What came before the Big Bang?

26:05The universe does this when it has a phase transition as it cools, like when water goes from steam to liquid, it forms droplets. Here, the phase transition was predicted to make all these magnetic monopoles, and they should stick around. They don't go anywhere. So if they were supposed to have been made in the early universe, they should still be here for us to see. But of course, we don't see them anywhere. We've looked. We can't find any. So that's a problem. And you need to find some way to tweak the theory so it doesn't predict a bunch of monopoles that we know don't exist in the universe.

26:37I love how thinking about weird magnets helps us in the end accidentally understand the origins of the universe. All right. So then tell us what happens next. So what happened was two scientists, Henry Ty and Alan Guth, were trying to solve this monopole problem. And they imagined there could be like phase transitions in the early universe. Phase transitions you might be familiar with. I'm sitting out in my garden right now. It's very hot. So if I had some ice in my drink, it's going to melt. It's going to go from solid to liquid. That's a phase transition. So these are the sorts of phase transitions we're familiar with.

27:13However, there can be facial transitions that are a bit weird that we're not so familiar with. One of them is called supercooling. So supercooling is if you put some water, very, very pure, you can do this experiment at home. Who would think you could do an experiment about the very early universe and the origin of the Big Bang in your freezer at home? So what you have to do is get some very, very pure water and keep it nice and still and put it in the freezer. Leave it in there. and after a while you take it out it should have frozen but actually if it's pure enough and you were careful enough it will not freeze it's what's in what's called a super cooled state it will stay liquid then if you shake it it will very quickly freeze so this sort of delayed transition is called super cooling why it's just the way that the the molecules can be in a certain state that sort of resist being frozen chemistry yeah chemistry is the answer this chemistry but it's Also super interesting.

28:11I know that's unusual for me to say, but this one I love. For freezing to start, the liquid needs a tiny seed of a solid, like an ice crystal or a dust speck or a surface bump, to organize molecules into the solid lattice. If no seed is present and the liquid is very pure and undisturbed, the molecules stay disordered, even though they are cold enough to be a solid. It's like a crowd waiting for someone to start clapping. Nobody does anything until the first person starts to clap. And this chemistry trivia is actually important because it helps us understand the universe cooling. It lets the universe cool without making those monopoles.

28:48The universe passes that point, but it stays supercooled and doesn't make monopoles the way supercooled liquid doesn't make ice crystals. Basically, the Tyengu's imagined that the universe would be in a supercooled state, and they calculated this would actually stop monopole production. Like, great, we've solved the monopole problem. and then they said well let's just see if this would affect the expansion rate of the early universe and what they found was that it would expand exponentially it would if it's in this super cool state it would expand an incredibly rapid rate the sorts of rates we're talking about is doubling in size every 10 to the minus 37 seconds and so that in words that is let me think 10 trillionth of a trillionth of a trillionth of a second.

29:36So that is a very, very fast rate of expansion. So they did this trick to avoid predicting monopoles would be made, and then discovered that it also predicted that the universe expanded super fast. That's awesome. But then what happened was, Gooth had heard a lecture about another problem in cosmology called the flatness problem. And the flatness problem basically is that the universe can have a sort of different geometries at large scale. Now it could be curved, positively curved like a ball or negatively curved like a saddle, or it could be flat like a piece of paper. And observations showed it was reasonably close to flat in the 1970s.

30:14But what had been pointed out by another scientist called Bob Dickey was that this flat solution is unstable. So if it doesn't start out really, really flat, it will be driven away from flatness. So if the universe has positive curvature, that means it has enough mass density to curve in on itself and gravity wins and it curves more and eventually collapses and becomes super duper dense. Even if it's very slightly curved in the early universe, it will get more curved and then more curved and it's a runaway effect. And the same thing happens in the opposite direction if it has negative curvature.

30:46It will get slightly more negatively curved and then more and then more. It's a runaway effect towards negative curvature. But the universe as we see it today is still very close to flat, if not perfectly flat. That's weird because in order to be flat now, the universe had to have been born exactly on the knife's edge of flat. Any tiny deviation from flatness would, after almost 14 billion years, make the universe either collapse or explode. That's the flatness problem. So it's very surprising then how the universe could be so flat because it's this unstable solution. When Guth thought about inflation, he realized that if you're going to go inflation, then actually it'll be driven towards flatness and the the way you can think about this is imagine have you ever seen like a circus show where people walk on uh like pilates balls and you ever seen that okay quite difficult i imagine uh yeah you need some skills for that i imagine so imagine you were standing on that ball or you tried and you fell off let's say but then you expanded the ball rapidly to the size of the earth be pretty easy to stand on that ball You wouldn't even notice any curvature.

31:55I rarely fall off the earth. That's true, yeah. Yeah, I don't fall off the earth very often either. So then anything will automatically appear flat if it undergoes exponential expansion. So you realized it would fix this flatness problem. So now it solves two problems at once. And then it turns out it solves many other problems at once. So I won't go all of them, but I'll do one more. Wait, hold on. I understood how the rapid expansion solves the flatness problem. Like it seems curved. You expand it. all of a sudden it doesn't seem very curved. How does it solve the monopole problem exactly? Like why?

32:28Because you're not putting the universe in a freezer. It's not, no 10-year-old is doing the experiment on us. The monopoles would be thrown out of the horizon because there would only be like a handful of monopoles in any patch. So as the universe expands, they'd be thrown out of the horizon and you wouldn't see any. I like that as a solution. Anything that you don't like gets exploded out of the picture. Just throw it away. Throw it out. Yeah, yeah, exactly. I think that's a fascinating sort of bit of science where you're like, let me calculate what I think should have happened in the early universe.

32:59And then I'm gonna compare that to what I'm seeing. Like, yeah, I don't see a lot of monopoles. So obviously something must be wrong. I'm missing a piece. Yeah. And what can I add to the universe? So like, now it's more likely to describe the universe I see today. I think that's super fascinating. Let's digest that and take a break. And when we come back, Phil is gonna tell us more about how inflation solves these problems and whether or not we should believe in it.

33:31Hey, everyone. It's Cal Penn. I'm the host of Earsay, the Audible and iHeart Audiobook Club. This week on the podcast, I am sitting down with Ray Porter, the narrator of Andy Weir's audiobook project Hail Mary, massive sci-fi adventure about survival and science and what happens when you wake up alone very far from earth. I really had to make a decision because I caught myself getting that frog in my throat and starting to get teary as I'm narrating some of these sections. And it's like, okay, yo, yo, yo, is this indulgent? And I really thought about it. I was like, no, at this point, it would kind of be betraying the trust the author and the listener have in telling this story if I don't go through it.

34:15But there's places in this book that deeply emotionally affected me, and I left it on the mic. That's great. Because it served the story. People will say like, oh my God, I cried at the end. It's like, yeah, dude, me too. Listen to Earsay, the Audible and iHeart Audiobook Club on the iHeartRadio app or wherever you get your podcasts. The official language of football is trash talk, late night group chats, memes, and unbelievable highlight clips. That's why Boost Mobile brings you our new global connection plan. The first plan ever made for WhatsApp. Get unlimited data, talk and text, international roaming, and calls to over 100 countries for just$40 a month.

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36:46Okay, we're back and we're talking to Phil about the state of the early universe, what we know about the universe before it was hot and dense. And we've been talking about inflation, this theory that the universe expanded super rapidly in a very short amount of time. So tell us, Phil, inflation sounds a lot like the expansion that we have now. We talk about dark energy and the universe is accelerating in its expansion. Is inflation a different mechanism for expansion? Is it the same thing, just at a different moment in the universe? How do those two things connect? They are similar because the universe is currently accelerating in its expansion.

37:20So you could say the dark energy we see today is a very dilute form of inflation. and so that does raise the question are they really the same physics but i think that's still to be determined like uh there's a lot unknown about inflation if it even happened so whether inflation and a dark energy are the different manifestations of the same phenomenon or whether they're they're different things that just result in something broadly similar i think it's still an open question but one thing i do want to just highlight is that one of the things that inflation solves, and there are a number of problems.

38:00But there's one in particular that I think is the most relevant, and that is how you get galaxy structures. Because if you had a very uniform start to the universe, you've got to ask the question, well, how on earth do all these networks of clusters of galaxies form? What laid the seeds? And in inflation, the idea is there would be quantum fluctuations, and these would be stretched by inflation to create the seeds of galaxies. So amazingly, these enormous, enormous structures, you know, hundreds of thousands of light years across for a particular galaxy and for clusters of galaxies, even millions of light years across, you know, these were seeded by tiny subatomic quantum fluctuations that were stretched by inflation.

38:44And I think out of all the problems that inflation is supposed to address, I think that's the one that's the most impressive and where cosmologists are really thinking this is the leading candidate to explain the properties of our universe. So I think I get bogged down by this idea that the Big Bang started at a tiny point. And so what I'm imagining is we're looking at before the tiny point where it's inflating and there's areas where you're going to get galaxies eventually, but then it all kind of sucks down to a little point and then blows back out again. But that is not the right way to be thinking about it, right?

39:16Because I don't see how stuff that happened before the Big Bang is going to result in galaxies after the Big Bang. What am I missing? I mean, there are ideas that the universe could undergo cycles like that. It could expand and contract and expand and contract. But that's independent of inflation. So that depends, I guess, on the properties of the dark energy we see today. If it's a cosmological constant, i.e. if the energy of empty space is sort of a constant, I should say better, that what's driving the accelerated expansion is that empty space has a constant energy, then the universe will not really collapse.

39:53However, there have been observations recently suggesting that the dark energy is not a cosmological constant, that it could be some dynamical field that changes over time. And in that case, it could re-collapse. So that hopefully addresses this issue of, you know, getting sucked back down. But to answer your question, how could it be that this tiny fluctuating sea of space could have anything to do with what we see today? Well, you need basically density fluctuations. So if you imagine the universe being perfectly smooth, then you wouldn't get the universe we see today because some regions are more dense than others.

40:30So those regions that have galaxies in them are more dense and there are voids in space that are under dense. Also, when you look at the cosmic microwave background, this oldest light that we can see is very, very, very, very uniform. Like there's almost no differences across the sky until you get to a point of about one part in 100 ,000. then you start to see these tiny fluctuations so that's telling you there were definitely density fluctuations in the early universe um so they have to come from somewhere and inflation is very nice but not the only possible mechanism to to give you those density fluctuations now i said before that the universe could have been infinitely big at the big bang but what wouldn't have been infinitely big is our patch of the universe that would have been very very small so if you're struggling to think i want to think of this very very small universe you can think of the observable universe that we see around us.

41:22Think of that being very, very small. So now in this quantum state, there would be fluctuations. That's just part of quantum theory. And then they get stretched as the universe expands very, very rapidly. And that gives you some regions that are more dense than others. And then gravity sculpts them, putting more matter into the denser regions, less matter in the under-dense regions. And that gives you the seeds for galaxies to form. Thanks, Phil. And I think there's a possibility there of getting confused about the two ideas of the Big Bang, right? What Phil is talking about is the hot Big Bang.

41:56So not that the universe started from a point, just that the universe started from a hot, dense soup. And he's saying that soup is pretty uniform. So how does that soup then grow up to give you galaxies? And the answer is that soup plus quantum fluctuations. We're not zooming all the way back to the singularity. We're leaving the singularity aside for now. Right. But what's interesting is that during inflation, the universe is as cold as it can possibly be. And it's only when inflation ends that it heats up. So then inflation, we can say, is a pre-Big Bang model. Because a lot of textbooks tell you that inflation happened after the Big Bang.

42:28But actually, if we use the definition of the Big Bang that everyone, well, not everyone, but most scientists adopt, then we're going to say it's the hot, dense state. So inflation happened before that hot, dense state. It was cold during inflation, as cold as it can possibly be. And then when inflation ends, it heats up the universe. All the energy in the inflating space gets converted into matter and radiation. And then you have our Big Bang. So our Big Bang is like a bubble that appeared from this soup of inflating space. Where does the heat come from? How do you go from cold to hot? And let me clarify, because cold means something very specific here.

43:08It doesn't mean low energy like you might imagine. Because remember that energy can take many forms. It can be in the form of motion or mass or heat, but there can also be potential energy, like when you put a book high on a shelf or a spring that's squeezed down. And that doesn't make the universe hot. And sometimes fields like the Higgs field can get stuck in a state with a lot of potential energy. and so that energy can fill the universe and the universe still be cold. Inflation theory says that the inflation field had a lot of this potential energy, which is exactly also what you need to make the universe expand.

43:45In general relativity, matter and energy density make the universe contract, that's gravity. But potential energy, like dark energy or the Higgs field or the inflaton field, makes the universe expand. So there's a lot of energy in the universe, but it's not heat. it's in the potential energy the inflation field so the universe is nearly empty nothing is moving very fast but it is expanding now when inflation ends that potential energy is converted into normal matter fields and into mass and motion so then the universe is hot that's reheating it went from cold and full of potential energy to hot and full of mass in motion but there's another way you can think of it in that is when particles pop in and out of existence from the vacuum they have to go back into existence very very quickly this is a function of the uncertainty principle and there's an equation which will tell you how long they can exist for and so on and so forth now they pop into existence in pairs but in inflation they can't get back together again because the universe has sort of ripped them apart so you kind of get you can actually expanding space can create literally create matter and radiation because it rips these virtual particles which would otherwise just appear and disappear out of the vacuum.

44:58And they form into real particles. And this is similar to what you see in black holes. Because in black holes, Hawking famously showed that virtual particles can also get ripped apart. Some would go into the black hole, some would come out, and this would emit radiation. It's called Hawking radiation. So it's something similar to that, basically. So we have the hot, dense universe a long time ago, which we're pretty confident about. these questions and problems and theoretical issues. People come up with this idea of inflation. The universe before that hot, dense state expanded super duper rapidly, and that solves a lot of those problems.

45:33But doesn't it also just kick the questions down the road? Like you say, if you have this incredible inflation, then it solves those problems. But where does that inflation come from? What causes that? So that's an excellent question. And the short answer is you don't know. I mean, we're not sure that inflation happened. I mean, some people are pretty confident it happened. And we did a survey for this about that. And we didn't get more than 50 % saying inflation happened. But I had to be fair. It was a black hole conference that we were at. If we did a cosmology conference, I guess it would be higher.

46:06I can't remember exactly what we got, about 40%. But it was the most popular candidate. It didn't get past the 50 % mark. So now, one idea is that inflation is eternal into the past and the future. So let me try and unpack what that means. So you might have heard of the idea of a multiverse. Surely anyone that switches on the TV these days must see some sci-fi with a multiverse, whether it's Doctor Strange or The Man in the High Castle or whatever. You know, it's very pervasive now in popular culture. But its origins in the cosmological setting is with inflationary cosmology. So remember I said you can think of our universe as like this bubble that appears out of an inflating sea.

46:52But the idea is that it wouldn't produce one bubble, it would produce an infinite number of bubbles. And the way this works is pretty straightforward. Just think of the inflating space as something that decays, like a radioactive particle decays. So it decays with a half-life. So when it decays, that's that moment, what we talked about, you know, where all the energy gets converted into mountain radiation. Boom, a big bang, the universe is born. But what has happened to the bit that hasn't decayed yet? Well, it's undergoing exponential expansion. So as long as that exponential expansion is faster than the exponential decay, then the amount of inflating space can never go down.

47:32It can only go up. So the analogy I always give is my mum makes this fantastic chocolate cake. It's really yummy. and I go around there for Sunday afternoon tea. She puts the chocolate cake down on the table and we eat half the cake. Then at some point we go back for seconds and now the cake is gone. You can't have your cake and eat it, right? However, what would happen if when we went back for that second piece, the cake had expanded exponentially? Now we could have more cake. We have the same volume of cake that we had in the first bite, you know, but the cake's expanded. Then we go back for thirds.

48:10Well, the same things happen. The cake has grown faster than we could have eaten it. In which case, the amount of cake can never, ever go down. So you get infinite number of pieces of cake. And you can have your cake and eat it. I think you also get infinite fill in that scenario, don't you? Yeah. Yeah, you'd have to have a very big belly. All right, so I'm imagining space filled with this inflationary material we don't understand or don't know its origin of. and random little bits of it are decaying into our normal universe kind of stuff. So we get these bubbles of normal universes that appear in random places, but they're separated by this rapidly inflating space.

48:47Yes, that's exactly right. Yep. Yep. So then you get this multiverse and it's eternal. Now, when I say it's eternal, there's a bit of a subtlety there. It's eternal into the future, but is it eternal into the past? Right. Now, there is a theorem called the Borde, Guth, and Vilenkin theorem that says it can only be eternal into the future, but it is not eternal into the past. So we still have to ask what came before inflation or what might have caused inflation. However, there have been people that have disputed this theorem and said, no, it could be eternal into the past. So if you want to know what came before inflation in that scenario, it's just more inflation and it just goes back forever and ever for eternity.

49:28However, if we take the Bordegus-Velenkin theorem, then we have to ask, okay, what came before inflation? And there are a number of suggestions. And I should also add that there are people that don't like inflation. So one idea is, well, inflation didn't happen at all, and there's some other thing that happened. But let's stick with inflation since you asked. So I would say there's a few ideas out there. The first one that probably came on the scene was 1982. And this was proposed by Alex Vilenkin. It's called the tunneling from nothing idea. So the idea is that what if we treat space quantum mechanically?

50:09So normally when they do this cosmological modeling, you're using Einstein's theory of gravity. So you're assuming space-time is classical. But if you assume space-time is quantum mechanical, as Vilenkin did, then the suggestion is that space itself could fluctuate into existence from a state where there was no space so that's really hard to get your head around but this is why it's called the tunneling from nothing idea the idea is what controls the expansion of your universe so it's partly its radius so if you have a small universe it would actually just collapse back in on itself so how would you go from a small universe to a bit a universe big enough to inflate at least and classically it seems to be impossible.

50:51However, quantum mechanically it can, what's called tunnel, it can tunnel from one state to another. So the small one could tunnel to the larger one. And then what he asked was, well, what's the smallest size that the universe could tunnel from? And he concluded it was zero. So that's pretty hard to get your head around. So that's the tunneling idea, tunneling from nothing idea. Then you have this thing with the Hartle-Hawking, no boundary state. Hold on, let's dig into the Vilenkin idea a little bit more. Yeah. Because this is still pre-inflation. This is not an alternative to inflation. This is saying, where does the inflationary units come from?

51:25Yeah, yeah, yeah. And you're saying that we're adding quantum mechanics to it. So it's not full quantum gravity. It's sort of like semi-classical. No, no, this is, yeah, we'd call it semi-classical. It's not full quantum gravity. And we should come to full quantum gravity in a moment. And so this is speculating that the inflationary conditions before the hot Big Bang fluctuated into existence from, and I'm just going to kick the can down the road further here, from, and you said something that has no space-time, so it's a universe, but without space-time, or it's nothing, meaning not a universe?

51:57What's the difference? Yeah, well, that was going to be my next question. That was a trap. You avoided it. There's no space there at all. I mean, there's nothing sort of physical there. That's at least one conception of it. But how can you have the laws of the universe and follow those laws if there is no universe? So there is a universe, but without space-time? Well, that depends on your view of laws. What are laws of physics? Now, some people would say they're just descriptions, so they can't cause the universe. Another view might be we don't need a cause because there's no time, and you need time for causality.

52:33If there's no time, don't worry about what the cause was. You're asking the question, what cause? But if there's no time... It is a question that is asked in a condition. The condition is time exists. But if the time doesn't exist, then don't worry about causality. Yeah, but if you have... But how can you speculate about a transition to evolution of the universe from this to that if there's no time in the universe, right? How does that... How do I wrap my mind around this? Well, it is hard to wrap your head around. You know, we're answering in analogies, but, you know, it's all a mathematical description.

53:08so the question is you know could you compute what would happen if the universe had zero size and then what is there a tunneling amplitude for once yeah and people have challenged this i mean i don't want to claim this all is worked out and everyone understands it and it's all agreed upon this is one of like 20 something ideas that we talk about in the book and this is a problem with it so i don't you know some people have said well you're always tunneling from one quantum state to another. So maybe we shouldn't consider this model. However, one idea that Vilenkin suggests is that actually laws are more than just descriptions, that they actually exist in a sort of platonic sense, in a sense.

53:49And this has some advantages to it because you can ask, why is it that objects obey the laws of physics? If you have an electron, let's say, it gets excited, it shoots out a photon how does it know to shoot out a photon you know you know is it's all that information written inside the electron it seems hard to believe so the idea is that laws are actually sort of platonic objects in some sense they're pretty weird and when you say platonic objects for those of us who are not reading philosophy papers all the time you mean that they exist outside of our ability to observe them yeah i think i think that's a fair fair description yeah they don't sit on something else you know if you think of a table all right it's made of particles and you might even say they're made out of quantum fields or you know so the laws themselves have a have their own sort of physical existence well i don't know physical existence is the right word uh independent existence um so that may be required by of valenkin's model um and if you don't like that idea then maybe you don't want to entertain valenkin's model um but i do think that it's uncertain what the status of laws is so those that say that cannot be right because laws are just descriptions uh i challenge that and say are you sure that they're just descriptions you know how do you solve problem of induction you know we ask how do we know that there are these regularities new why why don't we think the sun might stop rising tomorrow.

55:19You know, if you just think they're descriptions, it's hard to solve this problem of induction. But one possible solution is no, the laws are more than that. They're sort of ironclad objects that the other particles have to sort of obey. And then you can see why induction makes sense. So there's a lot of debate in the philosophical literature about the nature of laws. And I think as long as that is not settled, and I think it's right to say isn't settled, then you can entertain this view. But, you know, let's be honest, it's pretty wacky and out there. So people have come up with other views, and maybe, you know, we can get onto those if you want.

55:55I do want to get onto those. And I meant to ask you about the philosophical implications later, but I can't not follow up on that fascinating conversation. Okay. You know, because it makes me wonder about the future of this line of inquiry. Like, if we discover the hot Big Bang, and then we find proof of inflation, then we find proof of what became before that, Is this an infinite line of study where we're always going to be asking what came before that? Or do you think there's some point at which we find something where like, ah, this caused itself, or this is obviously something which is fundamental?

56:24And isn't that just some philosophical slate of hand where we're like, this requires a cause. Now we found something which we define to not require a cause, and therefore we don't have to ask questions anymore. I mean, why isn't this going to be an infinite line of inquiry? Or do you think it will be? Well, it could be, but there are sort of ideas out there that might stop that infinite regress, shall we say. I mean, Vilenkin thinks that he stops the infinite regress because, you know, we've got this solution, if you like. The universe doesn't need a cause because it's quantum mechanical and causes are emergent properties.

56:58They exist for the macroscopic world, but not for the quantum world. So we don't need to ask what the cause for the universe is. It's a meaningless question, maybe. or maybe not meaningless, but it's just, you know, you don't need to demand. You can't demand there must be a cause when you get into the quantum realm. So that's one approach. Another approach is that maybe the universe just existed eternally into the past. So you can always just go back one step further and further and there's no end. It just goes on forever into the past. That's certainly an idea. Infinite grants for cosmologists.

57:29Yeah, maybe. Yeah. So it may just go on forever, but that's certainly a logical possibility. And it's certainly something that I think many physicists entertain. Certainly, that's one of the battles, actually. The battle for the Big Bang is, was there a beginning? Even if it wasn't the Big Bang, maybe there was some other beginning. And some physicists think there was, and some physicists think there wasn't. Another idea is that there could be what's called a closed time-like curve. So if you've seen the movie Groundhog Day, think of that. so you wake up you know and you're just experiencing yesterday all over again so now there are solutions in Einstein's theory of relativity which describes you know gravity as the curvature of space-time and there are solutions to say it gets so curved that it curves back on itself and it forms a loop so there are a couple of models that sort of take advantage of this and say the universe would cause itself because it curls back in a loop.

58:33And so there is no origin point of a circle. Even though the circle is not infinitely long, it doesn't have a starting point. So you can't ask what happened at the start. There is no star. It just goes around in a loop. So in the book, Battle of the Big Bang, we talk about two different models that exploit this. So there are some of the different ideas. One, maybe there was a beginning and you describe the universe maybe without the language of causality, or maybe there was no beginning and it's infinitely far into the past, or maybe there's a sort of loop in time, so there's no starting point, even though maybe it's not sort of eternal in some sense.

59:13All right, so let's take another break, and when we come back, we're going to explore some of these other ideas. Some proposing the universe has no first moment.

59:30Hey, everyone. It's Cal Penn. I'm the host of Earsay, the audible and iHeart audiobook club. This week on the podcast, I am sitting down with Ray Porter, the narrator of Andy Weir's audiobook project Hail Mary, massive sci-fi adventure about survival and science and what happens when you wake up alone very far from Earth. I really had to make a decision because I caught myself getting that frog in my throat and starting to get teary as I'm narrating some of these sections. And it's like, OK, yo, yo, yo, is this indulgent? And I really thought about it. I was like, no, at this point, it would kind of be betraying the trust the author and the listener have in telling this story if I don't go through it.

1:00:14But there's places in this book that deeply emotionally affected me. And I left it on the mic. That's great. Because it served the story. People will say like, oh my God, I cried at the end. It's like, yeah, dude, me too. Listen to Earsay, the Audible and iHeart Audiobook Club on the iHeartRadio app or wherever you get your podcasts. The official language of football is trash talk, late night group chats, memes, and unbelievable highlight clips. That's why Boost Mobile brings you our new global connection plan. The first plan ever made for WhatsApp. Get unlimited data, talk and text, international roaming, and calls to over 100 countries for just$40 a month.

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1:02:45Okay, we're talking to Phil about the origins of the universe, what we know, what we might know, and what we can only speculate while smoking banana peels. You referenced earlier this fascinating idea, this no boundary proposal, this alternative to like a singularity or a first moment. Tell us about this idea. How does it come about and how does it help us avoid a first moment in time? Well, it's not clear whether it does avoid the first moment. If I I was going to suggest models that avoid a first moment in time. I'd probably go to another model, like a bouncing model, which was, or some other, maybe some cyclic models that I think are more unambiguously don't have a beginning.

1:03:27The no boundary proposal, I worked with Stephen Hawking and Jim Hull and Thomas Hogue to make a film to explain it to the public. And I did get the impression they didn't quite agree on how to interpret it. um i think i think hawking saw it as like something closer to what vilenkin proposed like a universe from nothing whereas jim hartle i asked him you know could could this realize the idea of a universe from nothing and he's like what do you mean by nothing quantum mechanics is always something i know that hawking's special sauce is getting gravity and quantum mechanics to play together even without a full theory of quantum gravity he did for black holes and that's how And we came up with his prediction for Hawking radiation.

1:04:09So he started to think, well, what if we do the same for the Big Bang? Because the singularity theorem that he proved with Penrose was just classical. It didn't include quantum mechanics. So he said, all right, let's try and include quantum mechanics. And when he did that, he found that, to cut a long story short, the description that we have with space having three dimensions and time having one dimension changes such that the time dimension turns into a space dimension. So now you have four space dimensions and no time dimension. Okay, that's really weird. Let's unpack it. So Hawking is saying that the universe used to have four spatial dimensions and one of them became a time dimension.

1:04:53So we had four spatial dimensions and then we had three spatial dimensions and one time dimension, which we're familiar with now. That's really confusing. So let's try to think of an analogy. And Hawking's famous analogy is like, if you're standing at the North Pole, it's not only that there's no more northiness, there's also no sense of east or west. East and west have no meaning at the North Pole. But as you move away from the North Pole, you don't change the number of dimensions on the surface of a sphere. But now the concept of east and west makes sense. It's a direction that emerges smoothly as you move away from the North Pole.

1:05:28one of the directions on the sphere becomes east-west-like. The idea here is that the universe has one end where all the directions are space-like, and as you move away from that end, one dimension changes to have new time-like properties. It's pretty hard to wrap your mind around, honestly. And what this does, it actually smooths out the singularity. You don't get this infinite dense state. You get a smooth state, and think of it unlike the point of a cone. think of it more like a shuttlecock like a smooth surface now this it's bounded it's not infinite but it doesn't have a starting there's no point on the surface this is many better than any other point um so you could say it doesn't have a beginning but you might say well it's not infinite to the past either and then there's some more complications to it which we go into in the book but bottom line is whether it has a beginning or not is sort of slightly ambiguous and it depends on how you interpret the model.

1:06:29But there are other models that I think have less ambiguity and clearly don't have a beginning in them. So the most obvious one, I would say, is one where you replace the singularity with a bounce. So here, the idea is that there's a... So remember we said for the singularity, the universe goes to infinite density. Now, the idea in some theories of quantum gravity, the suggestion has been that you will actually get a maximum density. So think of a sponge. You pour water on a sponge and it absorbs the water. But there comes a point where it won't absorb the water anymore. It will switch its properties from being water absorbent to water repellent.

1:07:13So space might be like that. And in certain theories of quantum gravity, that's what happens. Space is like a limit. So when you try and squeeze more and more energy into space, it gets to a point where it gets full up. and then if you try and squeeze more in it'll bounce back out it becomes repellent so gravity switches from becoming an attractive force to a repulsive force and that triggers a bounce so then if we could go back in time what we would see is the uh well if we started today 14 billion years since the big bang roughly we go back in time it's getting denser and denser and denser and denser then when we get to this maximum density it just bounces back out again so you'd get another expanding universe or if you wanted to think of it as going from the past to today it would be a contracting universe and then an expanding universe and that contracting universe could have been contracting for infinitely long ago um you might just have it mirror like it doesn't have to be cyclic although it could be it could just be one contracting universe mirrored by one expanding universe something like a little like an hourglass so that's that's the idea of a bounce And I think that that is less ambiguous that it does not have a beginning in this model.

1:08:23So that's one idea. And of course, there are cyclic universes as well and all kinds of other ideas we explore. So this idea that at some point gravity stops pulling things in and starts to repel energy, do we have evidence for that in other domains? Or like, where did this idea come from? Arguably, we do. the fact that the universe is accelerating in its expansion is an effect of the vacuum having a pressure but think of it this way I mean this is different to what we're talking about in the quantum gravity case but I just want to answer your question is there some evidence of a repulsive gravity so in Newton's theory the only thing that contributes to gravity is mass so you can't have negative mass as far as I know so you can't have negative gravity therefore gravity is always attractive However, in Einstein's theory, there's also a pressure term.

1:09:15So it's not just mass. And the pressure can be negative. It's like a suction. And in fact, vacuum has negative pressure. So it is a repulsive gravity force. And the fact that we see the universe accelerating in expansion is direct empirical evidence of repulsive gravity. So that is clear that there is repulsive gravity. Now, that's not necessarily what's going on here at the Big Bounce because there you're assuming it's coming from quantum gravity. So there you have to use a different type of geometry. So the geometry that's used in relativity is classical geometry, whereas in these quantum gravity theories, it's a quantum geometry.

1:09:55So it's sort of fluctuating. And the idea is that then, because it's discrete, it can't have infinite compression. It will bounce back at some point, and then the gravity switches signs, and you get repulsive gravity. So that's the theoretical extrapolation from the quantum gravity theory. So in particular, loop quantum gravity is a candidate for quantum gravity. They've done a lot of work on this bouncing cosmology. But there have been ideas even in string theory that you might get bouncing cosmology from this fact that if you discretize space, then it will have a maximum limit of what you can put into it.

1:10:32And then if you try to go beyond it, it pushes back. I like these bouncing ideas because they sort of avoid the question of a first moment. but they're like, let's just bounce forever. And that's cool. But I wonder if there's any evidence for that. Like, you know, if the universe compresses to a singularity or a near singularity, some quantum version of it, does it do so intensely that all evidence of the previous, you know, pre-bounce universe is lost? Or can we find some hints, some clues in the universe today that show that it had to have a bounce? Yeah, so this is an active research program.

1:11:07So as I said, I think it's in the loop quantum gravity case where there's the most consensus that you get a bounce. As I said, there have been ideas in string theory for a bounce as well, and even in some other proposals for quantum gravity. But in the loop case, loop quantum gravity, which is one of the candidates for a theory to mix iso-serial relativity and quantum mechanics, as we get this quantum theory of gravity, because we should point out to the listener, if they're not familiar, these two theories are the cornerstones of modern physics, but yet they contradict each other. So we know we need a deeper theory.

1:11:42So we need to modify one of the existing theories or maybe both of them. But we know we need new physics in some way. So one of the contenders is this theory called loop quantum gravity. And what they've got this program called loop quantum cosmology, where what they want to do is calculate what we should see in the cosmic microwave background if there was a bounce. and they claim that they've already done this and it matches their observations. Now, obviously, not everyone agrees that this is correct. So they have to make certain assumptions and then the question is, are they valid assumptions?

1:12:16And then, you know, in particular, I'll give you one I think is important or especially important, I should say. And that is you have to assume whether there was inflation or not. And as we said, not everyone agrees there was inflation. So they have to put in inflation and then there's different models of inflation. So what they do is they try and say, well, which one is favored by the data? Put that in, then we calculate corrections to what we see in the cosmic microwave background. And then they claim that there's actually much better than the standard model. But the differences are not big enough to be decisive.

1:12:52And of course, as I said, you could challenge the assumptions. So it's still an ongoing program and people are still working on the theory to see if they can make the predictions more robust. So maybe it doesn't depend on some of these assumptions. The other thing you could try and do is look at black holes and how black holes might behave, because there also we think we need quantum gravity. So people have made models of black holes using quantum gravity, and then maybe you could look for signatures of what they might do. Maybe there are signs of quantum gravity in black holes. So those are the two areas that I think are the most exciting about looking for signs of quantum gravity.

1:13:37And if we could find those, then we might know what the right theory of quantum gravity is. And then we might know whether this bounce took place or if it didn't. That would be exciting. Yes. Oh, yeah. Well, now we've been looking into the past. Tell us about the future of looking into the past. What do you think we're going to learn in the next 10 years or 50 years that could help us understand what came before the hot Big Bang? Well, there's a number of avenues we can explore. So one is to look more at this cosmic microwave background. So this is the oldest light that we can see. You can't see beyond that with light.

1:14:09It's emitted 380 ,000 years after the Big Bang. And the reason that you can't see anything earlier is that if you went earlier, as I said, the universe would look more like the sun. and if you if you look at the sun you can't look into the interior because it's opaque so same with the with the universe before the emission of the cosmic microwave background it was opaque so you cannot look earlier but there are these patterns of hot and cold spots and they give you information that you could try and guess as to what came before and some theories make different predictions for those patterns of hot and cold spots also there's patterns of polarization So this is a way that light sort of twirls around.

1:14:47That's a new frontier. So looking for polarization of the cosmic microwave background. And some different models make different predictions for what we might see there. Another avenue you could look at is the distribution of galaxies because that was set in the very earliest moments of the Big Bang. So different models might make different predictions for the distribution of galaxies. but i think the most exciting idea for how we can probe much earlier into the into the big bang is something called primordial gravitational waves so this you might people probably might have heard in 20 let me think was it 2016 um ligo which was these giant lasers that they have in louisiana and washington state and they detected sort of um a ripple in the fabric of space and time they're called gravitational waves and they came not from the big bang they came from colliding black holes but they send out this ripple in the fabric of space and time and we can detect them amazingly because they're very very feeble when they get to the earth uh they they change the distance of um like these lasers that basically have these lasers they're at four kilometers apart and they bounce between mirrors and if there are no gravitational waves they should stay in phase with each other.

1:16:08When a gravitational wave passes through, they go out of phase. And so you can detect their existence. And they have two of them, one in Louisiana and one in Washington State. Initially, I mean, they've been more built since then. There's one now in Italy and India and Japanese. They're building one of, I don't know what the status of that one is. But so the idea is to have stations of them around the world. So these ripples can go through that plasma that you can't see through. So even though you can't see light from the Big Bang, you could, in some sense, see these gravitational waves. You don't see them.

1:16:44Maybe you hear them. You know, they're kind of sound waves, actually, in the early universe. Well, they cause sound waves in the early universe, I should say. So these ripples in the fabric of space-time are potentially detectable. Either they might change the polarization of the light, of the cosmic microwave background, or we could detect them directly via building something like these giant laser observatories. But the ones that we have today are optimized to see them from black hole collisions. They can't even see them from supermassive black holes, which are the really big black holes that sit in the center of galaxies.

1:17:17However, we are building a space-based observatory called LISA, the Laser Interprometure Space Antenna. And that will be able to detect supermassive black hole mergers. So maybe it could see signatures of quantum gravity in these extreme conditions. Cool. So that might help us understand the Big Bang. But beyond LISA, I mean, LISA's not going to get launched until the 2030s, but then beyond that, there are projects, one called DeSygo, another one called Big Bang Observer. These are kind of pie-in-the-sky ideas, right? So we don't think that they're going to be built anytime soon. But often what you do is just dream big.

1:17:54Just say, what would you do if you had endless money and resources? The idea is just get something on the table, And then, you know, maybe decades into the future, maybe people find cheaper ways to do it, and then you can actually launch these things. So the Big Bang Observer, for example, is like LISA. It's a similar idea, but it has 12 spacecraft. LISA has three. And LISA's funded. That is happening, being built as we speak. But Big Bang Observer is much, much more ambitious. But that could potentially see these ripples from the Big Bang. And now, why is that important? Because some models predict that there should be these ripples and some don't.

1:18:35So a lot of cyclic models say there are no ripples. And some of these cyclic models are alternatives to the inflationary screen, which says there are these ripples. Not only that, but they actually have different properties. So they have different strengths at different wavelengths. And so we call that the spectrum of the gravitational waves. so by probing the gravitational wave universe and this is a an area of astronomy that is brand new i mean we only detected the first gravitational wave in 2015 it's like galileo first looking up in his telescope in 1610 think of what a small telescope we had and and how radically it changed our view of the universe because before galileo looked through that telescope most people were sure that we lived in a geocentric universe with everything going around the earth and i think when galileo took through that telescope and he saw that there were moons going around jupiter it was clear as clear as day that not everything goes around the earth and then he saw the phases of venus which was a direct prediction of the heliocentric model uh or particular properties of the phases of venus so it was incredibly revolutionary and now we're at the birth of this new revolution, gravitational wave astronomy.

1:19:46And this could probe which models of the Big Bang or even pre-Big Bang universe are right. And that is the incredibly exciting frontier for early universe cosmology in the decades or maybe centuries to come, depending on whether we decide to fund this area of science. That's right. It'll finally tell us whether we're in the Marvel multiverse or the DC multiverse or another version. Right. Yes. Exactly right. Yeah. All right. Well, thank you, Phil, very much for coming on the podcast and talking to us about all these crazy ideas. It's amazing to me we can know anything about the universe so long ago, and we can even have debates about various ideas.

1:20:28I really enjoyed the book. The book is called Battle for the Big Bang, The New Tales of Our Cosmic Origins.

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