the universe, stars and galaxies. - Is dark matter everywhere? - Yes, yes, so there probably is dark matter in this room. - It's not just far away in space.
It's permeating. - No, no. About a third of a proton mass per cubic centimeter is roughly how much dark matter is around here, and it's passing right through us. That's most likely sort of where we're at with dark matter. There's a lot of uncertainties in this- - And this makes up most of the universe. - Most of the matter in the universe. - Okay, right. - When I get to most of the universe, we have to talk about dark energy. It's a totally different thing, but most of the matter, yes.
But yeah, so we're pretty sure dark matter is there.
It seems to be important to the functioning of matter in the universe, to the growth of galaxies, to the formation of structure on the largest scales, but we don't know what it is, and there's a hope that maybe if dark matter particles, if they really are particles, probably they are, if dark matter particles collide in just the right way, they might annihilate with each other and create regular particles like things like positrons and electrons or quark pairs or something like that.
And if that's the case, then regions of really dense dark matter should glow with high-energy particles that we can see just to some tiny degree. A lot of people have followed that possibility and looked for evidence of dark matter annihilating in the center of the galaxy or in small galaxies nearby or various places like that. One thing that I've been interested in recently is, what if that does happen? How would it have affected the first galaxies in the universe?
So these clumps of dark matter where the first gas got together and formed stars and galaxies, how would those structures be affected by a little bit of energy coming out of the centers of these dark matter clumps?
And then furthermore, if that is happening, how does that, or if that did happen in the past, how does it change what we can see with radio telescopes and with infrared telescopes, things that can look at those first galaxies, so things like the James Webb Space Telescope, which hopefully will be launched by the time this podcast comes out. (laughs) Hopefully it's up there doing great science. Now I'm getting nervous about it.
Anyway, that telescope and other space telescopes designed to look for the very first galaxies, they might see something different if dark matter is annihilating in those first galaxies or if it's not. - When our telescopes look out really, really far, they're looking at things the way they were. Was dark matter around at the very beginning? Has it been around forever?
- Yeah, as far as we can tell, dark matter was part of the sort of primordial soup of the very, very early universe, and it was crucial to building up the first matter structures in the universe, the first galaxies, the first stars. It helped bring all that gas together and allow it to form those first stars and galaxies, and we have some idea of kind of how that worked.
We have a reasonably good idea of the fact that if dark matter were not there, then the gas that makes up our own galaxy, the Milky Way, would not have been able to come together enough to form the Milky Way as we see it today. So it's been a factor in the evolution of structure since the beginning.
Whether or not it's been injecting high-energy particles and photons and energy into these clumps, we don't know, and so that's what I'm trying to figure out, trying to model what that would look like, how it would affect those first stars and galaxies, what you would see with space telescopes, what you would see with radio telescopes that can sort of probe the neutral hydrogen that formed the first stars and galaxies at very, very early times, and it is great.
As you say, these telescopes are time machines. You can look at the past. You can see directly things that happened in the first billion years of the universe. We're at 13.8 billion years now.
We can see galaxies that were before half-a-billion years, just very, very early in the universe, and of course, we can see the background light from the Big Bang itself, the cosmic microwave background, and we get clues about dark matter from all of that, and hopefully we'll get some clues as to whether or not it does this annihilation thing when we start to be able to look at those first galaxies more directly. - I'm curious what specifically you're looking for with those telescopes.
What is that evidence that helps you be more sure that dark matter played a role at different stages of the universe? - So in terms of how it affects, just played a role gravitationally, how it brought matter together, the way you learn that is from modeling the gravitational growth of structure.
So you do computer models to simulate matter coming together, and you see what happens if that matter coming together has pressure and acts like gas where it can kind of puff up again, or if it's dark matter where it just has gravity and doesn't have pressure. It doesn't puff up when you... If you let dark matter sort of fall toward itself, it's not gonna bounce off and it's not gonna kind of heat up the way that gas, if it falls together, it kind of gets puffy.
So you have different dynamics around how things grow through gravity if it's dark matter or if it's regular matter, and so computer modeling is a big part of figuring out how dark matter affected the gravitational sort of development of these structures.
In terms of how we'll know if it's annihilating or not, that's a different question, and that's also something where you have to do computer modeling to see where that energy goes within that dark matter structure, where it goes when it goes into the gas, and how that changes the physics of that gas and how it changes.
Maybe what it does is it blows out all the gas in the smallest little clumps of dark matter, and so you can only form galaxies in larger clumps of dark matter, and that would be something you would be able to tell the difference in a sort of large survey with telescopes. - You've mentioned that you look into the beginnings of the universe, and the ends of the universe hasn't happened yet. Is looking at one imperative for understanding the other?
- I think that what we really want is a big picture of the whole evolution of the universe and the structure of the universe, and so the beginning is part of that question. How did the universe begin? - How did it begin? Tell us now, hurry. - (laughs) Well, we're kind of still working on that.
But yeah, the beginning of the universe is one part of the question, and the end of the universe is another part, and if you have a theory for the beginning of the universe, it generally has an implication for the end as well, and if you have a theory for the end, maybe it'll lead to a new beginning. There are some theories that have a sort of cycling universe.
So they are kind of parts of the same question because they're both asking about this kind of big-picture question of, what is the nature of the universe?
Is it embedded in some larger multiverse, or is there some part of the universe that's so far away from us it's not observable to us and how does that affect the evolution of the universe, and if you really understand the beginning, you know if that beginning is the result of the end of a previous universe, for example, so there are ways that these things are connected.
But also we learn a lot about what the universe is made of by looking at the beginning of the universe, by looking at things like the cosmic microwave background, which is the light from the Big Bang itself really, but it's also something that we can study carefully to learn about the components of the universe because it encodes a lot of really important information, but if we know what the universe is made of completely, then that also helps us to extrapolate into the future
of how those things will evolve in time. So for example, dark energy is some mysterious stuff that's making the universe expand faster all the time, and we don't know what dark energy is, but if we can understand the early universe and what was present in the early universe and how all the pieces fit together then and how it's evolved over time, then we can extrapolate into the future what dark energy will do and how it may or may not destroy the universe in the future.
- And what pieces are needed, do you think, to help understand what dark energy really is? - Well, dark energy is tough because, as far as we can tell, all it does is make the universe expand faster. It doesn't seem to interact with anything else in any other way. It stretches space, and that's it.
So all you can really study with dark energy, as we understand it, is you can study the evolution of the expansion of the universe, how it's changed over time and the expansion rate and so on, and you can study the evolution, the sort of growth of structure in the universe, so how galaxy clusters come together, and you can do that by looking at the past and seeing, watching kind of that growth happen, and that's kind of it.
There are some theories about dark energy that involve things that could interact with experiments, and so people are really hoping to find some connection with an experiment with dark energy, but it might just be a sort of aspect of the universe that there's sort of some number that designates how this expansion works and it's just part of how, it's just written into the equations of gravity. That's called a cosmological constant.
It's just an aspect of the universe that's got this sort of stretchiness in it, and it's also a challenge to understand, why that number? Why does that term exist? We don't know. - So from hearing what you're describing about your work, it just seems like you're almost trying to put together a lot of pieces of the puzzle to talk about how we can go from the beginning to the end and everything in between. From your perspective, what are the most interesting chapters of that story?
- On the timeline, the beginning and the end are, of course, the exciting bits, but in terms of what we're trying to learn, I think the big mysteries, dark matter, dark energy, are the huge questions. The Big Bang, there are a bunch of questions around that.
There's this idea of cosmic inflation, that at some point very, very early on in the universe, after whatever the beginning was, a tiny fraction of a second after that, there was a rapid expansion, and it sort of stretched out space to an extreme degree, and then that rapid expansion calmed down to the normal expansion, and then sort of the kind of hot Big Bang that we talk about, the sort of hot glowing plasma phase of the universe started, and then we got stars and galaxies and so on.
We don't know if cosmic inflation happened or not. There's good reasons to believe it probably did, but there are also theories that are out there that involve not cosmic inflation, so something else that sort of set up the conditions for that hot Big Bang. We don't know where to go with that right now, and it's difficult to study. It's difficult to get strong evidence either way and- - Will newer telescopes help with that? Are we still getting further and further back?
- Well, new ways to observe the cosmic microwave background can help with that. What we're looking for there is, by looking at the details of the light from the cosmic microwave background, this first light in the universe, we might be able to see signs of gravitational waves in the very, very early universe. So this is sort of waves of space-time stretching. If we can see evidence of those, then that can give us a clue that, yes, inflation really did happen.
And back in 2014, we thought we did see that with an experiment called BICEP2. Turned out we were fooled by cosmic dust, so we didn't see that, and there are experiments going on now, observations with new telescopes, hoping to actually see a signature, and that would give us a big hint. Then there are other sort of indirect things that might tell us something about inflation, but it's hard because it's a process that doesn't leave a lot of clues necessarily.
There are a number of things that are very consistent with inflation having happened, but those observations are also consistent with a few other theories that involve different evolutions in the very early universe that led to this hot Big Bang phase. - You wrote a book a year or two ago with the very uplifting title, "The End of Everything." - "The End of Everything." - That was about the end of everything. - "The End of Everything: Astrophysically Speaking." - Astrophysically speaking.
Thanks for clarifying, 'cause it would've been even more terrifying had you not. (Katie and Lauren laugh) Why did you write a book about the end of everything, and can you tell us, what are some of the ways that everything might end astrophysically?
- Right, right, so I think the reason I wrote about the end of the universe as opposed to, say, the beginning, well, for one thing, there are already lots of books about the beginning of the universe, and I didn't think that I needed to write another book about the beginning of the universe, but also, in my various studies in cosmology, I've frequently come across papers or talks that are about different ways the universe might end, and I'm always just fascinated by that question,
and I notice that when I give public talks, the audience gets really excited about the question of the end, and I realized that it's just not out there in the public consciousness enough, how do we think the universe is gonna end, what are the possibilities, and it seemed like a fun opportunity to dig down on those and present what we really know about the future of the universe now, what are the different possibilities, how are we distinguishing between them, and what's all the physics
that sort of comes into all that? It was really fun because I was able to bring in all of my favorite cosmology fun facts and little bits of interesting physics along the way while also talking about this sort of big, scary destruction, and so (laughs) I probably shouldn't laugh at the destruction of the universe, but it's hard- - It's gonna happen way down the road, right?
- Yeah, it's not an immediate fear, and yet it's so overwhelmingly huge that you kinda have to laugh, because what else are you gonna do? The whole universe is gonna be destroyed. Okay. - And if I'm right, one of your scenarios, not your scenarios. You're not the orchestrator of the end of the universe, but a chronicler of it. It could happen right now, right? - Technically, yeah, yeah.
So technically, one of the scenarios called vacuum decay is something that would be triggered by a quantum event that is unpredictable and you wouldn't know that it happened. In principle, that could happen anytime, anywhere. In practice, based on what we think we understand, the timeline for that actually to occur is like 10 to the power of 100 years from now, something like that. Well, we don't know 'cause it's a hard calculation and there's still a lot we're trying to figure out.
I mean, we don't even know if the theory that suggests the possibility of vacuum decay is valid. It's the standard model of particle physics, which is this theory of particle physics that we've validated with experiment but we know has some holes in it, and there's things that aren't explained by it. Maybe vacuum decay will happen. Maybe it'll happen in five minutes, probably not. - I assume you have to tell a lot of people probably not. - I do.
Every time I talk about vacuum decay, I have to be really, really careful to say, "Please do not worry about this," because people do worry about this 'cause some people get very anxious about the idea of the universe suddenly ending, which, on some level, I can understand, but you wouldn't even notice it if it happened because it would happen so quickly. - And it happens to everybody at once.
- And it happens to everyone at once, or like in a sort of bubble of doom that expands at the speed of light, and so it doesn't matter. - Bubble of doom expanding at the speed of light? - Yeah, what is that? What is a bubble of doom? - When the quantum event occurs in one spot, it creates a bubble of a new kind of space called a true vacuum, and that bubble expands at about the speed of light, and therefore you can't see it coming and it just destroys everything immediately when it hits it.
But anyway, the point is- - Don't worry.
- The point is don't worry because there's nothing you can do about it, you wouldn't see it coming, nothing would be left, you wouldn't notice it, and it's all, as I said, based on these ideas about the standard model of particle physics where we know that there are missing pieces to that theory, and so we don't know which pieces may or may not come into play in real possibility of vacuum decay, and there are much more immediate things that we should worry about that are not a tiny,
infinitesimally small chance of happening in like 100 billion years, right? So don't worry about vacuum decay. - Is there a more likely scenario that people billions of years from now should worry about? - I think the most likely scenario, as far as what we know about the universe now, is something called the heat death, which is where the universe basically kind of fizzles out. So we know the universe is currently expanding.
We know it's accelerating in its expansion, and what's happening is really that galaxies are getting farther apart from each other. Everything's getting more and more isolated, and so if we follow that, extrapolate that into the future, in 100 billion years, every galaxy will be kind of on its own, unable to see other galaxies. In 100 billion years, if you put the Hubble Space Telescope up, it won't see anything. It'll just be darkness out there. You might see a few lights in the Milky Way.
- Because everything's expanding away from everything else all the time? - The Milky Way Galaxy, by that time, will have merged with the Andromeda Galaxy, so there will be some stars still in our galaxy. Most of them will have died by then, but some will be around, and that's it. All the other galaxies will be so far away from us moving so quickly we won't be able to see their light anymore. - And this is even if we have a major technological advance. - Oh yeah, yeah.
No, this is a fundamental limit of the universe that, in a 100 billion years, we will not be able to see other galaxies. - Is it like how now we can only see so far until we can't see any further? The observable universe ends, and then whatever is past that. Do we have any idea what's... No? - No, no. I mean, we're pretty sure the universe continues more or less as it is past the edge of the observable universe, but we don't know.
We have no direct information about anything beyond the observable universe. So anyway, in the future, like in 100 billion years, astronomers, physicists, will have no evidence that other galaxies exist. They'll have no evidence of the Big Bang because they won't have any direct data about that. - That's under the assumption that there will be people around to make observations.
Will our galaxy have smashed into Andromeda in a catastrophic way or in a... - It depends on what you mean by catastrophic. - You have a different definition- - Yeah, yeah. Most of the stars will survive when that happens. Even in a galaxy collision, stars don't hit each other generally. There's a lot of empty space. There will be new bursts of star formation, not a whole lot in that collision, but some, so a few things might get fried by supernovae.
Supermassive black holes in the centers of the galaxies will merge, and that could create jets of radiation that might be hazardous, but basically it'll be fine. - That should be the subtitle of your book: "It'll Be Fine." - It'll be fine, yeah, yeah. But of course the Earth will be long dead because- - That's the spirit.
- Yeah, because the Sun only has about 5 billion years more of burning hydrogen, and even before that, in only about a billion years or so, it'll get so hot or so bright, and it'll expand a little bit and it'll boil off the oceans of the Earth, and the Earth will become uninhabitable, so maybe we'll live somewhere else. I don't know, but the Earth will not... Humans will not be on Earth. - Is there anything that can happen after the end of the universe?
Like in this vacuum decay situation, there's this new vacuum. Can anything come out of that? - Unfortunately, based on what we understand of the new vacuum... I'm sorry. (laughs) - I love that you're laughing as you tell us all this bad news about our future. - So once you're inside the new vacuum, the true vacuum, so first of all, your atoms dissociate because you have new laws of physics in there and you don't have electromagnetism anymore.
That's bad, but also it turns out, (laughs) turns out there was a calculation in 1980 suggesting that the new vacuum is gravitationally unstable. Once you're inside and you've been dissociated, you also collapse into a black hole. So, sorry. (laughs) - That's the way I've always wanted to go.
- There's an amazing paper by Coleman and De Luccia from 1980 that goes through this process and that explains that this collapse will probably happen, and they have this wonderful paragraph about how you might have had hope that after the new vacuum, there'd be a new concept of nature, and not only is life as we know it impossible, so is chemistry as we know it impossible, but had some stoic comfort from the fact that perhaps in the course of time,
the new vacuum would sustain, if not life as we know it, at least some structures capable of knowing joy, and then they say, "This possibility has now been eliminated." - Great. - (laughs) It's like, oh man. - I'm curious. You've looked at the universe in its entire lifetime so far and then some. Where do we sit now in the age of the universe?
- Well, so if we're assuming that the heat death is where we're headed, where after you stop being able to see other galaxies, then the universe continues to expand and stars burn out in our galaxy and matter decays and you end up with black holes and the black holes evaporate and then you're just sort of like this cold, dark, empty universe, if that's where we're headed, then on the time scale, we're at the very beginning because the- - Still.
- Yeah, because the amount of time it takes to get to that end stage is like you putting exponents on exponents on exponents. There are not good words for the number of years that you'd have to write down for that. - So we're roughly at 14 billion since the beginning now, and that's dwarfed by the time ahead?
- Yeah, yeah, I mean, it's 100 billion before we just stop being able to see other galaxies, and then trillions and trillions and trillions and trillions onward before black holes evaporate, and then onward and onward before you get to what you would call the end, the true heat death. But if you judge by how much has happened, we're almost at the end.
So you can calculate how many stars have formed in the universe, the rate of star formation in the universe, and it depends on a lot of things, and one of the things it depends on is how often galaxies are colliding with each other and coming in to mix their gas and form new stars that way, right?
And so as the universe is expanding, galaxy collisions are happening less often and starbursts are happening less often, and so we can look back and we can say, somewhere 6 or 7 or 8 or 9 billion years ago, there was way more star formation and it's been declining since then, right? And you can work out that, of all the stars that ever formed in the past or that ever will form in the future based on our evolution, about 90% have already happened, from now until the end of time.
- Does the universe just get kinda more boring and spread out? Oh, great. - Yeah, and just the last five or 10% of stars are gonna form, but all the others have already been born and are either burning or died. So in that sense, we're almost at the end. So I don't know, it depends on whether you wanna- - You still seem so optimistic. - Yeah, it depends on whether you wanna think about how much time you have or how much is gonna happen. - But these are time scales that boggle anyone's- - Yeah.
- What's the term? Vertigo. - Cosmic vertigo? - Cosmic vertigo? - Yeah. - When your mind reels at the scales and the time scale and the size. - I don't know, maybe some people can, but I can't really hold those numbers in my head in any meaningful way. This is why you use scientific notation for everything, 10 to the 11 years, those kinds of numbers, because you have to try and think sort of and factor in powers of 10, or you just get... It's meaningless.
Conceptually, I know that a billion is a thousand times as much as a million, but in my head, it's like it's about twice as much, right? No, it's not. - Billionaires are much richer than millionaires. - Yeah, to an absurd degree, but my own sort of conception is like, oh, it says million and then there's a billion, and it's like it's about twice, but no, no. - I'm glad to hear you do that too.
- Yeah, so I still have to remind myself that these are, when you're thinking and trying to think in a logarithmic scale, you're not really conceptualizing it. You just have to kind of trust the numbers and try and sort of fake the intuition. Again, maybe some people can hold those numbers in their head, but I really can't.
- And talking about these different scenarios where the universe might end, would you be able to put any odds on what percentage you would say it's gonna be this heat death versus something else? - I'd put pretty good odds on the heat death, I'd say, I don't know, maybe like 80% or something like that. There are other possibilities.
So we don't know what dark energy is, and the idea of the heat death depends on dark energy being a cosmological constant where it's just a property of the universe, it has this stretchiness built in, it's just that's a thing that the universe does. Dark energy could be something that's dynamic, that changes with time, that's a sort of field in the universe that has a behavior, and if that's the case, then it could do anything, right?
It could get more powerful over time, and that would lead to something called a Big Rip, where not only are galaxies isolated from each other, they're also torn apart from the inside, and then stars are destroyed and atoms and nuclei and you just tear apart the whole universe. - So violent. - Yeah, yeah, and that one's unlikely for some... There's theoretical reasons to not favor that idea, but the data can't rule it out just yet.
And then there's the Big Crunch, which is something that they used to think in the 60s was most likely where, in the Big Crunch, the expansion of the universe stops and reverses and everything kind of comes back together. We don't think that's likely now 'cause the expansion is accelerating, but if dark energy is something that can change and turn around, it could collapse the universe again.
Because we don't know what dark energy is, we don't know which of those possibilities might happen, and then there's cyclic models, models where the universe ends one way or another and then starts again, and we don't know if those might have happened, and there are some reasons to believe that there are sort of advantages to those models versus an inflationary early universe 'cause you can set up the initial conditions of the universe differently if you have a previous cycle to draw from.
So the cyclic models could give you something else, and those could end with something like a heat death or something like a Big Crunch, depending on what's governing that cycle. There are other possibilities, but if I had to bet on it and if I thought that it would ever, I'd actually ever see the result of that wager, then I would probably put it on the heat death. - A lot of people may know you not so well as Katie Mack and even better as AstroKatie.
How and when did AstroKatie become a thing on Twitter, and how did it... I don't know how many followers you have, but- - A lot. - It's astronomical numbers. - Yeah, I think it's around 400,000 or something now. I don't know. - And that's just when we record, not when we're airing this. - That's true. Yeah, who knows? Maybe they'll all wander off. - Oh, I meant it would grow, not- - Yeah, I know, I know, but you never know. You always wonder. Like dark energy, you don't know which way it'll go.
- Yeah, might turn around. - Yeah. Yeah, so I started on Twitter when I was in grad school, and I just chose the name AstroKatie just as like something... I wanted to throw in astronomy in my name. I don't know, it just seemed like a reasonable choice.
I started it just as a way of kind of like, Twitter was new, I wanted to see what people were doing, and then when I was a postdoc, I saw one of my colleagues was using Twitter to talk about physics, to talk about astronomy, and I thought that was a really interesting way to do things, and he would do things like he would live tweet a conference and a little like one tweet per talk or something about what was going on in a conference, and I thought that was a cool idea,
and at some point I was visiting... He was based at Oxford. His name is Phil Marshall. He was based at Oxford at the time, and I was at Oxford to attend a conference, and he was also at Oxford, but he couldn't make it to the meeting. He was like, "Oh, can you live tweet this for me?" I'm like, "Okay." So I live tweet the talks, and he got a bunch of his followers to, he retweeted my stuff to a bunch of his followers, so it started there.
So it started really just talking to other physicists and astronomers and a few non-scientists who just enjoy following physicists and astronomers, and then it just kind of snowballed. I would tweet more and get more followers through retweets and stuff and it compounds, and there were a few times when I would tweet something that would go kind of viral and then that would give me a huge chunk of new followers.
- Can you think of the first time you had like a, where @AstroKatie had like a viral... - The biggest one was when I was tweeting about climate change, and somebody who doesn't believe in climate change replied to my tweet saying, "Oh, this is a big scam. "It's a hoax. "You should go learn some science." - (laughs) Oops. - (laughs) And I said, "Well, I don't know, man. "I already went and got a PhD in astrophysics. "I feel like more than that would be overkill."
I was just amusing myself by replying to this guy. I didn't think anybody would see it. I wasn't trying to make a big thing. I wasn't quote tweeting him or whatever. It was just a nothing reply, but people saw it and started sharing it and started retweeting it and talking about it like, oh, this is a smackdown. I just wanted... - Just wanted to answer a guy- - Yeah, I was just kind of making a little joke to myself.
Anyway, and it just got super viral, and I went from 40,000 followers to 80,000 in like a week, and then a bunch of minor internet celebrities started following me, and then J.K. Rowling tweeted a screenshot of it on her feed and that got a bunch of followers. It just kind of became this thing. - It seems like you've rolled with it though, because it's an outlet for you to share science. - Yeah, it's been great. I really like Twitter because I don't talk just about science.
I talk a lot about science on Twitter, but I also talk about what's going on in the world and I make jokes about random things and share funny images or whatever, but it's a way for me to both talk about science and get immediate feedback on that, like have conversations, answer questions. That's really valuable as a science communicator to see what people are interested in, see what people are confused about, see how different metaphors work and stuff like that.
But then also I can present myself as a scientist who is not a science robot, and I think that's really valuable as a science communicator to show that, just 'cause I'm a physicist, doesn't mean that I only ever think about physics and I have nothing else going on in my life, because the sort of media perception of scientists is these incredibly cloistered, single-minded people who don't know how to interact with humans, and I think that's a harmful stereotype
for a number of reasons, and I think that it's helpful for a lot of things for scientists to be more visible, be more obviously human. It's a very important, I think, role to play, and so Twitter allows me to do that. It allows me to give people an insight into what's going on in my life, what I care about, and it gives me a platform for advocating for things I think are important as well.
When I tweet about politics or whatever, part of that's because people listen to me and I wanna get ideas out there that I care about, and I don't think that's a contradiction. I think it's sort of intentional oversharing in terms of I want people to see me as a human with lots of different facets, not just representing physics.
- One of the previous times you and I hung out was at Space Camp in Huntsville, Alabama, and that was at a conference full of science communicators who are doing it through social media, through YouTube, really creative ways. When you started to get momentum on Twitter and got connected to all these other science communicators, was that sort of the impetus for, oh, I wanna do this, or had you always thought, "I wanna communicate this science."
- The way I got started into communicating science in general is just that I get really excited about things and I wanna share that excitement, and I think it's just an abundance of enthusiasm that causes me to wanna tell everybody about like, oh, this amazing thing I learned about how orbits work or whatever, and also I've done a lot of writing, so I've always been somebody who's done a ton of writing.
When I was little, I used to write stories and letters and poems and stuff like that, and then I got into science writing as a freelancer through grad school and postdoc, years writing articles for newspapers, magazines, and so I just love communicating about the universe and sort of sharing what's exciting to me, what's really fascinating. Helping people to have those insightful moments, that's just hugely fun for me, and so I think Twitter is part of that.
Twitter helped me a lot in developing my understanding of how to explain things in a simple way 'cause- - In a very small space. - Yeah, and I have a question about that because I've heard a lot of researchers say, and I really agree, that giving a long presentation is a lot easier than giving a short presentation because, and I find that really challenging when I have to give a 15-minute presentation on my work.
You have to take out all these details that are maybe not necessary to the fundamental point, but figuring out what those are is really not easy, and so I think writing a tweet where you're really limited in how much you can share is kind of the ultimate challenge. So how do you face that and how do you decide what details to share, what details the public needs to know, whether it's about science or some of these political issues, whatever it is.
- Well, I mean, it got a lot easier when they went from 120 to 240 characters, (laughs) so that's one thing. It's also possible now on Twitter to do long threads, and so that also takes away some of the pressure, but mostly it's about trying to... It's hard.
I don't think there's a quick, easy method, but you have to think about the wording, so it helps to be really good with sort of a mental thesaurus to be able to choose really compact words to express the same idea, but then also you wanna give a mental picture. Maybe that's through an analogy or maybe it's through helping someone to visualize something.
You wanna give someone something to connect to personally one way or another, and how to do that, it just depends on what you're talking about, but yeah, it's super hard, and even longer-form stuff. I used to write for Cosmos Magazine, which is a magazine in Australia, a science magazine kind of like Discover in the US or something, and I had a column with them, and it was like 700 or 800 words and I'd write every couple of months, and I could write about whatever I wanted.
At one point, I decided I wanted to write about Noether's theorem, which is this idea that there's a connection between conserved quantities and symmetries of nature, and explaining what those two things mean is incredibly difficult, and I won't try and go through it now because it's actually really hard, but this is an idea that's really, really fundamental in physics like the idea of symmetries in general, the idea of if you change something about an equation,
what is it that changes about the physics or doesn't and how is that important, and does the experiment work the same forward or backward in time? Is there rotational symmetry? All these kinds of things are just super fundamental to how physics works, and so I wanted to explain that. It took me like two months to get that into 700 words in a way that was understandable by somebody who has no physics background.
Some of those concepts are super, super hard to explain simply, and it's just a matter of practicing, and sometimes you do need extra words. I couldn't compress Noether's theorem into a tweet in any way that would be giving meaningful information, but it's a really fun challenge I really enjoy. It's like putting together a puzzle.
I enjoy that challenge of trying to find a way to explain something that gets the idea across simply and accessibly without being wrong, 'cause it's very easy to give a bad answer that's short, and people do that. A lot of times, science communicators will do that.
They'll use a metaphor that's not a perfect metaphor, but they won't make it clear that it's not a perfect metaphor, and then people get confused and it's a whole problem trying to give the right amount of detail and make it clear what you're brushing under the carpet and what you're not. It's just hard, but it's something that, if you have a ton of practice 'cause you're on Twitter every day, you get better at it.
- Science communication and outreach is gonna be part of what you're doing here at Perimeter. Can you tell us why you wanted to take on this role? - I've been very fortunate in my career to have opportunities to do both research and public engagement in various ways.
As a postdoc, it was a little bit harder 'cause I was really just being evaluated on my research, and the outreach was sort of my nights-and-weekends job, but when I started at NC State, where I'm currently a professor in the physics department, that job was explicitly written as a job for a public scientist, somebody who does science and also interfaces with the public one way or another, and there's a whole group of us, the public science cluster,
people who are connecting with the public in different ways through either their research or disseminating their work in some way. Going into that job, I was explicitly given the freedom to do public engagement as part of my tenure package and all of that. It wasn't gonna be a detriment to my advancement in the job, and they gave me some extra time by reducing the teaching that I was doing. That's been hugely helpful.
That allowed me to write a book before tenure, which is something that most people do not attempt to do if they're in the physical sciences. When I started talking with Perimeter about this job here, I already knew how that balance could work well.
I really wanted to find a way to continue these two things that I'm really passionate about: doing my research, trying to actually contribute to discoveries and the development of the field, and also sharing everything with the world and sharing my enthusiasm and helping people to understand physics.
And so, fortunately, we were able to put together a role for me here that really does both of those things where I get to have the same research support as any other researcher here, and also explicitly use part of my time to connect with the public, connect with the media, to be a sort of public face of the research side of the institution, and that's super exciting to me.
I love the idea of both working with the amazing people in both of those groups, both cosmology and the public engagement side, and also representing Perimeter Science to the media or the public or whatever when it's possible to do that. I'm thrilled about it. - So are we. - I think it's gonna be an amazing job. Thank you. - We're thrilled as well. We do have some questions that were submitted by people other than us. You wanna take the first one? - Yeah, we have some.
Sure, yeah, there are some graduate students here at Perimeter that sent in some questions. So the first one is a written question sent in from Barbara, who's a PhD student here. She asks, "If you could know one thing, "anything you want, what would it be?" - I would wanna know how the universe began, if inflation really happened, if there was ever a singularity, how that came about. I guess that's asking a lot, but I really wanna know what set off the universe, what set off the Big Bang.
- If you had to take a guess today, we won't hold you to it. - If I had to take a guess, oh my gosh. - Was there a universe before the Big Bang? - I don't know. - That's okay. It's an unfair question. I know it requires a lot of research and math, but I thought I'd just ask you. - I don't know. I think I like the idea that the universe came from nothing and there was some kind of singularity and then the inflation period and then the hot Big Bang. Aesthetically, I kinda like that idea.
I don't know. I can't support that on physics grounds 'cause we just don't have that much information about that, but it's a neat idea. I don't know, I don't know. It's a good question, but anyway, I wanna know. That's what I wanna know. It'd be great to know what dark matter is. I think we'll figure that out. We may never know what the first moment was. - And our next question is from Anna, who's a student in our PSI master's program. I think you met with her. - I've met Anna, yeah.
- Has the process of communicating science and the scientific method to the public changed the way you actually do your own research? - I think it definitely has changed what I work on to some degree.
I mentioned that a lot of what I do is I talk to the theorists, I find out what they're excited about, I talk to the observers, I find out what they're excited about, and I try and make connections, and there have definitely been times when, because I was excited about something to share it with the public or give a talk on it or something like that, I learned more about a topic and then used that information in my research.
So there's definitely been times like, as somebody who's really trying to do big-picture science, really trying to... Cosmology in general, you have to know a lot of things about a lot of different topics, and then the area I work in, it's helpful to have that big picture, helpful to know what a lot of different people are doing and what the big exciting things are.
It's an area where talking to the public a lot is good because it really forces you to read more broadly and to talk to more people and get that big picture, and so certainly the public engagement has changed what I work on to some degree just by giving me sort of more tools, more information. In terms of if it's changed how I work, that's hard to say. It's probably changed how I write my papers to some degree. It's certainly changed how I give talks.
I used to give talks with way more words and equations and bullet points, and now it's way more pictures just because when you give a talk to the public audience, you get used to the fact that you can't just put a bunch of words up there 'cause it's distracting, and people will try and read while you're talking and you can't communicate well that way, and I realized that actually that also applies to professional talks, to research talks.
Unless you're really going through the information on the page as you go, people are not gonna... It's just gonna distract people, so I use more pictures, I do more explaining, I bring information on more slowly because of the experience I've had with the public where I've just learned a lot more about how people absorb information. - Okay, and our last question is from another PhD student named Nitika here at Perimeter.
She asks, "What would you like to share with students "who are entering your field of research?" - I think that as a student, and as a PhD student especially, it can get very lonely and very stressful. There are times when it's just a hard, it's a hard field to be in. Academia in general is just, it can be sort of mentally, emotionally hard. I think the pieces of advice I would give to people who are embarking on something like that would be look after yourself.
Don't sacrifice your mind and body to the field. Try and stay healthy as much as you can and get sleep if you can, and really look after your wellbeing so it doesn't destroy you so you don't burn out and get sick. - Have you had to learn that the hard way? Have you pushed yourself too hard? - Of course, of course, yeah, at times, at times. And then also you're gonna be around a lot of people who are really smart and doing really amazing things, and you can't constantly be comparing yourself.
Everybody feels levels of inadequacy when getting into physics. That is a normal feeling, but also it's important to remind yourself you really do know stuff and try and maintain that sort of enthusiasm and excitement about the field.
For me, one of the ways that I dealt with that when I was going through my academic career was to do a lot of public engagement because when I'm around my colleagues, a lot of times, it's like, oh, I feel like I'm the stupidest person in the room, like I can't keep up or whatever. Everybody has those feelings.
You can get caught up in that mindset, but then when you go and talk to a general public audience, you know so much more about the topic than they do, and so people will come up to you and they'll be like, "Wow, that's amazing. "You're really smart," and you're like, "Oh yeah, I know some stuff." (laughs) - Imposter syndrome is context-dependent. - Yeah, yeah, yeah, so it's really good for keeping up the morale.
And the thing about imposter syndrome specifically, so the idea behind imposter syndrome is you're really not good enough, but you've fooled everyone, and they're gonna find you out someday. My impression of that is like, if you really think that you're an imposter, just keep doing what you're doing 'cause it's going great. (laughs) You're doing way better than you ought to be, so just keep doing that. - Until you get heckled by Stephen Hawking, just assume that you're doing everything right.
- Yeah, it's obviously going super well, much better than it should be, and you can just go with that as long as you can. Milk it. (laughs) I try and keep that perspective on imposter syndrome. - If you could travel back in time to give yourself advice, would it be the same advice? - I would tell myself those things for sure. Depends on how far back I get to travel. - Big Bang. The initial conditions- - Well, there are a lot of things I would change if I could go back to the Big Bang.
I would also try desperately to learn some better time management skills early on 'cause it's really hard to pick those up later, and there are a lot of things where I just really wish I had better balanced my time, but I think that's just, that's a challenge that exists throughout life for all people. I don't know, but maybe I would've been able to get some habits that would serve me well in the future. I'm not sure.
I feel like I balance a lot of things and I don't always do a good job of that, and it would be nice to be better at it. - One last question from me: Is there anything in particular that you're really excited about scientifically or personally and professionally?
- Scientifically, I'm excited by what these new observational programs are gonna show us, so the space telescopes that are coming up, the Square Kilometer Array, the radio telescope array that's gonna show us a lot about the first stars and galaxies. The Vera Ruben Observatory is gonna show us, it's doing a survey that's gonna show us like a billion galaxies and a million supernovae, something like that.
We're gonna get a ton of data, and then we're gonna have much better maps of the universe than we ever did before, and that's gonna be exciting, and gravitational waves are a huge, huge deal, and I'm very excited to see where that goes. I'm not specifically working in gravitational waves myself, but I think that it's just such an exciting area and we're gonna learn so much about the universe. It's just astonishing technology, so I'm very excited about that.
And personally, I'm excited to move to Canada. I'm excited to live here and start this new chapter in my life. - Have you lived in a place with snow before? - Yes, I have. (laughs) Not quite like this, but yes. Princeton got snow. I did my grad school there. I've got good boots. I've got a couple of nice coats. I've got scarves and things. I think I'll make it. - There's a pretty much endless supply of coffee, hot drinks here. - Yeah, that's true.
- Well, we're so excited that you are gonna be joining us at Perimeter very soon, and we're really grateful that you took the time to chat with us. - Thank you so much. This has been really great, and I'm excited to become part of the institute. - Thanks so much for stepping inside the Perimeter. Be sure to subscribe so you don't miss a conversation. We've interviewed a lot of really brilliant scientists whose research spans from the quantum to the cosmos, and we can't wait for you to hear more.
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