Speaker 1: Hey, Jorhan Daniel here, and we want to tell you
Speaker 1: about our new book. It's called Frequently Asked Questions about
Speaker 1: the Universe because you have questions about the universe, and
Speaker 1: so we decided to write a book all about them.
Speaker 1: We talk about your questions, we give some answers, we
Speaker 1: make a bunch of silly jokes as usual, and we
Speaker 1: tackle all kinds of questions, including what happens if I
Speaker 1: fall into a black hole? Or is there another version
Speaker 1: of you out there that's right? Like usual, we tackle
Speaker 1: the deepest, darkest, biggest, craziest questions about this incredible cosmos.
Speaker 1: If you want to support the podcast, please get the
Speaker 1: book and get a copy, not just for yourself, but
Speaker 1: you know, for your nieces and nephews, cousins, friends, parents, dogs, hamsters,
Speaker 1: and for the aliens. So get your copy of Frequently
Speaker 1: Asked Questions about the Universe is available for pre order now,
Speaker 1: coming out November two. You can find more details at
Speaker 1: the book's website, Universe f a Q dot com. Thanks
Speaker 1: for your support, and if you have a hamster that
Speaker 1: can read, please let us know. We'd love to have
Speaker 1: them on the podcast. Hey Daniel, how far back do
Speaker 1: you know? Your family story. Oh you mean like where
Speaker 1: my family comes from? Yeah, you know, like how many
Speaker 1: generations back do you know? Well? I actually met my
Speaker 1: great grandfather when I was a kid, and I know
Speaker 1: some family history back a couple more generations than that,
Speaker 1: So I guess that makes like four or five generations.
Speaker 1: How about you. That's pretty good. I actually have only
Speaker 1: met my grandparents through to the four of them. But
Speaker 1: then it gets a little fuzzy. You know, they're all immigrants,
Speaker 1: and we know at least one future generation, I mean
Speaker 1: our kids. Yes, children are the future, and hopefully there
Speaker 1: are enough future generations that one day we become fuzzy memories. Well,
Speaker 1: I'm not sure if I will have great grandkids, but
Speaker 1: if I do, I'm sure they'll remember us, right, they
Speaker 1: can always listen to this podcast. If nothing else, they'll
Speaker 1: remember us as a cautionary tale, assuming they care. Hi
Speaker 1: am or hammy cartoonist and the creator of PhD comics. Hi.
Speaker 1: I'm Daniel. I'm a particle physicist, but I'm the first
Speaker 1: person in my family to get a PhD. You're the
Speaker 1: first doctor or the first academic doctor. I'm definitely the
Speaker 1: first doctor of any kind in my direct line. Though
Speaker 1: there is another Daniel Whiteson out there somewhere who I
Speaker 1: think has a degree. Interesting, it's like your long loss twin,
Speaker 1: maybe another version of the multiverse version of you. There's
Speaker 1: another Daniel whites In which is a distant cousin of
Speaker 1: mine who's an excellent artist and lives in London. Actually
Speaker 1: you should switch places. Sounds like he has a coulder life.
Speaker 1: I'm pretty happy with my situation. Thanks very much. Do
Speaker 1: you think you'll be the last PhD in your family?
Speaker 1: I don't know. My brother got a PhD, but that
Speaker 1: might be it. I'm not sure which direction my kids
Speaker 1: are headed. But anyways, welcome to our podcast. Daniel and
Speaker 1: Jorge explained the university but that of I Heart Radio,
Speaker 1: in which we sum up the knowledge and the thinking
Speaker 1: of many, many generations of deep thinkers and scientists and
Speaker 1: philosophers and explorers who are trying their hardest to understand
Speaker 1: this incredible, beautiful universe that we find ourselves in. We
Speaker 1: talk about everything that we know about science, things that
Speaker 1: we don't know about science, the way the universe works,
Speaker 1: and the way the universe definitely doesn't work. We talk
Speaker 1: about the latest results of the craziest thought experiments and
Speaker 1: everything in between, and throwing a few banana jokes to
Speaker 1: keep you awake and hopefully not to slip you up.
Speaker 1: But it is a pretty big universe, pretty amazing, and
Speaker 1: science has discovered a lot about it. We know a
Speaker 1: lot about how the universe started, how it's evolved, and
Speaker 1: what explains everything we see today, and a big job
Speaker 1: of science is also to think about the future and
Speaker 1: what's going to happen to this crazy cosmos. That's right,
Speaker 1: because one thing we know about the universe for sure
Speaker 1: is that it's not static. It's not just hanging out
Speaker 1: like this forever. It's evolving. It's not quite alive, but
Speaker 1: it's definitely developing and changing and has different modes to it. Yeah,
Speaker 1: the universe hasn't always been the way it is right now,
Speaker 1: and it's not going to be the same wave in
Speaker 1: the future. It's it's always changing, evolving and growing, hopefully
Speaker 1: getting more mature. Do you think the universe is getting
Speaker 1: more mature. I'm not sure it's getting better behaved, but
Speaker 1: it's definitely getting older. It's still getting into trouble. You
Speaker 1: thinking the universe that learns its lessons, I'm not sure
Speaker 1: who's teaching the universe anything. But I think it's fun
Speaker 1: to realize that the universe seems sort of static on
Speaker 1: our time scale, like the universe is not going to
Speaker 1: look any different the day you die than the day
Speaker 1: you are born, but that these processes are happening on
Speaker 1: a much much longer time scale, and that if you
Speaker 1: look at the universe over like millions of years or
Speaker 1: billions of years, it's very much dynamic. It's changing, it's growing,
Speaker 1: it's evolving. It's gonna look very different in five billion
Speaker 1: years than it does today. Yeah, or not even billions
Speaker 1: of years, Like millions of years, I mean, the Earth
Speaker 1: looked a lot different. That even our Solar system look
Speaker 1: pretty different, right, and even a few million or hundreds
Speaker 1: of millions of years. Yeah, that's something we're learning about.
Speaker 1: You know, the planets are doing a dance where they're
Speaker 1: moving in and they're moving out, and we think maybe
Speaker 1: Jupiter spent some time near the Sun and then Saturn
Speaker 1: swooped in and saved it and pulled it back out
Speaker 1: to the colder parts of the Solar system where it
Speaker 1: can't survive. So there's definitely a lot of stuff going on.
Speaker 1: If you look at the Solar system or our galaxy
Speaker 1: on like a super time lapse, you would think it
Speaker 1: was crazy. Yeah, it's a big action movie. But only
Speaker 1: if you hit the fast forward button a couple of
Speaker 1: times and then don't forget to rewind it before you
Speaker 1: return the tape. Just you know, be kind. Hopefully some
Speaker 1: people out there get that joke. Probably not if you're
Speaker 1: under thirty or thirty five, you would get that at least,
Speaker 1: I guess maybe what's the equivalent now you have to
Speaker 1: take it off your Netflix queue. Maybe the courtesy to
Speaker 1: not to nobody. But yeah, it's a big, beautiful universe,
Speaker 1: and we often wonder what's going to happen in the future,
Speaker 1: and in particular to the things we see around us,
Speaker 1: you can think about the sort of age and cycle
Speaker 1: of the stuff around us. Not just the planets are
Speaker 1: spinning around the Sun, but the solar is to itself
Speaker 1: is moving around the galaxy. It takes like two hundred
Speaker 1: and fifty million years to do one loop around the
Speaker 1: center of the galaxy for the Sun to orbit the
Speaker 1: center of the galaxy and came back to where it started.
Speaker 1: So from that point of view, you know, the galaxy
Speaker 1: itself is not that old, like it hasn't done that
Speaker 1: many spins. It's like, you know, thirty to forty galactic
Speaker 1: years old, it's still searching for itself. Maybe it still
Speaker 1: hasn't figured out what it wants to do with it
Speaker 1: that the rest of its life. It's like running through
Speaker 1: cosmic fields towards the Andromeda Galaxy. There's gonna be a
Speaker 1: very dramatic moment there where they both learn who they
Speaker 1: really are. They're going to find themselves. You're going to
Speaker 1: become one with the cosmos and with each other exactly.
Speaker 1: And then within those galaxies there's stuff happening. Stars are
Speaker 1: being born, stars are dying and exploding, is all sorts
Speaker 1: of crazy stuff. Yes, stars are probably the thing that
Speaker 1: people most noticed or think about even when they think
Speaker 1: about space and the entire universe, and it's a big
Speaker 1: part of the universe. There are a lot of stars
Speaker 1: out there, and we kind of have to ask what's
Speaker 1: going to happen to all those stars eventually in the
Speaker 1: near future and forever perhaps, Yeah, because stars do not
Speaker 1: live forever. Some of them last millions of years, some
Speaker 1: billions of years, some potentially trillions of years. But there
Speaker 1: are stars that formed and burned and died even before
Speaker 1: our solar system came to be, the things that you
Speaker 1: and I are made out of, and then our solar
Speaker 1: system are built out of our remnants of ancient stars
Speaker 1: which shine through the universe and no longer exist. So
Speaker 1: we can look into the past and think about, like,
Speaker 1: how many generations of stars have there been so far
Speaker 1: that burned and died before we even came to being. Yeah,
Speaker 1: it's kind of like people, you know, we humans have
Speaker 1: generations that come and go, and each time that they're
Speaker 1: a little bit different, hopefully. And if we're made of
Speaker 1: star dust, then by analogy, are you made out of grandparents?
Speaker 1: Doesn't Yeah? Yeah, So there have been a lot of
Speaker 1: generations of stars since the beginning of the universe, and
Speaker 1: so today we'll be tackling the question how many generations
Speaker 1: of stars will there be? I guess, Daniel, that number
Speaker 1: could be finite. Is that the idea like, maybe there
Speaker 1: aren't that many generations of stars that can happen, or
Speaker 1: is that number infinite? Perhaps? Yeah, exactly, That's what we're
Speaker 1: gonna dig into. There's a lot of different ideas about
Speaker 1: the future of the universe and how this might happen.
Speaker 1: A lot of things we still don't even really understand
Speaker 1: about the conditions for star formation where it's happening universe,
Speaker 1: where it's not happening in the universe, and all that's
Speaker 1: going to come together to give us a picture for
Speaker 1: how many times stars can burn and then explode and reform. Yeah,
Speaker 1: I guess it's interesting that what you said earlier is
Speaker 1: that maybe a lot of people don't realize that stars
Speaker 1: kind of have a lifespan, right, Like, you know, your
Speaker 1: the Sun is not going to be there forever. It
Speaker 1: wasn't always there since the beginning of time. It came
Speaker 1: about at some point in the in the past, and
Speaker 1: it's not going to be there forever into the future,
Speaker 1: and in its place, maybe there will be another star exactly.
Speaker 1: The Sun came around sort of late in the universe,
Speaker 1: and universe four billion years old. The Sun is only
Speaker 1: like four and a half billion years old, So there
Speaker 1: was nine or so billion years of stuff happening in
Speaker 1: the universe before our sun even existed, Right, that's a
Speaker 1: lot of time for stuff to happen. Stars formed and died,
Speaker 1: and then our star formed from the leftover bits of
Speaker 1: other stars and also you know, untouched material from the
Speaker 1: Big Bang and our son will not last forever. It's
Speaker 1: only got a five more billion years or so, And
Speaker 1: so it's a fun question to think about, like how
Speaker 1: many times can you gather stuff together to make stars,
Speaker 1: burn it, blow it up again, and then repeat. Can
Speaker 1: you do that forever? Or is there some fundamental limit
Speaker 1: to how many times the universe can get right? Yeah?
Speaker 1: And if we run out of generations of stars, well,
Speaker 1: that does that mean the universe will be dark forever
Speaker 1: at the end of light of sunny days in the universe.
Speaker 1: That's a dim weather forecast. Man, you know, it's a
Speaker 1: cloudy future, zero percent chance of radiation forever the sunblocks.
Speaker 1: That's that's a positive. Don't invest in sunscreen companies people,
Speaker 1: at least not in the billion year bond market. But anyways,
Speaker 1: we're wondering how many people out there have thought about
Speaker 1: this idea of solar or star generations and how many
Speaker 1: there will be in the future. So it's usual Daniel
Speaker 1: went out there and ask people how many generations or
Speaker 1: stars do you think there will be? And as always,
Speaker 1: I am deeply grateful to those of you who are
Speaker 1: willing to answer these crazy questions online. If you'd like
Speaker 1: to hear your voice speculating on difficult physics questions on
Speaker 1: the podcast. Please write to us new questions at Daniel
Speaker 1: and Jorge dot com. Here's what people had to say.
Speaker 1: I think I heard somewhere there's been three generations of stars.
Speaker 1: So if we're supposed to the universe is supposed to
Speaker 1: last for billions of years more, at least four or
Speaker 1: five more, let's say, Um, possibly, and I'm limited amount
Speaker 1: of generations. We don't really know what's going to happen
Speaker 1: in the future exactly. Um, you might, you're smarter than me,
Speaker 1: but um, yeah, I don't know. I don't know. It
Speaker 1: depends on the time, depends if the time is infinite,
Speaker 1: I don't know. Probably they can be a lot, a
Speaker 1: lot of generations eleven, Okay, how many generations of stars
Speaker 1: will there be? I think so, I know that we've
Speaker 1: got the original and then we've got the next generation. Um,
Speaker 1: I'm gonna say we're going to have all the generations
Speaker 1: of stars. I have no idea. Well, we're in the
Speaker 1: third generations of star at the moment, even though this
Speaker 1: generation is called population one. I bet Jorge has something
Speaker 1: fun to say about that naming logic, But I'm not
Speaker 1: sure how much of the matter in the universe has
Speaker 1: now been used to create stars. So let's say it's
Speaker 1: ten percent. Sure it is, but let's say ten percent,
Speaker 1: and we are three generations into the universe, so then
Speaker 1: ten times as many, let's say thirty generations. I've thought
Speaker 1: about this because we know how long the universe is
Speaker 1: gonna last and how long it's gonna be dense enough
Speaker 1: for new star formation. Our son is like four billion
Speaker 1: years old in the universe is like fourteen, so maybe
Speaker 1: there's been two or three generations there, and Son's got
Speaker 1: another four billion years left and it's kind of an
Speaker 1: average star. So maybe that's we're just on the second
Speaker 1: generation right now, so maybe ten more generations. It's my
Speaker 1: best guess. Five billion seems like a good number of
Speaker 1: star generations. I mean, if we're taking the average life
Speaker 1: spent at a star to be somewhere around five billion years,
Speaker 1: and you know, at some point, you know, all the
Speaker 1: stars exploding, our decaying that we're going to kind of
Speaker 1: reach a point where gas and dust is to spread
Speaker 1: out to create more stars. Yeah, we're gonna reach a plateau.
Speaker 1: So I'm just gonna get five billion years, I guess
Speaker 1: infinite until the universe ends because and you can't really
Speaker 1: count them because different stars generations and at different times,
Speaker 1: because the lickspans of stars is so different. All right,
Speaker 1: So a lot of guessing. I mean, everyone seemed to
Speaker 1: have sort of an idea. Maybe they're like three infinite.
Speaker 1: I like that as a guess. That's a good guess.
Speaker 1: They said that sounds like a good number, Like, why
Speaker 1: not like a good number? Yeah, next time they asked
Speaker 1: me if i'd like a raise, I'll say, yeah, you
Speaker 1: know what, five billion seems like a good number. Pennies
Speaker 1: or nano dollars or something. All Right, So that's a
Speaker 1: pretty interesting question. How many generations of stars will there be?
Speaker 1: Are we gonna have stars until the end of time
Speaker 1: or are we going to run out of fuel or
Speaker 1: ability to form these stars eventually in the future. Start
Speaker 1: us off, Daniel, I guess how do you define a
Speaker 1: generation of a star? And how did those kind of
Speaker 1: come about? Yeah, it's a good question. How do you
Speaker 1: even define a generation of a star? It's actually not
Speaker 1: that easy to like crisply say what generation of stars
Speaker 1: in because every star is made out of a bunch
Speaker 1: of material that just happened to be around and some
Speaker 1: of it could be like leftover pristine material from the
Speaker 1: Big Bang, and other bits could have been in other stars.
Speaker 1: But I think it's important to understand this sort of
Speaker 1: process of how stars are formed and then burn and
Speaker 1: then die, so we can think about how often that
Speaker 1: can happen um And so you know, the way that
Speaker 1: stars form is that you have these big clumps of
Speaker 1: gas and dust, these things like these giant molecular clouds.
Speaker 1: And I think the thing that people might not realize
Speaker 1: is that for stars to form, you need cold stuff
Speaker 1: because what you need is gravity to pull this stuff together. Remember,
Speaker 1: the stars are a delicate balancing app between gravity is
Speaker 1: trying to pull things together to make it more dense,
Speaker 1: and pressure that's like resisting being compacted too much. But
Speaker 1: gravity is really weak. So to get a star to form,
Speaker 1: you need like a really pretty cold, pretty huge clump
Speaker 1: of stuff near each other and it gathers together to
Speaker 1: form a star and reach that critical density where fusion
Speaker 1: can start. So you need to start with something like
Speaker 1: ten to twenty degrees kelvin m m. And it has
Speaker 1: to be cold because if it's too hot, it won't
Speaker 1: clump together, like it'll just kind of keep missing itself
Speaker 1: and it won't compress. Yeah, because if it's too hot,
Speaker 1: that means that the particles are moving around too fast,
Speaker 1: and so gravity just can't slow them down exactly. So
Speaker 1: they need to be like basically motionless so that gravity
Speaker 1: can gently tug on them and pull them together into
Speaker 1: a star. Maybe it's too hot, it just won't happen, right,
Speaker 1: And we've talked about in another episodes about how you
Speaker 1: need like a certain minimum amount of stuff, right, like
Speaker 1: more than a jupiter's worth of stuff. And also it's
Speaker 1: about kind of the kind of stuff it is, right like,
Speaker 1: the only certain kinds of stuff will clump and form
Speaker 1: into start. Yeah, in order to get fusion going, you
Speaker 1: need like at least like eighty times the massive Jupiter.
Speaker 1: You can get clumps forming that are smaller than that,
Speaker 1: they just won't necessarily start fusion. But typically these cloud
Speaker 1: it's where stars are formed, or like a thousand light
Speaker 1: years long, and they have a huge amount of material
Speaker 1: like thousands two million times the mass of our sun,
Speaker 1: and inside that you have like denser regions, which astronomers
Speaker 1: referred to by the technical word clumps, and then inside
Speaker 1: that are like slightly denser regions they call cores, and
Speaker 1: that's usually where stars are actually formed, but it's not
Speaker 1: something we understand in great detail, you know, like what
Speaker 1: actually makes those cores, what triggers them to collapse into
Speaker 1: a star or some people think like and nearby supernova
Speaker 1: has to come through and the shock wave there can
Speaker 1: trigger the collapse to make the star. But you're right.
Speaker 1: You can also be a variety of material. But you know,
Speaker 1: when the Big Bang happened, it made mostly hydrogen, and
Speaker 1: so most of the stuff in the universe is still hydrogen.
Speaker 1: There's a little bit of helium also, and so most
Speaker 1: of the stars in the universe are made of mostly
Speaker 1: hydrogen and helium. And then there's heavier stuff, right, And
Speaker 1: it's important that it's hydrogen and or helium because those
Speaker 1: are sort of the lightest elements, right, And so to
Speaker 1: make a proper star, you need fusee in and so
Speaker 1: it's easier to sort of merge together the lighter elements
Speaker 1: than it is to merge together like the heavy elements.
Speaker 1: That's right. To fuse hydrogen, you need a lower temperature
Speaker 1: than you do to fuse helium, which is a lower
Speaker 1: temperature than you need to fuse lithium. Etcetera, etcetera. So
Speaker 1: if you want to start a sun, you better start
Speaker 1: with a lot of hydrogen and something I think it's
Speaker 1: funny is that astronomers referred to anything that's not hydrogen
Speaker 1: or helium as a metal, by which I think they
Speaker 1: just mean like, oh, this is a serious heavy element.
Speaker 1: But you know, like chemists or like oxygen is not
Speaker 1: a metal. You know, carbon is not a metal, but
Speaker 1: according to astronomers, it's helium, hydrogen or metals. It's like
Speaker 1: there's only three elements of the periodic table for astronomers, hydrogen, helium,
Speaker 1: and metal. That's it. It's sort of like musical taste,
Speaker 1: like someone who's really into classical music thinks anything not
Speaker 1: classicals like heavy metal inten that's right e either Mozart
Speaker 1: or it's hip hop exactly. Yeah, So you need a
Speaker 1: lot of hydrogen and helium, which is good because the
Speaker 1: universe started with a whole bunch of hydrogen and lium, right,
Speaker 1: But you can also make it like if I have
Speaker 1: a whole bunch of oxygen, can I make a star
Speaker 1: out of just oxygen? You could make a star out
Speaker 1: of just oxygen, and if you had enough of it
Speaker 1: and it was cold enough and near enough to itself,
Speaker 1: then it could pull itself together with gravity, and you
Speaker 1: could even you know, get oxygen fusion happening to make
Speaker 1: heavy your stuff. That certainly is possible. Could that happen naturally?
Speaker 1: It wouldn't happen naturally because the amount of oxygen in
Speaker 1: the universe is tiny compared to the other stuff in
Speaker 1: the universe. So, you know, most of the stuff in
Speaker 1: the universe still hydrogen. You know, we've been burning stars
Speaker 1: for billions of years to make quote unquote metals like oxygen,
Speaker 1: but we haven't made that much progress. You know, it's
Speaker 1: still overwhelmingly hydrogen. So you make a random star, it's
Speaker 1: gonna be mostly hydrogen helium. Now, the like fraction of
Speaker 1: metals in stars has been increasing as the universe goes up,
Speaker 1: just because there's more of that stuff around. But to
Speaker 1: get like a star sized blob of oxygen by itself,
Speaker 1: that's never gonna happen. Well, I mean, I guess in
Speaker 1: infinite universe somewhere it's happening, right, Or like we could
Speaker 1: maybe engineering maybe somehow. That sounds like a fun project.
Speaker 1: Let's make an oxygen Why do you do that? What
Speaker 1: are you doing this? Weekend. Oh, I got some you know,
Speaker 1: house projects going and make an oxygen star. Yeah, clean
Speaker 1: mic bathroom, and also make a star. All right, So
Speaker 1: then that's kind of how the stars form, and I
Speaker 1: think we've talked in other episodes about kind of what
Speaker 1: happens then, right, like, eventually all of that hydrogen and
Speaker 1: helium merges into heavier elements, and those merging two even
Speaker 1: heavier elements, and at some point the star burns out
Speaker 1: or kind of implodes. Right, there's a couple of possibility therapy.
Speaker 1: As fusion happens, it creates heavier elements, and those heavier
Speaker 1: elements are then fuel for the next round of fusion,
Speaker 1: which are fuel for the next round of fusion. But
Speaker 1: at some point it stops. When you get up to
Speaker 1: iron and iron can't fuse and create energy. If you
Speaker 1: fuse iron and iron, you actually lose energy, and so
Speaker 1: that cools down the star, and so it's sort of
Speaker 1: like it creates I should eventually it snuffs the star out,
Speaker 1: and so the star is no longer able to resist
Speaker 1: the gravitational forces because it's not producing enough radiation pressure
Speaker 1: to resist that collapse. And then depending on the mass
Speaker 1: of the star, either you know, just like cools down
Speaker 1: into a white dwarf, or maybe it goes supernova and
Speaker 1: blows its material out, or maybe it goes supernova and
Speaker 1: the core becomes a black hole. Depends on exactly how
Speaker 1: much stuff you started from. But yeah, eventually stars do
Speaker 1: fizzle out, right, So the star is born, it lives,
Speaker 1: and it dies, and that's one generation of star. And
Speaker 1: then how it the next generation of star form? Then
Speaker 1: if it just snuffs out, or if it turns into
Speaker 1: a black hole, because it doesn't capture all of the
Speaker 1: materials into the star and sort of hold onto them forever.
Speaker 1: Even in the scenario where you create a black hole,
Speaker 1: a large part of the material of the original star
Speaker 1: is blown out into the universe. Like our son for example,
Speaker 1: it won't go supernova and it won't go into a
Speaker 1: black hole, but still it's going to have this big
Speaker 1: red giant phase when it's burning helium and it puffs
Speaker 1: up to be really really huge, and a lot of
Speaker 1: the material gets really dispersed, and then it blows that
Speaker 1: stuff out into the universe. So when you end up
Speaker 1: with like a core that's left over from a star
Speaker 1: doesn't have all the material at the star, some of
Speaker 1: the stuff from the star is blown out into the universe,
Speaker 1: and then you can get remixed into the basic ingredients
Speaker 1: of hydrogen helium to form the next stars. So that's
Speaker 1: how you can sort of recycle material that's made in
Speaker 1: a star into other future stars or planets or people. Oh,
Speaker 1: I see, it's like when a star dies, most of
Speaker 1: its materials go out back into space, like you compost
Speaker 1: it kind of, you know, you don't throw it on
Speaker 1: in the trash, you know, it doesn't all get buried
Speaker 1: in a coffin, is put bike into the soil. Yes,
Speaker 1: some of it is sort of lost to black holes
Speaker 1: or maybe to a white dwarf that eventually will cool
Speaker 1: into a black dwarf and can't really be used again.
Speaker 1: But a lot of it is tossed back out there
Speaker 1: as fodder or ingredients for the next generation of stars,
Speaker 1: which will have a higher metal percentage than the previous generation,
Speaker 1: just because this star has now made more metals out
Speaker 1: of the wrong ingredients. Right, they'll be heavier metal, more extreme.
Speaker 1: But I guess you know, one question I have is, like,
Speaker 1: you know, stars are so far apart, like do you
Speaker 1: actually get mixing of like you know, left or star
Speaker 1: and stuff from one star mixing with left door stuff
Speaker 1: from another star, or is it mostly like it all
Speaker 1: stays within the same you know, recycling area. Stars are
Speaker 1: far apart, but you know they tend to be made
Speaker 1: in clumps. So you have like stellar nurseries, these big
Speaker 1: gas clouds where stars are made, and those gas clouds
Speaker 1: are collected both from the interstellar medium and the intergalactic
Speaker 1: medium and also from old stars. So along a long
Speaker 1: time scale, this stuff really does move around and gather,
Speaker 1: and so stuff doesn't just like stay in one place.
Speaker 1: There are flows and ebbs and currents of all of
Speaker 1: this stuff. All right, Well, so that's one generation of
Speaker 1: a star, and so you can have multiple generations as
Speaker 1: the stars and the stuff goes out and it comes
Speaker 1: back in. And so let's talk about how many generations
Speaker 1: there have been of stars in the universe, and then
Speaker 1: let's talk about what the future holds. But first let's
Speaker 1: take a quick break. Al Right, how many star generations
Speaker 1: have there been and will there be in the universe? Thaniel,
Speaker 1: we talked about one generation of a star, and we
Speaker 1: know that if a star eventually dies and all this
Speaker 1: stuff kind of goes out into space and then it
Speaker 1: maybe gets combined, and then that stuff then by gravity,
Speaker 1: I guess it cools off and then comes together again,
Speaker 1: and then maybe it ignites and then creates a new
Speaker 1: generation of a star. But eventually that star will die.
Speaker 1: So and this happens over I guess millions of years
Speaker 1: or billions of years. It depends a lot on the
Speaker 1: size of the star. So a larger star will burn
Speaker 1: hotter because it's core has a lot more pressure on it,
Speaker 1: so it's temperature is higher. It burns through its material
Speaker 1: much much faster. So the bigger the star, the shorter
Speaker 1: its lifespan. Like the stars a few hundred times the
Speaker 1: mass of the Sun, it might only live like two
Speaker 1: to five million years. If a star is really really small,
Speaker 1: like much smaller than the mass of the Sun, like
Speaker 1: right on the threshold, it might burn for a trillion years,
Speaker 1: whereas our star, you know, the Sun is going to
Speaker 1: burn for about ten billion years. So the serving size
Speaker 1: you get at the very beginning totally determines how long
Speaker 1: you will burn for. Interesting, it's sort of like rock stars.
Speaker 1: Some of them, you know, flame out after a one album,
Speaker 1: and some of them have a long and nice career.
Speaker 1: I guess Bob Dylan is very low mass, right, because
Speaker 1: he's like on album fifty. Yeah, and whereas you know,
Speaker 1: Rick Astly was a supernova. But so you're telling me
Speaker 1: that each generation of a star, there's sort of no
Speaker 1: fixed time period. Like in human years, you can think
Speaker 1: of a generation as being roughly, I don't know, thirty
Speaker 1: forty years, but in a star it could be like
Speaker 1: one year or hundred years. Yeah, but it is a
Speaker 1: sort of similar to humans, right. Some humans live a
Speaker 1: long time and have kids in their nineties, like Charlie Chaplin.
Speaker 1: Some people have kids when they're teenagers, and so over
Speaker 1: fifty years you might have like three generations. It's sort
Speaker 1: of similar with stars. And that's why I was saying earlier,
Speaker 1: it's not exactly clear, you know, to say like which
Speaker 1: generation a star is in, because if I have material
Speaker 1: from all sorts of sources, including two generation stars or
Speaker 1: three generation stars, or even pristine material left over from
Speaker 1: the Big Bang. So it's tricky, but you can sort
Speaker 1: of organize roughly into a few generations when we look
Speaker 1: back into the cosmic history, you mean, sort of like
Speaker 1: the average or maybe just looking at like our son,
Speaker 1: we know how many generations it's at yeah, Well, we
Speaker 1: don't know actually how many generations the history of our
Speaker 1: son features, because in theory, you could have a series
Speaker 1: of really really massive stars hundreds and hundreds of times
Speaker 1: the mass of the Sun that die and burnout and
Speaker 1: die and burnout and dying burnout. You could have, you know,
Speaker 1: material that's been in a hundred of those stars that's
Speaker 1: around there in the universe right now. So we don't
Speaker 1: actually know for any given piece of material how many
Speaker 1: stars it's been in. What we can do is look
Speaker 1: at the stars we see in our galaxy and in
Speaker 1: other galaxies, and we notice something interesting. We noticed sort
Speaker 1: of like two rough populations of stars. Stars that seem
Speaker 1: to be sort of a lot older and have less
Speaker 1: medals in them, and then start the tend to be
Speaker 1: younger and bluer and hotter and have more medals in them.
Speaker 1: But then each of those would be in a sort
Speaker 1: of different generation, right, Like some of them might be
Speaker 1: you know, a hundred ten generation and someone might be,
Speaker 1: you know, fifteen or five. That's right. But the interesting
Speaker 1: thing about these two populations, so we have like the
Speaker 1: older ones and the younger ones, the older ones we
Speaker 1: call population two stars, is that they all seem to
Speaker 1: be really really old. They all seem to have formed
Speaker 1: like eleven, twelve, thirteen billion years ago and to still
Speaker 1: be around. So those stars probably are a second generation
Speaker 1: stars at most because they formed very very early on
Speaker 1: in the universe and they're still around. So that limits
Speaker 1: like how many generations of stars there could be before them.
Speaker 1: The other population of stars we see, what we call
Speaker 1: population one. They're still forming today. Oh, I see, you're
Speaker 1: sort of categorizing what do you see out there in
Speaker 1: the universe. You're not categorizing by generation. You just sort
Speaker 1: of looking out there and categorizing by age, Like, Wow,
Speaker 1: does over there look pretty young, so they must be
Speaker 1: later generation, but these over here look really old, so
Speaker 1: they must be kind of like one of the O
Speaker 1: G generation. Yeah. It's just like looking at humans and
Speaker 1: you're like, well, this bunch of people all are similar
Speaker 1: and come from a similar era and act the same way.
Speaker 1: So we'll call them boomers, right, and these folks will
Speaker 1: call gen z ers. And you know, there's not a
Speaker 1: crisp delineation between generations between millennials and gen xers and whatever.
Speaker 1: But it's sort of a rough rule of thumb, especially
Speaker 1: when we look out there we notice, just like we
Speaker 1: noticed in human populations, these sort of clusters of stars
Speaker 1: that have similar properties. All right, So then you can
Speaker 1: categorize kind of age out there by what we see
Speaker 1: right now, and so step us through what are the
Speaker 1: different populations. So what we've seen are these two populations
Speaker 1: population one in population too. And you know these are
Speaker 1: historical names given by a German astronomer back in the
Speaker 1: forties when he was looking at these stars and he
Speaker 1: saw that a bunch of them were bluer stars and
Speaker 1: these were tend to be like in the galactic disc,
Speaker 1: right far from the center, and that closer to the
Speaker 1: center you had more red stars. So we called them
Speaker 1: population one in population two. He didn't understand at the
Speaker 1: time what it meant that population two stars were probably
Speaker 1: much much older. In population one stars were more recent,
Speaker 1: But we know that now and it makes sort of
Speaker 1: sense because you know, as stars live in the galaxy,
Speaker 1: they tend to slow down in their orbit and sort
Speaker 1: of fall towards the center. So the center of the
Speaker 1: galaxies mostly these older stars that formed, like you know, eleven, twelve,
Speaker 1: thirteen billion years ago, and they have less metals in
Speaker 1: them than the other stars because they were formed in
Speaker 1: the time when the verse had less metal in it,
Speaker 1: it was more hydrogen. So those are the population two stars.
Speaker 1: They tend to be like making up the bulge of
Speaker 1: the galaxy. And then also they're in these weird globular
Speaker 1: clusters that sort of orbit the galaxy that we had
Speaker 1: a whole fun podcast episode about. I guess maybe a
Speaker 1: question is how do we know how old they are?
Speaker 1: And how do we know how much metal is in them?
Speaker 1: Like is it from like the spectrum of the light
Speaker 1: that comes from them or the distance? Like how do
Speaker 1: we know their age from how far they are? Or
Speaker 1: like how can we tell their age? And is that
Speaker 1: polite to ask? That's a little tricky their age. What
Speaker 1: you can do is you can look at the color
Speaker 1: of the star. Stars tend to be bluer when they're
Speaker 1: younger because bluer means hotter, and so hotter stars don't
Speaker 1: last as long, they don't live as long, and so
Speaker 1: if you see a star that's blue, that means it
Speaker 1: must be younger because they just don't have that long
Speaker 1: a life cycle. Like if you see a cat, you
Speaker 1: know that cat is not a hundred years old because
Speaker 1: there just aren't any hundred year old cats. So if
Speaker 1: you see blue stars, you know that they tend to
Speaker 1: be younger. Red stars are either old stars or they
Speaker 1: might be smaller stars. And so it's not exactly clear
Speaker 1: always when you look at a star's color to tell
Speaker 1: its age. But what we do see is that population
Speaker 1: one stars tend to have a lot of blue stars
Speaker 1: in them, which means that they're young, whereas in the
Speaker 1: bulge there aren't very many blue stars. So let's suggests
Speaker 1: that there aren't many young stars there, and most of
Speaker 1: those are pretty old. Oh I see, Wait, you're grouping
Speaker 1: them by location or by how old you think they are? Well, both,
Speaker 1: and there's a correlation there, right. The stars in the
Speaker 1: center tend to be reader and older, and the stars
Speaker 1: in the disc tend to be bluer and younger. All right,
Speaker 1: So then I guess you can assume that the younger
Speaker 1: stars are maybe a later generation, right because they were
Speaker 1: born more recently, whereas the older stars they might be
Speaker 1: even one of the original generations, right, because if you're
Speaker 1: saying they're fourteen billion years old, that's when the universe started. Yeah,
Speaker 1: we don't think that they're part of the original generation.
Speaker 1: They are like you know, eleven to thirteen billion years old,
Speaker 1: so we think they formed, like you know, a billion
Speaker 1: years after the start of the universe. He also asked
Speaker 1: about how we can tell what they're made at it.
Speaker 1: That's another clue. When we look at the spectrum from
Speaker 1: the stars, how they're glowing, we can tell what's inside
Speaker 1: the star because different elements glow at different temperatures. They
Speaker 1: tend to like get excited at different energy levels, so
Speaker 1: they have like a characteristic fingerprint. So just as you said,
Speaker 1: we can look at the spectrum of light that tells us, like,
Speaker 1: you know, how much light in there at this frequency
Speaker 1: and how much of that frequency tells you exactly the
Speaker 1: composition of the star. And what we see is that
Speaker 1: these stars tend to have a lot less metal in
Speaker 1: them than the stars that are forming today, like even
Speaker 1: our sun. So these population two stars can have like
Speaker 1: a hundreds or thousands as much iron in them, for example,
Speaker 1: as our sun. So that also suggests that they were
Speaker 1: formed earlier in the universe when the universe had less
Speaker 1: metal in it. Oh, I see right, because as the
Speaker 1: as the star progresses through its life, it makes metals, right,
Speaker 1: But then if it's been alive for that long or
Speaker 1: burning for that long, wouldn't it have made a lot
Speaker 1: of metals, But by now it makes metals, but you know,
Speaker 1: not that much. And that's when a star burns. It's
Speaker 1: mostly burning helium and hydrogen. It doesn't convert all of
Speaker 1: that into iron, for example. But the fast burning ones
Speaker 1: do create metals more quickly, I guess, or at east
Speaker 1: generation burns and is born, then you sort of increment
Speaker 1: in metalicity, but not every star makes it all the
Speaker 1: way up to iron. Like, you need enough stuff in
Speaker 1: the star to create the conditions so you can get
Speaker 1: hot enough so you can fuse the stuff to make iron.
Speaker 1: Some stars stop after making helium or lithium or carbon
Speaker 1: or neon or whatever, depending on how much mass they
Speaker 1: have in the temperature that they achieve. All right, so
Speaker 1: then what does that tell us about how many generations
Speaker 1: there have been in the universe? Since we know that
Speaker 1: you know, the older stars are only a few generations
Speaker 1: in but do we know how many generations the younger
Speaker 1: stars are or what generation they're in. Yeah, we're not sure,
Speaker 1: but the current thinking is that there are roughly three generations.
Speaker 1: So these stars we call population one. These younger stars
Speaker 1: like our sun that are out around the disc, including
Speaker 1: stars that are just forming and stars that are a
Speaker 1: few billion years old. These are the ones with a
Speaker 1: lot of metals in them, like they start with like
Speaker 1: one to four percent of them are made out of metal.
Speaker 1: So that's population one. And then the population to the
Speaker 1: one sort of in the bulge of the galaxy, the
Speaker 1: older ones. We call those population two. And we think
Speaker 1: that there was a population before that, that very early
Speaker 1: on in the universe, before any of the stars that
Speaker 1: are burning today were formed, that there was an initial
Speaker 1: star forming phase, but that all those stars are gone.
Speaker 1: Now that those stars didn't last very long, just a
Speaker 1: few million years, maybe tens or hundreds of millions of years,
Speaker 1: but that those are all gone, and we call those
Speaker 1: population three stars. So we've never actually seen one because
Speaker 1: they're so old, they would be very very distant and
Speaker 1: so very hard to make out. So that's sort of
Speaker 1: the rough timelines. Population three stars were the first in
Speaker 1: population too, and now today we're making population one stars.
Speaker 1: I feel like you picked the opposite order, like the
Speaker 1: higher than the number of population the first in order
Speaker 1: of time. I know, because the next generation of stars
Speaker 1: gonna be what population zero zero and then minus one.
Speaker 1: I think you named yourself until corner there. Physicist, I
Speaker 1: think we certainly did. It's sort of like you know,
Speaker 1: deciding the charge of the electron, like whoops, that was
Speaker 1: not the best choice. But I don't think at the
Speaker 1: time we really understood the context is sort of the
Speaker 1: historical sweep of all of this stuff, or we definitely
Speaker 1: would have named it something else. All Right, So there
Speaker 1: was an original generation of stars. But those stars you're
Speaker 1: saying they're all gone because I guess in the early
Speaker 1: universe things were sort of like hot and volatile, and
Speaker 1: so all those stars burned out pretty quickly. Yeah, we
Speaker 1: think that those stars were really big. The very very
Speaker 1: first stars were like hundreds of millions of times the
Speaker 1: mass of the Sun. It was harder to make smaller
Speaker 1: stars early on because there wasn't as much metal, so
Speaker 1: it's difficult to get like a big blob of stuff
Speaker 1: too cool. Like if you have some metal that can
Speaker 1: sede a core to gather stuff together, it's like a
Speaker 1: heavier spot. But if you just have a big cloud
Speaker 1: of gaseous hydrogen, it's harder to get like a small
Speaker 1: clump to other. So these first stars were probably like
Speaker 1: hundreds of times the mass of the Sun and then
Speaker 1: burning for only like a few million years and dying
Speaker 1: at supernova after making a little bit of you know
Speaker 1: what astronomers would call medals. But again, we haven't seen those,
Speaker 1: so they're they're hypothetical. Like we've seen really really distant galaxies,
Speaker 1: some of the first galaxies that ever formed, but we
Speaker 1: can't resolve the stars in those galaxies, so we can't
Speaker 1: say we've ever seen a population three star. Interesting that
Speaker 1: they're only sort of in our imagination or in our
Speaker 1: I guess theories about where the second population of stars
Speaker 1: came from. Yeah, it's like the oral history of your family, right,
Speaker 1: maybe you don't have any pictures of great great great
Speaker 1: grandma Janine or whatever, but maybe your family knows something
Speaker 1: about what she liked for breakfast and that she was
Speaker 1: a rock star. Maybe it was very bright back in
Speaker 1: Lithuania or whatever. So then that first generation burned out
Speaker 1: and that gives the population to which are redder but
Speaker 1: a little bit cooler. And in that population, some of
Speaker 1: that population burned out, and that where the population one
Speaker 1: that we see now and like our son comes from,
Speaker 1: but our son, right, it has a mix of stuff
Speaker 1: in it. It has some stuff, certainly from population two
Speaker 1: stars that burned out, probably some stuff from population three stars,
Speaker 1: but also it has a lot of stuff that hasn't
Speaker 1: done anything since the Big Bang. Because our son is
Speaker 1: seventy hydrogen and twenty percent helium, so it's only like
Speaker 1: one to two percent metals. Most of the stuff in
Speaker 1: our sun is basically on its first act since the
Speaker 1: Big Bang happened. But we still think it's a third
Speaker 1: generation star. Yeah, because it has stuff in it that
Speaker 1: was created from other suns like that one to two
Speaker 1: percent that really changes what a star is. And that
Speaker 1: stuff was made by other suns. And you know, like
Speaker 1: most of the Earth is that kind of stuff, Like
Speaker 1: most of the Earth is not hydrogen or helium. Right,
Speaker 1: So basically everything on our planet came from the death
Speaker 1: of a star, whereas the Sun is mostly pristine. Stuff
Speaker 1: from the Big Bang still got a lot to go
Speaker 1: on and ply more generations. And so I guess the
Speaker 1: question is how good is that stuff in the Sun,
Speaker 1: Like it's good for one more generation or a billion
Speaker 1: more generations? What will the future hold? So let's get
Speaker 1: into that, But first let's take another quick break. Al Right,
Speaker 1: how many generations, so stars will there be in the future.
Speaker 1: We know that our son is sort of like the
Speaker 1: third generation star in the universe's history, and so the
Speaker 1: question is is this like the beginning of the history
Speaker 1: of stars or you know, or do we only have
Speaker 1: a few more generations left. Yeah, it's really fun to
Speaker 1: think about what the future might look like, and you
Speaker 1: have to like think deep, deep into the future of
Speaker 1: the universe. And I think there's sort of two big questions.
Speaker 1: You know. One is like, if you had perfect conditions
Speaker 1: for making stars, so that you could always gather the
Speaker 1: hygien together and healing together to burn it, how long
Speaker 1: would it take to burn all that fuel and convert
Speaker 1: it all to iron for example? You know, that's one question,
Speaker 1: But the reality is that the universe is not a
Speaker 1: perfect laboratory form. Making starts. You need very specific conditions.
Speaker 1: So I think we should also think about, like how
Speaker 1: long the universe will be conducive to star making. You
Speaker 1: might have the ingredients you need to make stars unburned hydrogen,
Speaker 1: but that doesn't necessarily mean that you're gonna be making stars. Well,
Speaker 1: let's think about it. Maybe just our star, Like what's
Speaker 1: gonna happen to our start. We know, we talked about
Speaker 1: how it's going to burn out and sort of blow up,
Speaker 1: get big and then cool down eventually. But and then
Speaker 1: do you think another star will take its place eventually? Well,
Speaker 1: our star is probably going to turn into a white dwarf, right,
Speaker 1: which is just like a hot lump of stuff. No
Speaker 1: longer fusion is happening, but it's still really hot and
Speaker 1: so it's glowing, which is why it's called a white dwarf.
Speaker 1: And white dwarfs are stable, like, we don't think they
Speaker 1: really do anything else. They just sit there and gradually
Speaker 1: cool off until they become a black dwarf, and that
Speaker 1: could take, you know, trillions of years. We don't think
Speaker 1: there are any black dwarfs in the universe right now.
Speaker 1: There's a bunch of white dwarfs sitting there glowing hot,
Speaker 1: but none of them have had enough time to cool
Speaker 1: the black dwarfs. But that doesn't mean that our sun
Speaker 1: won't contribute to the next generation of stars because the
Speaker 1: white dwarf doesn't take all the material from the Sun.
Speaker 1: There's a lot of the material from the Sun that
Speaker 1: will get blown out into maybe a new planetary disk
Speaker 1: for that white dwarf or just out into the interstellar
Speaker 1: medium and contribute to another generation of stars. So our
Speaker 1: star it's going to become a white dwarf and then
Speaker 1: blow out its stuff out into space, which then is
Speaker 1: gonna maybe combined with the hydrogen helium from other stars
Speaker 1: that burned out and then make other stars. Yeah, and
Speaker 1: this happens because the sun before it burns out, before
Speaker 1: it stops fusing, it gets really really big, and the
Speaker 1: outer shells tend to get blown out while the inner
Speaker 1: part collapses. So it seese outer layers of the star
Speaker 1: they're gonna get blown out and they can definitely contribute
Speaker 1: to future stars or a planet. There could be aliens
Speaker 1: ten billion years from now that are eating their cereal
Speaker 1: and thinking, wow, this could have been another star billions
Speaker 1: of years ago, and they would be right. I see,
Speaker 1: when you're eating your cereal, you you are maybe? I
Speaker 1: mean everything is made in the chorus stars, right, and
Speaker 1: anything about hydrogen and yeah, unless you're eating hydrogen for breakfast,
Speaker 1: what you're eating was made in a star. Interesting, not recommended,
Speaker 1: but not as filling or it is I guess pretty
Speaker 1: filling hydrogen the cereal Oh the humanity, Oh, I see,
Speaker 1: so it's not like a star blows up and then
Speaker 1: in its place and you star forms. It's like you
Speaker 1: need this kind of like mixing between the spaces of stars, right, Yeah,
Speaker 1: it's more like you know, when a tree dies and
Speaker 1: it gives its nutrients back into the ground. You don't
Speaker 1: automatically just get a new trine exactly the same spot.
Speaker 1: It just provides nutrients for a future plant to gobble
Speaker 1: up and to build something else. So you're saying one
Speaker 1: scenario is that this keeps happening for a long time.
Speaker 1: You know, you get more generations of star but eventually,
Speaker 1: like all of the hydrogen and helium in the universe
Speaker 1: is going to have been consumed, maybe could be by
Speaker 1: stars and turn into heavier metals. Yeah, I don't think
Speaker 1: that's likely to actually happen in our universe, and we
Speaker 1: can talk about why it'd be difficult to arrange that.
Speaker 1: But in theory, if you engineer the universe to be
Speaker 1: a perfect star making laboratory, then yeah, you could eventually
Speaker 1: burn all the fuel. Like it's one direction. Or we're
Speaker 1: not making more hydrogen, right, We're just decreasing the amount
Speaker 1: of hydrogen in the universe as years go by. It's
Speaker 1: not an unrenewable resource, right right, yeah, because I guess
Speaker 1: you can fuse things together, but it's kind of hard.
Speaker 1: Once you made all this iron, eventually it's hard to
Speaker 1: like turn it back into hydrogen. Yeah, these things are stable,
Speaker 1: Like if you go far enough and you make uranium
Speaker 1: and then that stuff is unstable, it'll break down, but
Speaker 1: it'll break down into something else stable. It's not gonna
Speaker 1: go all the way back down to hydrogen. Helium is
Speaker 1: pretty stable, doesn't split spontaneously into hydrogen. So yeah, hydrogen
Speaker 1: is not a renewable resource. Like you know, we got
Speaker 1: a lot of it. It's gonna take a long time
Speaker 1: to burn through all of it. But as the years
Speaker 1: go on, the hydrogen for action of the universe is dropping.
Speaker 1: So like, if you made a whole universe made out
Speaker 1: of iron, it wouldn't do anything, like you would just
Speaker 1: sit there. It depends on the distribution, but it probably
Speaker 1: would form a lot of black holes. And that's pretty
Speaker 1: dense stuff. So you know, if you had like a
Speaker 1: solar sized blob of iron, it will collapse into a
Speaker 1: black hole. All right. So then I guess technically, if
Speaker 1: you were to engineer the universe, how like how many
Speaker 1: generations of stars. Do you think we could get in
Speaker 1: It's hard to know. And I asked them aster physicists
Speaker 1: this question, and they were all just like, WHOA such
Speaker 1: a big number. I can't even imagine, um, you know,
Speaker 1: hygrogenive depletion. I got some estimates between a hundred trillion
Speaker 1: and tend to the one hundred years to deplete all
Speaker 1: the hydrogen in the universe years. But how much is
Speaker 1: that in generations? Well, it depends, right. Stars can burn
Speaker 1: for maybe ten billion years or a trillion years, depending
Speaker 1: on their mass, or they could even burn short amounts
Speaker 1: of time if you have more massive stars. We don't
Speaker 1: really see a lot of really really massive stars. But
Speaker 1: so if you say, for example, the average length of
Speaker 1: a lifespan of the stars maybe ten billion years, then
Speaker 1: that's still a lot of generations, right Then a trillion
Speaker 1: years has a hundred generations in it. A hundred trillion years, right,
Speaker 1: it's ten thousand generations in it. If it's even longer
Speaker 1: time spans, and we're talking thousands and thousands of generations.
Speaker 1: So from that point of view, like we're on generation three,
Speaker 1: we're really just getting started. I would have thought that
Speaker 1: you can maybe just computed from the fact that, for example,
Speaker 1: we're on our son isn't the generation three, and it
Speaker 1: already has one of other stuff. So wouldn't each generation
Speaker 1: sort of take up another one to two percent of
Speaker 1: the hydrogen and helium. Yeah, that's a good question. I
Speaker 1: don't think this stuff that gets thrown out in the
Speaker 1: universe is an equal sampling of the stuff that the
Speaker 1: star made. Like the stuff in the core is the
Speaker 1: stuff that's most likely to get kept into the white Dwarf, right,
Speaker 1: So the heavy stuff is less likely to get distributed
Speaker 1: out into the universe. So the next generation of star
Speaker 1: is not going to have like all of the iron
Speaker 1: that was made in the previous generation. Most of that
Speaker 1: stuff is gonna end up either in the black hole
Speaker 1: or the white dwarf or the neutron star that's left over.
Speaker 1: But I guess if you're engineering it though, like you,
Speaker 1: I'm gonna burn my son. My son is gonna burn
Speaker 1: until it has one or two percent of other stuff.
Speaker 1: Then I'm gonna throughout all that one or two percent
Speaker 1: of stuff and take all the hygiene and healing and
Speaker 1: make an e star eventually. That's how I'm gonna run
Speaker 1: out right, Because I'm gonna be losing each generation. Yeah,
Speaker 1: if you're optimal about it, then I suppose you could
Speaker 1: spend one generation burning about a percent or so of
Speaker 1: the stuff in the universe, in which case maybe we
Speaker 1: would run out at some point right through a hundred
Speaker 1: generations maybe. Yeah. So it depends a lot on how
Speaker 1: this stuff is distributed and how you organize it, and
Speaker 1: the mass of the stars that you are making, how
Speaker 1: long it takes for these things to happen. But yes,
Speaker 1: somewhere between hundreds or thousands of generations of stars. Wow,
Speaker 1: and then that's it, no more stars. And then that's it,
Speaker 1: no more stars exactly. And in that scenario, the universe
Speaker 1: is dark, you know, it's just like populated by a
Speaker 1: bunch of white dwarfs that are slowly who link to
Speaker 1: black dwarfs, and it's basically not generating any light. And
Speaker 1: that's just like the ideal you know, horehy magical engineering
Speaker 1: scenario where you are able to extract all the hygiene
Speaker 1: and helium you're saying like that, in real life, the
Speaker 1: physics of like for me and you start are actually
Speaker 1: much harder exactly. But before we leave that, I want
Speaker 1: to throw out one thing which is that in that
Speaker 1: future really dark universe, there won't be any stars made,
Speaker 1: but occasionally you might get a bright flash of light
Speaker 1: because white dwarfs can actually create light, like if two
Speaker 1: of them come together, they can combine and give you
Speaker 1: like a type one a supernova. This is very special
Speaker 1: kind of supernova, and so for a few weeks it
Speaker 1: can like brighten up the neighborhood it's in before dimming again.
Speaker 1: So the deep deep far future would be mostly dark
Speaker 1: with these like occasional few week long bursts of light.
Speaker 1: And then again this is still like the optimal scenario, right,
Speaker 1: so it could be a hundred to a thousand generations
Speaker 1: of starts optimally, but really it could be a lot less. Really,
Speaker 1: it could be a lot less. And when you look
Speaker 1: around in the orse, you notice something, which is that
Speaker 1: the rate of star formation in the universe is dropping,
Speaker 1: Like we used to be making more stars sort of
Speaker 1: per year a billion years ago than we are now,
Speaker 1: Like the rate of new star creation is falling in
Speaker 1: our universe. So meaning what would you put the estimate
Speaker 1: of the number of generations ever add like would it
Speaker 1: be It might be less than a hundred, then it
Speaker 1: might be less than a hundred. Absolutely, it might be
Speaker 1: less than twenty. You know, a lot of it depends
Speaker 1: on what's going to happen with dark energy. In order
Speaker 1: to form stars, what you need is a bunch of
Speaker 1: stuff near each other, like these cold gas clumps near
Speaker 1: each other. But what dark energy is doing is that
Speaker 1: it's pulling galaxies away from each other, and so that
Speaker 1: makes it harder for like gas to clump together to
Speaker 1: fall into these galaxies and create new stars. And what
Speaker 1: we see around us is that there are lots of
Speaker 1: dead galaxies, galaxies with lots of material in them, but
Speaker 1: there's just no more stars being formed. That's kind of sad.
Speaker 1: I guess they're like graveyard galaxies, nothing but embers. Yeah,
Speaker 1: because they don't have any like more gas falling into
Speaker 1: them to stimulate star formation. And also sometimes in the
Speaker 1: center of these galaxies, the black hole that's formed these
Speaker 1: supermassive black hole can be emitting so much energy that
Speaker 1: basically heats up those gas clouds so that they don't
Speaker 1: form stars because remember these gas clouds have to be cold.
Speaker 1: So you can get in these configurations where you have
Speaker 1: this huge amount of mass stuck in a galaxy but
Speaker 1: no light being created no stars being formed, and that's
Speaker 1: not something we understand very well. It's called star quenching.
Speaker 1: It's a really active area of research. But it might
Speaker 1: be that every galaxy is headed in that direction. It
Speaker 1: might just be a few more generations before all these
Speaker 1: galaxies sort of die and stop forming stars. And then
Speaker 1: what's going to happen after that? Like want the black
Speaker 1: hole eventually cooled down? And what want things cool down
Speaker 1: for that galaxy and maybe stars could kick back up again.
Speaker 1: We don't know. We don't think those black holes will
Speaker 1: cool down. We think they're just keep absorbing stuff. You know,
Speaker 1: stars will keep falling into them. They'll get it bigger
Speaker 1: and bigger. Some stars might get thrown out of those galaxies.
Speaker 1: Right the way that stars fall into the black holes,
Speaker 1: that they're basically like sort of bumping against each other,
Speaker 1: not physically bumping, but like exchanging kinetic energy. One of
Speaker 1: them slows down, the other one speeds up. So you'll
Speaker 1: throw some stars out of the galaxies into intergalactic space.
Speaker 1: And then these galaxies will just become bigger and bigger
Speaker 1: black holes. And if dark energy takes over, then you'll
Speaker 1: have these black holes separated by larger and larger distances,
Speaker 1: and so that's the future of the universe is these
Speaker 1: galaxies collapsing into ever distant black holes. So it sounds
Speaker 1: like the answer then too, the question of how many
Speaker 1: generations of stars will there be is maybe not that many,
Speaker 1: maybe only less than twenty to go before the whole
Speaker 1: universe is completely dark. Yeah, and it all depends on
Speaker 1: what happens with dark energy. Like if dark energy decides, hey,
Speaker 1: we're done with this expansion, let's turn everything around and
Speaker 1: bring galaxies together. Remember, we just don't understand dark energy
Speaker 1: at all. We have no mechanism to explain what it's doing,
Speaker 1: which means we can't predict its future. And it might,
Speaker 1: for example, turn around and bring everything back together, which
Speaker 1: could stimulate whole new periods of star formation, you know,
Speaker 1: before the universe is squeezed back down into a new
Speaker 1: big crunch. So, really, are ignorance of the number of
Speaker 1: future generations comes from our ignorance of the overall fate
Speaker 1: of the future of the universe. So I guess the
Speaker 1: lesson is a don't invest in sunscreen, maybe invest in
Speaker 1: flashlight batteries or anti dark energy devices. I guess if
Speaker 1: you know you're saying that if dark energy reverses or
Speaker 1: goes away, then then you might get possibly more stars
Speaker 1: in the future, but right before the universe crunches down,
Speaker 1: So it's it's not that useful. Nobody be a bright ending.
Speaker 1: We'll go out with a bang, with a flash, We'll
Speaker 1: be our goodbye tour. Alright, Well, I think that answers
Speaker 1: the question. It kind of makes you appreciate the sun
Speaker 1: right now, like it could be maybe only in the
Speaker 1: middle of its like universal lifespan of stars. That's right.
Speaker 1: We don't know how many times this magical thing will happen,
Speaker 1: that this blob of gas and dust and a little
Speaker 1: bit of heavier stuff will collapse into this incredible right
Speaker 1: ball of heat that's capable of burning and burning and
Speaker 1: burning so stably that life has a chance to evolve
Speaker 1: on the service of planets near it. We don't know
Speaker 1: how many more times that will happen, so we should
Speaker 1: definitely cherish this one experience. Yeah, that that means that,
Speaker 1: like you said, it's the only reason life exists at all,
Speaker 1: So you know, maybe the universe won't get them any
Speaker 1: chances in the future to make more life. That's right,
Speaker 1: So we better figure out space travel before that happens,
Speaker 1: and better flashlight technology as well. All right, well, we
Speaker 1: hope you enjoyed dad, Thanks for joining us, see you
Speaker 1: next time. Thanks for listening, and remember that Daniel and
Speaker 1: Jorge explain the Universe is a production of I Heart
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