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Speaker 1: Everybody wants to know where we came from, how we

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Speaker 1: got to be here. That means understanding the events that

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Speaker 1: set in motion your life, all of its ups and downs.

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Speaker 1: Historians can tell you about the journey of your ancestors,

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Speaker 1: how it shapes your culture and way of life. Anthropologist

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Speaker 1: can tell us the story of humanity itself, why we

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Speaker 1: walk on two feet, and how we got to be

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Speaker 1: so darn smart. But physicists can take us deepest into

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Speaker 1: the past, even beyond the chaotic formation story of our

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Speaker 1: solar system or of the galaxy itself. Incredibly, we can

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Speaker 1: look billions of years deeper into history, to a time

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Speaker 1: before there were galaxies or stars, when the universe was

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Speaker 1: filled with hot, dense plasma. But then we hit a wall.

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Speaker 1: Beyond thirteen point eight billion years ago, the universe was opay,

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Speaker 1: and all photons emitted before then have been lost, reabsorbed,

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Speaker 1: and beyond another three hundred and eighty thousand years, the

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Speaker 1: universe was so hot and dense that our theories of

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Speaker 1: physics no longer apply, like trying to explain steam using

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Speaker 1: fluid dynamics. Our curiosity, of course, is limitless, and so

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Speaker 1: we desperately want to know what came before, What is

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Speaker 1: the original fundamental context of the universe, and what does

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Speaker 1: it say about those of us scratching out a living

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Speaker 1: on a tiny dot of rock. Today we'll take a

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Speaker 1: tour of the current ideas about the earliest moments in

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Speaker 1: the universe, if there even were any, and think about

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Speaker 1: what we might learn in the future. Welcome to Daniel

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Speaker 1: and Kelly's Extraordinary Ancient Universe.

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Speaker 2: Hello, I'm Kelly Wiener Smith. I study parasites and space,

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Speaker 2: and today we're talking about where it all began.

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Speaker 1: Hi, I'm Daniel. I'm a particle physicist, and I love

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Speaker 1: physics because it subsumes every other question in science.

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Speaker 2: So today we're talking about, like, what happened before the

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Speaker 2: Big Bang? Do you think will we ever get solid

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Speaker 2: answers where we're like, Bam, we don't have to debate

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Speaker 2: this anymore. We've got to figure it out. Or is

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Speaker 2: this the kind of thing that we will always be

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Speaker 2: tinkering with. I think either answer is okay and exciting.

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Speaker 1: I should say yeah. I don't think there's going to

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Speaker 1: be a moment where we're like, yeah, we figured it out,

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Speaker 1: and here's the rest of the grant money back. By

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Speaker 1: the way, we have nothing else we're curious about, and

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Speaker 1: we don't want to think about it anymore.

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Speaker 3: Yeah.

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Speaker 1: No, I think we're always going to wonder what about this?

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Speaker 1: What about that? Where did that come from? Why not this?

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Speaker 1: Why the other thing? I think it is a lot

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Speaker 1: of philosophical questions, just thinking about the origins of the universe,

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Speaker 1: but also wondering which answers are acceptable, which ones we go, yeah,

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Speaker 1: that makes sense, let's move on, and which ones were like,

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Speaker 1: wait a second, why that? I think that reveals a

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Speaker 1: lot of about our humanity and our curiosity, which is

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Speaker 1: one of the reasons why I love this topic so much.

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Speaker 2: Yeah, and we've talked on past shows about why there

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Speaker 2: are some explanations we get where we're like, oh, that

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Speaker 2: makes sense, we don't have to dig any deeper, and

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Speaker 2: how that can like sort of send us down the

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Speaker 2: wrong path actually by just you know, oh, that makes sense,

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Speaker 2: no more questions needed?

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Speaker 1: Yeah, exactly, And whether aliens would find those answer satisfactory

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Speaker 1: or not?

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Speaker 2: I know, Dan, the constant question that is ringing in

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Speaker 2: Daniel's mind, what would the alien say.

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Speaker 1: Exactly? Well, you know, they're not here to speak for themselves,

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Speaker 1: so I feel like some pressure to speak up for

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Speaker 1: the aliens.

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Speaker 2: I'm so glad that they have an advocate in Daniel Whitson.

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Speaker 1: Well, look, if they're aliens all over the galaxy, then

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Speaker 1: they are literally the silent majority, right because everybody's speaking

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Speaker 1: for them. So yes, I stand here to speak for

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Speaker 1: the aliens. But today we didn't have an alien on

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Speaker 1: the podcast. We instead had a human being. We thought

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Speaker 1: a lot about cosmology and how to communicate it to

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Speaker 1: the public because we wanted to dig deep into this

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Speaker 1: question of what is the Big Bang and what came

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Speaker 1: before it? And so before we get to that interview,

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Speaker 1: let's hear what folks on the street, by which I

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Speaker 1: mean podcast listeners who volunteered think came before the Big Bang.

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Speaker 1: Here's what folks had to say.

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Speaker 3: Our understanding of physics breaks down with a big bang,

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Speaker 3: but one idea so a turn of inflation. It could

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Speaker 3: be that there was something that was just so different

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Speaker 3: from our current experience or understanding that we don't even

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Speaker 3: have the language to describe it.

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Speaker 1: According to Pastafarian scripture, the great flying spaghetti Monster made

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Speaker 1: us all hail the cosmic Cannloni. It's just all theories.

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Speaker 1: I guess at the singularity, there was no space time,

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Speaker 1: thus no time, no causation, no before. But how can

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Speaker 1: there be an after without a before?

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Speaker 3: That's like asking what the NOI at the Pope. I

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Speaker 3: don't think that's an answer, but prove me wrong, please.

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Speaker 1: Nothing came before the Big Ban, because as I understand it,

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Speaker 1: it's when time started. All right. What a wonderful spectrum

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Speaker 1: of answers as usual? Aren't our listeners wonderful? Kelly?

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Speaker 2: Yeah, obviously, obviously, clearly they have a good sense of

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Speaker 2: taste for podcasts. But exactly, but we've got a real

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Speaker 2: professional on today to tell us about the mini theories

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Speaker 2: actually for what came before the Big Bang. I think

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Speaker 2: we don't even manage to get to all of the

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Speaker 2: ones we had thought about, because there's a lot of

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Speaker 2: them out there. So instead we dug deep into about

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Speaker 2: two of them. And let's go ahead and jump in.

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Speaker 1: It's my pleasure to welcome to the podcast Phil Helper.

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Speaker 1: He's a Fellow of the Royal Astronomical Society and a

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Speaker 1: science popularizer. He's a creator of the popular YouTube series

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Speaker 1: Before the Big Bang. His astronomy images have been featured

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Speaker 1: in The Washington Post, BBC, and The Guardian. He's one

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Speaker 1: of the rare breed of pop physics authors that also

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Speaker 1: who has deep credentials in physics, and together with cosmologist

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Speaker 1: naish Ash forty, he's the co author of Battle for

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Speaker 1: the Big Bang The New Tales of Our Cosmic Creation. Phil,

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Speaker 1: welcome to the podcast.

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Speaker 3: Thank you great to be on.

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Speaker 2: We're excited to have you. And if I can get

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Speaker 2: the ball rolling. So, like my for my PhD, I

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Speaker 2: studied fish, and I really like things that you can

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Speaker 2: have in the lab and you can see and manipulate,

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Speaker 2: and studying something like the Big Bang, which happened so

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Speaker 2: long ago, sounds really difficult. What got you interested in

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Speaker 2: this question in particular?

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Speaker 4: Well, who cannot be absolutely fascinated by the origin of

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Speaker 4: the universe. I mean, I think that's deeply ingrained in

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Speaker 4: right in human nature. I mean, it's no surprise that

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Speaker 4: every culture, well maybe not every culture, where many many

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Speaker 4: cultures have an origin story, something where they can point

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Speaker 4: to and say, this is how the universe came to be.

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Speaker 4: So I think we all have that deep curiosity in us.

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Speaker 4: And the beauty is that science has actually found a

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Speaker 4: way to probe the very origin of the universe and

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Speaker 4: that's cosmology. So why not follow follow us down that

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Speaker 4: rabbit hole and see how far it goes?

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Speaker 2: Amazing?

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Speaker 1: Well, I like how you appeal to our innate curiosity,

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Speaker 1: but I think in the end there is something subjective,

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Speaker 1: right about what you find exciting? Would you find interesting?

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Speaker 1: What questions you think are worth exploring? And so you know,

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Speaker 1: some of us are excited about fish guts and some

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Speaker 1: of us are excited about the whole universe. So it's

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Speaker 1: all about it, for sure.

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Speaker 2: I can see the fish guts in front of me.

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Speaker 2: I like that.

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Speaker 3: Oh I have actually published a paper on fish.

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Speaker 4: Oh yeah, scientific und yeah, yeah, so I'll have.

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Speaker 3: Been interested in fish as well. Okay, good, Literally it's

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Speaker 3: about fish pains.

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Speaker 2: Oh that's an important topic, I think.

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Speaker 1: So.

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Speaker 4: Yeah, we tried to show that the case of fish

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Speaker 4: pain is stronger than some people think.

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Speaker 3: Yeah.

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Speaker 1: Well. The thing I love about the BANG is that

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Speaker 1: it explains everything. Like literally, we're going back to the

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Speaker 1: beginning and trying to find the cause of you know,

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Speaker 1: planets and life and fish guts and Kelly and everything.

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Speaker 1: So it's all inclusive, but something we have to clear

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Speaker 1: out before we dig deeper into theories about what happened

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Speaker 1: before the Big Bang is what we mean when we

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Speaker 1: say the big bang. And in your book, I really

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Speaker 1: appreciated that you attack this head on. You're like, look,

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Speaker 1: there's a lot of confusion about what this means, and

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Speaker 1: cosmologists aren't even always consistent about what they mean by

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Speaker 1: the words. So can you give us a clear and

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Speaker 1: crisp definition of what we mean when we save the

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Speaker 1: big Bang?

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Speaker 4: Well, the answer is now, I can't, because there's all

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Speaker 4: than one definition of the big Bang, and that's kind

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Speaker 4: of the whole problem. People mean different things when they

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Speaker 4: say a big bang. But what we can do, which

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Speaker 4: I hope will be really helpful, is to explain the

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Speaker 4: different meanings and then people might try and infer which

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Speaker 4: meaning is being used in which context. So we sol

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Speaker 4: highlight two definitions of the big Bang. So one is

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Speaker 4: that the big Bang is a theory that says the

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Speaker 4: universe evolved from a very hot, dense state. So it

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Speaker 4: was different in the past, very different in the past

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Speaker 4: than it is today. So it was very hot, very dense,

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Speaker 4: highly curved, and that's very very different to the sort

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Speaker 4: of cold, sparse universe we see today. So that's one

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Speaker 4: definition we call without the hot Big.

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Speaker 1: Bang, and that's what scientists mean when they refer to

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Speaker 1: the Big Bang, because we know the universe is expanding

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Speaker 1: and getting less dense as time goes forwards. But we

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Speaker 1: can also run the clock backwards and figure out that

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Speaker 1: it was more dense in the past. And if we

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Speaker 1: run it back thirteen point eight billion years, we get

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Speaker 1: to a very hot and very dense state, and that's it.

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Speaker 1: The hot Big Bang doesn't go any further than that

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Speaker 1: because it can't. That state is so hot and so

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Speaker 1: dense you'd need quantum gravity to predict what happens before that,

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Speaker 1: So it doesn't go all the way to a singularity.

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Speaker 1: It can't without quantum gravity, so it doesn't tell us

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Speaker 1: what happened before or how time began. It assumes that

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Speaker 1: initial state and explains what happens afterwards as time goes forward,

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Speaker 1: and it does it very well, and there's a lot

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Speaker 1: of experimental evidence for it.

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Speaker 4: Another definition we call the Big Bang singularity. So that's

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Speaker 4: an idea that says the universe start a denist state

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Speaker 4: that's infinitely dense, infinitely hot, infinitely curved, and that marks

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Speaker 4: the beginning of time.

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Speaker 3: So there is nothing before the Big Bang, and this idea.

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Speaker 1: The Big Bang singularity is what most people think of

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Speaker 1: when they hear the phrase big Bang. This takes that hot,

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Speaker 1: dense state from thirteen point eight billion years ago and

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Speaker 1: extrapolates it even further backwards in time, but ignoring quantum mechanics.

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Speaker 1: It says, if we just account for gravity, what would happen?

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Speaker 1: So you get a singularity. It's a collapse. That's like

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Speaker 1: how general relativity predicts the singularity inside a black hole,

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Speaker 1: which also ignores quantum mechanics. So we don't really believe it.

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Speaker 1: So the Big Bang singularity is an extrapolation past what

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Speaker 1: we know using an approximation of quantum gravity that we

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Speaker 1: know is wrong, which ignores all of the quantum effects.

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Speaker 1: And there's no experimental data for this extrapolation. It's all

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Speaker 1: very speculative.

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Speaker 4: Now here's the interesting thing. And we did a survey

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Speaker 4: of physicists. We went to a conference in Copenhagen, very

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Speaker 4: large conference. It was interdisciplinary. We had theorists, we had observers,

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Speaker 4: we had like numerical relativists, we had people working in

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Speaker 4: quantum gravity or kind and lead some of the leading

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Speaker 4: figures in the field. And we asked various questions about

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Speaker 4: controversies within physics, such as what's the right interpretation of

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Speaker 4: quantum mechanics, what's the best candidate for quantum gravity, what

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Speaker 4: do you think dark matter is? And we got consensus

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Speaker 4: on almost nothing. I can't think of any topic where

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Speaker 4: we got fifty percent for any one thing except one

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Speaker 4: one exception, and that was how should we define the

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Speaker 4: term big And the consensus was that it should only

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Speaker 4: be defined as this evolution from a hot, dense stay.

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Speaker 4: So the idea that the universe began at the Big

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Speaker 4: Bang or there was a singularity is not perceived as

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Speaker 4: the way we should understand the Big Bank. That is

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Speaker 4: a theoretical extrapolation that most people don't trust, I would say.

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Speaker 1: And let's dig into that a little bit more. Like,

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Speaker 1: we have this theoretical extrapolation, the Big Bang singularity, as

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Speaker 1: you say, which might predate the hot early universe that

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Speaker 1: you described as the hot Big Bang. And that's very speculative.

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Speaker 1: But we have a lot of evidence for the hot

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Speaker 1: Big Bang. Right when we say the universe was dense

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Speaker 1: and hot thirteen point eight billion years ago, that's not speculation.

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Speaker 1: That's something we have unfairly solid grounds, right.

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Speaker 3: That's right.

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Speaker 4: I don't think there's any serious doubt about the hot

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Speaker 4: big bank. So that's very well established. We've got lots

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Speaker 4: of independent lines of evidence for that. People will probably

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Speaker 4: be familiar with, you know, the expansion given by the

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Speaker 4: red shifted galaxies. We've got the cosmic microwave background, the

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Speaker 4: abundance of elements, and there's various properties of the cosmic

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Speaker 4: microve background that we should see if the Big Bank

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Speaker 4: had happened, and we see them. So I don't think

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Speaker 4: there's any doubt that there was a hot Big Bang.

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Speaker 4: But the observational evidence stops there. We can't have observational

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Speaker 4: evidence of a singularity. They are sort of hidden from

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Speaker 4: us if they were to exist, but I think most

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Speaker 4: physics would say they don't really exist. They're just part

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Speaker 4: of our physics that breaks down, and we need better

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Speaker 4: physics and that will sort of get rid of the singularities.

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Speaker 4: But how to do that is an open question, and

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Speaker 4: what would replace a singularity is where all the debate is.

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Speaker 4: That's why we call our book the Battle of the

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Speaker 4: Big Bang, because once you concede, Okay, we don't really

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Speaker 4: know the universe began with a big bank singularity. It

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Speaker 4: might have had a prior stay, Okay, so what was

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Speaker 4: that prior's day? And that's the battle because there's all

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Speaker 4: kinds of ideas out there and no one knows which

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Speaker 4: one is right.

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Speaker 2: So for the biologist, if I were to be floating

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Speaker 2: in and I was observing the big bangs of the

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Speaker 2: two different varieties happening, what would I be seeing in

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Speaker 2: a hot big bang and what would I be seeing

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Speaker 2: in a big bank's singularity?

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Speaker 4: So in a hot big bang, well, I think the

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Speaker 4: name kind of gives you a clue. It's very, very

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Speaker 4: hot and dense basically, but soon you know, as you

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Speaker 4: go back in time. It's a bit like looking at

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Speaker 4: the sun. You know, if you look at the surface

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Speaker 4: of the sun, you can see that it's about five thousand,

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Speaker 4: seven hundred colvin, but you can't it's.

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Speaker 3: Opaque, right.

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Speaker 4: If you to go through it, all the photons would

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Speaker 4: be bouncing off the materials, you couldn't really see very far.

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Speaker 3: It'd be like a fog. So that's this sort of hot,

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Speaker 3: dense state.

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Speaker 1: And to clarify, you're saying that the whole universe was

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Speaker 1: hot and dense, like the entire universe was thirteen point

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Speaker 1: eight billion years ago, something like the inside of the

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Speaker 1: sun is now and photons made inside the sun get

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Speaker 1: reabsorbed almost immediately, which is why the sun is opaque.

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Speaker 1: You can't see through it, so it's not a great view.

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Speaker 4: Now the singularity again, most people would say it's just

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Speaker 4: a part with a mass breaks down. But but the

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Speaker 4: description involves you know, there was what was called a curve.

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Speaker 4: It's your singularity. So here the temperature would literally be infinite.

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Speaker 2: So it's hot too.

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Speaker 4: It's also hot, yes, yes, okay, yeah, it would.

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Speaker 3: Be hotter, hotter a big bang, yeah, the holter big bang.

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Speaker 2: Oh wait, so the hot Big Bang is not the

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Speaker 2: hardest of the Big Bass.

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Speaker 4: Not the hot good naming, h guys, it is all

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Speaker 4: right yeah, but no, but we'll come. We'll come to

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Speaker 4: what might have come before the Big Bang, and that

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Speaker 4: could have been something very cold.

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Speaker 3: Okay.

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Speaker 4: So yeah, that's to do with something called inflationary cosmology.

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Speaker 4: So if we believe that story of the Big Bang

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Speaker 4: or then actually the universe is very cold before the

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Speaker 4: Big Bang.

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Speaker 1: All right, So we have this scientific conception that the

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Speaker 1: universe is cold and sparse now and we run the

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Speaker 1: clock backwards, we get to a hot, dense state thirteen

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Speaker 1: billion years ago, and the big question is what came

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Speaker 1: before that? Where did that hot dance state come from?

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Speaker 1: We know a lot about that state and its evolution

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Speaker 1: from that point to now, but not a lot from

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Speaker 1: before that. That's the scientific conception of the Big Bang.

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Speaker 1: But I think if you talk to people in the

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Speaker 1: general public and you ask them about the Big Bang,

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Speaker 1: they mostly think about the Big Bang singularity. They think

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Speaker 1: the universe started from a tiny dot that exploded into

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Speaker 1: empty space. Why do you think there's such a persistent

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Speaker 1: gap between the scientific view and the popular view. I mean,

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Speaker 1: you work on both sides of the aisle. Why do

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Speaker 1: you think there's been a disconnect there.

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Speaker 3: Well, I think there's a couple of reasons.

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Speaker 4: One, when you're doing animation, and you know, I've got

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Speaker 4: YouTube videos that we try and animate the big fact,

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Speaker 4: you kind of it's hard not to draw bit a

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Speaker 4: light exploding outwards, right, because that's how you're going to

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Speaker 4: animate it. So it's hard for people to not have

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Speaker 4: that visualization, which is, you know, a rough approximation, but

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Speaker 4: it's not precise in their head.

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Speaker 1: And I want to be clear here that it's not

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Speaker 1: precise because applies that the universe was empty, that a

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Speaker 1: dot of matter exploded into empty space. This is misleading

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Speaker 1: because the universe was never empty. Matter was always everywhere.

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Speaker 1: If the universe was infinite, then matter was infinite and

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Speaker 1: then expanded everywhere simultaneously. If the universe was finite, then

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Speaker 1: it was small but still always filled with matter. There

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Speaker 1: was never a tiny dot exploding out into empty space.

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Speaker 4: But the other thing is, I think two things happened

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Speaker 4: at the same time. Roughly in the mid nineteen sixties,

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Speaker 4: we got the evidence now clear that there was a

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Speaker 4: cosmic microwave background, that's the afterglow of the Big Bang.

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Speaker 4: It was a very hot surface and then it cooled

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Speaker 4: down into microwaves as the universe expanded and stretched, so

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Speaker 4: it stretched that light into into the microwaves, and that

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Speaker 4: was very clear evidence of the hot Big Bank. At

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Speaker 4: the same time, Roger Penrose and Stephen Hawking, roughly at

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Speaker 4: the same time, we're establishing these singularity theorems that say

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Speaker 4: the Big Bang must have been a singularity. So that

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Speaker 4: looked like you've got the theory and the evidence all

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Speaker 4: dancing in harmony. So it would appear then that the

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Speaker 4: universe had this definite beginning of the singularity, and of

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Speaker 4: course one of the authors of these Penrose Hawking. Theorems

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Speaker 4: of Stephen Hawking, and he was an incredible figure popularizing science.

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Speaker 4: And whilst Roger Penrose was a bit reluctant to even

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Speaker 4: user RaSE singularity, wasn't sure that we should trust it

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Speaker 4: this distrapolation, I think Stephen Hawking was much more brash,

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Speaker 4: you know, so he was sort of proclaimed, you know,

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Speaker 4: this is the beginning of the universe. But what hers

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Speaker 4: happened is that some of the assumptions of those singularity

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Speaker 4: theorems have started to unravel. And this happened, you know,

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Speaker 4: in the decades after the singularity theorems were proven. So

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Speaker 4: physical theory is only good as the assumptions that it has,

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Speaker 4: and those assumptions in the peneris hooking theory. We can

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Speaker 4: go over them one by one if you wish, But

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Speaker 4: bottom line is people started to question those assumptions. So

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Speaker 4: then it was like, well, maybe there isn't really a

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Speaker 4: singularity or it maybe it's just an artifact of pushing

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Speaker 4: the equations beyond their domain of validity, and we need

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Speaker 4: new physics to explore what really happened to fourteen billion

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Speaker 4: years ago.

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Speaker 2: So The problem is that the popular science conception of

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Speaker 2: the Big Bang hasn't caught up with where we are

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Speaker 2: now in our understanding of the Big Bang. Would that

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Speaker 2: be fair to say.

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Speaker 1: Yeah, But I think there's more than that. Two ideas

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Speaker 1: were developed at the same time, the hot big Bang

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Speaker 1: and the big Bang singularity, and they were both just

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Speaker 1: called the bing bang, and so they get confused for

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Speaker 1: each other. The hot big Bang is still a very

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Speaker 1: solid idea scientifically, and the big Bang singularity kind of

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Speaker 1: never was and we've moved on from it. But most

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Speaker 1: people still think of the big Bang singularity when you

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Speaker 1: say the big Bang.

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Speaker 3: I think that's right.

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Speaker 4: Yes, although there were people even at the time in

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Speaker 4: the sixties saying these singularity theorems don't prove the universe

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Speaker 4: at a beginning, but I don't think they were as

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Speaker 4: loud a voice as those He said it did.

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Speaker 1: Sounds like we should blame Stephen Hawking. Yeah, exactly, But

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Speaker 1: it sounds also like a familiar story. You have one

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Speaker 1: story that somebody tells in a compelling way and it

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Speaker 1: sticks in people's mind. It's like, even if it's hard

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Speaker 1: for people to wrap their mind around this idea of

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Speaker 1: the universe, beginning in a point. It is a compelling story,

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Speaker 1: it's easy to tell, and it's stuck in the popular

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Speaker 1: imagination long after people are like, well, we actually only

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Speaker 1: know a certain part of the story. The rest of

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Speaker 1: it's speculative. That's the nuance, that's the subtlety that's hard

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Speaker 1: to convey. I feel like that's sort of what's happening

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Speaker 1: with popular science everywhere, that the details are being lost

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Speaker 1: and the compelling clickbait headlines are getting propagated and embedded

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Speaker 1: in people's minds. As a science popularizer yourself, how do

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Speaker 1: you feel about the sort of state of science journalism

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Speaker 1: right now?

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Speaker 3: Yeah, it's depressing.

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Speaker 4: I Well, one thing I do want to say, just

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Speaker 4: before I come on to that, another correction that we

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Speaker 4: want to make to the popular I'm saying is that

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Speaker 4: the Big Bang wasn't a point. Rather, it could have

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Speaker 4: happened everywhere. Well if it would have happened everywhere, and

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Speaker 4: in fact, the universe could be infinite today, and it

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Speaker 4: could have been infinitely big even at the Big Bang,

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Speaker 4: So it wasn't a point. But anyway, no, siche journal

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Speaker 4: isn't very very depressing at the moment. I think you

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Speaker 4: see people just trying to get headlines clickbaits. They're not,

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Speaker 4: i think, being rigorous and of course probably underfunded. So

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Speaker 4: you just get people, you know, copying press releases or

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Speaker 4: they're going for like the big angry headline. You know,

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Speaker 4: Oh everyone's got everything wrong, and that's usually also dubious too.

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Speaker 4: So yeah, I'm not optimistic about the state of journalism.

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Speaker 1: All right, Well, let's do our best to push back,

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Speaker 1: and so to reiterate, we know a lot about the

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Speaker 1: last thirteen point eight billion years of the universe. We

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Speaker 1: have evidence, it all comes together, we have multiple lines

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Speaker 1: of evidence. It all tells a very compelling story, and

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Speaker 1: it tells us that there was a hot density a

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Speaker 1: long time ago. But then the question, of course is

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Speaker 1: where does that come from? And so let's explore some

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Speaker 1: of those theories. One of the most popular ones is

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Speaker 1: the theory of inflation. Can you give us a quick

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Speaker 1: primer on what inflation is and why it's a compelling

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Speaker 1: explanation for how we got that hot density?

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Speaker 4: Right, So before we say what inflation is, it's probably

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Speaker 4: worth saying why people take it so seriously? What the

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Speaker 4: problems that are supposed to solve, And then maybe we

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Speaker 4: can some one will explain what it is. So the

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Speaker 4: problems that inflation are supposed to solve, I, well, there

437
00:22:44,640 --> 00:22:47,400
Speaker 4: are kind of a few. One is called the monopole problem.

438
00:22:47,720 --> 00:22:49,520
Speaker 4: So this is that if you think of a magnet,

439
00:22:50,359 --> 00:22:52,439
Speaker 4: it has a north and a south pole. If you

440
00:22:52,560 --> 00:22:55,080
Speaker 4: cut it in two, you don't get one with a

441
00:22:55,119 --> 00:22:57,680
Speaker 4: north pole, one with a south pole. You just get

442
00:22:57,720 --> 00:23:02,600
Speaker 4: another two magnets with the northern sealf pole. However, theorists

443
00:23:02,600 --> 00:23:05,160
Speaker 4: in the nineteen seventies thought that in the whole early

444
00:23:05,200 --> 00:23:08,959
Speaker 4: conditions of the universe you would get something called monopoles,

445
00:23:09,000 --> 00:23:13,000
Speaker 4: which would literally have only one pole, and these monopoles

446
00:23:13,040 --> 00:23:16,679
Speaker 4: would be very, very abundant and so should dominate the universe.

447
00:23:16,720 --> 00:23:19,000
Speaker 4: But yet we don't see any There are no monopoles

448
00:23:19,040 --> 00:23:21,920
Speaker 4: ever observed, and also they probably be too heavy to

449
00:23:22,280 --> 00:23:24,800
Speaker 4: allow the universe to spand anyway, So this was called

450
00:23:24,800 --> 00:23:28,560
Speaker 4: the monopole problem. And actually this was a motivation to

451
00:23:29,320 --> 00:23:30,280
Speaker 4: come up with inflation.

452
00:23:30,560 --> 00:23:33,760
Speaker 1: That's super fascinating and not something I think is widely

453
00:23:33,880 --> 00:23:38,560
Speaker 1: enough appreciated. Inflation wasn't conceived of to explain the origins

454
00:23:38,600 --> 00:23:41,560
Speaker 1: of the universe, but to solve a little technical problem.

455
00:23:41,800 --> 00:23:44,040
Speaker 1: The theory at the time predicted that when the universe

456
00:23:44,119 --> 00:23:46,639
Speaker 1: was hot and dense and cooling as it cooled, it

457
00:23:46,640 --> 00:23:49,640
Speaker 1: shouldn't just make protons and electrons, but it should also

458
00:23:49,720 --> 00:23:53,840
Speaker 1: make magnetic monopoles, weird particles that have just a magnetic

459
00:23:53,960 --> 00:23:57,120
Speaker 1: north or south, the way electrons just have a negative

460
00:23:57,280 --> 00:24:00,600
Speaker 1: and protons just have a positive. The use does this

461
00:24:00,640 --> 00:24:03,080
Speaker 1: when it has a phase transition as it cools, like

462
00:24:03,359 --> 00:24:06,880
Speaker 1: when water goes from steam to liquid, it forms droplets. Here,

463
00:24:07,000 --> 00:24:10,520
Speaker 1: the phase transition was predicted to make all these magnetic monopoles,

464
00:24:10,560 --> 00:24:13,359
Speaker 1: and they should stick around. They don't go anywhere, So

465
00:24:13,480 --> 00:24:15,119
Speaker 1: if they were supposed to have been made in the

466
00:24:15,160 --> 00:24:17,680
Speaker 1: early universe, they should still be here for us to see.

467
00:24:17,720 --> 00:24:20,439
Speaker 1: But of course we don't see them anywhere we've looked.

468
00:24:20,640 --> 00:24:24,080
Speaker 1: We can't find any. So that's a problem, and you

469
00:24:24,200 --> 00:24:26,320
Speaker 1: need to find some way to tweak the theory so

470
00:24:26,359 --> 00:24:28,879
Speaker 1: it doesn't predict a bunch of monopoles that we know

471
00:24:29,000 --> 00:24:32,240
Speaker 1: don't exist in the universe. I love how thinking about

472
00:24:32,359 --> 00:24:36,080
Speaker 1: weird magnets helps us, in the end accidentally understand the

473
00:24:36,080 --> 00:24:38,840
Speaker 1: origins of the universe. All right, so then tell us

474
00:24:38,880 --> 00:24:39,920
Speaker 1: what happens next.

475
00:24:40,200 --> 00:24:45,120
Speaker 4: So what happened was to scientists Henry Tyane, and we're

476
00:24:45,119 --> 00:24:47,960
Speaker 4: trying to solve this monopole problem. And I imagine there

477
00:24:48,000 --> 00:24:50,600
Speaker 4: could be like phase transitions in the early universe.

478
00:24:51,359 --> 00:24:52,840
Speaker 3: Phase resistion might be familiar with.

479
00:24:52,960 --> 00:24:54,919
Speaker 4: If you have I'm setting out my going and right

480
00:24:54,920 --> 00:24:57,720
Speaker 4: now is very hot, So if I had some ice

481
00:24:57,760 --> 00:25:00,919
Speaker 4: similar drink, it's going to melt, It's going to go

482
00:25:01,000 --> 00:25:04,000
Speaker 4: from solid to liquid. That's a phase transition. So these

483
00:25:04,000 --> 00:25:07,600
Speaker 4: are the sorts of phag transitions we're familiar with. However,

484
00:25:07,640 --> 00:25:10,120
Speaker 4: there can be phase transitions that are a bit weird

485
00:25:10,520 --> 00:25:12,320
Speaker 4: that we're not so familiar with. One of them is

486
00:25:12,359 --> 00:25:18,320
Speaker 4: called supercooling. So supercooling is if you put some water

487
00:25:18,560 --> 00:25:20,960
Speaker 4: very very pure. You can do this experiment at home.

488
00:25:21,200 --> 00:25:23,119
Speaker 4: Who would think you could do an experiment about the

489
00:25:23,200 --> 00:25:25,200
Speaker 4: very early universe and the origin of the Big Bang

490
00:25:25,520 --> 00:25:27,840
Speaker 4: in you your breezer at home. So what you have

491
00:25:27,880 --> 00:25:30,800
Speaker 4: to do is get some very very pure water, keep

492
00:25:30,840 --> 00:25:32,760
Speaker 4: it nice and still, and put it in the freezer.

493
00:25:33,200 --> 00:25:36,200
Speaker 4: Leave it in there, and after a while you take

494
00:25:36,240 --> 00:25:39,040
Speaker 4: it out. It should have frozen. But actually, if it's

495
00:25:39,080 --> 00:25:41,840
Speaker 4: pure enough and you are careful enough, it will not freeze.

496
00:25:42,119 --> 00:25:44,200
Speaker 4: It's what's in it. What's called a super cooled state,

497
00:25:44,240 --> 00:25:46,879
Speaker 4: it will stay liquid. Then if you shake it, it

498
00:25:46,960 --> 00:25:50,600
Speaker 4: will very quickly freeze. So this sort of delayed transition

499
00:25:50,680 --> 00:25:51,600
Speaker 4: is called supercooling.

500
00:25:51,720 --> 00:25:51,960
Speaker 2: Why.

501
00:25:52,280 --> 00:25:55,040
Speaker 4: It's just a way that the molecules can be in

502
00:25:55,040 --> 00:25:57,320
Speaker 4: a certain state that sort of resists being frozen.

503
00:25:57,880 --> 00:26:04,240
Speaker 1: Chemistry. Yeah, chemistry, this chemistry, but it's also super interesting.

504
00:26:04,760 --> 00:26:07,080
Speaker 1: I know that's unusual for me to say, but this

505
00:26:07,160 --> 00:26:10,000
Speaker 1: one I love. For freezing. The start, the liquid needs

506
00:26:10,000 --> 00:26:12,760
Speaker 1: a tiny seed of a solid like an ice crystal

507
00:26:12,920 --> 00:26:15,560
Speaker 1: or a dust spec or a surface bump to organize

508
00:26:15,560 --> 00:26:18,959
Speaker 1: molecules into the solid lattice. If no seed is present

509
00:26:19,040 --> 00:26:22,359
Speaker 1: and the liquid is very pure and undisturbed, the molecules

510
00:26:22,480 --> 00:26:25,439
Speaker 1: stay disordered, even though they are cold enough to be

511
00:26:25,520 --> 00:26:28,520
Speaker 1: a solid. It's like a crowd waiting for someone to

512
00:26:28,560 --> 00:26:32,040
Speaker 1: start clapping. Nobody does anything until the first person starts

513
00:26:32,040 --> 00:26:35,639
Speaker 1: to clap. And this chemistry trivia is actually important because

514
00:26:35,640 --> 00:26:38,879
Speaker 1: it helps us understand the universe cooling. It lets the

515
00:26:39,040 --> 00:26:44,320
Speaker 1: universe cool without making those monopoles. The universe passes that point,

516
00:26:44,520 --> 00:26:48,000
Speaker 1: but it stays super cooled and doesn't make monopoles the

517
00:26:48,040 --> 00:26:50,920
Speaker 1: way super cooled liquid doesn't make ice crystals.

518
00:26:51,280 --> 00:26:55,440
Speaker 4: Basically, they had time, because imagine that the universe would

519
00:26:55,440 --> 00:26:57,879
Speaker 4: be in a super cooled state, and they calculate this

520
00:26:57,920 --> 00:26:59,479
Speaker 4: would actually stop monopole production.

521
00:27:00,440 --> 00:27:01,879
Speaker 3: We've solved the monopare problem.

522
00:27:02,320 --> 00:27:04,000
Speaker 4: And then they said, well, let's just see if this

523
00:27:04,040 --> 00:27:06,800
Speaker 4: would affect the expansion rate of the early universe. And

524
00:27:06,840 --> 00:27:10,760
Speaker 4: what they found was that it would expand exponentially if

525
00:27:10,800 --> 00:27:14,280
Speaker 4: it's in this super called state. It would expand an

526
00:27:14,359 --> 00:27:17,960
Speaker 4: incredibly rapid rate. The source of race we're talking about

527
00:27:18,440 --> 00:27:22,680
Speaker 4: is doubling in size every ten to the minus thirty

528
00:27:22,840 --> 00:27:26,639
Speaker 4: seven seconds, and so that in words, that is and

529
00:27:26,720 --> 00:27:29,000
Speaker 4: I think ten trillionth of a trillionth of a trillionth

530
00:27:29,040 --> 00:27:32,400
Speaker 4: of a second. So that is a very very fast

531
00:27:33,040 --> 00:27:34,000
Speaker 4: rate of expansion.

532
00:27:34,320 --> 00:27:37,280
Speaker 1: So they did this trick to avoid predicting monopoles would

533
00:27:37,320 --> 00:27:40,600
Speaker 1: be made, and then discovered that it also predicted that

534
00:27:40,640 --> 00:27:42,919
Speaker 1: the universe expanded super fast.

535
00:27:43,040 --> 00:27:46,840
Speaker 4: That's awesome, But then what happened was Gooth had heard

536
00:27:46,920 --> 00:27:50,840
Speaker 4: a lecture about another problem in cosmology called the flatness problem.

537
00:27:51,080 --> 00:27:54,199
Speaker 4: And the flatness problem basically is that the universe can

538
00:27:54,240 --> 00:27:56,280
Speaker 4: have a sort of different geometries at large scale. It

539
00:27:56,280 --> 00:27:59,920
Speaker 4: could be curved, positively curved like a bore or negatively

540
00:28:00,320 --> 00:28:02,280
Speaker 4: like a saddle, or it could be flat like a

541
00:28:02,320 --> 00:28:06,280
Speaker 4: piece of paper, and observation showed it was reasonably close

542
00:28:06,280 --> 00:28:09,439
Speaker 4: to flat in the nineteen seventies. But what had been

543
00:28:09,480 --> 00:28:12,440
Speaker 4: pointed out by another scientist called Pop Dickie was that

544
00:28:12,480 --> 00:28:15,600
Speaker 4: those flat solution is unstable. So if it doesn't start

545
00:28:15,640 --> 00:28:18,439
Speaker 4: out really, really flat, it will be driven away from flatness.

546
00:28:18,520 --> 00:28:21,800
Speaker 1: So if the universe has positive curvature, that means it

547
00:28:21,840 --> 00:28:24,879
Speaker 1: has enough mass density to curve in on itself and

548
00:28:25,000 --> 00:28:28,520
Speaker 1: gravity winds and it curves more and eventually collapses and

549
00:28:28,520 --> 00:28:32,160
Speaker 1: becomes super duper dense. Even if it's very slightly curved

550
00:28:32,160 --> 00:28:34,199
Speaker 1: in the early universe, it will get more curved and

551
00:28:34,200 --> 00:28:36,720
Speaker 1: then more curved, and it's a runaway effect. And the

552
00:28:36,760 --> 00:28:38,880
Speaker 1: same thing happens in the opposite direction. If it has

553
00:28:38,960 --> 00:28:42,240
Speaker 1: negative curvature, it will get slightly more negatively curved, and

554
00:28:42,240 --> 00:28:44,400
Speaker 1: then more and then more. It's a runaway effect towards

555
00:28:44,560 --> 00:28:47,760
Speaker 1: negative curvature. But the universe as we see it today

556
00:28:47,880 --> 00:28:50,800
Speaker 1: is still very close to flat, if not perfectly flat.

557
00:28:51,200 --> 00:28:53,640
Speaker 1: That's weird because in order to be flat now, the

558
00:28:53,720 --> 00:28:56,920
Speaker 1: universe had to have been borne exactly on the knife's

559
00:28:57,040 --> 00:29:00,520
Speaker 1: edge of flat any tiny deviation from flatness would after

560
00:29:00,600 --> 00:29:05,040
Speaker 1: almost fourteen billion years, make the universe either collapse or explode.

561
00:29:05,400 --> 00:29:06,800
Speaker 1: That's the flatness problem.

562
00:29:07,080 --> 00:29:09,440
Speaker 4: So it's very surprising then how the universe could be

563
00:29:09,480 --> 00:29:13,760
Speaker 4: so flat because it's this unstable solution. When Gooth thought

564
00:29:13,760 --> 00:29:18,840
Speaker 4: about inflation, he realized that if you're undergo inflation, then

565
00:29:18,920 --> 00:29:22,480
Speaker 4: actually it'll be driven towards flatness, and the rays you

566
00:29:22,480 --> 00:29:24,920
Speaker 4: can think about this is it. Imagine have you ever

567
00:29:24,960 --> 00:29:28,200
Speaker 4: seen like a circle show where people walk on like

568
00:29:28,240 --> 00:29:32,480
Speaker 4: pilates balls and you're saying that, m okay, quite difficult.

569
00:29:32,520 --> 00:29:35,920
Speaker 4: I imagine you need some skills for that.

570
00:29:35,960 --> 00:29:39,640
Speaker 3: I imagine. So imagine you were standing aren't that ball?

571
00:29:40,240 --> 00:29:41,360
Speaker 3: Or you tried and he fell off.

572
00:29:41,440 --> 00:29:43,960
Speaker 4: Let's say, but then you expanded the ball rapidly to

573
00:29:44,000 --> 00:29:46,280
Speaker 4: the size of the Earth. Be pretty easy to stand

574
00:29:46,320 --> 00:29:48,960
Speaker 4: on that ball. You wouldn't even notice any curvature.

575
00:29:49,120 --> 00:29:50,840
Speaker 1: I rarely fall off the Earth, that's true.

576
00:29:50,920 --> 00:29:53,280
Speaker 3: Yeah, yeah, I don't fall off the Earth often either.

577
00:29:53,360 --> 00:29:57,160
Speaker 4: So then anything will appear will automatically appear flat if

578
00:29:57,160 --> 00:30:00,600
Speaker 4: it goes undergoes this exponential experience so real, it would

579
00:30:00,640 --> 00:30:04,080
Speaker 4: fix this flatness problem. So now it solves two problems

580
00:30:04,080 --> 00:30:06,040
Speaker 4: at once, and then it turns out it solves many

581
00:30:06,080 --> 00:30:06,800
Speaker 4: other problems it once.

582
00:30:06,840 --> 00:30:08,640
Speaker 3: I won't go all of them, but I'll do one more.

583
00:30:08,880 --> 00:30:12,760
Speaker 1: Wit. Hold on, I understood how the rapid expansion solves

584
00:30:12,760 --> 00:30:15,920
Speaker 1: the flatness problem, Like it seems curved, you expand it,

585
00:30:15,920 --> 00:30:18,560
Speaker 1: all of a sudden, it doesn't seem very curved. How

586
00:30:18,600 --> 00:30:22,200
Speaker 1: does it solve the monopole problem? Exactly? Like why because

587
00:30:22,200 --> 00:30:24,400
Speaker 1: you're not putting the universe in a freezer. It's not.

588
00:30:24,480 --> 00:30:26,880
Speaker 1: No ten year old is doing the experiment on us.

589
00:30:26,960 --> 00:30:29,360
Speaker 4: The monopoles would be thrown out of the horizon because

590
00:30:29,360 --> 00:30:32,320
Speaker 4: there would only be like a handful of monopoles in

591
00:30:32,360 --> 00:30:35,440
Speaker 4: any patch. So as the universe expands, they'd be thrown

592
00:30:35,480 --> 00:30:38,400
Speaker 4: out of the horizon and you wouldn't see any.

593
00:30:38,480 --> 00:30:40,360
Speaker 2: I like that as a solution. Anything that you don't

594
00:30:40,400 --> 00:30:42,120
Speaker 2: like gets exploded out of the picture.

595
00:30:43,480 --> 00:30:46,200
Speaker 3: Throw it out. Yeah, yeah, exactly.

596
00:30:46,400 --> 00:30:48,880
Speaker 1: I think that's a fascinating sort of bit of science

597
00:30:48,920 --> 00:30:51,440
Speaker 1: where you're like, let me calculate what I think should

598
00:30:51,440 --> 00:30:53,240
Speaker 1: have happened in the early universe, and then I'm going

599
00:30:53,280 --> 00:30:55,280
Speaker 1: to compare that to what I'm seeing, Like, yeah, I

600
00:30:55,280 --> 00:30:57,840
Speaker 1: don't see a lot of monopoles, so Obviously something must

601
00:30:57,920 --> 00:31:00,800
Speaker 1: be wrong. I'm missing a piece. What can I add

602
00:31:00,800 --> 00:31:03,000
Speaker 1: to the universe is like now it's more likely to

603
00:31:03,040 --> 00:31:06,120
Speaker 1: describe the universe I see today. I think that's super fascinating.

604
00:31:06,600 --> 00:31:08,480
Speaker 1: Let's digest that and take a break, and when we

605
00:31:08,520 --> 00:31:10,240
Speaker 1: come back, Phil is going to tell us more about

606
00:31:10,240 --> 00:31:13,960
Speaker 1: how inflation solved these problems and whether or not we

607
00:31:13,960 --> 00:31:36,200
Speaker 1: should believe in it. Okay, we're back and we're talking

608
00:31:36,200 --> 00:31:38,840
Speaker 1: to Phil about the state of the early universe. What

609
00:31:38,840 --> 00:31:41,480
Speaker 1: we know about the universe before it was hot and dense,

610
00:31:41,520 --> 00:31:44,080
Speaker 1: and we've been talking about inflation, this theory that the

611
00:31:44,160 --> 00:31:47,920
Speaker 1: universe expanded super rapidly in a very short amount of time.

612
00:31:48,640 --> 00:31:51,680
Speaker 1: So tell us, Phil, inflation sounds a lot like the

613
00:31:51,720 --> 00:31:54,360
Speaker 1: expansion that we have now we talk about dark energy

614
00:31:54,400 --> 00:31:57,920
Speaker 1: in the universe is accelerating in its expansion. Is inflation

615
00:31:58,080 --> 00:32:01,360
Speaker 1: a different mechanism for expansion? Is it the same thing,

616
00:32:01,520 --> 00:32:03,760
Speaker 1: just at a different moment in the universe? How do

617
00:32:03,800 --> 00:32:05,000
Speaker 1: those two things connect?

618
00:32:05,160 --> 00:32:08,200
Speaker 4: They are similar because the universe is currently accelerating in

619
00:32:08,240 --> 00:32:11,360
Speaker 4: its expansion. So you could say the dark energy we

620
00:32:11,400 --> 00:32:16,640
Speaker 4: see today is a very dilute form of inflation, and

621
00:32:16,680 --> 00:32:19,120
Speaker 4: so that does raise the question are they really the

622
00:32:19,200 --> 00:32:23,840
Speaker 4: same physics? But I think that's still to be determined,

623
00:32:24,080 --> 00:32:27,520
Speaker 4: Like there's a lot unknown about inflation, if it even happened.

624
00:32:28,040 --> 00:32:31,880
Speaker 4: So whether inflation and the dark energy are are the

625
00:32:31,880 --> 00:32:35,520
Speaker 4: different manifestations the same phenomenon, or whether they're different things

626
00:32:35,600 --> 00:32:38,960
Speaker 4: that just result in something broadly similar.

627
00:32:39,600 --> 00:32:41,240
Speaker 3: I think it's still an open question.

628
00:32:41,680 --> 00:32:44,480
Speaker 4: But one thing I do want to just highlight is

629
00:32:44,760 --> 00:32:47,160
Speaker 4: that one of the things that inflation solves, and there

630
00:32:47,160 --> 00:32:49,640
Speaker 4: are a number of problems, but there's one in particular

631
00:32:49,720 --> 00:32:52,560
Speaker 4: that I think is the most relevant, and that is

632
00:32:52,600 --> 00:32:55,880
Speaker 4: how you get galaxy structures. Because if you had a

633
00:32:56,040 --> 00:32:59,280
Speaker 4: very uniform start at the universe, you've got to ask

634
00:32:59,320 --> 00:33:01,560
Speaker 4: the question, how on Earth to all these networks of

635
00:33:01,680 --> 00:33:06,480
Speaker 4: clusters of galaxies form what laid the seeds? And in inflation,

636
00:33:06,560 --> 00:33:10,920
Speaker 4: the idea is there will be quantum fluctuations and these

637
00:33:10,960 --> 00:33:15,360
Speaker 4: would be stretched by inflation to create the seeds of galaxies.

638
00:33:15,360 --> 00:33:19,680
Speaker 4: So amazingly, these enormous, enormous structures, you know, hundreds of

639
00:33:19,680 --> 00:33:22,720
Speaker 4: thousands of light years across for a particular galaxy, and

640
00:33:23,080 --> 00:33:25,800
Speaker 4: for clusters of galaxies even millions of light years across.

641
00:33:26,360 --> 00:33:28,680
Speaker 3: You know, these are succeeded.

642
00:33:28,240 --> 00:33:32,520
Speaker 4: By tiny subatomic quantum fluctuations that were stretched by inflation.

643
00:33:32,960 --> 00:33:35,400
Speaker 4: And I think, out of all the problems that inflation

644
00:33:35,440 --> 00:33:37,440
Speaker 4: is supposed to address, I think that's the one that's

645
00:33:37,800 --> 00:33:42,520
Speaker 4: the most impressive, and where cosmologists so really thinking, this

646
00:33:42,600 --> 00:33:46,360
Speaker 4: is the leading candidate to explain the properties of our universe.

647
00:33:46,520 --> 00:33:48,640
Speaker 2: So I think I get bogged down by this idea

648
00:33:48,640 --> 00:33:50,800
Speaker 2: that the Big Bang started at a tiny point. And

649
00:33:50,840 --> 00:33:53,440
Speaker 2: so what I'm imagining is we're looking at before the

650
00:33:53,480 --> 00:33:56,840
Speaker 2: tiny point where it's inflating, and there's areas where you're

651
00:33:56,840 --> 00:33:59,000
Speaker 2: going to get galaxies eventually, but then it all kind

652
00:33:59,080 --> 00:34:01,520
Speaker 2: of such down to a little point and then blows

653
00:34:01,560 --> 00:34:03,960
Speaker 2: back out again. But that is not the right way

654
00:34:03,960 --> 00:34:05,760
Speaker 2: to be thinking about it, right because I don't see

655
00:34:05,760 --> 00:34:08,879
Speaker 2: how stuff that happened before the Big Bang is going

656
00:34:08,880 --> 00:34:11,200
Speaker 2: to result in galaxies after the Big Bang?

657
00:34:12,160 --> 00:34:12,840
Speaker 3: What am I missing?

658
00:34:13,200 --> 00:34:16,760
Speaker 4: I mean, there are ideas that the universe could undergo

659
00:34:16,840 --> 00:34:19,560
Speaker 4: cycles like that, I could expand and contract and expand

660
00:34:19,600 --> 00:34:24,360
Speaker 4: and contract, But that's independent of inflation. So that depends

661
00:34:24,440 --> 00:34:26,480
Speaker 4: on I guess, on the properties of the dark energy

662
00:34:26,520 --> 00:34:30,560
Speaker 4: we see today, if it's a cosmological constant, I if

663
00:34:30,640 --> 00:34:33,040
Speaker 4: the energy of empty space is sort of a constant

664
00:34:33,520 --> 00:34:36,680
Speaker 4: I should say better, what's driving the accelerated expansion is

665
00:34:36,920 --> 00:34:40,240
Speaker 4: that empty space has a constant energy, then the universe

666
00:34:40,280 --> 00:34:45,640
Speaker 4: will not recollapse. However, there have been observations recently suggesting

667
00:34:45,960 --> 00:34:48,680
Speaker 4: that the dark energy is not a cosmological constant, that

668
00:34:48,719 --> 00:34:51,279
Speaker 4: it could be some dynamical field that changes over time,

669
00:34:51,840 --> 00:34:55,080
Speaker 4: and in that case it could recollapse. So that I

670
00:34:55,080 --> 00:34:57,520
Speaker 4: hopefully address as this issue of you know, getting sack

671
00:34:57,600 --> 00:35:00,759
Speaker 4: back down. But to answer your question, how could it

672
00:35:00,840 --> 00:35:05,400
Speaker 4: be that this tiny fluctuating sea of space could have

673
00:35:05,440 --> 00:35:08,080
Speaker 4: anything to do with what we see today where you

674
00:35:08,160 --> 00:35:11,840
Speaker 4: need basically density fluctuations. So if you imagine the universe

675
00:35:11,880 --> 00:35:16,719
Speaker 4: being perfectly smooth, then you wouldn't get the universe we

676
00:35:16,760 --> 00:35:19,000
Speaker 4: see today because some regions are more dense than others.

677
00:35:19,200 --> 00:35:21,920
Speaker 4: So those regions that have galaxies in them are more dense,

678
00:35:22,280 --> 00:35:26,200
Speaker 4: and there are voids in space that are under dense. Also,

679
00:35:26,239 --> 00:35:29,040
Speaker 4: when you look at the cosmic microwave background, this oldest

680
00:35:29,120 --> 00:35:31,920
Speaker 4: light that we can see is very very very very uniform,

681
00:35:32,000 --> 00:35:36,640
Speaker 4: like there's almost no differences across the sky until you

682
00:35:36,680 --> 00:35:38,200
Speaker 4: get to a point of about one part in one

683
00:35:38,280 --> 00:35:41,200
Speaker 4: hundred thousand then you start to see these tiny fluctuations.

684
00:35:41,560 --> 00:35:44,400
Speaker 4: So that's telling you there were definitely density fluctuations in

685
00:35:44,440 --> 00:35:45,360
Speaker 4: the early universe.

686
00:35:46,440 --> 00:35:47,120
Speaker 3: So they have to.

687
00:35:47,040 --> 00:35:51,040
Speaker 4: Come from somewhere, and inflation is a very nice but

688
00:35:51,160 --> 00:35:55,640
Speaker 4: not the only possible mechanism to give you those density fluctuations. Now,

689
00:35:55,719 --> 00:35:58,560
Speaker 4: I said before that the universe could have been infinitely

690
00:35:58,560 --> 00:36:01,040
Speaker 4: big at the Big Bang. What wouldn't have been infinitely

691
00:36:01,080 --> 00:36:02,799
Speaker 4: big is our patch of the universe that would have

692
00:36:02,840 --> 00:36:05,279
Speaker 4: been very very small. So if you're struggling to think, oh,

693
00:36:05,280 --> 00:36:07,160
Speaker 4: I want to think of this very very small universe,

694
00:36:07,480 --> 00:36:09,759
Speaker 4: you can think of the observable universe that we see

695
00:36:09,760 --> 00:36:13,160
Speaker 4: around us. Think of that being very very small. So

696
00:36:13,680 --> 00:36:17,439
Speaker 4: now in this quantum state, there would be fluctuations. That's

697
00:36:17,480 --> 00:36:20,280
Speaker 4: just part of quantum theory. And then they get stretched

698
00:36:20,719 --> 00:36:24,799
Speaker 4: as the universe expands very very rapidly, and they gives

699
00:36:24,840 --> 00:36:27,239
Speaker 4: you some regions that are more dense than others, and

700
00:36:27,280 --> 00:36:30,880
Speaker 4: then gravity sculpts them, putting more matter into the denser

701
00:36:30,920 --> 00:36:33,719
Speaker 4: regions less matter in the under dense regions, and that

702
00:36:33,760 --> 00:36:36,319
Speaker 4: gives you the seeds for galaxies to form.

703
00:36:36,400 --> 00:36:39,080
Speaker 1: Thanks well, and I think there's a possibility there of

704
00:36:39,120 --> 00:36:41,719
Speaker 1: getting confused about the two ideas of the Big Bang. Right,

705
00:36:42,040 --> 00:36:44,400
Speaker 1: what Phils talking about is the hot Big Bang, So

706
00:36:44,520 --> 00:36:47,239
Speaker 1: not that the universe started from a point, just that

707
00:36:47,280 --> 00:36:49,759
Speaker 1: the universe started from a hot dense soup. And he's

708
00:36:49,760 --> 00:36:52,080
Speaker 1: saying that soup is pretty uniform. So how does that

709
00:36:52,160 --> 00:36:55,080
Speaker 1: soup then grow up to give you galaxies? And the

710
00:36:55,120 --> 00:36:58,560
Speaker 1: answer is that soup plus quantum fluctuations. We're not zooming

711
00:36:58,600 --> 00:37:00,800
Speaker 1: all the way back to the singularity with that's singularly

712
00:37:00,840 --> 00:37:01,399
Speaker 1: aside from.

713
00:37:01,320 --> 00:37:05,279
Speaker 4: That, right, But what's interesting is that during inflation, the

714
00:37:05,400 --> 00:37:07,520
Speaker 4: universe is as cold as it can possibly be, and

715
00:37:07,560 --> 00:37:10,480
Speaker 4: it's only when inflation ends that it heats up. So

716
00:37:10,520 --> 00:37:13,320
Speaker 4: then inflation, we can say is a pre Big Bang model,

717
00:37:13,600 --> 00:37:15,759
Speaker 4: because a lot of textbooks tell you that inflation happened

718
00:37:15,800 --> 00:37:18,680
Speaker 4: after the Big Bang. But actually, if we use the

719
00:37:18,719 --> 00:37:21,280
Speaker 4: definition of the Big Bang that everyone, well not everyone,

720
00:37:21,320 --> 00:37:25,759
Speaker 4: but most scientists adopt, then we're going to say it's

721
00:37:25,800 --> 00:37:28,239
Speaker 4: the hot dense state. So inflation happened before that hot

722
00:37:28,320 --> 00:37:31,239
Speaker 4: dense state. It was cold during inflation, as cold as

723
00:37:31,239 --> 00:37:34,160
Speaker 4: it can possibly be, and then when inflation ends, it

724
00:37:34,200 --> 00:37:36,840
Speaker 4: heats up. The universe lots all the energy and the

725
00:37:36,880 --> 00:37:41,240
Speaker 4: inflating space gets converted into matter and radiation, and then

726
00:37:41,719 --> 00:37:44,319
Speaker 4: you have our Big Bang. So our Big Bang is

727
00:37:44,440 --> 00:37:50,320
Speaker 4: like a bubble that appeared from this soup of inflating space.

728
00:37:50,600 --> 00:37:52,520
Speaker 2: Where does the heat come from? How do you go

729
00:37:52,560 --> 00:37:53,319
Speaker 2: from cold to hot?

730
00:37:53,560 --> 00:37:56,839
Speaker 1: And let me clarify because cold means something very specific here.

731
00:37:56,840 --> 00:38:00,160
Speaker 1: It doesn't mean low energy like you might imagine. Is

732
00:38:00,200 --> 00:38:03,279
Speaker 1: Remember that energy can take many forms. It can be

733
00:38:03,280 --> 00:38:06,040
Speaker 1: in the form of motion or mass or heat, but

734
00:38:06,080 --> 00:38:08,719
Speaker 1: there can also be potential energy, like when you put

735
00:38:08,760 --> 00:38:10,800
Speaker 1: a book high on a shelf or a spring that

736
00:38:10,960 --> 00:38:14,960
Speaker 1: squeezed down, and that doesn't make the universe hot. And

737
00:38:15,040 --> 00:38:18,160
Speaker 1: sometimes fields like the Higgs field can get stuck in

738
00:38:18,200 --> 00:38:20,640
Speaker 1: a state with a lot of potential energy, and so

739
00:38:20,920 --> 00:38:23,680
Speaker 1: that energy can fill the universe and the universe still

740
00:38:23,719 --> 00:38:27,440
Speaker 1: be cold. Inflation theory says that the inflation field had

741
00:38:27,480 --> 00:38:30,640
Speaker 1: a lot of this potential energy, which is exactly also

742
00:38:30,680 --> 00:38:34,640
Speaker 1: what you need to make the universe expand. In general, relativity,

743
00:38:35,040 --> 00:38:38,360
Speaker 1: matter and energy density make the universe contract. That's gravity,

744
00:38:38,640 --> 00:38:41,680
Speaker 1: but potential energy like dark energy or the Higgs field

745
00:38:41,800 --> 00:38:45,719
Speaker 1: or the inflant On field makes the universe expand. So

746
00:38:46,160 --> 00:38:48,279
Speaker 1: there's a lot of energy in the universe. But it's

747
00:38:48,320 --> 00:38:51,360
Speaker 1: not heat. It's in the potential energy the inflation field.

748
00:38:51,760 --> 00:38:55,239
Speaker 1: So the universe is nearly empty, nothing is moving very fast,

749
00:38:55,320 --> 00:38:58,880
Speaker 1: but it is expanding. Now when inflation ends, that potential

750
00:38:58,960 --> 00:39:02,960
Speaker 1: energy is converted into normal matter fields and into mass

751
00:39:03,000 --> 00:39:06,279
Speaker 1: and motion. So then the universe is hot. That's reheating.

752
00:39:06,520 --> 00:39:08,920
Speaker 1: It went from cold and full of potential energy to

753
00:39:09,120 --> 00:39:10,680
Speaker 1: hot and full of mass in motion.

754
00:39:11,080 --> 00:39:13,359
Speaker 4: But there's another way you can think of it in

755
00:39:13,719 --> 00:39:16,440
Speaker 4: that is, when particles pop in and out of existence

756
00:39:16,719 --> 00:39:19,360
Speaker 4: from the vacuum, they have to go back into existence

757
00:39:19,520 --> 00:39:23,160
Speaker 4: very very quickly. This is the function of the uncertainty principle.

758
00:39:23,680 --> 00:39:25,680
Speaker 4: And there's an equation which will tell you how long

759
00:39:25,719 --> 00:39:27,839
Speaker 4: they can exist for and someone and so forth. Now

760
00:39:27,840 --> 00:39:31,920
Speaker 4: they pop into resistance in pairs, but in inflation they

761
00:39:31,920 --> 00:39:33,400
Speaker 4: can't get back together again.

762
00:39:33,239 --> 00:39:35,280
Speaker 3: Because the universe is all ripped them apart.

763
00:39:35,760 --> 00:39:38,680
Speaker 4: So you kind of get you can actually expanding space

764
00:39:38,760 --> 00:39:43,279
Speaker 4: can create literally create massuin radiation because it rips these

765
00:39:43,360 --> 00:39:46,000
Speaker 4: virtual particles which would otherwise just appear and disappear out

766
00:39:46,040 --> 00:39:50,120
Speaker 4: of the vacuum and they form into real particles. And

767
00:39:50,160 --> 00:39:52,600
Speaker 4: this is similar to what you see in black holes,

768
00:39:53,040 --> 00:39:57,320
Speaker 4: because in black holes Hawking famously showed that virtual particles

769
00:39:57,400 --> 00:39:59,520
Speaker 4: can get also get ripped apart. Someone go into the

770
00:39:59,520 --> 00:40:01,640
Speaker 4: black hole, some would come out and this would emit

771
00:40:01,719 --> 00:40:06,239
Speaker 4: Radiation's called Hawking radiation. So something similar to that basically, So.

772
00:40:06,280 --> 00:40:09,439
Speaker 1: We have the hot Danse universe a long time ago,

773
00:40:09,520 --> 00:40:12,920
Speaker 1: which were pretty confident about. There's questions and problems and

774
00:40:13,000 --> 00:40:15,560
Speaker 1: theoretical issues. People come up with this idea of inflation.

775
00:40:15,960 --> 00:40:20,000
Speaker 1: The universe before that hot Dnse state expanded super duper rapidly,

776
00:40:20,000 --> 00:40:22,440
Speaker 1: and that solves a lot of those problems. But doesn't

777
00:40:22,440 --> 00:40:24,680
Speaker 1: it also just kick the questions down the road. Like

778
00:40:25,239 --> 00:40:29,319
Speaker 1: you say, if you have this incredible inflation, then it

779
00:40:29,320 --> 00:40:31,560
Speaker 1: solves those problems. But where does that inflation come from?

780
00:40:31,800 --> 00:40:32,799
Speaker 1: What causes that?

781
00:40:33,120 --> 00:40:36,440
Speaker 4: So that's an excellent question and the short answer as

782
00:40:36,480 --> 00:40:39,200
Speaker 4: you don't know. I mean, we're not sure that inflation happened.

783
00:40:39,200 --> 00:40:41,879
Speaker 4: I mean, some people are pretty confident it happened. And

784
00:40:42,080 --> 00:40:45,080
Speaker 4: we did a survey physicist about that and we didn't

785
00:40:45,080 --> 00:40:47,879
Speaker 4: get more than fifty percent saying inflation happened, but they

786
00:40:48,160 --> 00:40:49,680
Speaker 4: I had to be fair. It was a black hole

787
00:40:49,680 --> 00:40:52,440
Speaker 4: conference that we were at. If we did a cosmology conference,

788
00:40:53,520 --> 00:40:54,960
Speaker 4: I guess it would be high. But I think I

789
00:40:55,000 --> 00:40:57,000
Speaker 4: can't remember exactly what we've got about forty percent, but

790
00:40:57,040 --> 00:40:58,560
Speaker 4: it wasn't most popular candidate.

791
00:40:58,960 --> 00:41:00,400
Speaker 3: It didn't get past fifty.

792
00:41:01,480 --> 00:41:05,959
Speaker 4: So now, one idea is that inflation is eternal into

793
00:41:06,000 --> 00:41:08,800
Speaker 4: the past and the future. So let me try and

794
00:41:08,880 --> 00:41:10,680
Speaker 4: unpack what that means. So you might have heard of

795
00:41:10,719 --> 00:41:15,480
Speaker 4: the idea of a multiverse. Surely anyone that's witches on

796
00:41:15,520 --> 00:41:18,759
Speaker 4: the TV these days, we must see some sci fi

797
00:41:18,840 --> 00:41:22,600
Speaker 4: with a multiverse, whether it's Doctor Strange or the Man

798
00:41:22,600 --> 00:41:27,000
Speaker 4: in the High Castle or whatever. You know, it's very

799
00:41:27,000 --> 00:41:30,520
Speaker 4: pervasive now in popular culture, but its origins in the

800
00:41:30,520 --> 00:41:35,439
Speaker 4: cosmological setting is with inflationary cosmology. So remember I said,

801
00:41:35,440 --> 00:41:37,280
Speaker 4: you can think of our universe as like this bubble

802
00:41:37,320 --> 00:41:41,560
Speaker 4: that appears out of inflating sea. But the idea is

803
00:41:41,600 --> 00:41:43,719
Speaker 4: that it wouldn't produce one bubble, it would produce an

804
00:41:43,719 --> 00:41:47,160
Speaker 4: infinite number of bubbles. And the way this works is

805
00:41:47,320 --> 00:41:52,320
Speaker 4: pretty straightforward. Just think of the inflating space as something

806
00:41:52,360 --> 00:41:56,200
Speaker 4: that decays, like a radioactive particle decays, So it decays

807
00:41:56,200 --> 00:41:59,359
Speaker 4: with a half life. So when it decays, that's that.

808
00:41:59,400 --> 00:42:00,600
Speaker 3: Moment what we talked about.

809
00:42:00,600 --> 00:42:04,880
Speaker 4: You know where all the energy gets converted into Madgine radiation. Boom,

810
00:42:04,920 --> 00:42:08,000
Speaker 4: a big bang, the universe is born. But what has

811
00:42:08,040 --> 00:42:11,120
Speaker 4: happened to the bit that hasn't decayed yet? Well, it's

812
00:42:11,239 --> 00:42:15,160
Speaker 4: undergoing exponential expansion. So as long as that exponential expansion

813
00:42:15,200 --> 00:42:18,600
Speaker 4: is faster than the exponential deka, then the amount of

814
00:42:18,600 --> 00:42:20,200
Speaker 4: inflating space can never go down.

815
00:42:20,280 --> 00:42:21,239
Speaker 3: It can only go up.

816
00:42:21,800 --> 00:42:24,879
Speaker 4: So the analogy I always give is my mum makes

817
00:42:24,880 --> 00:42:29,000
Speaker 4: this fantastic chocolate cake is really yummy, and I go

818
00:42:29,080 --> 00:42:32,200
Speaker 4: around there for Sunday afternoon tea. She prints the chocolate

819
00:42:32,200 --> 00:42:35,080
Speaker 4: cake down on the table and we eat half the cake.

820
00:42:36,480 --> 00:42:38,920
Speaker 4: Then at some point we go back for seconds, and

821
00:42:38,960 --> 00:42:41,080
Speaker 4: now the cake is gone. You can't have your cake

822
00:42:41,080 --> 00:42:44,600
Speaker 4: and eat it right. However, what would happen if when

823
00:42:44,600 --> 00:42:47,719
Speaker 4: we went back for that second piece the cake had

824
00:42:47,760 --> 00:42:52,560
Speaker 4: expanded exponentially? Now we could have more cake. We have

825
00:42:52,600 --> 00:42:54,239
Speaker 4: the same volume of cake that we had in the

826
00:42:54,239 --> 00:42:57,560
Speaker 4: first bite, you know, but the cakes expanded. Then we

827
00:42:57,719 --> 00:42:59,600
Speaker 4: go back for thirds. Well, the same thing's happened. The

828
00:42:59,640 --> 00:43:02,120
Speaker 4: carown faster than we could have eaten it, in which

829
00:43:02,160 --> 00:43:04,200
Speaker 4: case you rut, the cake can never ever go down,

830
00:43:04,960 --> 00:43:07,520
Speaker 4: so you get infinite number of pieces of cake and

831
00:43:07,560 --> 00:43:09,040
Speaker 4: you can have your cake and eat it.

832
00:43:09,280 --> 00:43:11,440
Speaker 1: I think you also get infinite fill in that scenario,

833
00:43:11,480 --> 00:43:11,959
Speaker 1: don't you.

834
00:43:12,080 --> 00:43:16,080
Speaker 4: Yeah, yeah, you have to have a very big belly.

835
00:43:16,360 --> 00:43:20,440
Speaker 1: All right. So I'm imagining space filled with this inflationary

836
00:43:20,480 --> 00:43:23,480
Speaker 1: material we don't understand or don't know it's original, and

837
00:43:23,840 --> 00:43:27,040
Speaker 1: random little bits of it are decaying into our normal

838
00:43:27,160 --> 00:43:29,560
Speaker 1: universe kind of stuff. So we get these bubbles of

839
00:43:29,719 --> 00:43:33,000
Speaker 1: normal universes that appear to train in places, but they're

840
00:43:33,000 --> 00:43:35,160
Speaker 1: separated by this rapidly inflating space.

841
00:43:35,320 --> 00:43:38,759
Speaker 4: Yes, that's exactly right, yep, yep. So then you get

842
00:43:38,760 --> 00:43:43,200
Speaker 4: this multiverse and it's eternal. Now, when I say it's eternal,

843
00:43:43,719 --> 00:43:46,879
Speaker 4: there's a bit of a subtlety there. It's eternal into

844
00:43:46,880 --> 00:43:51,520
Speaker 4: the future, but is it eternal into the past? Now

845
00:43:51,600 --> 00:43:54,640
Speaker 4: there is a theorem called the Bordais Gooth and Velenkad

846
00:43:54,680 --> 00:43:56,560
Speaker 4: theorem of that is, it can only be eternal into

847
00:43:56,640 --> 00:43:59,280
Speaker 4: the future, but it is not eternal into the past.

848
00:44:00,000 --> 00:44:01,880
Speaker 4: Still have to ask what came before inflation or what

849
00:44:01,960 --> 00:44:05,160
Speaker 4: might cause inflation. However, there have been people that have

850
00:44:05,200 --> 00:44:07,720
Speaker 4: disputed this theorem and said, no, it could be eternal

851
00:44:07,760 --> 00:44:09,520
Speaker 4: into the past. So if you want to know what

852
00:44:09,560 --> 00:44:12,920
Speaker 4: came before inflation. In that scenario, it's just more inflation,

853
00:44:13,000 --> 00:44:16,800
Speaker 4: and it just goes back forever and ever for eternity. However,

854
00:44:16,920 --> 00:44:20,239
Speaker 4: if we take the body Goose for Lincoln theorem, then

855
00:44:20,320 --> 00:44:23,480
Speaker 4: we have to ask, okay, what came before inflation? And

856
00:44:23,560 --> 00:44:27,000
Speaker 4: there are a number of suggestions. And I should also

857
00:44:27,040 --> 00:44:30,480
Speaker 4: add that there are people that don't like inflation. So

858
00:44:30,760 --> 00:44:33,319
Speaker 4: one idea as well, inflation didn't happen at all, and

859
00:44:33,320 --> 00:44:36,440
Speaker 4: there's some other thing that happened, but let's stick with

860
00:44:36,520 --> 00:44:40,879
Speaker 4: the inflation. Since you asked, so, I would say there's

861
00:44:40,880 --> 00:44:44,200
Speaker 4: a few ideas out there. The first one that probably

862
00:44:44,200 --> 00:44:47,319
Speaker 4: came on the scene was nineteen eighty two, and this

863
00:44:47,520 --> 00:44:50,840
Speaker 4: was proposed by Alex for Lincoln. It's called the tunneling

864
00:44:50,920 --> 00:44:54,440
Speaker 4: from Nothing idea. So the idea is that what if

865
00:44:54,480 --> 00:45:00,200
Speaker 4: we treat space quantum mechanically. So normally, when they do

866
00:45:00,239 --> 00:45:05,520
Speaker 4: this cosmological modeling, you're using Einstein's theory of gravity, so

867
00:45:05,560 --> 00:45:09,120
Speaker 4: you're assuming space time is classical. But if you'd seen

868
00:45:09,120 --> 00:45:11,319
Speaker 4: in space time as quantum mechanical as the linking did,

869
00:45:11,840 --> 00:45:16,120
Speaker 4: then the suggestion is that space itself could fluctuate into

870
00:45:16,160 --> 00:45:19,640
Speaker 4: existence from a state where there was no space, so

871
00:45:19,719 --> 00:45:22,359
Speaker 4: that's really hard to get your head round that. This

872
00:45:22,400 --> 00:45:24,960
Speaker 4: is why the tunneling from nothing idea. The idea is

873
00:45:25,400 --> 00:45:27,600
Speaker 4: what controls the expansion of the universe, so it's partly

874
00:45:27,600 --> 00:45:29,719
Speaker 4: it's radius. So if you have a small universe, so

875
00:45:29,760 --> 00:45:32,400
Speaker 4: we'd actually just clapse back in on itself. So how

876
00:45:32,400 --> 00:45:34,640
Speaker 4: would you go from a small universe to a universe

877
00:45:34,640 --> 00:45:38,719
Speaker 4: big enough to inflate? At least and classically it seems

878
00:45:38,719 --> 00:45:43,320
Speaker 4: to be impossible. However, quantum mechanically it can what's called tunnel.

879
00:45:43,800 --> 00:45:46,120
Speaker 4: It can tunnel from one set to another, so the

880
00:45:46,160 --> 00:45:48,640
Speaker 4: small one could tunnel to the larger one. And then

881
00:45:48,760 --> 00:45:51,719
Speaker 4: what he asked was, well, what's the smallest size that

882
00:45:51,760 --> 00:45:54,600
Speaker 4: the universe could tunnel from? And he concluded it was zero.

883
00:45:55,560 --> 00:45:58,080
Speaker 4: So that's pretty hard to get your head round. So

884
00:45:58,160 --> 00:46:01,759
Speaker 4: that's the tunneling idea. It tunneling from nothing idea. Then

885
00:46:01,800 --> 00:46:03,880
Speaker 4: you have to sink with a hard tour hawking no

886
00:46:04,000 --> 00:46:04,759
Speaker 4: boundary state.

887
00:46:05,080 --> 00:46:07,319
Speaker 1: Hold on, let's dig into the linking idea a little

888
00:46:07,320 --> 00:46:09,880
Speaker 1: bit more. Yeah, because this is still pre inflation. This

889
00:46:09,920 --> 00:46:12,400
Speaker 1: is not an alternative inflation. This thing where does the

890
00:46:12,440 --> 00:46:15,560
Speaker 1: inflation areyas come from? And you're saying that we're adding

891
00:46:15,600 --> 00:46:18,160
Speaker 1: quantum mechanics to it, so it's not full quantum gravity.

892
00:46:18,160 --> 00:46:20,520
Speaker 1: It's certain sort of like semi classical.

893
00:46:20,960 --> 00:46:23,360
Speaker 4: No, no, this is yeah, we'd call it some classic.

894
00:46:23,440 --> 00:46:25,279
Speaker 4: It's not full quantum gravity. And we should come to

895
00:46:25,560 --> 00:46:27,360
Speaker 4: full quantum gravity and in a moment.

896
00:46:27,800 --> 00:46:31,480
Speaker 1: And so this is speculating that the inflationary conditions before

897
00:46:31,520 --> 00:46:36,160
Speaker 1: the hot Big Bang fluctuated into existence. From and I'm

898
00:46:36,160 --> 00:46:37,680
Speaker 1: just going to kick the can down the road further

899
00:46:37,680 --> 00:46:40,439
Speaker 1: here from and you said something that has no space time.

900
00:46:40,520 --> 00:46:43,359
Speaker 1: So it's a universe but without space time, or it's

901
00:46:43,800 --> 00:46:45,400
Speaker 1: nothing meaning not a universe.

902
00:46:45,520 --> 00:46:46,160
Speaker 3: What's the difference?

903
00:46:46,800 --> 00:46:48,560
Speaker 1: Yeah, well that was gonna be my next question. That

904
00:46:48,640 --> 00:46:51,080
Speaker 1: was a trap you avoided it.

905
00:46:52,239 --> 00:46:55,120
Speaker 4: There's no space there at all. I mean, there's nothing

906
00:46:55,400 --> 00:46:58,759
Speaker 4: so physical there. That's at least one conception of it.

907
00:46:58,800 --> 00:47:01,440
Speaker 1: But how can you have the laws of the universe

908
00:47:01,760 --> 00:47:04,040
Speaker 1: and follow those laws if there is no universe? So

909
00:47:04,080 --> 00:47:06,560
Speaker 1: there is a universe but without space time, Well.

910
00:47:06,360 --> 00:47:10,160
Speaker 3: That depends on your view of laws. What are laws

911
00:47:10,160 --> 00:47:10,800
Speaker 3: of physics?

912
00:47:11,200 --> 00:47:14,239
Speaker 4: Now some people would say they're just descriptions, so they

913
00:47:14,280 --> 00:47:17,839
Speaker 4: can't cause the universe. Another view might view, we don't

914
00:47:17,840 --> 00:47:20,560
Speaker 4: need a cause because there's no time and time you

915
00:47:20,640 --> 00:47:21,919
Speaker 4: need time for causality.

916
00:47:22,200 --> 00:47:24,480
Speaker 3: If there's no time, don't worry about what the cause was.

917
00:47:25,360 --> 00:47:27,320
Speaker 3: You're asking the question what caused?

918
00:47:27,440 --> 00:47:29,879
Speaker 1: But if there's no time, it is.

919
00:47:29,800 --> 00:47:33,360
Speaker 4: A question that is asked in a condition. The condition

920
00:47:33,440 --> 00:47:36,399
Speaker 4: is time exists. But if the time doesn't exist, then

921
00:47:36,480 --> 00:47:38,239
Speaker 4: don't worry about causality.

922
00:47:38,400 --> 00:47:41,040
Speaker 1: Yeah, but if you have that, but how can you

923
00:47:41,160 --> 00:47:44,640
Speaker 1: speculate about a transition and evolution of the universe from

924
00:47:44,640 --> 00:47:47,040
Speaker 1: this to that? If there's no time in the universe? Right,

925
00:47:47,080 --> 00:47:49,279
Speaker 1: how does that? How do I wrap my mind around this?

926
00:47:49,680 --> 00:47:53,520
Speaker 4: Well, it is hard to head round. You know, we're

927
00:47:53,560 --> 00:47:56,840
Speaker 4: answering in analogies. But you know, I saw a mathematical description.

928
00:47:57,440 --> 00:48:01,279
Speaker 4: So the question is, you know, you compute what would

929
00:48:01,320 --> 00:48:03,960
Speaker 4: happen if the universe of zero size? And then what

930
00:48:04,040 --> 00:48:06,120
Speaker 4: is there a tunneling aptitude for one? Yeah, people have

931
00:48:06,160 --> 00:48:08,279
Speaker 4: challenged this. I mean, I don't want to claim it's

932
00:48:08,320 --> 00:48:11,280
Speaker 4: always worked out and everyone understands it and it's all agreedable.

933
00:48:11,600 --> 00:48:14,600
Speaker 4: This is one of like twenty something ideas that we

934
00:48:15,000 --> 00:48:17,400
Speaker 4: talk about in the book, and this is a problem

935
00:48:17,440 --> 00:48:20,040
Speaker 4: with it. So I don't you know, some people have said, well,

936
00:48:20,080 --> 00:48:23,759
Speaker 4: you're always tunneling from one quantum state to another, so

937
00:48:23,920 --> 00:48:28,040
Speaker 4: maybe we shouldn't consider this this model. However, one idea

938
00:48:28,640 --> 00:48:32,040
Speaker 4: that Valncan suggests is that actually laws are more than

939
00:48:32,120 --> 00:48:35,840
Speaker 4: just descriptions that they actually are. They exist in a

940
00:48:35,880 --> 00:48:38,600
Speaker 4: sort of platonic sense in a sense. And this has

941
00:48:38,680 --> 00:48:42,120
Speaker 4: some advantages to it because you know, you can ask

942
00:48:42,200 --> 00:48:44,600
Speaker 4: why is it that objects obey the laws of physics?

943
00:48:44,680 --> 00:48:46,600
Speaker 4: You know, if you have an electron, let's say it

944
00:48:46,600 --> 00:48:49,920
Speaker 4: gets excited, it shoots out a photon. How does it

945
00:48:50,000 --> 00:48:53,440
Speaker 4: know to shoot out a photon? You know, it's all

946
00:48:53,480 --> 00:48:56,240
Speaker 4: that information written inside the electronic That seems hard to believe.

947
00:48:56,719 --> 00:48:59,799
Speaker 4: So the idea is that laws are actually sort of

948
00:49:00,680 --> 00:49:02,759
Speaker 4: photonic objects in some sos it's pretty weird.

949
00:49:03,320 --> 00:49:05,400
Speaker 1: And when you say platonic objects, for those of us

950
00:49:05,440 --> 00:49:07,920
Speaker 1: who are not reading philosophy papers all the time, you

951
00:49:08,000 --> 00:49:10,839
Speaker 1: mean that they exist outside of our ability to observe them.

952
00:49:11,040 --> 00:49:14,400
Speaker 4: Yeah, I think that's a fair fair description. Yeah, they

953
00:49:14,440 --> 00:49:17,200
Speaker 4: don't sit on something else. You know, if you think

954
00:49:17,280 --> 00:49:21,239
Speaker 4: of a table, all right, it's made of particles, and

955
00:49:21,280 --> 00:49:23,560
Speaker 4: you might even say they're made out of quantum fields

956
00:49:23,640 --> 00:49:27,359
Speaker 4: or you know, so the laws themselves have their own

957
00:49:27,640 --> 00:49:29,080
Speaker 4: sort of physical existence.

958
00:49:29,640 --> 00:49:30,360
Speaker 3: Well, I don't know.

959
00:49:30,400 --> 00:49:35,480
Speaker 4: Physical isn't the right word independent existence, So that may

960
00:49:35,520 --> 00:49:39,239
Speaker 4: be required by a the Lincoln's model, And if you

961
00:49:39,239 --> 00:49:42,200
Speaker 4: don't like that idea, then maybe you don't want to

962
00:49:42,320 --> 00:49:46,719
Speaker 4: entertain the Lincoln's model. But I do think that it's

963
00:49:46,800 --> 00:49:49,279
Speaker 4: uncertain what the status of laws is. So those that

964
00:49:49,400 --> 00:49:52,200
Speaker 4: say that cannot be right because laws are just descriptions.

965
00:49:53,440 --> 00:49:55,879
Speaker 4: I challenged that and say, are you sure that they're

966
00:49:55,920 --> 00:49:59,320
Speaker 4: just descriptions? You know, how do you solve problem of induction?

967
00:50:00,000 --> 00:50:02,440
Speaker 4: You know, we ask how do we know that there

968
00:50:02,440 --> 00:50:05,440
Speaker 4: are these regularities? Why do why don't we think the

969
00:50:05,440 --> 00:50:08,840
Speaker 4: sun might stop rising tomorrow? You know, if you just

970
00:50:08,840 --> 00:50:13,360
Speaker 4: think their descriptions, it's hard to solve this problem of induction.

971
00:50:13,480 --> 00:50:16,279
Speaker 4: But one possible solution is, no, the laws are more

972
00:50:16,480 --> 00:50:19,399
Speaker 4: than that. They're sort of ironclad objects that the other

973
00:50:19,440 --> 00:50:23,080
Speaker 4: particles have to sort of obey, And then you can

974
00:50:23,120 --> 00:50:26,440
Speaker 4: see why induction makes sense. So there's a lot of

975
00:50:26,440 --> 00:50:28,920
Speaker 4: debate in the philosophical literature about the nature of laws,

976
00:50:29,200 --> 00:50:31,240
Speaker 4: and I think as long as that is not settled,

977
00:50:31,520 --> 00:50:33,160
Speaker 4: and I think it's right to say it isn't settled,

978
00:50:33,440 --> 00:50:36,200
Speaker 4: then you can entertain this view, but you know, let's

979
00:50:36,200 --> 00:50:40,040
Speaker 4: be honest, it's pretty wacky and out there. So people

980
00:50:40,040 --> 00:50:41,799
Speaker 4: have come up with other views and maybe, you know,

981
00:50:41,800 --> 00:50:42,960
Speaker 4: we can get onto those if you want.

982
00:50:43,160 --> 00:50:44,640
Speaker 1: I do want to get onto those, and I'm meant

983
00:50:44,680 --> 00:50:46,800
Speaker 1: to ask you where the philosophical implications later, But I

984
00:50:46,840 --> 00:50:50,600
Speaker 1: can't not follow up on that fascinating conversation, you know,

985
00:50:50,719 --> 00:50:53,359
Speaker 1: because it makes me wonder about the future of this

986
00:50:53,480 --> 00:50:56,160
Speaker 1: line of inquiry, Like if we discover the heart big being,

987
00:50:56,239 --> 00:50:58,719
Speaker 1: and then we find proof of inflation, then we find

988
00:50:58,760 --> 00:51:01,480
Speaker 1: proof of what became before that? Is this an infinite

989
00:51:01,520 --> 00:51:03,640
Speaker 1: line of study where we're always going to be asking

990
00:51:03,719 --> 00:51:06,319
Speaker 1: what came before that? Or do you think there's some

991
00:51:06,400 --> 00:51:08,399
Speaker 1: point at which we find something where like, ah, this

992
00:51:08,680 --> 00:51:12,879
Speaker 1: caused itself, or this is obviously something which is fundamental.

993
00:51:13,080 --> 00:51:15,759
Speaker 1: And isn't that just some philosophical sleight of hand where

994
00:51:15,760 --> 00:51:18,279
Speaker 1: we're like, this requires a cause and now we found

995
00:51:18,280 --> 00:51:20,759
Speaker 1: something which we define to not require a cause and

996
00:51:20,800 --> 00:51:23,160
Speaker 1: therefore we don't have to ask questions anymore. I mean,

997
00:51:23,400 --> 00:51:25,640
Speaker 1: why isn't this going to be an infinite line of

998
00:51:25,680 --> 00:51:27,560
Speaker 1: inquiry or do you think it will be what.

999
00:51:27,640 --> 00:51:28,319
Speaker 3: It could be?

1000
00:51:28,480 --> 00:51:31,359
Speaker 4: But there are sort of ideas out there that might

1001
00:51:31,480 --> 00:51:34,640
Speaker 4: stop that infinite regress, shall we say, I mean the

1002
00:51:34,719 --> 00:51:37,719
Speaker 4: Lincoln thinks that he stops the infinite regress because you know,

1003
00:51:38,120 --> 00:51:41,520
Speaker 4: we've got this solution, if you like. The universe doesn't

1004
00:51:41,520 --> 00:51:44,319
Speaker 4: need a cause because it's quantum mechanical and causes our

1005
00:51:45,000 --> 00:51:48,600
Speaker 4: emergent properties. They exist for the microscopic world, but not

1006
00:51:48,640 --> 00:51:50,959
Speaker 4: for the quantum world. So we don't need to ask

1007
00:51:51,000 --> 00:51:53,279
Speaker 4: what the cause for the universe is. It's a meaningless

1008
00:51:53,719 --> 00:51:56,640
Speaker 4: question maybe, or maybe not meaningless, but it's just you know,

1009
00:51:56,680 --> 00:51:59,319
Speaker 4: you don't need to demand. You can't demand there must

1010
00:51:59,320 --> 00:52:01,280
Speaker 4: be a cause when you get into the quantum realm.

1011
00:52:01,560 --> 00:52:05,120
Speaker 4: So that's one approach. Another approaches that maybe the universalist

1012
00:52:05,120 --> 00:52:08,160
Speaker 4: existed eternally into the past, so you can always just

1013
00:52:08,239 --> 00:52:11,560
Speaker 4: go back one step further and further and there's no end.

1014
00:52:12,040 --> 00:52:14,960
Speaker 4: It just goes on forever into the past. That's certainly

1015
00:52:15,040 --> 00:52:15,560
Speaker 4: an idea.

1016
00:52:15,960 --> 00:52:17,640
Speaker 1: Infinite grants for cosmology.

1017
00:52:17,719 --> 00:52:22,080
Speaker 4: Yeah maybe, yeah, so it may just go on forever.

1018
00:52:22,160 --> 00:52:25,960
Speaker 4: But that's certainly a logical possibility, and it's certainly something

1019
00:52:26,000 --> 00:52:30,719
Speaker 4: that I think many physicists entertain. Certainly that's one of

1020
00:52:30,719 --> 00:52:33,560
Speaker 4: the battles. Actually the Battle of the Big Bang is

1021
00:52:34,120 --> 00:52:35,839
Speaker 4: was there a beginning even if it wasn't the Big Bang,

1022
00:52:35,880 --> 00:52:38,440
Speaker 4: maybe there was some other beginning, and some physicists think

1023
00:52:38,520 --> 00:52:41,680
Speaker 4: there was, and some physicis think there wasn't. Another idea

1024
00:52:42,080 --> 00:52:44,359
Speaker 4: is that there could be what's called a closed time

1025
00:52:44,480 --> 00:52:48,319
Speaker 4: like curve. So if you've seen the movie Groundhog Day,

1026
00:52:48,920 --> 00:52:53,920
Speaker 4: think of that. So you wake up, you know, and

1027
00:52:54,040 --> 00:52:57,640
Speaker 4: you're just experiencing yesterday all over again. So now there

1028
00:52:57,680 --> 00:53:03,120
Speaker 4: are solutions in ice Sei's Theoria relativity, which describes you know,

1029
00:53:03,200 --> 00:53:06,719
Speaker 4: gravity as a curvature of space time, and there are

1030
00:53:06,719 --> 00:53:09,279
Speaker 4: solutions to say it gets so curve, it curves back

1031
00:53:09,280 --> 00:53:12,719
Speaker 4: on itself and it forms a loop. So there are

1032
00:53:12,840 --> 00:53:15,520
Speaker 4: a couple of models that sort of take advantage of

1033
00:53:15,560 --> 00:53:19,840
Speaker 4: this and say the universe would cause itself because it

1034
00:53:19,960 --> 00:53:22,160
Speaker 4: curves back in a loop. And so there is no

1035
00:53:22,280 --> 00:53:25,200
Speaker 4: origin point of a circle. Even though the circle is

1036
00:53:25,200 --> 00:53:28,640
Speaker 4: not infinitely long, it doesn't have a starting point, so

1037
00:53:28,719 --> 00:53:31,240
Speaker 4: you can't ask what happened at the start.

1038
00:53:31,280 --> 00:53:33,919
Speaker 3: There is no start. It just goes around in a loop.

1039
00:53:34,600 --> 00:53:37,040
Speaker 4: So in the book Battle the Big Bang, we talk

1040
00:53:37,040 --> 00:53:40,239
Speaker 4: about two different models that exploit this. So there are

1041
00:53:40,239 --> 00:53:42,640
Speaker 4: some of the different ideas. One, maybe there was a

1042
00:53:42,680 --> 00:53:46,440
Speaker 4: beginning and you describe the universe maybe without the language

1043
00:53:46,480 --> 00:53:49,160
Speaker 4: of causality. Or maybe there was no beginning and it's

1044
00:53:49,200 --> 00:53:52,960
Speaker 4: infinitely far into the past. Or maybe there's a sort

1045
00:53:53,000 --> 00:53:57,359
Speaker 4: of loop in time, so there's no starting point, even

1046
00:53:57,360 --> 00:54:00,880
Speaker 4: though maybe it's not sort of eternal in some sense.

1047
00:54:01,400 --> 00:54:03,600
Speaker 1: All right, so let's take another break, and when we

1048
00:54:03,640 --> 00:54:06,279
Speaker 1: come back, we're explore some of these other ideas, some

1049
00:54:06,360 --> 00:54:29,560
Speaker 1: proposing the universe has no first moment. Okay, we're talking

1050
00:54:29,560 --> 00:54:32,279
Speaker 1: to Phil about the origins of the universe, what we know,

1051
00:54:32,360 --> 00:54:34,640
Speaker 1: what we might know, and what we can only speculate

1052
00:54:34,680 --> 00:54:39,800
Speaker 1: while smoking banana peels. You referenced earlier, this fascinating idea,

1053
00:54:39,800 --> 00:54:44,040
Speaker 1: the no boundary proposal, this alternative to like a singularity

1054
00:54:44,160 --> 00:54:46,719
Speaker 1: or a first moment. Tell us about this idea. How

1055
00:54:46,719 --> 00:54:48,799
Speaker 1: does it come about and how does it help us

1056
00:54:48,840 --> 00:54:51,000
Speaker 1: avoid a first moment in time?

1057
00:54:51,280 --> 00:54:54,960
Speaker 4: Well, it's not clear whether it does avoid the first

1058
00:54:55,400 --> 00:54:58,000
Speaker 4: If I was going to suggest models that avoid the

1059
00:54:58,040 --> 00:54:59,480
Speaker 4: first moment and so on, I might probably go to

1060
00:54:59,520 --> 00:55:03,440
Speaker 4: a another model, like a bouncing model, which was or

1061
00:55:03,800 --> 00:55:06,759
Speaker 4: you know, some other maybe some cyclic models. Now I

1062
00:55:06,760 --> 00:55:10,200
Speaker 4: think I'm more unambiguously don't have a beginning that the

1063
00:55:10,400 --> 00:55:11,640
Speaker 4: no boundary proposal.

1064
00:55:11,920 --> 00:55:13,680
Speaker 3: I work with.

1065
00:55:13,600 --> 00:55:15,839
Speaker 4: Stephen Hawking and Jim Hartl and Thomas hog to make

1066
00:55:15,880 --> 00:55:19,040
Speaker 4: a film to explain it to the public, and I

1067
00:55:19,040 --> 00:55:21,279
Speaker 4: did get the impression they didn't quite agree on how

1068
00:55:21,320 --> 00:55:26,680
Speaker 4: to interpret it. I think, I think Corking sawy it

1069
00:55:26,880 --> 00:55:30,960
Speaker 4: is like something closer to what for Lincoln proposed, like

1070
00:55:31,040 --> 00:55:34,359
Speaker 4: a universe for nothing. Whereas Jim hart Or I asked

1071
00:55:34,440 --> 00:55:36,840
Speaker 4: him he could just realize the idea of the universe

1072
00:55:36,840 --> 00:55:39,440
Speaker 4: fy nothing, and he's like, what do you mean by nothing?

1073
00:55:39,560 --> 00:55:41,320
Speaker 4: Quantum mechanics is always something.

1074
00:55:41,760 --> 00:55:44,520
Speaker 1: I know that hacking special sauce is getting gravity and

1075
00:55:44,640 --> 00:55:47,440
Speaker 1: quantum mechanics to play together, even without a full theory

1076
00:55:47,440 --> 00:55:49,960
Speaker 1: of quantum gravity. He did for black holes, and that's

1077
00:55:50,000 --> 00:55:52,480
Speaker 1: how we came up with his prediction for Hockeing radiation.

1078
00:55:52,760 --> 00:55:54,200
Speaker 4: So he started to think, well, what if we do

1079
00:55:54,239 --> 00:55:57,520
Speaker 4: the same for the Big Bang? Because the singularity theorem

1080
00:55:57,680 --> 00:56:01,279
Speaker 4: that he approved with Penrose was just classical. It didn't

1081
00:56:01,280 --> 00:56:03,799
Speaker 4: include quantum mechanics. So he said, loris, let's try and

1082
00:56:03,960 --> 00:56:08,800
Speaker 4: include quantum mechanics. And when it did that, he found

1083
00:56:09,080 --> 00:56:12,600
Speaker 4: that it's cut a long story short, the description that

1084
00:56:12,640 --> 00:56:16,080
Speaker 4: we have with space having three dimensions and time having

1085
00:56:16,120 --> 00:56:21,440
Speaker 4: one dimension changes such that the time dimension turns into

1086
00:56:21,480 --> 00:56:22,320
Speaker 4: a space dimension.

1087
00:56:22,640 --> 00:56:26,040
Speaker 3: So now you have four space dimensions and no time dimension.

1088
00:56:26,239 --> 00:56:29,800
Speaker 1: Okay, that's really weird. Let's unpack it. So Hawking is

1089
00:56:29,840 --> 00:56:33,399
Speaker 1: saying that the universe used to have four spatial dimensions

1090
00:56:33,520 --> 00:56:37,000
Speaker 1: and one of them became a time dimension. So we

1091
00:56:37,120 --> 00:56:40,320
Speaker 1: had four spatial dimensions, and then we had three spatial

1092
00:56:40,320 --> 00:56:43,520
Speaker 1: dimensions and one time dimension, which we're familiar with. Now

1093
00:56:43,920 --> 00:56:46,880
Speaker 1: that's really confusing, So let's try to think of an analogy.

1094
00:56:46,920 --> 00:56:49,759
Speaker 1: And hawking student's analogy is like, if you're standing at

1095
00:56:49,760 --> 00:56:53,120
Speaker 1: the north pole. It's not only that there's no more northiness,

1096
00:56:53,200 --> 00:56:56,440
Speaker 1: there's also no sense of east or west. East and

1097
00:56:56,480 --> 00:56:59,000
Speaker 1: west have no meaning of the north pole. But as

1098
00:56:59,040 --> 00:57:02,200
Speaker 1: you move away from the north pole, you don't change

1099
00:57:02,200 --> 00:57:04,640
Speaker 1: the number of dimensions on the surface of a sphere.

1100
00:57:04,800 --> 00:57:07,120
Speaker 1: But now the concept of east and west makes sense.

1101
00:57:07,480 --> 00:57:10,480
Speaker 1: It's a direction that emerges smoothly. As you move away

1102
00:57:10,560 --> 00:57:13,400
Speaker 1: from the north pole. One of the directions on the

1103
00:57:13,440 --> 00:57:17,360
Speaker 1: sphere becomes east west. Like the idea here is that

1104
00:57:17,400 --> 00:57:21,120
Speaker 1: the universe has one end where all the directions are spacelike,

1105
00:57:21,440 --> 00:57:24,480
Speaker 1: and as you move away from that end, one dimension

1106
00:57:24,600 --> 00:57:28,040
Speaker 1: changes to have new time like properties. It's pretty hard

1107
00:57:28,040 --> 00:57:29,720
Speaker 1: to wrap your mind around, honestly.

1108
00:57:29,840 --> 00:57:30,479
Speaker 3: What this does.

1109
00:57:30,640 --> 00:57:34,680
Speaker 4: It actually smooths out the singularity. You don't get this infinite,

1110
00:57:34,720 --> 00:57:38,240
Speaker 4: dense state. You get a smooth state. And think of

1111
00:57:38,320 --> 00:57:41,400
Speaker 4: it unlike the point of a cone. Think of it

1112
00:57:41,440 --> 00:57:45,400
Speaker 4: more like a shuttlecock, like a smooth surface. Now this

1113
00:57:45,760 --> 00:57:48,920
Speaker 4: is bound it. It's just not infinite, but it doesn't

1114
00:57:48,960 --> 00:57:51,920
Speaker 4: have a starting. There's no point on the surface. This

1115
00:57:52,040 --> 00:57:55,720
Speaker 4: is many better than any other point. So you could

1116
00:57:55,800 --> 00:57:57,880
Speaker 4: say it doesn't have a beginning, but you might say, what,

1117
00:57:58,000 --> 00:58:01,040
Speaker 4: it's not infinite to the past either, And then there's

1118
00:58:01,080 --> 00:58:03,240
Speaker 4: some more complications to it, which we go into in

1119
00:58:03,240 --> 00:58:05,640
Speaker 4: the book. But bottom line is whether it has a

1120
00:58:05,640 --> 00:58:09,800
Speaker 4: beginning or not is sort of slightly ambiguous, and it

1121
00:58:09,840 --> 00:58:12,480
Speaker 4: depends on how you interpret the model. But there are

1122
00:58:12,520 --> 00:58:16,160
Speaker 4: other models that I think are They have less ambiguity

1123
00:58:16,240 --> 00:58:18,800
Speaker 4: and clearly don't have a beginning in them. So the

1124
00:58:18,800 --> 00:58:21,520
Speaker 4: most obvious one, I would say, is one with where

1125
00:58:21,520 --> 00:58:25,240
Speaker 4: you replace the singularity with a bounce. So here the

1126
00:58:25,280 --> 00:58:28,640
Speaker 4: idea is that there's so remember we said with the singularity,

1127
00:58:29,160 --> 00:58:33,720
Speaker 4: the universe goes to infinite density. Now, the idea in

1128
00:58:33,840 --> 00:58:37,440
Speaker 4: some theories of quantum gravity, the suggestions being that you

1129
00:58:37,480 --> 00:58:42,360
Speaker 4: will actually get a maximum density. So think of a sponge.

1130
00:58:42,760 --> 00:58:45,640
Speaker 4: You pour water on a sponge and it absorbs the water,

1131
00:58:46,360 --> 00:58:49,840
Speaker 4: but there comes a point where it won't absorb the

1132
00:58:49,880 --> 00:58:53,360
Speaker 4: water anymore. It will switch its properties from being water

1133
00:58:53,400 --> 00:58:57,840
Speaker 4: absorbent to water repellent. So space might be like that,

1134
00:58:57,960 --> 00:59:00,000
Speaker 4: and in certain theories of quantum gravity that's what happen.

1135
00:59:00,760 --> 00:59:03,160
Speaker 4: Spaces are like a limit. So when you try and

1136
00:59:03,200 --> 00:59:06,040
Speaker 4: squeeze more and more energy into space, it gets to

1137
00:59:06,080 --> 00:59:08,240
Speaker 4: a point where it gets fill up, and then if

1138
00:59:08,280 --> 00:59:10,040
Speaker 4: you try and squeeze more in, it will bounce back out.

1139
00:59:10,040 --> 00:59:10,880
Speaker 3: It becomes repellent.

1140
00:59:11,800 --> 00:59:15,360
Speaker 4: So gravity switches from becoming attractive force to a repulsive force,

1141
00:59:15,640 --> 00:59:18,080
Speaker 4: and that triggers a bounce. So then if we could

1142
00:59:18,080 --> 00:59:21,480
Speaker 4: go back in time, what we would see is, well,

1143
00:59:21,480 --> 00:59:24,040
Speaker 4: if we started today fourteen billionaires, it is a big bang.

1144
00:59:24,120 --> 00:59:26,320
Speaker 4: Roughly you go back in time is getting denser and

1145
00:59:26,360 --> 00:59:28,760
Speaker 4: dancer and dancer and denser. When we get to its

1146
00:59:28,840 --> 00:59:32,439
Speaker 4: maximum density, it just bounces back out again. So you'd

1147
00:59:32,480 --> 00:59:35,680
Speaker 4: get another expanding universe, or if you wanted to think

1148
00:59:35,720 --> 00:59:38,640
Speaker 4: of it as going from the past today, it would

1149
00:59:38,640 --> 00:59:41,640
Speaker 4: be a contracting universe and then an expanding universe, and

1150
00:59:41,680 --> 00:59:45,040
Speaker 4: that core attracting universe could have been contracting for infinitely

1151
00:59:46,160 --> 00:59:50,400
Speaker 4: long ago. You might just have it mirror like. It

1152
00:59:50,440 --> 00:59:52,160
Speaker 4: doesn't have to be cyclic, or though it could be.

1153
00:59:52,640 --> 00:59:55,360
Speaker 4: It could just be one contracting universe mirrored by it

1154
00:59:55,360 --> 00:59:56,000
Speaker 4: one expanding it.

1155
00:59:56,280 --> 00:59:57,800
Speaker 3: Something like that, like an hour class.

1156
00:59:58,400 --> 01:00:00,560
Speaker 4: So that's that's the idea of a. And I think

1157
01:00:00,600 --> 01:00:04,880
Speaker 4: that is less ambiguous, that it does not have a

1158
01:00:04,920 --> 01:00:06,040
Speaker 4: beginning in this model.

1159
01:00:06,640 --> 01:00:07,760
Speaker 3: So that's one idea.

1160
01:00:07,800 --> 01:00:11,400
Speaker 4: And of course there are cyclic universes as well, and oh, guys,

1161
01:00:11,440 --> 01:00:12,640
Speaker 4: of other ideas we explaw.

1162
01:00:13,000 --> 01:00:15,560
Speaker 2: So this idea that at some point gravity stops pulling

1163
01:00:15,600 --> 01:00:18,479
Speaker 2: things in and starts to repel energy, do we have

1164
01:00:19,040 --> 01:00:22,080
Speaker 2: evidence for that in other domains or like, where did

1165
01:00:22,080 --> 01:00:23,000
Speaker 2: this idea come from?

1166
01:00:24,000 --> 01:00:24,760
Speaker 3: Arguably we do.

1167
01:00:25,400 --> 01:00:28,880
Speaker 4: The fact that the universe is accelerating in its expansion

1168
01:00:29,600 --> 01:00:33,200
Speaker 4: is an effect of the vacuum having a pressure.

1169
01:00:33,280 --> 01:00:34,360
Speaker 3: But think of it this way.

1170
01:00:34,480 --> 01:00:37,120
Speaker 4: I mean, this is different to what we're talking about

1171
01:00:37,280 --> 01:00:39,200
Speaker 4: in the quantum gravity case. But I just want to

1172
01:00:39,240 --> 01:00:42,360
Speaker 4: ask your questions, is there some evidence of a repulsive gravity.

1173
01:00:42,800 --> 01:00:46,400
Speaker 4: So in Newton's theory, the only thing that contributes to

1174
01:00:46,440 --> 01:00:49,760
Speaker 4: gravity is mass, so you can't have a negative mass

1175
01:00:49,760 --> 01:00:52,800
Speaker 4: as far as I know, so you can't have negative gravity.

1176
01:00:52,840 --> 01:00:57,520
Speaker 4: Therefore gravity is always attractive. However, in Einstein's theory there's

1177
01:00:57,560 --> 01:01:00,280
Speaker 4: also a pressure term, so it's not just mass, and

1178
01:01:00,320 --> 01:01:02,840
Speaker 4: the pressure can be negative. It's like a suction, and

1179
01:01:02,880 --> 01:01:07,640
Speaker 4: in fact, vacuum has negative pressure, so it is a

1180
01:01:07,680 --> 01:01:10,200
Speaker 4: repulsive gravity force. And the fact that we see the

1181
01:01:10,240 --> 01:01:14,640
Speaker 4: universe accelerating an expansion is direct emperical evidence of repulsive gravity.

1182
01:01:15,040 --> 01:01:17,720
Speaker 3: So that is clear that there is repulsive gravity.

1183
01:01:18,200 --> 01:01:21,760
Speaker 4: Now that's not necessarily what's going on here at the

1184
01:01:21,760 --> 01:01:25,840
Speaker 4: big bounce, because there you're assuming it's coming from quantum gravity.

1185
01:01:26,520 --> 01:01:30,760
Speaker 4: So there you have to use a different type of geometry.

1186
01:01:30,960 --> 01:01:34,680
Speaker 4: So the geometry that's used in relativity is classical geometry,

1187
01:01:35,440 --> 01:01:38,680
Speaker 4: whereas in these quantum gravity theories it's a quantum geometry,

1188
01:01:39,040 --> 01:01:41,720
Speaker 4: so it's sort of fluctuating. And the idea is that

1189
01:01:41,840 --> 01:01:47,240
Speaker 4: then because it's discrete, it can't have infinite compression. It

1190
01:01:47,280 --> 01:01:49,240
Speaker 4: will bounce back at some point and that and then

1191
01:01:49,280 --> 01:01:52,640
Speaker 4: the gravity switch assigned and you get repulsive gravity. So

1192
01:01:52,680 --> 01:01:56,200
Speaker 4: that's the theoretical trapulation from the quantum gravity theory. So

1193
01:01:56,480 --> 01:01:59,720
Speaker 4: in particular, Luke quantum gravity is that it's a candidate

1194
01:01:59,720 --> 01:02:02,080
Speaker 4: for for quantum gravity. They've done a lot of work

1195
01:02:02,120 --> 01:02:04,320
Speaker 4: on this bouncing cosmology, but there have been ideas even

1196
01:02:04,360 --> 01:02:06,520
Speaker 4: in string theory that you might get a bounce in

1197
01:02:06,520 --> 01:02:11,120
Speaker 4: cosmology from this fact that if you discretize space then

1198
01:02:11,160 --> 01:02:13,920
Speaker 4: it will have a maximum limit of what you can

1199
01:02:13,920 --> 01:02:16,120
Speaker 4: put into it, and then if you try to go

1200
01:02:16,200 --> 01:02:17,479
Speaker 4: beyond it, it pushes back.

1201
01:02:17,960 --> 01:02:20,800
Speaker 1: I like these bouncing ideas because they sort of avoid

1202
01:02:20,840 --> 01:02:22,840
Speaker 1: the question of our first moment. They're like, lit's just

1203
01:02:22,840 --> 01:02:26,040
Speaker 1: bounce forever, and that's cool. But I wonder if there's

1204
01:02:26,080 --> 01:02:28,800
Speaker 1: any evidence for that, Like, you know, if the universe

1205
01:02:28,840 --> 01:02:32,280
Speaker 1: compresses to a singularity or a near singularity, some quantum

1206
01:02:32,320 --> 01:02:35,440
Speaker 1: version of it, does it do so in so intensely

1207
01:02:35,600 --> 01:02:38,920
Speaker 1: that all evidence of the previous you know, pre bounce

1208
01:02:39,160 --> 01:02:43,040
Speaker 1: universe is lost? Or can we find some hints, some

1209
01:02:43,120 --> 01:02:45,680
Speaker 1: clues in the universe today that showed that it had

1210
01:02:45,720 --> 01:02:46,440
Speaker 1: to have a bounce.

1211
01:02:46,840 --> 01:02:49,920
Speaker 3: Yes, So this is an active research program.

1212
01:02:50,520 --> 01:02:52,280
Speaker 4: So, as I said, I think it's in the lib

1213
01:02:52,360 --> 01:02:55,280
Speaker 4: quantum gravity case where there's the most consensus that you

1214
01:02:55,400 --> 01:02:58,160
Speaker 4: get a bounce. As I said, they have been ideas

1215
01:02:58,200 --> 01:03:00,320
Speaker 4: in string theory for a bounce as well, and even

1216
01:03:00,360 --> 01:03:02,920
Speaker 4: in some other proposals of quantum gravity. But in the

1217
01:03:02,960 --> 01:03:05,920
Speaker 4: loop case, loop quantum gravity, which is one of the

1218
01:03:05,960 --> 01:03:11,840
Speaker 4: candidates for a theory to mix ie thereogenerativity and quantum mechanics,

1219
01:03:11,880 --> 01:03:15,320
Speaker 4: as we've got this quantum theory gravity. Because we should

1220
01:03:15,360 --> 01:03:17,720
Speaker 4: point out to the listener if they're not familiar, these

1221
01:03:17,760 --> 01:03:21,280
Speaker 4: two theories are the cornerstones and modern physics. But yet

1222
01:03:21,320 --> 01:03:23,720
Speaker 4: they contradict each other. So we know we need a

1223
01:03:23,720 --> 01:03:27,320
Speaker 4: deeper theory. So we know or we need to modify

1224
01:03:27,440 --> 01:03:29,439
Speaker 4: one of the existing theories, or maybe both of them,

1225
01:03:29,600 --> 01:03:32,240
Speaker 4: but we know we need new physics in some way.

1226
01:03:32,400 --> 01:03:34,640
Speaker 4: So one of the contenders this is theory called loop

1227
01:03:34,680 --> 01:03:37,120
Speaker 4: quantum gravity. And what they've got this program called loop

1228
01:03:37,160 --> 01:03:41,840
Speaker 4: quantum cosmology, where what they want to do is calculate

1229
01:03:42,520 --> 01:03:44,760
Speaker 4: what we should see in the cosmic microwave background if

1230
01:03:44,760 --> 01:03:48,320
Speaker 4: there was a bounce, and they claim that they've already

1231
01:03:48,360 --> 01:03:53,240
Speaker 4: done this and they it matches their observations. Now obviously

1232
01:03:53,440 --> 01:03:55,960
Speaker 4: not everyone agrees, so this is correct so they have

1233
01:03:55,960 --> 01:03:57,800
Speaker 4: to make certain assumptions, and then the question is are

1234
01:03:57,800 --> 01:04:02,000
Speaker 4: they valid assumptions? And then you know, in particular, I'll

1235
01:04:02,000 --> 01:04:05,080
Speaker 4: give you one I think is important or especially important,

1236
01:04:05,120 --> 01:04:06,920
Speaker 4: and I should say, and that is you have to

1237
01:04:06,960 --> 01:04:10,439
Speaker 4: assume whether there was inflation or not. And as we said,

1238
01:04:10,480 --> 01:04:13,600
Speaker 4: not everyone agrees there was inflation, so they have to

1239
01:04:13,600 --> 01:04:17,000
Speaker 4: put in inflation. And then there's different models of inflation.

1240
01:04:17,120 --> 01:04:18,800
Speaker 4: So what they do is they try and say, well,

1241
01:04:18,800 --> 01:04:20,240
Speaker 4: which one is favored by the data.

1242
01:04:21,000 --> 01:04:21,600
Speaker 3: Put that in.

1243
01:04:21,680 --> 01:04:25,640
Speaker 4: Then we calculate corrections to what we see in the

1244
01:04:25,640 --> 01:04:29,440
Speaker 4: couse of micro background, and then they claim that there's

1245
01:04:29,880 --> 01:04:32,280
Speaker 4: actually much is better than the standard model, but the

1246
01:04:32,320 --> 01:04:36,160
Speaker 4: differences are not big enough to be decisive. And of course,

1247
01:04:36,200 --> 01:04:39,840
Speaker 4: as I said, you could challenge the assumptions. So it's

1248
01:04:39,840 --> 01:04:43,920
Speaker 4: still an ongoing program and people are still working on

1249
01:04:43,960 --> 01:04:45,560
Speaker 4: the theory to see if they can make the predictions

1250
01:04:45,600 --> 01:04:49,040
Speaker 4: more robust. So maybe it doesn't depend on some of

1251
01:04:49,080 --> 01:04:51,680
Speaker 4: these assumptions. The other thing you could try and do

1252
01:04:52,280 --> 01:04:55,320
Speaker 4: is look at black holes and how black holes might

1253
01:04:55,360 --> 01:04:59,120
Speaker 4: behave because there also we think we need quantum gravity,

1254
01:04:58,920 --> 01:05:02,480
Speaker 4: so people have made models of black holes using quantum gravity.

1255
01:05:02,920 --> 01:05:05,160
Speaker 4: And then maybe you could look for signatures of what

1256
01:05:05,560 --> 01:05:09,480
Speaker 4: they might do. Maybe there are signs of quantum gravity

1257
01:05:09,720 --> 01:05:14,240
Speaker 4: in black holes. So those are the two areas that

1258
01:05:14,320 --> 01:05:18,040
Speaker 4: I think are the most exciting about looking for signs

1259
01:05:18,640 --> 01:05:22,320
Speaker 4: of quantum gravity. And if we can find those, then

1260
01:05:22,320 --> 01:05:24,280
Speaker 4: we might know what the right theory of quantum gravity is.

1261
01:05:24,800 --> 01:05:27,320
Speaker 4: And then we might know whether this bounce took place

1262
01:05:27,400 --> 01:05:28,000
Speaker 4: or if it didn't.

1263
01:05:28,360 --> 01:05:29,200
Speaker 2: That would be exciting.

1264
01:05:29,400 --> 01:05:31,680
Speaker 1: Yes, oh yeah, Well, now we've been looking into the past.

1265
01:05:31,680 --> 01:05:33,920
Speaker 1: Tell us about the future of looking into the past.

1266
01:05:34,240 --> 01:05:35,600
Speaker 1: What do you think we're going to learn in the

1267
01:05:35,600 --> 01:05:37,840
Speaker 1: next ten years or fifty years that could help us

1268
01:05:37,880 --> 01:05:40,480
Speaker 1: understand what came before the hot Big Bang.

1269
01:05:40,560 --> 01:05:43,440
Speaker 4: Well, there's a number of avenues we can explore. So

1270
01:05:43,520 --> 01:05:46,480
Speaker 4: one is to look more at this cosmic microwave background.

1271
01:05:46,960 --> 01:05:49,440
Speaker 4: So this is the oldest light that we can see.

1272
01:05:49,840 --> 01:05:52,880
Speaker 4: You can't see beyond that with light. It's admitted three

1273
01:05:52,960 --> 01:05:55,240
Speaker 4: hundred and eighty thousand years after the Big Bang. And

1274
01:05:55,280 --> 01:05:57,680
Speaker 4: the reason that you can't see anything earlier is that

1275
01:05:57,680 --> 01:06:00,400
Speaker 4: if you went earlier, as I said, the university more

1276
01:06:00,480 --> 01:06:02,920
Speaker 4: like the sun, and if you look at the Sun,

1277
01:06:03,000 --> 01:06:05,080
Speaker 4: you can't look into the interior because it's opaque.

1278
01:06:05,440 --> 01:06:07,280
Speaker 3: So same with the universe.

1279
01:06:07,360 --> 01:06:11,040
Speaker 4: Before the emission of a cosmic microwave background, it was opaque,

1280
01:06:11,200 --> 01:06:15,160
Speaker 4: so you cannot look earlier. But there are these patterns

1281
01:06:15,200 --> 01:06:17,440
Speaker 4: of hot and cold spots, and they give you information

1282
01:06:17,600 --> 01:06:20,680
Speaker 4: that you could try and guess as to what came before.

1283
01:06:20,720 --> 01:06:23,560
Speaker 4: And some theories make different predictions for those patterns of

1284
01:06:23,600 --> 01:06:27,960
Speaker 4: hot and cold spots. Also, there's patterns of polarization, so

1285
01:06:28,000 --> 01:06:29,880
Speaker 4: this is a way that light sort of twirls around.

1286
01:06:30,360 --> 01:06:32,840
Speaker 4: That's a new frontier, So looking for polarization of the

1287
01:06:32,880 --> 01:06:36,600
Speaker 4: cosmic microwave background, and some different models make different predictions

1288
01:06:36,600 --> 01:06:38,280
Speaker 4: for what we might see there.

1289
01:06:39,040 --> 01:06:40,400
Speaker 3: Another avenue you.

1290
01:06:40,280 --> 01:06:44,960
Speaker 4: Could look at is the distribution of galaxies because that

1291
01:06:45,640 --> 01:06:48,000
Speaker 4: was set in the very earliest moments of the Big Bang,

1292
01:06:48,080 --> 01:06:52,400
Speaker 4: So different models might make different predictions for the distribution

1293
01:06:52,480 --> 01:06:57,480
Speaker 4: of galaxies. But I think the most exciting idea for

1294
01:06:57,600 --> 01:07:01,280
Speaker 4: how we can probe much earlier into the into the

1295
01:07:01,280 --> 01:07:07,600
Speaker 4: Big Bang is something called primordial gravitational waves. So this

1296
01:07:07,800 --> 01:07:10,280
Speaker 4: you might people might have heard in twenty let me

1297
01:07:10,280 --> 01:07:14,360
Speaker 4: think was it twenty sixteen Ligo, which was these giant

1298
01:07:14,440 --> 01:07:18,000
Speaker 4: lasers that they have in Louisiana and Washington State, and

1299
01:07:18,280 --> 01:07:22,160
Speaker 4: they detected sort of a ripple in the fabric of

1300
01:07:22,160 --> 01:07:25,040
Speaker 4: space and time. They're called gravitational waves, and they came

1301
01:07:25,280 --> 01:07:27,680
Speaker 4: not from the Big Bank. They came from colliding black holes.

1302
01:07:28,280 --> 01:07:30,600
Speaker 4: But they send out this ripple in the fabric of

1303
01:07:31,080 --> 01:07:34,919
Speaker 4: space and time, and we can detect them amazingly because

1304
01:07:35,120 --> 01:07:37,040
Speaker 4: they're very, very feeble. When they get to the Earth,

1305
01:07:37,800 --> 01:07:42,600
Speaker 4: they change the distance of like these lasers that they

1306
01:07:42,600 --> 01:07:45,680
Speaker 4: basically have. These lasers, they're aout four kilometers apart and

1307
01:07:45,760 --> 01:07:49,439
Speaker 4: they bounce between mirrors and if there are no gravitational waves,

1308
01:07:49,440 --> 01:07:51,360
Speaker 4: they should stay in phase with each other. When a

1309
01:07:51,360 --> 01:07:54,080
Speaker 4: gravitational wave passes through, they go out phase, and so

1310
01:07:54,120 --> 01:07:56,840
Speaker 4: you can detect their existence. And they have two of them,

1311
01:07:56,840 --> 01:08:01,040
Speaker 4: one in Louisiana and one in Washington State. Initially, I

1312
01:08:01,040 --> 01:08:03,040
Speaker 4: mean they've been more built since then. There's one now

1313
01:08:03,080 --> 01:08:08,320
Speaker 4: in Italy and India and Japanese that they're building one

1314
01:08:08,400 --> 01:08:09,800
Speaker 4: or I don't know what the status of that one is.

1315
01:08:09,840 --> 01:08:13,160
Speaker 4: But so so the idea is have a station stations

1316
01:08:13,160 --> 01:08:16,160
Speaker 4: of them around the world, so these ripples can go

1317
01:08:16,240 --> 01:08:20,160
Speaker 4: through that plasma that you can't see through. So even

1318
01:08:20,200 --> 01:08:22,720
Speaker 4: though you can't see light from the Big Bang, you

1319
01:08:22,760 --> 01:08:25,240
Speaker 4: could in some sense see these gravitational ways.

1320
01:08:25,280 --> 01:08:25,960
Speaker 3: You don't see.

1321
01:08:25,800 --> 01:08:28,559
Speaker 4: Them, maybe you hear them, you know, they're kind of

1322
01:08:29,080 --> 01:08:31,599
Speaker 4: sound ways actually in the early universe. That were they

1323
01:08:31,640 --> 01:08:33,080
Speaker 4: cause dounways in the early universe.

1324
01:08:32,880 --> 01:08:33,400
Speaker 3: They should say.

1325
01:08:33,800 --> 01:08:37,280
Speaker 4: So, these ripples in the fabric of space are potentially detectable.

1326
01:08:37,600 --> 01:08:41,000
Speaker 4: Either they might change a polarization of the light of

1327
01:08:41,000 --> 01:08:44,000
Speaker 4: the cosmic microwave background, or we could detect them directly

1328
01:08:44,120 --> 01:08:47,160
Speaker 4: via building something like these giant laser observatories. But the

1329
01:08:47,160 --> 01:08:50,960
Speaker 4: ones that we have today are optimized to see them

1330
01:08:51,000 --> 01:08:54,920
Speaker 4: from black hole collisions. They can't even see them from

1331
01:08:55,400 --> 01:08:57,679
Speaker 4: super massive black holes, which are the really big black

1332
01:08:57,680 --> 01:08:58,519
Speaker 4: holes that.

1333
01:08:58,600 --> 01:08:59,960
Speaker 3: Sit in the center of galaxies.

1334
01:09:00,360 --> 01:09:04,320
Speaker 4: However, we are building a space based observatory called LISA,

1335
01:09:04,800 --> 01:09:08,360
Speaker 4: the Laser Interformance of Space Antenna, and that will be

1336
01:09:08,400 --> 01:09:12,320
Speaker 4: able to detect super massive black hole mergers. So maybe

1337
01:09:12,360 --> 01:09:16,480
Speaker 4: it could see signatures of quantum gravity in these extreme conditions,

1338
01:09:16,800 --> 01:09:20,080
Speaker 4: So that might help us understand the Big Bang. But

1339
01:09:20,160 --> 01:09:22,479
Speaker 4: beyond LISA, I mean lisa's not going to get launched

1340
01:09:22,479 --> 01:09:25,960
Speaker 4: on the twenty thirties. But then beyond that there are projects,

1341
01:09:26,040 --> 01:09:28,920
Speaker 4: one called the Psycho, another one called Big Bang Observer.

1342
01:09:29,000 --> 01:09:30,920
Speaker 4: These are kind of pie in the sky ideas, right,

1343
01:09:30,960 --> 01:09:34,320
Speaker 4: so we don't think that they're going to be built

1344
01:09:34,360 --> 01:09:37,280
Speaker 4: anytime soon. But often what you do is just dream big,

1345
01:09:37,280 --> 01:09:38,680
Speaker 4: because just say, what would you do if you had

1346
01:09:38,760 --> 01:09:43,720
Speaker 4: like endless money and resources, and the idea is just

1347
01:09:43,760 --> 01:09:46,000
Speaker 4: get something on the table and then you know, maybe

1348
01:09:46,080 --> 01:09:48,720
Speaker 4: decades into the future, maybe people find cheaper ways to

1349
01:09:48,720 --> 01:09:50,639
Speaker 4: do it, and then you can actually launch these things.

1350
01:09:51,000 --> 01:09:54,759
Speaker 4: So the Big Bang Observer, for example, is like Lisa,

1351
01:09:54,960 --> 01:09:58,759
Speaker 4: it's a similar idea, but it has twelve spacecraft. Lisa

1352
01:09:58,760 --> 01:10:02,599
Speaker 4: has three that is happening as being built as we speak.

1353
01:10:02,920 --> 01:10:05,800
Speaker 4: But Big Bang Obsurvey is much much more ambitious. But

1354
01:10:06,000 --> 01:10:09,479
Speaker 4: that could potentially see these ripples from the Big Bang.

1355
01:10:10,080 --> 01:10:14,280
Speaker 4: And now why that is that important because some models

1356
01:10:14,640 --> 01:10:17,400
Speaker 4: predict that there should be these ripples and some don't.

1357
01:10:18,200 --> 01:10:21,280
Speaker 4: So a lot of cyclic models say there are no ripples.

1358
01:10:21,520 --> 01:10:23,840
Speaker 4: And some of these cyclic models are alternatives to the

1359
01:10:23,840 --> 01:10:25,519
Speaker 4: inflationary screen, which says.

1360
01:10:25,360 --> 01:10:26,560
Speaker 3: There are these ripples.

1361
01:10:27,000 --> 01:10:30,120
Speaker 4: Not only that, but they actually have different properties, so

1362
01:10:30,439 --> 01:10:33,800
Speaker 4: they have different strengths at different wavelengths, and so we

1363
01:10:33,920 --> 01:10:36,920
Speaker 4: call that the spectrum of the gravitational waves. So by

1364
01:10:37,040 --> 01:10:40,920
Speaker 4: probing the gravitational wave universe. And this is an area

1365
01:10:40,920 --> 01:10:43,360
Speaker 4: of astronomy that is brand new. I mean, we only

1366
01:10:43,439 --> 01:10:46,320
Speaker 4: detected the first gravitational wave in twenty fifteen. It's like

1367
01:10:46,479 --> 01:10:50,400
Speaker 4: Galileo first looking at in this telescope in sixteen ten.

1368
01:10:50,880 --> 01:10:54,280
Speaker 4: Think of what a small telescope we had and how

1369
01:10:54,400 --> 01:10:57,200
Speaker 4: radically it changed our view of the universe. Because before

1370
01:10:57,280 --> 01:11:01,040
Speaker 4: Galileo looked through our telescope, most people will sure that

1371
01:11:01,400 --> 01:11:04,720
Speaker 4: we lived in a geocentric universe with everything going around

1372
01:11:04,960 --> 01:11:07,800
Speaker 4: the Earth. And I think mccalilet took through that telescope

1373
01:11:08,080 --> 01:11:10,920
Speaker 4: and he saw that there were moons going around Jupiter.

1374
01:11:10,960 --> 01:11:14,080
Speaker 4: It was clear as clear as day that not everything

1375
01:11:14,080 --> 01:11:16,400
Speaker 4: goes around the Earth. And then he saw the phases

1376
01:11:16,400 --> 01:11:19,480
Speaker 4: of Venus, which was a direct prediction of the helocentric

1377
01:11:19,520 --> 01:11:23,040
Speaker 4: model or particular properties of the phases of Venus. So

1378
01:11:23,200 --> 01:11:26,559
Speaker 4: it was incredibly revolutionary. And now we're at the birth

1379
01:11:26,600 --> 01:11:30,479
Speaker 4: of this new revolution gravitational wave of astronomy. And this

1380
01:11:30,600 --> 01:11:34,360
Speaker 4: could probe which models of the Big Bang or even

1381
01:11:34,400 --> 01:11:38,600
Speaker 4: pre Big Bang universe are right. And that is the

1382
01:11:38,720 --> 01:11:44,120
Speaker 4: incredibly exciting frontier for the universe cosmology in the decades

1383
01:11:44,240 --> 01:11:47,560
Speaker 4: or maybe centrics to come. Depending on whether we decide

1384
01:11:47,800 --> 01:11:49,280
Speaker 4: to find this area of science.

1385
01:11:49,600 --> 01:11:51,720
Speaker 1: That's right, it'll finally tell us whether we're in the

1386
01:11:51,840 --> 01:11:56,599
Speaker 1: Marvel Multiverse or the DC Multiverse or another version. Right, yes,

1387
01:11:57,439 --> 01:12:02,360
Speaker 1: exactly right, all right, well, thank you Phil very much

1388
01:12:02,360 --> 01:12:04,240
Speaker 1: for coming on the podcast and talk to us about

1389
01:12:04,280 --> 01:12:06,680
Speaker 1: all these crazy ideas. It's amazing to me we can

1390
01:12:06,760 --> 01:12:09,400
Speaker 1: know anything about the universe so long ago, and we

1391
01:12:09,400 --> 01:12:12,719
Speaker 1: can even have debates about various ideas. I really enjoyed

1392
01:12:12,760 --> 01:12:15,080
Speaker 1: the book. The book is called Battle for the Big Bang,

1393
01:12:15,120 --> 01:12:17,280
Speaker 1: The New Tales of our Cosmic Origins.

1394
01:12:24,280 --> 01:12:28,120
Speaker 2: Daniel and Kelly's Extraordinary Universe is produced by iHeartRadio. We

1395
01:12:28,160 --> 01:12:29,559
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1396
01:12:29,680 --> 01:12:32,600
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1397
01:12:32,840 --> 01:12:35,439
Speaker 1: have about this Extraordinary Universe.

1398
01:12:35,560 --> 01:12:38,480
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1399
01:12:38,520 --> 01:12:41,519
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1400
01:12:41,560 --> 01:12:41,960
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1401
01:12:42,240 --> 01:12:45,760
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1402
01:12:45,800 --> 01:12:49,000
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1403
01:12:48,080 --> 01:12:50,160
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1404
01:12:50,240 --> 01:12:54,040
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01:12:54,120 --> 01:12:56,080
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1407
01:12:58,240 --> 01:13:01,360
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