Did She Just Prove the Multiverse Is Real? (Ft Laura Mersini-Houghton) [Ep. 501]

What if the Big Bang wasn’t the beginning? What if our universe is just one in a vast cosmic ocean of universes, and we have the evidence to prove it? In this episode of Into the Impossible, I’m joined by theoretical physicist Laura Mersini-Houghton to explore one of the most provocative ideas in modern cosmology: the multiverse is not only real—it’s testable. Mersini, author of Before the Big Bang, walks us through her bold predictions about the structure of the cosmos, including the mysterious cold spot in the cosmic microwave background (CMB) that she foresaw years before it was confirmed by the Planck satellite. Together, we dissect her groundbreaking theory that our universe began as one branch of a quantum wave function stretching across a multiverse landscape. We talk quantum decoherence, cosmic scars, and how entanglement with other universes could leave measurable fingerprints in our sky. We also debate criticisms from fellow physicists and dive into what these revelations mean for the future of dark energy and cosmological theory. — Key Takeaways: 00:00 What happened before the Big Bang? 01:56 The CMB cold spot prediction 05:16 Quantum entanglement and decoherence 11:31 Criticism and evidence for the multiverse 17:06 The wave function of the universe 20:48 The string landscape and constants of nature 23:54 The cold spot and the hemispherical anomaly 37:20 Thoughts on the recent DESI suggestions 40:46 Judging a book by its cover 47:31 The multiverse and religion 57:29 Outro — Additional resources: ➡️ Follow me on your fav platforms: ✖️ Twitter:⁠ ⁠⁠https://twitter.com/DrBrianKeating⁠ 🔔 YouTube:⁠ https://www.youtube.com/DrBrianKeating?sub_confirmation=1⁠ 📝 Join my mailing list:⁠ ⁠⁠https://briankeating.com/list⁠ ✍️ Check out my blog:⁠ ⁠⁠https://briankeating.com/cosmic-musings/⁠ 🎙️ Follow my podcast:⁠ ⁠⁠https://briankeating.com/podcast⁠ — Into the Impossible with Brian Keating is a podcast dedicated to all those who want to explore the universe within and beyond the known. Make sure to follow/subscribe so you never miss an episode! Learn more about your ad choices. Visit megaphone.fm/adchoices

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:00Brian Keating?

  Was the Big Bang really the beginning? What if our universe is just a ripple scarred by a cosmic collision?

• 0:06Speaker 01

  Yes, you can get evidence. Yes, you do not need to go beyond the horizon of your universe in order to see the multiverse.

• 0:14Brian Keating?

  One physicist not only works on this, but she predicted an observable signature, a cold spot in the sky that would not only indicate the presence of other universes potentially, but give meaning to the question of what came before the Big Bang. Stephen Hawking was once asked, "What came before the Big Bang?" And he said, "That's as stupid as asking what's south of the South Pole." Well, I've been to the South Pole twice, and I think he's wrong. And this ties into today's guest in a most beautiful way. Today's guest is the renowned scientist Laura Anderson Houghton, and here's her book, which is called Before the Big Bang. So Laura, who is right? Stephen Hawking or Brian Keating? Is it sensible to ask what happened before the Big Bang?

• 0:57Speaker 01

  Stephen Hawking was right the second time around because he changed his mind about that question. In his book, he was paraphrasing St. Augustine. There is help to pay for those that ask what was there before. But on the last few years of his life, he was asking exactly that question. What was there before our universe came into existence? And he had his own ideas, but unfortunately he did not finish them. So, yes, I think it would be a very simplistic view to have one universe that is 10 to the power 27 centimeters in size and is 13.8 billion years old. It would be very simplistic for us to say we can't ask what was there 14 billion

• 1:41Speaker 01

  or 15 billion years or was beyond the horizon of our universe. So I think as scientists, we are trained to be curious and to ask the questions even more aggressively whenever we are told that those are forbidden questions.

• 1:55Brian Keating?

  In 2006, you predicted this cold spot. And that was seven years before Planck confirmed it. I have with us today... Here's an actual universe. I think the cold spot is right there, but we'll talk more about it. You're the world's expert on it. But let me ask you this important question. Nobody saw this coming. So what did you see that nobody else did?

• 2:14Speaker 01

  The cold spot was a byproduct of a long program of research. What I really wanted to find out was what was there before our universe came into existence? And why does our universe have such a special beginning, such a small entropy to start with? Those questions led me to a wider, more complex and more beautiful picture of the cosmos. We are extending the Copernican principle and our universe is just one humble member in a vast, beautiful cosmos full of other stuff, other universes and whatnot. And ultimately, being happy with the theoretical answer, I'm a theorist, I'm not an experimentalist, but getting the right answer, deriving it for the first time in history,

• 2:58Speaker 01

  that's what got me excited, was that I didn't need to have an hypothetical study. I could actually, using, following the evolution of the dynamics of the degrees of freedom, I could derive the answer to why we started the way we did. It was me and my collaborators, Rich Holman and Tomo Takahashi, to wonder if there is any way that we could make predictions that could test this theory. And then that was in 2005 and 2006. And I know, I get excited from the theory side, from being able to derive the answer to the origin. But everybody else got excited on the predictions papers that we call the avatars of the landscape. And the reason why, I can understand the reason why the rest of the community

• 3:42Speaker 01

  got excited about those predictions is that if you look at the long history of a multiverse, of many universes, it goes back all the way to atomism, democritism, the vicarious and whatnot. And then you come back to, you have read "Many Worlds Interpretation", and Everett had a very sad ending to his life. So there has been this constant dislike or fear of the idea that our cosmos is not just one universe, but it's a lot more beyond what we can see. And then part of the reason was that as scientists, we want to be able to test our theories.

• 4:26Speaker 01

  So if there was a scientific theory of the multiverse, we should have been able to see and observe and test the validity of that theory. And that was exactly at the crux of the problem. We were convinced that since we can go beyond the horizon of our universe, and we cannot travel beyond fourteen billion years in the life of our universe, then there is no way, even if the multiverse is there, there is no way that we'll ever be able to test it. And therefore, any theory of the multiverse cannot be scientific. With our work, for the first time, we showed you don't really need to go outside the horizon of our universe. You can actually see the fingerprints

• 5:08Speaker 01

  of the multiverse right here, inside our universe, in our sky. And we made a series of seven predictions, including the cold spot.

• 5:16Brian Keating?

  You have some of the most fascinating ideas that I've encountered. And I'm an experimentalist, but I dabble in theory. So before we get to the multiverse, we're soon going to get there in more detail. And I have been yelled at by Andre Linde. He screamed at me. He said on this very podcast, "Why should it be universe? Why should it be universe? It should be multiverse until you prove to me that it's a universe." We'll get there, we're gonna cover that. But first, I'm gonna break down the quantum physics of string theory landscape. So for somebody out there, my audience is very smart, but if somebody out there understands Schrodinger's cat, but not string theory, what does it mean to have entanglement? Can you please explain for the audience what quantum entanglement is?

• 5:59Brian Keating?

  And why the microphysics isn't all relevant to the macroscopic universe?

• 6:04Speaker 01

  Since our universe started very small, it had to be a quantum particle described by a wave function of the universe. Now, whenever you solve Schrodinger-type equations on the wave function of the universe, you don't get one solution, you get a family. of solutions for possible universes, for possible outcomes. All of those are branches of the wave function of the universe. Now, it's in the nature of quantum mechanics that all these branches are cross-talking to each other. That's the quantum entanglement. It comes with the territory of being a quantum species. As our universe and all the other branches are very early on and they are smaller than the size of an electron.

• 6:46Speaker 01

  So this quantum entanglement is always present in the wave function of the universe. The problem is that as each of these branches takes the energy, say, from the landscape of string theory, which makes it go through a big bang, through a cosmic inflation period, then that universe is growing very large, very quickly. So it's not quantum anymore. It is a classical universe. And there is the problem. If all these branches of the wave function, that were quantum back then, in the first fraction of a second, continue, remain quantum entangled to each other,

• 7:26Speaker 01

  then as the universe is going through that accelerated expansion to produce our CMB sky, the large-scale structure that we see in our universe, then I should not see just one sky. I should see multiple skies superimposed onto each other, because all these branches were entangled to each other. That's not what we see. We see one universe, one uniform distribution of nearly uniform, except anomalies of matter and large-scale structure and cosmic microwave background and whatnot. So that tells us that something happened early on to separate these branches of the wave function from each other. In physics, we call that decoyards.

• 8:11Speaker 01

  There is a simple way to think of how decoherence works. But anyway, the moment decoherence takes place and then breaks away this cross top between the branches of the wave functions, then that triggers the quantum to classical transition. Because each of those branches now can go through its own big bang and grow and become a classical universe on its own right without being entangled with other universes. So this separation, this decoupling, happens very early on. And I don't know if you'd like me to explain decoherence for a minute.

• 8:45Brian Keating?

  I do want to explain decoherence, because I'm an experimentalist, as I keep saying. And in our laboratories, we use dilution refrigerators, which can get down to one or two millikelvin, you know, fractions of a thousandth of a degree above absolute zero. And they're used in quantum computing applications. But that is very tricky, because they are not maintained very easily. And in fact, the entanglement is very fragile. It can get destroyed very easily. So can you explain how the universe, the violent period of cosmic inflation that I hope to shed light on with the Simons Observatory, how can that not destroy all coherence and lead to a completely decohered universe mess, a total spaghetti monster mess?

• 9:26Speaker 01

  In the case of the universe, you want exactly to have that decoherence take place, because you want a classical universe. You want that quantum to classical transition. In the case of quantum computers, it's the reverse. We want the quantum computer to continue to be quantum. So we don't want to wash out the quantum nature of that computer, which is what decoherence would do in any setting. So decoherence is the factor responsible for washing out the quantum nature out of any, whether it's a particle, a universe, or a computer. And in the case of the universe, as I said, you actually do want your universe to wash out its quantum nature as it grows large. The way decoherence takes place is through an interaction with an environment.

• 10:11Speaker 01

  And now we are getting very close to another big problem that you are very familiar with in cosmology, the role of the observer. For this separation of the branches of the wave function to take place, you need something to watch that wave function, to make a measurement on that wave function. In my theory, we took the very long fluctuations in the landscape as well as the wave function, which are always present because we are dealing with a quantum system. Now, you want the object that is doing the observing, you want that object to interact very weakly with what it is trying to measure, otherwise it will mess up the measurement, it will give a false result on the measurement.

• 10:55Speaker 01

  So in our case, including the very long wavelength fluctuations that are present in the wave function and the landscape, they are weakly coupled to the branches of the wave function because they are talking to each other only gravitationally, and a long wavelength, even Newton's law tells you that that coupling is very weak. But on the other hand, you have an infinite number of those fluctuations. So there is your buck, your environment, that is watching the wave function of the universe, and that is what is inducing that interaction, is what is inducing the separation, the decoherence.

• 11:31Brian Keating?

  In all of science, we always have to be comfortable with criticism of our work, and certainly you're no stranger to controversy because of your boldness and your courage in what you do. And so, what do you say to friends of mine like Paul Steinhardt, who would say, "Hold up, Laura, you're now tying together string theory and the multiverse," and these are two untested, and according to some people, like Paul, untestable ideas, that string theory's landscape can't be directly seen, and the multiverse can't be disproven and falsified. So what do you say to people that say, "If you can't test it, it's just a story"? Are you stacking a speculation on top of a speculation? How do you answer those critics?

• 12:12Speaker 01

  When it comes to testing, as conservative as it gets, because it's the only way to let your imagination fly free. And and come up with all this, what some people, like the ones you mentioned, might call speculative or crazy ideas. The only way forward is to really have strong evidence to back them up. So as as far as the string theory landscape is concerned, you, since I used the landscape derived from string theories, you can take that as evidence that string theory is in the right direction. Now, a bitter story, because of the whole endeavor of string theory was based on Einstein's stream of a theory of everything for one universe. And suddenly you end up with a whole pool of many possible universes with the landscape of a string theory.

• 12:58Speaker 01

  Most string theories, the landscape was discovered, they saw that as a crisis and there were books and papers written about that. As a cosmologist, I'm not a string theorist, I'm a cosmologist. As a cosmologist, I saw that as a virtue, because I've been spending time going through Penrose's argument that our universe has such a special beginning is very unlikely to start with cosmic inflation and so on. I spent so much time thinking about this and I realized that the only way that question makes sense is if you start with many possible, a pool of possible beginnings. Then you can ask the question, why did I start with this one rather than something else?

• 13:41Speaker 01

  So that, I'd already think, I've been thinking along the lines of a multiverse when the landscape of string theory was discovered and for me it was right, I just borrowed it from string theorists and did quantum cosmology on it, I applied the Wheeler-Twitty equation to it. Now, back to the evidence of the, of a scientific theory. As I said at the beginning, that's why I understand why most of the community until this work in 2005, 2006 was very much against multiverse being considered scientific. Because we thought, as we always do,

• 14:19Speaker 01

  That if we can't go outside the universe in time or in space, beyond the horizon, we can't see what's out there, therefore, even if it exists, nobody, this is not scientific because we can't test it. That game changed with the work that you referred to at the beginning, the work I did with Paris Schollmann and Tomo Takahashi, because we showed, yes, you can get evidence, yes, you do not need to go beyond the horizon of your universe in order to see the multiverse. If something is out there, you will feel the effect of interaction with everything that is out there, and that will then, it will modify your own sky.

• 14:59Speaker 01

  And because we were in a position to have a scientific and coherent theory, we started from before the Big Bang. You have the wave function of the universe is spreading through the landscape, it is interacting with this path of fluctuation, so all these branches are decohering. Each branch that settles in a high-energy valley of the landscape will go through its own individual inflation, but meanwhile, decoherence, the washing out of entanglement is happening. So that remains of that entanglement are still leaving dents on the primordial fluctuations that eventually make our stars, galaxies, cosmic microwave background, and so on.

• 15:41Speaker 01

  Because we could follow that story from before the Big Bang through the Big Bang, after the Big Bang, to present day, we were able to predict the cold spot, the asymmetry between the northern and the south matter power spectrum, and then the series, the very low, the power suppression at very low multiples, and a series, oh, and the most importantly, the overall suppression of the amplitude of fluctuations, what is known as sigma eight in cosmology. So we predicted that if you have one universe, you expect that amplitude to be 100%, but if you include into the story the second source, which is interaction of your universe with everything out there, very early on, of course, when they are still entangled,

• 16:25Speaker 01

  then that will suppress the sigma eight by about 20%, so you should expect 0.8. Now, sigma eight and the cold spot. Have been observed at the level of discovery at the five sigma. Other stuff like the suppression of power, the larger scales or the lowest multiples. That has been observed, but we'll never know for sure because of cosmic variance.

• 16:49Speaker 02

  Many of you are watching this on a television. And I know that if you love the cosmos as much as I do, you'll want to subscribe now. It's a little more tricky on TV, but it's well worth your time. Click down below and don't forget to leave a thumbs up. More minds, more mysteries, more multiverse awaits you.

• 17:06Brian Keating?

  Yeah, so I want to get to cosmic variance and in particular, the polarization of the CMB, which might help to alleviate that. But before we get there, I want to talk about the way that I would say most scientists would have approached it and just said, oh, it's just a statistical fluke. But you connected your work to something that's much deeper. The collapse of the wave function of the universe in collaboration with Bryce DeWitt. So first of all, I want to ask you, what was Bryce like? And what is the Bryce DeWitt equation? Let's take a step back. Can you explain what does it mean to have a wave function of the universe? I thought the universe was everything. So how can it have a possibility wave function? And where does that wave function exist? So take a step back. What is the Bryce DeWitt equation? What is it operating on? Explain all the little parts of it, please.

• 17:51Speaker 01

  Wheeler DeWitt equation is the Schrodinger equivalent for quantum cosmology. Quantum cosmology is quantum theory, but applied to the whole universe. Wheeler DeWitt equation tells you how each branch of the wave function will evolve, given the potential energy on which this wave function is propagating. So this wave function is, because we're doing what's known as third quantization. This wave function is not spreading in real spacetime. Real spacetime does not exist yet. It's you're creating it once those branches will produce universes. But That wave function is propagating on a abstract space of energies of.

• 18:36Brian Keating?

  Is that a Hilbert space?

• 18:37Speaker 01

  Very similar to Hilbert space, but you are in third quantization, so it's more like a Fox space, but.

• 18:43Brian Keating?

  This physical space doesn't exist yet. What causes physical space to become initiated? What causes it to convert from fictitious space or, you know, this third quantization space into real, honest to goodness, three plus one dimensions or, you know, ten plus one dimensions? How does that actually take place physically?

• 19:01Speaker 01

  The landscape of string theory, you have already gotten rid of the seven extra dimensions. That's how you end up with a pool of energies, is the compactification, the wrapping up of the extra dimensions that dumps energies on the remaining four. So in that sense, this wave function is not spreading in eleven dimensions. It's spreading in this abstract space of energies that string theory gave after compactification. As far as the wave function, the way to picture it is just think what the founding father of quantum mechanics did, Max Planck. He gave us a wave particle duality. So in this case, the universe, at the very first instant of its existence, is the tiniest quantum particle you can imagine.

• 19:46Speaker 01

  So by the duality equivalence, I can think of that particle as a wave. That's what the wave particle duality is. In the wave function of the universe, you have many such waves that we call branches, in their woven, braided together into a wave function of the universe. Now, this wave function of the universe is propagating, is traveling through an abstract space of energies. As it travels through, different branches will settle on different valleys. Think of, I don't know, the old or the rocky mountains where you have marbles. Those would be the wave particle universes. And you are sitting on top of a mountain, but you have many valleys around you.

• 20:31Speaker 01

  You let the marbles go, different marbles will settle in different valleys.

• 20:38Speaker 01

  The depth of the valley is the energy, because this is an energy field. So the depth of the valley will determine the energy that wave will take to go to its own big bang.

• 20:48Brian Keating?

  One thing I've had trouble comprehending in my conversations with your, you know, friend of mine, Max Tegmark, who's written about the multiverse as well, is in the string landscape, you know, pictures, I understand it as a layperson effectively, the different landscapes have different, potentially different constants of nature, even the speed of light, the gravitational force. What prevents them from having different laws of physics altogether? For example, not having, you know, Planck's, you know, formula for energy versus frequency. It could be completely different, not just the constant. And maybe what prevents them from having different laws of mathematics? Where does this separation take place?

• 21:27Brian Keating?

  In other words, what features are common among every universe, every possible universe in the landscape versus our actual instantiation of them in our particular universe, where we have C and G and H bar and so forth? What prevents the laws of physics and even laws of mathematics from varying from place to place and getting a complete mess?

• 21:48Speaker 01

  Very good. We shall never know.

• 21:53Speaker 01

  In principle, anything can happen. And different constants of nature, different mathematical equations, different laws of nature, and so on. I was talking, Galixi Starobinski, in a conference in Stockholm about this. I'd just come out with, thinking along similar questions to yours. I'd come out with a proposal for two principles that we can use to make sense of that question. I mean, it's even hard to conceive and make sense of it, never mind to answer it. So my first principle is what I call domains correlation. If a subsector of the multiverse, all the universes there are embedded in the same background spacetime.

• 22:36Speaker 01

  And they are correlated to each other, so they are talking to each other. In any way possible, it can be just gravitational. Particles with mass will pull on each other. But if there is any correlation at all, then first, you can test their existence because you can measure that correlation. And secondly, they have to obey the same laws of nature that you have. They might have different constants of nature, like a different speed of light, different Newton's constant, but the laws of nature, the mathematical equations that relate those constants will be the same. So that was a proposal in terms of answering the question, what if there is some other sector that has totally different laws of nature?

• 23:21Speaker 01

  Well, if they are correlated with us, we, in principle at least, have a glimmer of a hope to know of their existence because we can measure that correlation. Look our future with better technology. If they are not correlated with us and if the multiverse is infinite, then of course there will be many sectors that are just far beyond and not correlated with ours. Then we'll never know of their existence and we can't make any significant or meaningful statements about them. Can they exist? Absolutely, but we'll never know.

• 23:54Brian Keating?

  Here's what I want to know. If the universe is a quantum wave and the cold spot right here is... And the cold spot is a scar from a collision, what on earth or in the universe, what did we collide with? Is that the proper way to think of it? Okay, so go ahead. How should I think of it?

• 24:13Speaker 01

  Absolutely. It's not a collision. It's never been a collision. There is no collision because then you are getting into dangerous territory of anthropic considerations where the collision has to be just right. You know, if somebody gets in a car accident and you say, "Oh, your car was dented only at the headlights, but nobody got hurt and no major damage done", that would require a lot of fine tuning. So that collision just gave you a little cold spot in the sky, but nothing else. In principle, if there are collisions, they are going to be catastrophic. Imagine two universes colliding, that would be the worst boom stage scenario, much worse than the big grid. But in my picture, there is no collision. I mean, each of those branches of the wave function

• 24:57Speaker 01

  that settled in some energy of the landscape and went through its own big bang. Has a similar story to ours, but the space in between is also expanding. So there is no touching of this universe. They just exist independently of us, except that interaction, that early on quantum entanglement interaction, left a scar in all our skies. So all of us can measure each other's existence as we can in our own sky. That cold spot is exactly such a scar left over from the very early moment. So imagine that our branch, the one that settled at very high energies and started inflating,

• 25:37Speaker 01

  as it is going through the first ephors of inflation, is also entangled with the other branches. And is going through decoherence, is gradually washing out that entanglement. But that entanglement with many other branches, for all practical purposes, you can have an infinity number of other branches that are going through similar growths. So that interaction is doing something to the primordial fluctuations inside your universe. We calculated that kind of denting or modification, because now you have a second source. Besides inflation, you have an entanglement with other universes adding to your cosmic picture.

• 26:21Speaker 01

  So that entanglement, that second source is modifying, is changing your primordial fluctuations, which 300,000 years later becomes CMB and Large Scale Structure. But whatever that entanglement did in the very first fraction of a second to primordial fluctuations, those scars will remain there forever. I mean, they make our CMB skies. So whatever happened early on will continue to remain in our sky. And we calculated in this picture, we calculated the entanglement of our branch, of our initial universe, to everything else. And that's how that cold spot prediction happened to be. And all the other predictions.

• 27:02Brian Keating?

  Yeah, I want to cover those. I want to cover the axis of evil and the hemispherical anomaly. And especially, I want to get your take on the recent DESI results because we just had here at UCSD, the former past spokesperson of DESI, Kyle Hansen, from the University of Utah. And he spoke about a variety of different tensions that have been maybe relaxed, but others that have been enhanced and multiplied, especially with regard to Lambda CDM maybe being in trouble. And I want to ask about how your model perhaps might explain the existence of the deviation, if you will, from perfect cosmological constant to something that varies. In just a minute, we'll get there in just a minute. But before I get there, I want to ask, what is the axis of evil?

• 27:46Brian Keating?

  And let me get an expert to define what that is. We can't actually show it on this beach ball. It didn't exist when my friends made the beach ball, you know, thirty, twenty-five years ago. But I want to ask you, what is the axis of evil? And was this a retrodiction, a postdiction, or was it really a prediction that you and your colleagues have made?

• 28:03Speaker 01

  That's been around before our work in 2005 because I remember Max Tegmark gracing that issue when I was a student in a paper. So what is known as anomalies in the sky now, all of those were predictions because they're not, did not exist back then. About the axis of evil, if you think of the cosmic microwave background, the multiples, we will take a picture of the sky and we're looking for temperature maps of the sky. And we break them down into harmonics, into multiples. So the analogy would be with a musical instrument. If you have the fundamental harmonic, the first harmonic, second, the third, and so on.

• 28:47Speaker 01

  So similarly, we break this map, this temperature map in harmonics, and we call those multiples. The alignment of the quadruple to the octuple would give you that preferred direction. So that would, that I think was the one that Max Tegmark and Alan Starkman called the axis of evil. There is no way and no reason why they should be aligned to each other unless there is something else, another. Interaction or force or something that is triggering that alignment. The quadrupole is, we are talking scales, wavelengths compared to the horizon of the universe. So whatever that something is that is triggering the alignment is really taking place

• 29:32Speaker 01

  at scales comparable to the horizon of the universe, so at the largest scales possible.

• 29:37Brian Keating?

  So could that be related to your model of decoherence and particles?

• 29:42Speaker 01

  Yeah, I mean, in our case, we didn't kind of guess, speculate on those. We just had that model of the wave function of the universe put in some landscape. The only crucial feature to our results was the fact that you have disorder in the distribution of energies in the landscape. So as long as you give me that disorder structure for landscape energies, then the answer will always be the same. But you are touching something that is very close to my heart and I am going to give in to the temptation of bragging.

• 30:16Brian Keating?

  You should, please do. I mean, that's why I'm having you here. You're a fan favorite. Take off the Albanian, you know, kind of armor and let's brag a little bit. Let's get a little bit of credit where credit's due. So go ahead, please, Lauren.

• 30:27Speaker 01

  So in this case, it's first you have a complete picture before, through and after, and that allows you to really trace down every, all the signatures, all the anomalies that we saw and predicted for the present sky. The other thing that that made me, for the first time, start thinking that there is something more to this picture than just a clever idea, is the fact that it wasn't one prediction or two predictions, but all seven of them were observed and reported as anomalies in 2018 by Planck satellite experiment. Some of them, we discussed at the beginning, some of them we'll never know because we are limited by cosmic variance. They have been observed, but I cannot declare them victory

• 31:10Speaker 01

  because there is a statistical built-in error we call cosmic variance that is 50%. But there are other in this list, like the sigma eight, the amplitude of fluctuations and the cold spot that we call the giant void. Because in our model, that part of the sky is completely empty of galaxies and stars and structure. So those have been not only observed, but they have been observed at the level of discovery, the five sigma level.

• 31:40Speaker 01

  The fact that what started off as an innocent, curious inquiry on to why did we start with such a special universe? Deriving the answer that in fact, this is the most likely way to start the universe. It is not at high energies rather than low energies. And that it led to a series of predictions, all of which have been observed. That gives me hope that at least part of this story is on the right path. Even after the anomalies were observed and, you know, in our field, we all get excited and curious when things go wrong in experiments, not when things do right. Whenever we see something we didn't expect to be there, then we all get excited. So there's been a flurry of papers.

• 32:25Speaker 01

  After 2018, after Planck announced their results and they called them anomalies. They shouldn't be wrong. The sky should be uniform. It shouldn't have a hole in it of 10 degrees in the sky. BBC got me actually to tell them the story that I was in Cambridge when Planck in a conference, when Planck made that announcement and I couldn't believe my ears. I was listening before going to the conference to BBC breaking news. BBC Planck has found these anomalies. And I remember I stopped jumping up and down on the balcony saying, yeah.

• 32:57Brian Keating?

  Well, you know, you mentioned a few times this concept of cosmic variance. I want to ask you, to what extent can polarization, which is how I, you know, put butter on the bread over here at my household. You know, that's basically my living comes from studying the polarization and building polarimeters and deploying them to the South Pole with BICEP or Chile with my colleagues in the Simons Observatory. So I want to ask you to define what cosmic variance is. And then how possibly the, say, hemispherical anomaly, once you explain that, could be corroborated by a completely separate probe, which is polarization. So please explain cosmic variance, then the hemispherical anomaly. And then we can get into a little bit more technical detail. And you can be very technical, by the way.

• 33:42Speaker 01

  Cosmic variance, the bottom line of it is that we can only measure one universe, the one we are inside of. And when we are measuring. I don't know, a galaxy or a star, the temperature, the chemical composition. We have many such samples in our sky because their size is small and there are billions and trillions of those. So we can repeat our measurement on other stars until our statistical error improves to as much of an accuracy as we want it to be. In the case of measuring stunting, like the quadrupole that we're talking about before, that we're talking then making a measurement on a wavelength that is the size of the horizon of our universe.

• 34:26Speaker 01

  In that case, the only sample we have is half of the sky of our universe. So the error is one over square root of two, which is quite a large error. The reason is simple. We can't get out of this universe and repeat the same experiment on other universes. In that case, we just have to admit that it doesn't matter how good the technology is, there is a built-in statistical error by the fact that we are stuck inside this universe.

• 34:53Brian Keating?

  And so the hemispherical anomaly, it could arise, as I understand it, from the large-scale existence of a large-scale void or under-density. Can you talk about the void picture within the context of your work, but also how recent people, especially David Wiltshire, how that might play a little bit of havoc with dark energy? So explain what the, how a void could potentially impact our understanding of the hemispherical anomaly, and then let's talk about dark energy.

• 35:24Speaker 01

  So when we talk of void, just to go on the cure and not set panic out. In that context of having half of the sky have slightly more or less matter much later than the other half of the sky. A void means exactly this mild difference between the fluctuations content that electron becomes matter content and the CMB content. So in our picture, again, you have the usual story of inflation. The universe is going to accelerate its expansion and all the primordial fluctuations are produced during that.

• 36:00Speaker 01

  Period of inflation. And those later on, as the universe grows and cools down, those become cosmic microwave background and the large scale structure. In the case of one universe, since everything is happening uniformly, you expect that this distribution of those fluctuations that later on become structure to be uniform throughout the spike. Now, add to this picture an interaction and entanglement with all the other universes that are going through similar cosmic storage. That interaction is very weak, is entanglement, and it gets washed out pretty quickly.

• 36:43Speaker 01

  But before it gets washed out, it has already left a trace on the e-foldings that were produced during that period. Those e-foldings, then, are not quite uniform as they should have been because they received a second source, an influence of something else. Besides inflation, there was something else that dented or scarred them or tweaked them. So one of those, the very first e-fold, if you like, will fill the most of this quantum entanglement because then it will be washed out. That is the one that creates this power asymmetry between the two hemispheres.

• 37:20Brian Keating?

  What are your thoughts on the recent DESI suggestions? Not quite, you know, discovery, as you say, it's one in a million, five sigma is necessary, they're only at 4.2. But Kyle Hansen, recently here, posted his episode recently. He suggests that at least the lambda part of lambda CDM might be in trouble. How would that impact your thinking and your model building?

• 37:41Speaker 01

  So dark energy is as fascinating, if not more, than the origin of the universe because it determines how our universe will end. And again, it's since 1998, since the discovery from the supernovae team, thousands of papers written, none of it. We are all fascinated, we all spend a lot of time thinking hard about it, none of us really has got an answer. I'm very excited about the DESI results because rough three choices that we have with dark energy is either a big rip.

• 38:14Speaker 01

  Or a big chill, that is the lambda part, or a big crunch. None of those is a pretty ending, but the big chill is the worst of all. Because if the universe has a pure vacuum energy, first of all, we have absolutely no intuition into that. We know how to mimic dark energy through a slow-rolling particle like inflation, but we have no idea of what exactly a pure energy of the vacuum of empty spacetime looks like. And why the more spacetime you produce, the more of that stuff you are producing. So we are at a total loss. But suppose that we take that in faith and say there is lambda, there is vacuum energy.

• 38:56Speaker 01

  The end of that lambda is a cosmic heat death of observers. The universe grows large, big, cold, empty, and it stays that way for eternity. That's the big chill, the most lingering way of death for a universe. On the other hand, you have the big rip, and in that case, you don't have a pure vacuum energy, but you have a scalar field that is mimicking, that is moving so slowly that it makes you think that we have vacuum energy. It can change behavior by having a very strange motion, a kinetic term, and change behavior such that the universe not only accelerates, as it would with vacuum energy,

• 39:39Speaker 01

  but it super-accelerates much more, at a faster rate than even vacuum energy. In that case, the expansion is so fast, so quickly, that the whole fabric of spacetime gets ripped apart. All the gravitationally bound objects, galaxies, stars, etc., all of that gravitational binding will become unbound because of the super-expended spacetime. Robert Caldwell had some really nice papers on the big rip, calling them the doomsday scenario, and calculating that if that is the case, that can happen quite fast. And the last one is the big crunch, where the universe ends up in a black hole eventually.

• 40:22Speaker 01

  None of those is pretty, but as a theorist, the most important... Question that I want from experimentalists, whether it's Euclid or Desi or whatnot, is exactly that time evolution of dark energy. How is it changing over time? So at least we are, as theorists, we are kind of forced to go in the right direction.

• 40:44Brian Keating?

  Ah, okay. So Laura, we forgot to do what I love to do, which you're not supposed to do, which is to judge a book by its cover.

• 41:04Brian Keating?

  In this case, I want you to take us through the title, the subtitle and the cover art. And you've got two copies of it. This one has a multiplicable universes, galaxies, stars, et cetera. And you have another version, which is available in bookstores, I think in the UK. So explain to us, what's the meaning of the title and the subtitle and the cover art? Is there a reference to the Stephen Hawking quote that I opened the interview with to begin with?

• 41:30Speaker 01

  There is a long and a short answer to your question. The short answer is you wrote a beautiful book yourself, so you know that you don't get much choice on the cover or the title. The long answer is myself and the publishers, the whole team that that really were wonderful in helping me finish this book, wanted to convey exactly the idea of what the book is about. The book is about a question that almost all of us as humans are curious about, have been curious ever since the caveman and before. And that's what was before our universe existed, in a very straightforward manner that made it into the title.

• 42:15Speaker 01

  I was told that in, again, I, as a scientist, I spend most days either taking long walks and thinking, going in the same path so I don't get run over by cars. We're reading when I'm not teaching, so I don't have a lot of interactions with the outside world, except when I teach. But I was told that the world has changed quite a lot since I was... New school and now with the Twitter culture and the Facebook culture, the attention span and the TikTok, the attention span is such that you don't use subtlety, you get straight to what you exactly what you mean.

• 42:50Brian Keating?

  I love this book and it's got three people on the back have endorsed it that have all been on the podcast, Roger Penrose, Paul Davies, and of course, the inimitable Stefan Alexander, my best man at my wedding. I want to talk to you about something you brought up and I could tell that you're not happy with it from reading the book. And it's the anthropic principle. And in the book, you talk about the anthropic principle as in sort of negative terms. Maybe I'm wrong, but please explain to me, for example, what Stefan might not be right about, even though he's a friend, we have to ask. Stefan's argued, you know, maybe even the anthropic principle could be quantum in nature. Can you talk about this? Could the valleys that you depict in the figures in this book, could they be regions where the anthropic principle would lead us to a very different conclusion?

• 43:35Brian Keating?

  Or maybe the anthropic principle is wrong. So first of all, what's the anthropic principle? For those that aren't familiar, what's a quantum anthropic principle? And why would things like the Born rule or unitarity, why would they not vary from universe to universe?

• 43:49Speaker 01

  So you're absolutely right in assuming that I don't, I'm not a fan of the anthropic principle and I don't hide that in the book either. With Stefan, we worked together and Fred Adams, we worked together to show that what is used as an argument in favor of the anthropic principle, namely, the fine tuning of the constants of nature, is not necessarily a fine tuning of the constants of nature. So Stefan and I joined forces into scrutinizing whether there is any virtue, any merit to the anthropic principle. So what is the anthropic principle? The strong version is that for the universe to exist, we have to witness its existence.

• 44:31Speaker 01

  So it has to allow for habitat, for habitable planets, structure and whatnot, from which we can arise and observe. By we, I don't mean human species. A star can observe the existence of the universe. Cosmic dust, photon can observe the existence of the universe. But the key Argument of the anthropic principle is that the universe, you can have many universes out there, but none of them are any good. They might as well not exist if they have nothing that can observe them. So, for anthropic reasons, you always require, you put a set of constraints that require that universe to be habitable.

• 45:14Speaker 01

  That in turn, and there was a really important and beautiful paper by Martin Rees and Max Tegmark a long time ago, arguing that all the constants of nature, the alpha, the fine structure constant, the Newton's constant, the mass of the electron, everything has to be fine tuned in order for a universe to be habitable. So that paper kind of showed that you need everything to be arranged by end in order to have habitable universes. What Fred Adams and Stefan and I looked at was, just for fun, let's see what happens.

• 45:55Speaker 01

  If we allow the fine structure constant and the Newton's constant to float, do you get structure there? So you put a set of conditions, you need the time of equality to occur at a certain period, you need the cloud of hydrogen, you need long-lived stars, so that eventually they can cook the heavier elements that you need for life, and you need enough complexity, enough number of atoms in the universe. So we put all those conditions, but allowed the fine structure constant and the Newton's constant to float. And surprise, of course, you do get other universes. If you think of stars, you are balancing out two forces. The gravitational force, the star is trying to collapse under its own weight,

• 46:41Speaker 01

  and the nuclear forces that are having an outward pressure. If you can balance those two forces out, then you have a long-lived star. It will explode, neither collapse. One is controlled, the gravitational part is controlled by Newton's constant, the other one is controlled by fine structure constant. If you let them float, then you can find, we found a whole wide range of where you can vary those constants by three to six orders of magnitude, still get long-lived stars. In fact, it turned out that our universe was bordered line between habitable and inhabitable.

• 47:17Speaker 01

  So that was one one example where we were looking and tuning argument and showing that you really don't have much of a fine tuning in our universe. You can have many other universes with different constants of nature that are good for life.

• 47:31Brian Keating?

  I had Fred on recently on the podcast. He was here in San Diego, as I hope you will come. Maybe next year we'll get you in person here and we'll do some events surrounding that, a colloquium perhaps. And I talked to Fred about that. And we said, in particular, everyone always talks about how finely tuned the universe. But if dark energy were zero or two or three times as big, we'd still be here. We wouldn't notice it. And that's perhaps the most mysterious and vexing aspect of the future of the universe. But getting back to the origin of the universe as we wrap up, the notion of the multiverse, of course, is controversial. It's exciting. It borders many different types of fields of physics, from quantum mechanics, obviously, to cosmology. But I want to run a biological

• 48:15Brian Keating?

  analogy by you, because I make the analogy of the following way. I discussed this in my first book, Losing the Nobel Prize. I say, imagine there's a bacteria, you know, there's some bacteria, and it's inside of a Petri dish. The mere fact that bacteria exists, he or she or it, you know, whatever you want to call bacteria, I don't know if it's insulting to a woman to not call bacteria a woman. But anyway, she can infer the existence of the Petri dish. And from the Petri dish's existence, she could say, well, perhaps there are other colonies of bacteria. And these bacteria are genius. They go to war with each other. They have toxins that secrete. They make barriers. Could it be that we

• 48:55Brian Keating?

  can postulate the existence of the multiverse from our own existence, as I think Andrei Linde suggests? In other words, it's more likely that we live in a multiverse than a universe. How do you react to that? And how would you criticize that? In other words, what would you say as a steel man against Andrei Linde? I know you believe in the multiverse, but how, what do you think is the most strong objection to the multiverse and my crazy bacteria argument?

• 49:21Speaker 01

  This belief. This simplified belief that we cannot test the existence of the multiverse. Now that we have shown, but this is only in the last twenty years, so it is quite new. Now that we have shown ways that you can test the existence of the multiverse, then I don't see any reason anymore why people should insist that there is only one universe and not a multiverse. Now, I can understand before we had all the scientific tools and experimental tools, why people insisted in one universe, because we live in it, we see it. And anything you see, it's easier to comprehend and explore and judge. And there is also this need that many humans have to feel special.

• 50:06Speaker 01

  And we have had that forever, it goes back to Copernicus times, you know, we wanted the Earth to be the center of the universe. And we wanted the solar system to be the center and whatnot. Now, what I and colleagues that work on this field are saying is that even the whole universe is just one tiny particle, a humble member. Even that universe is not the center of the cosmos, but the cosmos is much more complex, much more beautiful and vast than with one stop. And that goes with the territory, the more we learn, the more our thinking expands and the more our picture of the cosmos gets explored. But there is another reason, and I've been teaching this first year seminar this year for the first time.

• 50:52Speaker 01

  I was surprised, my students absolutely loved it. And it was beautiful to see their horizons opening and their brain clicking, being, asking these big questions and speculating about them. But one of them had been in some seminar, a religious seminar, and wrote to me, and she said, "I'm confused about the multiverse, because there was this guy that was saying, 'Only one universe, anything else, the multiverse is against religion.'" She said, "In her religion, she was Hindu, in her religion, the multiverse was a good thing." But in this, so I said, well, first of all, science and religion ask the same important questions of existence, but address them with totally different thoughts.

• 51:37Speaker 01

  We use the scientific method, the other group uses faith. Either one is is fine. You're you asking the same question, but using totally two different methods in exploring that question. The second part, I said, from where I stand, if I, if my little brain can actually imagine a world that is bigger, vaster, more beautiful than just this little vicinity that I see around me, then it would have, if there is a God, it would be an insult to the that super divine being to have a more simplified version of thinking than I can from from this universe. So the bottom line is that I was trying to tell her is I don't see a conflict between

• 52:22Speaker 01

  science and religion. I think that's why the Vatican has has its own astronomy and observatory with some really good scientists.

• 52:28Speaker 02

  Just before we wrap up, I want to make sure that you hit subscribe and join me beyond the big bang every week right here. Click to subscribe and make sure to leave a thumbs up. And for bonus extra credit homework, leave a comment. Now back to the ending.

• 52:42Brian Keating?

  Laura, as we wrap up, I want to leave you with a saying that means a lot and I think is poetic for this book, which is a beautiful book. It's a love story of a young woman who's fascinated by the night sky and her interactions with some of the greatest figures in cosmology as well as with her own family. And I'll leave that at that. But I want to ask you to react to the following saying. Okay, you ready for this, Laura? Here's my Albanian. Nocel ka shum u yu ye por se cila ka driten e vet.

• 53:18Brian Keating?

  So I think that meant in the night sky, there are many stars, but each one has its own light. Now, your work suggests the same of the universe, that it's not just the stars that are manifold, but maybe universes too. So is the universe kind of devoid of meaning, where each universe is isolated, cold and sterile? Or like the proverb from Albania, does each universe have its own light, its own story?

• 53:44Speaker 01

  Absolutely, I strongly believe that the latter. If we were special and we were the only thing there is out there, that would be meaningless to me. Eventually, it's a finite system. Eventually, we would explore, there is to explore and understand about this system. And that would be my version of hell. When there is no more questions left to be asked, there is no more discoveries left to be made. In that case, I cannot imagine existence. When we know everything and there is no, nothing left, no curiosity. The cosmos being made up of many universes, of a multiverse, there is so much to discover. Each one of those universes will have its own stars and its own light,

• 54:29Speaker 01

  its own creatures, asking their questions of existence. Then eventually, I hope, knowing that none of them is alone in the cosmos, that there are other fellow universes and creatures out there. But that last story, in that case, will never end. Because the universe or the multiverse is a physical entity that we can ask and explore and then perhaps never finish exploring and understanding. But there is another realm that I think is extremely important, extremely hard to understand. And that is the laws of nature. In everything we do, ultimately, we're using the toolbox, the laws of nature, sitting down with those laws and calculating and understanding that

• 55:14Speaker 01

  eventually, we can get the solutions to those equations. And finally, we understand what's going on in our little world. But if I change those laws of nature, as you were talking before, some universes might have their own laws of nature, then the whole story changes. The answer changes, our understanding, everything we know to be true is turned upside down. So I would like to understand. What determines the laws of nature and do they vary across? And also the realm of mathematics? And is that an unfinished story? If you follow along the lines of Gödel and Cantor, then of course the mathematics is incomplete.

• 55:54Speaker 01

  So perhaps laws of nature encompass the mathematical realm. This might seem as very big mundane questions that perhaps fall more under philosophy than science. But not so, because we are right now at an era of quantum computing and AI. And one of the big questions that we have, these are tools that we use every day. One of the big questions in AI is artificial general intelligence. Right now, the AI tool is very straightforward. A human decides, it gives it one job to do, one duty to perform, it does it very well. And you train the machine,

• 56:36Speaker 01

  the math behind it is very easy by Asian. You train the machine, you write that algorithm, and you're done. But what if there is a new generation of machines that have a set of cognitive abilities? Not just one or two, but a set. And will they become these big questions? Will they acquire their own identity and their own ego? And perhaps even consciousness? And all those questions can only be answered relying on the same theory of Gödel and Cantor and the laws of nature. So that's why I think anything that seems very far-fetched, incomprehensible right now, at the very golden, lucky stage

• 57:21Speaker 01

  where all those big ideas and questions are actually right here in our universe and in our planet.

• 57:29Brian Keating?

  Laura, I want to thank you so much, not only for your time today, which has been a delight and an honor for me, but for this wonderful book. It's really, it's touchingly beautiful, it's poetic, and it's hardcore mathematics, hardcore physics for my audience. And I especially love the illustrations. I think a lot of your colleagues that do write these books come out with books, and I won't name names, but huge tomes, very dense, very brilliant and great contributions. But they don't have any way of illustrating their point. I think that's a mistake. But the illustrations in this book are wonderful. They help guide the reader through some of the most complex topics. In the known multiverse. So for now, though, I want to thank you for your time, and I hope that we do get to meet in person finally.

• 58:10Speaker 01

  Yes, I hope so. Wonderful meeting you even.

• 58:13Brian Keating?

  Remotely. Thank you so much. It's been a great day.

• 58:16Speaker 02

  If Laura's description and prescience about the multiverse, the cold spot, and many more topics beyond the Big Bang gave you chills, just wait till you hear what Eric Weinstein said when I challenged his theory's predictions and how geometric unity may just have been proven by the DESI team. And David Wiltshire, he thinks we've misunderstood gravity itself. The universe might be bigger and weirder than anyone imagined. Tap one of these to explore. Don't forget to subscribe and like.

• 58:43Speaker 03

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