Daniel and Kelly’s Extraordinary Universe - Journey to the Beginning of Time (featuring Dan Hooper)

Episode Date: October 31, 2019

A conversation with astrophysicist Dan Hooper about his new book, At the Edge of Time Learn more about your ad-choices at https://www.iheartpodcastnetwork.comSee omnystudio.com/listener for privacy information.

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Search all the smoke and listen now. One of the deepest goals of physics is to help us understand our context. at the center of everything, or are we in an irrelevant little corner of the universe? Was the universe created with us in it? Or did it exist for unimaginable eons before we arrived? The answers to each of these questions helps us know our place or lack of it in the universe. It helps us know how to live our lives. But nothing touches these issues more deeply than understanding the very birth of the universe.

But, if anything, can we ever hope to reveal about those first few moments of creation? Hi, I'm Daniel Whiteson. I'm a particle physicist and a professor at UC Irvine, and I am the co-host. of today's podcast, Daniel and Jorge Explain the Universe, brought to you by iHeartRadio. Listeners of the podcast know that we love to examine big questions, deep questions, questions about things really far away, questions about things under our feet, questions about how things around us work, but we're also interested in the really deep questions, not just questions of space, but also questions of time. And so while Jorge is still away and not available today, I'm very pleased to have

on the podcast today, a friend of mine, a collaborator, a colleague, and a upcoming author of a book I think all of you would be excited about. His name is Dan Hooper. He is a theoretical astrophysicist at Fermi National Accelerator Laboratory. In fact, he is the head of the theoretical astrophysics group there. And he has a new book coming out about the beginning of the universe. It's called At the Edge of Time. And it's going to be available November 5th from Princeton University Press. Now, I've had the opportunity to take a look in an advanced copy of this book, and I think it's awesome. It talks about a lot of the really amazing questions we like to dig into on the podcast. So without further ado, let me introduce to you, my friend and colleague, Dan Hooper.

Thanks. I'm really excited to be here. Yeah, well, thanks for coming on the podcast and talking to us about all the amazing and incredible things that we like to think about and that apparently you like to write about. One thing we like to do in this podcast is talk about things that are on the cutting edge of science. things that scientists themselves are thinking about, but then trying to break it down in a way that makes sense to people. People can actually come away, feeling like they understand what we're talking about, not just repeating various jargon. Thanks. I really enjoy trying to think of ways to convey some of the scientific ideas that I explore in my research for people who aren't scientists, whether that be my non-scientist friends or my family members. I really like stretching that part of

my brain that one uses in communicating these exciting and very different ideas. I think your book does a great job of this of really conveying not just what we know, but also what we don't know, where the edge of knowledge is. And it does something else. It shows us that science is personal. I think one of the great things about your book is that it reflects who you are. It doesn't just show science for being some monolith of knowledge or some sort of objective intellectual pursuit, but it shows us that science really is of the people, by the people, and

for the people, because in the end, science is just humans answering human questions for other humans. Science is always just a work in progress. The questions we're asking today will probably not be the questions that we find answers to, ultimately. And when it comes to the sort of stuff that I work on, I would be shocked and maybe a little disappointed if it turns out that the ideas we have about how things are going to play out turn out to be right. I really like the mystery that's involved and the surprise when we find out something we weren't expecting. I certainly hope so. I love scientific surprises. But tell me, what was your motivation for writing a popular science book about this rather than just sort of continuing in the conversation at the

level of academia? Why bring this question to the people? Long before I ever became a scientist, I loved popular physics books. I used to read any number. of books by books like Paul Davies, Michiokaku, and Kip Thorne. And this stuff just blew my mind, learning about quantum mechanics and learning about relativity, cosmology, and kind of the philosophical implications of all of it. So when I became a scientist, I decided it would be fun to kind of stretch my brain and try to try my hand at popular science writing myself. This isn't the first time I've written a popular science book, but I haven't written popular science in a long time. And it's an exciting new challenge. I love new challenges. And this was no exception.

Wonderful. So as a theoretical astrophysicist and a cosmologist, you're dealing with questions about like the origin of the universe and the beginning of space and time, the very creation of our cosmos. When you travel around, say you're on an airplane and some random person asks you, what do you do? Do you have an easy time explaining to them what you do and why it's? interesting or do you get a sort of a lot of glazed looks the reactions I get are kind of all over the map occasionally you get lucky and you start that conversation and the person is excited and you know maybe they think that's the the perfect person to sit next to for the course of the flight they always wanted to know about cosmology and finally have an opportunity to to ask somebody

all the questions they built up over time and sometimes you sit next to somebody who just for whatever reason, they just don't have the kind of intellectual curiosity for this sort of subject that you or I might have. And then sometimes you get the people who confuse cosmologists with cosmetologist, and that's pretty awkward. So yeah, you can have just about any kind of experience on a plane when you tell them about my line of work. Are you willing to give advice on lipstick colors or not? I mean, I'd be willing to give you my advice on just about anything, but I don't think you should take it. For one thing, I'm, I'm colorblind, so I'd probably be pretty bad at that job. All right. Well, I think that these kind of topics are totally accessible, because I think

everybody wants to know the origins of where we came from, because it tells us something about why we're here and what it means. And I posted a question on Twitter this week, and I said, hey, I get to ask a leading cosmologist questions about the beginning of the universe. What should I ask and boy our listeners really showed up we got a long list of questions and we're going to listen to some of those questions and answer some of those questions but i was just impressed at how much of a vein it touched in people it doesn't surprise me i'm excited about this stuff i guess our listeners of course are also excited about this stuff but i think it goes to something else about cosmology and early universe physics is that it really borders with philosophy you know some of the

questions we ask are hard physics questions like when was dark matter made do we have a model for the production of these nuclei. But the answers to those questions have broad-reaching implications for philosophy, for the nature of our existence, the meaning of it, the context of it. Throughout history, human beings of all times and all cultures have looked up at their night sky and wondered about the universe and how it came to be the way that it is. In that respect, we're just like all of those people. But in one important way, we're really different. for the first time in human history, when we look up at the night sky, we more or less know what it is we're looking at. We understand these things. And that's a truly new development.

I think it's just amazing that we can take pictures of things in the sky. And when we see a star, we know how nuclear fusion works in its core. And when we see planets, we understand how they formed and why they behave the way they do and what they're made of. When we look at the expansion of the universe, and we look at the big bang, we understand how our universe evolved from its first second up to the current era, like over 13.8 billion years. I think that's absolutely flabbergasted, just amazing that we've been able to make this incredible human accomplishment. It's the kind of thing that if you went back a few hundred years and dropped that knowledge on leading minds of the day, their minds would be blown, right? It'd be hard for them to really

even understand what you're talking about. And now we know those things. things. And that gives me enthusiasm that today's questions will one day be answered. The humans will know the answer to the questions we are struggling with today. Makes me want to jump in a time machine and fast forward. In the long run, I'm definitely a scientific optimist. I think only a fool bets against the progress of science in the very long run. We might not solve every question tomorrow, but as long as human beings manage to exist and not destroy themselves, I don't think there are any answerable questions that we won't eventually answer. Wonderful. Well, I noticed in your book that while your topics touch on these important matters that connect to philosophy,

unlike some other noted cosmologists, you sort of stayed in your lane and talked mostly about the physics. And so I want to take the opportunity to push you a little bit. On this podcast, when we have an expert come in, we like to play a game we call Ask the Wrong expert. So I'm going to ask you some questions about philosophy, and this gives you an opportunity to, you know, pontificate ignorantly, and we don't expect you to be an expert. First question is about whether the universe actually exists. So do you think the universe, the physical universe, A, exists sort of outside of our human experience, like it would be there even if we weren't here to experience it? B, only exists as a mathematical model in our minds. C is an unanswerable question

we can never know, or D, you're already regretting coming on to our podcast. I definitely come down on C for this one. All we can really do is organize our consciousness experiences, including our observations of the world, try to make sense of them, try to come up with organizing principles or theories, if you will, that explain as much about our observations as we can, and then use those theories to make predictions about what will happen in our conscious experience going forward. It could be that those theories we construct in that way map very precisely or closely or closely onto something real, a real world that those theories describe, or maybe not.

We don't really have any way of finding out. But it doesn't really matter because science works even if the world it describes is not a real thing. I have a supercomputer in my pocket in the form of a cell phone, and that thing works because of the scientific method. And, you know, modern medicine and transistors and any number of other amazing modern technologies work because of the scientific method, even if the world that it underpins is very different from that described in our theories. Wow, that's amazing. I agree with you. we might not be able to answer it, but to me it matters deeply whether what we're doing

is just sort of playing in our minds or answering real questions about the universe. And that's one of the reasons why I'm very much looking forward to the day when we meet alien physicists and perhaps get a chance to understand how a different kind of consciousness might probe the universe and maybe draw some sort of triangulation there about what's really happening. But in the end, I agree with you. We probably can't ever know. But that leads me to my second question about the working of a human brain. Do you think that the human brain is either, A, deterministic, like a big complicated mechanical watch in which we have no free will? B, deterministic, but yet there's somehow still room in there for free will.

C, non-deterministic because of quantum mechanics like Penrose thinks. Or D, non-deterministic because of some sort of magic, supernatural, extra physical force. I think this is a really good question, but I don't think any of my answer really falls into any of these four categories, or A, B, C, or D. So I'm going to kind of give you my own E, if you will, answer. So I think the laws of nature are not deterministic. Quantum mechanics doesn't appear to be deterministic. It might be in some sort of Everettian mini-world sense, but as far as any experiment I would conduct, I can only probabilistically work out what's going to happen in that experiment. for all intents and purposes, the laws of physics are not deterministic. And since the human brain is a machine that follows the laws of physics in our world, it also is not deterministic. But as far as free will is concerned, I don't think that matters. What I mean by that is just because something in my brain is random and not predictable

doesn't mean I'm free to make any choices. If I walked around flipping a coin to decide whether I'm going to do thing A or thing B next, that doesn't give me any freedom. It just means I'm not predictable. So at least in any morally culpable sense, I don't believe there's any reason to think there's free will in the universe. That's a very sophisticated answer. I think I agree with you on all points. And we're actually going to dig into that in depth in a future episode of this podcast. So thanks for playing along with our silly game.

but the reason we brought you onto the podcast is to talk about what you are an expert in, and that's the early universe in the very beginning of time. And so I want to dig into the details and pick your brain about how our universe began. But first, let's take a quick break. Your entire identity has been fabricated. Your beloved brother goes missing without a trace.

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Okay, we're back and we're talking with Dan Hooper. He's a theoretical physicist at Fermi National Accelerator Laboratory and the author of the upcoming book At the Edge of Time, which explores the very beginning of the universe. And Dan, first question for you I have about what you actually know about is about how the universe began. I would love if you would sort of walk us through the very beginning of the universe. And I'll give you two options here.

Either walk us through forwards from the moments of creation or backwards from what we actually know into what we don't know. But I'd love a sort of tour of the very first moments of the universe. So even if you hadn't given me the option, I definitely would have suggested going from the present backwards because that's just a lot easier way to describe it. So let me do it that way. When we look out at our universe today,

we see that space is expanding. And what I mean by that is all the objects in space, at least the objects that are far away, like galaxies, for example. They're all moving away from us. And the farther away something is from us, the faster it's moving away from us. This is because any two points in space, the amount of space between them is growing as time goes on. This is something we call Hubble's Law. So because space is expanding, that means that in the past, our universe was more compact, more dense, and as a consequence, it was hotter.

And in the future, it will be less dense and even cool. than it is today. So if you run those equations backwards, you'll eventually point in time where the universe was very hot. So 13.8 billion years ago, only a few hundred thousand years after the Big Bang, you reach a point where the entire universe was filled with some light and electrons and protons and things that were all at a temperature of about 3,000 degrees. So 3,000 degrees is an important point in the history of the universe. Because at 3,000 degrees, you find that atoms begin to melt. This is what I mean by that.

So if I take some ordinary atoms and I dump it in some thermal bath somewhere that has a temperature of more than 3,000 degrees. Well, if I do that, those atoms, all the electrons that are bound up on those atoms are going to break off. They're going to basically those atoms are going to fall apart into their protons and nuclei and electrons. So that means that before this key point, 380,000 years after the Big Bang, the universe was full of electrons and protons and nuclei, but no neutral atoms. And then after this point, basically all those things glued together into electrically neutral atoms. Before that transition, the universe was opaque, meaning light couldn't move through space because of all of these charged particles in it. But after this point, the universe became transparent to light. And that means that at this transition, an awful lot of light was dumped into the universe.

And that light exists everywhere today. It's moving in all directions and in all places. And in fact, in this very room or any room, every cubic centimeter of space has over 400 photons that were produced in this transition. We call that the causing microwave background. And over the last 50 years or so, cosmologists have been studying this in greater and greater detail. A lot of what we know about our universe's history comes directly from observing that light that was released when the first atoms were formed only a few hundred thousand years after the Big Bang. All right, but let me ask you a question there to clarify.

So you're saying we look out of the universe, we see that things are expanding. And if we want to run the clock backwards, we say, well, therefore things must have been denser before because things are getting less dense now. And so the universe now is transparent. Light can fly through it. It seems, you know, we can look out in the night sky and see billions of light years away. So you run the clock backwards

until everything sort of scrunches back together. And you talk about this plasma that fills all of space. Now, I think a lot of our listeners probably imagine that the Big Bang is sort of the creation from at one point, that everything in the universe came from one spot. And so if you talk about running the clock back from the current universe and getting to something that fills all of space,

and I think, I wonder if our listeners have a clear mental picture of what that means. Like, are you saying that the cosmic microwave background was created by a plasma that literally filled the entire universe, or was the stuff in the universe sort of smaller and more localized back then? Probably the single biggest misconception about the Big Bang is that it was some event that took place at some place, some explosion that all the stuff came out of. But that kind of misses the point. So when I say the cosmic microwave background fills all of space today, I mean all of space everywhere.

And when it was formed, it was formed at a point in time where the entire universe, all of space was filled with this 3,000 degree plasma that slowly or slowly transformed into a 3,000 degree gas of electrically neutral particles. And if you go back farther, it's not that the Big Bang happened somewhere. It's that the entire universe was in this hot and dense state. The Big Bang wasn't something that happened in one place. It was a state that the universe started out in. So I wonder if people would find it more natural to talk about space being more dense or the stuff in space being more dense rather than actually being smaller. Because it sounds like you're talking about sort of stretching out the space between the stuff,

not actually shrinking it down into a dot. But it's pretty hard to get your mind around an infinite universe filled with an infinite amount of stuff. and having it still squish down into an infinite universe. Well, there are a couple of different ways you can think about it. One way you can think about it is to imagine that the universe might not go on in all directions forever. It might not be infinite, and we don't know. It's possible that that's true. Maybe the universe, if you go far enough in one direction, wraps around on itself.

And this would be a much farther way than we can see at the present time. But maybe if you went far enough, you'd find you'd come out back. where you started. I like to use the analogy of the old arcade game from my youth, asteroids. If you fly the spaceship off the side of the screen, asteroids, you come out on the opposite side of the screen. Maybe our universe works this way too. And if that's the case, then essentially the screen that you're playing on, to take my analogy further, has been expanding. And that means that the total volume of the screen or area of the screen in the two-dimensional example was smaller in the past, but still the screen occupied all of the space that existed

at the time. So if that helps you to think about it better, that's one way you can imagine expanding space without imagining, for example, space growing into something or the Big Bang happening somewhere as opposed to everywhere at the same time. Yeah, and I think that it's just hard for us to grasp the concept of infinity. Like if you take a ruler, there's an infinite number of places on that ruler between, you know, one inch and two inch because, you know, there's an infinite number of real numbers. If you shrunk that ruler, there would still be an infinite number of places, right? The infinity doesn't get less infinite just because you shrunk it, which is sort of counterintuitive. Okay, so let's go back even farther in time

now. So instead of talking about the universe as it was a few hundred thousand years after the Big Bang, let's go back to the first seconds or minutes after the Big Bang. In this state, the universe was at a billion degrees, everywhere throughout all of space, and at a billion degrees, things start to resemble what you would find today inside the core of very massive stars. And that means that nuclear reactions can efficiently go on. So throughout the entire universe, during these first seconds and minutes, the entire universe functioned like a giant nuclear fusion reactor. Protons and neutrons, which up until this point have been free, were being combined

to form things like deuterium and helium and lithium and beryllium and releasing energy in the process. And we can use our theories to calculate how much of all of this should have been formed, how much helium, hydrogen, deuterium, lithium, lithium, and beryllium. and when we go out and measure how much of these things there are in the universe, it turns out that it gives the right answer. So that gives us a lot of confidence that we understand how our universe is expanded and evolved from about the first second after the Big Bang up to the present.

All right, but that's sort of more indirect evidence than the stuff we know about later. Like when we talk about this cosmic microwave background radiation, that's sort of a smoking gun that that plasma existed because, we're seeing it, whereas the indirect evidence is just sort of like the expansion of the universe. Now if we're talking about things that happened before that we can't directly see because the universe was opaque, you're talking about developing models that predict what we would see today if that were true, and then we find that stuff, that's confirmation, but could we find more direct evidence? It would be possible to see more crisply into that sort of initial plasma, those hot

fusion seconds and prove more directly that that really happened? Well, first of all, I think the evidence that the universe played out in the way that the Big Bang theory predicts from the first few seconds onward is pretty strong. It would be quite a coincidence if the ratios of all those light nuclear elements matched what we observed just by, you know, just sheer coincidence. So I think probably a pretty good reason to think that that's how things played out. That being said, there are ways that we one day could hope to more directly measure this era of cosmic history. It's a little bit science fictiony because it's very hard to do.

But someday, I think we will directly measure the neutrinos that were released from our universe about a second after the Big Bang. So kind of like the light was released into the universe a few hundred thousand years after the Big Bang. Those neutrinos started to be able to travel safely through the universe without interacting too much. at about a second after the Big Bang. In other words, the universe became transparent to neutrinos very shortly after the Big Bang. Now, these neutrinos are very hard to detect. And there are some ideas about how one might go about doing it.

But I think, you know, some decades from now, it's very possible that we'll be measuring these neutrinos and studying them, studying those neutrinos in the same sort of way we currently study the photons that were released much later. Wonderful, that's a great point. I think the cosmic microwave background radiation is fascinating because it's light we directly see from the early universe.

And, of course, it's limited because before that time, the universe was opaque, the light that was created before that was reabsorbed. But as you point out, neutrinos operate differently. And the universe is transparent to neutrinos today, and it was transparent earlier, right? That cosmic microwave background, or sorry, that initial plasma in the first 100,000 years or 50,000 years, or first few minutes of the universe, the universe was still transparent to neutrinos then. That's what you're saying. can see those initial neutrinos.

That's right. I mean, it won't be easy. The same reason that the universe was transparent to neutrinos so early makes those neutrinos really hard to detect. But we do imagine one day we'll be able to conduct a sort of measurements that would actually be able to detect these neutrinos and learn what our universe was like only a second after the Big Bang much more directly than we currently can. And that's just another reason why we should keep sort of opening new eyes to the universe,

looking at the universe through electromagnetic radiation, through neutrinos, through gravitational waves, because they give us power to look further and further back in the universe and see different kinds of stuff. But we haven't seen that yet, right? That's right. We can't do these sort of direct observations of the first second or fraction of a second yet.

There's no reason to think that in the distant future, cosmologists won't be able to do precisely that. Well, this is a perfect spot to take a break. We'll be right back. Your entire identity has been fabricated. Your beloved brother goes missing without a trace. You discover the depths of your mother's illness, the way it has echoed and reverberated throughout your life,

impacting your very legacy. Hi, I'm Danny Shapiro. And these are just a few of the profound and powerful stories I'll be mining on our 12th season of Family Secrets. With over 37 million downloads, we continue to be moved and inspired by our guests and their courageously told stories. I can't wait to share 10 powerful new episodes with you, stories of tangled up identities, concealed truths, and the way in which family secrets almost always need to be told. I hope you'll join me and my extraordinary guests for this new season of Family Secrets.

Listen to Family Secrets Season 12 on the IHeart Radio, app, Apple Podcasts, or wherever you get your podcasts. Hey, sis, what if I could promise you you never had to listen to a condescending finance bro? Tell you how to manage your money again. Welcome to Brown Ambition. This is the hard part when you pay down those credit cards. If you haven't gotten to the bottom of why you were racking up credit or turning to credit cards, you may just recreate the same problem a year from now. When you do feel like you are bleeding from these high interest rates, I would start shopping for a debt consolidation loan, starting with your local credit union, shopping around online, looking for some

online lenders because they tend to have fewer fees and be more affordable. Listen, I am not here to judge. It is so expensive in these streets. I 100% can see how in just a few months you can have this much credit card debt when it weighs on you. It's really easy to just like stick your head in the sand. It's nice and dark in the sand. Even if it's scary, it's not going to go away just because you're avoiding it. And in fact, it may get even worse. For more judgment-free money advice listen to brown ambition on the i heart radio app apple podcast or wherever you get your podcast i had this like overwhelming sensation that i had to call her right then and i just hit call said you know hey i'm jacob shick i'm the CEO of one tribe foundation and i just wanted to call and let her

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One Tribe saved my life twice. There's a lot of love that flows through this place, and it's sincere. Now it's a personal mission. Don't have to go to any more funerals, you know. I got blown up on a React mission. I ended up having amputation below the knee of my right leg and the traumatic brain injury

because I landed on my head. Welcome to Season 2 of the Good Stuff. Listen to the Good Stuff podcast on the IHeart Radio app, Apple Podcasts, or wherever you get your podcast. All right, so take us further back. We were, what, a few minutes after the Big Bang? So going back even further into the first seconds or first fractions of a second after the Big Bang, we don't really have any direction. way to create images or even to see the stuff that emerged from this period of our universe's

history. So instead, what we have to do is we have to rely on experiments that we can do in the laboratory where we try to recreate the conditions of the very early universe and just to understand what the laws of physics were at that very, very early time. So the main experiments I'm talking about are what we call particle accelerators, which you know very well, of course, Daniel. So right now, the world's most powerful particle accelerator is the Large Hadron Collider. The Large Hadron Collider is a 17-mile underground circular tunnel, and around that tunnel, powerful magnets accelerate protons to nearly a speed of light. I think the number is 99.9997% of the speed of light, awfully close to the maximum speed limit of the universe. We then take those protons and collide them head on inside of big detectors.

And the goal here is to put as much energy at one place at one time. And through Einstein's equals MC squared, we convert that energy into mass. So we can create exotic forms of matter that don't exist very assessably or readily in our universe today. In 2012, we discovered the Higgs boson this way, but there are a bunch of different kinds of quarks and leptons and things called gauge bosons. And all of these things we can study in these particle accelerators. And all of these things we think were plentiful and abundant throughout the universe's early fraction of a second. I see. So we develop models that we think describe what happened, and then we can go test those models by creating similar situations in the laboratory. Yeah, that's exactly right. So if we don't know what the laws of physics were under these conditions, how the universe works under these really, really high temperatures or energies, we can't really put forth an educated guess about how.

how the early universe might have played out. If we can study those laws of physics in these particle accelerators, we can at least intelligently speculate about what the first, say, trillions of a second after the Big Bang was likely like. Right. So it lets us test our models, so let us understand whether what we think happened might have actually happened. But again, it's not as direct as we'd like.

It's another piece of the evidence that constrains what could have happened. But of course, as humans, we like visual proof. We like very direct evidence. Sometimes I think about solving science questions as the way a detective might be solving a murder mystery. In the end, you'd love to have the body and a lot of physical evidence. But sometimes all you have is indirect constraints.

You know when the person was by video somewhere else, and you have an alibi here and an alibi there. You can sort of piece the story together. Without the direct evidence of the body or the smoking gun, you're never 100% sure, but you can do your best with what you have. Sure, I of course agree, but I think it's important to not say that just because your evidence is indirect, that it's necessarily weak. There are a lot of things that science has done by accumulating indirect evidence that

has led to really strong conclusions, conclusions we have enormous confidence in. Sometimes the right array of indirect evidence can lead you very. confident you understand the problem you're looking at. No, I'm very sensitive to that as well because everything we discover in particle colliders, we have seen indirectly. We never observe these particles in our hands or can play with them or touch them where we're looking at their indirect decays and then the observations in the detectors. That's right.

But just because we haven't ever seen a Higgs boson doesn't mean we're in any way not confident that it exists. We've measured it in numerous number of indirect ways. We measured all these things about it, and as a consequence, we're really sure that the Higgs boson is a real thing that we're observing at the Large Hadron Collider. All right, and so our knowledge of physics lets us extrapolate back, and we can check our understanding of how that works using particle colliders to create really hot, dense, energy-rich environments.

How far back does that take us? How far back do we think we might understand the universe? Well, the protons that we're colliding together at the Large Hadron Collider, they're colliding with the kinds of energies that the particles had about a trillionth of a second after the Big Bang. So by studying these collisions at the Large Hadron Collider, we get a pretty good picture for what the early universe was very likely to be, have been like about a trillionth of a second after the Big Bang. Before that, we don't really have a clue as to what the laws of physics were or how the sequence of events might have played out. And is that because we don't have

accelerators that are big enough? Like, if we built an accelerator the size of the solar system that could collide particles at even higher energy, would that let us see further back in time? Yeah, that's right. If we had a particle accelerator that accelerated particles to even higher speeds and collided them with more energy than a large hadron collider does, we could push back even farther and closer to the Big Bang. We'd understand a laws of physics at earlier times and be able to reasonably construct that early history of our universe. So what do we imagine, what do we think might have happened before a trillionth of a second? Well, we don't know for sure, but we have at least some good reasons to think that at some early point in our universe's history,

space then just expand quickly and steadily, but in kind of a giant burst. This is what we call cosmic inflation. So when we look at, for example, the uniformity of our universe, it's basically got the same amount of stuff everywhere, or when we look at the geometrical flatness of the universe, by which I mean that space on large scales doesn't seem to be curved or warped, but follows the sorts of laws of geometry that you learned in high school, these things lead us to think that the universe probably underwent this burst of inflationary growth at a very early time. That being said, we can't really be sure that happened. We have some, you know, provisional evidence that it probably did. But we don't know much about this period or why or how it took place. All right. And here is a perfect opportunity to ask you a question from Twitter.

Here's a question from Twitter user, myself Barath, who says, how does physics actually test or prove inflation theory? What kind of test would you propose to verify whether inflation was reality or just a model we use? that explains the data we have. That's a great question. So let me start, though, by going back a little bit. So in the 1970s, when the Big Bang theory was kind of becoming the established consensus view of our universe's history, at that point in time, there were a couple of problems that emerged. One is that the universe really seems to be quite uniform, and it's very hard to understand why some piece of the universe way over there and some other piece of the universe.

in some opposite direction, billions and billions and billions of light years away, why they would be so much alike. It really seemed like these parts of the universe had had a chance to synchronize with each other, and we didn't have any way of explaining that. Also, we didn't have any way of understanding why the universe was so flat. And I mentioned this before, but what I really mean by that is if I take three points in space and I draw a triangle between them, this is a huge triangle, billions of light years across, If I add up the angles of that triangle, I always get about 180 degrees. In other words, like the Euclidean geometry you learned about in 9th or 10th grade, that seems to apply to our universe in the largest scales. And that doesn't have to be the case.

Einstein showed us that space can be curved positively or negatively, and we should have kind of expected our universe to have been curved, or at least people argued that. So to solve these puzzles, people around 1980, Alan Gooth and others, proposed that the early universe may have had this inflationary phase where it grew really fast. When it grows, it flattens out space. That's kind of a natural dynamical consequence of inflation. And also, it gives all of the points that we see in space a chance to synchronize early on, explaining why there's so much alike now. Okay, so if that were the end of the story,

I think it would be unclear whether inflation would be a popular theory. It would have been really hard to say that we're really convinced that happened. It would just not be enough evidence. But inflation back in the 80s was shown to make a couple of predictions. For one thing, it said that when you get around one day to measuring the details of the temperature patterns and the cosmic microwave background, you're going to find that those temperature patterns are what we call nearly scale invariant and adiabatic. Now, those are some complicated sounding words, but they predicted fairly specific kinds of patterns in this light. And when we got around to measuring that in the 90s, 2000s, and as recently as the last few years with the Planck satellite, it turns out that those predictions panned out.

The way that these temperature patterns actually appear in the universe are consistent with what inflationary theory predicted. And as a result, most cosmologists today think it's probably pretty likely that inflation or something like it took place. We're not sure, but we think it's pretty likely for the most part. And so that's very important because sometimes you cook up a scientific theory to sort of describe what you've seen. You have a lot of freedom there to sort of tweak the parameters and make sure it describes what you've seen. But the real test, of course, of whether it's real is can it predict something it hasn't

seen yet? And so you're saying that inflation is sort of past that test. It says, if this was true, you should expect to see these weird particular fluctuations in the energy from the early universe, and we have seen that. That's right. If it weren't for these predictions and the fact that they turned out to be correct, it wouldn't be nearly as much confidence that our universe really had an inflationary era shortly after the Big Bang. Do you think that's a widely held view in cosmology? Would a random cosmologist I asked on the street agree with you about that? Yeah, more or less. I mean, there are a few cosmologists out there who, you know, argue against inflation as the best answer. and they're constructing competing theories and things.

But I think if you did a survey, you'd find the vast majority of cosmologists would agree with a statement that our universe probably had an inflation area here. All right. So you've taken us back to the very, very early moments of the universe where we have inflation when the universe expands by a ridiculous quantity in a ridiculously short time. What about before that? What caused inflation? What happened before inflation?

Well, the real answer is we just don't know. We don't have any way to observe how our universe was in this extremely early era of cosmic history, and we don't have any experiments that we know how to do, at least yet, to tell us what the laws of physics that dictated that era might have been. We do know that if you go back far enough in time, the theories we have that describe the laws of physics and our universe must break down. We know this because the general theory of relativity that describes gravity and space and time isn't compatible at, extremely high energies with the laws of quantum mechanics as we know them. So one or both of those theories must break down as it turns out sometime in the first 10 of the minus 43 seconds after the Big Bang.

We simply have no clue what the universe might have been like or even if we're asking the right questions about it during that era that we call the quantum gravity era. Well, that sounds like the way we talk about the interior of black holes. We know that general relativity is a strong theory. It's been tested in lots of ways, but we suspect that inside a black hole, it might be wrong because it gives predictions that disagree with quantum mechanics. Is it a similar way to think about it? Yeah, it's a lot like that.

In fact, I would go as far as to say that it's possible that when we do have a, you know, real theory of quantum gravity, questions like what's inside of a black hole, those questions won't even make sense anymore. They'll have a complete description of nature, but there won't be an investigation. interior of black holes. And maybe something equally surprising pertains to the quantum gravity era of our universe. Who knows? Wonderful. Well, this is the perfect time to ask you a question from a listener. Here's an audio question from Anders from Norway. Hi, this is Anders Moen from Oslo, Norway. I was wondering about time. Did it behave differently when the universe was younger

and denser? That's a great question. So the first thing to appreciate is that time is awfully weird even in the universe today. The sort of linear series of events that physics used to be based on, like in the Newtonian worldview, was overturned by Einstein

more than a century ago. And in general relativity, time really behaves pretty weird. So the length of time that passes between two events will depend on, for example, what frame of reference you're doing the measuring in and things like this.

And being in the presence of a strong gravitational field can make time pass differently and things like this. So time is very weird. But what I would say with that being said is that the way that time works in the universe today is not meaningfully different from how it worked a thousand years or a year or a second after the Big Bang or even a trillionth of a second. But if you go back even farther, if you reach the point of the quantum gravity era, we know that time must have been very different. than anything we're currently imagining. We don't know what it was like, but I think it's a safe bet that it was very different

from anything one might experience today. So you're painting a pretty big question mark earlier than 10 to the minus 43 seconds as in we don't know what's there, we can't even really imagine it. But you're a cosmologist, you spent your life thinking about this stuff. You must have a sort of a mental picture.

When you think about what happened before inflation, when you think about the moment of creation with T equals zero, what do you have in your mind? I'm usually the kind of person who's perfectly happy to speculate about things we don't know anything about. But when it comes to that quantum gravity era, I'm not even, you know, super comfortable doing it. I just, we have no foundation to really build upon. But that being said, you know, some people in the worlds of string theory or loop quantum gravity do try to construct ideas of what sort of things may have existed at this time. maybe the universe wasn't four-dimensional or with three dimensions of space and one of time,

but it had more dimensions of space. And maybe space consisted of, you know, concluded things like, you know, strings and membranes and other sorts of exotic objects. You know, maybe the space itself was in a superposition of different states of curvature and all this sort of stuff. And you can put all these sorts of words of things. I'm not sure that your listeners are going to really be able to, wrap their head around this stuff I'm saying right now, but frankly, I'm not sure that I'm able to either, so we're all in the same boat.

All right, but it was fascinated here anyway. I was wondering, what would you sort of hope for in terms of future experiments? If we're going to get a grasp on what happened before 10 to the minus 43, what future experiments would you like to fund? If you had infinite resources, what would you build in order to give us a clue as to what happened in the very first instance of the universe? Well, in the more near term, we're going to measure the cosmic microwave background in greater and greater detail. We're going to look for things like B-mode polarization and non-gaussianity. These are the sorts of signatures that if we were to see them, would tell us something about the inflationary epoch.

So, for example, if we measure these what we call B-mode polarization signals, you'd be able to know roughly what the energy density of the universe was during inflation. That allows us to like take the list of all of our different inflationary theories and shrink it down into a much more manageable number of possibilities. It won't tell us everything we want to know about inflation, but it will give us a lot closer and it will make us a lot more confident that, you know, something like inflation in fact took place. In the more distant future, a little bit more science fictiony, I imagine one day we're going to study the cause of neutrino background and we're not only going to detect it, but we're going to measure it with the kind of precision that we've already made. measured the cosmic microwave background. So we will learn as much about the universe as it was a second after the Big Bang as we currently know about the universe hundreds of thousands of years after the Big Bang. This is something that will happen a long, long time from now. It's not something that I'm going to see happen in my career probably. But there's lots of reasons to think

that the long-term future of a cosmology is going to be a very exciting endeavor. All these experiments that you envision, they all sound wonderful. And I'd like to know the answers to them also, but would any of them give us an insight to what happened in those very first few moments before 10 to the minus 43? Some of them will give us a clue as to what happened in the later epics, but will any of them pierce that veil and tell us what happened in the quantum gravity era? Well, the veil that separates us from the quantum gravity era is a very thick veil indeed. It's hard to imagine how we're really going to figure out what that period of our universe's history might have been like. I don't know, maybe one day string theorists

will make progress in such a way that allows us to make testable predictions that we'll get at this period of time. But I suspect that when or if we ever do get some insights in this period of time, it will be in the context of theories that we haven't even thought about yet or experiments that I can't even wrap my heads around, like head around. It would be like asking a philosopher from a thousand years ago to speculate about how 20th century physics is going to play out. Um, you know, there's no one could have imagined relativity in quantum mechanics, uh, you know,

some, some distance in time ago like that. And, uh, similarly, I imagine that, uh, if you, you know, if we tried to imagine what physics 300 years from now will look like, uh, we would come up very, very short in trying to put our heads around anything like that or even imagining what that might look like. I agree. I think if you showed a philosopher from a thousand years ago, a children's book about astrophysics, they would not understand it. And in a similar way, if you could somehow steal a children's book about astrophysics from the year 3000, you and I would be baffled. We wouldn't be able to get past the first page, I expect. But those concepts would be very natural to people thinking and breathing and living and asking questions then.

Something I really liked about your book is that you said, we are in a time of reckoning. And it gives me the sense that we expect physics to be revolutionized. We expect that we might learn things about the universe that would fundamentally change our ideas about them. I think this connects back to the sort of philosophical implications of this kind of research. And so to close out, I want to ask you, what do you imagine the sort of deep problems with physics might be reconciled in the next 100 or 200 years? I can't expect you to know the answers. But at least, what do you think are the questions we might get answers to? Well, of course, I don't know for sure. No one does. does. But when I look at the various puzzles and problems faced by cosmologists today, it gives me reason to at least suspect that the early universe played out very differently than the textbooks currently described. So here's what I have in mind. So when I, if we just take the laws of physics as we currently understand them and run them through the early universe, those laws of physics say that all of the matter and all of the antimatter,

have been destroyed. They should have destroyed each other in the first fraction of a second. And that would have left our universe without any atoms in it. And yet, our universe is full of atoms. I'm made of atoms. You're made of atoms. Everything we know and directly experience is made of atoms. So somehow things must have played out differently than anything we currently understand in that first fraction of a second after the Big Bang. Similarly, a problem that I work on a lot is that of dark matter. If you asked a bunch of people specializing in dark matter 10 years ago, they would probably told you that it's likely that dark matter consists of these things called WIMS, weekly interacting massive particles.

But we've looked for WIMS and we know what kind of experiments we needed to do to find WIMS, and we've done those experiments and we just haven't found anything. Now it's possible that WIMS will be discovered any day now, and they're right around the corner. But I think at a minimum, it's fair to say that it's surprising that those WIMS haven't shown up. So that could be that the dark matter is just made of something different. than we had currently imagined, or it might mean that the early universe played out differently. Our arguments for what WIMPs should look like and what experiments we would have to do to discover them were based on our understanding of how things played out in the early universe

when the WIMS were being created. If the early universe played out differently than we had imagined, then the way that dark matter would have been created and the kind of experiments we'd have to do to find dark matter could be very different. And then, of course, there's a problem of inflation. Somehow the universe got very flat, and somehow the universe got very uniform. And inflation's a good description of that, but we don't know how that played out. We don't know how or why inflation happened the way it did. I think it's fair to say that we have more questions than answers when it comes to the inflationary era. and possibly related to inflation is the issue of dark energy.

We've learned in the last 20 years that our universe isn't just expanding. It's expanding at an accelerating rate, and that seems to suggest that empty space has a certain amount of energy built into it, a kind of vacuum energy. Maybe this is similar to the kind of energy that drove inflation shortly after the Big Bang and is happening now in a more gentle way. We don't know, but all of these things, to my mind, collectively point to some very weird and counterintuitive stuff that might have played out in that first second or millionth or billionth or trillions of a second after the Big Bang. That's where my money is on new big revolutions and physics. Well, I appreciate your scientific honesty that you're willing to admit what we don't know. And also, your scientific optimism that one day scientists will unravel these ideas and maybe, a podcast in 100 years, they'll be chatting casually about answers to these questions. Thanks very

much for coming on our podcast today and talking to us about these amazing questions about the nature of the universe and its origins. And remember everybody, Dan's book is called At the Edge of Time. It comes out on November 5th from Princeton University Press. I totally encourage you to check it out if you're into origins of the universe and cosmic questions. Thanks again, Dan, for joining us. And thank you, listeners, for tuning in. If you still have a question after listening to all these explanations, please drop us a line. We'd love to hear from you. You can find us at Facebook, Twitter, and Instagram at Daniel and Jorge, that's one word,

or email us at Feedback at Danielandhorpe.com. Thanks for listening, and remember that Daniel and Jorge Explain the Universe is a production of IHeartRadio. For more podcasts from IHeartRadio, visit the IHeartRourth, Radio app, Apple Podcasts, or wherever you listen to your favorite shows. Get fired up, y'all. Season two of Good Game with Sarah Spain is underway. We just welcomed one of my favorite people, an incomparable soccer icon, Megan Rapino, to the show. And we had a blast. Take a listen.

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