#378 – Anna Frebel: Origin and Evolution of the Universe, Galaxies, and Stars

Anna Frebel is an astronomer and astrophysicist at MIT. Please support this podcast by checking out our sponsors: – Hexclad Cookware: https://hexclad.com/lex and use code LEX to get 10% off – Numerai: https://numer.ai/lex – House of Macadamias: https://houseofmacadamias.com/lex and use code LEX to get 20% off your first order EPISODE LINKS: Anna’s Twitter: https://twitter.com/annafrebel Anna’s Instagram: https://instagram.com/annafrebel Anna’s Book – Searching for the Oldest Stars: https://amzn.to/3pi2Ci6 PODCAST INFO: Podcast website: https://lexfridman.com/podcast Apple Podcasts: https://apple.co/2lwqZIr Spotify: https://spoti.fi/2nEwCF8 RSS: https://lexfridman.com/feed/podcast/ YouTube Full Episodes: https://youtube.com/lexfridman YouTube Clips: https://youtube.com/lexclips SUPPORT & CONNECT: – Check out the sponsors above, it’s the best way to support this podcast – Support on Patreon: https://www.patreon.com/lexfridman – Twitter: https://twitter.com/lexfridman – Instagram: https://www.instagram.com/lexfridman – LinkedIn: https://www.linkedin.com/in/lexfridman – Facebook: https://www.facebook.com/lexfridman – Medium: https://medium.com/@lexfridman OUTLINE: Here’s the timestamps for the episode. On some podcast players you should be able to click the timestamp to jump to that time. (00:00) – Introduction (05:26) – First elements (12:35) – Milky Way (16:11) – Alien worlds (19:16) – Protogalaxies (24:29) – Black holes (29:27) – Stellar archeology (38:42) – Oldest stars (46:32) – Metal-poor stars (1:02:05) – Neutron capture (1:07:01) – Neutron stars (1:12:30) – Dwarf galaxies (1:17:10) – Star observation (1:45:27) – James Webb Space Telescope (1:51:17) – Future of space observation (1:54:26) – Age of the universe (2:07:34) – Most beautiful idea in astronomy (2:11:23) – Advice for young people (2:20:17) – Meaning of life

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:00Lex Fridman?

  The following is a conversation with Anna Frebel, an astrophysicist at MIT studying the oldest stars in the Milky Way galaxy in order to understand the chemical and physical conditions of the early universe, and how from that our galaxy formed and evolved to what it is today, the place we humans call home. And now, a quick useful mention of each sponsor. Check them out in the description. It's the best way to support this podcast. We got Hexclad for well-designed and well-engineered cookware. Nummerai for the world's hardest data science tournament. And House of Academius for delicious snacks. Choose wisely, my friends. Also, if you want to work with our team, we're always hiring.

• 0:45Lex Fridman?

  Go to lexfridman.com/hiring. And now, onto the full ad reads. Never any ads in the middle. I try to make this interesting, but if you skip them, please still check out the sponsors. I enjoy their stuff. Maybe you will too.

• 0:59Lex Fridman?

  This episode is brought to you by a new sponsor, Hexclad, the maker of well-engineered and patented, in quotes, hybrid cookware. I don't know what that means. All I know, it looks badass. I got it a couple of weeks ago. I already cooked a couple of steaks on it. It's just perfect. My goal for this weekend, actually, is to cook an omelet on it. But it works perfect for steak, non-stick. I don't know how they do it, but as they say, it has the performance of stainless steel, the durability of cast iron, and it has non-toxic and non-stick coating. The steaks, in case you were wondering, were delicious.

• 1:43Lex Fridman?

  I like it about medium rare. And there's probably a lot more to be said about how I like to cook steak in different conditions, when I'm traveling, when I'm at home, all that kind of stuff. But steak is the simple meal I return to time and time again for a source of simple happiness and fulfillment. Almost exclusively, I've been eating one time a day. And so, it's steak, big steak, with a bunch of veggies on the side if I'm going keto, and just steak if I'm going carnivore. Anyway, go to hexclad.com and use code LEX to get 10% off your entire order. That's hexclad.com and use code LEX for 10% off your entire order.

• 2:26Lex Fridman?

  This show is also brought to you by Numera, a hedge fund that I've talked a bunch about in the past. It uses machine learning to make investment decisions and it's a tournament that challenges data scientists from all over the place to construct predictive models for financial markets and then it uses those models to help people make financial decisions. If you're a data scientist and you want to be involved, this is an amazingly interesting, complex, difficult, and impactful machine learning tournament and challenge. I think too often in the machine learning community, the problems we work with are toy problems.

• 3:06Lex Fridman?

  And so I really love the idea that Numera is creating this problem, this giant problem that is not at all a toy. It's working with real markets and real money. That's to me, super exciting. Head over to numer.com/lex to sign up for a tournament and hone your machine learning skills. That's numer.com/lex for a chance to play against me, yes, me, and for a chance to win a share of the tournament's prize pool. This show is brought to you by House of Macadamias, a company that ships delicious, high-quality

• 3:46Lex Fridman?

  and healthy macadamia nuts and macadamia nut-based snacks directly to your door. They're perfectly portioned. I give it to the guests, they love it. I mean, it's everything you want in a snack in terms of healthiness, in terms of deliciousness, in terms of bringing variety and joy to your life. They got bars, they got whole nuts, they got whatever. It's 30% less carbs than almonds. It's the only nut rich in omega-7s. I think a long time I was reading, what is the healthiest nut? And macadamias were up there. I believe they were at number one in the website I was looking at. And I was heartbroken to find out that I think peanuts were at the bottom.

• 4:29Lex Fridman?

  And you know, so much of my life I've wasted on peanuts when I could have been spending all this valuable time with macadamia nuts.

• 4:40Lex Fridman?

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• 5:01Lex Fridman?

  This is the Lex Fridman Podcast. To support it, please check out our sponsors in the description. And now to your friends, here's Anna Fribell.

• 5:26Lex Fridman?

  Let's go back to the early days. What did the formation of the Milky Way galaxy look like? Or maybe we want to start even before that. What did the formation of the universe look like?

• 5:37Speaker 01

  Well, we scientists believe there was the Big Bang, some big beginning. But what is important for my work, and I think that's what we're going to talk about, is what kind of elements were present at that time? So the Big Bang left a universe behind that was made of just hydrogen, helium, and tiny little sprinkles of lithium. And that was pretty much it. As it turns out, it's actually quite hard to make stars or any structure from that. That's fairly hot gas. And so the very first stars that formed prior to any galaxies were very massive stars, big stars, 100 times the mass of the sun.

• 6:22Speaker 01

  And they were made from just hydrogen and helium. So big stars explode pretty fast after a few million years only. That's very short on cosmic time scales. And in their explosions, they provided the first heavier elements to the universe. Because in their cores, all stars fuse lighter elements like hydrogen, helium into heavier ones. And then that goes all the way up to iron. And then all that material gets ejected in these massive supernova explosions. And that marked a really, really important transition in the universe. Because after that first explosion, it was no longer chemically pristine.

• 7:06Speaker 01

  And that set the stage for everything else to happen, including us here talking today.

• 7:11Lex Fridman?

  So what do you mean by pristine? So there's a whole

• 7:16Lex Fridman?

  complex soup of elements now as opposed to just hydrogen, helium and a little bit of lithium?

• 7:22Speaker 01

  Yeah, so after the big bang, just hydrogen and helium. We don't really need to talk too much about lithium because the amount was so small. And after these very first stars formed and exploded, they, heavier elements like carbon, oxygen, magnesium, iron, all of that stuff was suddenly present in the gas clouds. Tiny amounts only, very tiny amounts. But that actually helped, especially the carbon and the oxygen, to make the gas cool. These atoms are more complicated than hydrogen, that's just a proton. And so it has cooling properties, can send out photons outside of the gas cloud. So the gas can cool.

• 8:05Speaker 01

  And when you have gas that gets colder and colder, you can make smaller and smaller stars. So you can fragment it and clump it and turn it into stars like the sun. And the cool thing about that is that when you have small stars like the sun, they have a really long lifetime. So those first low mass stars that formed back then are still observable today. That is actually what I do. I try to find these early survivors. Because they tell us what the gas looked like back then. They have preserved that composition of these early gas cloud, the chemical compositions, until today. So I don't need to look very far into the universe to study all the beginnings.

• 8:48Speaker 01

  I can just chemically analyze the oldest stars. And it's like unpacking everything that happened back then. It's very exciting.

• 8:58Lex Fridman?

  So to just reiterate, so in the very early days, in the first few million years. There was giant stars that's mostly hydrogen and helium, and then they exploded in these supernova explosions. And then they made these clumps.

• 9:13Speaker 01

  Yeah, so the first.

• 9:14Lex Fridman?

  Non pristine, non pristine clumps.

• 9:17Speaker 01

  Yeah, pretty much. So it took a few hundred million years for the first stars to emerge. And then they exploded after a few million years. Kaboom. And then it's like, I always consider the universe like a, you know, a nice soup. And then these first supernova explosions kind of provided the salt. You know, just a little sprinkle of heavier elements and that made it really tasty. It's just changed it completely, right? And that changed the physics of the gas. So that meant that these, these gas clouds that were, you know, surrounding the, the, the former first stars. They could now cool down and clump and form the next generation of stars. That now included also little stars.

• 10:01Speaker 01

  And as I just mentioned, the small stars have these really long lifetimes. The sun has a lifetime of 10 billion years. Any star that is even less massive will have an even longer lifetime. So that gives us a chance to, to still observe some of the stars that formed back then. So we are testing the, the conditions, the chemical and physical conditions of the early universe, even before the galaxy formed.

• 10:27Lex Fridman?

  So what's the timeline that we're talking about? What is the age of the universe and what is the earliest time we got those salty delicious soup? Clump soups with heavy elements.

• 10:37Speaker 01

  Well, the universe is 13.8 billion years old.

• 10:40Lex Fridman?

  Allegedly, yeah.

• 10:43Lex Fridman?

  Okay.

• 10:44Speaker 01

  When I was in high school, the universe was 20 billion years old.

• 10:48Lex Fridman?

  Oh, yeah. So the estimate.

• 10:50Speaker 01

  Changed.

• 10:50Lex Fridman?

  Do you think that estimate will evolve in interesting ways or no? Is that, is it pretty stable at this?

• 10:55Speaker 01

  Mostly converged, yes, because the techniques are very different now, much more precise. The whole business of precision cosmology by mapping out the cosmic microwave background, you know, that, that's a marvelous feat.

• 11:09Speaker 01

  Maybe, you know, the digits will still move around a little bit, but that's all right.

• 11:13Lex Fridman?

  Plus the gravitational waves and all that, so all the different sources of data.

• 11:17Speaker 01

  Yeah.

• 11:18Lex Fridman?

  Kind of mapping out this detailed picture of the early universe. Yeah.

• 11:21Speaker 01

  Totally. And so we think the earliest little stars formed, I don't know, maybe half a billion years after the big bang, right? Again, a few hundred million years for the first stars to emerge and then, you know, took some time. So give or take half a billion years. And that was the time when sort of the very first proto galaxies formed, early stellar structures, stellar systems, from which the Milky Way eventually formed, right? So it was, the Milky Way was probably a bigger, slightly bigger one. And we know today that galaxies grow hierarchically, which means they eat their smaller neighbors.

• 12:01Speaker 01

  So if you're the bigger one and have a few, few friends around, you're just gonna eat them, absorb them, and then you grow bigger. And so all these, these little early stars, you know, kind of came into the Milky Way through that kind of process. And that's why we find them in the outer parts of the galaxy today, because they're just kind of deaf and just left there since.

• 12:26Lex Fridman?

  So the old stuff is on the outskirts of the galaxy and the new stuff is in closer to the middle? Is there?

• 12:31Speaker 01

  Broadly speaking.

• 12:32Lex Fridman?

  Okay.

• 12:32Speaker 01

  Yes.

• 12:33Lex Fridman?

  So that's where you would look for it. So maybe just to step back, like, what is a galaxy? What is a proto galaxy?

• 12:39Speaker 01

  I love that question. So the galaxy is a huge assembly of stars. The Milky Way contains something like 200 to 400 billion stars. And most of the material and the stars are in the disk. And when we look at the night sky, what we see as the Milky Way band on the sky, that is actually the inner, the next inner spiral arm, because we actually live in a spiral disk galaxies, or the Milky Way is a spiral disk galaxy. And we're looking, actually, it depends a little bit, in the northern hemisphere, we're looking out of the galaxy. So we're seeing the next outer spiral arm.

• 13:26Speaker 01

  And as you can imagine, there's only dark space behind that. So we don't see it all that nice on the sky. But if you travel to south, to the southern hemisphere, let's say, South America, you see the Milky Way and it looks so different on the sky because that's the next inner spiral. I mean, that's backlit by the galactic center. The galactic center is a very big, puffy, you know, region of gas. There's a lot of star formation, the galactic party is happening there. So it's very bright and it makes for this very beautiful Milky Way on the night sky that we see. So actually, if you if you ever get the chance to experience that, I encourage you to almost like close your eyes while seeing this

• 14:11Speaker 01

  and imagining that you're sitting in this kind of disk, in this pancake, and you're just kind of looking right into it. And you can you can really feel that we're in this 2D disk. And then you can imagine that there's a top and a bottom and that we're really part of the galaxy. You can really experience that. We're just not not just lost in space somewhere, but we're really a part of it. And, you know, knowing a little bit about the structure of the Milky Way really helps.

• 14:38Lex Fridman?

  Do you feel small when you think about that? When you look on that spiral on the inside of the Milky Way and then you look out to the outside? How are we supposed to feel?

• 14:49Speaker 01

  I I don't know. I I don't feel small necessarily. I feel in awe and I feel I'm a part of it because I can really feel that I'm a part of it. I think for many people, they think like, oh, there's just the planet and then there's nothing. And that's almost a little bit sad, but that's really not the case, right? Because there's there's so much more. And I really like to imagine, wow, I'm I'm sitting in this big galactic merry-go-round and we're going around the center and I can see the center above me, right? And I can almost feel like we're going going there.

• 15:27Speaker 01

  Of course, we can't really feel that. But the sun does circle the galactic center.

• 15:33Lex Fridman?

  But there's a kind of sadness to like looking pictures of a nice vacation place. All we get is that light, an old light. Do you feel like sad that we don't get to travel? Or you and I will not get to travel there? And maybe humans will never get to travel there?

• 15:51Speaker 01

  Yeah, I always wanted to travel into space and see the earth and other things from up there. There's there's certainly that. But I don't know. It's it's also OK. It would just be at our vantage point and and see it from from here.

• 16:08Lex Fridman?

  With the sensors, with the telescopes that we have and explore the possibility.

• 16:11Speaker 01

  Yeah.

• 16:11Lex Fridman?

  I mean, there is a kind of wonder to the mystery of it all. What what's out there? What interesting things that we can't possibly imagine? You know, there could be all kinds of life forms, bacteria, all this kind of stuff. I tend to believe that, you know, it depends on the day. I tend to believe there's just a lot of very primitive organisms just spread out throughout. And they build their little things like bacteria type organisms. And just to think what kind of worlds there are, because they're probably really creative living organisms. Because the conditions, I guess the question I'm wondering to myself when I look out there to the stars, how different are the conditions on the different planets that orbit those stars?

• 16:52Speaker 01

  It will definitely be very different. I mean, the variety out there is is huge. We know now that, I think, it's about every other star has at least one planet. I already mentioned the number of stars in the galaxy. I mean, you know, that's it's a huge number of planets out there. So who knows what that looks like? All we know is that there is there is a lot of variety. We don't quite yet understand what drives that, what governs that, why that is the case? Why is it not all one size fits all?

• 17:29Lex Fridman?

  You mean the dynamics of planet formation, like exoplanet formation or star formation? The whole?

• 17:34Speaker 01

  All of it, all of it. Star formation is remains a much researched topic. We kind of we definitely know that it works because all the stars are there. Same for the planets. But the details are so varied per gas cloud, right? It's very hard to to come up with very detailed prescriptions. Broadly, we have figured it out. You need a gas cloud, you need to cool it. Something clumps in fragments and somehow it makes a star with planets or without.

• 18:08Lex Fridman?

  But the dynamics of the clumping process is not fully understood.

• 18:11Speaker 01

  No, no. And the local conditions are so varied, right? I mean, it's the same with, you know, all people look like people, but individually, we look very different.

• 18:22Lex Fridman?

  So even the subtle diversity of the formation process creates all kinds of fun.

• 18:26Speaker 01

  Yes. So we just don't know how this turned out in an individual case. And it's kind of hard to to figure it all out and to take a look, certainly with planets, right? The chance for ever to ever actually take a picture of a planet is miniscule because they don't shine. They're really dark. So I'd say there's a lot of possibility out there. But we have to be a little bit more patient.

• 18:56Lex Fridman?

  Or come up with technologies where patience becomes less necessary by extending our lifetimes or or increasing the speed of space travel, all the kind of stuff. Humans are pretty, pretty intelligent. They're pretty.

• 19:09Speaker 01

  Sometimes, yeah.

• 19:11Lex Fridman?

  For the most part, I hope. On the optimistic days, well, maybe just to linger on what a galaxy is. What should we know about our understanding of black holes in the formation? Is that an important thing to understand in the formation of a galaxy? Like, so all the orbiting, all the spiraling that's going on, how important is that to understand?

• 19:35Speaker 01

  All of the above. That's what makes astronomy really hard, but also really interesting, right? No day is like another because we always find something new. I want to come back to the idea of the proto-galaxy because it actually matches or relates to the black hole formation. So most large, well, pretty much all large galaxies have a supermassive black hole in the center. And we don't actually know, we don't really know where they come from. Again, we know that they are there, but how do we get there? So we go back to the to the early universe, right? We had a. A little galaxy that just sort of, you know, I don't know, had some small number of stars.

• 20:18Speaker 01

  It was the first gravitationally bound structure that that was held together by dark matter because dark matter actually kind of structured up, you know, first before the luminous matter could because that's what dark matter kind of does. And it it it started to hold um gas and then stars sort of together in these first very shallow um what we call potential wells, so these gravitationally bound systems. And then the Milky Way grew from absorbing neighboring smaller, even smaller systems. And somewhere in that process,

• 20:56Speaker 01

  there must have been a seed for one of these supermassive black holes. And I'm I'm not actually sure that it's clear right now, kind of what was there first, the supermassive black hole uh or the galaxy. So lots of people are trying to study that. And of course, the the black hole wasn't as massive back then as it is these days. Um but it's that's a it's a big area of of research. And the new um James Webb, the JWST, the telescope, the infrared telescope in space, is um is working on, many people are working on that to to figure out exactly what what happened. And there are some surprising results um that we really don't understand right now, so.

• 21:39Lex Fridman?

  So to solve the uh the chicken or the egg problem of uh, do you need a supermassive black hole to form a galaxy? Or does the galaxy naturally create the supermassive black hole?

• 21:48Speaker 01

  Yeah, yeah, I mean, I think to some degree we we can answer that because there are lots of little dwarf galaxies out there. You know, the Milky Way remains surrounded by many um dozens of of small dwarf galaxies. I have studied a a bunch of them. And to the extent that we can tell, they do not contain black holes. So there certainly were gravitationally bound structures. So either you can call them proto galaxies or dwarf galaxies or first galaxies. They were definitely there. But there must have been bigger things, like the proto Milky Way, where something was different, right? What made them more massive so that, you know, they would gravitationally attract these smaller systems to to integrate them.

• 22:33Speaker 01

  So we'll have to see.

• 22:35Lex Fridman?

  How do we look into that, into the dynamics of the formation, the evolution of the proto galaxies? Is it possible? Do they shine? I mean, what are the set of data that we can possibly look at? So we've got gravitational waves, which is really insane that we can even detect those. There's light. What else can we?

• 22:58Speaker 01

  So that would fall into the category of observational cosmology and the JWST is the prime telescope right now to, and it promises big, big steps forward. This is in its early days because it's only been online like a year or so.

• 23:17Speaker 01

  But that collects the infrared light from the furthest, like literally proto galaxies, earliest galaxies. That light has traveled some 13 billion years to us and they are observing these faint little blobs.

• 23:34Speaker 01

  And folks are trying to, you know, again, study the early, the onset of these early supermassive black holes, how they shape galaxies. So they are seeing that they are, they were there, you know, surrounded by already bigger galaxies. Ideally, I'd like for my colleagues to push a little bit further. Hopefully that will eventually happen.

• 23:55Lex Fridman?

  In terms of looking towards the older and older one?

• 23:57Speaker 01

  Yeah, yeah, more and more sort of primitive in terms of the structure. But of course, as you can imagine, if you make your system smaller and smaller, it becomes dimmer and dimmer and it's further and further away. So we're reaching the end of the line from a technical perspective pretty quickly.

• 24:14Lex Fridman?

  But it's dimmer and dimmer means older and older.

• 24:17Speaker 01

  Yes, in a sense, because it all started really small.

• 24:21Lex Fridman?

  Yeah, because it's smaller and smaller, which correlates to older and older.

• 24:25Speaker 01

  In that phase of the universe, it would, otherwise it doesn't.

• 24:29Lex Fridman?

  Just to take a small attention about black holes and You know, because you do quite a bit of observational cosmology and maybe experimental astrophysics. What's the difference to you between theoretical physics and experimental? So there's a lot of really interesting explorations about paradoxes around black holes and all this kind of stuff, about black holes destroying information. Do those worlds intermix to you, especially when you step away from your work and kind of think about the mystery of it all?

• 25:05Speaker 01

  Well, at first glance, there isn't actually much crosstalk. Personally, I mostly observe stars, so I don't usually actually think too much about black holes.

• 25:18Lex Fridman?

  And stars is a fundamentally kind of chemical, physical phenomenon that doesn't...

• 25:22Speaker 01

  That's right. The physics is kind of different. It's not extreme.

• 25:25Lex Fridman?

  Yeah.

• 25:26Speaker 01

  I mean, you know, you could consider a nuclear fusion sort of be perhaps extreme. You need to tunnel. There's some interesting physics there.

• 25:34Lex Fridman?

  Yeah.

• 25:35Speaker 01

  But it's just a different flavor, and I don't do these kinds of calculations myself either. I very much like to talk with my theory colleagues about these things, though, because I find there's always an interesting intersection. And often, it's just... I've written a number of papers with colleagues who do simulations about galaxies, and so they're not quite as far removed as, let's say, the black hole, you know, pen and paper folks. But even in those cases, we have the same interests and the same topics, but it was almost like we're speaking two different languages. And we weren't even that far removed, you know, both astronomers and all.

• 26:19Speaker 01

  And it was really interesting just to take the time and really try to talk to each other. And it's amazing how...

• 26:30Speaker 01

  How hard that is. You know, even amongst scientists, we already have trouble talking to each other. Imagine how hard it is to talk to non-scientists and other people to try, you know, to. We're all interested in the same things as humans at the end of the day, right? But everyone has sort of a different angle about it and different questions and way of formulating things. And sometimes it really takes a while to to converge and to to get, you know, to the common ground. But if you take the time, it's so interesting to participate in that process. And it feels so good in the end to say like, yes, we tackled this together, right? We overcame our our differences, not not so much in opinion, but just in expressing ourselves about this and how we go about solving a problem.

• 27:15Speaker 01

  And these were some of my most successful papers, and I certainly enjoyed them the most.

• 27:20Lex Fridman?

  It can also lead to big discoveries. I mean, there's a, I think you put it really well in saying that we're all kind of studying the same kind of mysteries and problems. I mean, I see this in the space of artificial intelligence. You have a community, maybe it seems very far away, artificial intelligence and neuroscience. You know, you would think that they're studying very different things. But one is trying to engineer intelligence and in so doing, try to understand intelligence. And the other is trying to understand intelligence and cognition in the human mind. And they're just doing it from a different set of data, a different set of backgrounds and the researchers that do that kind of work. And probably the same is true in observational cosmology and simulation.

• 28:05Lex Fridman?

  So it's a it's like a fundamentally different approach to understanding the universe. Let me use for simulation, let me use the things I know to create a bunch of parameters and create some, just play with it, play with the universe, play God, create, create a bunch of universes and see in a way that matches experimental data. It's a it's a fun, it's like playing Sims, but at the cosmic level.

• 28:33Speaker 01

  Yes, yes.

• 28:34Lex Fridman?

  So but and then probably the set of terminology used there is very different. And maybe you're allowed to break the rules a little bit more. Let's have, you know, yeah, it's like the Drake equation. Yeah, you don't really know. You kind of come up with a bunch of values here and there and and just see how it evolves. And from that kind of intuit the different possibilities, the dynamics of the evolution of a galaxy, for example. Yeah, but it's cool to play between those two because we it seems like we understand so little about our cosmos. So it's good to play.

• 29:03Speaker 01

  Yes, it's it's like a big sandbox, right? And everyone kind of has their little corner, they do things, but we're all in the same sandbox together at the end of the day.

• 29:13Lex Fridman?

  But in that sandbox does have super powerful and super expensive telescopes that everybody's also all the children are fighting for the resources to to make sure they guess get to ask the right questions using that big cool tool. Well, can we actually step back on the the the big field of stellar archaeology? What is this process? Can you just speak to it again? You've been speaking to it, but what what is this process of archaeology in the cosmos?

• 29:41Speaker 01

  Yeah, it's it's it's really fascinating. So I mentioned the the lesser the mass of the star, the longer it lives. And again, for reference, for the next dinner party, the sun's lifetime is 10 billion years. So if you have a star that's point six or point eight solar masses, then its lifetime is going to be 15 to 20 billion years. And that's that's an important range for our conversation because again, if you assume that such a small star formed soon after the Big Bang, then it is still observable today. You mentioned old light before. Yeah, that light is like a few thousand years old, but compared to the age of these stars is nothing.

• 30:26Speaker 01

  So to me, that's young.

• 30:29Speaker 01

  Comes straight from from our galaxy of, you know, it's not far. These stars are not far away. They're in our galaxy in the outskirts. They probably did not form in the galaxy. Because again, hierarchical assembly of a Milky Way meant. Exactly. They formed in a little other galaxy in the vicinity. And at some point, the Milky Way ate that, which means absorbed all the stars, including, you know, these little old stars that are now in the outskirts of the Milky Way that I use to point my telescope to. So.

• 31:04Speaker 01

  What can we learn from these stars? Why should we study them? Now, these little stars are really, really efficient with their energy consumption. They are still burning, for the experts, just burning hydrogen to helium in their cores. And they have done so for the past 12, 13 billion years, however old they are. And they're going to keep doing that for another few billion years. Same as the sun, the sun also just does hydrogen to helium burning and will continue that for a while. Which means the outer parts of the star, well, pretty much actually most of the star, that gas doesn't talk to the core.

• 31:43Speaker 01

  So whatever composition that that star has, you know, in its outer layers, is exactly the same as the gas composition from which the star formed. Which means it has perfectly preserved that information from way back then all the way to today and going forward. So I'm a stellar archaeologist because I don't dig in the dirt to find remnants of past civilizations and whatnot. I dig for the star, for the old stars in the sky because they have preserved that information from the first billion years in their outer stellar atmosphere,

• 32:28Speaker 01

  which is what I'm observing with telescopes. So I'm getting the best look at the chemical composition early on that you could possibly wish for.

• 32:37Lex Fridman?

  What kind of age are we talking about here? Are we talking about something that's close to that, you know, like a 13 billion, 12, 13 billion age range?

• 32:47Speaker 01

  Yeah, that's what we, what we think. Now, as a small caveat here, we cannot Accurately date these stars, but we use a trick to say, oh, these stars must have formed as some of the earliest generations of stars. Because we need to talk about the chemical evolution of the universe in the Milky Way for a second. So already mentioned the the pristiness of the universe after the Big Bang, right? Just hydrogen and helium. Then the first stars formed, they produced a sprinkle of heavier elements up to iron. Then the next generation of stars formed, that included again massive stars that they

• 33:28Speaker 01

  would explode again, but also the little ones that keep on living, right? And then the massive ones again explode as supernovae, so they provide again another sprinkle of heavier elements. And so over time, all the elements in the periodic table have been built up. There have been other processes, for example, neutron star mergers and other exotic supernovae that have provided elements heavier than iron, all the way up to uranium from very early on. We're still trying to figure out those details, but I always say pretty much all the elements were done from like day three.

• 34:08Lex Fridman?

  So iron is where, like, once you get to iron, you got all the fun you need, most of the fun?

• 34:14Speaker 01

  Yes or no? I really like the heavier elements, you know, gold, silver, platinum, that kind of stuff.

• 34:22Lex Fridman?

  For personal reasons or for star formation?

• 34:25Speaker 01

  Well, both.

• 34:26Lex Fridman?

  I mean, like, what's the importance of these heavier metals in the evolution of the stars?

• 34:32Speaker 01

  So they're the spice of life, right? So every supernova gives you elements up to iron. That's cool, but at some point it gets a little bit boring, because that always works. But that's the baseline. We need that. And that's certainly what came out of the first stars and then all the other supernova explosions that, you know, followed with every generation. And it took about a thousand generations, give or take, until the sun was made. So the sun formed from a gas cloud that was enriched by roughly thousand generations of supernova explosions. And that's why the sun has its chemical composition that it has, including, you know, and somehow

• 35:16Speaker 01

  the planets were made from that as well.

• 35:18Lex Fridman?

  So the supernova explosions, the many generations, are creating more and more complex.

• 35:24Lex Fridman?

  Elements.

• 35:25Speaker 01

  No, it just goes all the way up to iron.

• 35:27Lex Fridman?

  Yeah.

• 35:27Speaker 01

  And then it's just, it's a little bit more of, of all of these elements.

• 35:31Lex Fridman?

  Just more.

• 35:31Speaker 01

  Yeah, just, yeah, it's one sprinkle then another and it just kind of adds up, right? Now, the heavy elements form in very different ways. They are not fusion made. They are made typically through neutron capture processes, but for that you need seed nuclei. Ideally, you know, iron or carbon or something. So the supernova made elements are a very good seed nuclei for other processes. They then create heavy elements. And because they cannot be made everywhere, they, when you, when, you know, so I, my, some of my stars have huge amounts of these heavy elements in them. And they tell us in much more detail, something really interesting happened somewhere.

• 36:14Lex Fridman?

  Well, wait, I thought, I thought the really old ones we would not have. So what does that mean if, if the old?

• 36:19Speaker 01

  Ah, yes, important clarification. Um, so the stars that we are observing today, these old ones, they formed from the gas. And the question is, what enriched that gas? So it could have been just a first star dumping their elements into that gas all the way up to iron.

• 36:43Speaker 01

  And we have found some stars that we think are second generation stars. So they formed from gas enriched by just one first star. That's super cool.

• 36:53Lex Fridman?

  Yeah.

• 36:54Speaker 01

  Then we find other old stars that have a much more complicated, um, heavy element signature. And that means, okay, they are probably formed in a gas cloud that had a few things going on. Such as maybe a first star, maybe another more normal supernova. And maybe some kind of special process, like a neutron star merger that would make heavy elements.

• 37:22Speaker 01

  And so they created a local chemical signature from which the next generation star then formed. And that is what we're observing today. So all these old stars basically carry the signature from all their, these progenitor events. And it's, it's our job then to unravel, okay, which processes and which events and how many, you know, may have occurred in the early universe that led to exactly that signature that we observe 13 billion years later.

• 37:54Lex Fridman?

  Is it possible to figure out like the number of generations that resulted in this, in these stars?

• 38:00Speaker 01

  Well, we can, we, we think we can sort of say, okay, this was like second generation or third, because the amounts of heavy elements in, in the stars that we observe is so tiny. One supernova, one normal supernova explosion is actually already basically too much. It would give us too much of it. And the thing is, you can never take away things in the universe, you can only add. There's no cosmic vacuum cleaner going around sucking things away. Black holes are probably the closest to that, but they would have taken the whole star.

• 38:36Lex Fridman?

  Yeah, they'd take the whole thing, not just.

• 38:37Speaker 01

  They wouldn't take the stuff out of the gas, you know.

• 38:41Speaker 01

  So we have a, maybe 10 stars or so now where we, where we are saying that they contain so little of these heavy elements that there must be second generation, because how else would you have made them? And again, I want to, I want to stress that the elements that we observe in these stars were not made by the stars themselves that we observe. They, that's just a reflection of the gas cloud. So we don't actually, I had to say that because I love stars. We don't, at the end of the day, we don't really care for the stars that we're observing. We care for the story that they're telling us about the early universe.

• 39:17Lex Fridman?

  So, yeah, so the stars are kind of a small mirror into the, the, the early universe.

• 39:22Speaker 01

  Yeah, yeah.

• 39:23Lex Fridman?

  And so what are you detecting about those stars? Can you tell me about the process of archaeology here? Like, what kind of data can we possibly get to tell the story about these heavy elements on the stars?

• 39:34Speaker 01

  Yeah, it depends really on what star you find. There are many different chemical signatures. We actually pair up these days our our our element signatures with also kinematic information, how the star moves about the galaxy. That actually gives us clues as to where the star might have come from. Because again, all these old stars are in the galaxy, but they are not off the galaxy. That's a small but important distinction, so they all came from somewhere else.

• 40:09Lex Fridman?

  So you can rewind back in time, kind of estimate where it came from?

• 40:12Speaker 01

  Yeah, so we can't really say, oh, it came from that dwarf galaxy. But interestingly enough, so I'm just, just a few days ago, I submitted a paper with three women undergrads. It was so good to work together. And we found a sample of stars that have very, very low abundances in strontium and barium, so very heavy elements. And I had a hunch for a while that these stars would probably be some of the oldest. Because, as I said, heavy elements give you extra information about special events. And again, finding something that's really low means it must have for it,

• 40:53Speaker 01

  that must have happened either really early on or in a very special environment, right? Because we can only ever add. So if you find something that's incredibly low in terms of the abundance, maybe just one event contributed that max. So we looked at the kinematics, how are these stars moving? And they're all going the wrong way in the galaxy.

• 41:19Speaker 01

  How how is that possible? Well, it is possible because consider now we come back to the proto galaxy. The proto galaxy was like a beehive. It just didn't really know what it was or what it wanted to become when it grew up. So and it was absorbing all these little galaxies to grow fast. Some galaxies, some absorbed galaxies were thrown in going the main way. And some came in the wrong way, huh? Happens.

• 41:46Lex Fridman?

  Yeah, happens.

• 41:47Speaker 01

  But this could only happen early on when, you know, there wasn't left and right and up and down. So stuff would come in from all ways. So now thirteen billion years later, we're looking. Yeah, A, they're still doing it. And B, we just looked for stars that have low strontium barium abundances. And then we look at the kinematics and lo and behold, they're all at hundreds of kilometers per second going the wrong way. It's like, dude, you must have come in really early on from somewhere else. So we call this retrograde motion. That's a clear sign of accretion. So something that has come into the galaxy.

• 42:28Speaker 01

  And because they are so fast, and it's really all of them, that that must have happened early on, right? You can't throw a galaxy into the Mickey Ray right now the wrong way. It eventually will turn around.

• 42:41Lex Fridman?

  Can you actually just on a small tangent speak to the the three women undergrads? Like this little, it's pretty cool that you were able to use a hunch to find this really cool little star. Yeah, what's the process like, especially with undergrads? I think that would be very interesting and inspiring to people.

• 42:59Speaker 01

  Yes, it was a wonderful little collaboration that actually emerged in the fall. I so I like, I really like working with with undergrads and grad students, postdocs. And I came up with a new concept for a class at MIT where I wanted to integrate the research process into the classroom. Because sometimes people find it really hard to called email a professor, hey, you know, this, I'm this and that person, and I'm interested in your research could have possibly, you know, come.

• 43:33Lex Fridman?

  Yes.

• 43:34Speaker 01

  And I wanted to streamline that and give an initial trial, how it would work to provide a sort of the safe confines of a classroom where you just sign up. And do research in a very structured way. And I developed it, it was a lot of work, a little bit more than I thought, to map up an entire research project, basically from scratch in ten worksheets, so that they could do it, again, in a very structured and organized fashion.

• 44:08Lex Fridman?

  Oh, so you created this whole framework for them to do it?

• 44:10Speaker 01

  Yes, the whole thing. But the promise was, you come, sign up for my class. In terms of two, you each get your own old star that has not been analyzed before. I don't know what the solution is, because in research, we don't look up the solution at the end of the book. We do not know what we're going to find. Our job is to do the work and then to interpret the numbers, because our job as scientists is to find the story.

• 44:38Lex Fridman?

  Yeah.

• 44:39Speaker 01

  Anyone can crunch numbers, anyone. It's kind of complicated sometimes, but it's doable, right?

• 44:47Lex Fridman?

  Yes.

• 44:47Speaker 01

  But coming up with a story, when you only have three puzzle pieces, what does the puzzle look like? That you have to be a little bit bold. You need to have some experience. And you need to, you need to kind of see the universe in 3D. You just need to kind of go for it. And that's the beautiful thing. I really love that.

• 45:06Lex Fridman?

  And so this was a story of weird kinematics going the wrong way, combined with this particular weird signature in terms of the heavy elements.

• 45:14Speaker 01

  Exactly.

• 45:15Lex Fridman?

  And you have to come up with a story.

• 45:16Speaker 01

  Yes, and so the story of that paper is now, usually I don't say I find the oldest stars. You know, when I talk to my research colleagues, I talk to them about, we find the chemically most pristine stars, because that's actually what we measure, the chemical abundance that tells us, okay, it must have been second or third or fifth generation of stars, right? But these low strontium stars that go in the wrong way, like they're getting paid for it, they must be the oldest stars that came into the galaxy because they formed before the galaxy was the Milky Way, right? And this is so cool, and it was so wonderful. So this class, it went so well in the fall. I had nine people sign up.

• 46:01Speaker 01

  That's not unusual for a class, a specialty class at MIT, so small number. It was eight women, and they were so into it that I said, okay, let's use this opportunity. You're gonna do some extra work with me. And we're going to publish this.

• 46:18Lex Fridman?

  Try to publish.

• 46:19Speaker 01

  Yes.

• 46:20Lex Fridman?

  I also like that you're using the terminology of chemically more pristine. When I'm talking to younger people, I'll just say that I'm more chemically pristine than them. I like that description of age. So there's this term of metal poor stars. So most of these old stars are going to be metal poor.

• 46:38Speaker 01

  Yes, I I search for the most metal poor stars.

• 46:41Lex Fridman?

  And what is that? Can we just define?

• 46:42Speaker 01

  Yeah, what does that mean? I don't know who came up with this. I would I would love to know, but um. The universe is a complicated place. So many decades ago, someone clever came up with the idea to say, let's simplify things a little bit. Let's call hydrogen X, helium Y, and all the other elements combined metals Z.

• 47:10Speaker 01

  When when I give public talks, I always ask, is there a chemist in the audience? Let me just tell you, neon is a wonderful metal. And they're like, oh, my God, what's he saying? But I'm an astronomer. I'm not a chemist, so I'll get away with it. So if you just roll with it for a moment, all the elements except hydrogen and helium are called metals. Now, if we look again at chemical or the concept of chemical evolution, it means more and more of all the elements, everything heavier than hydrogen and helium, gets produced slowly but surely by different types of source and events. So that's a, you know, a monotonously increasing function.

• 47:51Speaker 01

  And so we look for the stars that have the least amounts of heavy elements in them. Because that means we are going further and further back in this process, in that function, almost all the way to the very beginning. And that is the first stars, right? They they started that that process. That's why I said it was such an important transition phase, because it things were, we we call, you know, the the post Big Bang universe pristine, just hydrogen, helium. And after that, the mess started. If you soon as you add elements to it, things kind of get a little out of hand. That that's that ends in this beautiful variety that that we have everywhere these days.

• 48:33Lex Fridman?

  Yeah, and you're looking at the very early days of the introduction of the variety.

• 48:37Speaker 01

  Yes, exactly, when it was still a little bit more organizable.

• 48:44Speaker 01

  But the variety of different types of metal poor stars we have is stark. Many different types of stars, many patterns we have sort of identified, but they are still crazy ones out there that we're still trying to kind of fit in.

• 48:58Lex Fridman?

  So what kind of stars have been discovered? So you've already a while ago helped discover the star HE 1327 2326, great name.

• 49:10Speaker 01

  Yes.

• 49:11Lex Fridman?

  And HE 1523 0901. What can you say about these stars and others that have been found?

• 49:19Speaker 01

  I love them. They're my baby stars.

• 49:22Lex Fridman?

  What do you call your baby stars?

• 49:26Speaker 01

  Well, I'm probably the only one who can spit out these names without cheating.

• 49:30Lex Fridman?

  Are there nicknames?

• 49:32Speaker 01

  Well, no, that's.

• 49:33Lex Fridman?

  It's not allowed? Okay.

• 49:35Speaker 01

  Well, some colleagues at conferences have just called them Anna star or Freiberg star because they didn't want to learn the phone number. I get it.

• 49:45Speaker 01

  These numbers are actually based on older sets of coordinates for these stars. So they, yes, the minus in the middle means that they're in the southern hemisphere. So negative is in the southern hemisphere, positive is in the northern. And then 13 and 15 means that's sort of observable in the middle of the year.

• 50:01Lex Fridman?

  Okay, so it has to do with the observation and where it was observed?

• 50:04Speaker 01

  Yes, yes, yes. But they have very different stars, both absolutely significant,

• 50:12Speaker 01

  career defining actually for me, but really pushed the envelope in very different ways. So HE 1327, the first one that you mentioned, that was the second second generation star that we found. And usually people say like, oh, the first one is the big one and the rest is nobody cares. But to us, it proved that yes, we can do it. Because one, astronomers live in this sort of way of, you know, there are a lot of serendipitous discoveries and we. That's really great, but we need to show that we can do it again.

• 50:50Lex Fridman?

  Mm hmm reliably.

• 50:51Speaker 01

  Because then then we're on to something and it's not just some kind of weird quirk. And there are a lot of quirks in the universe, but we want to know, is that a real thing? Does that happen regularly? Is there something that we can learn? What is that a piece of the story? And so finding the second one that was even a little bit more extreme than the first one really showed, yes, our search techniques work. We can find these stars. They provide an important part to the story in the sense that if we had more than two stars, and by now we have about tenish or so, what do they tell us about the nature of the very first stars?

• 51:33Speaker 01

  And what we found, again, working with the theorists, of course, who run these supernova models, is that, so actually, let me, let me, before I get into this, these two stars had huge amounts of carbon relative to iron. So we usually use iron as a reference element for what we call the metallicity. So the overall metal content, the overall amount of heavy elements in it.

• 52:02Lex Fridman?

  So that's why it's called iron deficient.

• 52:04Speaker 01

  That's right. So these stars are incredibly iron deficient, which means they must be of the second generation because there was, and interestingly enough,

• 52:16Speaker 01

  there was this discrepancy.

• 52:19Speaker 01

  A normal supernovae, until then, we thought would get us so much iron. You know, you would distribute that in the gas cloud and then you would form this little star that we're observing, but the iron abundance that we measured was actually much lower than that. And already mentioned, you can't take things away. That must mean these early massive pop three, we call them population three, the first stars, they must have exploded in a different way than we previously thought. They can't output as much iron because. They just can't. Otherwise, it wouldn't match our observations.

• 52:55Lex Fridman?

  Got it.

• 52:56Speaker 01

  And so that's when we started to work with several theory groups on supernova yields. So what comes out of?

• 53:05Lex Fridman?

  From the explosion of the supernova? That's cool. Supernova yields. And so this one was not yielding much iron.

• 53:12Speaker 01

  Well, we needed to concoct a theoretical supernova that made less. And it's actually surprisingly difficult. Because you can always add more in the universe, right? But you can't take stuff away. So Japanese colleagues kind of came up with the idea of a fainter supernova. That just doesn't have much, enough oomph, you know, when it explodes. So somehow, there's less iron coming out. But at the same time, then these stars showed huge overabundance of carbon, you know, a thousand times more carbon. So how do you now get a thousand times more carbon out of these poor first supernovae? That was the theoretical challenge.

• 53:56Speaker 01

  And because we didn't have just one star, but two, that really spurred the field to think about, what was the nature of the first stars? How did they explode? What are the implications? Because if they are not as luminous and bright and energetic, that has consequences for these early protogalaxies in which, you know, they must have been located in terms of, you know, blowing the gas out, let's say, and disrupting the system. So much higher chance for the earlier system to stay intact for longer, right? So there's a whole tale of consequences. And this is what I mean with, we need to find the story. Because you do one thing, and it's like the dominoes,

• 54:41Speaker 01

  the consequences everywhere, and suddenly you have a different universe, right?

• 54:44Lex Fridman?

  What could possibly be a good explanation for something that yields a lot of carbon and doesn't yield a lot of iron?

• 54:53Speaker 01

  Well, it's not so much an explanation, more like finding a mechanism for what happens in supernovae. And the official term, what was sort of, as I said, cooked up in order to explain the observations. And we have, by the way, found a whole bunch more of these stars, so that holds. And it's called a fallback mechanism. So actually, during the supernova explosion, a massive black hole emerges. And so some of the material falls back onto the black hole. So here is a vacuum cleaner now plopped into the middle, right?

• 55:27Lex Fridman?

  Like a temporary one that just cleans up some of the elements?

• 55:29Speaker 01

  Well, sort of, right? Because if you think of the, we haven't talked about this yet, but if you know what a star looks like, a massive star looks like in its interior before it explodes, you have hydrogen, helium still on the outskirts, and then you have your layers of heavier and heavier elements all the way up to iron. So you have an iron core in the center.

• 55:49Lex Fridman?

  Yep.

• 55:50Speaker 01

  And because you can't get any energy out of iron when you want to fuse to iron atoms anymore, right? That's when the supernova explodes, occurs really. It's actually an implosion first, and then you have a bounce of the sort of neutron star phase that occurs in the process.

• 56:09Lex Fridman?

  That is so awesome.

• 56:11Speaker 01

  And then the star gets disrupted. Yeah, it's like this giant basketball, and then whoa, it all goes out.

• 56:17Lex Fridman?

  Implosion first, explosion after.

• 56:19Speaker 01

  Yeah. And so in the process, right, if you make your black hole basically big enough, it will suck away some of the iron, because that's the closest in terms of the layers. You hold on to it, you don't let it escape, and carbon is much further out, you let it all go.

• 56:36Lex Fridman?

  Nice.

• 56:37Speaker 01

  And so...

• 56:38Lex Fridman?

  So that explains why you can have a big oomph and not much iron yield.

• 56:41Speaker 01

  Yes, yes.

• 56:43Lex Fridman?

  So is this explained the HE1327?

• 56:46Speaker 01

  Correct.

• 56:47Lex Fridman?

  And others like it?

• 56:49Speaker 01

  Yes. So there's a, well-established now that the lower the iron abundance of the stars are, the higher the carbon sort of gets. And carbon is such an interesting element in that regard.

• 57:04Speaker 01

  If we come back to the formation of the first low-mass stars, right, so we had the hotter gas, just hydrogen and helium, that made the first stars. There were 100 solar masses or so because the gas couldn't cool enough. So they were big and puffy. Carbon, then, coming from the first stars, probably led to enough cooling in these gas clouds that enabled the formation of the first low-mass stars. So think about what happened if there wouldn't have been any carbon or the properties of the carbon atom would be different. It would not have cooled the gas in such significant ways, perhaps. There wouldn't be any low-mass stars. We wouldn't be here today, right?

• 57:49Speaker 01

  And we're carbon-based. And so I think carbon is really the most important element in the universe for a variety of reasons because it just enabled this whole evolution that we're now observing and literally seeing in the sky. And it's really fascinating.

• 58:04Lex Fridman?

  So combined with the fact that you have the iron deficient, so all of that is probably important to creating humans.

• 58:11Speaker 01

  Yeah, yeah, we need all the elements. But if you don't have stars, you know, like the sun, small stars that can actually host planets that have long lifetimes, you need long, long lifetimes if you want to have a stable planet and develop humans.

• 58:25Lex Fridman?

  So carbon is kind of important in many ways.

• 58:28Speaker 01

  Yes, yes.

• 58:30Lex Fridman?

  This is perhaps an interesting tangent. If I could just mention that you interviewed Milja Dresselhaus, carbon queen, The Remarkable Life of the Nanoscience Pioneer. Is there something you could say about the magic of carbon and the magic of Milli?

• 58:50Speaker 01

  Well, Milli was certainly magic. She was a professor at MIT for many decades. I met her a number of times. Her photograph, actually, a young and an older Milli is still on the wall. Every time I step out of the elevator in one of the buildings, I see it. She pioneered all sorts of carbon nano-work. So she was a material scientist.

• 59:17Speaker 01

  Very far removed from what I do on a daily basis. But yes, carbon has amazing properties when you study it. And again, that's indeed another aspect of why carbon is so fascinating. Not just in the cosmos, but also for us, you know, making us, creating us in the way that we can use it. It's wonderful.

• 59:42Lex Fridman?

  Do you sometimes think about this chemical evolution in this big philosophical way? That we're

• 59:50Lex Fridman?

  we're the results of that chemical evolution, like we're made of this stuff. We're made of carbon.

• 59:55Speaker 01

  Yes, we're made of sore stuff.

• 59:56Lex Fridman?

  Yeah.

• 59:57Speaker 01

  Cause they can go right.

• 59:59Lex Fridman?

  I mean, it's almost like a cliche statement, but it's it's also a materials, a chemical, a physics statement. It came from hydrogen and helium. And somehow this formation has created this interesting complexity of soup that made us. What are we supposed to make of that?

• 1:00:19Lex Fridman?

  Like, what, did we just get really lucky? Why, why did we get all this cool stuff?

• 1:00:24Speaker 01

  Yeah, that's, that's a good question.

• 1:00:26Lex Fridman?

  I don't think it's a question that has an answer. I keep just asking why.

• 1:00:29Speaker 01

  Yeah.

• 1:00:30Lex Fridman?

  But it's, it's just this incredible mystery. So much cool stuff had to happen. So much, sorry, hot stuff had to happen to create us.

• 1:00:39Speaker 01

  And so much could have gone wrong and there would have been another outcome, you know? And it's actually amazing how, how many things kind of fell in place. I mean, maybe that's all sort of self deterministic in some ways, right? We are who we are because that, that was the path.

• 1:00:57Speaker 01

  Maybe we would have ended up being robots. I don't know. But it's, it's, it's certainly wonderful to, you know, as scientists for us to, to help contribute unraveling our, our cosmic history. Right? I always say the biological evolution on earth was you know, absolutely facilitated by the chemical evolution of the universe. Right? And one doesn't go without the other.

• 1:01:21Lex Fridman?

  And that evolution.

• 1:01:22Speaker 01

  From a human perspective.

• 1:01:24Lex Fridman?

  That evolution seems to be creating more and more complexity. The kind of interesting clumping of cool stuff seems to be accelerating and increasing. And it's hard not to see as humans that there's some kind of purpose to it. Like a momentum towards complexity and beauty, you know?

• 1:01:44Speaker 01

  Well, beauty is in the eye of the beholder. But yes, everything gets more complicated.

• 1:01:50Lex Fridman?

  But there's also a beauty to the chemically pristine universe in the early days.

• 1:01:55Speaker 01

  Certainly, yes, yes. I love the desert with its nothingness.

• 1:01:59Lex Fridman?

  Yeah.

• 1:01:59Speaker 01

  It has so much aesthetics and appeal.

• 1:02:03Lex Fridman?

  We came from nothing, we'll return to nothing. So what about HE1523? What's exciting? A red giant star.

• 1:02:13Speaker 01

  Yes.

• 1:02:14Lex Fridman?

  That's another one of your babies.

• 1:02:15Speaker 01

  Yes.

• 1:02:16Lex Fridman?

  Thirteen point two billion years old.

• 1:02:19Speaker 01

  Yeah, so that one isn't quite as iron deficient as the other one. So probably not a second generation star, but easily second, third, sorry, third, fourth, fifth or so. We can't really pin it down, but it's also not super important for us. What is important is that that star has a very different chemical composition. In a sense that, yes, we have all the elements up to iron there. They have sort of normal ratios, which means kind of the same as most other old stars and not too different from the sun, or at least, you know, different in quantifiable ways.

• 1:03:03Speaker 01

  But it has this huge overload of very heavy elements. And what was so nice about that star in particular was that I could measure the thorium and the uranium abundance. And again, that was the second of its kind. But the uranium abundance was, could be more well determined, so we had a better grasp on that. Now, why are thorium and uranium interesting? They are radioactive elements. They decay. Thorium has a half-life of fourteen billion years, I believe, and uranium of four point seven.

• 1:03:42Speaker 01

  Which, you know, two folks on us on Earth is a really long time, but those kind of timelines are really good when you want to explore the early universe. So there are two questions now that that kind of come to mind. Where do these elements come from? And what do they tell us, right? And these, as we know, these heavy elements are made in a specific process. It's a neutron capture process, usually referred to as the R process for rapid neutron capture process. We talked about seed nuclei before, right? So we still don't exactly know where this process can occur.

• 1:04:24Speaker 01

  So you have, let's say, a lone iron atom somewhere, and it is in an environment where you have a strong neutron flux, which means there must be lots of neutrons around. And again, when we talk about the site, we can surmise and ponder where that might be the case. But you have this iron atom and you bombard it with neutrons and you do it incredibly fast. Now, what happens in the process? That iron atom, you know, you collect lots of neutrons. It becomes really big and unstable. So it's a heavy neutron-rich nucleus that wants to decay because it's not stable, it's way too big. And so let's say you add only one neutron to it.

• 1:05:10Speaker 01

  That would already make it unstable. So it will then, it has a characteristic decay time. That's called the beta decay timescale. So it will decay to a stable nucleus. So the neutron will convert to a proton and that makes it stable.

• 1:05:24Speaker 01

  If you now bombard lots and lots and lots of neutrons onto that seed nucleus within that time scale of the beta decay, that's how you get to this huge fat neutron-rich nucleus that then wants to decay, right? So the R, the rapid process is you have your seed nuclei, they get bombarded. You create these really heavy neutron-rich nuclei. They're heavier than uranium even. The neutron flux stops and then all these heavy nuclei, they decay. And they make all these stable isotopes that we know of, all the way up to thorium and uranium.

• 1:06:03Lex Fridman?

  So that rapid nuclei decay is what creates all the functions.

• 1:06:07Speaker 01

  Correct, and the whole thing is done within two seconds.

• 1:06:12Speaker 01

  So just to add to the rapid here, literally the snapping on my hand, it's all there. In my talks, I often, I have this nice simulation that illustrates, you know, this creation of these rap- of these heavy nuclei, and I always say, this is the only simulation you will ever see that's slower than real time. Because in astronomy, you know, we show, oh, this is how a galaxy forms, 13 billion years in 30 seconds. Really short, right? This is the opposite. Me showing you this, the elements are already long made.

• 1:06:48Lex Fridman?

  So where and when does this happen? Does this process happen?

• 1:06:51Speaker 01

  So you need the strong neutron flux.

• 1:06:55Lex Fridman?

  That's the clumping of the neutrons.

• 1:06:57Speaker 01

  Yes, that's right. And so there are not that many options, right? So where do you find lots of neutrons in the universe? So it's neutron stars, right? Neutron stars form in the making of supernovae, of the explosions. Okay, so maybe some of this heavy material gets sort of made in the making of the supernova explosion and then gets expelled. Or you have neutron stars, so the, you know, if the neutron star, I mean, usually that's the leftover of the supernova. If you have two from a binary pair, so stars usually actually show up in pairs, and so it's not too unusual to create a pair of neutron stars that will still orbit each other after

• 1:07:42Speaker 01

  both of their progenitor stars have exploded. And those two neutron stars will orbit each other diligently, but as we know now, thanks to LIGO, the Gravitational Wave Observatory, I mean, we know already that

• 1:07:57Speaker 01

  Before, but now it's been measured by LIGO, is that these two neutron stars, they will orbit each other for like forever, but in the process, they will, they will lose energy. So that orbit is what we call the orbit decays. And eventually, the two neutron stars will merge. And that results in a, in an explosive event that has roughly the energy of a supernova. But the process is completely different. And the cool thing is, when these two neutron stars collide, they produce a gravitational wave signature. Because neutron stars are super dense objects. They are like giant atomic nucleuses. So there's a lot of interesting physics happening already.

• 1:08:41Speaker 01

  And so if you basically form a super neutron star by smashing two into each other, more interesting physics happens. And that means that there's this ripple sent out, you know, into the space, you know, the spacetime continuum, basically, you know, the, what do people say, the ripples of spacetime, you know, it's like, it's like you drop a rock into water, right? You see the waves coming. So that's exactly what happens when two neutron stars merge. And this is neutrons galore, right? It's really violent to smash two neutron stars, you know, so that are so dense already into each other.

• 1:09:20Speaker 01

  And they, in 2017, one of these events occurred, and the LIGO and Virgo gravitational wave observatories, they detected that. And then the astronomers pointed their telescopes in that direction, and they indeed observed what we call the electromagnetic counterpart. So there was something seen in the sky that faded over the course of two weeks. And that light curve, that light, was exactly what you get when you create all these heavy neutron-rich nuclei in the art process, and then the neutron flux stops. And then it takes about two or three weeks for most of them of these nuclei to decay

• 1:10:05Speaker 01

  to stability. So we saw, the astronomers saw, in this electromagnetic counterpart, the nucleus synthesis of heavy elements occurring. And that's, that's just

• 1:10:19Lex Fridman?

  That's amazing.

• 1:10:19Speaker 01

  Awesome.

• 1:10:20Lex Fridman?

  So that's electromagnetic counterpart to the gravitational waves that were detected with

• 1:10:25Speaker 01

  Yes.

• 1:10:26Lex Fridman?

  Two neutron stars

• 1:10:28Speaker 01

  Yes.

• 1:10:28Lex Fridman?

  Colliding aggressively, violently to create a supernutron star. And that's where you get all the neutrons and neutron flux somehow. And then that, the whole shebang that happens in two seconds and creates a bunch of

• 1:10:41Speaker 01

  So that confirmed that one of the sites, for sure, is for the R process to occur is neutron star mergers. Interestingly enough, I have to mention this here, a year prior in 2016, my former grad student Alex G. and I, we discovered a small dwarf galaxy

• 1:11:03Speaker 01

  that is currently orbiting the Milky Way, it's called Reticulum II, that was full of ancient iron deficient stars that also had a strong signature of these heavy elements, exactly like AT1523. We weren't looking for that. I actually wanted to prove that they had really low levels of heavy elements because that's what we had seen in all the other dwarf galaxies. And I was dead set on showing yet, that that is yet the case again, and that that is a typical signature of early star formation. We already talked about low strontium and barium abundances and the oldest stars, right? This is what we had seen anecdotally in, in the ancient dwarf galaxies that are surrounding us.

• 1:11:47Lex Fridman?

  So that's an ancient dwarf galaxy. That dwarf galaxy has a bunch of ancient stars in it.

• 1:11:51Speaker 01

  Yes, yes. And so now we find Reticulum II, and it has these, the stars show the signature of the rapid neutron capture process, the R process. And we are like, okay, these stars are located in a dwarf galaxy right now. We have environmental information. They are not lost in the galaxy where we don't know where they actually came from. No, we know these stars were formed in that galaxy because they're still in it.

• 1:12:19Speaker 01

  And that we already deduced from that that it must have been a neutron star merger that went off in reticulum II at early times that polluted the gas from which all our little stars formed.

• 1:12:30Lex Fridman?

  Can you speak to what a dwarf galaxy is? Can you speak to what this reticulum II dwarf galaxy is that is orbiting the Milky Way galaxy?

• 1:12:37Speaker 01

  Yeah.

• 1:12:37Lex Fridman?

  It's going to be eaten by it presumably.

• 1:12:39Speaker 01

  It totally is going to be eaten.

• 1:12:40Lex Fridman?

  Okay.

• 1:12:41Speaker 01

  I can't tell you exactly when. Um, yeah, the Milky Way remains surrounded by dozens of small dwarf galaxies. Um, they're collections of stars. Um, some of them, uh, we call them ultra faint dwarf galaxies because they now only contain, I don't know, a few thousand stars, um, very, very faint.

• 1:13:02Lex Fridman?

  But still detectable?

• 1:13:02Speaker 01

  Uh, yes, because they're fairly close and, and we detect actual individual stars in them. So I've observed some of the, the faintest stars, you know, you possibly observe with current telescopes in, in these dwarf galaxies because I was like, I need to know what the chemical composition is because the, there are leftovers from the early universe, right?

• 1:13:23Lex Fridman?

  Yeah.

• 1:13:23Speaker 01

  They, they did not get eaten. So they're still in their native surroundings. I, I go, it's like getting the lions in the wild, right? I, I gotta study those.

• 1:13:32Lex Fridman?

  Yeah.

• 1:13:32Speaker 01

  And compare to the counterparts that got eaten and are now in the Milky Way. And so I-

• 1:13:38Lex Fridman?

  So presumably most of those stars, it's not all those stars in that dwarf galaxy are really ancient.

• 1:13:42Speaker 01

  They're all really ancient because actually, as it turns out, if you have a small galaxy, um, there, there was a process early on in the universe called reionization that kind of heated up everything.

• 1:13:55Lex Fridman?

  Mm-hmm.

• 1:13:55Speaker 01

  And together with some supernova explosions in, in early shallow, you know, bound system, all these little systems lost their gas. It was sort of blown out or it, it simply evaporated or both, probably both. Um, and so these systems have been unable to continue to form stars since.

• 1:14:17Lex Fridman?

  Mm-hmm.

• 1:14:17Speaker 01

  So it's, it's, it's the best for us stellar archaeologists that you could hope for because it's a whole bunch of stars still sitting there. It's not just one, it's a whole bunch of them still sitting there ever since and nothing has, literally nothing has happened to them. They've just been waiting there for us.

• 1:14:35Lex Fridman?

  So from the stellar archaeology perspective, what is like juicier, more interesting? The, uh- The old stars in the outskirts that have been eaten are the outskirts of Milky Way or the stars in the dwarf galaxies. What's, of all the things you love about the world? You said you love stars, so which do you love more of your children?

• 1:14:58Speaker 01

  That's a hard one. I mean, I love them all, of course. They serve different purposes. The stars in the Milky Way, I can get much, much, much better data for them because they're brighter. They're closer, so they're brighter. And that tickles my fancy.

• 1:15:16Lex Fridman?

  And they have interesting kinematics presumably?

• 1:15:18Speaker 01

  Yes, and we can get that. And so H2-1523, for example, you know, that one is really bright. Only, it's a red giant, so it's intrinsically bright and it's fairly close. And so the data I got for that was insanely good. And that yielded this uranium detection, anthropium detection. I can never get that kind of data for a dwarf galaxy star. So that's a big trade off. But the environmental information that we get along with the basic information of these stars in each dwarf galaxy is really, really valuable in establishing, you know, these, for example, these site information, right?

• 1:15:54Lex Fridman?

  Sure.

• 1:15:54Speaker 01

  Because the galaxy is still there, so nothing crazy could have happened. So to close that loop, probably some heavy elements come out of supernovae here and there. But somehow, my theory colleagues tell me that the normal supernova just doesn't have enough oomph to really get an R process going and doing it all.

• 1:16:15Lex Fridman?

  So you need these orbiting supernova?

• 1:16:18Speaker 01

  We need probably the neutron star mergers or we need a special kind of supernova that's maybe extremely massive or heavily rotating or does something else funny, right? To really kind of get that particular process going. But the normal supernovae don't do it, right? So only a little bit comes out. But you could come along and say, Anna, why don't you just take 100 supernovae together to build up the yield, right? But then I come along and say like, look, this dwarf galaxy is still intact today. If you would have plugged in 100 supernovae into this little system early on, it would have blown apart. It would have blown apart past five supernovae or 10. So that's a really important constraint that we have, that these systems are still alive, right?

• 1:16:59Speaker 01

  So it helps us to pin down where certain processes could have possibly happened. And so it's just a different type of information that we get.

• 1:17:11Lex Fridman?

  It'd be amazing if we could talk about the observational aspect of this, the tools of observation. So what telescopes have you used, do you use? And what does the data look like? And I think I've read a few interesting stories about the actual process of day to day observation, a bunch of probably late nights.

• 1:17:31Speaker 01

  Well, yeah, astronomers are doing it all night long, so lots of late nights.

• 1:17:35Lex Fridman?

  Can you explain the all night long aspect of it?

• 1:17:38Speaker 01

  Well, let me start by saying I mostly these days use the Magellan telescopes in Chile. They are 6.5 meter telescope, which means the mirror diameter is 6.5 meter. That's not the largest that is out there, but it's among the largest. And I use a spectrograph because I'm a spectroscopist. I don't take pictures. And that particular spectrograph at that telescope is actually unusually efficient. So it kind of makes up for the fact that the mirror isn't as large in, let's say, the eight meter telescopes from the Europeans or so. So I'm very happy with that.

• 1:18:18Lex Fridman?

  Efficiency meaning?

• 1:18:19Speaker 01

  How many photons get collected sort of per time unit? Because that's always the limiting factor.

• 1:18:30Speaker 01

  Prior to the pandemic, we would travel to Chile to do our observations. Those telescopes are the, that's the last observatory where people were sort of supposed to travel there and take their own observations. Most other observatories basically have staff there by now who take the observations for you.

• 1:18:50Lex Fridman?

  So there's the directly, the scientists are specifying where to point the telescope and sitting there and collecting the data, making sure the data is collected well, the cleaning of the data, the offloading of the data, all that kind of stuff.

• 1:19:03Speaker 01

  Yeah, so it's mostly done for them.

• 1:19:05Lex Fridman?

  Yeah.

• 1:19:07Speaker 01

  Obviously, that's super convenient, but it also takes, takes away a central part of what the work of an astronomer is, which is data collection. Right, we don't have an experiment in the basement where we can go day and night or whenever we please and ask a certain question of the apparatus, right? Let's turn this knob and see what happens. Let's turn that knob and see what happens. No, you know, we, we only have one experiment, uh, which is the universe. And we, what we see is what we get. And I think it's, it's so important to, to take an active role in that. So I really loved going to the observatory.

• 1:19:48Speaker 01

  I've taken many students there over the years to, to teach them and to just show them what it means to, to be an astronomer because you, you go to the, these remote mountain tops and it's such a magical environment and you wait there, you know, for the sun to go down and then you get ready and you look outside and it's, it's such a serene environment. Um, it's, it's a little bit out of this world.

• 1:20:19Lex Fridman?

  You're sitting there, so the sun goes down, it's evening, late evening. And what does it look like? What are some of the most magical experiences of that process?

• 1:20:27Speaker 01

  Well, you know, when you're on top of a mountain, uh, you know, climbers, I guess, get to see that probably, um, otherwise, um, it's, it's very calm and the colors are so beautiful and I always become much calmer when I'm there. I'm just, A, because I'm just there for one purpose only, that's data collection. I can say no to my emails, I can say no to everything else because I'm observing. So there, there's literally less, less distractions because, you know, you're just there to do one thing.

• 1:21:04Lex Fridman?

  And also the emails somehow seem less significant.

• 1:21:07Speaker 01

  Yeah, yeah. It's, it's just, you can afford to focus on this one thing and you, it, it just kind of does something to you. It's, it's, it's a little hard to describe, but, um, You know, if you then fast forward, maybe I can speak a little bit about that. And I have done a lot of astrophotography there as well. So, and, and I, observing faint dwarf galaxy stars, you know, these are like forty five minutes, fifty five minute exposures. So you actually have a lot of time. So I would run outside and just lay on the ground under the Southern Milky Way. Beautiful, right up, you know, there. And I would just lay there like the snow angel, you know.

• 1:21:49Speaker 01

  And I'd just stare up there and just kind of let my thoughts sort of pass through my brain and just like, I'm, I'm one of it, right? We talked about this in the beginning. This is when I personally have the feeling that I'm a part of it. I, I belong here rather than feeling kind of small. Yes, I'm small, but there are many other small things and lots of small things make one big whole.

• 1:22:13Lex Fridman?

  Yeah, we're a part of that big whole.

• 1:22:14Speaker 01

  And.

• 1:22:15Lex Fridman?

  So that's looking at the inner spirals.

• 1:22:18Speaker 01

  Yes.

• 1:22:19Lex Fridman?

  Milky Way galaxy.

• 1:22:19Speaker 01

  And just, you know, this, this dark sky with a, with a bright stars. And I have described this in my, my book years ago. If the Milky Way is all bright above you, you don't need a moon or anything. You can walk in the starlight and you will find your way. There are no trees there for safety reasons, but you wouldn't even run into a tree, right? I mean, you can see, you can almost see the shadow, you know, from, from the starlight because it's such a dark sight and, and the stars are so bright. And these are kind of moments that, that kind of change you a little bit. And.

• 1:22:56Lex Fridman?

  You see the unity of it all.

• 1:22:58Speaker 01

  Yeah, and it's just you and nature and, you know, with modern civilization and all of that, we, I think we often try a little bit too hard to be removed from, from nature, you know, to, to be independent of it and figuring it all out. But at the end of the day, we're, we're just a part of it. And, and that really helps me to remember that, that, you know.

• 1:23:23Speaker 01

  Well, one in the same.

• 1:23:25Lex Fridman?

  Well, that fills me with hope that, because I tend to think of us humans as in the very early days of whatever the heck we are. And so that makes me think thousands, tens of thousands, hundreds of thousands of years from now, that we'll be reaching, whatever we become, we'll be traveling out there to explore more and more and more. So what you're doing is the early days of exploration with the tools we have.

• 1:23:50Speaker 01

  Yes, the early seafarers looking at the sky for navigation.

• 1:23:54Lex Fridman?

  Coming up with different theories of what's on the other side, that the Earth is starting to gain an intuition that the Earth may be round. And then we might be able to navigate all the way around to get to the financial benefits of getting spices from India, whatever the reason, whatever the grant funding process is all about. But ultimately, it actually results in a deep understanding of the mystery that's all around us. And I mean, it's just to travel out there. To me, the discovery of life in the solar system, I really hope to see that in my lifetime. Some kind of, some kind of life, bacteria, something, maybe dead, because that means

• 1:24:37Lex Fridman?

  there's life everywhere. And that's just the kind of stuff that might be out there. All the different, all the different environmental conditions, chemically speaking, that are out there. And it just seems like when you look at Earth, life finds a way to survive, to thrive in whatever conditions. And so maybe that process just kind of humbles you, is super exciting to know that there is life out there of different forms. And of course, that raises the question of what is life even? We tend to have a very human-centric perspective of what is a living organism and what is intelligence and all this kinds of stuff.

• 1:25:21Lex Fridman?

  And all the work in artificial intelligence now is starting to challenge our ideas of what makes human beings special. And I think we're doing that through all kinds of ways. And I think you're working in some part doing that as well. Like, the unity you feel is realizing we're, we're part of this big mechanism of nature, whatever that is, that's creating all kinds of cool stuff, from the humble, pristine origins to today.

• 1:25:50Lex Fridman?

  So what is, if you could just kind of linger on the, on the process of the data, what does the data look like? And how does the data, the raw data lead to a discovery of an ancient star?

• 1:26:04Speaker 01

  Well, as a spectroscopist, we have to, I guess, talk for, for a brief moment about what, what a spectrum is.

• 1:26:13Speaker 01

  Everyone, I hope, has seen a rainbow in the sky. That is, that is basically what we're doing.

• 1:26:21Speaker 01

  We don't send the starlight through a raindrop that then gets bounced around and splits up the light into the rainbow colors. We, we do it with a spectrograph, so basically a prism. So we send the starlight through a prism of sorts and that splits it up. And then we record exactly that. So it's a little 2D picture, actually, of a spectrum. Now, it's not going to look colorful, just black, black and white. Different, different colors have, of course, different energies. That's what, what we record.

• 1:26:58Speaker 01

  More specifically, we, we record it as, as wavelengths. So wavelengths and frequency and energy is all, all the same at the end of the day.

• 1:27:08Speaker 01

  We process that, that little image in a sense that we do a crosscut and then sum up a few columns so that we get all the data that we recorded. And what we see is a, it's a bit funny to describe just with words, but a wiggly line with lots of dips. So the 2D process spectrum, we call it continuum. So it's just a flat line, basically, and then there are dips. So the interesting things are the dips. If you think back of the rainbow, what we actually see in our stars is not just a rainbow, but it would be a rainbow with lots of black lines in it, which means certain little pieces of color have been eaten away by a certain amount.

• 1:27:53Speaker 01

  And so we can no longer see it as well, or not at all.

• 1:27:58Speaker 01

  Why is that happening? So if we come back to our stars, what we're observing, we're observing the stellar surface. We can actually never peer with our telescopes inside. We only ever go, can go after the surface. And the surface contains, or the surface layer contains different kinds of elements. Every one of those types of atoms, so elements are just different types of atoms, they absorb different photons that are coming from the hot core where the fusion is occurring. And so that means that if you're the observer, you know, with a spectrograph or without, you will see the starlight, but certain frequencies, certain energies of that light

• 1:28:43Speaker 01

  will have been absorbed by all the different atoms in the gas. So you see less of them. And so those are the dips. And the strength of the dips tell us, you know, which element was it? And how much of that element was or is in the star? So we have many, many, many dips. The solar spectrum, for reference, you know, all the dips are overlapping because the abundance of all the elements is so high. It's actually a very complicated spectrum. My spectral really look like a straight line and then there's a dip here and then you have the straight line again, there's a dip there. The sun doesn't have straight lines.

• 1:29:24Speaker 01

  I mean, it's just all absorbed in some form or another. But the old stars have so little of all the elements that they're only occasionally these dips that then indicate, okay, that one at that wavelengths was iron and here we have carbon and there's magnesium and sodium. And oh, there's a little strontium line here. So we have a much easier way to map out this barcode that the spectrum, you know, pretty much is at the end of the day. And to then measure the strength of these, we call it absorption lines, to then calculate with existing codes that mimic the physics of the stellar atmospheres, like how much was absorbed, how many, what kind of elements were present

• 1:30:09Speaker 01

  in the stellar atmosphere. And so this is how we get to our abundance measurements and then all together that gives us the chemical composition and that particular signature in that star.

• 1:30:23Lex Fridman?

  If you, do you ever look at like the raw spectrograph and the absorption line? And are able to see, intuit some interesting, non-standard outlier kind of patterns? Or does this have to do a heavy amount of processing?

• 1:30:40Speaker 01

  We actually process our, it's fairly straightforward to do our processing. We do it at the telescope. So I often take a shorter exposure first, let's say 10 or 15 minutes. So mostly when I do discovery work, we would just take a quick look spectrum. Then we process it while we observe the next star. Then we take a quick look. We have what I call the summary plot. It's a collection of little areas in the spectrum that have the key positions, the positions of the key elements in it. And it's kind of like reading the tea leaves. I have stared at so many spectra.

• 1:31:21Speaker 01

  I just need to know, I just need to see our summary plot and I can tell you exactly what the numbers are going to be.

• 1:31:27Lex Fridman?

  And also to tell if it's going to be promising to look at further?

• 1:31:30Speaker 01

  Exactly. And so that's it. Thumbs up, thumbs down? Are you worth my time or not? In most cases, it's not. Or it's good enough, we can do a basic analysis, maybe publish this as part of a larger sample. Just so, you know, we output that we have observed the star and their basic nature. That's an important part to publish as well. And yeah, I had a, I had a run. So now we do remote observing. I do all of this now from my home, from my living room, all night long. And I often work with colleagues. So we do it over Zoom and we process the data. We look at it, same thing still.

• 1:32:12Speaker 01

  And we, we just found a star that had a very low iron abundance. And then we decided, okay, that looks interesting. We're just going to keep exposing. So we took more data on it on the spot and we're writing up the paper right now.

• 1:32:27Lex Fridman?

  How do you know where to point the telescope?

• 1:32:29Speaker 01

  It's not random. There's a lot of work that goes into that. I began my career by Answering, trying to answer that question as in like doing the search process. That's why I called my, my, my book that I've written some time ago, Searching for the Oldest Stars, because searching is one thing, it's very time consuming. And then on top of that, not everyone finds, right? And I often don't find, but I keep searching. Because, you know, techniques have established that yes, we can do it if we're just patient enough and keep going because it's a numbers game. And that's often the case in science.

• 1:33:11Speaker 01

  And that's something that not a, that not enough is talked about. How tedious it is and how long it takes to get to that one

• 1:33:22Speaker 01

  discovery, right? That, that moves the field further.

• 1:33:26Lex Fridman?

  And how difficult it is to believe that there is a thing to be discovered.

• 1:33:30Speaker 01

  Yes, yes. Um, we have the saying, I, I learned this, I think from my supervisor. One star is a discovery. Two is a, is a sample. And three is a population. So as soon as you found three of roughly the same kind, you're done. But you need to get there.

• 1:33:50Lex Fridman?

  Yeah, probably the first is the hardest, right?

• 1:33:53Speaker 01

  Yes, but it, it kind of remains really hard. And, but the thing is then at past three, many of us are like, okay, we solved that problem. We've done it three times, we can do it. That's a thing, right? That's a population. Three iron deficient stars, let's say, right? That's one puzzle piece. Now we can move on to the next thing.

• 1:34:14Lex Fridman?

  That's an indicator that there's many more of them.

• 1:34:16Speaker 01

  Yes.

• 1:34:16Lex Fridman?

  Potentially.

• 1:34:17Speaker 01

  Yes, yes, yes. So to cut a long story short about the searching. We started early on with, um, what's called low resolution spectroscopy of many stars. So for example, my thesis work almost 20 years ago was piggybacking off a Quasar survey that had collected. So Quasars are basically giant, supermassive black holes that are really far away. So you only see a one big bright light point. So it looks like a star, but it's actually just a giant, supermassive black hole that outshines its, its, its own galaxy. And people had been trying to study those and they had taken little spectra

• 1:34:58Speaker 01

  of, you know, all things in the sky. And it turns out, oh, you can fish out the actual stars from that and, and look for certain signatures that might indicate low metallicity stars, so stars with low abundances.

• 1:35:14Speaker 01

  And so it was painstaking work to then take medium resolution spectroscopy to get a little bit more information and to use approximations and to kind of get candidates that we can then eventually take to the big class like Magellan to get a high resolution spectrum. So we really see the dips of all the individual elements that then give us the final answer. Is it yay or nay?

• 1:35:37Speaker 01

  These days, with another grad student, I just, I developed a new technique to use images actually of all the stars in the sky taken with very narrow filters. So it's like you're wearing very specific glasses that only let so much light through. And so we can do similar things through having several narrow band filters, what we call it, to fish out things that have, you know, no absorption over here, so just the, the straight line, and then a little dip here, so a little something there. And that has proven fairly successful in recent years.

• 1:36:17Lex Fridman?

  So looking at the entire, looking at broader regions of space.

• 1:36:21Speaker 01

  That's right, because these stars are a little bit like the needle in the haystack, right? There are not that many left over and certainly the galaxy has made plenty of stars in between. We need to comb through all of those to, to get to the goods. So we always start with millions and then work our way down. And in the end, we have like three good candidates.

• 1:36:42Lex Fridman?

  I wonder how those ancient stars feel that they were noticed. They probably know that nobody pays attention. No, I'm just kidding.

• 1:36:50Speaker 01

  We're all special, right? So are the stars.

• 1:36:52Lex Fridman?

  It's good. It's inspiring, even if you're the outcast.

• 1:36:57Lex Fridman?

  In, in your pristine nature, you still might nevertheless be noticed. I'm hoping the same about humans if somebody's observing us.

• 1:37:06Lex Fridman?

  Is there something else you could say that's about the challenges of this kind of high-precision measurement that you're doing? So this kind of collection of data looking, trying to pull out the signal from the noise out there?

• 1:37:24Speaker 01

  Well, that's literally what we're doing in multiple ways, actually. We're trying to find the needle in the haystack. And then we find something and then it turns out it's just a little bit too faint to actually get the kind of data quality on it that we would like or that would be warranted, given the potential of the star, right? It's like, ugh!

• 1:37:46Lex Fridman?

  So there's always noise. There's always a little bit of noise and you have to try to say like, what? Yeah, how special is this when you're looking at the absorption line?

• 1:37:55Speaker 01

  Yeah. So the most ironed-out stars, their iron lines are so tiny that they're literally, you know, almost in the noise. So you need incredibly good data to make detections. And the funny thing is, we're looking for the nothingness of, let's say, the iron lines. But then we don't want nothing because if there's nothing in the spectrum, we can't measure anything. We can only get an upper limit. But we'd really like a measurement. So we are looking for the last little bit that you could possibly detect. And that's the strong function of the brightness of the star because the telescopes have the size that they do. That's not going to change for a while. Hopefully, eventually it will, but it's going to be at least 10 years out.

• 1:38:39Speaker 01

  And so, yes, we're often literally stuck in the noise because we can't make the measurement. So actually, the record holder for the most ironed-out star only has an upper limit. We can't get enough data on this to actually pinpoint a measurement to then take it to our theory colleagues and say like, "Give me this little iron out of your first star."

• 1:38:58Speaker 01

  So it's a bit frustrating, but also super exciting at the same time.

• 1:39:02Lex Fridman?

  So let's go to both sides of that spectrum. What's like the most exciting discovery to you personally? Where is there a moment you remember that you saw a piece of data? And you kind of your heart skipped a bit?

• 1:39:17Speaker 01

  Yeah, yeah, of course.

• 1:39:19Lex Fridman?

  Is it, is it HE 1327?

• 1:39:23Speaker 01

  That was, that was definitely one of those moments. I wasn't actually present at the telescope, but we were sent the data immediately from our colleague. And we just looked at it and our eyes got really wide and it's like, oh, my God.

• 1:39:37Speaker 01

  This is this really what you think it is? So we had to run some numbers and, and it was, and it, these are magical little moments. The thing is, you know, often we, we have false positives.

• 1:39:51Lex Fridman?

  Yeah.

• 1:39:52Speaker 01

  And so there's always this, this kind of period and often it's, it's, I don't know, 10, 15 minutes where you need to make some tests to, to kind of make the decision. Is this really something I should keep observing now? Is this really as good as I think, or, or am I being fooled by something? Right? So actually, if you take a spectrum of a white dwarf, a white dwarf is the leftover core of a star like the sun that has gone extinct. And white dwarfs have lost all their outer atmosphere. So it's just the hydrogen helium core. So they look like a metal poor star because that's only hydrogen helium left. Right? But the hydrogen lines that you can see in the spectrum of our stars and of, of the white dwarfs are a little bit wider than normal.

• 1:40:34Speaker 01

  So you need to have a good eye just to check, you know, does this look a little bit wider than us? Is this a white dwarf who's fooling me here? Right? And so it's like this moment, it's like, oh, my God.

• 1:40:46Lex Fridman?

  It's just minutes of nervousness.

• 1:40:47Speaker 01

  Yes, yes. And sometimes, you know, it's, it's a dud and sometimes it's not.

• 1:40:53Lex Fridman?

  What's been, what's been a big that you remember heartbreak? Like a painful low point? Is it all leading up to the first? Is it all about HE 1327 again? Just the leading up to it? Or has there been like a, yeah, has there been like low points in the search?

• 1:41:10Speaker 01

  Um, that's a good question.

• 1:41:14Speaker 01

  I mean, you know, it starts with mundane things as in like you you won your telescope time, you travel there and the weather is completely cloudy, it rains and you you had three nights, which is a lot, and you go home empty handed. So that's definitely a low point. Probably not what you were thinking of, but there is a certain occupational hazard to it.

• 1:41:38Lex Fridman?

  Which requires a kind of resilience and a patience.

• 1:41:42Speaker 01

  Yeah, and you just got to learn to to live with it. Coming back to reticulum too, actually, you know, that little dwarf galaxy, that was a run that we had and the weather was incredibly bad. And I had sent my student there. And I was at home and he calls me at 2am and he was like, Anna, I think I observed the wrong star. I'm so sorry. There is this line there, this europium line, and it looks like a metal rich star. And I was like, it's cool. We all make mistakes. Send me the data. Send me that summary plot. And so I look at it, you know, I was like, super tired. It's like, I can't really tell. It doesn't

• 1:42:25Speaker 01

  look wrong, but I can't tell you right now that it's right either. So why don't you go to the next target? And he calls me back an hour later. Anna, it looks just the same. What am I supposed to do? And then I joked, well, maybe we found an R process galaxy. Let's go to the next one. And the weather was degrading. And so to cut a long story short, we had to come. So he was observing the right stars. It was an R process galaxy, the first one we had ever discovered, totally, and I mean, unpredicted. We had no idea that this was a thing. I mean, you know.

• 1:43:10Speaker 01

  Of course, we we thought that, you know, such a thing might possibly exist because why not? Right? Neutron star mergers happen somewhere. Crazy supernovae probably too. But we were not prepared in that moment to to find this thing. And in the end, the weather was getting worse and worse. And we wanted to see how many our processed stars are in this galaxy. So we managed by a hairline to observe the nine brightest stars. But the data quality was atrocious.

• 1:43:46Lex Fridman?

  And the weather affects the data quality?

• 1:43:47Speaker 01

  Yes, absolutely, because these were really faint stars. And so we we were really lucky by making a very tight strategy of getting the absolute bare minimum for all the stars. So we could at least take a very crude look. Is it a yay or is it a nay? We couldn't even say yes or no, just just to get an idea. Because we needed to know. Why was that important? Because we could only observe this system again nine months later.

• 1:44:18Lex Fridman?

  So there's always a window of observation.

• 1:44:20Speaker 01

  Yes, it was setting. This was our chance and it was going away with the clouds, you know?

• 1:44:28Lex Fridman?

  That was super high stakes.

• 1:44:30Speaker 01

  But we we we just made it. Like, really, it was almost impossible. And it was just the the thing is, this is such a serendipitous moment. In a serendipitous moment, the enhancement of these heavy elements was so strong that even in this really crappy data, we could still see the enhancement. Right? The absorption was so strong, it stuck out of the noise. If the enhancement wouldn't have been as strong, we would not have been able to say anything because we wouldn't have been able to tell. But because it was so extreme, it it lent us a hand, despite the weather and all, to say like, yes, this is it. So that was quite the night.

• 1:45:17Lex Fridman?

  Luck, I mean, a lot of this is just luck. So that was the first our process galaxy discovered.

• 1:45:22Speaker 01

  Yes, I didn't sleep all that much.

• 1:45:26Lex Fridman?

  Do you have hoped, are you excited about James Webb Space Telescope and other telescopes in the future that increase the resolution and the precision of what can be detected out there?

• 1:45:38Speaker 01

  Absolutely. JWST is fantastic already. I am not planning to use it personally, although I think I'm on one or two observing proposals actually, because similar to what we already spoke about, we're interested in the same thing, we're just kind of looking at a different sides of the fence, right? I have my old surviving stars and I concoct these little stories about what the earliest galaxies may have looked like, what the objects were that contributed, you know, energy and elements and all these things. And my JWST colleagues, they try to detect some of these earliest photons from these earliest systems to look at the energetics and other things, you know, what was there? How many, these kinds of things, right?

• 1:46:23Speaker 01

  So together, we're trying to explore this first billion years, but we do it in very complimentary ways. And so I'm very excited to see what they can come up with and how that helps me to inform my stories better and more comprehensively.

• 1:46:41Lex Fridman?

  What do you think is the future of the field of stellar archaeology? How much can we, maybe what are the limits of our understanding of this first billion years of our universe?

• 1:46:55Speaker 01

  Well, obviously lots of limitations in the sense that I always say, I have a metal pore star for any of your questions, because there are so many different kinds out there. And we still find new patterns sometimes, right? And there needs to be an explanation. The question is, is it ultimately just one quirky star or is it two, is it three, right? Is it a sample of the population? So we haven't concluded that kind of work yet.

• 1:47:20Lex Fridman?

  So every metal pore star is a kind of data point that you can use to improve the quality of your model of how is the evolution of the early universe?

• 1:47:29Speaker 01

  Yes, yes. And I would say we're, we've made huge progress over the last 20 years. When I joined that field, it was in its infancy. And there was this serendipitous discovery of that first second generation star. And we have filled in the canvas a great deal since then. And this is what I have greatly enjoyed about doing so. Because there was so much discovery potential. And it's been it's been dying down a little bit because of all the progress. Um, it's gonna, it's gonna, it's on, on the up and coming again because there's so many large spectroscopic surveys in the works now. That will just provide a different level of data that we haven't had before.

• 1:48:13Speaker 01

  I'm sort of of this older generation. I have only very few colleagues, I work in small teams and I observe every single star myself. That, you know, I, whatever I can, I do myself. I don't generally take other people's data, at least not certainly not in the end stage. And, and, uh, you know, I'm, I'm not a big data kind of person, although we all headed that that way. I, I certainly use, uh, data from the Gaia, um, astrometric satellite for the kinematics, for example. But that's personally a new thing for me to, to use sort of big sky surveys, um, that are available. Um, so it's still very sort of hand grown field, you know, where we do

• 1:48:57Speaker 01

  our individual observations. Um, I have enjoyed that a lot, um, but that's about to change.

• 1:49:03Lex Fridman?

  So one star at a time?

• 1:49:04Speaker 01

  Yes.

• 1:49:05Lex Fridman?

  I mean, there's power to that, to build up intuition of the early universe by looking one star at a time.

• 1:49:10Speaker 01

  Yeah. And this is how you can really drill down on the questions that you have, right? Because you control what data you get. Um, otherwise you have the data that you have, right? You get what you get and you don't get upset. Uh, I don't like that. I'm a little bit snobby. I, I really like to formulate my questions, go to the telescope and then come what may, I will, I will try to get it.

• 1:49:33Lex Fridman?

  And also develop the intuition of where the data can be relied upon and when it can't and all the different quirks of the data and all that kind of stuff.

• 1:49:39Speaker 01

  Yeah.

• 1:49:40Lex Fridman?

  Sometimes a lot is lost. In the aggregation of the noisy data.

• 1:49:44Speaker 01

  Yeah, yeah, yeah. And, and that's always the danger if you have someone else's data that you just don't really understand the, you know, the limitations, completeness things, how certain things were set up. And, you know, you get out what you put in. So I'm, I'm really particular about that. And it certainly paid off for me. That's one of the main notions that I try to teach in my classes and to my, my students, that you need to be able to formulate your quest question really well, because otherwise you're going to get an answer to a different question, but you won't notice that it had, that the goalpost has shifted in the meantime, right? So your interpretation can only be

• 1:50:24Speaker 01

  as good as the question. If you need to change your question, that's cool, do it. But then, you know, it needs to pair up with your interpretation again. And so knowing, really being in the know about every step of what happens, that really leads to quality results, I think. That's why I have sometimes little trouble with, with sort of big data and statistical analysis. Yes, on average, that's true. I'm not debating that. But I, I'm the kind of person, I like to look at the outliers, so not the bulk, but, you know, the special ones.

• 1:50:57Lex Fridman?

  Yeah.

• 1:50:58Speaker 01

  And they just need to be treated in a different way. And there needs to be an acknowledgement of that, different ways for different things.

• 1:51:04Lex Fridman?

  So, uh, big data can look at divorce rates. And perhaps you and I are more interested in the individual love stories.

• 1:51:12Speaker 01

  Yes. That, that works for me.

• 1:51:16Lex Fridman?

  So, I don't know if it's possible to say, but what do you think is the big discoveries that are waiting? Is it on the different dynamics of the yield, the common narrative, the common story of how some of these metal poor stars are formed? Is it where are the discoveries in this field that you think will come?

• 1:51:39Speaker 01

  I think the individual discoveries are actually, we've made most of those, certainly through individual stars.

• 1:51:49Speaker 01

  Um, finding yet another second generation star is incredibly important for me, but isn't, isn't really going to move the needle. Finding fifty of them or a hundred of them, that would move the needle, but that's in order or two magnitudes up. And um, new search techniques and new uh, surveys may enable that, but would you still call that a discovery? Right?

• 1:52:14Lex Fridman?

  So that's just a scale, that's a scale?

• 1:52:16Speaker 01

  Yes, so I think about it more like literally of the puzzle. Let's say you have a thousand piece puzzle and you know, you have nine hundred pieces in there.

• 1:52:26Speaker 01

  If you're a person like me, I want to get to the last ones. I'm not gonna leave it, it's like, okay, I see broadly what this is gonna look like, right? I'm done now. No, I want to get to the last one.

• 1:52:38Speaker 01

  So is the picture globally going to change? No. Are we going to figure out all the details and how it really works? Yes, right?

• 1:52:46Lex Fridman?

  So really careful detail map out the, the ancient, uh, the ancient stars of our universe.

• 1:52:54Speaker 01

  Yeah, because I think that's what many of us scientists are real little bit detailed obsessed, but I think that's, that's our job too, right? To really kind of make it airtight, to really walk away saying, I fully understand this. Not just broadly, but you know, I really know, we really know now. And so more and more of that is going to happen. And so I think this is probably true across astronomy, these individual ten sigma discoveries become less and less. If they were easy, we would have made them already, right? Which means we have made many of them.

• 1:53:35Speaker 01

  But really filling in the details is, is, is, is the next sort of level of discovery. Maybe we need to find a new word for that.

• 1:53:45Speaker 01

  The, the hopes and expectations that go along with the word discovery are so enormous, we, we may not always be able to live up to that. But it doesn't mean that we're not finding out new things. It's just a different kind of quality because the questions have shifted. You close one door, suddenly there are ten new open doors that, that we want to explore and march through. And that's the, you know, finding these last puzzle pieces here and there that really make it airtight.

• 1:54:14Lex Fridman?

  And so there's a lot of value, a lot of power and beauty. To the discovery in the big picture of our universe and in the details.

• 1:54:23Speaker 01

  Yes.

• 1:54:23Lex Fridman?

  So both.

• 1:54:24Speaker 01

  We need both, absolutely.

• 1:54:27Lex Fridman?

  Perhaps drifting into the philosophical, let me ask about the Big Bang as we kind of encroach onto it. So your work is kind of taking steps back through time in a weird way. Do you think we'll get to deeper and deeper understand the really, really early days of the Big Bang? And the philosophical question, do you think we'll be able to understand what was before the Big Bang or why the Big Bang happened? Do you think about that stuff?

• 1:54:59Speaker 01

  Not with stars, for better or for worse, because, you know, stars only probe the time when they were formed and the Big Bang is surely before then. I mean, I often talk to my students about the difference between math and physics. Let me give you an example. We talked earlier about AG 1523 and, you know, I was happy to share with you that I measure thorium and uranium, but I actually didn't quite close that loop. So we did this to try to attempt to calculate an age for these stars, right? But they rely on us knowing how the R process works, how these elements are created, where it happens, and then how those elements

• 1:55:43Speaker 01

  get dispersed into the gas and end up in the next generation star. So quite a few question marks. So that's how we got to the age of 13.2 billion years. This is probably not accurate, but this is the best calculation we could do. And the reason why I'm bringing this up is that that was actually the average of multiple elemental ratios that each gave a certain age and then we averaged that because for better or for worse, this is the best we can do. So some of these numbers said, oh, this star is 15 billion years old. And then others said, oh, this is 10 billion years old. And so I often use that in my class to say like,

• 1:56:25Speaker 01

  What's the good news and what's the bad news here? Some ratios say fifteen, some tend ten, right? Is fifteen correct? And then I ask them, and some people will say something. And so the thing here is that it's an absolutely correct calculation, given the mathematical and physical model that we constructed. But does it make sense? No, it doesn't. If we believe the universe is 13.8 billion years old, 15 is ridiculous, yet it is correct. Isn't that interesting?

• 1:56:59Lex Fridman?

  Correct from a mathematics perspective.

• 1:57:01Speaker 01

  Yes, it is not incorrect, because this is what I calculated. Nobody made a mistake. Now, we can question whether that's a good model, but that's a separate issue.

• 1:57:09Lex Fridman?

  So you're saying physicists are much closer to truth than mathematicians?

• 1:57:13Speaker 01

  Well, it depends. Sometimes yes, and sometimes no, right? So what our job as physicists is, is to take the mathematical model, calculate our numbers, and then ask the question, does this make sense? Now, in the case of 15, it doesn't, but we took the average anyway, because that was the best we could do, right? So, all right, let's put that aside. Let's apply the same sort of thinking to the Big Bang, right? Math can tell us things that we, as physicists, cannot grasp, because it doesn't make sense to us. Now, in the case of the Big Bang, that's a special case, because we don't actually know what's supposed to make sense.

• 1:57:55Lex Fridman?

  Yeah.

• 1:57:56Speaker 01

  And this is where things get interesting. But this is where math will ultimately be the winner, because we can no longer say this makes sense or this doesn't make sense, because the physics is broken down.

• 1:58:07Lex Fridman?

  But math breaks down too, at the singularity of things.

• 1:58:10Speaker 01

  Well, depending on who you ask.

• 1:58:12Lex Fridman?

  Okay, sure, sure.

• 1:58:15Speaker 01

  This is the current question, right? How far, how much further can we push math, let's say, to the front of the Big Bang, if there is such a thing?

• 1:58:24Lex Fridman?

  What's the front and the back? What's the front? The front is the...

• 1:58:27Speaker 01

  Before the Big Bang.

• 1:58:28Lex Fridman?

  Oh, before the Big Bang, the front, okay.

• 1:58:32Lex Fridman?

  To clarify, all the doorways and the entrances.

• 1:58:35Speaker 01

  So how far can we let the math go before that stops to make sense, right? And I don't know what the answer is to that. But it's really cool that because math doesn't have, is not limited by our physical nature, it can probably go a little bit further than the physics.

• 1:58:53Lex Fridman?

  Yeah.

• 1:58:53Speaker 01

  Right?

• 1:58:53Lex Fridman?

  And math can go into more dimensions than four dimensions comfortably.

• 1:58:58Speaker 01

  And it's judgment free because it just calculates things on its own. Whereas as physicists, we are so judgmental.

• 1:59:05Lex Fridman?

  Yeah.

• 1:59:06Speaker 01

  This makes sense, this doesn't make sense, right? It doesn't get any worse.

• 1:59:09Lex Fridman?

  It's such a beautiful dance. And it's such a, it's so amazing that through this dance, you can explore the origins of the universe. Like, doesn't the Big Bang just blow your mind? That this thing has just started from a point.

• 1:59:27Speaker 01

  Yeah.

• 1:59:27Lex Fridman?

  And now we're here.

• 1:59:28Speaker 01

  Yeah, yeah, yeah.

• 1:59:29Lex Fridman?

  Hydrogen and helium. And then all the stuff you're studying. I mean, this, this, this evolution of chemistry created humans. And we're here talking. And there's a lot more to the story. It's amazing.

• 1:59:46Speaker 01

  Yeah, yeah, yeah.

• 1:59:50Lex Fridman?

  And this kind of march that you're doing is observing data. And is there, you're looking at old light, an old data.

• 2:00:01Speaker 01

  But only a few thousand years, right?

• 2:00:03Lex Fridman?

  Just a few thousand years.

• 2:00:04Speaker 01

  That's, that's the difference between me and my J W S T colleagues.

• 2:00:07Lex Fridman?

  Yes.

• 2:00:08Speaker 01

  Their objects, that light has traveled 13 billion years or whatever it was to us. And they're observing that now. My light has only traveled a few thousand years. It's, it's nothing.

• 2:00:19Lex Fridman?

  So whatever you observe now is likely still going on.

• 2:00:22Speaker 01

  Yes. These stars are alive and kicking and having a blast.

• 2:00:27Lex Fridman?

  Thousand years. Just a few thousand years is all it takes. If we can travel at close to the speed of light.

• 2:00:33Speaker 01

  Yeah.

• 2:00:34Lex Fridman?

  Maybe we can reach out there.

• 2:00:36Speaker 01

  We wouldn't have any planets around those stars, though.

• 2:00:38Lex Fridman?

  So that's, is that a definitive intuition?

• 2:00:41Speaker 01

  Well, what are planets made of? Elements, right? To take the earth, it was all heavy elements, right? The universe needed to reach a certain stage first to have produced enough of all these elements to actually make a planet.

• 2:00:55Lex Fridman?

  So on average, you got, so, okay, right.

• 2:00:57Speaker 01

  So that took quite a few billion years.

• 2:00:59Lex Fridman?

  So they're not going to have a mechanism for forming planets? You could have visitors, probably, but the kinematics of that are weird, are unlikely.

• 2:01:07Speaker 01

  Yeah, I would say so.

• 2:01:09Lex Fridman?

  Okay. So they're interesting in that they reveal the early chemical evolution of the universe.

• 2:01:15Speaker 01

  Yes.

• 2:01:16Lex Fridman?

  Not that they're, they could be good vacation spots, but not.

• 2:01:20Speaker 01

  Well, if you're like a worm. Just no, no planet islands to, to go to, to chill.

• 2:01:28Lex Fridman?

  In your book, you highlight the major contributions in the field by many women. Some of these women were not, as you describe, immediately credited for their discoveries. So for me, from, from a computer science perspective, the story you also tell is Harvard computers. Who were these women and what can you just say about the nature of science and humanity?

• 2:01:54Speaker 01

  Discovering things is, is in, is part of the human nature, right? And so it has happened for the longest time, not just by men, but also by many women. The field of stellar astronomy, which is, is my field, has particularly benefited from, from many discoveries made by women. You mentioned the Harvard computers. That's a, a term used for women who worked about a hundred years ago at the Harvard College Observatory, and they were hired for their low wages.

• 2:02:32Speaker 01

  And willingness to do diligent and patient work to comb through the big data of the day. So the Observatory Director, they were carrying out large sky surveys at the time and they needed

• 2:02:50Speaker 01

  that that data needed to be processed and and looked at and analyzed. And so many women or several dozens of one or two dozen women over over the years were

• 2:03:04Speaker 01

  were hired to to do this work. And in the process, because they were looking at the actual data and they were smart, even though they had often no formal education, they made a lot of discoveries simply by by being in tune with what they were doing. So they weren't robots as you know, the the term computer would perhaps let on, uh, lead on. Um, so any jump cannon classified thousands and thousands of spectra and found out that you can, you know, stars have different temperatures and their spectra look according. We still use that classification sequence today.

• 2:03:49Speaker 01

  Cecilia Pein der Poschkin later on in, I think, nineteen twenty five was one of the first women to obtain a PhD

• 2:03:59Speaker 01

  in in stellar astronomy. And she figured out, she calculated that the sun is mostly made of hydrogen and helium.

• 2:04:10Speaker 01

  That seems normal to many of us these days, but at the time it was thought that celestial objects are made of the same thing as the earth.

• 2:04:22Lex Fridman?

  That's a gutsy, amazing discovery.

• 2:04:24Speaker 01

  Yes. It was later termed the most important thesis of humankind or something like that.

• 2:04:33Speaker 01

  What a revelation to realize that stars are made of hydrogen and helium, right? And this was exactly the time when people figured out why stars are shining, namely because of nuclear fusion and that it's protons and, you know, the tunneling effect that leads to the actual fusion. Otherwise, you know, the protons repulse each other, they don't come together. And so what an incredible time it was back then. And so stars and nuclear physics were very closely related and it remains. Now it's called nuclear astrophysics. And so many women had many contributions to that. Of course, prior to that, Marie Curie discovered two new elements. Ah, so awesome.

• 2:05:20Speaker 01

  Radium and polonium. Lisa Meitner discovered nuclear fission. That is the basis for understanding the R process. This is exactly what happens in the R process. You know, the heavy nuclei, let's say uranium, if you bombard it with a neutron, we talked at length about it, it will decay, it will, well, not decay, actually, it will fission, it will split into barium and krypton, let's say. So two lighter elements. That's exactly what we observe. I have always a higher abundance of barium than the heavier elements because of this

• 2:05:58Speaker 01

  fission cycling that she calculated in 1938, 1939. So many, many contributions and it's just so remarkable if you just take that body of work, that that changed how we, how we do things, how we see the universe, how we understand things has led to so many subsequent discoveries, good ones and bad.

• 2:06:28Lex Fridman?

  Well, all of it is taken together.

• 2:06:31Speaker 01

  That's progress, right? It's, it's, it's, science is what it is. We have to decide what we do with that knowledge, right? We can always use things for good or for bad. That's, that's part of the human endeavor as well.

• 2:06:45Lex Fridman?

  And also part of the human endeavor and the human nature is the issues with corruption and credit assignment and all these kinds of things that are, that make this whole ride so damn interesting about what's right and wrong and about the nature of good and evil. And that seems to surface itself in all kinds of places, all the time.

• 2:07:03Speaker 01

  Yes, yes. Lisa Maitner was nominated for the Nobel Prize forty times, more than that even. It's amazing. She holds the record for that. She never received it.

• 2:07:15Speaker 01

  Case in point.

• 2:07:18Lex Fridman?

  Yeah, and of course, the Nobel Prize is, is complexities. One is the credit assignment, but two, even in astronomy, sort of assigning credit to a handful of folks when so many more contributed, is a complicated story also.

• 2:07:32Speaker 01

  Yeah, it's very complex.

• 2:07:35Lex Fridman?

  Okay, sorry for the romantic question, but what do you use the most beautiful idea in astronomy, in stellar astronomy?

• 2:07:42Speaker 01

  Well, so early on, you know, when, when I was in high school, I, I was thinking like, okay, well, what, what, what do I want to do when I'm growing, when I grow up, right? I knew I wanted to do astronomy, but I was a little bit torn because my interests were definitely stars, stellar astronomy, but also chemistry. I always had a fascination about the elements, so Marie Curie was, was a, a big role model. My friend actually made a, a beautiful, produced a beautiful movie about the discovery of, of, of, of the elements. This is a theater play, but digitized, where, when I saw it, I could actually kind of relive the sort of discovery moment that, that Marie Curie had.

• 2:08:27Speaker 01

  It, it sent shivers down my spine. It, it was fantastic. I mean, this is, this is the kind of thing that, that I wanted to experience.

• 2:08:37Speaker 01

  But yeah, so nuclear physics and element creation and formation was really interesting to me, chemistry, the elements, stars and all of that. And I was like, I don't know if I ever find something that combines all of these things. And then I ended up in Australia and I I met this this person and he was working on old stars. And as I was sitting in his talk, hearing about this for the first time, it kind of it clicked all over my head and it's like, oh, my God. It it all fell in place because we can use these old stars to study the elements, to learn how they're formed. We can get these clean signatures that help us inform the nuclear synthesis processes,

• 2:09:19Speaker 01

  you know, and I know, of course, I need to know a lot about stars too. So it's it's like all together and that that was sort of a moment of magic. And then the fact that I have now done that for 20 years is just like I won the lottery.

• 2:09:36Lex Fridman?

  It all clicked into place.

• 2:09:37Speaker 01

  So in some sense, it's an it's an ongoing love story for me, if I could say it like that, where, you know, I found my stars, my thing. And I am fortunate enough to be able to keep doing that. And I'm happy to see where where it will take me. You know, it's an evolution, as with every relationship. You have to, if you don't march forward, you move backwards. I'm I'm not interested in moving backwards. So I'm I'm letting the field and the discoveries and the findings lead me to, you know, and I'm often, um, I'm I'm it's it's not hard for me to follow sort of my hunches.

• 2:10:20Speaker 01

  And sometimes even at the telescope, it's like, hmm, let's take a look at this one. I have a good feeling. And then usually something good or, you know, not bad pops pops out at the end. And I um, I really like that, A, that I have the freedom to to do that, that I'm allowed to follow my hunches. Um, too many people, I think, are sort of boxed in with their job or their life, that they they don't have that kind of freedom, that that's really important to me. And I certainly try to make use of that. I also try to teach that to others, to trust them, to learn. You know, you need to learn your things, but then you need to also trust that knowledge and that you have a grasp on it, right? You get out what you put in.

• 2:11:02Speaker 01

  And um, being able to contribute in meaningful ways to our knowledge about our cosmic ancestry, our cosmic history.

• 2:11:14Speaker 01

  That's a wonderful thing.

• 2:11:17Lex Fridman?

  And in this way, your personal love story with the stars evolves.

• 2:11:23Lex Fridman?

  What advice, you've already spoken to it a little bit, but what advice would you give to young people that are trying to find the same kind of love story in their career, in their life?

• 2:11:34Speaker 01

  It seems increasingly hard for folks to find that.

• 2:11:40Speaker 01

  Sometimes I feel that, you know, young people have all the opportunities these days, and that's wonderful, but it's almost like that leads to some, what's the right word? They're a little bit of tired, too tired to make all the decisions because at some point you need to put your eggs in a basket and you need to be okay with that. We can't do all the things, even though we're often told you can be president too. And I think that's really important to convey. But at the end of the day, we can only have sort of one job or one type of profession. I'm not saying, you know, you need to be locked in, but it's hard to change 180 degrees.

• 2:12:22Speaker 01

  And so lots of people, I think, are often afraid to really dig in, at least for some time, and get their hands real dirty and really learn from the bottom up.

• 2:12:35Lex Fridman?

  On one thing.

• 2:12:36Speaker 01

  On one thing, because they're afraid they're missing out on 99 other things. But life is a little bit missing out on 99 other things because we only have 24 hours in a day. I have that feeling very often. There are so many things I would like to do, many things I would like to try, to be good at. Sometimes I wish I had a different job, you know, because I have other interests too, but I realized, okay, I can only do one thing, so I have no regrets. But this is a general feeling that I think, I would think, most of us have. But if it lets, if it stops you from really digging, drilling down on one thing, to become

• 2:13:18Speaker 01

  an expert in one thing, to become really good at one thing that you call your own.

• 2:13:24Speaker 01

  Then that it just makes it difficult.

• 2:13:27Lex Fridman?

  And so a fulfilling life is in part likely to be discovered in the singular pursuit of a thing, of one thing.

• 2:13:34Speaker 01

  Well, yeah.

• 2:13:35Lex Fridman?

  For at least for a time.

• 2:13:36Speaker 01

  Yeah, for some time with your with your heart and your hands.

• 2:13:42Speaker 01

  Because I think most people long to own something. You know, we all, I think, wanna leave some legacy of some sorts, you know, for our children, for humanity, for this planet. And I think it's really important for young people to strive for that and not lose sight or trade that for all the opportunities, because an opportunity is nothing if you don't do anything. You need to you need to do something at the end of the day. So I chat with lots of people about this and I often start by just saying, hey, tell me what you don't like. Because it's much easier to to.

• 2:14:22Lex Fridman?

  Just narrow down, narrow down, narrow down.

• 2:14:24Speaker 01

  Let out what what's not on your plate.

• 2:14:27Lex Fridman?

  Yeah.

• 2:14:27Speaker 01

  And then this way we get a little bit closer and then it's like, well, why don't you take a risk?

• 2:14:32Lex Fridman?

  Yeah.

• 2:14:33Speaker 01

  And just sign up for something for three months.

• 2:14:35Lex Fridman?

  But that's what it feels like.

• 2:14:36Speaker 01

  You can't afford that.

• 2:14:36Lex Fridman?

  That's what it feels like, and it is that, is a risk. Commitment is a risk.

• 2:14:40Speaker 01

  Yes.

• 2:14:41Lex Fridman?

  Because it's you're basically sacrificing all the other possible options. But then I guess you have to trust the magic you you noticed in that thing.

• 2:14:49Speaker 01

  Yes.

• 2:14:49Lex Fridman?

  If you notice one thing, just stick with it. And then and then maybe there's something there.

• 2:14:54Speaker 01

  Right, right. And and this moment of kind of feeling it in in your entire body and mind that this is the right thing, you know, getting there is is probably really hard. But if you don't try, you won't find out.

• 2:15:08Lex Fridman?

  The hard stuff is the fun stuff. That's also another thing you find out.

• 2:15:11Speaker 01

  And then there is that, yes.

• 2:15:13Lex Fridman?

  Somehow, it doesn't make sense. You also mentioned that. You've taken a little stroll into the artistic representation of yourself. Can you speak to that for a little bit?

• 2:15:26Speaker 01

  Yes, well, I already just mentioned.

• 2:15:29Speaker 01

  Sometimes I wish I, you know, had more time to do other things. So I find little, little sideways, I guess, to pursue things that, that I like besides astronomy, or at least I try to find connections. And so some years ago, I, again, with the help of, of my friend who made this Marie Kiri movie, she and I wrote a one-woman play where I actually portray Lisa Meidner, who was an Austrian German physicist, nuclear physicist, from Germany. So I have the right accent for that.

• 2:16:09Speaker 01

  And we wrote this play about this moment of discovery of nuclear fission. Again, this is an absolutely critical piece that explains my work today. And we all stand on the shoulder of giants. She was one of those giants. And in some ways, it's, it's, of course, a way for me to acknowledge other people's work that have come before me. It's a wonderful way to highlight the contribution by a prominent woman. And the way I, I do it is it's a 25-minute play in costume, where I relive for people the moment of discovery.

• 2:16:55Speaker 01

  Then I turn into myself. And then I give a 30-minute presentation on the art process and the creation of heavy elements, because the audience can now perfectly understand that, the public audience, given the historic backdrop of this discovery, that they just lived through my presentation. And it's, it's a wonderful compliment that almost spends 100 years, from one woman to the next, passing on the torch. And, you know, when we write up our results in, let's say, you know, in magazines like Nature and Science, it's always about the result, on the golden platter, perfectly prepared.

• 2:17:39Speaker 01

  It's the discovery is never described, only ever the results. You asked me beforehand, right? What does it feel to be at the telescope in this moment, right? I'm happy to talk about this, but it's nowhere written, never. Nobody, nobody really talks about it. And so having a form of, you know, theater, of the arts, to bring this, this exciting moment, that, that is what we all want to experience as scientists, to a wider audience, is so profound and so rewarding. And they all love it because everyone can understand a moment of discovery. I was looking for something and then I found it. It's like you misplace car keys, right?

• 2:18:24Lex Fridman?

  Or love.

• 2:18:27Speaker 01

  Yes, yes. It, it, everyone can understand.

• 2:18:30Lex Fridman?

  What the glorious experiences, yes.

• 2:18:32Speaker 01

  The, the implications and the findings, that is much harder to understand for the, for anyone. This is where the scientist's work truly lies. This is our job. But the moment of discovery is easy and it's beautiful. And it needs to be said. And so taking my audience on this journey, what is the perils? What are my worries? And then, oh, here is the moment of discovery. Let me tell you about it. It, it profoundly transformed me and here, here's how it went, right? It, it, it's so good.

• 2:19:07Lex Fridman?

  And art is a way to reveal this fundamentally human side of science.

• 2:19:11Speaker 01

  Yes. It's, the problem with science is that's people doing it.

• 2:19:15Lex Fridman?

  That's also the.

• 2:19:17Speaker 01

  Maybe not a problem, but that is it.

• 2:19:18Lex Fridman?

  That's also what makes it beautiful, right? I mean, humans are fascinating and that we're able to come up with these ideas through all the struggle, through all the hardship, through all the hope, through all the search.

• 2:19:28Speaker 01

  And so the art's a great way to, to portray that and to broadcast that, right? I think this is how the audience really should be interacting with scientists, much less about the findings, but really more about this yearning for answers, right? I need to find these car keys. I need, I need it because I need to go, right? It's like now, now. And then, oh God, here it is. Now I can go my, my merry ways. It's, it's so relatable. We just need to find more and better ways to, to do that. So I hope to turn this into also a digitized version at some point to again, make it more accessible.

• 2:20:08Lex Fridman?

  I hope so too.

• 2:20:08Speaker 01

  So far, I'm just doing it in person.

• 2:20:12Speaker 01

  But it's.

• 2:20:13Lex Fridman?

  I would, I would love it. I think a lot of people would love to see it. So I hope you do just that. Let me ask you a big ridiculous question. You look up at the stars. You look up at the early, early, early stars. So let me ask the big question that we humans often ask and struggle to answer. What's the meaning of this whole thing? Why, why are we here?

• 2:20:37Speaker 01

  We talked about, you know, the biological evolution requires the chemical evolution for all of this to kind of play out. And carbon played this important role. And, you know, in some sense, we're, we're just a consequence of all of these things being the way they are. Right? So maybe this is just where we are supposed to be because, you know, the, the laws of physics sort of work the way they do. And we talked much about the variety of, of everything really, and certainly, you know, from over here to over there. And things in the vicinity of where the sun and the solar system formed, they were the way they were.

• 2:21:19Speaker 01

  And life maybe was a necessary consequence of that. And in some sense, I like to believe that because then it becomes reproducible and we can apply that same argument elsewhere. If it's total chance, right, that makes it harder. And that's not, not truly satisfying to, to a scientist.

• 2:21:37Lex Fridman?

  So it's a, it's a consequence of psychological evolution, which is a consequence of biological evolution, which is a consequence of chemical evolution, consequence of physical evolution, whatever, whatever disciplines, it's turtles on top of turtles.

• 2:21:52Speaker 01

  Turtles all the way down. Yes.

• 2:21:55Speaker 01

  I, yeah.

• 2:21:56Lex Fridman?

  And you have studied some of the most ancient turtles.

• 2:21:58Speaker 01

  Yes.

• 2:21:58Lex Fridman?

  At the very bottom of the thing.

• 2:22:01Speaker 01

  That's right. They live for quite a while.

• 2:22:03Lex Fridman?

  Yeah, they do. Well, thank you for your incredible work. Thank you for highlighting both the human side and the deep scientific side. It's just, I'm a huge fan of your work and thank you for everything you do. And thank you for talking today. This is awesome.

• 2:22:18Speaker 01

  Of course, it was wonderful. Thank you.

• 2:22:21Lex Fridman?

  Thanks for listening to this conversation with Anna Fribell. To support this podcast, please check out our sponsors in the description. And now, let me leave you with some words from Douglas Adams in Hitchhiker's Guide to the Galaxy. Far out in the uncharted backwaters of the unfashionable end of the western spiral arm of the galaxy lies a small unregarded yellow sun. Orbiting this at a distance of roughly 92 million miles is an utterly insignificant little blue-green planet, whose ape-descendant lifeforms are so amazingly primitive that they still think digital watches are a pretty neat idea. Thank you for listening. I hope to see you next time.