What Is Humanity’s Place in the Cosmos?

The Permanent Questions With David Brooks

In this episode, David Brooks interviews astrophysicist Priyamvada Natarajan about the mysteries of black holes, dark matter, and our place in the cosmos. The conversation traces

Key takeaways

• Priyamvanda Natarajan's research explores how supermassive black holes can form through the direct collapse of gas, bypassing the traditional star-formation process.
• The James Webb Space Telescope provided crucial empirical evidence to verify Natarajan's 2017 predictions regarding early universe black hole populations.

Main topics

• Black hole formation and dark matter
• The philosophy of scientific discovery

Notable quotes

We are significant because we can actually shape our own realm.

Conclusion

The episode provides a deeply reflective look at how scientific inquir

Transcript preview

Speaker 1 (0:00) I was like any other eight-year-old. I looked up in the night sky and I was transfixed. Later, I discovered astronomy involves math, and so it's not for me. But I never lost my taste for the poetry of the night sky. So I'm super excited to talk about the existential issues that peering to the universe raises. With one of the world's leading astrophysicists, Priyanada Rajan grew up in New Delhi and in high school developed a method to map the night sky over that city. Now she studies black holes and other stuff out there in our ever-expanding universe. But what's great about her is that she isn't just a bunch of data and equations. She's a deeply humanistic thinker who ponders all the existential questions the universe poses and writes about them with lucidity and grace. I'm pleased to welcome Priya Nadarajan to this table. Speaker 1 (0:50) Priya Nadarajan, welcome to The Permanent Questions. Thank you so much for being here. Speaker 2 (0:54) Delighted to be here. Thank you for the invitation. Speaker 1 (0:57) Now, I am fascinated by how scientists find their field. So, how do you find the night sky? I don't have such a dramatic Speaker 2 (1:04) story, but it's one that's sort of filled with a lot of wonder and awe. Because, you know, the night sky is basically, you don't have to go anywhere. It's there for everyone, right? And I think that... When I was a young child growing up in India, I was a very curious child, so I was always pestering my parents with questions, and ultimately my parents bought me a telescope and a microscope, and Speaker 1 (1:30) I made my choice. I Speaker 2 (1:32) was always fascinated with stars and, you know, the moon, usual kid stuff. I felt attracted much more to the night sky because I think you couldn't reach out and touch. there was something about it being not quite available in the same way that you could make a little specimen in a glass plate and look at it under the microscope. The fact that it was somewhat unreachable and elusive. I think was what sort of seduced me. But I don't think I actively thought about becoming an astrophysicist at that age. I was clearly interested in science. There was no question about it. And physics. I think I had a sort of, you know, interesting, very blessed in terms of the opportunities that I got. My parents are academics. So I was, again, you know, won the birth lottery, a house full of books. people, interesting people. I got a Commodore 64 at home for anybody in India ever had a computer. So I learned to program myself. And there was this fantastic woman scientist, Nirupama Raghavan, who came back from the U.S. to run the Nehru Planetarium in Delhi. And so I was an amateur astronomer, so I would go there. And when I heard she had come and, you know, she was really encouraging young students to read more about astronomy. I showed up, you know, a young teenager. I said, well, you know, I have a computer and I can calculate and I want to do some research. Can I do some work for you? And so she said, okay, what do you love? So I've been obsessed with maps and atlases and cartography my entire life. And even as a child, you know, atlases were sort of my favorite of the sky and the earth. So she said, okay, what's your favorite? I said, I love that sky. you know, map that is produced in the newspaper in Delhi, monthly night sky, what can you see? She said, okay, make me a map. Make me the star map, right? And so then that was a lot of work. I had to teach myself spherical geometry and, you know, I had to learn to program properly, input a lot of data about the positions of the stars and the planets and their orbits. And finally I did it. Speaker 1 (3:45) What's up with you and maps? Like you call your book mapping is and there's a lot of maps in there like and you mentioned this girl you were interested in maps like Why do you think maps have a special interest? Speaker 2 (3:56) One of the things that always fascinated me, you know, if you look at old maps, especially the sort of, you know, the explorer, voyager, sort of voyages of exploration maps, at some point, these chaps would map and say terra incognita. I love the fact that they said, we don't know what that is. And it's that same impulse that as a child I had to something that's kind of unknown. had like magnetic seductive value for me. And I was like, oh, wow. So there are things that are really not known. Some things are exquisitely mapped, you know, land routes, you know, shipping routes are mapped, you know, cities and, you know, down to villages. And then suddenly there's like a terra incognita. Then I went to MIT, but then at MIT, I studied a lot of different things. You know, I was very interested in philosophy of science. I'd encountered Thomas Kuhn, who had retired at that point, but he would come and many Speaker 1 (4:56) arguments. Speaker 2 (4:56) Thomas Kuhn wrote Speaker 1 (4:57) the book, The Structure of Scientific Revolutions. Speaker 2 (4:59) So at the time, string theory, which is very abstract mathematical sort of theoretical ideas about, you know, what happened before the Big Bang. So that's sort of the domain of string theory. I was well placed to kind of do that because I had a strong mathematics background as well as physics. But I was not interested in those ideas because they were not testable. They were not experimentally testable. And somehow to me, the excitement always was in being sort of. prove, make predictions and have them tested, you know, that kind of back and forth to me was what was exciting about science, right? So instead, I deferred PhD admissions at MIT in physics and started a PhD in history and philosophy of science because I always like to write. And I've... You know, I was slightly torn always also between the humanities and sciences because I love to read. I love poetry and love history. And I think Thomas Kuhn also influenced me deeply in the sense, you know, his book was something I read with great interest. But even then I felt that there were bits in his wonderful book that still missed things. And that's because he was not a practitioner. Speaker 1 (6:20) And the basic idea, correct me if I summarize this wrong, is that science moves forward in paradigm shifts. You've got a paradigm, Newtonian physics, it's working, working, working, and suddenly the data starts not working. And then somebody comes along, chops up the Newtonian paradigm, and we get a new one. Speaker 2 (6:36) Absolutely. And that it's all revolution. So I think... Even then, I felt that that was a simplistic sort of view of how science progresses, because it's a combination, it's a complex combination of evolution of ideas and revolutions, right? And that the practice of science was something that really interested me. And I realized that, okay, now I really need to learn to read and write. like the human is. I was going to look at simulations, and in particular in cosmology and astrophysics, because, you know, cosmology and astronomy, astrophysics are very interesting science, right? They're not your standard science because you can't do controlled experiments. The night sky, there's a supernova that goes off there. That's all you have. You cannot summon it up tomorrow again. Unlike chemistry, we can keep mixing, you know, reagent A and reagent B like millions of times anywhere around the world. So that fascinated me, the fact that these fields were somehow kind of. edgy in terms of our definition of the scientific method and so on. And so I wanted to understand this process of what the simulation is really doing. Is it actually testing, validating theories? So it turned out that took me to Princeton because there was one person at the time who was alive who knew John von Neumann and all the computational greats, and it was Martin Schwarzschild. Martin Schwarzschild is the son of Karl Schwarzschild, the person who discovered the black hole solution. While he was a soldier at the front, World War I, Einstein had just given his set of lectures on general relativity in the Prussian Academy of Sciences. He could not be there, but he heard. and got a copy of the lectures. And within days, he found the first solution, exact solution to his theory. Einstein even didn't expect there would be an exact solution, right? Anyway, black holes. Which is what Speaker 1 (8:38) was in your main field of study. Speaker 2 (8:40) So, you know, during this conversation with him, he was like, what are you doing this for? You have to be doing science. Then I told him what I just told you, that I couldn't find a thesis problem that I found enticing enough. And that's why I was kind of exploring other things. And he said, what do you like? So I said, I like... building storylines for the universe, you know, how things happen and make predictions, use all the data we currently have, make a prediction for future data. That's the kind of thing I like. So he said, well, I know the person you should work with. And his name is Martin Rees. And he's a professor at Cambridge. And so I ended up there. I ended up working with Martin. I am ABD in that PhD still. A Speaker 1 (9:20) major career failure. You mentioned earlier in our conversation that you didn't want the microscope because you didn't want to be able to touch the thing you were studying. Well, now you've chosen to study something you can't even see, and that's black holes. Like no one has ever or will ever see a black hole. And so what was the interest and obsession with black holes? Speaker 2 (9:40) Well, I mean, you can ask any kid what. They are obsessed with what they think is the most enigmatic thing in the universe, and they tell you it was black holes. I also work on dark matter. So all these invisible entities that seem to fundamentally shape our universe, right, their true nature is not well understood. So that's already a sort of an invitation to kind of go there and try to understand. And the draw about black holes is really they have the most bizarre properties. Speaker 2 (10:14) As you said, you never quite directly see them. You only indirectly infer their presence, just as dark matter. You sort of indirectly infer the presence of vast amounts of dark matter in the universe. Bulk of the matter in the universe, 86 % is dark matter. And so the only way you kind of infer the presence of dark matter is the gravity that it exerts. Similarly for black holes. So the only way we infer the presence of black holes is because they are places in the universe where there's extreme gravity. And so they bend light. All matter bends light. But when the matter is very densely, compactly arranged, it very severely and dramatically bends light. So we actually see that around black holes. But most importantly... what black holes really are are sort of, you know, they represent the sort of limits of our knowledge. And I'll explain what that is, right? So a black hole is basically a place where matter is so concentrated and gravity is so intense that nothing can escape sort of this sort of sacred boundary. It's called the event horizon. Not even light, if it crosses it, can actually escape it. The gravity is so intense, right? And they seem to be ubiquitous in nature. Almost every galaxy in the universe, including our own, harbors what we call a supermassive black hole. It's a million times the mass of the sun that's sitting at the center. And the question is, why are they there? What are they actually doing? How did they form? How did they grow? So this is sort of the big open questions. Speaker 2 (11:55) It's this idea of extreme gravity. And of course, you know, it was Einstein who completely reformulated gravity. You know, we moved away from the sort of neat kind of idea of Newton's gravity. You know, it's the force between two masses and it's mediated by the distance between them, one over r-square. Newton was never able to explain why. Why do two objects that have mass actually feel this force? How is that force mediated? That's why Einstein is so, his theory is just so remarkable and his imagination is just, you know, all making. Speaker 1 (12:41) This is a question about the process of scientific discovery. And so Einstein has one year. In 1905, he's 26 years old, and he publishes four literally universe-shaking papers. Like, how the hell does that happen where one guy in one year, which he never replicates, like, what's going on in that process of discovery? Are there periods of where a scientist just goes through? some