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Speaker 1: Hey, Jorhan Daniel here, and we want to tell you

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Speaker 1: about our new book. It's called Frequently Asked Questions about

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Speaker 1: the Universe because you have questions about the universe, and

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Speaker 1: so we decided to write a book all about them.

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Speaker 1: We talk about your questions, we give some answers, we

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Speaker 1: make a bunch of silly jokes as usual, and we

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Speaker 1: tackle all kinds of questions, including what happens if I

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Speaker 1: fall into a black hole? Or is there another version

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Speaker 1: of you out there that's right? Like usual, we tackle

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Speaker 1: the deepest, darkest, biggest, craziest questions about this incredible cosmos.

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Speaker 1: If you want to support the podcast, please get the

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Speaker 1: book and get a copy, not just for yourself, but

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Speaker 1: you know, for your nieces and nephews, cousins, friends, parents, dogs, hamsters,

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Speaker 1: and for the aliens. So get your copy of Frequently

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Speaker 1: Asked Questions about the Universe is available for pre order now,

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Speaker 1: coming out November two. You can find more details at

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Speaker 1: the book's website, Universe f a Q dot com. Thanks

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Speaker 1: for your support, and if you have a hamster that

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Speaker 1: can read, please let us know. We'd love to have

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Speaker 1: them on the podcast. Hey Daniel, how far back do

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Speaker 1: you know? Your family story. Oh you mean like where

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Speaker 1: my family comes from? Yeah, you know, like how many

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Speaker 1: generations back do you know? Well? I actually met my

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Speaker 1: great grandfather when I was a kid, and I know

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Speaker 1: some family history back a couple more generations than that,

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Speaker 1: So I guess that makes like four or five generations.

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Speaker 1: How about you. That's pretty good. I actually have only

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Speaker 1: met my grandparents through to the four of them. But

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Speaker 1: then it gets a little fuzzy. You know, they're all immigrants,

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Speaker 1: and we know at least one future generation, I mean

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Speaker 1: our kids. Yes, children are the future, and hopefully there

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Speaker 1: are enough future generations that one day we become fuzzy memories. Well,

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Speaker 1: I'm not sure if I will have great grandkids, but

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Speaker 1: if I do, I'm sure they'll remember us, right, they

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Speaker 1: can always listen to this podcast. If nothing else, they'll

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Speaker 1: remember us as a cautionary tale, assuming they care. Hi

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Speaker 1: am or hammy cartoonist and the creator of PhD comics. Hi.

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Speaker 1: I'm Daniel. I'm a particle physicist, but I'm the first

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Speaker 1: person in my family to get a PhD. You're the

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Speaker 1: first doctor or the first academic doctor. I'm definitely the

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Speaker 1: first doctor of any kind in my direct line. Though

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Speaker 1: there is another Daniel Whiteson out there somewhere who I

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Speaker 1: think has a degree. Interesting, it's like your long loss twin,

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Speaker 1: maybe another version of the multiverse version of you. There's

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Speaker 1: another Daniel whites In which is a distant cousin of

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Speaker 1: mine who's an excellent artist and lives in London. Actually

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Speaker 1: you should switch places. Sounds like he has a coulder life.

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Speaker 1: I'm pretty happy with my situation. Thanks very much. Do

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Speaker 1: you think you'll be the last PhD in your family?

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Speaker 1: I don't know. My brother got a PhD, but that

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Speaker 1: might be it. I'm not sure which direction my kids

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Speaker 1: are headed. But anyways, welcome to our podcast. Daniel and

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Speaker 1: Jorge explained the university but that of I Heart Radio,

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Speaker 1: in which we sum up the knowledge and the thinking

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Speaker 1: of many, many generations of deep thinkers and scientists and

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Speaker 1: philosophers and explorers who are trying their hardest to understand

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Speaker 1: this incredible, beautiful universe that we find ourselves in. We

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Speaker 1: talk about everything that we know about science, things that

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Speaker 1: we don't know about science, the way the universe works,

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Speaker 1: and the way the universe definitely doesn't work. We talk

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Speaker 1: about the latest results of the craziest thought experiments and

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Speaker 1: everything in between, and throwing a few banana jokes to

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Speaker 1: keep you awake and hopefully not to slip you up.

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Speaker 1: But it is a pretty big universe, pretty amazing, and

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Speaker 1: science has discovered a lot about it. We know a

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Speaker 1: lot about how the universe started, how it's evolved, and

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Speaker 1: what explains everything we see today, and a big job

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Speaker 1: of science is also to think about the future and

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Speaker 1: what's going to happen to this crazy cosmos. That's right,

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Speaker 1: because one thing we know about the universe for sure

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Speaker 1: is that it's not static. It's not just hanging out

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Speaker 1: like this forever. It's evolving. It's not quite alive, but

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Speaker 1: it's definitely developing and changing and has different modes to it. Yeah,

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Speaker 1: the universe hasn't always been the way it is right now,

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Speaker 1: and it's not going to be the same wave in

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Speaker 1: the future. It's it's always changing, evolving and growing, hopefully

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Speaker 1: getting more mature. Do you think the universe is getting

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Speaker 1: more mature. I'm not sure it's getting better behaved, but

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Speaker 1: it's definitely getting older. It's still getting into trouble. You

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Speaker 1: thinking the universe that learns its lessons, I'm not sure

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Speaker 1: who's teaching the universe anything. But I think it's fun

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Speaker 1: to realize that the universe seems sort of static on

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Speaker 1: our time scale, like the universe is not going to

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Speaker 1: look any different the day you die than the day

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Speaker 1: you are born, but that these processes are happening on

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Speaker 1: a much much longer time scale, and that if you

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Speaker 1: look at the universe over like millions of years or

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Speaker 1: billions of years, it's very much dynamic. It's changing, it's growing,

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Speaker 1: it's evolving. It's gonna look very different in five billion

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Speaker 1: years than it does today. Yeah, or not even billions

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Speaker 1: of years, Like millions of years, I mean, the Earth

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Speaker 1: looked a lot different. That even our Solar system look

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Speaker 1: pretty different, right, and even a few million or hundreds

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Speaker 1: of millions of years. Yeah, that's something we're learning about.

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Speaker 1: You know, the planets are doing a dance where they're

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Speaker 1: moving in and they're moving out, and we think maybe

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Speaker 1: Jupiter spent some time near the Sun and then Saturn

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Speaker 1: swooped in and saved it and pulled it back out

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Speaker 1: to the colder parts of the Solar system where it

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Speaker 1: can't survive. So there's definitely a lot of stuff going on.

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Speaker 1: If you look at the Solar system or our galaxy

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Speaker 1: on like a super time lapse, you would think it

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Speaker 1: was crazy. Yeah, it's a big action movie. But only

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Speaker 1: if you hit the fast forward button a couple of

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Speaker 1: times and then don't forget to rewind it before you

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Speaker 1: return the tape. Just you know, be kind. Hopefully some

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Speaker 1: people out there get that joke. Probably not if you're

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Speaker 1: under thirty or thirty five, you would get that at least,

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Speaker 1: I guess maybe what's the equivalent now you have to

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Speaker 1: take it off your Netflix queue. Maybe the courtesy to

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Speaker 1: not to nobody. But yeah, it's a big, beautiful universe,

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Speaker 1: and we often wonder what's going to happen in the future,

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Speaker 1: and in particular to the things we see around us,

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Speaker 1: you can think about the sort of age and cycle

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Speaker 1: of the stuff around us. Not just the planets are

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Speaker 1: spinning around the Sun, but the solar is to itself

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Speaker 1: is moving around the galaxy. It takes like two hundred

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Speaker 1: and fifty million years to do one loop around the

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Speaker 1: center of the galaxy for the Sun to orbit the

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Speaker 1: center of the galaxy and came back to where it started.

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Speaker 1: So from that point of view, you know, the galaxy

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Speaker 1: itself is not that old, like it hasn't done that

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Speaker 1: many spins. It's like, you know, thirty to forty galactic

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Speaker 1: years old, it's still searching for itself. Maybe it still

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Speaker 1: hasn't figured out what it wants to do with it

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Speaker 1: that the rest of its life. It's like running through

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Speaker 1: cosmic fields towards the Andromeda Galaxy. There's gonna be a

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Speaker 1: very dramatic moment there where they both learn who they

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Speaker 1: really are. They're going to find themselves. You're going to

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Speaker 1: become one with the cosmos and with each other exactly.

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Speaker 1: And then within those galaxies there's stuff happening. Stars are

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Speaker 1: being born, stars are dying and exploding, is all sorts

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Speaker 1: of crazy stuff. Yes, stars are probably the thing that

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Speaker 1: people most noticed or think about even when they think

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Speaker 1: about space and the entire universe, and it's a big

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Speaker 1: part of the universe. There are a lot of stars

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Speaker 1: out there, and we kind of have to ask what's

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Speaker 1: going to happen to all those stars eventually in the

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Speaker 1: near future and forever perhaps, Yeah, because stars do not

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Speaker 1: live forever. Some of them last millions of years, some

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Speaker 1: billions of years, some potentially trillions of years. But there

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Speaker 1: are stars that formed and burned and died even before

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Speaker 1: our solar system came to be, the things that you

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Speaker 1: and I are made out of, and then our solar

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Speaker 1: system are built out of our remnants of ancient stars

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Speaker 1: which shine through the universe and no longer exist. So

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Speaker 1: we can look into the past and think about, like,

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Speaker 1: how many generations of stars have there been so far

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Speaker 1: that burned and died before we even came to being. Yeah,

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Speaker 1: it's kind of like people, you know, we humans have

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Speaker 1: generations that come and go, and each time that they're

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Speaker 1: a little bit different, hopefully. And if we're made of

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Speaker 1: star dust, then by analogy, are you made out of grandparents?

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Speaker 1: Doesn't Yeah? Yeah, So there have been a lot of

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Speaker 1: generations of stars since the beginning of the universe, and

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Speaker 1: so today we'll be tackling the question how many generations

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Speaker 1: of stars will there be? I guess, Daniel, that number

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Speaker 1: could be finite. Is that the idea like, maybe there

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Speaker 1: aren't that many generations of stars that can happen, or

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Speaker 1: is that number infinite? Perhaps? Yeah, exactly, That's what we're

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Speaker 1: gonna dig into. There's a lot of different ideas about

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Speaker 1: the future of the universe and how this might happen.

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Speaker 1: A lot of things we still don't even really understand

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Speaker 1: about the conditions for star formation where it's happening universe,

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Speaker 1: where it's not happening in the universe, and all that's

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Speaker 1: going to come together to give us a picture for

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Speaker 1: how many times stars can burn and then explode and reform. Yeah,

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Speaker 1: I guess it's interesting that what you said earlier is

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Speaker 1: that maybe a lot of people don't realize that stars

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Speaker 1: kind of have a lifespan, right, Like, you know, your

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Speaker 1: the Sun is not going to be there forever. It

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Speaker 1: wasn't always there since the beginning of time. It came

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Speaker 1: about at some point in the in the past, and

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Speaker 1: it's not going to be there forever into the future,

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Speaker 1: and in its place, maybe there will be another star exactly.

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Speaker 1: The Sun came around sort of late in the universe,

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Speaker 1: and universe four billion years old. The Sun is only

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Speaker 1: like four and a half billion years old, So there

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Speaker 1: was nine or so billion years of stuff happening in

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Speaker 1: the universe before our sun even existed, Right, that's a

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Speaker 1: lot of time for stuff to happen. Stars formed and died,

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Speaker 1: and then our star formed from the leftover bits of

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Speaker 1: other stars and also you know, untouched material from the

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Speaker 1: Big Bang and our son will not last forever. It's

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Speaker 1: only got a five more billion years or so, And

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Speaker 1: so it's a fun question to think about, like how

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Speaker 1: many times can you gather stuff together to make stars,

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Speaker 1: burn it, blow it up again, and then repeat. Can

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Speaker 1: you do that forever? Or is there some fundamental limit

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Speaker 1: to how many times the universe can get right? Yeah?

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Speaker 1: And if we run out of generations of stars, well,

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Speaker 1: that does that mean the universe will be dark forever

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Speaker 1: at the end of light of sunny days in the universe.

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Speaker 1: That's a dim weather forecast. Man, you know, it's a

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Speaker 1: cloudy future, zero percent chance of radiation forever the sunblocks.

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Speaker 1: That's that's a positive. Don't invest in sunscreen companies people,

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Speaker 1: at least not in the billion year bond market. But anyways,

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Speaker 1: we're wondering how many people out there have thought about

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Speaker 1: this idea of solar or star generations and how many

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Speaker 1: there will be in the future. So it's usual Daniel

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Speaker 1: went out there and ask people how many generations or

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Speaker 1: stars do you think there will be? And as always,

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Speaker 1: I am deeply grateful to those of you who are

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Speaker 1: willing to answer these crazy questions online. If you'd like

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Speaker 1: to hear your voice speculating on difficult physics questions on

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Speaker 1: the podcast. Please write to us new questions at Daniel

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Speaker 1: and Jorge dot com. Here's what people had to say.

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Speaker 1: I think I heard somewhere there's been three generations of stars.

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Speaker 1: So if we're supposed to the universe is supposed to

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Speaker 1: last for billions of years more, at least four or

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Speaker 1: five more, let's say, Um, possibly, and I'm limited amount

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Speaker 1: of generations. We don't really know what's going to happen

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Speaker 1: in the future exactly. Um, you might, you're smarter than me,

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Speaker 1: but um, yeah, I don't know. I don't know. It

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Speaker 1: depends on the time, depends if the time is infinite,

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Speaker 1: I don't know. Probably they can be a lot, a

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Speaker 1: lot of generations eleven, Okay, how many generations of stars

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Speaker 1: will there be? I think so, I know that we've

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Speaker 1: got the original and then we've got the next generation. Um,

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Speaker 1: I'm gonna say we're going to have all the generations

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Speaker 1: of stars. I have no idea. Well, we're in the

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Speaker 1: third generations of star at the moment, even though this

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Speaker 1: generation is called population one. I bet Jorge has something

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Speaker 1: fun to say about that naming logic, But I'm not

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Speaker 1: sure how much of the matter in the universe has

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Speaker 1: now been used to create stars. So let's say it's

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Speaker 1: ten percent. Sure it is, but let's say ten percent,

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Speaker 1: and we are three generations into the universe, so then

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Speaker 1: ten times as many, let's say thirty generations. I've thought

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Speaker 1: about this because we know how long the universe is

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Speaker 1: gonna last and how long it's gonna be dense enough

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Speaker 1: for new star formation. Our son is like four billion

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Speaker 1: years old in the universe is like fourteen, so maybe

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Speaker 1: there's been two or three generations there, and Son's got

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Speaker 1: another four billion years left and it's kind of an

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Speaker 1: average star. So maybe that's we're just on the second

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Speaker 1: generation right now, so maybe ten more generations. It's my

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Speaker 1: best guess. Five billion seems like a good number of

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Speaker 1: star generations. I mean, if we're taking the average life

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Speaker 1: spent at a star to be somewhere around five billion years,

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Speaker 1: and you know, at some point, you know, all the

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Speaker 1: stars exploding, our decaying that we're going to kind of

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Speaker 1: reach a point where gas and dust is to spread

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Speaker 1: out to create more stars. Yeah, we're gonna reach a plateau.

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Speaker 1: So I'm just gonna get five billion years, I guess

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Speaker 1: infinite until the universe ends because and you can't really

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Speaker 1: count them because different stars generations and at different times,

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Speaker 1: because the lickspans of stars is so different. All right,

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Speaker 1: So a lot of guessing. I mean, everyone seemed to

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Speaker 1: have sort of an idea. Maybe they're like three infinite.

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Speaker 1: I like that as a guess. That's a good guess.

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Speaker 1: They said that sounds like a good number, Like, why

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Speaker 1: not like a good number? Yeah, next time they asked

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Speaker 1: me if i'd like a raise, I'll say, yeah, you

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Speaker 1: know what, five billion seems like a good number. Pennies

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Speaker 1: or nano dollars or something. All Right, So that's a

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Speaker 1: pretty interesting question. How many generations of stars will there be?

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Speaker 1: Are we gonna have stars until the end of time

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Speaker 1: or are we going to run out of fuel or

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Speaker 1: ability to form these stars eventually in the future. Start

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Speaker 1: us off, Daniel, I guess how do you define a

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Speaker 1: generation of a star? And how did those kind of

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Speaker 1: come about? Yeah, it's a good question. How do you

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Speaker 1: even define a generation of a star? It's actually not

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Speaker 1: that easy to like crisply say what generation of stars

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Speaker 1: in because every star is made out of a bunch

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Speaker 1: of material that just happened to be around and some

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Speaker 1: of it could be like leftover pristine material from the

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Speaker 1: Big Bang, and other bits could have been in other stars.

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Speaker 1: But I think it's important to understand this sort of

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Speaker 1: process of how stars are formed and then burn and

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Speaker 1: then die, so we can think about how often that

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Speaker 1: can happen um And so you know, the way that

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Speaker 1: stars form is that you have these big clumps of

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Speaker 1: gas and dust, these things like these giant molecular clouds.

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Speaker 1: And I think the thing that people might not realize

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Speaker 1: is that for stars to form, you need cold stuff

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Speaker 1: because what you need is gravity to pull this stuff together. Remember,

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Speaker 1: the stars are a delicate balancing app between gravity is

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Speaker 1: trying to pull things together to make it more dense,

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Speaker 1: and pressure that's like resisting being compacted too much. But

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Speaker 1: gravity is really weak. So to get a star to form,

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Speaker 1: you need like a really pretty cold, pretty huge clump

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Speaker 1: of stuff near each other and it gathers together to

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Speaker 1: form a star and reach that critical density where fusion

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Speaker 1: can start. So you need to start with something like

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Speaker 1: ten to twenty degrees kelvin m m. And it has

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Speaker 1: to be cold because if it's too hot, it won't

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Speaker 1: clump together, like it'll just kind of keep missing itself

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Speaker 1: and it won't compress. Yeah, because if it's too hot,

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Speaker 1: that means that the particles are moving around too fast,

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Speaker 1: and so gravity just can't slow them down exactly. So

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Speaker 1: they need to be like basically motionless so that gravity

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Speaker 1: can gently tug on them and pull them together into

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Speaker 1: a star. Maybe it's too hot, it just won't happen, right,

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Speaker 1: And we've talked about in another episodes about how you

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Speaker 1: need like a certain minimum amount of stuff, right, like

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Speaker 1: more than a jupiter's worth of stuff. And also it's

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Speaker 1: about kind of the kind of stuff it is, right like,

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Speaker 1: the only certain kinds of stuff will clump and form

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Speaker 1: into start. Yeah, in order to get fusion going, you

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Speaker 1: need like at least like eighty times the massive Jupiter.

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Speaker 1: You can get clumps forming that are smaller than that,

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Speaker 1: they just won't necessarily start fusion. But typically these cloud

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Speaker 1: it's where stars are formed, or like a thousand light

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Speaker 1: years long, and they have a huge amount of material

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Speaker 1: like thousands two million times the mass of our sun,

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Speaker 1: and inside that you have like denser regions, which astronomers

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Speaker 1: referred to by the technical word clumps, and then inside

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Speaker 1: that are like slightly denser regions they call cores, and

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Speaker 1: that's usually where stars are actually formed, but it's not

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Speaker 1: something we understand in great detail, you know, like what

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Speaker 1: actually makes those cores, what triggers them to collapse into

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Speaker 1: a star or some people think like and nearby supernova

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Speaker 1: has to come through and the shock wave there can

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Speaker 1: trigger the collapse to make the star. But you're right.

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Speaker 1: You can also be a variety of material. But you know,

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Speaker 1: when the Big Bang happened, it made mostly hydrogen, and

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Speaker 1: so most of the stuff in the universe is still hydrogen.

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Speaker 1: There's a little bit of helium also, and so most

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Speaker 1: of the stars in the universe are made of mostly

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Speaker 1: hydrogen and helium. And then there's heavier stuff, right, And

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Speaker 1: it's important that it's hydrogen and or helium because those

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Speaker 1: are sort of the lightest elements, right, And so to

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Speaker 1: make a proper star, you need fusee in and so

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Speaker 1: it's easier to sort of merge together the lighter elements

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Speaker 1: than it is to merge together like the heavy elements.

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Speaker 1: That's right. To fuse hydrogen, you need a lower temperature

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Speaker 1: than you do to fuse helium, which is a lower

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Speaker 1: temperature than you need to fuse lithium. Etcetera, etcetera. So

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Speaker 1: if you want to start a sun, you better start

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Speaker 1: with a lot of hydrogen and something I think it's

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Speaker 1: funny is that astronomers referred to anything that's not hydrogen

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Speaker 1: or helium as a metal, by which I think they

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Speaker 1: just mean like, oh, this is a serious heavy element.

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Speaker 1: But you know, like chemists or like oxygen is not

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Speaker 1: a metal. You know, carbon is not a metal, but

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Speaker 1: according to astronomers, it's helium, hydrogen or metals. It's like

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Speaker 1: there's only three elements of the periodic table for astronomers, hydrogen, helium,

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Speaker 1: and metal. That's it. It's sort of like musical taste,

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Speaker 1: like someone who's really into classical music thinks anything not

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Speaker 1: classicals like heavy metal inten that's right e either Mozart

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Speaker 1: or it's hip hop exactly. Yeah, So you need a

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Speaker 1: lot of hydrogen and helium, which is good because the

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Speaker 1: universe started with a whole bunch of hydrogen and lium, right,

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Speaker 1: But you can also make it like if I have

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Speaker 1: a whole bunch of oxygen, can I make a star

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Speaker 1: out of just oxygen? You could make a star out

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Speaker 1: of just oxygen, and if you had enough of it

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Speaker 1: and it was cold enough and near enough to itself,

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Speaker 1: then it could pull itself together with gravity, and you

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Speaker 1: could even you know, get oxygen fusion happening to make

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Speaker 1: heavy your stuff. That certainly is possible. Could that happen naturally?

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Speaker 1: It wouldn't happen naturally because the amount of oxygen in

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Speaker 1: the universe is tiny compared to the other stuff in

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Speaker 1: the universe. So, you know, most of the stuff in

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Speaker 1: the universe still hydrogen. You know, we've been burning stars

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Speaker 1: for billions of years to make quote unquote metals like oxygen,

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Speaker 1: but we haven't made that much progress. You know, it's

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Speaker 1: still overwhelmingly hydrogen. So you make a random star, it's

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Speaker 1: gonna be mostly hydrogen helium. Now, the like fraction of

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Speaker 1: metals in stars has been increasing as the universe goes up,

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Speaker 1: just because there's more of that stuff around. But to

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Speaker 1: get like a star sized blob of oxygen by itself,

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Speaker 1: that's never gonna happen. Well, I mean, I guess in

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Speaker 1: infinite universe somewhere it's happening, right, Or like we could

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Speaker 1: maybe engineering maybe somehow. That sounds like a fun project.

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Speaker 1: Let's make an oxygen Why do you do that? What

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Speaker 1: are you doing this? Weekend. Oh, I got some you know,

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Speaker 1: house projects going and make an oxygen star. Yeah, clean

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Speaker 1: mic bathroom, and also make a star. All right, So

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Speaker 1: then that's kind of how the stars form, and I

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Speaker 1: think we've talked in other episodes about kind of what

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Speaker 1: happens then, right, like, eventually all of that hydrogen and

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Speaker 1: helium merges into heavier elements, and those merging two even

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Speaker 1: heavier elements, and at some point the star burns out

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Speaker 1: or kind of implodes. Right, there's a couple of possibility therapy.

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Speaker 1: As fusion happens, it creates heavier elements, and those heavier

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Speaker 1: elements are then fuel for the next round of fusion,

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Speaker 1: which are fuel for the next round of fusion. But

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Speaker 1: at some point it stops. When you get up to

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Speaker 1: iron and iron can't fuse and create energy. If you

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Speaker 1: fuse iron and iron, you actually lose energy, and so

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Speaker 1: that cools down the star, and so it's sort of

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Speaker 1: like it creates I should eventually it snuffs the star out,

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Speaker 1: and so the star is no longer able to resist

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Speaker 1: the gravitational forces because it's not producing enough radiation pressure

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Speaker 1: to resist that collapse. And then depending on the mass

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Speaker 1: of the star, either you know, just like cools down

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Speaker 1: into a white dwarf, or maybe it goes supernova and

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Speaker 1: blows its material out, or maybe it goes supernova and

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Speaker 1: the core becomes a black hole. Depends on exactly how

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Speaker 1: much stuff you started from. But yeah, eventually stars do

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Speaker 1: fizzle out, right, So the star is born, it lives,

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Speaker 1: and it dies, and that's one generation of star. And

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Speaker 1: then how it the next generation of star form? Then

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Speaker 1: if it just snuffs out, or if it turns into

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Speaker 1: a black hole, because it doesn't capture all of the

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Speaker 1: materials into the star and sort of hold onto them forever.

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Speaker 1: Even in the scenario where you create a black hole,

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Speaker 1: a large part of the material of the original star

402
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Speaker 1: is blown out into the universe. Like our son for example,

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Speaker 1: it won't go supernova and it won't go into a

404
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Speaker 1: black hole, but still it's going to have this big

405
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Speaker 1: red giant phase when it's burning helium and it puffs

406
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Speaker 1: up to be really really huge, and a lot of

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Speaker 1: the material gets really dispersed, and then it blows that

408
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Speaker 1: stuff out into the universe. So when you end up

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Speaker 1: with like a core that's left over from a star

410
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Speaker 1: doesn't have all the material at the star, some of

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Speaker 1: the stuff from the star is blown out into the universe,

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Speaker 1: and then you can get remixed into the basic ingredients

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Speaker 1: of hydrogen helium to form the next stars. So that's

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Speaker 1: how you can sort of recycle material that's made in

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Speaker 1: a star into other future stars or planets or people. Oh,

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Speaker 1: I see, it's like when a star dies, most of

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Speaker 1: its materials go out back into space, like you compost

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Speaker 1: it kind of, you know, you don't throw it on

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Speaker 1: in the trash, you know, it doesn't all get buried

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Speaker 1: in a coffin, is put bike into the soil. Yes,

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Speaker 1: some of it is sort of lost to black holes

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Speaker 1: or maybe to a white dwarf that eventually will cool

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Speaker 1: into a black dwarf and can't really be used again.

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Speaker 1: But a lot of it is tossed back out there

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Speaker 1: as fodder or ingredients for the next generation of stars,

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Speaker 1: which will have a higher metal percentage than the previous generation,

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Speaker 1: just because this star has now made more metals out

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Speaker 1: of the wrong ingredients. Right, they'll be heavier metal, more extreme.

429
00:22:06,680 --> 00:22:09,040
Speaker 1: But I guess you know, one question I have is, like,

430
00:22:09,160 --> 00:22:11,199
Speaker 1: you know, stars are so far apart, like do you

431
00:22:11,240 --> 00:22:14,240
Speaker 1: actually get mixing of like you know, left or star

432
00:22:14,359 --> 00:22:16,760
Speaker 1: and stuff from one star mixing with left door stuff

433
00:22:16,760 --> 00:22:18,920
Speaker 1: from another star, or is it mostly like it all

434
00:22:18,960 --> 00:22:23,000
Speaker 1: stays within the same you know, recycling area. Stars are

435
00:22:23,080 --> 00:22:25,720
Speaker 1: far apart, but you know they tend to be made

436
00:22:25,800 --> 00:22:28,680
Speaker 1: in clumps. So you have like stellar nurseries, these big

437
00:22:28,720 --> 00:22:31,520
Speaker 1: gas clouds where stars are made, and those gas clouds

438
00:22:31,560 --> 00:22:36,200
Speaker 1: are collected both from the interstellar medium and the intergalactic

439
00:22:36,240 --> 00:22:39,840
Speaker 1: medium and also from old stars. So along a long

440
00:22:39,920 --> 00:22:42,879
Speaker 1: time scale, this stuff really does move around and gather,

441
00:22:43,320 --> 00:22:45,639
Speaker 1: and so stuff doesn't just like stay in one place.

442
00:22:45,680 --> 00:22:48,119
Speaker 1: There are flows and ebbs and currents of all of

443
00:22:48,119 --> 00:22:51,240
Speaker 1: this stuff. All right, Well, so that's one generation of

444
00:22:51,280 --> 00:22:54,360
Speaker 1: a star, and so you can have multiple generations as

445
00:22:54,400 --> 00:22:56,760
Speaker 1: the stars and the stuff goes out and it comes

446
00:22:56,800 --> 00:22:59,639
Speaker 1: back in. And so let's talk about how many generations

447
00:22:59,640 --> 00:23:02,080
Speaker 1: there have been of stars in the universe, and then

448
00:23:02,160 --> 00:23:05,120
Speaker 1: let's talk about what the future holds. But first let's

449
00:23:05,119 --> 00:23:20,800
Speaker 1: take a quick break. Al Right, how many star generations

450
00:23:21,119 --> 00:23:24,679
Speaker 1: have there been and will there be in the universe? Thaniel,

451
00:23:24,680 --> 00:23:27,480
Speaker 1: we talked about one generation of a star, and we

452
00:23:27,560 --> 00:23:29,879
Speaker 1: know that if a star eventually dies and all this

453
00:23:29,920 --> 00:23:31,840
Speaker 1: stuff kind of goes out into space and then it

454
00:23:32,240 --> 00:23:36,000
Speaker 1: maybe gets combined, and then that stuff then by gravity,

455
00:23:36,080 --> 00:23:39,680
Speaker 1: I guess it cools off and then comes together again,

456
00:23:39,760 --> 00:23:42,160
Speaker 1: and then maybe it ignites and then creates a new

457
00:23:42,200 --> 00:23:45,680
Speaker 1: generation of a star. But eventually that star will die.

458
00:23:47,000 --> 00:23:49,640
Speaker 1: So and this happens over I guess millions of years

459
00:23:49,760 --> 00:23:52,119
Speaker 1: or billions of years. It depends a lot on the

460
00:23:52,200 --> 00:23:55,440
Speaker 1: size of the star. So a larger star will burn

461
00:23:55,520 --> 00:23:58,280
Speaker 1: hotter because it's core has a lot more pressure on it,

462
00:23:58,359 --> 00:24:01,320
Speaker 1: so it's temperature is higher. It burns through its material

463
00:24:01,440 --> 00:24:04,399
Speaker 1: much much faster. So the bigger the star, the shorter

464
00:24:04,520 --> 00:24:07,679
Speaker 1: its lifespan. Like the stars a few hundred times the

465
00:24:07,720 --> 00:24:10,120
Speaker 1: mass of the Sun, it might only live like two

466
00:24:10,200 --> 00:24:14,000
Speaker 1: to five million years. If a star is really really small,

467
00:24:14,240 --> 00:24:16,320
Speaker 1: like much smaller than the mass of the Sun, like

468
00:24:16,440 --> 00:24:19,560
Speaker 1: right on the threshold, it might burn for a trillion years,

469
00:24:19,960 --> 00:24:22,359
Speaker 1: whereas our star, you know, the Sun is going to

470
00:24:22,440 --> 00:24:26,000
Speaker 1: burn for about ten billion years. So the serving size

471
00:24:26,080 --> 00:24:28,840
Speaker 1: you get at the very beginning totally determines how long

472
00:24:28,880 --> 00:24:32,080
Speaker 1: you will burn for. Interesting, it's sort of like rock stars.

473
00:24:32,080 --> 00:24:35,840
Speaker 1: Some of them, you know, flame out after a one album,

474
00:24:35,960 --> 00:24:39,480
Speaker 1: and some of them have a long and nice career.

475
00:24:39,560 --> 00:24:42,000
Speaker 1: I guess Bob Dylan is very low mass, right, because

476
00:24:42,000 --> 00:24:45,000
Speaker 1: he's like on album fifty. Yeah, and whereas you know,

477
00:24:45,359 --> 00:24:48,199
Speaker 1: Rick Astly was a supernova. But so you're telling me

478
00:24:48,240 --> 00:24:51,320
Speaker 1: that each generation of a star, there's sort of no

479
00:24:51,480 --> 00:24:53,720
Speaker 1: fixed time period. Like in human years, you can think

480
00:24:53,720 --> 00:24:56,919
Speaker 1: of a generation as being roughly, I don't know, thirty

481
00:24:57,040 --> 00:24:59,359
Speaker 1: forty years, but in a star it could be like

482
00:24:59,480 --> 00:25:01,800
Speaker 1: one year or hundred years. Yeah, but it is a

483
00:25:01,880 --> 00:25:04,480
Speaker 1: sort of similar to humans, right. Some humans live a

484
00:25:04,520 --> 00:25:07,480
Speaker 1: long time and have kids in their nineties, like Charlie Chaplin.

485
00:25:07,600 --> 00:25:10,080
Speaker 1: Some people have kids when they're teenagers, and so over

486
00:25:10,119 --> 00:25:13,280
Speaker 1: fifty years you might have like three generations. It's sort

487
00:25:13,280 --> 00:25:15,200
Speaker 1: of similar with stars. And that's why I was saying earlier,

488
00:25:15,240 --> 00:25:17,840
Speaker 1: it's not exactly clear, you know, to say like which

489
00:25:17,920 --> 00:25:20,560
Speaker 1: generation a star is in, because if I have material

490
00:25:20,600 --> 00:25:23,919
Speaker 1: from all sorts of sources, including two generation stars or

491
00:25:23,920 --> 00:25:27,040
Speaker 1: three generation stars, or even pristine material left over from

492
00:25:27,080 --> 00:25:29,720
Speaker 1: the Big Bang. So it's tricky, but you can sort

493
00:25:29,760 --> 00:25:33,960
Speaker 1: of organize roughly into a few generations when we look

494
00:25:34,000 --> 00:25:36,439
Speaker 1: back into the cosmic history, you mean, sort of like

495
00:25:36,640 --> 00:25:39,680
Speaker 1: the average or maybe just looking at like our son,

496
00:25:39,920 --> 00:25:42,000
Speaker 1: we know how many generations it's at yeah, Well, we

497
00:25:42,040 --> 00:25:44,920
Speaker 1: don't know actually how many generations the history of our

498
00:25:44,960 --> 00:25:48,600
Speaker 1: son features, because in theory, you could have a series

499
00:25:48,800 --> 00:25:52,600
Speaker 1: of really really massive stars hundreds and hundreds of times

500
00:25:52,640 --> 00:25:55,040
Speaker 1: the mass of the Sun that die and burnout and

501
00:25:55,119 --> 00:25:57,879
Speaker 1: die and burnout and dying burnout. You could have, you know,

502
00:25:58,080 --> 00:26:00,880
Speaker 1: material that's been in a hundred of those stars that's

503
00:26:00,920 --> 00:26:03,240
Speaker 1: around there in the universe right now. So we don't

504
00:26:03,280 --> 00:26:05,720
Speaker 1: actually know for any given piece of material how many

505
00:26:05,800 --> 00:26:08,400
Speaker 1: stars it's been in. What we can do is look

506
00:26:08,480 --> 00:26:11,119
Speaker 1: at the stars we see in our galaxy and in

507
00:26:11,200 --> 00:26:14,400
Speaker 1: other galaxies, and we notice something interesting. We noticed sort

508
00:26:14,400 --> 00:26:18,560
Speaker 1: of like two rough populations of stars. Stars that seem

509
00:26:18,640 --> 00:26:21,000
Speaker 1: to be sort of a lot older and have less

510
00:26:21,040 --> 00:26:23,040
Speaker 1: medals in them, and then start the tend to be

511
00:26:23,119 --> 00:26:26,720
Speaker 1: younger and bluer and hotter and have more medals in them.

512
00:26:26,840 --> 00:26:28,880
Speaker 1: But then each of those would be in a sort

513
00:26:28,880 --> 00:26:31,119
Speaker 1: of different generation, right, Like some of them might be

514
00:26:31,760 --> 00:26:34,960
Speaker 1: you know, a hundred ten generation and someone might be,

515
00:26:35,440 --> 00:26:38,400
Speaker 1: you know, fifteen or five. That's right. But the interesting

516
00:26:38,480 --> 00:26:41,280
Speaker 1: thing about these two populations, so we have like the

517
00:26:41,320 --> 00:26:43,920
Speaker 1: older ones and the younger ones, the older ones we

518
00:26:44,000 --> 00:26:47,240
Speaker 1: call population two stars, is that they all seem to

519
00:26:47,240 --> 00:26:49,959
Speaker 1: be really really old. They all seem to have formed

520
00:26:50,000 --> 00:26:54,280
Speaker 1: like eleven, twelve, thirteen billion years ago and to still

521
00:26:54,359 --> 00:26:58,879
Speaker 1: be around. So those stars probably are a second generation

522
00:26:58,960 --> 00:27:02,360
Speaker 1: stars at most because they formed very very early on

523
00:27:02,480 --> 00:27:04,800
Speaker 1: in the universe and they're still around. So that limits

524
00:27:04,800 --> 00:27:08,000
Speaker 1: like how many generations of stars there could be before them.

525
00:27:08,400 --> 00:27:10,760
Speaker 1: The other population of stars we see, what we call

526
00:27:10,800 --> 00:27:14,480
Speaker 1: population one. They're still forming today. Oh, I see, you're

527
00:27:14,520 --> 00:27:16,560
Speaker 1: sort of categorizing what do you see out there in

528
00:27:16,560 --> 00:27:19,400
Speaker 1: the universe. You're not categorizing by generation. You just sort

529
00:27:19,440 --> 00:27:23,040
Speaker 1: of looking out there and categorizing by age, Like, Wow,

530
00:27:23,080 --> 00:27:26,040
Speaker 1: does over there look pretty young, so they must be

531
00:27:26,280 --> 00:27:29,040
Speaker 1: later generation, but these over here look really old, so

532
00:27:29,080 --> 00:27:30,560
Speaker 1: they must be kind of like one of the O

533
00:27:30,720 --> 00:27:33,720
Speaker 1: G generation. Yeah. It's just like looking at humans and

534
00:27:33,720 --> 00:27:36,440
Speaker 1: you're like, well, this bunch of people all are similar

535
00:27:36,480 --> 00:27:38,640
Speaker 1: and come from a similar era and act the same way.

536
00:27:38,640 --> 00:27:41,240
Speaker 1: So we'll call them boomers, right, and these folks will

537
00:27:41,240 --> 00:27:43,400
Speaker 1: call gen z ers. And you know, there's not a

538
00:27:43,400 --> 00:27:48,080
Speaker 1: crisp delineation between generations between millennials and gen xers and whatever.

539
00:27:48,240 --> 00:27:51,000
Speaker 1: But it's sort of a rough rule of thumb, especially

540
00:27:51,000 --> 00:27:53,200
Speaker 1: when we look out there we notice, just like we

541
00:27:53,320 --> 00:27:56,680
Speaker 1: noticed in human populations, these sort of clusters of stars

542
00:27:56,720 --> 00:27:58,960
Speaker 1: that have similar properties. All right, So then you can

543
00:27:59,000 --> 00:28:03,120
Speaker 1: categorize kind of age out there by what we see

544
00:28:03,200 --> 00:28:04,919
Speaker 1: right now, and so step us through what are the

545
00:28:04,960 --> 00:28:08,520
Speaker 1: different populations. So what we've seen are these two populations

546
00:28:08,520 --> 00:28:11,680
Speaker 1: population one in population too. And you know these are

547
00:28:11,720 --> 00:28:14,320
Speaker 1: historical names given by a German astronomer back in the

548
00:28:14,359 --> 00:28:16,199
Speaker 1: forties when he was looking at these stars and he

549
00:28:16,240 --> 00:28:19,240
Speaker 1: saw that a bunch of them were bluer stars and

550
00:28:19,280 --> 00:28:21,680
Speaker 1: these were tend to be like in the galactic disc,

551
00:28:21,920 --> 00:28:24,520
Speaker 1: right far from the center, and that closer to the

552
00:28:24,520 --> 00:28:26,960
Speaker 1: center you had more red stars. So we called them

553
00:28:27,040 --> 00:28:29,639
Speaker 1: population one in population two. He didn't understand at the

554
00:28:29,640 --> 00:28:32,320
Speaker 1: time what it meant that population two stars were probably

555
00:28:32,400 --> 00:28:35,840
Speaker 1: much much older. In population one stars were more recent,

556
00:28:36,080 --> 00:28:38,640
Speaker 1: But we know that now and it makes sort of

557
00:28:38,720 --> 00:28:42,160
Speaker 1: sense because you know, as stars live in the galaxy,

558
00:28:42,200 --> 00:28:45,680
Speaker 1: they tend to slow down in their orbit and sort

559
00:28:45,680 --> 00:28:48,440
Speaker 1: of fall towards the center. So the center of the

560
00:28:48,440 --> 00:28:53,160
Speaker 1: galaxies mostly these older stars that formed, like you know, eleven, twelve,

561
00:28:53,240 --> 00:28:56,600
Speaker 1: thirteen billion years ago, and they have less metals in

562
00:28:56,640 --> 00:28:59,240
Speaker 1: them than the other stars because they were formed in

563
00:28:59,280 --> 00:29:01,640
Speaker 1: the time when the verse had less metal in it,

564
00:29:01,640 --> 00:29:04,840
Speaker 1: it was more hydrogen. So those are the population two stars.

565
00:29:04,840 --> 00:29:07,360
Speaker 1: They tend to be like making up the bulge of

566
00:29:07,400 --> 00:29:10,480
Speaker 1: the galaxy. And then also they're in these weird globular

567
00:29:10,560 --> 00:29:12,959
Speaker 1: clusters that sort of orbit the galaxy that we had

568
00:29:13,000 --> 00:29:15,400
Speaker 1: a whole fun podcast episode about. I guess maybe a

569
00:29:15,480 --> 00:29:17,400
Speaker 1: question is how do we know how old they are?

570
00:29:17,720 --> 00:29:20,160
Speaker 1: And how do we know how much metal is in them?

571
00:29:20,200 --> 00:29:22,840
Speaker 1: Like is it from like the spectrum of the light

572
00:29:22,880 --> 00:29:25,920
Speaker 1: that comes from them or the distance? Like how do

573
00:29:25,960 --> 00:29:27,960
Speaker 1: we know their age from how far they are? Or

574
00:29:28,280 --> 00:29:29,920
Speaker 1: like how can we tell their age? And is that

575
00:29:29,960 --> 00:29:33,160
Speaker 1: polite to ask? That's a little tricky their age. What

576
00:29:33,240 --> 00:29:34,640
Speaker 1: you can do is you can look at the color

577
00:29:34,680 --> 00:29:37,680
Speaker 1: of the star. Stars tend to be bluer when they're

578
00:29:37,760 --> 00:29:42,520
Speaker 1: younger because bluer means hotter, and so hotter stars don't

579
00:29:42,600 --> 00:29:45,080
Speaker 1: last as long, they don't live as long, and so

580
00:29:45,120 --> 00:29:47,560
Speaker 1: if you see a star that's blue, that means it

581
00:29:47,680 --> 00:29:50,040
Speaker 1: must be younger because they just don't have that long

582
00:29:50,040 --> 00:29:52,400
Speaker 1: a life cycle. Like if you see a cat, you

583
00:29:52,440 --> 00:29:54,320
Speaker 1: know that cat is not a hundred years old because

584
00:29:54,320 --> 00:29:56,520
Speaker 1: there just aren't any hundred year old cats. So if

585
00:29:56,520 --> 00:29:58,600
Speaker 1: you see blue stars, you know that they tend to

586
00:29:58,640 --> 00:30:03,719
Speaker 1: be younger. Red stars are either old stars or they

587
00:30:03,800 --> 00:30:06,760
Speaker 1: might be smaller stars. And so it's not exactly clear

588
00:30:06,800 --> 00:30:09,640
Speaker 1: always when you look at a star's color to tell

589
00:30:09,680 --> 00:30:12,040
Speaker 1: its age. But what we do see is that population

590
00:30:12,120 --> 00:30:14,240
Speaker 1: one stars tend to have a lot of blue stars

591
00:30:14,240 --> 00:30:16,000
Speaker 1: in them, which means that they're young, whereas in the

592
00:30:16,040 --> 00:30:19,200
Speaker 1: bulge there aren't very many blue stars. So let's suggests

593
00:30:19,200 --> 00:30:21,280
Speaker 1: that there aren't many young stars there, and most of

594
00:30:21,280 --> 00:30:24,160
Speaker 1: those are pretty old. Oh I see, Wait, you're grouping

595
00:30:24,200 --> 00:30:27,560
Speaker 1: them by location or by how old you think they are? Well, both,

596
00:30:27,600 --> 00:30:29,560
Speaker 1: and there's a correlation there, right. The stars in the

597
00:30:29,600 --> 00:30:33,280
Speaker 1: center tend to be reader and older, and the stars

598
00:30:33,280 --> 00:30:36,520
Speaker 1: in the disc tend to be bluer and younger. All right,

599
00:30:36,560 --> 00:30:38,640
Speaker 1: So then I guess you can assume that the younger

600
00:30:38,720 --> 00:30:42,560
Speaker 1: stars are maybe a later generation, right because they were

601
00:30:42,560 --> 00:30:45,960
Speaker 1: born more recently, whereas the older stars they might be

602
00:30:46,080 --> 00:30:48,400
Speaker 1: even one of the original generations, right, because if you're

603
00:30:48,440 --> 00:30:51,440
Speaker 1: saying they're fourteen billion years old, that's when the universe started. Yeah,

604
00:30:51,480 --> 00:30:53,560
Speaker 1: we don't think that they're part of the original generation.

605
00:30:54,040 --> 00:30:57,240
Speaker 1: They are like you know, eleven to thirteen billion years old,

606
00:30:57,280 --> 00:30:59,200
Speaker 1: so we think they formed, like you know, a billion

607
00:30:59,280 --> 00:31:02,240
Speaker 1: years after the start of the universe. He also asked

608
00:31:02,240 --> 00:31:03,800
Speaker 1: about how we can tell what they're made at it.

609
00:31:03,840 --> 00:31:06,719
Speaker 1: That's another clue. When we look at the spectrum from

610
00:31:06,760 --> 00:31:09,760
Speaker 1: the stars, how they're glowing, we can tell what's inside

611
00:31:09,840 --> 00:31:13,600
Speaker 1: the star because different elements glow at different temperatures. They

612
00:31:13,600 --> 00:31:16,080
Speaker 1: tend to like get excited at different energy levels, so

613
00:31:16,080 --> 00:31:18,960
Speaker 1: they have like a characteristic fingerprint. So just as you said,

614
00:31:18,960 --> 00:31:21,280
Speaker 1: we can look at the spectrum of light that tells us, like,

615
00:31:21,600 --> 00:31:23,520
Speaker 1: you know, how much light in there at this frequency

616
00:31:23,520 --> 00:31:26,040
Speaker 1: and how much of that frequency tells you exactly the

617
00:31:26,080 --> 00:31:28,480
Speaker 1: composition of the star. And what we see is that

618
00:31:28,560 --> 00:31:30,959
Speaker 1: these stars tend to have a lot less metal in

619
00:31:31,000 --> 00:31:33,760
Speaker 1: them than the stars that are forming today, like even

620
00:31:33,800 --> 00:31:37,560
Speaker 1: our sun. So these population two stars can have like

621
00:31:37,880 --> 00:31:41,400
Speaker 1: a hundreds or thousands as much iron in them, for example,

622
00:31:41,760 --> 00:31:44,280
Speaker 1: as our sun. So that also suggests that they were

623
00:31:44,280 --> 00:31:47,560
Speaker 1: formed earlier in the universe when the universe had less

624
00:31:47,600 --> 00:31:49,640
Speaker 1: metal in it. Oh, I see right, because as the

625
00:31:49,760 --> 00:31:53,240
Speaker 1: as the star progresses through its life, it makes metals, right,

626
00:31:53,320 --> 00:31:55,479
Speaker 1: But then if it's been alive for that long or

627
00:31:55,520 --> 00:31:57,240
Speaker 1: burning for that long, wouldn't it have made a lot

628
00:31:57,280 --> 00:31:59,720
Speaker 1: of metals, But by now it makes metals, but you know,

629
00:31:59,800 --> 00:32:02,160
Speaker 1: not that much. And that's when a star burns. It's

630
00:32:02,200 --> 00:32:05,520
Speaker 1: mostly burning helium and hydrogen. It doesn't convert all of

631
00:32:05,520 --> 00:32:08,600
Speaker 1: that into iron, for example. But the fast burning ones

632
00:32:08,640 --> 00:32:13,000
Speaker 1: do create metals more quickly, I guess, or at east

633
00:32:13,000 --> 00:32:17,160
Speaker 1: generation burns and is born, then you sort of increment

634
00:32:17,240 --> 00:32:20,440
Speaker 1: in metalicity, but not every star makes it all the

635
00:32:20,440 --> 00:32:23,520
Speaker 1: way up to iron. Like, you need enough stuff in

636
00:32:23,560 --> 00:32:25,960
Speaker 1: the star to create the conditions so you can get

637
00:32:26,000 --> 00:32:29,160
Speaker 1: hot enough so you can fuse the stuff to make iron.

638
00:32:29,440 --> 00:32:32,560
Speaker 1: Some stars stop after making helium or lithium or carbon

639
00:32:32,800 --> 00:32:35,239
Speaker 1: or neon or whatever, depending on how much mass they

640
00:32:35,240 --> 00:32:37,360
Speaker 1: have in the temperature that they achieve. All right, so

641
00:32:37,360 --> 00:32:39,360
Speaker 1: then what does that tell us about how many generations

642
00:32:39,400 --> 00:32:41,800
Speaker 1: there have been in the universe? Since we know that

643
00:32:42,440 --> 00:32:44,840
Speaker 1: you know, the older stars are only a few generations

644
00:32:44,920 --> 00:32:47,920
Speaker 1: in but do we know how many generations the younger

645
00:32:47,960 --> 00:32:51,560
Speaker 1: stars are or what generation they're in. Yeah, we're not sure,

646
00:32:51,600 --> 00:32:55,360
Speaker 1: but the current thinking is that there are roughly three generations.

647
00:32:55,400 --> 00:32:58,800
Speaker 1: So these stars we call population one. These younger stars

648
00:32:58,840 --> 00:33:01,440
Speaker 1: like our sun that are out around the disc, including

649
00:33:01,440 --> 00:33:03,240
Speaker 1: stars that are just forming and stars that are a

650
00:33:03,280 --> 00:33:05,240
Speaker 1: few billion years old. These are the ones with a

651
00:33:05,280 --> 00:33:07,040
Speaker 1: lot of metals in them, like they start with like

652
00:33:07,320 --> 00:33:10,040
Speaker 1: one to four percent of them are made out of metal.

653
00:33:10,400 --> 00:33:12,960
Speaker 1: So that's population one. And then the population to the

654
00:33:12,960 --> 00:33:15,240
Speaker 1: one sort of in the bulge of the galaxy, the

655
00:33:15,280 --> 00:33:18,080
Speaker 1: older ones. We call those population two. And we think

656
00:33:18,120 --> 00:33:20,920
Speaker 1: that there was a population before that, that very early

657
00:33:21,040 --> 00:33:23,600
Speaker 1: on in the universe, before any of the stars that

658
00:33:23,600 --> 00:33:26,480
Speaker 1: are burning today were formed, that there was an initial

659
00:33:26,560 --> 00:33:29,200
Speaker 1: star forming phase, but that all those stars are gone.

660
00:33:29,280 --> 00:33:32,000
Speaker 1: Now that those stars didn't last very long, just a

661
00:33:32,000 --> 00:33:35,320
Speaker 1: few million years, maybe tens or hundreds of millions of years,

662
00:33:35,480 --> 00:33:37,640
Speaker 1: but that those are all gone, and we call those

663
00:33:37,760 --> 00:33:41,640
Speaker 1: population three stars. So we've never actually seen one because

664
00:33:41,640 --> 00:33:43,840
Speaker 1: they're so old, they would be very very distant and

665
00:33:43,880 --> 00:33:46,120
Speaker 1: so very hard to make out. So that's sort of

666
00:33:46,120 --> 00:33:48,680
Speaker 1: the rough timelines. Population three stars were the first in

667
00:33:48,800 --> 00:33:52,080
Speaker 1: population too, and now today we're making population one stars.

668
00:33:52,840 --> 00:33:55,480
Speaker 1: I feel like you picked the opposite order, like the

669
00:33:55,560 --> 00:33:58,960
Speaker 1: higher than the number of population the first in order

670
00:33:59,000 --> 00:34:01,320
Speaker 1: of time. I know, because the next generation of stars

671
00:34:01,360 --> 00:34:04,200
Speaker 1: gonna be what population zero zero and then minus one.

672
00:34:04,920 --> 00:34:07,720
Speaker 1: I think you named yourself until corner there. Physicist, I

673
00:34:07,760 --> 00:34:09,680
Speaker 1: think we certainly did. It's sort of like you know,

674
00:34:09,760 --> 00:34:12,680
Speaker 1: deciding the charge of the electron, like whoops, that was

675
00:34:12,800 --> 00:34:14,960
Speaker 1: not the best choice. But I don't think at the

676
00:34:15,000 --> 00:34:18,200
Speaker 1: time we really understood the context is sort of the

677
00:34:18,280 --> 00:34:20,960
Speaker 1: historical sweep of all of this stuff, or we definitely

678
00:34:20,960 --> 00:34:22,759
Speaker 1: would have named it something else. All Right, So there

679
00:34:22,840 --> 00:34:26,120
Speaker 1: was an original generation of stars. But those stars you're

680
00:34:26,120 --> 00:34:29,160
Speaker 1: saying they're all gone because I guess in the early

681
00:34:29,239 --> 00:34:32,320
Speaker 1: universe things were sort of like hot and volatile, and

682
00:34:32,400 --> 00:34:34,640
Speaker 1: so all those stars burned out pretty quickly. Yeah, we

683
00:34:34,719 --> 00:34:37,319
Speaker 1: think that those stars were really big. The very very

684
00:34:37,360 --> 00:34:40,799
Speaker 1: first stars were like hundreds of millions of times the

685
00:34:40,840 --> 00:34:43,200
Speaker 1: mass of the Sun. It was harder to make smaller

686
00:34:43,239 --> 00:34:46,200
Speaker 1: stars early on because there wasn't as much metal, so

687
00:34:46,200 --> 00:34:48,840
Speaker 1: it's difficult to get like a big blob of stuff

688
00:34:48,880 --> 00:34:51,239
Speaker 1: too cool. Like if you have some metal that can

689
00:34:51,320 --> 00:34:54,200
Speaker 1: sede a core to gather stuff together, it's like a

690
00:34:54,200 --> 00:34:56,520
Speaker 1: heavier spot. But if you just have a big cloud

691
00:34:56,560 --> 00:34:59,440
Speaker 1: of gaseous hydrogen, it's harder to get like a small

692
00:34:59,480 --> 00:35:02,359
Speaker 1: clump to other. So these first stars were probably like

693
00:35:02,719 --> 00:35:05,160
Speaker 1: hundreds of times the mass of the Sun and then

694
00:35:05,239 --> 00:35:08,080
Speaker 1: burning for only like a few million years and dying

695
00:35:08,120 --> 00:35:11,239
Speaker 1: at supernova after making a little bit of you know

696
00:35:11,280 --> 00:35:14,359
Speaker 1: what astronomers would call medals. But again, we haven't seen those,

697
00:35:14,400 --> 00:35:18,520
Speaker 1: so they're they're hypothetical. Like we've seen really really distant galaxies,

698
00:35:18,640 --> 00:35:20,920
Speaker 1: some of the first galaxies that ever formed, but we

699
00:35:20,960 --> 00:35:24,000
Speaker 1: can't resolve the stars in those galaxies, so we can't

700
00:35:24,040 --> 00:35:27,560
Speaker 1: say we've ever seen a population three star. Interesting that

701
00:35:27,840 --> 00:35:30,520
Speaker 1: they're only sort of in our imagination or in our

702
00:35:30,680 --> 00:35:33,680
Speaker 1: I guess theories about where the second population of stars

703
00:35:33,719 --> 00:35:36,960
Speaker 1: came from. Yeah, it's like the oral history of your family, right,

704
00:35:37,200 --> 00:35:39,319
Speaker 1: maybe you don't have any pictures of great great great

705
00:35:39,360 --> 00:35:43,240
Speaker 1: grandma Janine or whatever, but maybe your family knows something

706
00:35:43,280 --> 00:35:45,560
Speaker 1: about what she liked for breakfast and that she was

707
00:35:45,560 --> 00:35:48,680
Speaker 1: a rock star. Maybe it was very bright back in

708
00:35:48,719 --> 00:35:51,960
Speaker 1: Lithuania or whatever. So then that first generation burned out

709
00:35:52,000 --> 00:35:56,000
Speaker 1: and that gives the population to which are redder but

710
00:35:56,080 --> 00:35:58,239
Speaker 1: a little bit cooler. And in that population, some of

711
00:35:58,280 --> 00:36:01,759
Speaker 1: that population burned out, and that where the population one

712
00:36:02,320 --> 00:36:05,120
Speaker 1: that we see now and like our son comes from,

713
00:36:05,160 --> 00:36:07,440
Speaker 1: but our son, right, it has a mix of stuff

714
00:36:07,440 --> 00:36:11,000
Speaker 1: in it. It has some stuff, certainly from population two

715
00:36:11,080 --> 00:36:14,840
Speaker 1: stars that burned out, probably some stuff from population three stars,

716
00:36:14,840 --> 00:36:16,880
Speaker 1: but also it has a lot of stuff that hasn't

717
00:36:16,920 --> 00:36:20,120
Speaker 1: done anything since the Big Bang. Because our son is

718
00:36:20,320 --> 00:36:24,200
Speaker 1: seventy hydrogen and twenty percent helium, so it's only like

719
00:36:24,560 --> 00:36:28,000
Speaker 1: one to two percent metals. Most of the stuff in

720
00:36:28,000 --> 00:36:31,200
Speaker 1: our sun is basically on its first act since the

721
00:36:31,200 --> 00:36:33,520
Speaker 1: Big Bang happened. But we still think it's a third

722
00:36:33,560 --> 00:36:36,440
Speaker 1: generation star. Yeah, because it has stuff in it that

723
00:36:36,520 --> 00:36:39,000
Speaker 1: was created from other suns like that one to two

724
00:36:39,000 --> 00:36:41,960
Speaker 1: percent that really changes what a star is. And that

725
00:36:42,080 --> 00:36:44,880
Speaker 1: stuff was made by other suns. And you know, like

726
00:36:45,040 --> 00:36:47,279
Speaker 1: most of the Earth is that kind of stuff, Like

727
00:36:47,320 --> 00:36:49,759
Speaker 1: most of the Earth is not hydrogen or helium. Right,

728
00:36:49,800 --> 00:36:53,600
Speaker 1: So basically everything on our planet came from the death

729
00:36:53,640 --> 00:36:56,840
Speaker 1: of a star, whereas the Sun is mostly pristine. Stuff

730
00:36:56,880 --> 00:36:58,920
Speaker 1: from the Big Bang still got a lot to go

731
00:36:58,960 --> 00:37:02,400
Speaker 1: on and ply more generations. And so I guess the

732
00:37:02,480 --> 00:37:04,479
Speaker 1: question is how good is that stuff in the Sun,

733
00:37:04,560 --> 00:37:08,160
Speaker 1: Like it's good for one more generation or a billion

734
00:37:08,200 --> 00:37:11,560
Speaker 1: more generations? What will the future hold? So let's get

735
00:37:11,560 --> 00:37:26,640
Speaker 1: into that, But first let's take another quick break. Al Right,

736
00:37:26,680 --> 00:37:29,640
Speaker 1: how many generations, so stars will there be in the future.

737
00:37:29,719 --> 00:37:31,400
Speaker 1: We know that our son is sort of like the

738
00:37:31,480 --> 00:37:35,040
Speaker 1: third generation star in the universe's history, and so the

739
00:37:35,160 --> 00:37:37,760
Speaker 1: question is is this like the beginning of the history

740
00:37:37,760 --> 00:37:40,600
Speaker 1: of stars or you know, or do we only have

741
00:37:40,640 --> 00:37:43,200
Speaker 1: a few more generations left. Yeah, it's really fun to

742
00:37:43,239 --> 00:37:46,040
Speaker 1: think about what the future might look like, and you

743
00:37:46,080 --> 00:37:48,480
Speaker 1: have to like think deep, deep into the future of

744
00:37:48,520 --> 00:37:51,760
Speaker 1: the universe. And I think there's sort of two big questions.

745
00:37:51,800 --> 00:37:55,120
Speaker 1: You know. One is like, if you had perfect conditions

746
00:37:55,160 --> 00:37:57,759
Speaker 1: for making stars, so that you could always gather the

747
00:37:57,840 --> 00:38:00,839
Speaker 1: hygien together and healing together to burn it, how long

748
00:38:00,920 --> 00:38:03,760
Speaker 1: would it take to burn all that fuel and convert

749
00:38:03,800 --> 00:38:07,040
Speaker 1: it all to iron for example? You know, that's one question,

750
00:38:07,400 --> 00:38:09,640
Speaker 1: But the reality is that the universe is not a

751
00:38:09,800 --> 00:38:13,839
Speaker 1: perfect laboratory form. Making starts. You need very specific conditions.

752
00:38:14,160 --> 00:38:16,080
Speaker 1: So I think we should also think about, like how

753
00:38:16,120 --> 00:38:18,800
Speaker 1: long the universe will be conducive to star making. You

754
00:38:18,880 --> 00:38:22,160
Speaker 1: might have the ingredients you need to make stars unburned hydrogen,

755
00:38:22,440 --> 00:38:25,600
Speaker 1: but that doesn't necessarily mean that you're gonna be making stars. Well,

756
00:38:25,680 --> 00:38:28,040
Speaker 1: let's think about it. Maybe just our star, Like what's

757
00:38:28,040 --> 00:38:29,959
Speaker 1: gonna happen to our start. We know, we talked about

758
00:38:30,000 --> 00:38:32,160
Speaker 1: how it's going to burn out and sort of blow up,

759
00:38:32,280 --> 00:38:34,879
Speaker 1: get big and then cool down eventually. But and then

760
00:38:35,000 --> 00:38:37,440
Speaker 1: do you think another star will take its place eventually? Well,

761
00:38:37,440 --> 00:38:40,160
Speaker 1: our star is probably going to turn into a white dwarf, right,

762
00:38:40,200 --> 00:38:43,279
Speaker 1: which is just like a hot lump of stuff. No

763
00:38:43,320 --> 00:38:45,799
Speaker 1: longer fusion is happening, but it's still really hot and

764
00:38:45,840 --> 00:38:48,280
Speaker 1: so it's glowing, which is why it's called a white dwarf.

765
00:38:48,840 --> 00:38:50,960
Speaker 1: And white dwarfs are stable, like, we don't think they

766
00:38:51,000 --> 00:38:54,120
Speaker 1: really do anything else. They just sit there and gradually

767
00:38:54,160 --> 00:38:57,000
Speaker 1: cool off until they become a black dwarf, and that

768
00:38:57,040 --> 00:38:59,359
Speaker 1: could take, you know, trillions of years. We don't think

769
00:38:59,360 --> 00:39:01,799
Speaker 1: there are any black dwarfs in the universe right now.

770
00:39:01,800 --> 00:39:04,760
Speaker 1: There's a bunch of white dwarfs sitting there glowing hot,

771
00:39:04,920 --> 00:39:06,800
Speaker 1: but none of them have had enough time to cool

772
00:39:06,840 --> 00:39:09,279
Speaker 1: the black dwarfs. But that doesn't mean that our sun

773
00:39:09,320 --> 00:39:12,200
Speaker 1: won't contribute to the next generation of stars because the

774
00:39:12,239 --> 00:39:14,919
Speaker 1: white dwarf doesn't take all the material from the Sun.

775
00:39:15,080 --> 00:39:17,239
Speaker 1: There's a lot of the material from the Sun that

776
00:39:17,280 --> 00:39:20,279
Speaker 1: will get blown out into maybe a new planetary disk

777
00:39:20,400 --> 00:39:23,560
Speaker 1: for that white dwarf or just out into the interstellar

778
00:39:23,600 --> 00:39:27,200
Speaker 1: medium and contribute to another generation of stars. So our

779
00:39:27,360 --> 00:39:29,879
Speaker 1: star it's going to become a white dwarf and then

780
00:39:30,000 --> 00:39:32,320
Speaker 1: blow out its stuff out into space, which then is

781
00:39:32,360 --> 00:39:37,520
Speaker 1: gonna maybe combined with the hydrogen helium from other stars

782
00:39:37,560 --> 00:39:40,160
Speaker 1: that burned out and then make other stars. Yeah, and

783
00:39:40,200 --> 00:39:43,279
Speaker 1: this happens because the sun before it burns out, before

784
00:39:43,280 --> 00:39:45,920
Speaker 1: it stops fusing, it gets really really big, and the

785
00:39:45,960 --> 00:39:48,160
Speaker 1: outer shells tend to get blown out while the inner

786
00:39:48,160 --> 00:39:51,080
Speaker 1: part collapses. So it seese outer layers of the star

787
00:39:51,320 --> 00:39:53,680
Speaker 1: they're gonna get blown out and they can definitely contribute

788
00:39:53,719 --> 00:39:56,520
Speaker 1: to future stars or a planet. There could be aliens

789
00:39:56,560 --> 00:39:59,480
Speaker 1: ten billion years from now that are eating their cereal

790
00:39:59,520 --> 00:40:02,400
Speaker 1: and thinking, wow, this could have been another star billions

791
00:40:02,400 --> 00:40:04,919
Speaker 1: of years ago, and they would be right. I see,

792
00:40:04,920 --> 00:40:07,520
Speaker 1: when you're eating your cereal, you you are maybe? I

793
00:40:07,520 --> 00:40:10,800
Speaker 1: mean everything is made in the chorus stars, right, and

794
00:40:10,840 --> 00:40:14,640
Speaker 1: anything about hydrogen and yeah, unless you're eating hydrogen for breakfast,

795
00:40:14,760 --> 00:40:18,400
Speaker 1: what you're eating was made in a star. Interesting, not recommended,

796
00:40:18,480 --> 00:40:21,759
Speaker 1: but not as filling or it is I guess pretty

797
00:40:21,760 --> 00:40:25,359
Speaker 1: filling hydrogen the cereal Oh the humanity, Oh, I see,

798
00:40:25,360 --> 00:40:27,520
Speaker 1: so it's not like a star blows up and then

799
00:40:27,600 --> 00:40:30,120
Speaker 1: in its place and you star forms. It's like you

800
00:40:30,200 --> 00:40:34,600
Speaker 1: need this kind of like mixing between the spaces of stars, right, Yeah,

801
00:40:34,640 --> 00:40:36,640
Speaker 1: it's more like you know, when a tree dies and

802
00:40:36,680 --> 00:40:38,919
Speaker 1: it gives its nutrients back into the ground. You don't

803
00:40:38,960 --> 00:40:41,480
Speaker 1: automatically just get a new trine exactly the same spot.

804
00:40:41,840 --> 00:40:45,120
Speaker 1: It just provides nutrients for a future plant to gobble

805
00:40:45,200 --> 00:40:47,919
Speaker 1: up and to build something else. So you're saying one

806
00:40:47,960 --> 00:40:51,120
Speaker 1: scenario is that this keeps happening for a long time.

807
00:40:51,680 --> 00:40:54,120
Speaker 1: You know, you get more generations of star but eventually,

808
00:40:54,160 --> 00:40:56,720
Speaker 1: like all of the hydrogen and helium in the universe

809
00:40:56,920 --> 00:41:00,520
Speaker 1: is going to have been consumed, maybe could be by

810
00:41:00,600 --> 00:41:03,680
Speaker 1: stars and turn into heavier metals. Yeah, I don't think

811
00:41:03,719 --> 00:41:06,680
Speaker 1: that's likely to actually happen in our universe, and we

812
00:41:06,719 --> 00:41:08,920
Speaker 1: can talk about why it'd be difficult to arrange that.

813
00:41:09,000 --> 00:41:12,120
Speaker 1: But in theory, if you engineer the universe to be

814
00:41:12,160 --> 00:41:16,080
Speaker 1: a perfect star making laboratory, then yeah, you could eventually

815
00:41:16,120 --> 00:41:18,319
Speaker 1: burn all the fuel. Like it's one direction. Or we're

816
00:41:18,320 --> 00:41:21,720
Speaker 1: not making more hydrogen, right, We're just decreasing the amount

817
00:41:21,719 --> 00:41:24,879
Speaker 1: of hydrogen in the universe as years go by. It's

818
00:41:24,880 --> 00:41:28,840
Speaker 1: not an unrenewable resource, right right, yeah, because I guess

819
00:41:28,920 --> 00:41:31,720
Speaker 1: you can fuse things together, but it's kind of hard.

820
00:41:31,840 --> 00:41:35,279
Speaker 1: Once you made all this iron, eventually it's hard to

821
00:41:35,360 --> 00:41:38,160
Speaker 1: like turn it back into hydrogen. Yeah, these things are stable,

822
00:41:38,360 --> 00:41:40,600
Speaker 1: Like if you go far enough and you make uranium

823
00:41:40,600 --> 00:41:42,960
Speaker 1: and then that stuff is unstable, it'll break down, but

824
00:41:43,040 --> 00:41:45,359
Speaker 1: it'll break down into something else stable. It's not gonna

825
00:41:45,400 --> 00:41:47,920
Speaker 1: go all the way back down to hydrogen. Helium is

826
00:41:47,920 --> 00:41:51,920
Speaker 1: pretty stable, doesn't split spontaneously into hydrogen. So yeah, hydrogen

827
00:41:51,960 --> 00:41:54,400
Speaker 1: is not a renewable resource. Like you know, we got

828
00:41:54,440 --> 00:41:56,360
Speaker 1: a lot of it. It's gonna take a long time

829
00:41:56,440 --> 00:41:58,680
Speaker 1: to burn through all of it. But as the years

830
00:41:58,719 --> 00:42:01,640
Speaker 1: go on, the hydrogen for action of the universe is dropping.

831
00:42:01,880 --> 00:42:03,719
Speaker 1: So like, if you made a whole universe made out

832
00:42:03,719 --> 00:42:05,960
Speaker 1: of iron, it wouldn't do anything, like you would just

833
00:42:06,000 --> 00:42:08,720
Speaker 1: sit there. It depends on the distribution, but it probably

834
00:42:08,719 --> 00:42:10,720
Speaker 1: would form a lot of black holes. And that's pretty

835
00:42:10,760 --> 00:42:13,320
Speaker 1: dense stuff. So you know, if you had like a

836
00:42:13,360 --> 00:42:16,480
Speaker 1: solar sized blob of iron, it will collapse into a

837
00:42:16,480 --> 00:42:19,480
Speaker 1: black hole. All right. So then I guess technically, if

838
00:42:19,480 --> 00:42:21,480
Speaker 1: you were to engineer the universe, how like how many

839
00:42:21,520 --> 00:42:23,640
Speaker 1: generations of stars. Do you think we could get in

840
00:42:23,800 --> 00:42:25,960
Speaker 1: It's hard to know. And I asked them aster physicists

841
00:42:26,000 --> 00:42:29,680
Speaker 1: this question, and they were all just like, WHOA such

842
00:42:29,680 --> 00:42:32,279
Speaker 1: a big number. I can't even imagine, um, you know,

843
00:42:32,360 --> 00:42:37,000
Speaker 1: hygrogenive depletion. I got some estimates between a hundred trillion

844
00:42:37,400 --> 00:42:40,600
Speaker 1: and tend to the one hundred years to deplete all

845
00:42:40,640 --> 00:42:43,759
Speaker 1: the hydrogen in the universe years. But how much is

846
00:42:43,800 --> 00:42:47,359
Speaker 1: that in generations? Well, it depends, right. Stars can burn

847
00:42:47,440 --> 00:42:50,680
Speaker 1: for maybe ten billion years or a trillion years, depending

848
00:42:50,800 --> 00:42:54,000
Speaker 1: on their mass, or they could even burn short amounts

849
00:42:54,040 --> 00:42:56,279
Speaker 1: of time if you have more massive stars. We don't

850
00:42:56,320 --> 00:42:59,080
Speaker 1: really see a lot of really really massive stars. But

851
00:42:59,200 --> 00:43:01,640
Speaker 1: so if you say, for example, the average length of

852
00:43:01,680 --> 00:43:04,680
Speaker 1: a lifespan of the stars maybe ten billion years, then

853
00:43:05,040 --> 00:43:08,240
Speaker 1: that's still a lot of generations, right Then a trillion

854
00:43:08,320 --> 00:43:12,680
Speaker 1: years has a hundred generations in it. A hundred trillion years, right,

855
00:43:12,719 --> 00:43:15,880
Speaker 1: it's ten thousand generations in it. If it's even longer

856
00:43:16,440 --> 00:43:19,400
Speaker 1: time spans, and we're talking thousands and thousands of generations.

857
00:43:19,400 --> 00:43:22,160
Speaker 1: So from that point of view, like we're on generation three,

858
00:43:22,400 --> 00:43:24,440
Speaker 1: we're really just getting started. I would have thought that

859
00:43:24,480 --> 00:43:27,840
Speaker 1: you can maybe just computed from the fact that, for example,

860
00:43:27,880 --> 00:43:30,880
Speaker 1: we're on our son isn't the generation three, and it

861
00:43:30,960 --> 00:43:35,200
Speaker 1: already has one of other stuff. So wouldn't each generation

862
00:43:35,239 --> 00:43:37,520
Speaker 1: sort of take up another one to two percent of

863
00:43:37,600 --> 00:43:39,560
Speaker 1: the hydrogen and helium. Yeah, that's a good question. I

864
00:43:39,600 --> 00:43:41,160
Speaker 1: don't think this stuff that gets thrown out in the

865
00:43:41,200 --> 00:43:44,160
Speaker 1: universe is an equal sampling of the stuff that the

866
00:43:44,200 --> 00:43:46,600
Speaker 1: star made. Like the stuff in the core is the

867
00:43:46,640 --> 00:43:49,680
Speaker 1: stuff that's most likely to get kept into the white Dwarf, right,

868
00:43:49,719 --> 00:43:52,400
Speaker 1: So the heavy stuff is less likely to get distributed

869
00:43:52,440 --> 00:43:55,000
Speaker 1: out into the universe. So the next generation of star

870
00:43:55,120 --> 00:43:57,080
Speaker 1: is not going to have like all of the iron

871
00:43:57,239 --> 00:43:59,640
Speaker 1: that was made in the previous generation. Most of that

872
00:43:59,680 --> 00:44:01,520
Speaker 1: stuff is gonna end up either in the black hole

873
00:44:01,880 --> 00:44:04,640
Speaker 1: or the white dwarf or the neutron star that's left over.

874
00:44:04,760 --> 00:44:07,120
Speaker 1: But I guess if you're engineering it though, like you,

875
00:44:07,200 --> 00:44:09,399
Speaker 1: I'm gonna burn my son. My son is gonna burn

876
00:44:09,480 --> 00:44:11,600
Speaker 1: until it has one or two percent of other stuff.

877
00:44:11,600 --> 00:44:13,960
Speaker 1: Then I'm gonna throughout all that one or two percent

878
00:44:14,040 --> 00:44:16,360
Speaker 1: of stuff and take all the hygiene and healing and

879
00:44:16,400 --> 00:44:19,279
Speaker 1: make an e star eventually. That's how I'm gonna run

880
00:44:19,320 --> 00:44:22,719
Speaker 1: out right, Because I'm gonna be losing each generation. Yeah,

881
00:44:22,800 --> 00:44:24,640
Speaker 1: if you're optimal about it, then I suppose you could

882
00:44:24,680 --> 00:44:28,520
Speaker 1: spend one generation burning about a percent or so of

883
00:44:28,560 --> 00:44:30,800
Speaker 1: the stuff in the universe, in which case maybe we

884
00:44:30,840 --> 00:44:33,000
Speaker 1: would run out at some point right through a hundred

885
00:44:33,000 --> 00:44:35,839
Speaker 1: generations maybe. Yeah. So it depends a lot on how

886
00:44:35,840 --> 00:44:38,200
Speaker 1: this stuff is distributed and how you organize it, and

887
00:44:38,239 --> 00:44:40,480
Speaker 1: the mass of the stars that you are making, how

888
00:44:40,520 --> 00:44:42,839
Speaker 1: long it takes for these things to happen. But yes,

889
00:44:42,880 --> 00:44:47,000
Speaker 1: somewhere between hundreds or thousands of generations of stars. Wow,

890
00:44:47,080 --> 00:44:50,040
Speaker 1: and then that's it, no more stars. And then that's it,

891
00:44:50,400 --> 00:44:54,080
Speaker 1: no more stars exactly. And in that scenario, the universe

892
00:44:54,440 --> 00:44:57,680
Speaker 1: is dark, you know, it's just like populated by a

893
00:44:57,760 --> 00:45:00,320
Speaker 1: bunch of white dwarfs that are slowly who link to

894
00:45:00,560 --> 00:45:04,120
Speaker 1: black dwarfs, and it's basically not generating any light. And

895
00:45:04,160 --> 00:45:07,360
Speaker 1: that's just like the ideal you know, horehy magical engineering

896
00:45:07,440 --> 00:45:10,200
Speaker 1: scenario where you are able to extract all the hygiene

897
00:45:10,200 --> 00:45:12,520
Speaker 1: and helium you're saying like that, in real life, the

898
00:45:12,560 --> 00:45:14,960
Speaker 1: physics of like for me and you start are actually

899
00:45:15,400 --> 00:45:17,920
Speaker 1: much harder exactly. But before we leave that, I want

900
00:45:17,920 --> 00:45:20,080
Speaker 1: to throw out one thing which is that in that

901
00:45:20,239 --> 00:45:23,080
Speaker 1: future really dark universe, there won't be any stars made,

902
00:45:23,200 --> 00:45:25,919
Speaker 1: but occasionally you might get a bright flash of light

903
00:45:26,000 --> 00:45:29,359
Speaker 1: because white dwarfs can actually create light, like if two

904
00:45:29,440 --> 00:45:33,279
Speaker 1: of them come together, they can combine and give you

905
00:45:33,280 --> 00:45:36,040
Speaker 1: like a type one a supernova. This is very special

906
00:45:36,120 --> 00:45:38,560
Speaker 1: kind of supernova, and so for a few weeks it

907
00:45:38,640 --> 00:45:42,400
Speaker 1: can like brighten up the neighborhood it's in before dimming again.

908
00:45:42,880 --> 00:45:45,040
Speaker 1: So the deep deep far future would be mostly dark

909
00:45:45,080 --> 00:45:48,399
Speaker 1: with these like occasional few week long bursts of light.

910
00:45:48,600 --> 00:45:51,480
Speaker 1: And then again this is still like the optimal scenario, right,

911
00:45:51,680 --> 00:45:53,680
Speaker 1: so it could be a hundred to a thousand generations

912
00:45:53,680 --> 00:45:57,279
Speaker 1: of starts optimally, but really it could be a lot less. Really,

913
00:45:57,280 --> 00:45:59,239
Speaker 1: it could be a lot less. And when you look

914
00:45:59,280 --> 00:46:02,239
Speaker 1: around in the orse, you notice something, which is that

915
00:46:02,400 --> 00:46:05,760
Speaker 1: the rate of star formation in the universe is dropping,

916
00:46:06,200 --> 00:46:08,719
Speaker 1: Like we used to be making more stars sort of

917
00:46:09,000 --> 00:46:12,360
Speaker 1: per year a billion years ago than we are now,

918
00:46:12,719 --> 00:46:15,680
Speaker 1: Like the rate of new star creation is falling in

919
00:46:15,760 --> 00:46:18,760
Speaker 1: our universe. So meaning what would you put the estimate

920
00:46:18,800 --> 00:46:22,440
Speaker 1: of the number of generations ever add like would it

921
00:46:22,440 --> 00:46:24,320
Speaker 1: be It might be less than a hundred, then it

922
00:46:24,400 --> 00:46:26,640
Speaker 1: might be less than a hundred. Absolutely, it might be

923
00:46:26,719 --> 00:46:29,120
Speaker 1: less than twenty. You know, a lot of it depends

924
00:46:29,160 --> 00:46:31,960
Speaker 1: on what's going to happen with dark energy. In order

925
00:46:31,960 --> 00:46:33,799
Speaker 1: to form stars, what you need is a bunch of

926
00:46:33,800 --> 00:46:37,120
Speaker 1: stuff near each other, like these cold gas clumps near

927
00:46:37,160 --> 00:46:39,920
Speaker 1: each other. But what dark energy is doing is that

928
00:46:39,960 --> 00:46:43,239
Speaker 1: it's pulling galaxies away from each other, and so that

929
00:46:43,320 --> 00:46:46,360
Speaker 1: makes it harder for like gas to clump together to

930
00:46:46,400 --> 00:46:49,960
Speaker 1: fall into these galaxies and create new stars. And what

931
00:46:50,040 --> 00:46:51,879
Speaker 1: we see around us is that there are lots of

932
00:46:52,160 --> 00:46:55,640
Speaker 1: dead galaxies, galaxies with lots of material in them, but

933
00:46:55,680 --> 00:46:59,839
Speaker 1: there's just no more stars being formed. That's kind of sad.

934
00:47:00,040 --> 00:47:03,600
Speaker 1: I guess they're like graveyard galaxies, nothing but embers. Yeah,

935
00:47:03,680 --> 00:47:06,440
Speaker 1: because they don't have any like more gas falling into

936
00:47:06,480 --> 00:47:10,120
Speaker 1: them to stimulate star formation. And also sometimes in the

937
00:47:10,160 --> 00:47:13,000
Speaker 1: center of these galaxies, the black hole that's formed these

938
00:47:13,040 --> 00:47:16,680
Speaker 1: supermassive black hole can be emitting so much energy that

939
00:47:16,800 --> 00:47:19,320
Speaker 1: basically heats up those gas clouds so that they don't

940
00:47:19,400 --> 00:47:22,920
Speaker 1: form stars because remember these gas clouds have to be cold.

941
00:47:23,239 --> 00:47:25,080
Speaker 1: So you can get in these configurations where you have

942
00:47:25,120 --> 00:47:27,759
Speaker 1: this huge amount of mass stuck in a galaxy but

943
00:47:27,840 --> 00:47:31,279
Speaker 1: no light being created no stars being formed, and that's

944
00:47:31,320 --> 00:47:34,160
Speaker 1: not something we understand very well. It's called star quenching.

945
00:47:34,520 --> 00:47:36,920
Speaker 1: It's a really active area of research. But it might

946
00:47:36,960 --> 00:47:39,160
Speaker 1: be that every galaxy is headed in that direction. It

947
00:47:39,239 --> 00:47:42,279
Speaker 1: might just be a few more generations before all these

948
00:47:42,280 --> 00:47:46,080
Speaker 1: galaxies sort of die and stop forming stars. And then

949
00:47:46,080 --> 00:47:48,160
Speaker 1: what's going to happen after that? Like want the black

950
00:47:48,160 --> 00:47:51,239
Speaker 1: hole eventually cooled down? And what want things cool down

951
00:47:51,280 --> 00:47:54,400
Speaker 1: for that galaxy and maybe stars could kick back up again.

952
00:47:54,480 --> 00:47:56,080
Speaker 1: We don't know. We don't think those black holes will

953
00:47:56,120 --> 00:47:58,880
Speaker 1: cool down. We think they're just keep absorbing stuff. You know,

954
00:47:58,960 --> 00:48:01,200
Speaker 1: stars will keep falling into them. They'll get it bigger

955
00:48:01,200 --> 00:48:04,560
Speaker 1: and bigger. Some stars might get thrown out of those galaxies.

956
00:48:05,000 --> 00:48:06,960
Speaker 1: Right the way that stars fall into the black holes,

957
00:48:07,000 --> 00:48:09,239
Speaker 1: that they're basically like sort of bumping against each other,

958
00:48:09,280 --> 00:48:13,120
Speaker 1: not physically bumping, but like exchanging kinetic energy. One of

959
00:48:13,160 --> 00:48:15,279
Speaker 1: them slows down, the other one speeds up. So you'll

960
00:48:15,320 --> 00:48:18,480
Speaker 1: throw some stars out of the galaxies into intergalactic space.

961
00:48:18,840 --> 00:48:21,200
Speaker 1: And then these galaxies will just become bigger and bigger

962
00:48:21,239 --> 00:48:24,200
Speaker 1: black holes. And if dark energy takes over, then you'll

963
00:48:24,239 --> 00:48:27,800
Speaker 1: have these black holes separated by larger and larger distances,

964
00:48:27,880 --> 00:48:29,960
Speaker 1: and so that's the future of the universe is these

965
00:48:30,160 --> 00:48:34,400
Speaker 1: galaxies collapsing into ever distant black holes. So it sounds

966
00:48:34,440 --> 00:48:36,080
Speaker 1: like the answer then too, the question of how many

967
00:48:36,080 --> 00:48:39,280
Speaker 1: generations of stars will there be is maybe not that many,

968
00:48:39,320 --> 00:48:42,240
Speaker 1: maybe only less than twenty to go before the whole

969
00:48:42,320 --> 00:48:45,680
Speaker 1: universe is completely dark. Yeah, and it all depends on

970
00:48:45,719 --> 00:48:48,480
Speaker 1: what happens with dark energy. Like if dark energy decides, hey,

971
00:48:48,640 --> 00:48:51,759
Speaker 1: we're done with this expansion, let's turn everything around and

972
00:48:51,760 --> 00:48:55,400
Speaker 1: bring galaxies together. Remember, we just don't understand dark energy

973
00:48:55,440 --> 00:48:58,759
Speaker 1: at all. We have no mechanism to explain what it's doing,

974
00:48:58,800 --> 00:49:01,319
Speaker 1: which means we can't predict its future. And it might,

975
00:49:01,400 --> 00:49:04,560
Speaker 1: for example, turn around and bring everything back together, which

976
00:49:04,560 --> 00:49:07,520
Speaker 1: could stimulate whole new periods of star formation, you know,

977
00:49:07,600 --> 00:49:10,440
Speaker 1: before the universe is squeezed back down into a new

978
00:49:10,520 --> 00:49:13,360
Speaker 1: big crunch. So, really, are ignorance of the number of

979
00:49:13,400 --> 00:49:16,960
Speaker 1: future generations comes from our ignorance of the overall fate

980
00:49:17,040 --> 00:49:18,800
Speaker 1: of the future of the universe. So I guess the

981
00:49:18,840 --> 00:49:22,120
Speaker 1: lesson is a don't invest in sunscreen, maybe invest in

982
00:49:22,560 --> 00:49:26,680
Speaker 1: flashlight batteries or anti dark energy devices. I guess if

983
00:49:26,800 --> 00:49:29,480
Speaker 1: you know you're saying that if dark energy reverses or

984
00:49:29,560 --> 00:49:32,680
Speaker 1: goes away, then then you might get possibly more stars

985
00:49:32,680 --> 00:49:35,239
Speaker 1: in the future, but right before the universe crunches down,

986
00:49:35,719 --> 00:49:38,560
Speaker 1: So it's it's not that useful. Nobody be a bright ending.

987
00:49:38,640 --> 00:49:40,879
Speaker 1: We'll go out with a bang, with a flash, We'll

988
00:49:40,880 --> 00:49:43,840
Speaker 1: be our goodbye tour. Alright, Well, I think that answers

989
00:49:43,880 --> 00:49:46,279
Speaker 1: the question. It kind of makes you appreciate the sun

990
00:49:46,480 --> 00:49:49,520
Speaker 1: right now, like it could be maybe only in the

991
00:49:49,520 --> 00:49:53,200
Speaker 1: middle of its like universal lifespan of stars. That's right.

992
00:49:53,239 --> 00:49:56,240
Speaker 1: We don't know how many times this magical thing will happen,

993
00:49:56,280 --> 00:49:58,840
Speaker 1: that this blob of gas and dust and a little

994
00:49:58,840 --> 00:50:02,839
Speaker 1: bit of heavier stuff will collapse into this incredible right

995
00:50:03,040 --> 00:50:06,480
Speaker 1: ball of heat that's capable of burning and burning and

996
00:50:06,520 --> 00:50:09,720
Speaker 1: burning so stably that life has a chance to evolve

997
00:50:09,760 --> 00:50:12,200
Speaker 1: on the service of planets near it. We don't know

998
00:50:12,239 --> 00:50:14,160
Speaker 1: how many more times that will happen, so we should

999
00:50:14,160 --> 00:50:17,440
Speaker 1: definitely cherish this one experience. Yeah, that that means that,

1000
00:50:17,560 --> 00:50:19,799
Speaker 1: like you said, it's the only reason life exists at all,

1001
00:50:19,960 --> 00:50:22,600
Speaker 1: So you know, maybe the universe won't get them any

1002
00:50:22,680 --> 00:50:25,520
Speaker 1: chances in the future to make more life. That's right,

1003
00:50:25,640 --> 00:50:28,520
Speaker 1: So we better figure out space travel before that happens,

1004
00:50:29,160 --> 00:50:32,920
Speaker 1: and better flashlight technology as well. All right, well, we

1005
00:50:32,960 --> 00:50:36,400
Speaker 1: hope you enjoyed dad, Thanks for joining us, see you

1006
00:50:36,440 --> 00:50:46,719
Speaker 1: next time. Thanks for listening, and remember that Daniel and

1007
00:50:46,800 --> 00:50:49,720
Speaker 1: Jorge explain the Universe is a production of I Heart

1008
00:50:49,800 --> 00:50:53,000
Speaker 1: Radio or more podcast from my heart Radio, visit the

1009
00:50:53,040 --> 00:50:56,759
Speaker 1: I heart Radio app, Apple Podcasts, or wherever you listen

1010
00:50:56,880 --> 00:51:03,560
Speaker 1: to your favorite shows. No