Instant Genius - The story of black holes, with Marcus Chown

Episode Date: June 2, 2024

Black holes are surely one of the most fascinating and mysterious phenomena in the known Universe. But few people know that the story behind their discovery, and the cast of dogged, often ignored scientists behind it, is just as interesting. In this episode we catch up with the award-winning science writer and long-time BBC Science Focus contributor Marcus Chown. We talk about his new book A Crack in Everything: How black holes came in from the cold and took cosmic centre stage. He takes us through the gripping story that saw black holes go from being a mere mathematical curiosity to one of the most talked about cosmic objects ever observed. Learn more about your ad choices. Visit podcastchoices.com/adchoices

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Music just as the artist intended. Visit name audio.com to learn more. Hello and welcome to Instant Genius, a bite-sized masterclass in podcast form. Each week you'll hear world-leading scientists and experts talking about the most fascinating ideas in science and technology today. I'm Jason Goodyear, commissioning editor, the BBC Science Focus. Black holes are surely one of the most fascinating and mysterious phenomena in the known universe. But few people know that the story behind their discovery and the cast of Doors dogged, often ignored scientists behind it, is just as interesting.

In this episode, we catch up with the award-winning science writer and longtime BBC science focus contributor Marcus Chowne. We talk about his new book, A Crack in Everything, how black holes came in from the cold and took cosmic center stage. He takes us through the gripping story that saw black holes go from being considered to be a mere mathematical curiosity to one of the most talked-about cosmic objects ever observed. So hi Marcus, welcome to the podcast and thanks very much for joining us. Well, thanks for having me.

So today we're talking about your new book, A Crack in Everything. It's all about black holes, but rather than simply describing black holes and saying how they form an act, you weave a narrative that details how they were first theorised and then observed and the people that did this. And as you'd expect, it's a long and convoluted story, but a very interesting one. So in the book, you start the story back in 1916 in Alsace, smack in the middle of the First World War. And I bet this is a story most people won't be aware of. So can we start the story there? Yeah, well, this is incredible, really, because you're talking about Karl Schwarzschild,

and he was the director of the Berlin Observatory in autumn of 1914 at the outbreak of the First World War. But he was 40 years old, so there was no need for him to actually join the job. German army, but he did because anti-Semitism was on the rise in Germany. He was Jewish, and he wanted to show that a Jewish person could be patriotic and fight for Germany. So he ended up like running a weather station in Berlin, calculating shell trajectories. And as you just said, he ended up on the Alsace front, which was the only bit of the Western Front that was actually mountainous. And incredibly, he attended on leave one of the four lectures that Albert Einstein gave in November 1915, where he presented his new theory of gravity,

the theory of gravity which supplanted Newton's. I should tell you that Newton's describes gravity with a single formula, but Einstein described it with 10. And he discovered that basically gravity is the curvature of space. So what you need to do is you need to use this theory to find out the curvature of space around any particular body. But you have to solve these 10 equations. And Einstein himself thought it was impossible, but incredibly, Swarthshaw went back to the Alsace front and actually found an exact solution, an exact description of the curved space around something like a star, something that Einstein thought was impossible. And he wrote and sent this explanation to Einstein. And he later realized that if this mass that created this valley of space time were to get more and more concentrated,

the valley would get steeper and steeper and eventually it would become an infinitely deep well, from which nothing not even light could escape. So a black hole. Although I should say that term black hole was not coined until 1967, 50 years later. So you mentioned there that he sent a letter to Einstein. So this idea of the deep well seems so wild that even Einstein dismissed it. Well, that's exactly the point of my book, because his subtitle is how black holes came in from the cold and have taken up cosmic centre stage. So really they were considered too ridiculous to even be the preserve of science fiction.

You know, even Einstein didn't believe them. And of course, one of the good reasons for this was, of course, that a black hole would be black against the black of space. So, I mean, there's no chance. It appeared to be no chance of actually seeing one. People completely mistaken there. First of all, people thought they couldn't exist. There must be some force that stops, for instance, a star running out of fuel at the end of its life,

no longer generating any heat to push against gravity. There must be something that stops gravity crushing a star. And so then we've discovered that that's not actually possible. There's nothing that can do it. And then we think, well, maybe these things will be unobservable. And then they're detected in 1971. Then we think they're not very important. And then we discover there's one in the center of every galaxy.

Then we think, well, maybe they're in the center of every galaxy, but maybe they don't have any role to play. But then as my book finishes, we discover that actually they are incredibly important. And they are probably the reason we're having this conversation at this moment. Yeah, so let's dig into that a bit deeper then. So if we fast forward a little bit from Alsace, and I think somewhat surprisingly on the surface, given that, you know, these days people say relativity and quantum mechanics just don't see eye to eye. In a way, quantum physics actually came to the rescue of the idea of black holes with this idea of collapse. Yeah, I mean,

merely very, very few people thought about this solution that Schwartzschilder found. I should tell you that unfortunately had this disease called Penficus vulgaris, but when it was an immune reaction when your immune system attached your skin, and unfortunately died in May 1916. Even today, there's no cure for this disease, but we can use steroids or whatever. So very few people really thought about this, but those that did thought, well, maybe something will come to the rescue, you know, some other force that will stop a star collapsing downwards,

because the problem is that the collapse will go on forever, until everything, all physical continents skyrocket to infinity, we get what's called a singularity, which is telling you basically that the physics has broken down. So that's why people didn't like it. And then, of course, in the 1920s, we get quantum theory, which is the theory of the microscopic world of atoms, and a thing called a Pali exclusion principle, which is basically the reason that everything is solid. You know, the reason that electrons don't all collapse into each other and matter has an extension is because of this. And you can't put two electrons close together. There's this kind of repulsion.

It's called the Pallet Exclusion principle. So I thought that this, eventually, if you crush the material of a star into a small volume, eventually this would oppose gravity. But then a 19-year-old Indian en route on a ship from Bombay to Cambridge in England, sitting on the deck, he becomes about the first person to apply quantum theory to stars, and he realised that everyone has forgotten one thing. And the one thing is that it isn't just quantum theory that applies to stars. It's quantum theory and relativity.

So Einstein's theory of relativity of 1905 effectively tells us that nothing can travel fast and a speed of light. So as you compress something, you know, it gets hotter and everything flies around faster. If it's that flying around is kind of like, you know, you can imagine electrons in atoms, like kind of drumming, like the rain drumming on a roof, you know. So they apply, that drumming applies the outward pressure. but they can't drum fast and speed of light. That's the limit. And so he realizes that actually if the star is massive enough,

this problem means that the outward pressure cannot oppose gravity. And we get this thing, the man was called Supramanian Chandrasekha, and we get the Chandrasekhar limit, which we now know is about 1.5 times the mass of the sun. If anything's more than one and a half times the mass of the sun, even this quantum outward pressure cannot save a star from cloud. collapsing to form a black hole. So yet again, this idea was opposed by some of the big hitters in physics, wasn't it? Well, probably the biggest hitter of all, who was Arthur Eddington. I mean,

Arthur Eddington was a great British astronomer. His genius was to realize that you could understand the interior of the sun and the stars without knowing anything at all about what was powering them. You know, you just apply some basic logic and realize that, every bit of the sun is in balance. So the gravity pulling on any chunk of the sun is completely balanced by the outward pressure of the heat. And he was able to visualize the interior of a star, seeing side a star, not even knowing what powered the sun. So we didn't realize what that was until probably about late 1920s. And he was the real big hitter at Cambridge. And he opposed Chandra Saker's ideas. And we don't actually know why, because he really tried to humiliate

Chandlesa. Chalda's Saker. Chaldaqa presented his results at a Royal Astronomical Society meeting, Royal Society meeting in the 1920, about 1930. And Edicton stood up to afterwards and basically said, this is total rubbish in front of everyone. And of course, everyone believed Eddington. But Ellington was a strange character. He actually came up with a number, which I put in my book,

for how many electrons there are in the universe. I can tell you it's probably got about 75 digits. But he had some really strange. ideas. But of course, he was so powerful a figure that Chandrasekhar realized that he needed to move to another area of astronomy. And of course, what we know is that Eddington died in the Second World War. And it wasn't until 1983 that Chandlesaker got the Nobel Prize. So eventually, he was proved right. So that ended well, I guess, eventually. It did, but I don't think Chandlesa Laker ever got over it, you know. I mean, he really

respected Eddington and he respected the British, you know. And it really stung him very hard. And only his wife knew how painful it was. But of course, you know, from the perspective of history, he won. No one goes to Hank's for his spreadsheets. They go for a darn good pizza. Lately, though, the shop's been quiet. So Hank decides to bring back the $1 slice.

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And this leads us to another really interesting character named Roy Kerr. So what can you tell us about him? Probably the most interesting character in the book. So he was a New Zealander, and he was a New Zealander, and he basically did the impossible. I told you that there are 10 equations that describe formula that describe gravity, and you need to find the curvature of the space

around any realistic body. Schwarzen, in the First World War, had found the curvature of space or gravity around a static body because we know everything in the universe is rotating, stars, galaxies, everything. So it was thought that maybe, you know, rotation creates a kind of centrifugal force

that might oppose gravity. black holes might not fall. But enter Roy Kerr. You know, he grew up in poverty in New Zealand. And in fact, when he was at the University of Christchurch, he only learned physics from Victorian books. And then he was a bit of a prodigy. And he got a place at Cambridge in England, but he was only 16. So he spent two years playing billiards, took up boxing, played bridge, basically wasted a lot of time. But eventually he did get to Cambridge and eventually he turned up in Austin in Texas. and he found this solution, which he presented at a conference, actually, the conference which was hijacked because the people who were into relativity

had realised that quasars had been discovered only months before. And if they wrote in this topic of quasars, they would get a lot of interest from astronomers. So this was the first Texas symposium on relativistic astrophysics. They even made up that term relativistic astrophysics. It was just they just put together two words to attract people. And this conference went ahead only three weeks after Kennedy was assassinated in Dallas. And at that conference, Kerr presented his result.

And everyone was puzzling over quasars thinking, well, how can they pump out 100 times the light of, or 100 times the energy of a galaxy from a volume very small, smaller than the solar system? And everyone ignored his presentation of the curvature of space around a spinning mass, spinning black hole. And that was the solution. No one realized that was the solution because quasars are powered by spinning black holes. So yeah, as you say there, yet again, the idea was dismissed in a third or fourth time now. So a pattern's emerging here, isn't it? There is definitely a pattern, you're absolutely right.

I mean, it's just really difficult to believe that these things could be real. I mean, there are nightmare objects where physics actually breaks down. They're cut off cloaked from the universe, you know. Can these things possibly exist? I mean, a style would have to get to densities to which are just mind-bogglingly huge, you know, before a black hole form. How could they possibly exist? But, of course, what we have to realize is that often our fault is not that we take our theories too seriously, but that we don't take them seriously enough.

And really, time and time again, we see a prediction, which we think, well, that's absolutely ridiculous. So, for instance, Paul Dirac in the 1930, you know, he writes down an equation that describes the electron, and he sees that mysteriously, the machinery of the equation is duplicated. It seems to be describing not only an electron, but a positively charged electron. Well, of course, this was the prediction of antimatter, you know. So we do have to take our theory seriously, and black holes are predicted by and so theory of gravity. So let's move on to the astronomy sort of strand of the story then.

So this was with the observation of sickness X-1. Yes. So this goes back to two people in the book who really have been largely forgotten. One of them completely forgotten. But basically Paul Mirdin, he was about 30 years old. He'd just come back from America where he'd done a PhD. And he was at the First Mansour, which was the Royal Observatory, the Royal Observatory, Greenwich Observatory, which was in a 15th century castle in Sussex.

And he was wanted to make a name for himself because he had two young children. He had no permanent job. And he wanted to make a name for himself. The problem in astronomy, as we all know, is how do you find an interesting object? It literally is. Like, you know, you're given a beach and you've got to find an interesting sand grain. How'd you do that, you know? And he thought x-rays. X-rays would be given out by matter of millions degrees. You know, if you saw x-rays from something, it's bound to be an interesting object. And in the early 60s, the first sounding rockets were sent above the atmosphere. They would go up and come back down again. in a brief time there above the atmosphere,

they discovered these X-ray sources. The telescopes were so crude that they could only say the constellation in which they existed. So there was one of them called Signus X-1. And when Mirdin came back from America to Huss-Mansu, the first X-Rae satellite had been launched,

and he realized that the box of the possible position of Cygnus X-1 had shrunk. And there was only one interesting object in the box. A blue super-giant star, really massive, really luminous star. Now, that could not be the source of the x-rays. It wasn't hot enough.

But maybe it had a companion. So it turns out he shared an office with an Australian called Louise Webb, so she was also about 30. She was working with the director of the observatory on measuring the speeds of stars. So he said, can you measure the speed of this star in the hope that he would discover that it was varying its speed as it orbited an invisible object? And they actually did discover that this massive supergiant, was orbiting an invisible object every 5.6 days. And the only thing was that they used Newton's

law of gravity to deduce its mass. It had to be more than four, maybe six times the mass of the sun. And the only possible object that would be invisible would be a black hole. And this is how this book begins really, because my dad took me to a talk. I was a member of the Junior Astronomical Society, took me to a talk when I was 12 in Alliance Hall in Victoria in London, and a man on crutches hobbled towards the lectern, that was Paul Murdin, I didn't realise he had polio when he was a child, and he proceeded to talk about Cygnus X1, and it blew my 12-year-old mind. So actually, it was a real joy to be able to interview my book. But I ought to say, Louise Webster has been completely erased from the history of science.

Just what I should mention that, the co-discoverer of black holes. So since then there's been more sort of evidence for black holes. But let's, I reckon, fast forward a good amount of time to the LIGO experiment and the detection of gravitational waves. I think this is something that's really interesting. Well, it is because, I mean, really, there's a lot of hype often surrounding scientific discoveries, but this really was the most important development in the history of astronomy since Galileo turned his telescope, you know, on the heavens in 1610, really, because, you know, it was a new sense.

I mean, we can see the universe with our eyes, with our telescopes, we can even see invisible light with our telescopes, x-rays, radio waves. But gravitational waves are vibrations, you know, ripples of the very fabric of space. You know, they are literally sound. So, you know, we've added sight, we've added hearing to, our site. We know gravitational waves are the voice of space. So to actually detect them in 2015 from the two black holes that spiraled together and merged, that was quite incredible, especially as the search had taken about 40 years. So a lot of people staked a lot on making

this discovery. And the first merger, it always boggles my brain, that it was, I think, about 20 times brighter than the entire universe, something like that. So the gravity waves, for a brief instant, the power was greater than all the stars in the universe combined. So in other words, had this object given out light rather than gravitational waves, it would have shone brighter than the entire universe. So that's absolutely, yeah, as you say, mind-blowing. Mind is just bit mind-blowing, isn't it? But one of the interesting things you brought up this topic is that we've now seen about

100 of these events, and we discovered that a lot of them are much, much bigger. than anything we could have guessed. In particular, some of the mass, which we didn't even believe could happen, because there is a mass gap. There's a reason why stars of a certain mass would explode without leaving a black hole, and that should leave a mass gap probably something from about 80 to about 140 times the mass of the sun. And yet we see black holes in this range. And that's probably telling us that they didn't form from supernova explosions,

but they formed from previous merger. So we're seeing two black holes merge, but maybe one or both of them were actually a result of an even earlier merger. So this process is more common than we actually expected. So another sort of big key event in this story is when we were able to put together the first image of a black hole. Yeah, we talked about Paul Murdin and Louise Webster

discovering the first stellar mass black hole, but actually, incredibly, the first black hole had been discovered but eight years earlier and no one had actually realized. And that was really the discovery of quasars. You know, these are active galaxies, so most of their energy is coming not from starlight, but from what we now know, the superheated matter as it swirls into a very large black hole,

a black hole weighing maybe billions or even tens of billions and times the mass of the sun. And there's one of those in the center of every galaxy. We don't really know why, and we don't even know why, whether the supermassive black holes came first and were the seeds around which galaxies of stars formed, or wherever galaxies of stars formed first,

and then the supermassive black holes are formed. These are a huge, huge mystery. So you're talking about the Event Horizon telescope, and this was an array of eight radio dishes all around the planet, even in Antarctica. And they all looked at the same objects at the same time and basically synthesized what we would see from an earth-sized dish. There were only two black holes,

that we could possibly detect with this array. One would be the nearest one to us, which is 26,000 light years away in the center of the galaxy. That's called Sagittarius A-Star. We have a tidler, 4.2 million times the mass of sun. But it turns out there's a nearby galaxy called M-87 and has an absolutely gigantic black hole, about 1,000 times, 1,500 times bigger, 5 billion times the mass of sun.

And it was that that was originally imaged. And this image, which basically is a black, void, surrounded by a kind of orange glowing, superheated material swirling in, I think is one of the great images in the history of science, you know, to stand next to the image of the earth rising above the moon, you know, taken by Apollo 8, one of the great images. And inside the black hole, we don't have a theory to describe the very interior. We need what was called a quantum theory of gravity.

We don't know that, but we're pretty certain that space and time actually come apart and break apart. So, you know, sometimes I think we bash ourselves over the head, and that's our human beings have created global warming and pollution and all kinds of things. But we were an ape that came down from the trees onto an African plane a few million years ago. We've got a three-pound brain made of jelly and water, but we have seen to the very edge of space and time. And I think we should pat ourselves on the back sometimes because that's an incredible achievement.

Yeah, absolutely. Totally agree with you. So we've gone through a really fascinating story. there. And, you know, people say, oh, that's all well and good. You know, how fascinating black holes they're interesting in and of themselves. But there's more to the story than that, isn't that? They can actually teach us things about physics and the nature of the universe itself. Yeah, the reason why I can explain why my book is called The Cracking Everything, really. And that is that three of the main theories of physics collide in black holes. That is Einstein Theory of Gravity, which describes big things like stars and galaxies in the universe,

quantum theory which describes very small things like atoms and thermodynamics which actually describes heat. And one of the interesting thing is that when you apply all these things to a black hole, they predict different outcomes. And that is gold dust for physics because what you want is two theories or three successful theories to predict something different from each other. Then you know that one or more of them is incorrect. So it turns out that black holes are where there is a cracking out. understanding of physics and really if we can understand black holes we can maybe move physics on. You know we're pretty certain that we have this theory called quantum theory which describes three of the four fundamental forces that glue us together and it's phenomenally successful.

I mean it predicts the outcome of experiments to you know ridiculous numbers of decimal places and then we have a theory of gravity which is also fantastically accurate. So we have a theory of the small and a theory of the very big. But when black holes, they overlap. So a star shrinks down smaller than an atom to make a singularity. So we need to combine those theories to understand it. So we need what we call a quantum theory of gravity. So we may get hints as we try and wrestle with our understanding of black holes of what this deeper theory is in physics. But the other thing, of course, is the black holes really are about why we're here. So if we look in the very largest galaxies, they have really

our supermassive black holes, one of the characteristics is outflows, generally like jets of material, which extends stab outwards from the poles of a spinning black hole across millions of light years of space. These have the potential to push away the gas in a galaxy, the gas, which is the raw material for star formation. So in these really big galaxies, the gas was blown away very early on in their history, and they only got one generation of stars. Now remember, it's in successive generations of stars that heavy elements that you're made of, calcium and oxygen and carbon are made. So in these galaxies, the big galaxies, they're sterile, they're like wastelands,

they're like deserts. Okay, so then we come to our galaxy, which, for some ridiculous reason, we've got no idea why, has got a very, very tiny supermassive black hole, hugely smaller than the one in Andromeda, which is a galaxy almost identical to ours, you know, the nearest big galaxy. So that has not been able to push away the gas. So there have been multiple generations of stars that have produced heavy elements that are necessary for life,

for planets, and for technology. So really, we're having this conversation because our supermassive black hole is a titular. Thank you for listening to this episode of Instant Genius, brought to you from the team behind BBC Science Focus. That was science writer Marcus Chown. To read more about the topics we've just discussed, check out his latest book, A Crack in Everything,

How Black Holes Came in from the Cold and Took Cosmic Center Stage. If you liked what you just heard, please do leave us a rating in a review and consider subscribing to Instant Genius on your preferred podcast platform. The current issue of BBC Science Focus magazine is out now. Pick up a copy wherever you buy your favourite magazines or download us on your online.

app store of choice. You can also find us online at sciencefocus.com. This podcast is sponsored by Name, Audio and Focal. The texture and emotional depth of music can be lost through digital sources or poor signal. Name Audio believes you can have digital precision with analog warmth. Alongside French acoustic specialist focal, Name creates high-end audio systems, combining innovation with craftsmanship, so you can listen to music. as the artist intended. Discover more at name audio.com. Ambition comes in all shapes and sizes.

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