B (3:57)

Hi Greg, It's a pleasure to be here, so thanks for having me.

A (4:00)

Jonas, why did you write Basic Infinity and who is the target reader?

B (4:05)

Yeah, the starting point for this book was the image, the first ever published image of a Black Hole in 2019 by the event Horizon Telescope collaboration. And I remember when I saw that image, I was really awestruck. I thought it was amazing that it was possible to, I mean, know that black holes exist, but also to produce an image of them. So when I saw this image, I decided that I wanted to kind of learn more about our current state of knowledge about black holes. Like, what do we know about them, but what do they also mean for us as humans here on Earth? So that's why I set out to write this book. And the target audience is people who are maybe generally interested in space, but who doesn't necessarily have a technical background. So you don't need a physics or an astronomy background to read this book. So it's aimed for Everyone. And I also touch a lot on philosophical and cultural and even political questions. So it's a broad audience.

A (5:10)

Absolutely. And I want to talk about each of those questions. But just to start off, the book's divided into three parts. And in part one, titled Amid Stars, wars and Darkness, you discussed the candidly, the history of how we came to understand black holes. And that in itself is fascinating. The people who are involved, I mean, it was sort of standing on the discoveries of the others. But before we start, what is a black hole?

B (5:40)

Yeah, that's the big question, right? What is actually a black hole? And I think we are still trying to figure that out because there are such weird and mysterious objects. But a starting point is the definition of a black hole, which is a place or a region in the universe where gravity is so strong that nothing can escape it, and particularly not even light can escape it. And since light is a kind of. The speed of light is kind of speed limit in the universe, it means that nothing else can escape it. So that's kind of the starting definition of a black hole. And that's also why they appear as dark, because nothing can escape it. And for a long time it was very unclear if these kind of objects can exist at all.

A (6:27)

Okay, I want to move a little into the history. You begin the book with a very fascinating character, John Mitchell. He's the last person you'd expect to really, I guess, discover black holes. Could you talk a little bit about him and maybe his place and how we came to understand the existence of black holes?

B (6:49)

Yeah, so this is a very fascinating story. So, of course, if you write the history about black holes, you want to know. So who had this first kind of idea of something like black holes, that they could exist? And it was, rather surprisingly, a clergyman in England, in the little city of Thornhill, who was named John Mitchell. And this is towards the end of the 18th century. And in 1783, he published an article where he discussed if it's possible that among the stars there could be some kind of celestial body with such a strong gravity that light couldn't escape it. And you might ask, but why should a priest, a clergyman, come up with that idea? But John Mitchell had a very prosperous scientific background as a geologist, a mathematician, also doing astronomical studies. So he was definitely well suited to ask this question. And he did calculate that if it would take. So this was a completely hypothetical, hypothetical argument. If you would take something like the sun, keep its composition the same, but increase its size by a factor of 500, the gravity of the sun would increase so much that light couldn't leave this object. So that was a purely mathematical calculation that he did. And this idea spread at the time. So we're talking about. Yeah, around the time of the French Revolution and its aftermath. So this idea spread to Paris, where a French astronomer, Laplace, picked it up. And it also spread to Berlin, where a German astronomer picked it up, von Soldner. And they even tried to look after these objects. So there was even an observational attempt to see them, but nothing was seen. And the idea then kind of vanished out of the scientific imagination and appeared again much later in the modern form. Form of Einstein and general relativity, around the time of the First World War. So that's kind of the background story. And it's important to emphasize. Yes. Quickly. That they didn't call this black holes, that what we call black hole today. It's much more modern conception and much more complex thing than these kind of Newtonian objects that they thought about.

A (9:15)

And just for our readers, in contrast to the normal scientific method, we theorized or we speculated on the existence of black holes before we discovered one. Is that correct? It wasn't as if we saw the sun and then tried to determine the Earth's position or location relative to the Sun. But, you know, here it was almost as if there was a lot of speculation, even up until the time of Einstein and I think, candidly, up until maybe the last 30 or 40 years, whether or not black holes existed. Is that the right sequence?

B (9:54)

Yeah, yeah, that's absolutely correct. And that's what's so fascinating about black holes, that they first appear to us humans as a piece of mathematics. And like you said, for the sun, we first observe the sun and the stars, and then we create models to kind of figure out why they shine and how they work. But for black holes, it was pure mathematics. That was the way they appeared first. And as I said, that was around. The modern formulation was around the time of the First World War when a German astronomer called Schwarzschild discovered this. And Einstein did not believe that these kind of objects could exist. And the first kind of tentative evidence, empirical observational evidence that appeared until the 1960s. And then, as you said, also it was a long, long process before the scientific community was convinced that these objects exist.

A (10:50)

Just to offer a little background on Schwartzschild, he was a. I want to say a soldier in the World War I, but specifically tasked with calculating the trajectory of ballistics. And I believe in his downtime, he was doing this math. And corresponding with Einstein is that Correct. To suggest you. You could have the existence of a black hole.

B (11:14)

Yeah, kind of. So it's a very interesting story. So Einstein, he was struggling to understand what is gravity actually, how does gravity actually work? And in 1915, he came to the solution, which we still use today, which is called general relativity. And in that framework, gravity arises because of the way space and time gets deformed around objects such as the Earth or the sun. And we can talk much more about that. You could have an entire podcast about how that works. But to jump a little bit over that particular step. He published his equations in November 1915. He was in Berlin at the time. And as you said, Kol Schwarzschild, he was like an astronomer prodigy when he was young. So he was extremely skilled both in observation, developing technologies for astronomy, but also in calculations. And he was a lieutenant, and he was stationed on the western border towards Germany and France, so the western border there. And he learned about this new theory. He was a. A friend of Einstein, and I'd followed this development, and he immediately set up how to calculate. So what does this new theory tell us about the motion of planets and the internal structure of stars? What does it predict? And when he did those calculations, he discovered a formula for black holes that we use today. Now, unfortunately, he died just a few months after that. So he didn't live to see what this formula actually entailed and what a richness this mathematical formula contained. So it took several other researchers to develop this mathematics and understand it, because everything was so weird, it was so new. So it took a long time for people to actually understand this formula that Schwarzschild found.

A (13:14)

And just by way of reference, his last name means, I believe, in English, black shield. Always find that a little coincidental. But to your point, again, his. This is what's a fascinating thing in your book. His recognition or belief that there could be black holes, again, was based on his mathematical calculations rather than any observations. Is that accurate?

B (13:40)

Yeah, that's correct. So Schwarzel himself, he didn't. Nobody at the time knew, used the term black holes. That came much later, and they didn't understand exactly what his formula predicted. So Schwarzschild himself, he never said, oh, this should be this kind of objects that are completely dark. He never came to that conclusion from the formula, but other people at the time came to that conclusion. And just based on the mathematics, purely mathematical reasoning, and Einstein, he said that, no, I don't think this obvious can exist. I think this is just pure mathematics. There's no correspondence in reality. This can't exist. So Einstein himself doubted one of the most profound predictions from his own equations. And that kind of shows you how weird and complicated the mathematics was, that it was very hard for people to.

A (14:33)

Come to terms with this on that point of mathematics. Again, your book is focused on black holes, but you do a very nice job of weaving in tangential themes, one of which is the importance of non Euclidean geometry or Einstein's general theory of relativity. Could you briefly talk about why that's important for understanding space, time and black holes? And I believe you talk about the contributions of Bolyai, Gauss and Lobachevsky here in a chapter. And I found that really interesting on how they had a breakthrough or thought differently relative to Euclid and our entire understanding of geometry that time.

B (15:13)

Yeah, sure. So non Euclidean geometry, as the name suggests, it's kind of the opposite of Euclidean geometry. So you have to start by defining, what is that? What did Euclid do that's so important? And Euclidean geometry, it's about the stuff we learn in school, basically, about what's the sum of the angles in a triangle? Well, it's 180 degrees. What's the relationship between the ratio of, sorry, the radius of a circle and its circumsperence, these kind of things. And it's all spelled out in Euclidean geometry. But there was one property that Euclid himself, he felt very uneasy about, and that was the question. If you just take two lines that are parallel to each other, and then you imagine that you extend them out all the way to infinity, then it kind of makes sense that they should continue to be parallel to each other. But Euclid himself, he couldn't really prove this based on his axioms, based on his system, so he had to just assume that that was going to be true. And for a long time, this haunted mathematicians because they said, like, but this seems so obvious. Just place two lines next to each other, 1cm apart, extend them very, very far away. They should still be 1cm apart from if they are parallel. But then, very curiously, around the same time, at the Beginning of the 19th century, three mathematicians, Lobachevsky, Bolyai and Gauss, independently of each other, started to think, well, maybe it isn't true. Maybe these kind of parallel lines could still meet each other or maybe diverge from each other. So they started to investigate this kind of geometry and see what the implications would be. And that came to be known as non Euclidean geometry. So it's a kind of possible geometry that you could have where the Usual geometrical properties that we learn in school does not hold. The sum of a triangle does not have to be 180 degrees. Parallel lines could meet or diverge from each other. So it's a different kind of geometry. And this is something we actually use when we look at, for example, curved surfaces like the Earth. We have to use a kind of non Euclidean geometry on the surface of the Earth. But here it was the question if could space itself have such a non Euclidean geometry, so not only objects and surfaces in space, but space itself? And this became very, very important for Einstein because when he started to get a glimpse of the idea that maybe gravity is about how space deforms and how time ticks in different ways around objects, around planets, around stars, then he needed to use this non Euclidean geometry to put his physical intuition into a firm mathematical foundation. So that's how non Euclidean geometry entered Einstein's world. And it's quite fascinating that Einstein, he's often portrayed as someone who maybe when he was young, wasn't very well versed in mathematics, but that he had a great intuition. And this isn't exactly true. He was a very skilled mathematician for sure, but he needed help to develop this new mathematics. So this kind of view that Einstein was a lone genius sitting by himself and developing all these new theories, that's not true. Like he was a very collaborative person who sought help from other people to solve the problems he wanted to solve.

A (18:59)

Yeah, you do a nice job. I think his friend Marcel Grossman contributed to some of the map behind that. I want to help define black holes or ask you a little more before we jump into part two, but specifically I, your, I should mention the, the introduction to your book, the Forward is done by Frank Wilseck, who's a Nobel Prize winner himself. And he talks about black holes as having a mathematical purity. Is that something you, you view as part of black holes, this unique mathematical purity?

B (19:35)

Yeah, definitely. So maybe we should dive a little bit deeper down into what's actually the modern view of a black hole. This kind of Schwarzschild formula, what does it tell us? So, a black hole, there are two key concepts, which is the event horizon and the singularity. So if we would go towards a black hole, we would see this kind of dark object floating in space. And the surface of a black hole, that's what we call an event horizon. And it's not a surface like the surface of the Earth, which you can stand on and you can hit it and you can investigate it and try to determine its properties. The surface of a black hole is not made out of anything. It's pure space and time that kind of has curved so much that it closes in on itself. So the event horizon is a surface made out of space and time and with a property that light can't leave it. And once you have passed this event horizon, then you can't turn back. There's no road anymore, no path anymore that leads out of the black hole. So you have to be careful when you get closer inside the black hole you have this thing called the singularity. And that's a very famous word that often appears in all kinds of places, the singularity. But what it means is really that the theory breaks down there. So at the singularity, the space, time curvature and the forces acting on your body as you approach it, they become infinitely large and the theory can't really predict what happens there anymore. It's like a point in space and time that's gone missing. But before that, everything will be torn apart. But it's also important to know that you can't escape the singularity. And the reason for that is that it's not really a point in space, but it's a point in the future. It's a point in time and you can't escape the future, right? You will hit it no matter what happens. So that's when you fall into a black hole. You're going to reach the singularity sooner or later. It's Pro Savings days at Lowe's. Get up to 35% off, select major.

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$15 per month equivalent required. New customer offer first three months only, then full price plan options available, taxes and fees extra. See mintmobile.com it is such a mind boggling concept. I mean, almost up there with Einstein's breakthrough with general relativity and space time. I mean, black holes, it's just mind boggling. So I want to, now that we've defined it, you talk about the black hole at the center of the Milky Way referred to as Sagittarius A asterisk or star. And I know you point out the black hole, it isn't technically a star. Could you tell us about the black hole, the large black hole in our own neighborhood, our own galaxy here?

B (23:55)

Yeah, exactly. So now we talked a bit about the history and the theoretical aspect, so it makes perfect sense to see. So what's the closest black hole? What do we know? So this object called Sagittarius A, as you said, that's the black hole at the center of the Milky Way. And the name Sagittarius that comes just from the constellation where the center of the Milky Way is directed at, like where you have to look in the sky to peak towards the center of our galaxy. And A, that name is a remnant from the early days of radio astronomy when they mapped out that region of the Milky Way using radio telescopes. There seems to be two categories. There are stellar mass black holes that are formed when heavy stars die. And we might get into that. And then there are these supermassive cousins that are can weigh as much as billions of suns, the corresponding mass of billions of suns. And Sagittarius A has a mass of about 4 million suns compressed into a volume that's a bit smaller than the orbit of Mercury around our Sun. So how do we know that that black hole exists? So the first hint was looking at stars at the center of the Milky Way. So they lie 27,000 light years away. So it takes light 27,000 years to reach us from there. And astronomers like Andrea Ghez and Reinhard Genzel observed how these stars moved there and could see that there were stars whizzing about at enormous velocities. And it only took them 16 years to make one orbit around whatever this object was at the center compared to us. For us, it takes 230 million years to make a full orbit around the center of the Milky Way or around the galaxy. So the more they looked, the more they could constrain the volume that this enormous mass was compressed into. And it became clear that it had to be something like a black hole. And that's also what they were awarded with the Nobel prize for in 2020. So Andrea Gez and Rainer Gensel for discerning that it was called a supermassive object, because, you know, in science, you have to have an open mind. Maybe it's something even weirder than a black hole. But then the next step was called can we look even closer? Can we see even more closely at what's there to see if it's a black hole? And that's what the Event Horizon Telescope collaboration did. So they used an armada of different telescopes on Earth to peek as close as possible. And you could see the gas moving around the black hole. You could take a photo of that, because when the gas moves, it start to send out a lot of light. And you can. Some of that light will disappear forever in the black hole, but some of that light can reach us all the way here on Earth. And from that, you could reconstruct this image and see that there was this kind of missing light, this darkness in the middle of this glowing gas, which was the black hole. So it's our closest supermassive black hole, and it's quite well studied now. There's much more to learn about it. But yeah, it's. It's like our. Our neighboring black hole, you know, like our closest black hole. Our closest big supermassive black hole, I should say.

A (27:24)

Jonas, just to clarify, it is at the center of the Milky Way and we do rotate around it. I'm sorry, we, as the Earth, are we rotating around this Sagittarius?

B (27:36)

Yeah, this is an important point, that the solar system and the stars in the galaxy are moving around the center of the Milky Way, but they are moving around the center of a lot of stuff that's there. All the stars, there's gas, there's the supermassive black holes and other things. And it's not like our orbit here is affected by Sagittarius A. It's so far away, and there's so much mass in all the other gas and stars and so on there. So if you would remove the black hole, we would still go on the same orbit, but it sits dead center in the middle of the Milky Way. This Sagittarius, a star?

A (28:14)

Yeah, that really shocked me. You make the point in the book that if it were to be removed, it wouldn't impact our orbit at all. And that when you're a certain distance from a black hole, it really doesn't have any disproportionate impact on the rotation of planets or stars. It's when you get close that it feels like the physics starts to break down.

B (28:34)

Exactly. Yeah.

A (28:36)

You really gave a great answer and I want to unpack a little bit of that. You mentioned the two astronomers who won the Nobel in 2020, as you talk about repeatedly in the book, and not surprising in our conversation. The third individual was Roger Penrose, who I believe provided more mathematical support for a black hole. I mean, it seems to be a recurring theme. The math is helping us to some extent understand the black hole. Is that, is that fair?

B (29:03)

Totally. The mathematical investigation is super important for understanding black holes. And I would say, like our observations are, yes, starting to build up. We are starting to get these incredible observatories and telescopes to really get closer to study what happens near a black hole. But it's really our mathematics that gives us the deepest insight into black holes for sure. And if you want to know what happens inside a black hole, the only thing we can send there is our mathematics is our equations to probe the interior of a black hole.

A (29:37)

Yeah, I definitely want to talk about that. One more individual. Well, you have a bunch of great biographies, but someone who is a recurring theme as well when it comes to black hole and the Nobel Prize is the 1983 winner.

B (29:50)

We need to edit Chandrasekhar.

A (29:52)

Yeah, you got it. Could you talk a little bit about his contribution?

B (29:56)

Absolutely. So Chandrasekhar was a physicist of great importance for the study of black holes. He came from India and did his PhD in Cambridge in the. This was around. Okay, quick pause. I have to say right now, if it was 20s or 30s. I think it was early 30s. Cambridge PhD. Yeah, it should be early 30s.

A (30:24)

Yeah, I think that was Eddington.

B (30:27)

Yeah, with Eddington. 1933. Exactly. So let me see that here. So he was an Indian born physicist who did his PhD in Cambridge in the early 1930s. And his great contribution was the answer to this very, very profound question. I should say it formed a part of the answer because it was a long process to really understand this. What happens when a star dies? So we see the stars in the sky, in the night sky, and of course we want to know will they shine forever or will they stop shining at some point? And if they do, what happens then? And a star is imbalanced because of two forces, and that's gravity, which makes it contract and collapse. And then you have the pressure of the star, which makes it expand. And if you look at the sun, those two forces are imbalanced. So the sun has the same size today as it had yesterday. But at some point, the nuclear fusion inside the star will stop. It can't burn anymore. And at that point, a lot of this internal pressure does diminishes drastically and the star starts to collapse because of the force of gravity. And then the question is to what? What does it collapse to? And one answer is white dwarfs. So a star can collapse and a new pressure kicks in at a certain point, a quantum mechanical pressure that prevents further collapse, and you reach a new stage of equilibrium and everyone's happy. But what Chandrasekhar proved was that. Hold on a second, that doesn't quite work if the star has too much mass because then the force of gravity becomes too strong. And this is not a stable star anymore. At white dwarf is not stable anymore. And this is called the Chandrasekhar mass, and it's about 1.4 times the mass of our Sun. And this is what he proved and showed. And he was unfortunately ridiculed by another famous astronomer, Arthur Edison, for his result and didn't quite like that and moved on to being academically active in America, in the US instead. But he eventually got the Nobel Prize for this and other contributions to astrophysics. And he has to round that off. What Chandrasekhar discovered was this question. Could it be possible that gravity takes over completely, that you have indefinite collapse, that there's no new equilibrium state for a collapsing star? Because if that's true, then you would end up with a black hole. And that was a huge question at the time, if that would be true or not.

A (33:17)

And Jonas, to clarify, I know he won the Nobel in 83. The research that we're talking about here, it's in the 1930s and 40s, before he shifted into other areas of academia.

B (33:31)

Yeah, this is early 1930s and he did this. The first calculation he did was actually on the boat that took him from India to, eventually to England. So he did this calculation very, very early in his career.

A (33:46)

Yeah, another fascinating character. Before we shift to the second part, I was just floored by the estimate you gave of the number of black holes in the Milky Way galaxy. I think well in excess of 10 million, if I have my notes right. Even maybe up to 100 million. Is that, is that correct? And how many of those could be super massive black Holes, Yeah.

B (34:09)

So the number is above 100 million. We can't. Black holes in our galaxy, we can't know for sure, of course, but this is based on models of how many stars have become black holes throughout the history of the Milky Way. There's only one supermassive black hole, and that's the one that sits at the center. So we don't have any other supermassive black holes roaming around and maybe crashing into our solar system or something like that, so we don't have to worry about that. But 100 million is a lot, of course, and that's stellar mass black holes. So that's usually what you call than black holes that are formed and start. Start.

A (34:49)

Yeah.

B (34:49)

So it's a lot.

A (34:50)

So it was that number blew my mind. And that's a great segue into part two of your book, Black Holes in the Depths of Space. You've touched on this in a few answers. But could you talk about how black holes are formed from neutron stars and, you know, the, the dynamics there?

B (35:08)

Yeah. So as I mentioned, the big question is when a star stops shining and when it runs out of nuclear fuel to burn in its center and starts to collapse, what will it collapse to? And the modern answer that took several of the brightest minds of the 20th century, several of the best astrophysicists to answer, was that there really are only three options. It could become a white dwarf. And in a white dwarf, the pressure that prevents further collapse is supplied by the electrons that's whizzing around inside the white dwarf. But if you have more mass than this mass of Chandrasekhar that he found of 1.4 times the sun, it continues to collapse. Okay, but can it reach a new equilibrium state then? And the answer is yes, it can become a neutron star. And that's an extremely compact core made completely out of neutrons. So there's a lot of like, nuclear alchemy that happens in these collapsing processes when you reach extremely high densities and extremely high temperatures. So it transforms into this neutron dense core about the size of the Earth, and that can also be stable. But if it has even more mass than a certain threshold, which is a little bit hard to pinpoint because there's a lot of very difficult calculations you have to do to understand that then it can also continue collapsing and become a black hole. And in these processes, when very massive stars die and collapse, they also release copious amounts of energy in the same time in these kind of explosions known as supernovae. And certain of these supernova explosions will result In a black hole. And that's kind of like a beautiful way For a star to exit our world and become a black hole is without this huge bang and this huge emission of light and other particles.

A (37:14)

Very nice explanation. And just to clarify, Supermassive black holes not only have the mass of a billion times plus the sun, but do generally sit at the center of a galaxy. And in terms of how they are formed, Would they come from smaller black holes or other stars? How. How do we think about the origin of supermassive black holes?

B (37:39)

Yeah, that's one of the big unresolved questions in astrophysics today, and we are hopefully going to solve it soon with the help of the James Webb Space Telescope. So, supermassive helicals, like you said, they sit at the center of most galaxies in the universe. And there's a tight shared history between how the galaxy itself has evolved and how the supermassive black hole has evolved and what astronomers have seen when they peek out into space. You know, the fascinating thing or the great tool that astronomers have when they look out into space Is the further you look, the further back in time you see. Right. Since it takes light time to reach us, the entire sky is like a time machine that allows us to peek further and further back into the history of the universe. It's really amazing. And what they have seen is that these supermassive black holes, they arise very early in the history of the universe. So during the first billion years, you can see that there's plentiful of these supermassive black holes, and they have grown really, really large In a very short time by astronomical standards. So that has become quite a bit of a riddle. How could they grow so fast so early? So it's like looking at photos from kindergarten, and you see that everyone looks like an adult, but they should look like kids, like, there's something weird. And there are different models for how this kind of being created in the early universe, these supermassive black holes. Maybe it was from collapsing gas clouds. Maybe it was from the very first stars that arose in the universe that were extremely big and exploded and became black holes that then grew. Or maybe it was like you suggested, A merger of many smaller black holes that eventually built up into these supermassive black holes. Each of these explanations have certain problems, Certain scientific difficulties. So there's not that there's, like, one easy astrophysical answer that explains this. And that's why you need a telescope like the James Webb space telescope to see these very first galaxies, maybe even the first stars, and try to figure out what was the exact environment there in the early universe.

A (40:01)

Yeah, I should have asked you this. When do we think the first black hole may have come on the scene? The universe is roughly 13.8 billion years, give or take. When do we think black holes may have started or existed in that timeframe?

B (40:19)

So the earliest black holes that we see, they are created only a couple of hundred million years after the Big Bang. So I don't have freshly the exact number in my head right now, but it also feels like every time you say a number, then a couple of weeks later there's some new science results even and even earlier black hole. So it's within a time frame that's much, much less than 1 billion years. So a couple of hundred million years, that's what we have seen. God knows how when they were first created. There's also this theory of primordial black holes that were created in the very, very first moment of the universe. And maybe they later grew into supermassive black holes. It's one theory. And if that's true, then these objects were actually there all the way from the beginning of the universe, more or less. So, yeah, that's very fascinating too.

A (41:11)

And I want to get a little more into that, particularly the relationship between black holes and galaxy formation. But before we do that, as I said earlier, you do a really nice job of talking about individuals contribution to the larger, to our larger understanding of black holes, One of which is what happens to space and time around a black hole. And there I think it was an individual by the name of Roy Kerr who came up with the formula. He has a somewhat interesting background himself. But could you talk about his contribution to our understanding, particularly around space and time?

B (41:42)

Yeah, absolutely. So Roy Kerr is a guy from New Zealand. He's a very nice guy. I interviewed him for the book, as he mentioned, and he came up with this extremely important mathematical result in the 60s, 1960s. And it had been a long outstanding question that was unsolved. And that's okay. Suppose black holes exist. Suppose they exist, they should rotate, right? Because we know that the Earth rotates, the sun rotates. And if a star collapses into a black hole, then some of the rotation of the star should also be carried along to the black hole. So people were quite desperate to know, but what does a rotating black hole do? How does it work? What happens then? And to answer that question, you need Einstein's theory of general relativity. And you see, what does it predict? But there was one very difficult obstacle to understand that and to use Einstein's theory and that it's so mathematically complicated, it's so difficult to hammer out the consequences from the theory and to see what it says mathematically. But Roy succeeded. Roy Kerr succeeded. So he found the mathematical formula for a rotating black hole, and so Schwarzschild found the formula for a non rotating black hole. So that describes some very important features like the event horizon, for example. How does an event horizon work? But then when the black hole also spins, you get additional physical effect that are also very weird. So should I go into them or how much?

A (43:29)

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A (44:54)

Maybe just a minute. We do. There's a few other topics I want to touch on, but maybe just a minute in terms of his contribution there, why that spin or rotation is so important.

B (45:04)

Yeah, and one of the important things is that you get something called an ergosphere. So that's a region outside the black hole. Yeah. Where space itself is spinning along with the black hole. So if you go there with a spaceship, you're kind of forced to flow around with the rotation of the black hole. And inside the ergosphere, it's impossible to go in the opposite direction. And this ergosphere is very important. Ergo means work, from ancient Greek and Sphere is the sphere. So why do we call it a work sphere? It's kind of a funny name. And the reason is that you can actually extract energy and work from the black hole. It can power processes. And it's believed that this could be one reason why black holes have this extremely fascinating property that we haven't talked about, jet, which is jets. So they actually can shoot out light and matter away from them. And that's a big topic. So these jets, that's. For me, this is one of the biggest discoveries about black holes in terms of just observation because this was also unexpected. And it turns out that we have this image of black holes that is cosmic vacuum cleaners that suck all in matter around them and just grow and grow and grow. But that's not true. When they eat, they kind of eat like babies. Like things just end up all over the place. And jets are these huge structures that are shot away from the black holes, so they don't emerge from inside the black hole. So nothing can leave the black hole. But they are created outside of the black hole, thanks to this complicated interplay between the gas that's there, the magnetic fields, the rotation of the black hole, a lot of stuff going on. And these jets can be larger than the galaxies themselves that the black holes sit in, which is just amazing. And if you Google photos of these astronomical images, they're so beautiful images of these. And that's jets. And they are crazy.

A (47:17)

Perfect. Okay, I want to move. You know, you talk about our understanding of black holes having been improved with individuals contribution mathematics. But clearly telescopes and technology play a role here. Could you talk about gravitational waves and how important ligo, the Laser Interferometer Gravitational Wave Observatory has been in our understanding of black holes?

B (47:40)

Yeah, absolutely. So we all know light, what we see around us, so that's made out of electromagnetic waves. So waves in an electromagnetic field. And Einstein himself asked, well, could there be something equivalent like that, but for a gravitational field? Could there exist waves in a gravitational field which would actually then be waves in space time itself. Very weird. And after some calculation, it became clear that yes, the theory predicts that. It predicts that this should be possible. But it's extremely, extremely hard to create these gravitational waves. To do that you need very compact objects like black holes, like neutron stars that circle each other. And when they do that, they will create strong gravitational waves that shoot out into the cosmos with the speed of light. And some of those waves will reach Earth. But the effect that they induce here on Earth is extremely small. So it's Very hard to measure it. But in the 70s there was this idea pioneered by Rainer Weiss, who also got the Nobel Prize, who unfortunately passed away very recently at the age of 92. He was one of the nicest guys, most curious, helpful guys, interviewed it in his book. And we were emailing just this spring about the book. So very sad that he has passed away. But he came up with this idea that. Hold on. What if you just take lasers and you shoot them off in opposite directions and then you let them bounce off mirrors and then they meet again after a while. So let's build that. And then when a gravitational wave pass, that will disturb these laser beams a little bit, just enough so we can see it. And the precision required is insane. They need to monitor displacements of the mirrors that these lasers bounce off, that is of the order of less than 1 10,000 of the size of a proton. It's just crazy that they can do this. So it took several decades to design and build this instrument, but in 2015, they registered, they observed, they detected the first ever gravitational wave that was produced by two colliding black holes. And this is called ligo, the Laser Interferometer Gravitational Wave Observatory. Ligo, that's the name.

A (50:18)

That is fascinating. I'm sorry, I do have to ask you about Lisa. That seems even more boggling. And I think we're 10 years away from that. And that's a joint project between NASA and esa, I believe. But could you talk about how that would. What the goal there is and how that would even give us more insight into that?

B (50:36)

Absolutely. So LIGO can measure these waves, gravitational waves that are created from colliding stellar mass black holes. But what about the supermassive black holes, the ones that we have at the center of the galaxies? Because galaxies also collide and merge. And the supermassive black holes should, by all accounts, also merge and collide and merge at some point and send out gravitational waves. But these are harder to detect. So they have much lower frequency. They see really like a low frequency rumble in the universe that you want to detect. So to do that, you need even longer distances between these laser beams and where you detect them and bounce them and so on. So you have to go to space. Earth is not big enough or like there's not a big enough space on Earth to do this on. So you just have to go to space to do this. And you have to place three satellites in a very, very precisely controlled position and let laser beams go back and forth between them. And then you could, in principle, detect these super massive black hole collisions by observing this gravitational wave. And that's an ongoing project, like you said, It's a collaboration. NASA and esa, the European Space Agency is going for that. And if it all works out that I really, really hope it does, that will come to fruition sometimes in the middle of the next decade, hopefully. And that, yeah, it's like science on the border of science fiction for me.

A (52:13)

It really is. I mean, the lasers from space, it's amazing. But yeah, it seems like we're there and it might have been. Weiss, I forget you quote somebody saying like Lego was even on the forefront of technological innovation. I mean, it really is impressive how far we've come and how where we're continuing to go. I talk about the first two parts of the book. The third part of your book, Black Holes and Our Plant Place on Earth, I really found fascinating because you, you focus on some areas that you wouldn't normally associate with black holes as well as just overall astronomy. And could you briefly talk about the relationship between Hawaii and astronomy as, as you talk about in the book? The Thirty Meter Telescope is there, but, you know, there is a population as well that we have to interact with or the community has to interact with them. Just talk briefly about that.

B (53:08)

Yeah, exactly. So the book's titled Black Holes and Our Place on Earth. And that was the, for me, the shocking find when I did research that there is a lot of connection between black holes and us. And also in the way that we. Sorry, there is a lot of connection between black holes and us, both in direct terms that we're going to talk about, but also in the way we do research. So what happened on Hawaii was that astronomers wanted to build a new telescope, the Thirty Meter Telescope, which would be a great telescope to learn more about the universe, including black holes. But the local community there said, you know, this is one telescope too much. You already built a lot of telescopes on our mountain, Mauna Kea, which has a deep cultural, spiritual, environmental significance on Hawaii. So they said, no, we don't want to have one more telescope. So these were members from the indigenous population of Hawaii. And this sparked a lot of protests, a lot of debate. Many astronomers were maybe unaware or didn't expect this. And it became quite a crisis for astronomy when this happened, because I think many have the view that astronomers do great things. They build telescopes, they learn more about the universe. What could possibly be wrong about that? But it turned out that then the question of where the telescopes stand and how they're built and who has access to them and what happens to the local communities and what happens to the local environment where the telescopes are standing? That's a huge question and has a huge societal impact. So that happened on Hawaii. And then when I looked into this more and more and started reading about this, because this is not something I learned about when I had my science education, I found that this is a question that arises at a lot of places. It's also, for example, in Sweden, just a few hours drive from where I live, there's a space launch, space where they shoot up rockets that then come back to Earth. And that's situated right in the middle of indigenous territory. And there's been conflicts there around this, and they've been doing black hole research from there also. So you have a lot of places around the world where you have Western astronomy being made on places with a troubling colonial history and where you have ongoing colonial conflicts. So that's something I dedicated a chapter to describing.

A (55:42)

Some of the other areas where you talk about our relationship to black holes. And I have to say I found this, the most fascinating part of the book is the relationship between quasars and how we measure continental drift. And you actually have. I think Mitchell makes a reappearance in this. But could. I'm sorry. Actually, I think that's Schwarzschild and Wegener who are involved in black holes and continental drift. But could you talk about the relationship there, how we. I guess black holes help us understand our own Earth and the environment better?

B (56:16)

Yeah, absolutely. You were right with John Mitchell. He appears there, too. Yeah. Because he studied the problem of the longitude, how to determine longitudinal positions on Earth. Okay. But, yeah, I agree. This is also something I found mind blowing when I learned about this. And I was so shocked. Like, why don't people talk about this much more? Because it's so fascinating. And yes, it's the fact that we actually use black holes to learn more about how the Earth rotates and how the continents move. And how's that even possible? Because I hear myself saying that, and it just sounds weird. But as we talked about earlier, black holes do create a lot of light around them. So all this matter that moves around the black hole can start to glow. And it glows extremely brightly. So bright that you can see it all the way across the universe. So we can see very, very distant quasars, they're called. So these kind of A quasar is a black hole plus its environment that's glowing extremely bright. And imagine back in the days, what you need to learn more about how the Earth is rotating, moving, and also how you yourself is moving on or moving on the surface of the Earth. You need stars. That's what we used and still use for navigation because they appear as fixed points in the sky. So if you want to know how you are moving, you need to compare with something that's not moving. But the precision we have today is so good. So the stars, they don't appear as fixed, they are also moving. Right? They are not stationary in space, they're also moving. So we need something even further away that's even more fixed in the sky, and that's supplied by these quasars. So you have a network of telescopes around the Earth that constantly monitor these quasars, and then they feed all their observations into supercomputers, and then they can see with centimeter precision how all these telescopes, this network of telescopes, move relative to each other. And then you can establish very precisely how the Earth is rotating and also how the continents that the telescopes are standing on, how they are moving relative to each other. So that's the story. And I find it amazing also that.

A (58:39)

Yeah, it was just fascinating to see that black holes are even helping us, like you said, learn about the Earth. And we, if I'm correct, we use quasars for navigational positioning. I mean, they. I think you describe them as radio lighthouses for navigation. And our technology today using them as the. I think the International Celestial Reference Frame.

B (59:00)

Is that exactly. That's exactly it. So they are like cosmic beacons in the sky that we use for. To create this, what is called the cosmic. International. No, international cosmic reference frame. Exactly.

A (59:14)

Unbelievable. And perhaps the only thing we haven't really talked about on Earth yet is the origin of life. And amazingly, and I realize this thesis might still be developing, you suggest black holes could have contributed to that as well.

B (59:29)

Yes. So this is ongoing research being explored right now. So that's the question. Could black holes actually help with the emergence of life in the universe? And that sounds, of course, very speculative because we only know so far about one place, which is Earth, where life has emerged. But let's be a little bit speculative because that's an important part of science, too. So it's what you need for life to emerge. You need a lot of things. We're not exactly sure. But of course, you need water, you need the right conditions and so on, but you also need a lot of other elements, iron, magnesium, carbon, and so on. And what researchers have found out. So this is Aurora Simoniescu, a Romanian researcher, using an X ray telescope is that when you look out into space, you can see how matter. So different elements, they are distributed in a galaxy, but also between galaxies in a way that seems to highlight that maybe these supermassive black holes, through their jets, through their feedback mechanisms that shape and influence the galaxies that they sit in, maybe they could contribute even to how different elements spread in the universe. And maybe that could actually play a role for having the right kind of elements if life manages to emerge at some other place in the universe. So that's kind of a state of the art speculation in science today, in astrophysics.

A (61:07)

Fascinating. I think if the common or the public understanding of black holes, if it's associated with any physicist or cosmologist today, it's most likely Stephen Hawking. Could you talk about Hawking radiation and how it relates to the inflammation paradox?

B (61:25)

Yeah, absolutely. So Hawking is really a household name. Everyone has heard about Stephen Hawking, and for good reason. Yeah, absolutely. So Stephen Hawking is really a household name, and everyone has heard about him, and for good reason. So he mathematically discovered this thing that we today call Hawking radiation. What does that mean? It means that black holes are not completely black after all. It turns out that maybe they can create particles and radiation out of nothing, out of the vacuum surrounding them. And this is really a piece of black hole magic, the way they do it. And it took someone like Stephen Hawking to figure out how this could be possible. So what that means is that if you have a really, really good meshing device and you're pretty close to the black hole, you could see a constant stream of particles and radiation, like photons, for example. So the quantum mechanical particle of light emerging from there. But we here on Earth have so far not detected this yet. And the reason is that this radiation is extremely weak, like it's for the normal black holes that we have out there. So the stellar mass, or supermassive black holes, it's a radiation that's less than a millionth of a degree above absolute zero. So even if we had a telescope like the James Webb Space Telescope, and could place it right next to a black hole, it would be extremely hard to measure this radiation. Yeah.

A (63:13)

Okay. Towards the end of the book, you suggest if there's one word to describe black holes, its duality. Why? Why did you choose that word?

B (63:24)

Yeah, this is what struck me after spending five years writing this book. And I thought, okay, well, so what's the point then, about black holes? Well, what story is emerging here? And then I thought that, well, the word that really describes it is duality. Black holes are a kind of unity of opposites, in a sense. So they are black, but they create some of the brightest phenomena in the universe. They consist of an enormous compression of mass, a lot of mass, but at the same time, they are somehow just empty inside, and they are very far away. But at the same time, we can use them to navigate here on Earth. And they are the simplest objects, but because they only have mass, rotation, and potential electric charge. But from another perspective, they are actually the most complex objects in the universe. So there's a lot of this interplay between opposites all the time. And then there's even in the absolutely more most advanced and modern theoretical physics research, there's something called the ADS CFT duality. And we don't have time to go into what that is. But so there's also another kind of theoretical duality going on there. So for me, I think that word kind of encapsulates what black holes really are. Yeah.

A (64:47)

Last question. We've learned so much about black holes, but as we've discussed, there's still a number of open questions. What do you think is the next piece of knowledge will acquire black holes, and how will we get it?

B (65:00)

Yeah, if I would try to predict a little bit from what I learned talking with all these physicists and astronomers, there are several very exciting things coming up. So, of course, one thing is that the Event Horizon Telescope, they managed to create an image of black holes, but they want to create movies, so videos of what happens around the black hole. So that's the one next step. You know, something like ligo. They just came out with a science result where they could show that one of Hawking's other theorems about black holes held true about how their area behaves. So LIGO is starting to probe fundamental black hole physics, thanks to their measurements. And then you have a lot of theoretical work right now into these information paradoxes and Hawking radiation, which is about the fundamental question, what actually happens with the matter and information that falls into a black hole? And there's a lot of progress there. So maybe, hopefully that question could also be answered from a theoretical point of view in the coming years. So someone said that we live in the age of black hole astronomy, and I think that's really true.

A (66:23)

Wonderful. I think that's a great place to end our interview. Again, the book is Facing Infinity Black Holes in Our Place on Earth. We really just touched on the surface. But as I said at the beginning, it's a wonderful read. You just begin to realize how important black holes are in our own lives. And it's just really amazing the impact they have and how they've improved our understanding of our universe. With that, thank you very much for joining us, Jonas. Really enjoyed the conversation and thank you for writing such a thought provoking book.

B (66:55)

Thanks, Greg. It was a pleasure to be here.