John Green, Very Curious: So... we live in a universe. 

Dr. Katie Mack, Astrophysicist: Yes.

John: How big is it? 

Dr. Mack: [chuckles] That's a great question. It depends on what you mean by universe. So, already, it's complicated. 

John: Oh, no. Oh, no. 

Dr. Mack and John: [chuckles]

[Orchestral music plays]

John: A few years ago, I came across a book by the astrophysicist Katie Mack called The End of Everything: (Astrophysically Speaking). The book tells the story of our universe, how we understand its beginning, its expansion, and what we know about its future, including, well the end of everything. We are only here for a little while, of course, and the universe will be here for much longer. But everything we've seen so far in our universe will inevitably die, and it seems the universe itself will as well. In short, there will be no season two.

I was so moved by this book that I wrote Dr. Mack an email to thank her for writing it. She replied, and we struck up a friendship.

We make a bit of an odd couple. I'm a novelist by trade who barely passed high school physics largely by being the kind of student my teacher did not want to have in class for a second consecutive year. 

Dr. Mack, meanwhile, holds the Hawking Chair in Cosmology and Science Communication at the renowned Perimeter Institute, but she is a patient teacher and I am curious about the vast and strange universe in which I find myself. So we decided to make a podcast together about the history of the entire universe, including the parts of its history that haven't yet been written, and more broadly about why we seek to understand what's keeping the stars apart, as e.e. Cummings once wrote.

Here in the first episode, Dr. Mack helped me understand the Big Bang, which initially caused me a lot of anxiety.

John Green: But then by the end of our conversation, I learned something so phenomenally beautiful about the universe that I've been clinging with hope to it ever since, which is that we are not just made of stardust, we are also made of Big Bang stuff, with pieces of us directly born in the vast, first cacophony. Here's our conversation.

[Astral music fading out]

John: Okay. I already have a lot of questions. 

Dr. Katie Mack: Okay, great. 

John: I would like to ask why there is a universe, ...

Dr. Mack: Oh, why there is a universe.  

John: ... and then I wanna follow that up by saying that -

Dr. Mack: Yeah. 

John: - in my line of work, there's a famously boring question  -

Dr. Mack: Mhm.

John: - that is the question that everyone asks, which is, "where do you get your ideas from?".

[Dr. Mack chuckles.]

John: And in my wife's line of work, -

Dr. Mack: Mhm.

John: - she's a curator of contemporary art. There is a famously boring question, which is, "what is art?".

Dr. Mack: Right. 

John: Is the question of why there is a universe, the astrophysicist version of those questions?

Dr. Mack: I think that it's just a question that really has no answer. And there are very few people in astrophysics or physics or cosmology, any of those areas who are thinking really about that question in the sense that there are some people working on like, how did the universe begin? What started it? We kinda step away from that kind of question because that suggests purpose or intent or meaning in some way that, that there's, there's no empirical approach to that.

John: To establishing purpose.

Dr. Mack: Yeah, yeah.

John: Do we know why there's stuff in the universe?

Dr. Mack: (chuckles before continuing) We, we don't, 

John: or am I again, -

Dr. Mack: - we really, that's actually, -

John: - am am I again -

Dr. Mack: - that's a really (no) -

John: - asking a why question? And you don't want me to ask a why question?

Dr. Mack: No, no, it's not, that's not a why question. That's an embarrassing question because, because

Dr. Katie Mack: our current understanding of, of the theaories kind of suggest there shouldn't be stuff like so, -

John Green: Oh, there shouldn't be stuff. That's discouraging. 

Dr. Mack: Yeah. There's this concept of matter-antimatter asymmetry. So anti-matter is, it's kind of like a mirror image of matter in, in some sense. So there's an electron. An electron is a particle that's part of the, the atom. There's an antimatter version of electron called a positron that has the opposite charge, and there's some technical mathematical sense in which they're kind of reversed in some way. And if you take an electron and a positron and you put them together, they will annihilate with each other and create gamma rays. This is why, you know, spaceships and science fiction often use anti-matter as propulsion, because if you collide matter and anti-matter, you get a big, big boom, right? Like if you, if you started the universe with just a bunch of radiation and that radiation then turned into matter, it should turn into like a, an equal amount of matter and anti-matter. So if you just had some sort of radiation turned into matter and all that, and, and in the way that our equations kind of suggests it should work, you should get the same amount of both. And then they would just annihilate against each other. Like they would just, and then you would just have radiation again, you wouldn't have a whole bunch of matter and almost no anti-matter, which is what we see.  

John: Hmm.

Dr. Mack: So if you go out into the universe, everything we observe is matter. Unless there's been some kind of big high energy event like a pulsar or a supernova or you know, some kind of high energy beam of, of gamma rays that that splits into electrons and positrons. Then you can get antimatter in those high energy events and you get a little tiny bit of it, and then it annihilates against the matter. But all the stuff in the universe is matter. Like all the stars and planets and all of that, that's made of matter. So there's way more matter than there is antimatter, which means that some point, there had to have been something that like changed the balance that created an asymmetry between matter and antimatter so that all of the antimatter would be annihilated away and there'd be matter left over.

[ominious (?) orchestral music plays]

[Ominous (?) orchestral music fades away]

John Green: Okay, so I know we're only a few minutes in here, but this point is really, really important. So I want to emphasize what Dr. Mack is saying here. Matter is everything you see in the universe, it's you, it's me, it's planets, it's stars and galaxies and antimatter is essentially the opposite of matter. And when matter and antimatter meet, they basically ancel each other out so nothing but energy remains. Based on everything we know about the universe, there should be equal parts matter and antimatter, but that's clearly not the case because you're listening to this and I'm here trying to explain antimatter to you. So there is more matter than antimatter in our universe, and that is the reason our universe exists and we don't know why.  

[Ominous (?) orchestral music fades away]

Dr. Katie Mack: And we, we don't know why that happened. [chuckles] So we don't, we don't know the mechanism for that. There are theories, but we don't have an answer to that question. 

John: But it had to have happened at the, at the beginning. Right? Because we know there's been stuff for a long time. 

Dr. Mack: Yeah. Yeah. I mean, our best guess is that it happened like sometime within the first like fraction of a nanosecond, basically. 

John: What really?

Dr. Mack: Yeah. Yeah. So it happened, it happened very early on, like before. 

John: Whoa, whoa, whoa. We know what happened in the first second?

Dr. Mack: Oh, yeah. Yeah. We can go down way earlier than that. We have, we have a lot of information about the beginning. 

John: We know what happened in the first second of the universe, 

Dr. Mack: Yes.

John: the first nanosecond of the universe , the first fraction

Dr. Mack: Yes.

John: of a nanosecond of the universe. 

Dr. Mack: We can, we can go down with reasonable confidence to a microsecond, well, actually, let's see, maybe like a fraction of a nanosecond, something like that. 

John: Okay. 

Dr. Mack: We're pretty sure we have good, like theoretical

Dr. Katie Mack: and experimental evidence for what happened in that time. Before that things get fuzzy, we have a really, really good theory, but we're not certain.  

John Green: Okay. So that's great. That's great. We know what happened in the first fraction of a nanosecond. 

Dr. Mack: Yeah. 

John: Wh-What was that? 

[Dr. Mack chuckling.]

John: Take me back -

Dr. Mack: Okay. Okay.

John: - to the very beginning of the universe, and then after you tell me the story... of what? The first second? The first nanosecond?

Dr. Mack: I'll get, I'll get into the first minute or so. Yeah.

John: How the heck do we know what happened in the first minute of the universe?

[Dr. Mack chuckling even more.]

John: 13.8 billion years ago?

[Light yet twinkling orchestral music fades out.]

Dr. Mack: Okay. Okay. So I'll start with the Big Bang theory. When people talk about the Big Bang theory, usually what they mean is like they, they're like, oh yeah, I heard, you know, the universe was a singularity, is a tiny infinitesimal point that exploded in all directions. And that's not, that's not really what we as astronomers mean when we say the Big Bang theory. When astronomers say the Big Bang theory, we actually mean something a lot closer to the theme song of the TV show, The Big Bang Theory, 

[Both Dr. Mack and John chuckle.]

Dr. Mack: because I use this example 

[John lightly laughs.]

Dr. Mack: 'cause it's actually pretty good in that theme song that says the whole universe was in a hot, dense state, then nearly 14 billion years ago, expansion started, then the song goes on to other things, right? But that's, that's it. So the Big Bang theory is just the idea that the universe was hot and dense in the beginning, 13.8 billion years ago. It was, it was hot and dense and it's been expanding and cooling since then. The origin of that theory is the idea that currently the universe is expanding, right? So we observe that because we see all the distant galaxies are moving away from us.