Into the Impossible With Brian Keating - Does the Universe Bounce? A Conversation with Anna Ijjas (#236)

Episode Date: July 3, 2022

Was there a Big Bang? Did the universe emerge from a singularity? Is there any evidence for a Multiverse? Anna Ijjas and I explore these questions and much more, including her incredibly fascinating work on bouncing cosmological models. Anna Ijjas is a research faculty at New York University. Her research lies at the intersection of gravitational theory and cosmology. She has pioneered the application of mathematical and numerical relativity to cosmology with the goal of developing novel theories that explain the origin, structure and evolution of our universe. Her work has already led to several advances in this new field, including the establishment of slow contraction as a rapid and robust smoother. Currently, she is developing novel mathematical and computational methods for studying the effects of modifications of Einstein's relativity theory on cosmology and black holes. Her Website: https://anna-ijjas.com/ Topics discussed include: What should a theorist know about experimental cosmology? Why is the cyclic universe theory not often taught and often ignored? The Friedman Equations. What is geodesic complete? Some alternative theorems. Inflation and scalar fields. Quantum fluctuations in the scalar field. About the Hubble Tension! What's Anna's take? What should we be teaching young cosmologists? 📺 Watch my most popular video about Bouncing Cosmology and more: https://www.youtube.com/watch?v=Gvi2hL2FnOc A New Contender is Here! https://www.youtube.com/watch?v=-6A6myur--c Frank Wilczek https://youtu.be/3z8RqKMQHe0?sub_confirmation=1 Weinstein and Wolfram https://www.youtube.com/watch?v=OI0AZ4Y4Ip4?sub_confirmation=1 Sheldon Glashow: https://youtu.be/a0_iaWgxQtA?sub_confirmation=1 Neil deGrasse Tyson https://youtu.be/1kxgK6J4S5Y Michio Kaku: https://youtu.be/3to9ymn-XKI Michael Saylor: https://youtu.be/CaN_CDKqXOg?sub_confirmation=1 Sir Roger Penrose: https://youtu.be/AMuqyAvX7Wo Be my friend: 🏄‍♂️ Twitter: https://twitter.com/DrBrianKeating 🔔 Subscribe https://www.youtube.com/DrBrianKeating?sub_confirmation=1 📝 Join my mailing list; just click here http://briankeating.com/mailing_list.php ✍️ Detailed Blog posts here: https://briankeating.com/blog.php 🎙️ Listen on audio-only platforms: https://briankeating.com/podcast.php A production of http://imagination.ucsd.edu/ Support the podcast: https://www.patreon.com/drbriankeating Produced by Brian Keating & Stuart Volkow P.G.A. Learn more about your ad choices. Visit megaphone.fm/adchoices

I'm in cosmology, the map, the temperature and isotropy map of the CMB, with the equations that describe it. You know, it's really because in order to, first of all, we share this with everyone in the universe, right? This is just our universe. And in that map, it's all of our physics that we figure and also what we haven't figured. Einstein relativity, the black body radiation, that photons, that light is particle and wave, that electrons, the atomic theory, quantum field curate to understand the two and three-point function of all the statistics. Welcome everybody to an exciting episode of the Into the Impossible podcast featuring yours truly Brian Keating in conversation with a exceptional mind, a mind who is curious and passionate about

the orthodoxy or maybe the unorthodoxy of what has become the standard lore in cosmology. And that's Dr. Anna. of NYU. She's a brilliant theoretician who studies the early universe, cosmological models. She's extremely conversant in what we would consider maybe the standard model of cosmology, so-called Lambda CDM, with inflation layered on top. But she is one of a new breed of scientists who's not content to merely look at what exists and take it as given. She is instead coming up with new models, new ideas, and new theories in collaboration with some of our past guests on The Into the Impossible podcast, including Paul Steinhart, and upcoming guest, Neil Turrock,

who is the Higgs Professor of Physics at the Edinburgh University, where Peter Higgs is, and stay tuned for a biography of Peter Higgs by Frank Close. Wonderful biography, that episode is upcoming. But today's episode features new approaches on cosmology and how we can understand what the early universe was like, maybe without inflation being a required ingredient. And I find that fascinating. And we as scientists should be dispassionate. We shouldn't have a prejudice as to how the universe actually began. So understanding how the universe began is perhaps the most important thing you can do, according to me at least.

And we're trying to do that on the experimental side with the Simon's Observatory, but we should be dispassionate and guided not by prejudice as to how the universe actually began, just because a preponderance of eminent scientists have bequeathed that to us as sort of an inheritance. Some of the proponents from Alan Gooth, Andre Linday and others, including Paul Steinhart and as collaborator, they, you know, have had an evolution in their views on inflation. Over the last 42 years since Alan came up with the idea as a struggling young postdoc at slack But for now, you know, we really have to accept the fact that while many people believe inflation took place beyond a shadow of a doubt, we don't actually have physical evidence and it may be It may just be that we never do get physical evidence that could mean that inflation didn't happen Or it could mean another type of inflationary mechanism that occurred at energy scales too small for us to with cosmic microwave background experiments like this Simon's Observatory,

Simons Array, South Pole Telescope, Bicep, etc. And those will just be inadequate to measure any signatures of inflation which honest to goodness did take place, but we will never know it. So it's important to let many flowers bloom and in this conversation we look at the viewpoint of a practicing cosmologist who has to understand the orthodoxy but is not afraid to be a maverick and to explore things that are not among the orthodoxy, the unorthodox approach to cosmology. So I think you're going to enjoy her perspective. She's a wonderful teacher. She's a scholar and I found it a delight and I'm so glad

to present this conversation by popular demand, Dr. Anna Aegis, enjoy going into the impossible. Any sufficiently advanced technology is indistinguishable from magic. Welcome, everybody. It is not frequent that I get to talk to not only an eminent cosmologist, but someone who's also a friend and a very deep and critical thinker. And that is Dr. Anna Eges, who is joining us all the way across the country, I believe. Anna, where are you joining us from today? Right now from the New York area. New York, where I got my personal Big Bang began 50 years ago in New York State.

And it's a delight to talk to you. Thank you for agreeing to come on the podcast. Thanks for having me. You know, I'm teaching cosmology this quarter. and it's an undergraduate course. And we always conclude with the most interesting thing, which is where do the universe come from? And the answer, honest answers, we don't really know.

But I want to ask you, what is the most fascinating aspect of, why did you become a professional cosmologist? There's millions of things you could do. Why did you become theoretical cosmologists? No, that's a great question, because I didn't exactly have a straight path. I didn't go to undergrad and afterwards decided I've done a PhD in physics, at the public cosmology.

It really is that I did first a PhD, a quick one. And I was writing about the philosophy of science. And then afterwards, you know, I was done. I was 25. And people told, well, you are so young. And you have a physics degree. So why don't you look if you want to do another PhD in Germany. It's quite a common that one of the school PhDs.

And why don't you look if you want to do it in physics? You had such good grades, you know. talk to some people. And, you know, I was talking to the person who was the second leader of my thesis back then in Munich. And he said, well, why don't you look into cosmology? Because if some big discovery will be happening soon, that probably will come from cosmology. And, you know, I really cannot explain why I took that, you know, at face value. But I just then started to take cosmology courses.

I enrolled I was a PhD student and I you know it was fascinating I was really lucky I got my first

cosmology course to I got to hear it with doing it with Slava Mukanov is one of you know the best person you can learn from and I just think I really liked it and it's really

a lot of questions really intrigued me and I really liked also the question that, you know, as a cosmologist, and I'm sure this is something that you enjoy to, you really have to know a little about every part of physics. So I think the combination of, first, by somewhat of an accident coming to the subject, but also, you know, the fact that I would say I'm a conceptual thinker. I like, you know, on the one hand, I like to go into the smallest details of the equation and the computer program. On the other hand, I also like to keep the big picture. And Cosmoly is such a perfect subject for, for people who like both parts of the

story, both the details and the big picture. But, but, you know, really the most fascinating part of this is that we have so many open questions in cosmology. And that perhaps, because we are talking to an experimentalist, I should also say, you know, what's more fascinating that we have experimental access to all these questions? So coming from the philosophy background, you would think all those questions, where is the universe come from, where are we going, what is our place in the universe, those are all more metaphysical questions. And then you realize, no, actually, you guys can go out and measure all the theory

and test all the theories that the make up. So that certainly adds to it, right? So, that's so fascinating. Yeah, I agree with exactly your perspective. In fact, when I teach my students, the first day of class, I say, this is the only subject in the entire physics department that covers every subject in the physics department, except for one, which is biophysics, I've yet to get into how biophysics works into cosmola.

Although I do talk about the origin of life and things like that. Maybe it could be someday I'll get some, you know, I'll do a lab demonstration. I started doing lab demonstrations. You know, these classes are so theoretical. I use this book by my friend Barbara Ryden, which is a wonderful book. And, you know, everybody in it and everything in it is incredibly theoretical, except for, you know, we get into derivations and so forth with the Einstein equations and GR. And you and I will talk a little bit about that.

So I just said, I wonder if anyone's ever did, you know, experiments, you know, demonstrations in cosmology. It turns out there's a lot of things you can do. We have black body radiation. We have acoustic oscillations. Tomorrow I'm going to be doing some nuclear physics demonstrations. They're going to be splitting the atom. No, I'm not going to do that. They won't let me do that without some waivers.

But they will, hopefully I'll get some heavy water, some D2O, and I'll bring in some deuterium into the class and show them how regular water ice cubes flow. but Deuterium ice cubes the sink in ordinary water. We'll see if that actually works out if I have the budget for it. But it's fun to do experiments and people love it. And yet a lot of what most people are interested in when you talk to people like your colleague, Brian Green, or I've had on Neil deGrasse Tyson and I've had on Michi Okaku and all sorts of great names,

people are really interested in things like, well, can a wormhole tell us about ADS-CFT and black hole information, And some of these things are highly philosophical. And yet we never teach our students about philosophy. So I think you came at it from a great perspective, starting with the philosophy, moving in theoretical domain. And I wonder, you know, from your perspective, since you brought it up, I tell my students that it's harder to be an experimental cosmologist. Because not only do you have to know everything in your field of experiment, but you have to understand the theory of what's behind it.

But I say, you don't have to do new theory. In other words, I don't expect them to do the brilliant things that you and your colleagues and your students work on, but I do expect them to be familiar with what you're doing, but not create it. What you feel for an educated person as a theorist? What is the experimental minimum to use Lenny Susskin's kind of terminology? What would you say for a theoretical cosmologist? What should he or she know at a minimum about experiments in general? Well, you know, as much as one can, I think that there is, you know,

difficult to say the minimum. I never thought about this. I think, you know, maybe if it go concrete, I think a theoretical cosmology should definitely be able to read a paper that is about, let's say, CMB or dark energy, any survey data. And not just to read it, but also understand the statistical methods can read the, you know, the data, the maps. So I do think that, you know, it's important, not just to, let me say this way, it's not enough to know the six parameters. I go to the paper and look at the six cosmological parameters that are fine, but I have to fit with my theory. That's not the minimum. That's not even step minus one, I would say.

I think, you know, it's really important to be able to, you know, converse with theorists and know of the ongoing experiments. I think it's really, sorry, experimentalist, I miss a theory. And, you know, know what the most important experiments are. I also think it's very important, you know, at least for me it's very important. You mentioned, you know, we actually actually. know each other to talk to experimentalists. So it's important for experimentalists to talk to theorists. I think it's really important to know your experimentalists.

There are different experimentals go about the experiments differently. They have different interests. They have, you know, different, just as theorists have different strengths and weaknesses. I think it's really important for theorists to personally. So beyond being able to read the paper, I think the minimum is also that you know at least a bunch of leading experimentalists personally. So I would add that definitely. You know, know your experimentalist, know whom you can ask about something if you are not quite sure.

Follow every release. You know, be up to date and don't say, oh, I'm a theorist. I don't have to know everything. Know what a jack-knife test is, if you wish, you know, know when you guys go to at a comma, what everything it takes. And I have respect for what experimentalists are doing. I mean, I have immense respect for you guys what you are doing. It's just really amazing.

You know, just the fact that, you know, I suffer from autism, just the fact that you climb up those mountains and spend it a lot of time to build those telescopes. You know, just this minor aspect that's for you, probably second nature. You know, I think it's really important that apart from, you know, the theoretical minimum experiments, you have personal relationship and personal appreciation

and understand that it's really important to talk to one another. You know, learn on the language, Learn a language what experimentalists will understand. And experimentalists will understand what you're. So I think it's just like, you know, be friends. Be good friends. It's peak pollination season, and my business is scaling fast. To keep the nectar flowing, I need a phone plan with top priority data speeds.

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And have an open mind, open attitude, that it takes both of us to do what we do. And I think, you know, what's interesting to me is that, yeah, we come to the conclusion. The kids take this class, presumably because they're interested in the beginning of the universe. And on the first day, they're disappointed because I say, we don't really discuss the beginning of the universe. because, first of all, you don't know if there was a beginning, A, single beginning. B, we don't know much about its visibility and viability. But also because the subject that we study, just like biology, you don't start with the origin of life when you take a biology class.

You start dissecting frogs or, you know, I don't know what they do in biology. But I think the dean needs to check them out. But in reality, we don't really start with cosmogony. So most people, I don't teach cyclic cosmology in my cosmology class as interested as I am in it. So to what extent do people object to the study of the cyclic universe? What is the kind of objection that people most present about the cyclic universe? You know, I think we have to start probably historically what used to be the objections. And very often people come back with those objections.

also just to know if one already has an answer for them. So as you mentioned, probably if one took a survey among all people in the world, we would find more people who, for one reason or the other, whether it's religious, whether it's due to their upbringing, we would find more who have some cyclic worldview. So that's, I think comes very natural to people in certain parts of the world and people who grew up perhaps in a more Western culture, think more linearly, think that, you know, there has to be actually everything, a beginning and the end and in between some trajectory, very causal, linearly directed thinking.

And so that everything comes from, I think you feel a little uncomfortable. So I think the first feeling is, you know, this is not what I learned. When I was a child that I went to school, I always heard the universe had to have a beginning. That was some sort of an explosion, and that explosion gave rise to everything. And now you come to me and say that the big bang, even if it happened, wasn't an explosion, but maybe it didn't happen. Maybe it was just a transition from a contracting preface. And I think that the first, I think one really has to take it seriously. And this is always the case, right?

And we teach people something in physics that's against our everyday intuition. It doesn't really matter whether it's energy conversion or whether it's, you know, gravity or point out of field here. It's always the fact that people are uncomfortable with the idea that what the idea that they grew up, with. It might not be the idea or might not be how nature works. So I think that, you know, that is the basic attitude right now in certain parts of the world and most physicists grow up with this idea. So I think that that is really something that I take very serious to that, you know, people come with some preconceptions and they like those preconceptions. And then comes the physics, right? So when we, um, um, the first time realized as Einstein's theory,

of general relativity describes the evolution of the universe on large scales, then we, I should say, Alexander Friedman also realized that the universe could choose three different ways to evolve. And one of, so it could expand, it could contract, or it could oscillate between, and he called an oscillating model, between contraction to expansion, contraction to expansion. And that was, you know, he called it oscillating universe, but this is, I would say, the first modern version of a cyclic universe. Now, there were some issues with Friedman's model, and that was very quickly pointed out by Torman.

So, Torman was the person that is being most often quoted when it comes to what's wrong with a cyclic, why might the Cyclic Universe be a wrong idea? And we will probably get back to this, but Torman is very simply, very often quoted in a way, oh, or a Torman has shown that somehow a cyclic universe violates the second law of thermodynamics. So I think that that's what some people call it the entropy problem. So this is the thing, the critique that most people would bring up, not necessarily because they believe in it or they read Torman. But you have heard it one way or the other that probably a cyclic universe has some sort of entropy problem. So that's...

Because you're collapsing, because in his model... Yeah, so there are three aspects of this problem, and, you know, you tell me as to what degree you want to dive into this. But Thurman had... This aspect has three problems. Or the problem has three aspects. The one is... I turned around the sentence. The first one is, you know, that as Friedman imagined it, and that was the model that Thurman criticized...

Every single cycle is the same. So the universe contracts, then advances, then expands. Contracts, then bounces, then expands. And the contraction happens in a way that all physical distances eventually, and we know it doesn't make much sense. Since then, though, that is just from the quantum perspective, not makes sense, a collapse to a single point, right? That is, that is, and that everything crunches into a point,

or a point like something. So all black holes in the universe collapsed together and there is some big mass created. So that was one of the aspects of the problem. There are two more aspects of the problem. The second one is really the question if everything, you know, crunches. Don't you, do you need to infinite entropy stage? I can get out of that phase. And there was a third aspect to the problem.

And this is a more modern aspect of the problem that was people were and, And I have thought a lot about that aspect, namely higher space time. So people believe for a very long time, up until I would say a few years ago, that contracting universes are Einstein behave in a very specific way. And now we have to dive in a little bit. Because if you ask me what would be the most serious problem, it will turn out that the problem that people talk least about is physically the most serious problem that you have to overcome. And this has something to do with the fact, again, we go back to where does our intuition come from from contraction and how does Einstein relativity tells us all of our intuition actually how we imagine it is wrong, it's Newtonium.

And it is really the idea, if I tell you, you have to imagine some contracting space or space time. What you will think of is in homogeneity is growing, everything is collapsing eventually, probably. a mass is being created, or you end up with a big black hole, right? That's what most of us first thing, of a contraction, gravitational collapse is contraction. So a contracting universe is perhaps like a big black hole, is a back hole in the making. And that's not exactly a good condition for transitioning to a universe

that is simple, flat, smooth, as beautiful as you can imagine, both from the distribution of the geometry and then from a matter perspective. And I promise, you know, our intuition is never, never really right within Einstein gravity. Now, what turns out, really, if you look at contracting universes, contraction is anything but collapse. So instead of the gradients growing, Einstein theory tells you, and it has been, has been a long time conjecture, and mathematicians have been lately proving theorems about it, and I have been doing simulations, full numerical relativity simulations, just the same methods, you know, as people are used to simulate colliding black holes, to check this

conjecture, which says contraction is not collapse. Instead of your gradient, your inhomogeneity is your mess growing. Space time as it contracts, it actually inhomogeneity is vanish, and you become, instead of inhomogeneous, you become an isotropic. So the only thing what matters is all gradients, all connectedness within space time vanishes. So instead of a collapse, what happens is space time point starts to develop independently of one another. And so contraction is not collapsed, but is it good enough? Is it homogeneous but an isotropic universe good enough for a balance? Well, no.

You know, if you might want to show now one of the simulations as I send you, and I can show that to you. So we know how contracting universe we can check it. And it's really true that the gradients vanish, but what happens is something that's one cause a mix master chaos or mess. So because the space time points develop independently of one another, what really happens is that in each point, if you were sitting in one point,

what you would observe is that in one direction, space time contracts into other direction it expands and at different rates. And this is not great, because what happens is really that that's why people call it chaos. It's a chaotic behavior of the geometry itself. And this is a third aspect of what we can call under the Torman problem, that a contracting universe one way or the other is not a good precondition for a bounce,

for transitioning to an expanding universe. So that's, I think, you know, if you are a really sophisticated reader of the literature, this would be the three critic points that you would quote. What could be the problem with the contracting universe? It's the crunch problem. It's the entropy problem or contradiction with the same. second law and it is the mixed master chaos problem that space time geometries become really crazy even though you don't collapse you become chaotic and very an isotropic this was a long answer

for a short question right so do you think it's uh you know sometimes i i feel like all these things are problems of marketing like and because we're so used to teaching the story of the freedom and and it's so rich to teach the relativistic equations which can involve things like the spatial curvature of the universe. But you and I just finished singing the praises of my experimentalist friends, ranging from, you know, Lyman Page and the Toco experiment back in 1990, 8, and then the boomerang and Maxima experiments in 99, 2000. We known for 22 years now that the universe has zero spatial curvature,

and yet I spend a week teaching my students out of the 10 weeks I have about this. So is that because, you know, the math is so elegant, and so beautiful, even though, I mean, we don't teach about, well, there used to be that the universe could have essentially, you know, begun from a, you know, from a static or quasi-static state. And actually, we don't know how. Is it a problem of advertising or marketing, or is there some other reason why you think that people aren't as familiar with cyclic universes in the context of the history of cosmology, but even current work in investigations?

Do you feel like there's basically a marketing problem, so to speak? That's a tough question. You know, I actually think you can call it a marketing problem, but I believe that, you know, very often we teach different subjects and physics as people, as ideas developed, how we came to know about them. For example, and I don't, so when you mention spatial curvature, so a lot and we should also praise the theorist of the last 40 or 50 years, how we came to our current model, how we just came to appreciate that we might need something to patch the old Hot Big Bang model, that, you know, really describes our universe. We call it Hot Big Bang, but it's really the description between, let's say, nuclear synthesis and today, that people realized, well, first, you know, they looked out to the universe. Those were, you know, your previous colleagues, studying with Friedman.

And so this is, this is, the universe is expanding. And it's geometry. You already named the Friedman equations is very elegant. It doesn't matter where you are, in what direction you look. That's what we call homogeneous and isotropic. It's everywhere the same on large scales. Of course, not on small scales. This is crazy.

Well, everything looks different when we look around, But if we go to large enough scales beyond the scale of galaxies, then everything looks very elegant. And you would think that simplicity is maybe this is very natural, right? So that's what we're doing. How could it be different? Why would it not be simple? Why would it not be the simplest possibility? And I think, you know, in science, it's really important to be unconventional very often when you want to find something new.

And people said, well, let's check it. And let's check it again. Einstein Relativity. What does the relativity tells us? What if we let's just run the movie backwards, starting from today? Let's just be the simplest deviation. And the simplest deviation is your curvature term. Let's see that curvature term remains small if it started, start with it being small today.

A lot of people discover it's actually growing, right? So what really happened is that there is an instability. Even if you start with small but not exceeding this small curvature, you would have to see today, given the equations with which that you used to describe the large-scale evolution, what you would have to seize large curvature contributions. And that was really, I think, a very, very short history to the upcoming of this discomfort where maybe the hot big bank theory is incomplete. And that's why I think, you know, one teaches it this way.

Now, and that was also a very important insight that led them to the development of inflationary cosmology, of which I should say than the cyclic considerations grew out. Some people who develop inflationary cosmology, but also the same people who were the first contributors to the cyclic cosmology. And then I think, you know, it is really just, it stuck. It stuck this explanation that, you know, we just look at the Friedman equation with some curvature because it has been so helpful in the past. But, you know, what many people don't teach, you know.

And I find, you know, looking at just the contracting solution of the Friedman equation, so educational because it tells you so much about, you just learn so much about how gravity behaves in the context of Einstein relativity that we believe is a description of gravity on many, many scales is the correct description. And so if you, you know, I think that both the relativists

and the cosmologists just teach it for the first, you know, the first reason should be you learn so much. First of all, most people don't know that the Friedman equations, right, they admit both a contracting and an expanding solution. And it's in the initial conditions. We tell the equations whether we want to have the contracting or an expanding solution. But I don't not teach it.

I think it's historical. And now you tell me, should one teach it? Yeah, absolutely. One should teach it both to get the right intuition about gravity. But then afterwards, you know what, and that's what I got so excited about is, you know, it really opens up a completely new set of possibilities that might be actually. the right explanation of what we see when we look out, for example, into the microwave background. So I would agree with you, again, yeah, it has a marketing problem. Yeah. Yeah, I think so too.

And actually, you know, when I think about even the explanation that inflation purports to provide, I think where inflation has been successful is not in explaining where the universe came from or explaining where the elements came from or all sorts of things, because oftentimes it raises more questions than it actually answers, but rather as a theory of structure formation. And before we get to how structures can occur in a cyclic and the new cyclic cosmology that you and others have developed, I wonder if we could kind of explain this most common objection that I spoke about with Will Kinney a few months back for his book, An Infinity of Worlds, which involves, you know, doesn't shy away from, you know, the kind of quantum runaway, as you guys

call it the multiverse problem. In fact, it embraces it as a core tenant of his work, which I endorsed on the back of his book, along with your friend, the other more popular Brian of cosmology there in New York City area. But I want to ask you, what he seemed to say was an objection to the bouncing model was this issue of geodesic completion.

I wonder, what does that mean? And why doesn't it afflict the bouncing model? just the same way, or the inflationary model, perhaps, is it maybe worth detouring first to talk about the Bordeaux-Velan theorem? And can you talk about what is a geodesic and what does geodesically complete mean? And then maybe we'll get into this BGV ideas. Maybe, but, you know, it's actually a really technical concept, right? So I'm very happy to talk about it because...

Yeah, my audience is the most brilliant in the whole universe, or multiverse, according to the... Wait to hear. No, I actually just attended a conference last week, and I was chatting with Roger Penrose about geodesic completeness in cyclic cosmologists. So we share a lot of, you know, intuition ideas how it might work. But let's get back to, and I mentioned Roger for a particular reason, because one has to start really with him and Stephen Hawking when one starts to talk about geodesic completeness, since geodesic completeness is really a technical feature. of Einstein gravity. And this came up in their first

and probably upon today most prominently, more prominently, probably than the BGV or Borg-Welanquin theorems, the Halking Fenru's singularity theorems. They actually should be called incompleteness theorems because what they show is that in a certain sense, so if you follow the GED is the path that's within relativity, massive particles travel.

And the question was, you know, how far back in time can you follow the path of massive particles? Finitely or infinitely far? And what Penner's and Hawking have shown very simple speaking. So none of my mathematicians friend would, you know, probably approve this at a higher level. But if you want to have to show this explanation and they say what they have shown is that general relativity is incomplete, geodesically incomplete, because within finite time, massive particles reach a singular surface.

Your audience is brilliant, so I can call it this way. So you reach a singularity. And that's how the singularity theorem stuck, but it's really a juadisic incompleteness theorem about relativity. And what Penrose and Hawking have been interested in or very interested in

was expanding space time that expand at a deserated rate, let's say simply matter or radiation-dominated. space time. Those space times were also well describing the hot Big Bang model, those space times that start with radiation domination and then matter domination. It would apply also to

space times that are matter, dominate or universes and are described by Einstein gravity. And it's very simple. Now that you have this concept of what they were following, they were following the trajectories of massive particles. What Borgut and Wilhelm can add it to is

they extended the theorem to to space time that involve an inflation rate, that involve acceleration. And they have shown that space time that are expanding at an accelerated rate, inflationary space time, for example, are also geodesically incomplete. So if you follow the path of massive particles,

now what you will see is within a finite time in certain coordinates. They call it conformal coordinates, but this is really technical. So the important thing was that you reach, to singular surface. That was important about Bord-Gut-Welanken. Now, why is it important?

Why would one care about technical terms in cosmology? But some people actually use this to show that the universe necessarily needs to have a beginning, right? And I think that that's when one goes beyond what the mathematics tells you, what the theory tells you. It's really a feature of a theory. You cannot tell if you just use Einstein gravity, then the equations break down after at an answer to point. It's more like a no-go theorem, which is one of my problems with a lot of

inflation, you know, with the slow roll conditions, I often hear, and I can say this because I'm not working in this field, even if you don't, you know, subscribe to what I'm saying. But people say, oh, the slow roll inflation ends when the slow roll conditions end, you know, when they're violated. But I'm like, well, how does the Infelon know anything about what we call the slow roll? It just seems like that's a, that's a consistency problem for us to deal with. But, you know, It's like if they say about birds, you know, birds don't really need the study of ornithologists to, you know, to know how they go about their daily business. So isn't this just saying that the universe, that the math breaks down at a certain point and what we have now needs a quantum theory of gravity, not that there's a big bang or a singularity. Isn't that sort of an interpretation?

I think this is a perfect interpretation of it. By the way, pandros who introduced a singularity theorem's works on cyclicasmoges, right? I mean, I know that Roger is your good friend. So many people, because I should have started. Maybe I should not quote Tom. Maybe nowadays, of course, many people say, but don't the singular theorems prove the big bank. No, they prove really as you said it. I don't think that one can say it better than you said it, Brian.

That space time, no, no, no, no, honestly. It's a high praise from you. But if it's true, one has to say it. So that the Einstein equations are not, you know, that are suited to explain. explained a bit, but whatever is, what you call either a big bang or a bounce or whatever, or in Rogers model, a transition from one, as he called it, Eon to another. This is exactly what it is, but, you know, I should not, I don't think that it's good to, in a certain sense, there was, oh, is it important? I also think that it's important,

because whenever we see, whenever we can point out the limitation of a theory, that opens up a new question. We know, oh, okay, this is really important, the singularity theorems, or board, good, Wilynkin, are important because we know that those space, if you want to explain

where those space time come from, as, and you know, as theories, but also then later as experimentalists, you should be interested in explaining and then showing it, then we have to know

what the limitations of our theories are, and in that sense, it's helpful. But of course, that's what I'm saying, perfect formulation. It doesn't tell anything

about what replaces the Einstein equations there and what physics that represents, replacement know about the theorems. So it's mathematics. So the theorem rests on certain assumptions. And one assumption is, of course, that gravity is described by Einstein relativity, but there is a more important assumption. These theorems rest on the assumption that the masses of particles remain constant. And that's a very strong assumption. And under that assumption,

and it was already shown if you read the, I think, second to last or something like it, the last column in the printed version of Wordgood Willankin paper, they show that under that assumption, you can have a cyclic universe that includes infinitely many cycles

and is nevertheless geodesically incomplete. And this is true. This is definitely where the field was about 20 years ago. So whatever cyclic model would take whether this is the model that I work on, whether it's the model that colleagues worked on, let's say, whether it's Steinhardturok, whether it's Brandenberger, whoever works on these models, as long as you keep the mass of your particles constant, the theorems apply.

And as long as your theory of gravity is Einstein, gravity or certain energy condition, as we call it, which is somewhat of an equivalent statement that are satisfied. Now that was a brilliant recognition, and I think it came from really two directions. One of them is Roger, and the other one were Ipach bars, who is actually very close to you sitting at the University of Southern California, Neil Turok, and Paul Steinhart in about a little bit over 10 years ago. They say, well, we know from fundamental physics, whether you think of the Higgs or whether you think of some sort of symmetry restoration in the early universe,

that is probably not true that the masses of particles remain constant. Whether due to the Higgs mechanism, that, you know, for example, and that was the Bar-Stein-Harturok idea, the particles gain a very big mass during contraction, or the pendulose is a beautiful pontoon tithia that may be due to the restoration of conformal symmetry around the transition from one cycle to the other, the particles become massless.

So in two ways, you can break the assumptions of the, theorem. And, you know, really, this is unfortunate not my idea. I was a grad student back then I wrote to you earlier, and I was really envious of this idea, because then you can compute. This is, just talk about it, and I'm sure your audience knows it, since you have had a lot of more technical discussions with Guestan with me, and that one, one, one formulates this question of how far can I drag back the world line of massive particles in a form of an integral. And if one has a varying mass, whether due to the Higgs mechanism, you make them big and heavy during the contracting phase, or you make them massless during a conformer symmetry restoration,

or due to conform a symmetry restoration, it turns out that those integrals don't converge. As we say, they are not finite, so you evade the conclusions of the old singularity theorems or incompleteness So, you know, it's fairly well-sighted in the literature of these papers, especially the bars Steinhardturoc papers. So I would say that this is very elegant. So that's what shows that, you know, you can have cyclic universes that are geodesically complete. Now, I must say that, you know, I don't know if you couldn't apply this to just an eternally

expanding universe. one should look at it. I think it's an open question, but it's a really important insight, and I would want to emphasize it, that the assumptions of the theorems are really important, and loopholes are, of course, always in which of the assumptions are related to which of the assumptions might be relaxed,

might be meaningfully relaxed for the physical world, and this is here the constant mass of the particles. I should say really, I'm really, really sad that this wasn't my idea, something that I would have a lot of figures. Yeah, including one of the ones that I associate with you, maybe, maybe, you know, it's just, I can just give you so much praise. But, you know, this issue that really appeals to me so much is, you know, something that you pointed out to me a long time ago, or a couple of years now, which, you know, before COVID,

everything seems like decades ago. And that was this idea that the key kind of core idea is that the contraction is slow. and we have this in your model, and we have this notion, you know, the big crunch is like the inverse of the big bang, and therefore it's going to be this violent, you know, disruptive, incredibly, you know, monumental occurrence. But if you convince me, you know, that this is not the case. So maybe you can speak about these ideas that you've worked so assiduously on. What is the idea of slow contraction? How does that play in and really solve all these problems that play? previous attempts going back 100 years almost.

I think there are, you know, it's important to look at both aspects of the cyclic evolution. There are really three, but the third one we all know and don't question. That's the current expanding phase, right? So cyclic cosmologists have really have to tackle three parts. The one is, maybe I'll talk about it in the second, the slow contraction phase. That's the phase that precedes the bounce. and in models of cyclic cosmology, it's really important. This is the phase during which the conditions are being generated

that should explain the large-scale structure that we observe today, that you guys observe and you look into your telescopes. The contracting phase is connected to the hot expanding phase by a cosmological band. And typically, you know, cosmology and cosmologists since, you know, since,

really since the introduction of inflation work in a modular way. So Cosmojis are very modular, so you often focus on one phase, try to tackle the problems, and then you hope that you can attach them on to the next phase, and then you hope that you can attach them to the next phase. And in this sense, you know,

what I believe we all agree on, really, because, you know, you and your colleagues have shown it, so beautiful and convincingly is the hot expanding phase. So with nuclear synthesis and today, when we are just entering dark energy domination, there is very little room to big. One can work on what the dark matter is, but that, you know, the large-scale evolution is very well described by if we just, as you measure it, we know that about what percentage of the total energy density is matter.

That's enough for us. And it's a very important question about the dark matter is, but, you know, that it's not so important from the, from the perspective of can I describe the large-scale evolution? And now when we come to the contracting phase, so let's put, let's think in a modular way, so put the bounce aside a little bit, and let's talk about the contracting phase,

because that's really something, that is something that you can well-describe, simulate, and make predictions about, or using it by way of it. And the contracting phases, you know, for just to understand what's happening, it's really important that we often speak about contraction, expansion, axiress expansion, deserated expansion, slow contraction, fast contraction. But it's really important, you know, to invoke us that within relativity,

you always have to think of two scales. You cannot just talk about, you know, what do object in space time, for example, two black holes do relative to one another. That's, you know, if they move apart from one another, that's expansion, if the distance between them is shrinking, that's what they go contraction. But for cosmologists, it's very important to look at a second quantity. And this is the quantity that tells us as to how far we can see at a given time. This is a Hubble radius, right?

So we have, we have, or we can say it roughly, this is the distance of causal interactions. And now for Cosmology is really important. And this is something we learned from people who first developed inflation, how important it is to solve cosmological problems, to look at both scales at the same time and the relative dynamics of the two scales. And it's important as the beauty of Einstein relativity that the distance between objects or physical distances move at a different rate, evolve at a different rate, than the Hubble radius. so the scale of interactions of causal interactions. And what the rate is it is determined by the matter content of the universe. So what is slow contraction? But let's start with what is a disarrated expansion.

If the universe is dominated by radiation or matter, then what we know is then the hobo radius is expanding faster than the distance is between object. And that's the reason why we see more than what was in our causal past. And that's that's one way of saying. that we have an initial conditions problem. Today, we know we see actually 10 to the 28, 10 to the 29 hubble patches, that were Hubble patches in the early universe.

That is one way of saying we have a problem, because they should not have interacted with one another. Now, slow contract is decelerating because physical distances expands slower, and it will be important for slow contraction relative to the hubble radius. Now, if you want to solve this problem, what we learned since the 80s, what you have to do is that physical distance, distances, again, move at a different rate, but in a certain sense in an inverse way. What do we need? We need that when we start, and that was the original idea of inflation tool, when we started

one hubble patch that has almost the right features, we want to extend the features of that hubble patch over many, many hubble patches by the end of this phase. And what does slow contraction do? You start with a huge hubble patch, at very low energies. And what you say is we will hardly move physical distances towards one another. That's why it's slow. Well, what moves fastest, on the other hand, you shrink on your physical patch, the hubbub radius at a very fast rate.

So slow contraction is slow if you are a black hole or a local observer, but it's very fast from the perspective of the hubbop patch. So all of a sudden, you lose sight, very quickly lose sight of many things. Why is this good? Well, it is good because while this dynamics is occurring, two very important things happen, which we know, and you know, since you are a cosmologist, they are both important. The first thing is obviously the extend local features on super Hubble scales.

That's really important because we see today that the same feature extend over exponentially many Hubble scales. So that's given to you. And that's a really elegant, it comes out automatically of the theory. Slow contraction means you cannot help it. Features become extended over super Hubble scales. But it's a second more important thing. And this is something I've worked on a lot lately. It turns out you can write it on pencil and paper.

It's much nicer to do it with a computer. So you can start with any kind of initial conditions. And what I mean is metric configuration. You can very massive geometry. You can have lots of curvature. lots of anisotropies, the sheer, directionality in your geometry. Your matter content can be very messy. The only important thing is you have a particle scale in there.

If you have a particular scale of field, and it doesn't have to dominate the energy density, it doesn't have to have an elegant distribution, the only thing what you need for it is that it has a potential energy, which is negative, sufficient to negative, and the potential energy curve is sufficient to steep, then you can start with almost arbitrary initial, conditions. And this will give you a flat and smooth universe. So this is beautiful. And why it's

happening, well, it's happening for two reasons. The one reason is this, it looks, so space time, and this is something I want to get back to a point that people told you. Remember, I said, the concern with the contracting universe was not that it's collapsing within Einstein gravity, but it's becoming anisotropy dominated. So everybody is sheer. And that's not, I mean, you know, It's not how the microwave background looks. It's not how a large-scale universe look. But what happens really is if you have the differences, the difference between those considerations and our consideration is the scalar.

Once you drop into the scalar field, that could be the Higgs. It could be that the Hicks has a true negative minimum or some other scalar. And once you have the scalar, it turns out that space time becomes still local, the gradient vanish. So for free, as in every contracting space, you don't have to be buried out in homogeneity. Half of a price is done. Half of the task is done.

And the second thing, what happens is instead of going to a mess, this scalar with a negative potential energy density, task paste on, I'm talking here metaphorically, but it's really the case what you see, it makes all the difference. Since instead of going to this chaotic mess, which is sheer dominated, you go to a flat Friedman-Robbins-Walker.

So that's the beauty of it. And this is now, So both that the smoothness and flatness is on super Hubble scales, and that it's generated from starting from really, really arbitrary, nearly arbitrary conditions. You know, this is something that makes it very exciting to look at these cosmologists,

also because you didn't introduce any different theory of gravity. So everything what you need to explain flatness and smoothness is given to you with Einstein gravity, contracting universe, if there is a scale of field that has a sufficiently steep negative potential. To next, because you and I had a friendly debate. And again, I'm so grateful to have friends like you that can explain things to me. I'm a simple experimentalist, but I have a great detailed affection for ideas,

both classical and new ideas like you have brought so many creative new ideas to this field. But, you know, I always say that it would be great, you know, if there was an alternative to inflation that didn't have a scalar field. Because the thing that most troubles me until, you know, 2012, we didn't know of any scalar fields that existed, let alone one that was cosmologically important. And then, of course, we suspected the Higgs existed, but the Higgs is the only known scalar field. And so I thought, well, you know, it'll be great if instead of the inflaton, you shouldn't multiply hypotheses, as I think, Descartes said or somebody said way back when you should never have excessive, excessive, you know, parameters, if you will, and modern parlance. And you corrected me because you said, well, you know, what is, what's so bad about a scalar field? You didn't fight back, you know,

the way that, say, Sir Roger does, right? Sir Roger has these Aribons and, and again, he's a friend of mine. And so, and I push back on him too because I say, you know, he has these, he doesn't have a scalar field per se, but then he has to account for how dark matter evolves because the dark matter is providing some version of this effect that you are solving with a scalar field. So now you corrected me, and I wonder if you can recapitulate that. Why is it not so troublesome to have a scalar field in the bouncing alternative models to inflation? Well, I think, you know, in general, what I wrote to you is it's in general not troublesome to have a scalar field in my point of view, you know. It's probably one has to pan back a little bit because a lot of things, how you judge a theory

depends on what you expect from a theory, what you think a theory should deliver, and under what condition, what you accept as a good ingredient or as an acceptable ingredient and what you don't. And I believe, you know, the simple explanation is we haven't found any. anything simpler that delivers us the same. So I think that, you know, the idea of simplicity with respect to theorists is a little bit of a, it can be used in very different ways, but it's always a relative concept. Right? You have two theories.

And if they make, if they give you the same amount, if they deliver the same amount, then you can say the simpler theory should be preferred. And what do I mean here? Well, first of all, we need the background flatness and smoothness, but we also need the origin of structure. So we also need the source of what reveals its structure, which reveals itself as temperature and isotropies of the microwave background. So if we need that, then we know that those are sourced by some scalar degree of freedom.

Now, it might be a condensate. That would not be a scalar field. But right now, our best descriptions are using the scalar. And the second reason why I find, you know, the scales, and you know it because we have corresponded about that, that we know how to introduce quantum fluctuations for a scalar field on a locally flat background. We know quantum field here in flat background.

And our best knowledge tells us and our best observations of the microwave background, that the origin of the temperature and isotropies are quantum fluctuations in the curvature, which is a scalar degree of freedom, but we believe that was excited by some scalar matter density, which is a scalar field. So this is a complicated explanation, but the point is scalar fluctuations in a scalar field will lead to scalar fluctuations in the curvature which relate to temperature fluctuation in the microwave background. So you need some sort of scalar. my answer. And because we

excite a scalar degree of freedom of the metric, therefore it doesn't seem to be so unnatural to have a scale of field that does it. Now you could say, well, this is circular, right? You know what you have to do, therefore you introduce a scale of field. How do you know what condensate? It could not do it. How do you let something else could not do it?

But I don't. And you know, I think that it's important that people look into alternatives. I can live with it because it's overall in theoretical physics. But just just because I can live with it and I think, you know, for me it's more important right now to figure out if I can, you know, generate a good bounce model, can put it on the computer, and therefore I won't look at right now, look into it if I can have a better idea.

I think it's very important to explore. So therefore, you know, just because I can live with it, it doesn't mean that this is the simplest explanation possible. I think it's simple enough for the purposes that we need it for. But if we had a simpler explanation, then we need another ingredient, you know, because I appreciate that you experimentalists would like to measure directly whatever it generates the microwave background. And this invisible field, whether it's during inflation or during slow contraction, is a little bit bothersome, right? So I appreciated that, you know, this is something that, you know, you would like to exchange or trade for something that can be directly measured.

So I think people should go for it and see if one can replace it by something simpler. But right now for the reasons, it's a little bit of a theoretical reason I'm not bothered by. and because it's, you know, overall in theoretical physics. Have you ever rearranged your furniture and discovered the carpet underneath looks brand new, while the rest of it looks, well, not so new? It's time for a carpet upgrade. At the Home Depot, we have stylish choices at simple prices from all the top brands. Best of all, we can install it for you, starting at only 49 cents per square foot.

So all you have to do is pick your perfect floor. Start your carpet project today at the Home Depot. How doers get more done. Exclusions apply for licenses, see homedeeper.com slash license numbers. Let me ask if the final remaining minutes before I jump on, not a telescope, Anna, unfortunately I spend most of my time on telecons, but, and I do conversations like these because it makes me sane and I appreciate it.

I want to get, because I can't resist. What is your take on the Hubble tension? Is there something fundamental at work here? Is it more prosaic that, you know, we missed the systematic or, and so forth? I'm going to be talking with Adam Reese this, this. week. By the time my interview with you airs this interview, it'll be long in the past. So do tune in in the past. I don't know. That violates causality. But anyway, Anna, so he's going to be talking, obviously he has new measurement, kind of a percent level measurement of the Hubble constant.

Do you think there's anything else that could be going on? Or let me ask you, is there, do you have an explanation, you know, that you prefer hypothetically for resolving this? Is it, Is it a fundamental issue that could be shaking things up, or is it more likely to be a systematic error, as I think it was. You say, I was telling you, I think it's important if you are a theorist to have good friends. Among experimentalists, and you know whom you trust and maybe did a pre-selection or not, or whom you trust more. Of course, you trust everyone, but whom you trust more.

And I would say those people that I trust most tell me that it's likely not. physics, it's likely of systematics. I'm not, I'm not an analyst and I'm not an observer. So I would say the people whom I trust would not yet be ready to declare it. That is a mild expression. Some are very sure it's systematic. So, you know, I think it relates a little bit high view this, how have you everything, whether it was, you know, bicep two, whether it's,

this tension or the an isotopic spot. I like to wait, wait it out. You know, I, I don't like ambulance chasing. So I'm not the type of physicists that, that, you know, writes down a model

for every anomaly that one can have. I think it's important, actually. Probably it sounds little dismissive, but I don't mean it that way. I think it's really important to have, to have people in the field who are very creative, quick creative, and whenever something comes up,

they tell you, well, that's what you would need to do in order to accommodate that. But then the second step is also important. If it's complicated, then I would call early dark energy complicated. Then probably the lesson is maybe that hints us, you know, either you have to work harder to have a better explanation or it's really systematic. But I like to, you know, I actually am more of the years. I like to wait.

I like to let experimentalists and analysts work it out first. and then when it's really profoundly established, you know, at the five plus sigma level, that's when I would turn to it. So I like to follow these debates, but it's more, you know, it's really my approach to these things. I don't think that everybody should have the same approach, but, you know, I have my own approach. I'm more, you know, working on fundamental concepts and trying to make predictions, given the theoretical work and don't tend to jump, you know, at three sigma-ish results. I like to wait it out.

And, you know, I think it's very interesting to watch you guys work this out. And I think it's very interesting to see that the CMB measurements, all of them, whether it's Plunk or WMap, you know, and the upcoming, they agree. So that's probably, you know, I don't know where it comes from, whether it's a late universe, whether, you know, I do follow the talks. I do follow, you know, the discussion between Adam Rees and Wendy Friedman and others and the CMB community. but I would not be willing to write down a theory or even just say what it is. But I must also say that I believe that the early dark energy is not the most attractive explanation that I could imagine if it's really physics. Well, in a part two in the future we'll have to get into that,

as well as some similarities, perhaps, that you pointed out to me and to others and the potential for the Higgs field to play multiple roles in the bouncing or something. cyclic models. But I want to just touch on what you just said, because I think that's really important. We're talking about educating people. And earlier we talked about, do we teach about the that the

spatial curvature could be negative one? It's like, no, we shouldn't do that. I mean, it's like teaching, you know, that there's no evolution or something. But what bothers me, I guess, is that we, I almost see a parallel. Like, people don't want to teach about, we don't want

to teach bouncing models or alternatives in our standard cosmology classes. And it's kind of like, you know, cosmologists working in the field feel like they're teaching intelligent design or, like, it just feels so, so uncomfortable teaching about, I think it's stupid. I think we should, it's a, you know, it's a brilliant idea. It's an interesting idea. People have worked on this for decades and people have an opinion about it that's ill form, maybe from decades earlier. But thanks to you, and the reason I bring this up with respect to you and your unwillingness to ambulance chase,

which I think is a great metaphor, is a testament to your taste. And I think that you in particular, this new generation of young theorist, if I can call you young without being patronizing, are super creative and that you're not just riding bandwagons, chasing trends. I feel like you are incredibly courageous.

You personally, Anna, and I hope that this has inspired some young people in my audience to, to look deeper into what you've written, and I'll have links to all your vast biography and these phenomenal papers and talks that you give. It's just like whenever I get to hear one of your talks, and I was adamant a couple of years back when I organized the seminar series at Caltech, that you be one of the speakers because your way of communication is very forceful, it's very logical, it's methodical,

and I think it's open-minded, and I think that's lacking so much in our modern cosmology parlance. And I wonder a part of it is because you don't go on social media. You're, you know, it's frustrating because I can't like tag you in all these cool places when you do cool stuff. But anyway, you don't have to respond to any of that, Anna. I do. I do. I do. Actually, I'm happy to.

I am happy to. No, no, that's not a problem. Go ahead. Yeah. This is something, I actually think a lot about it. You know, I think what's really important, that's why it's probably a short answer. You know, I have been very lucky with my upbringing, with my family and my schools. You know, I don't think that one should be too afraid of what one.

teaches kids and what one teaches younger those, one should teach them to make up their own minds. And, you know, if you embrace them, it's, you know, very often they want to agree with you, but it's really important that you come from them, especially with ideas that you might not believe in so that they can make up their own mind. And yeah, I am not in social media because I believe a part, look, I appreciate what you are doing and many are doing. And I know that social media has nice aspects. But the problem is also, it is also, um, anchored. encouraging more and more in my view. And I don't think that, you know, you are prone to that, more, you know, an intellectual confirmity, something that, you know, people are afraid of having a different opinion that what's being established as a majority opinion. And, you know, this is not what I'm saying. This is unfortunately something that I experience and that, you know, right now, this is a problem in our country and the problem worldwide, that we have to address how to how to make it a positive experience without, you know, eliminating viewpoint diversity.

Because we know if we eliminate that and trade it for fear and for conformity out of fear, then we actually stop innovation. And my approach right now is not to participate in social media. I am happy to go on podcasts. I'm happy to give talks. That's my job. But I cannot take, I think, right now, the likes and the dislikes and the comments and the retreats. So this is a very conscious.

You know, if Galileo had been. around and Twitter had been around rather when Galileo was around back then or Einstein, you know, they would have had these blunders and people would have teased them. Or my favorite is Maxwell, you know, James Clark's Maxwell had the Maxwell equations and Maxwell Boltzman and he had these wonderful ideas. They're all true. They're all correct. But if you ask what was the microphysics behind Maxwell's equations, they were vortices and gears and whirlpools and luminephers, ether, and he would have been roasted. And maybe, you know, cosmologists would have then, how to wait decades, you know, to think about the implications for relativity and

the Yangmills equations and all sorts of things. So good for Maxwell, lucky for him that Twitter didn't exist back then. But Anna, now I want to turn to the final thrilling three questions that I ask all my honored guests who come on the show. So I wish to ask you final three questions in the remaining couple of minutes that we have. Are you willing to go into the impossible with me now, Anna? Let's go. Okay, great.

So the first one of the thrilling three questions has to do with what you put in your ethical will when you reach the age of 120 material will. But what sorts of wisdom you touched on some of this a minute ago? But what kind of wisdom would you most want to communicate, not knowledge of which you have replete, you know, storehouse. But what wisdom would you want to decrease you? I believe that. You know, I did mention it because this is something, you know, I. I find important, I think two aspects, perhaps. I think it's really important that one should always have the courage to make up one's own mind.

And then more importantly, one has the courage to stand up to one's convictions. I think it's really important, especially when it gets one into trouble, not to bend. No, no, no, I really think it's important, you know. It's really something that I keep as my life philosophy. Make up your own mind about what's right and do what's right. Very nice. Very good to hear that. The next question involves going even farther into the future, involves these unseen monoliths that are present in this movie, 2001.

A Space Odyssey came out long before you were born. But it's really kind of a version of Richard Feynman's cataclysm question. You know, when some cataclysm erases all human knowledge, what would you put in a time capsule that really encapsulates what humans are capable of? Kind of brag on behalf of humanity. What would you put in a billion-year lasting time? You know, that will be boring. But it leads us back to your very first question, why I'm in cosmology. I really would put in what that should please you.

The temperature and isotropy map of the CMB with the equations that describe it. You know, it's really because in order to, first of all, we share this with everyone in the universe, right? This is just our universe. And in that map, it's all of our physics that we figure. And also what we haven't figured. Einstein relativity, the black body radiation, that photons, that light is particle and wave, that electrons, the atomic theory, you know, quantum field theory to understand the two and three point functions, all the statistic. You know, and what we don't know, where is this coming from. what generated it, was there a beginning, where are we going? You know, dark matter as the, you know,

what matter made up what we need. You know, so I really would, you know, this is just, it is a little talking to the bag, but. Yeah. No, I, in fact, that was my answer to that same question. Oh, really? I didn't know. I put in the power spectrum because, you know, you can get, to get the power spectrum out is a little bit easier to understand. But like you said, it's visible throughout the whole universe. So actually, your answer contains slightly more information than mine. But I think Feynman would be proud of you

for answering that way. I hope he would, because your answer obliterates his. His was just that the universe has atoms in it. You've got now atoms, radiation, photos. I got everything. But Feynman didn't have access to the maps, right? Who knows what he would have said?

He's one of my great heroes, so I would hope that if I had ever met him. Absolutely. Last question goes back in time. and it's sort of advice to your former self. And it's the statement, famous statement from Arthur C. Clark, the only way of discovering the limits of the possible is to venture a little way past them into the impossible.

So it's the origin of this podcast name. So I want to ask you, and if you could go back to your 20-year-old self, what would you tell her? What would you give her to give her advice for the courage to go into the impossible as you have already done? Oh, wow. I'm not yet that old, right?

So this is only a little bit more than 10 years back. But I guess, you know, I would probably say that, you know, it's always worth taking the difficult path if that's what my convictions lead me. And that one manages more than one believes one does. So whatever comes at one actually, when one does the thing, one believes is the right thing to do. One actually gets through a lot more than one would have thought one can do. And I'm not yet old enough to say if it was worth it or not,

but I know that I think I would tell my 20 years, said that I'm actually stronger and I would believe I am if I follow what I believe is the right thing to do. But yet with the footnote, I'm not yet that old. So it's not really a vista, it's more like looking back 15 years in time. You know, I would say that that's what I would tell my 20 years. Well, Anna Eges, Dr. Anna Egesis, it's been a pleasure to talk to you. I hope we can get together in person for one of our long lingering conversations with you.

I always leave it inspired and educated. And I want to thank you for being a teacher to many around the world. an inspiration of what courage and what integrity looks like as a scientist. Anna, thank you so much for sharing. Thanks. I appreciate it. Thank you. Any sufficiently advanced technology is indistinguishable from magic. That's a wrap on another fascinating episode and conversation with my friend Anna Eges. If you'd like to see some of the animations and diagrams and explainers, you can see that on Dr.

Brian Keating, my YouTube channel. You can ask questions of all my guests. I usually post them a couple of days or a week ahead of time. You can do that on Twitter at Dr. Brian Keating or in the community tab on my YouTube channel, Dr. Brian Keating, or we can do it on my website, briankeating.com. I have a place where you can leave a voicemail. You can leave questions. I'm going to be doing an AMA and ask me anything based on me recently hitting 65,000 followers on YouTube and more than about that amount on audio

formats, such as the one you're listening to. So we've got 100,000 people into the impossible universe. I'm just so proud and pleased about it. And I only really ask for two things. One is that you leave a review, a rating, if you can do that on every podcast app nowadays. You can leave at least a rating of so many stars, and I hope you'll leave an asterism, a small constellation of five stars. Like was recently left by Phil Galinsky,

who left this review on Apple Podcasts, five stars, but he also left a review. So you can leave a review using Apple Podcasts exclusively. But Phil says it's one of the top science podcasts. Brian does a great job, making complex scientific ideas accessible to a general audience, and he always brings out the best in his guests. I'm excited to listen to his audiobook version of Galileo's dialogue.

I just got an audible. It's surprising that nobody has made this into an audiobook until now. Thank you, Phil. I swear I don't know Phil, and having his encomium is really a delight, especially about my audiobook. You can find that on Brian Keating.com as well under books. And I do giveaways. So if you're in the USA, I will send a meteorite sample,

a villain from losing the Nobel Prize, a piece of space schmutz, and you can get that at briankeating.com slash list. Join the list. If you're in the USA, I choose 100 people at random, and I send out meteorites, and I give away copies of my audio books and printed books and all sorts of cool stuff. Unfortunately, I can't ship out of the U.S. with my limited meteor production budget, but I will do my best to add value in other ways if you're outside of the country. For that, I ask you, join my mailing list, briankeating.com slash list, and join my YouTube channel, Dr. Brian Keating. And that's all the asks. I really don't charge, and I'm doing it because I love it. And I'd love to hear reviews.

So that's really one of the best ways you can get feedback. Got over 402 reviews as of today. And I'm looking to get 499 or maybe 500. Let's make it a round number. By December 31st. So please do your part. There's 100,000 of you. It shouldn't be so hard to get 500 more.

Sorry, 500. That would take me over 1,000. Almost 1,000. But at least give me 100 of you, 1%. Point 1%. Having trouble doing math after this heady conversation with the brilliant theorist. I hope you enjoyed it. I hope you will continue going into The Impossible with me

in future episodes. Stay tuned. We've got many exciting upcoming guest, Frank Close, author of the first biography of Peter Higgs, his book called Illusive. We have Neil Turrock, one of Anna's collaborators. He's coming on the podcast. We have Muti Milgram, who is the chief architect at the chief alternative to the dark matter paradigm called Mon, modified Newtonian Dynamics. That's kind of a bucket list interview that I was able to get, and you'll enjoy it. So stay tuned, leave a review, rating wherever you can. Thanks a lot. It really helps me out.