Darkness Visible: Shedding New Light on Black Holes

So thank you for being here this afternoon in this conversation about

black

holes

and you know you'll find online that Einstein himself is often quoted as saying that

black

holes

are what happens when God divides by zero. He never said he couldn't have done it. The phrase black holes was coined about 10 years after Einstein died, but poetically it's actually a pretty good way to describe what's going to be the focus here tonight because dividing by zero is a pretty extreme mathematical operation, right? and black holes are a very extreme physical object in the universe and what we would like to do here tonight is, of course, start to bring everyone up to speed and then take us right to the frontier of understanding these truly gigantic monsters of the universe. universe, now to get there.

There are many ways you can think about black holes, but a good way to approach the topic is to think about something that is much more familiar: thinking about escape velocity. Let me describe what I mean through a couple of sequences here, so imagine that you are on the surface of the earth, so we are going to approach our planet directly and ask if we fire a projectile from the surface of the earth towards above, what will happen and we all know pretty well what will happen, so if we take a cannon and we shoot a cannonball at a fairly modest speed, it will go up, it will go down again, if we shoot it with a s

light

ly higher speed, it will go up more, but still So it will go down again, but finally, if we launch it. with the right speed it will go up and barely escape the gravitational pull of the earth and go into space and the speed required for that to happen is what we call escape velocity on the surface of the earth, now what is escape velocity on the surface of the earth, yes, if someone actually said it was 11.2 km/s, thank you.

Wow, a gold star in the back, about 11 kilometers per second is what you needed to get to the surface of the earth, but here's the question if you were to look at a different planet, one that's bigger than the earth. , which will happen well again, you can imagine what will happen if it is bigger, it is more massive, you will need a bigger cannon to shoot that cannonball with greater velocity because the exhaust velocity will increase, it will be greater than on the surface of the earth, but of course if you have that big cannon, you actually fire it, the cannonball will increase and again, if its speed is greater than the escape velocity, it will be able to escape but now I want you to think about something a little less familiar imagine that this cannon does not shoot cannonballs but rather shoots balls of photons of

light

now the light goes very fast right, I mean the speed of light, what is the light from above?

For example, yes, everyone uses different units, which is good: 671 million miles per hour, 300 million comments per second, right, and meters per second, I should say, at that high speed, of course, the light will easily escape and go out into space, but here is the interesting thought experiment and this is a thought experiment that goes back a long time this is an experiment that this guy here John Michell this is in the year 1700 a long time ago he did The next question said look, what if you imagined yourself looking? In a star like the Sun, let's say, now clearly the escape velocity at the surface of the Sun is much less than the speed of light, so certainly all the light that the Sun emits escapes easily, but just as the speed escape velocity from a planet increases if you make it bigger, more massive, he asked, well, the same should happen with a star, so let's imagine making the star bigger where the escape velocity increases now, if it is still less than the escape velocity from the light, the light will escape, but he asked what would happen. if you made the star so big that the escape velocity on its surface would be greater than the speed of light, in that case imagined that if you made that gigantically massive star, the light could not escape, the escape velocity would be greater than the velocity . of light and if the light does not move away, the star would become dark, a dark star.

Now, this is again the year 1700, so you're thinking purely in a Newtonian framework, that's the only description of gravity we had back then, so the natural question. Is this reflection by John Mitchell? This theologian? We know that in the early years of the 20th century, Einstein reframed our understanding of gravity and gave us the general theory of relativity in which gravity is now thought of in a completely new way, not according to the Newtonian description, gravity is considered as deformations and curves in the fabric of space and time, then Einstein takes this idea, this new way of thinking about gravity, he writes his famous article on the general theory of relativity, this is in 1915, his article circulates widely and in fact, about a year later, 1916, on the Russian front there is a German astronomer mathematician named Karl Schwarzschild and he is in the trenches in charge of calculating artillery trajectories and somehow, by pure coincidence, what happens is that Einstein's paper just passes by, he grabs it, and he becomes so enthralled by Einstein's ideas that he forgets. artillery trajectories and start calculating with general relativity, discover that if you have a spherical body that you crush until it is reduced to a very small size according to Einstein's mathematics, the deformation in the structure of space would be so extreme that nothing could move it away, not even the light. can be zoomed out, so now it's a modern version, if you will, of what John Michell had imagined: an object that turns black because light can't move away from it, roughly speaking, it would be like if you had a flashlight near the edge of one of these. objects and when you turn on the light instead of the light going out into space as if it was dragged into the hole towards the black hole, this is the modern version of what a black hole would be, now the term black hole turned out like this it was coined at 112 Street and Broadway I'm not kidding at the Goddard Institute for Spatial Studies at 112 Broadway John Wheeler had a talk and this way of describing these dark stars came up and Wheeler pushed this idea and popularized it and advanced it. our understanding of it, but this is where the term black hole comes from.

This, of course, is a sort of cartoon version that gets to the basic idea for those who want to look at it a little more precisely. This is actually what happens nearby. of a black hole and if you don't understand this, it doesn't matter, we can put a space-time diagram if you remember from high school, this is where we have time on this vertical axis and you activate a ray of light that fills a cone. called a light cone and what happens is that the geometry of space and time is so distorted by a black hole that beyond what is called the event horizon, the direction of time and space is so twisted that as the light spreads cannot leave it. the edge cannot go beyond the event horizon of the black hole and that is why no light can come out, that is why the black hole is black now, the natural question is fine, these are interesting ideas, but how could one arise of these objects? and people started thinking about this idea for a long time 30, 40 and 50 and let me give you a possible scenario in which the type of object that we are looking at, a black hole, would form, and for that we can imagine that we have a big star like a red giant to support its incredible weight, this star has nuclear processes in the core that generate heat and light and pressure that sustains the star, but sooner or later the star uses up all its nuclear fuel and at that point it cannot support its own weight, so it begins to implode and, as it implodes, it becomes hotter and denser, eventually causing an explosion that propagates through the star and when the explosion reaches the surface of the star it causes the layers What is left if the star was big enough to begin with is a tiny core, a dense core that can no longer support its own weight at all and will collapse into one of these objects, these black holes, that It's the idea of ​​how these objects work. could form and what we would like to do here tonight is explore our current thinking about these objects, whether they are real, how we would actually view them and whether we can get some insight into what is going on inside these spectacular objects and to do that we are going to to name a few experts who spent their careers examining these very questions and let's get to them right now, so our first guest is one of the world's leading experts in observational astrophysics who leads the UCLA galactic center group, best known for her groundbreaking insights into the center of our galaxy, she is the winner, among other things, of the Crawford Prize for Astronomy of the Royal Swedish Academy of Sciences Anna MacArthur Fellow, please welcome Andre agos.

Very good, we are also joined by an astronomer from the Harvard-Smithsonian Center for Astrophysics who leads an international collaboration project. It's called the event horizon telescope, which aims to image the edge of a black hole's event horizon, so please welcome Shep Dollar Mark. Thank you both for joining us here tonight. Let me start with kind of a general question so people have been thinking about this idea of ​​black holes for a long time, as I said back in the 18th century, and there's been a lot of research done, thousands of pages of calculations, do you think that Are there really black holes out there or is our theoretical imagination overloaded?

I think it's pretty clear that there are black holes out there of course I'm a little biased since you spent your life trying to observe them yeah that's it think about the fact that there are two types of black holes yeah holes black that you were. we just talked about the ones that come from the lifetime of stars and then the supermassive black holes that we think are at the center of the galaxy and those are the ones that you've actually been studying in some detail so we can get to that in just a moment, but Shep, is your overall view pretty much the same or do you think there's a chance it's a red herring that these black things aren't really out there oh no, it's beyond a doubt, I really believe it .

There are, I mean, there are all these lines of evidence, you know, we see these scary engines, the centers of galaxies that spew these jets on either side of them and the only thing that can power them are supermassive black holes, so everything points to the fact. that actually exist, so I'm glad you said that because if you both had said no, I don't know what we're going to do with the rest of our time here today, but that's great, so Andreea, your job as I understand it. has been centered at the center of the Milky Way, so, first of all, give us an idea of ​​what you think resides at the center of our galaxy and then we will try to look at the evidence that led you to come to that conclusion, then we are quite convinced that there is a supermassive black hole at the center of our galaxy and, what do you say Superman?

When we say supermassive we mean a million; Well, in the case of our own galaxy, four million times the mass of the Sun. And in terms of these really big ones that are in the center of galaxies, that's on the low end because we think of things that are between a million and a billion times the mass of the Sun and for a block of a million solar mass as for the Sun, maybe let's start simply, if the Sun became a black hole, what would its radius be? It would be about the size of a university campus.

No, it depends on which university you are talking about. Well, then, a couple of kilometers wide for one. at the center of the galaxy, how big do we think it is? It is about ten times the size of a sudden, approximately ten thousand 10 million kilometers. Wow, so it's a big object, but it still follows the same basic pattern of it having an edge. and the event horizon and all the standard lore would apply to it, it's on a larger scale, right, it just scales with math, yeah, so, so what evidence do you have that it's a black hole?

Can you walk us through that? Yes so, to prove that there is a black hole directly, what you want to do is show that there is a lot of mass within a small volume or within a particular small region, you would like to show that it is confined within its short shield radius. that you just talked about is the radius for a given mass, where if you can squash the mass within that radius, it will naturally become a black hole, so that's the size we have. We're talking because of course the black hole itself is infinitely small so this is not the abstract size and our work just clarifies that so when you say you're talking about when the black hole forms the matter gets squashed together. down to a small size, yes, then the idea of ​​the Schwarzschild radius is that no light can escape from it like we were talking about, but it is alsoIt is true that once you reach that scale, gravity will overcome all other known forces and there is nothing that can stop the object from collapsing, from a scientific point of view, once you have shown that a mass is within its radius by Schwarzschild, you will have arrived at proof of a black hole, from the point of view of someone who is searching for black holes. holes their job is to show that there is a certain amount of mass within a small volume, so the way we have gotten closer to the center of the galaxy is to look for the stars that are at the heart of the galaxy and develop techniques that allow us not It only allows us to see the stars that are so close but it allows us to observe how they rotate around the center, so if you want to find the center of the galaxy you can look up in the night sky and find the constellation of Sagittarius, it is the teapot and the teapot pours into the center of the galaxy, okay, that's your way, it's very convenient and if you look at the night sky, not in New York of course, but in a place where you can actually see the night sky, you can see the Milky Way and the Milky Way is that band of white light that comes from the stars, but it's also missing light because of all the dust, so you can't actually see the center of the galaxy at wavelengths in your eye detects so a key to the work that we have done is to use infrared technology to look at light which is just a long word of what your eye detects, maybe we are the remote control of a working television, yes, and that tells us It allows you to see the stars that are in the center of the galaxy and we have found them and we have discovered that they go or one that we can see them, which is quite surprising and that they revolve around the center of the galaxy. pretty fast so my favorite star in the galaxy is called like this2 it spins around every time like this2 okay it probably needs a better name yeah it's very catchy so if you have a better name we'll let the audience figure it out but You can actually use Newton's laws of physics to show that if you rotate every 16 years and measure the size of the orbit, which is about the size of our solar system, that shows that there is about 4 million times the mass of the Sun within it. incredibly small region and to give you an idea of ​​the change in our knowledge about our understanding of what resides at the center of the galaxy, we have increased the density of dark matter by a factor of ten million compared to what was known before the works of art.

So in a sense, we have advanced the case for the existence of supermassive black holes by that amount. You can think of anything in your life that you would like more and be able to get ten million times more than right and that's it. what happened in the center right, then the basic argument, as I understand it, is that you are tracking these stars and their motion can only be explained if there is a black hole of that mass residing in the center of the galaxy. You're basically weighing this out. what's in the center was this real data, this is real, so we've seen two versions, one is the flat version that was shown, it was playing a moment ago and it showed my favorite star and this is actually a bigger view from the data that we've taken that we've taken in the last and I can't believe I'm saying this, you've been involved in this for twenty-five years?

Maybe I shouldn't ask, oh yeah, this is my state. From the beginning, this is, I mean, this is my baby, so it's actually interesting to reflect on because when I first proposed this experiment, when I got my job at UCLA, I thought I had a good idea, it was actually refused. They said the technique wouldn't work and even if it did we wouldn't see stars and even if we did see stars we wouldn't see them move, so it was a lot of no, no, no, and in fact we were asking to do a project that lasted only three years. just to see that the stars were moving fast no one anticipated that they were moving they would move so fast how fast is fast just to give it oh oh like three million miles an hour so they're, they're hauling and it's pretty remarkable that we can measure something in a human time scale and as this project progresses and maybe we can talk a little bit later about what is needed, technology has changed so much that it has allowed us to do more and more sophisticated types of work, so this three-dimensional animation actually shows the types of stars we see at the center of the galaxy and almost all predictions about what we should see near the black hole are inconsistent with observations that do that.

I mean, that means it's job security, you're trying to figure it out, yes, but it's still not inconsistent with, say, general relativistic prediction, no, so there's the physics side of this job that you're trying to figure out. ask physics questions like supermassive black. holes exist, how does gravity work near a supermassive black hole? So where we are today is that we can say definitively, or at least in my opinion, we can say definitively that the supermassive black hole exists and then where we are actually, we are in the middle of this we can test the theory of general relativity of Einstein and that's what you're doing now if I understand that we're actually in a special moment right now, yeah, we're in such a special moment.

Can't. I think I'm actually sitting here instead of in Hawaii. Thanks for taking the time, but tell us what's going on. The reason I'm so excited and we've been preparing for this for years. I've been waiting, there's no chance you'll miss this special moment, but I have graduate students, so we've been using the Keck telescopes shown here for 25 years and observing the star that rotates every 16 years and, if you want. To test Einstein's theory of general relativity near the supermassive black hole with these stars, what you have to do first is do your first spin, which gives you a baseline of what part of space these stars are probing and that It's 16 years, right there it's 16 years. right there, my various moments in my life around the star and then what you want to do is catch it the next time it passes closest approach and that next time was in the year 2018, so I've been thinking 2018 or bust for several years, so we're in this, we're in this season and for us there really is a season because the Earth revolves around the Sun and because we're looking at infrared light, you'll hear from Shep, there are different types of light, so to Shep It doesn't matter to you because the Earth revolves around the Sun.

There is only part of the year when we can see the center of the galaxy in infrared wavelengths, so for me we can see it from about March to about October. There was the beginning of the season and during these six months or so this star is experiencing incredible accelerations and is experiencing the most extreme forms of gravity as it gets closer, so there are actually three key moments, one that occurred on the 10th April and another that happened approximately. last week and one that will take place in September that they are going to finalize this experiment, so it is an exciting time for us and seeing the signal emerge from the data is just a pleasure, so if I understand correctly, I have a prediction based on general theory of relativity what should be the trajectory well here we have to be a little careful because there are a series of types of experiments that separate me there are a series of gravity tests, one is how the light is generated from the star the star for us, in other words, how it escapes the curvature of space-time, that's actually the first thing we'll see this summer;

The next thing is how the object itself moves through spacetime, which should actually emerge over the next few years, again, and if you continue, and of course that's what we want to do, you'll be able to measure the spin. of the black hole, so this experiment will continue to get better, and it's particularly interesting, I think, because you know what most people think. that Einstein's general relativity has been confirmed, but the correct way to think about it is, you know, that gravity is one of the four fundamental forces, but interestingly it's the least proven of those forces, so it's been proven in some regimes, but it has never been tested near a supermassive black hole and as some say, it is a supermassive black hole or black holes and the general ones represent the breakdown of this theory, so what you want to do is get as close to the point as possible Hat. where you really know that the theory no longer holds up and I think today we have to have all kinds of evidence that says that this theory is fraying around the edges, so we just push that frontier forward greatly in a direction that we never had before.

It was done. It hasn't been explored before, so in principle we could find the first concrete evidence that we need to go beyond Einstein's ideas to really describe what is happening. I am referring to the best of all worlds, which would be the result of more than 16 years of observation. Well, the result. It's really just finding out what's really going on, you're the black hole, whatever that is, yeah, yeah, yeah, it's spectacular, so Shep, you were in the business of looking at black holes too, there's no business like that. black hole business, there is no business like back there, so you.

We are going a different way, so we are hearing about infrared light, like the probe that is used in Andreas' work, you are using what radio, yes, we are using radio waves. It turns out that black holes are a paradox of their own. Gravity are some of the brightest things in the sky and that's because of a very simple construction: all the matter, all the gas and dust are trying to get into a very small region, so it heats up to hundreds of billions of degrees around Sagittarius, a star. the supermassive black hole at the center of our galaxy and it radiates in infrared which Andrea looks at and also radio waves, even a little bit in X-rays, so if you want to look at a black hole you can see it from many different angles.

No, no, the critical thing for both is that what you're saying is that you're not actually looking at the black hole, you're looking at its effect on its environment, so you can't actually see per se exactly what's happening in the hole. black. stays in the black hole, yeah, let's put that aside right now, but what we do is we make fun of the edges, so in that cannonball analogy that you had before the light came out of the black hole, but it also orbits around of the black hole. Think about that for a minute, light orbits something correctly and goes in a circle and Einstein 100 years ago when he came up with this relative general theory, those equations show that we should see the silhouette of light around the black hole and that's because This light orbits around so we look at it and we see light moving around the black hole and it gets brighter on one side, on the other side you see something that should be about five times the source or radii wide, do you know how big?

It should be like this, the event horizon is here, you're looking at exactly five times that distance, so you never see the inside of the black hole, but the outside, and that shows us the geometry of spacetime when you see something like this . This shadow feature you're really looking at the deepest drilling into space-time that we can imagine, and the ground is real. Is this what I mean? Can you share with us what you have seen? This is the event horizon. telescope I guess you're talking right, so the question is if you wanted to zoom in in orders of many thousands and see what's happening right at the edge of a black hole, you'd have to go much further than where Aundrea sees it. stars and they get much closer and those stars are about a thousand times farther away than this silhouette that you're seeing here and if we could measure the size of the silhouette on the shape, we would test Einstein's theory of gravity right at the edge of the hole. black right now, how's it going?

I guess there are a handful of radio telescopes, yes, to see something so small, these are the smallest objects in the known universe. Black holes are small and to see them you need magnifying power and as is with all telescopes, the larger the telescope, the more magnifying power you have. Now we can't make a huge telescope that sees radio waves. What we do is install atomic clocks, have multiple satellite dishes around the world. We record data and then we play. We bring it back to a central facility and we ourselves create a virtual telescope as big as the Earth, if it's as big as the Earth itself, these are some of the people who work in these different places, how many teams are there?

Well, we have eight. geographic locations right now we're going to get to nine and then ten next year and when you put all these telescopes together you end up getting a virtual dish that's the size of the Earth and that's exactly tuned and it happens to image the supermassive. black hole in the centerour galaxy and we just took some of the first data from this event horizon telescope a year ago and we're analyzing the data now and what have you found? I can not tell you. oh come on no it turns out if you really want to take one of these images it takes a long time to calibrate the data it's all about the details a lot of people think we just turn this telescope on and you see something right away but you know we're nerds from the heart and we love going to the telescopes and finding all these details and it turns out that you really have to analyze each of these possible sources of contamination of the data. before you can be sure that you've seen this kind of shadow silhouette, yeah, you know, we were able to talk to a couple of the team members who passed us some of the data.

I hope you don't mind if if we show it here, you show the program, this is, actually, I understand, this is the most accurate image of a black hole ever seen. Have? Can we dim the lights and show that this is doable, yeah? So, yeah, okay, there, that's great, yeah, so I guess that's not good for us, thank you, no, so, then, you can look really nervous for a second, yeah, so when are you going to release it? ? I saw an article recently. A couple of days ago, which is kind of a preview, it seemed like for a data release that was coming it's so early and no, it's probably going to be in the first part of 2019, 2019, yes, because right now we're analyzing the data .You know, we know that the event horizon telescope worked, so what we did was we also looked at supermassive black holes quasars that are very far away, where there are basically point sources and everything seems to have worked perfectly technically on the telescope, so We know that all the systems are up and running and then we turn all the telescopes to look at Sagittarius, a star, the supermassive black hole at the center of our galaxy, and we think everything is working fine there, but we are still analyzing the data. data I saw an article that had come from the South Pole and you had to wait for the winter to clear up to fly, that was the guy or yes, that's happening or well, so the whole point, like Andrea said, if you want to try.

Einstein's theory, you have to go to the most extreme points in the universe, you have to go to the ultimate testing ground, which is the edge of a black hole, and we have to go to some pretty extreme places, so we have equipment that We go down to the South Pole, we go to the tops of extinct volcanoes where there are satellite dishes that do the work we want to do, we go to the high desert plains of Hawaii Mauna Kea and Chile and you go up to these places and it's really a bit of work. love because all these teams go there, they work their hearts out, they capture data in this technique that we use, this event horizon telescope technique is really the ultimate, delayed gratification, okay, go see, this is what you should do.

When Andre goes to our telescope, it's pretty simple conceptually, the light bounces off a paraboloid, it goes to the focus, that's right, you get what you want right there. What happens with us is that the light hits one of our dishes, it is stored on high-speed instrumentation that we have built over the last decade on hard drives, the same type of hard drive that you would put in your computer, and they stay there until that they bring them back on a plane because nothing beats the bandwidth of a 747 full of angst nothing ok even when I walk down the aisle with two of these disks you know I'm beating the fastest internet in the world ok and we put them together again and The operation on this supercomputer that we use is equivalent to bouncing light off a perfectly shaped parabola coming together in coherence, so we play it back together and adjust it back and forth until we get it right and that effectively turns the Earth in a parabola if you think about it, so all this data has to come back and if it's at the South Pole, it's very frozen, so we have to wait six months just to get that data back, so that's one of the delays that we have faced, not only now.

I've run some simulations of what I anticipate will emerge from data looking at the magnetic field and vicinity of a black hole. Can you walk us through some of the things you anticipate will come out of the study? I think we've got some things going on, Serena, so what you're seeing here is the best guess we have from your high-speed simulations of what you'd see if you had infinite illusion glasses, so you end up seeing this shadow, the circular feature with some jets coming out of the north and south poles and that is because there are magnetic fields right around the edge of the black hole, there are relativistic particles that are orbiting these magnetic fields and they are releasing something called synchrotron emission, which is a kind of characteristic radio emission that you get from these types of sources and it's so bright in that synchrotron emission that it shines from the deepest part of the gravity well, so think about it, everything has to go well, it's a situation of Goldilocks, you have to be able to see through the Earth's atmosphere and radio waves can do that. that you have to be able to see across the distance between the Earth and the galactic center, radio waves can summarize that just to give people an idea, so it's about 25,000 light years away, so you know this one black hole.

It is not a threat to us, we observe it, it is good that these radio waves can reach the black hole, but we are not done yet because it has to go through the hot gas that rotates around the black hole. and then it has to go down into the gravity well, so it's a Goldilocks situation because we met all of those criteria with the radio waves and it turns out that the Earth is just the right size so that when you look at the radio waves with a wavelength of one millimeter are perfectly tuned to take the photograph of Sagittarius, a star, that's all, with a dish the size of the Earth, it was just a resolution, yes, sometimes nature throws us all these curveballs, You know what we can't do.

This or this is difficult. This is a case where everything is falling into place, so we really think we have a good chance of taking the first image of a black hole and is there any chance of also finding a deviation from the overall image? Theory of relativity. Can this be seen as another extreme testing ground? What we are looking for is never a good idea to bet against Einstein. Okay, it's not a career goal to do it, you know, but it's a confidence, but check. The situation is fine, I mean he was a very smart guy, let's put it that way, but every theory has to be tested well when you say he is a very smart guy.

That's true, but he wasn't a big fan of this idea of ​​black holes. Okay, I mean he didn't think they were very good at it, he was a little off on it, right, okay, so he had a bad time, but this really speaks to this kind of golden age that Dondre was. talking to the event horizon telescope where Keck is making the observations, we're really in this black hole discovery space and we might be at the point where we can start to answer these questions like, do black holes exist? Was Einstein right at the moment? very black hole limit, I mean, you know, you showed a little boy in the trenches in World War I, yeah, you know, and he died later that year, actually, so this was his last big discovery and wrote the Schwarzschild metric and gave what is the decay e the space outside the black the shape of the space outside the black hole and now we are participating in this handshake over 100 years in which we are completing this circuit and we say that you know you made these intense predictions and we "We're just at the point where we could test them correctly and that's extraordinary and it speaks to the fact that science is not linear, we don't go from point A to point B, we don't say." You're going to go out and try this, it's very erratic and that's why Einstein felt that black holes might not exist.

It took them a hundred years to become part of our lexicon. TRUE? You are now part of the reality of our daily conversation. Do either of you or both of you as you work on your observation projects have favorite ideas or theories about what the next phase could be beyond Einstein or do you basically move towards the data, the observations and that's the only thing that really motivates you or Do you have an idea what the next phase of this understanding of gravity might be? Well, let me take this for a second. I'm real, I'm a realist, I'm kind of a craftsman at heart I like to go to mountain tops and make observations I like to see what's around the black hole right I can understand and wrap my brain around the light coming out of the event horizon what's inside the event horizon you know that's a question that's even hard to ask, you know, little Otis asked it.

I didn't order to answer it. I did it. It's easy to wonder, you know, but, for example, one thing we're looking at with the event horizon telescope is look if that silhouette isn't round, ah, what if it's distorted? Well, and if it's distorted, then we have some framework for understanding how general relativity itself could be violated to give us those strange shapes, so we bet on Einstein, we bet he'll go away. be circular, but if it's not, we have some ways to understand what might make it non-circular, yes, so we're coming to the end of our section, but Andre, I want to ask you a question: how do you proceed in an era? when you might be going beyond the badge when you know you're right when when you know things have merged to the point that you're willing to make a statement like that interesting an important question that we really are the Because if you see things that they don't make sense, you don't have a context, you're kind of air and you're exposed and you have to convince yourself that what you're seeing is physics as opposed to experimental error, right, err, err, so I think there's a philosophical point Interesting here on how to convince yourself you have the right answer.

Yeah, I mean, there was an interesting case with bicep2, oh yeah, a few years ago, where some people did it. They said they knew so much what they were looking for that they were biased in evaluating what the father was telling them, it's a classic thing called confirmation bias, and this type of work where we have so much respect for Einstein and his ideas that we go with the premise that it must be correct, so it's interesting in terms of how you actually design your team's work to avoid getting a result that you think is true and allow your team to really trust what the data is telling you, so I think And that's certainly my goal as a scientist: to get to that point where you're really just listening or paying attention to information that may be unexpected, but trying to eliminate your desire to have a particular answer, whether that's Einstein or not.

Einstein is wrong, yes, just to be open to whatever the answer is actually right, yes, well I should say you know we all revere Einstein, but at the same time, how exciting would it be if one or both of us found evidence of that we need to go further. the ideas you gave us 100 years ago, so we wish you the best and we will have you back in a year or two, maybe then you can give us an idea of ​​what you have found, so everyone please join me to thank. our great guys Jeff: oh, thank you very much in 1916, this is the year after Einstein wrote his paper on the general theory of relativity.

Einstein continued to think about the theoretical ideas and wrote a paper that we have here where he was thinking about the possibility. that if space and time can warp and curve, then it might be the case that space and time can also ripple. The image to keep in mind is to think of a trampoline. On a trampoline, you put something heavy in the middle, it has a nice curvature. but if you have kids jumping on the trampoline, the shape doesn't stay nice and static, it ripples, it vibrates, so I was wondering if it could be the case that the space itself could suffer from these kinds of undulations. of vibrations and this would be known as a gravitational wave now, interestingly, he wrote a first paper in 1916, in 1918 he corrected an error in the 1916 paper and continued to fight over whether or not he really believed that gravitational waves were a prediction of the theory general relativity and he worked on this alone, he worked on it with his collaborators Nathan Rosen being one of them and a couple of years after this article where they expressed some confidence that gravitational waves were real, Rosen writes another article where he basically says who thinks that they are just a mathematical artifact and I think many historians think that Einstein himself had that opinion that there were actually these waves in the fabric of space and yet in the 1960s when mathematical methods were had refined, If I really couldBy observing Einstein's equations and extracting from them the real physical predictions with certainty, it became clear that gravitational waves were a prediction of Einstein's theory, what it would mean and that if you had, for example, two objects like two neutron stars spinning around, they would so disturb the environment that they're sending this train of gravitational waves into and that would mean, in principle, that you could detect them because downstream, if you're after one of these gravitational waves, you're going to experience this kind of stretch, squeeze, stretch effect. and squeezing now I must say that this animation is not to scale when you actually do the calculation, you find that for a typical astrophysical phenomenon you would find that the stretching and compression would be less than one atomic diameter, so the question is how would you measure? something so good and yet, as we'll discuss now, exactly that kind of measurement has been achieved and to talk about that, let's move on to our next guest and let me make sure that I can introduce her properly and I think you can do that now, okay, like this Join us for a closer look at gravitational waves. has the leading astrophysicist in the LIGO scientific collaboration.

She is a distinguished professor of physics and astronomy at Northwestern. Please join me in welcoming Vicki Calogero, so thank you for being here, thank you. you and we would like to have an idea how gravitational waves have been detected and LIGO is the facility so how is LIGO Stanford LIGO or is the double acronym it actually stands for Laser Interferometer Gravitational Wave Observatory and the laser itself is an acronym? So it's a double acronym and what is that acronym? Laser is so engraved in my head. I don't remember the full acronym and I think it was stimulated emission of radiation, but I'm not sure that's right, so here's our detector.

Telescope Our gravitational wave telescope is a new type of telescope, it does not look like your traditional telescope, it has this station in the corner where you can see it. Can we run it again? Yes, thank you, yes, and then you have these tubes and they are like the tubes of a normal telescope, except that they are on the ground and there are two and from the corner station you must lower the lasers in a triangle and they travel through these tubes of four kilometers, vacuum tubes and they reach the end, they bounce off the mirrors and come back and we study the light, the laser light that comes together and through the interference pattern of with the laser light we can know if the mirrors at the end of those arms They are being shaken in these tight and stretched, squeezed and stretched movements, where gravitational waves are supposed to affect space and time, but space is what we can think about most easily and you can actually measure the shakes by atomic distances in fact is even smaller than that is less than one thousandth of the nucleus on the scale of four kilometers is the most precise measurement that humans have ever achieved in any field of science or engineering now, how do you know the shaking is a gravitational wave and that someone just kicked the equipment?

There are a lot of tremors everywhere and that was the reason why we didn't just build one of these detectors, but we built two detectors, one in the state of Louisiana and one in Washington very far away from each other because if the tremor is happening and it's affecting a detector and it's coincidental, I'm sorry, and it's Earth-based, so it's very difficult to reproduce the exact type of tremor of the exact type of compression and stretching and that it occurred in two different places, independent locations and very far away. , so having a coincidence as we call it at the same time with exactly the same pattern of compression and stretching was extremely important, so we needed to be able to claim Faced with an unprecedented claim that we detect gravitational waves, it was really important to have observations of exactly the same signal at the same time in two different independent places and this first happiness was the first achieved in 2015, it obtained the 40th pot in the world.

The world didn't know it on September 14, 2015, some of us did and that was a day that changed the lives of the hundreds of scientists and engineers who are members of the LIGO scientific collaboration. The world discovered it on February 11, 2016, when we made the first announcement and then what was found then what was found is that basically two black holes, one in orbit around the other, were disturbing space-time not very close. from us, not in the center of our galaxy, but actually over a billion light years away somewhere. The other galaxy and the two black holes were coming together due to the emission of gravitational waves, they were disturbing the space-time around them generating these waves that you talked about before and these waves traveled for more than a billion years at the speed of light and so on.

On September 14 they approached Earth from the south, first they hit our Louisiana detector and seven, about seven milliseconds later, they hit our Washington state detector second and that's what they expected, the time it took for us to light at traveling is bad, so there has to be a finite delay because of course gravitational waves, just like light, don't travel instantaneously, by the way, next time it takes, so the two black holes, when They were uniting in their orbit, they lost energy due to the emission of gravitational waves, in the end they merged like in this other one.

They also came from the movie and I'll explain the sound in a minute because it's not self-explanatory. Yes, actually not everyone understands it well. I did a version of this on the Stephen Colbert show and his interpretation is God Bugs Bunny, that's how I should say Stephen Colbert is a college student from the northwest look at that and we've talked about the graduation of the discovery, so the two black holes are uniting and eventually they have nowhere to go, they come and basically they are physically. touching each other, except there is no real surface, there is no hard surface, which is that imaginary surface where light cannot escape and the two black holes merge into a single bigger black hole, form a single black hole and then that The single largest black hole settles down and the disturbance stops and the gravitational wave signal stops, so it's a finite transient signal, there's all this churn in spacetime and when the full single signal forms, everything ends now we talk about the real signature like shaking these devices in Washington and Louisiana for less than an atomic diameter, yes, but what was that signal like when the black holes really collided out there, a billion? it takes 1.3 for that first detection, if you take 1.3 billion light years away it was many times larger when it was generated so I'm calculating yes so it would be about 50 times the energy output of each star in the observable.

However, the basic lesson is that this is a big burst or gravitational wave energy over a very small period of time, so the signal was 0.2 seconds and for those 2 seconds it lasted within the frequency range that LIGO. LIGO detectors are sensitive. Then you should think that you have heard about electromagnetic waves and they come in different frequencies, our optics are the optical frequency range, infrared radio waves, etc., these are all different frequencies of the same type of wave, electromagnetic waves, the waves Gravitationals have frequencies in themselves, so God can do it. I don't see all the gravitational waves that exist, I can only see frequencies between about 20 Hertz and about now, maybe hundreds of Hertz, say 700 Hertz at best, so in that frequency range this first binary collision of a black hole lasted about 0.2 seconds in that short time. amount of time that the collision and the energy generated in gravitational waves eclipsed by a factor of 50 all the light generated by all the stars in the entire

visible

universe, not

visible

to the naked eye, but in the entire universe that we know we could often detect and it just dilutes as it travels hey, that's right, so you know, you've been asked about this, it's such an amazing discovery that you and your team I mean, it's just fantastic, but how am I looking?

Can we look at the data? I don't want to ask you a question, yeah, so can you go back to the sound? By the way, that's what I'm going to come back to right now, can you show the actual data of the two black holes colliding? Do we have that up there? Great, yeah, can you upload it? Can you turn up the volume? I can't really hear it, so that's the little signature you're talking about, so you can hold it up there if you want, so here's some. things, please move on. My general question is how does that small window of data give you so much information about what the source was?

Yeah, so the reason is that this scribble that we can see on the screen and the banana that you can see on the screen that contains a lot of information, okay, and I'll take a little bit, maybe a minute or two to explain it. First, let me start by explaining the meaning of the sound. Well, I don't want anyone in this room. To have some misunderstanding, gravitational waves are not sound waves, okay, so don't tell anyone that gravitational waves are sound waves, however, we can take the frequencies. Remember I said something about 20 Hertz to a few hundred Hertz, if you know anything about music and the frequency of sounds that are really sensitive to is roughly the range of sound frequencies that our ear is sensitive to, so we can take the frequencies of gravitational waves and pretend it's a sound, it's not a sound, but pretend it's a sound and make it sound and say what the gravitational wave would sound like if it were a sound and this is what it sounds like it sounds like the screech of a bird that's not exactly what you heard but that's how it came out of my mouth but I can't see a question In that question, it's commendable to be clear on that, but also because if our eardrums could vibrate through the influence of waves gravitational, if that's what we would do, if there is a distinction, fine, if I may.

It is not a transverse wave and Excise, so sound waves are transverse waves, so the oscillation is along the direction of propagation. Gravitational waves and electromagnetic waves oscillate perpendicular to the correct direction of propagation and that is important because of how it affects our geology. If we go back to the image above, the wobble that we measure, how the mirrors move at the end of that L-shaped telescope, is basically recorded by the squiggle that we can see on the bottom of each banana, the two graphs are what We measured at the two different detectors at Hanford in Washington Livingston in Louisiana, so the signal was detected independently at the two detectors at the same time with only a slight time delay, as I said, and what you see in the signal , the real data is the squiggle, so we see that the oscillation of the mirrors increases as time progresses, the duration of the axis below that squiggle is not shown, but the duration is those two seconds, the amplitude increased as You can see and finally I'm sorry, I'm following you. my vision, but you should know it's in your direction, it's this way it went up and then it went down and it went out, that's when the two black holes came together they formed a stable black hole and then there were no more gravitational waves, so that's it One thing is that the amplitude increased, the sound you hear becomes louder before fading away.

The second thing is that the peaks of each oscillation are getting closer and closer, which means that the frequency of the oscillation is increasing and that is the pitch of the sound. and higher, that's the cool chirp, that's what we call a gravitational wave chirp. The banana you see is another exact form of the same phenomenon. The banana becomes brighter. That's the amplitude of the stretch getting stronger and stronger and the frequency again, if I may turn. I turn my back on you momentarily, the frequency increases as a function of time and that is how you get that curvature and the closer the two black holes get, the faster the frequency increases until it dies because a single black hole is formed.

Right now I'm going to end by going back to your initial question: what we measure is the amplitude of the wave, the frequency of the wave and the fact that that frequency of the gravitational wave is changing as a function of time, so we are measuring a frequency derivative, these three pieces of information are encoding the masses of the two black holes and how far away this system was, that's how by studying that progression, that squiggle as I call it, and comparing it to the templates that we have of the Einstein theory to talk. In this regard, tell us about what the templates are.

The templates are basically if we take Stein's theory of general relativity and we ask ourselves if two black holes are at a certain distance and we follow space-time and solve with general activity equations the change in the space-time as the twoblack holes are moving while the eggbeater is ruining the space-time around them we can calculate what the amplitude, frequency and frequency contamination over time of the gravitational waves that are produced are calculated with computers so that the supercomputers of fact, because this calculation, this simulation is very, very difficult to do and you need supercomputers to do it and some of these simulations can last even four months at that time, but we have the real method, actually, this is not personal . work, but Relativities has been able to do these simulations for a little over 10 years, so we can create templates of these types of signals and when we correlate them with our detector data we can find the best fitting template that then indicates We were told That particular signal came from a couple of black holes that are very far away in masses, in this particular case it was around 20 or 30 solar masses or so, of course there are always errors in every measurement we make, so which were twenty. fifth twenty twenty-six, so there have been discoveries since he gives us an idea of ​​what has been happening in the last few years, yes, since the first one that shook our world and, honestly, shook humanity, if I may say so , because we are in it.

On the day of the announcement we were media people in all the universities, we didn't do the counting ourselves, but that day we were on the covers of more than 900 newspaper covers around the world, almost as much as the trauma, okay, yes, so after that so far we have announced another five more black hole collisions that we have detected in our data and another third gravitational wave detector in Italy has joined their operations, so now there is more confirmation of more of these events, independent confirmation and now we are discovering a population of binary black holes in the universe will now also be exactly in black and that has again made those types of them the second most significant detection, which are two neutron stars, details of the star of neutrons, yeah, and we're going to I'll tell you what a neutron studies and I'll have everyone in New York look at the Chicago skyline, since the northwest is in Chicago, so this is actually to scale as opposed to your movie, so this is the Chicago skyline.

A big city you know is about ten miles wide and the shadow you see hanging over the Chicago skyline is the edge of a scaled neutron star. Now a neutron star is the dead remnant of a star that can have ten times the mass of a Sun we know. It will end up forming when it runs out of nuclear fuel, so it will form about the dead remnant will be about one and a half times the mass of the Sun and will be about as big as the center of a large city, okay, that's about the scale.

You can imagine how big the circle is. Luckily, there aren't any neutron stars hanging over Chicago right now as we speak or over New York City, but that gives you some sense, so it's our second biggest discovery. which arrived to us on August 17, 2017, so we will soon be approaching the first anniversary. It was right in the clip which of course was another memorable day for many of us, so it was just a few days before the eclipse that now used to be. that the big event of that month was going to be the eclipse and if this had not happened I would remember the date of the eclipse but right now I forgot the day, thank you because what I remember is August 17, then two neutron stars came together In a similar way, the neutral cells were put together and we got another banana.

This time we had three detectors, so you go back to Hanford Livingston and we had the Italian detector working as well and we saw the two bananas on the two detectors on the scale. You see, the signal duration is much longer, it's no longer just a fraction of a second, what you see on the screen is about 30 seconds, but in reality, in our data, this is what you see visually here, but in From our data we extracted that the signal lasted one hundred and forty seconds, that is, a couple of minutes, a really long signal that tells us that the masses that came together in this death spiral were actually much smaller, approximately one solar mass and average instead of thirty years instead of certainly that much. the lower the mass, the longer the signal, the harder this death spiral now the third detector does not show a banana partly because the third detector is not as sensitive and partly because it was in a very special place in the sky where They said the detector didn't have good visibility, let's say, and then spectacular things happened after the two neutron stars collided, unlike two black holes that come together peacefully to form a single black hole and nothing else happens after that. , two neutron stars actually give us a whole set of fireworks in electromagnetic waves, so you can actually not only see them in gravitational waves, you can see them, yes, you can see them in light, real light, and that started it all. another type of astronomy.

Multimessenger astronomy, that is, two types of waves. came from the same source, gravitational waves and electromagnetic waves, and what did people learn from the collision of neutron stars. There is a lot of talk about new ways of thinking about nuclear astrophysics. Yeah, we learned a couple of different things, so first of all in the electrical you learn things from this multi-messenger character, the source, so one thing is that the first thing we saw in the electromagnetic waves was a gamma ray signal. These are the highest frequency electromagnetic waves that we can detect and we knew that short bursts of gamma rays existed.

We had detected them for many years since the late 1960s, but we had hypothesized that perhaps neutron star mergers were responsible for them, but we had no evidence that the evidence came from gravitational waves because only in the gravitational waves we can measure masses, so The measurement that made the banana ring tells us that it was two neutron stars that collided, so we partnered for the first time. We had shown that the collision of two neutron stars can generate a gamma ray burst, so the combination of multiple messengers proved the origin. Of the short gamma ray bursts are due to neutron star collisions, which was big, the second was that the two neutron stars came together and, when the neutrons collided, they actually formed the heavier elements that we know on Earth, so elements like gold and platinum are much heavier. that iron, of course, we know they exist, we have them on our planet, we have them, you know, in our rings and earrings or whatever, my wedding ring, so I used to have one of those that she has , it's a delicate point, but let's move on.

Okay, so we know they exist, but actually, astrophysically or physically, we didn't know for sure how they form. They are not formed in the centers of the stars we knew of or through nuclear reactions, so perhaps a hypothesis was formed in a neutron star. collisions with this event on August 17 we obtained experimental evidence through electromagnetic waves and gravitational waves that tell us that two new pants collided. We have now shown that gold was formed in this event and therefore we also solve that mystery. That's fantastic, congratulations. I take credit not just for myself, but there is a whole collaboration of hundreds of scientists, so we are coming to the end of our segment, but there is another question or maybe a question and a half, have you received any data that you don't Does it fit the question? templates or, more generally, how do you imagine testing Einstein's general relativity in this extreme environment using gravitational waves?

We always try to prove Einstein, yeah, okay, we push that frontier that he made. I mean your theory must collapse at some point because it involves the singularity at the center of the black hole and we don't like that that's what the Masters break exactly that's where division by zero doesn't make sense so somewhere the general activity has to be broken with gravitational wave observations we are observing black holes moving at half the speed of light 60% of the speed of light this is the strongest regime of gravity we have ever tested with anything nothing else has tested that regime until Now we haven't seen anything in the gravitational wave data that doesn't agree with general relativity, but keep pushing that frontier and maybe one day we'll see something that's always in the back of our minds and would you say that would be the culmination of this business?

Taking the understanding of gravity to the next place physicists are. I could say that, so that's something we always try to keep testing that theory. The astrophysicist in me wants to know about these black holes and neutron stars, how they form, what are their masses, how can nature form these pairs of black holes and neutron stars in such a way? Numbers so high that we see many of them well, so this is what we look for on the astrophysics side. Well, good luck with all those incredibly interesting projects and everyone, please join me in thanking Vicki Calogero and talking about black holes, of course, Stephen.

Hawking is the great scientist that comes to mind and this makes me think that you all no doubt know that, sadly, Stephen Hawking passed away this year, so I would like to spend a little time thinking about what Hawking told us. said about black holes. What were the insights that he gave us and what puzzles emerged from his work that we are still struggling to solve and will probably continue to struggle with for some time? And to that end, as a little background, we need to have some understanding of a concept that everyone is familiar with on some level or another, but let's take this opportunity to put us all on the same page and that is the concept of entropy, so entropy is a word that is used loosely in culture, we often use it to describe a certain amount of going from order to disorder, from low entropy to high entropy, that is a kind of intuition that the culture has about this word, so let's start with that very basic way of thinking about entropy and a good example would be, let's say, take my book.

I throw it in the air, it starts out very neat, all the pages were in complete numerical order, but as they go down it is overwhelmingly likely that they will not land in numerical order, they will land in a highly disordered state and that gives you some sense of what it means going from an ordered arrangement to a highly disordered arrangement, going from low entropy to higher entropy, of course, that's just kind of a fantastic everyday example. If we took a physics example more into account, we could imagine having a gas box. and imagine that you only have a small number of atoms there and imagine that they are all neatly arranged in this nice cubic lattice.

This would be a very ordered or low entropy configuration of the gas, like pages, all in numerical order. Now contrast that with a box of gas that has a large number of atoms, a large number of particles bounce around in a completely disordered way, this would be a very disordered state, a high entropy state and another way of thinking about the distinction between low and high entropy. What we'll use in a moment is the amount of information that would be required to describe these two configurations because look to the left, you don't need a lot of data, it's a cubic lattice that you have 3 by 3 by 3. atoms that fill that lattice and if I give you the separation of them, let's say 10 centimeters, that basically describes the configuration on the left, you don't need much information to describe a system that has low entropy, but let's say I wanted to describe the configuration on the right, basically I have to tell you where it is find each and every particle, that's the only way I could describe and see all the information I need to describe that configuration, so the idea is low entropy, not much information, high entropy.

It takes a lot of information that's hidden in this particle configuration and that's kind of the distinction between order low disorder and behind your P low information high information now of course I'm speaking in informal language so we can all get an idea of critical ideas, but you can make all of this pretty precise and this gentleman here you know who he is, who Ludwig Boltzmann is, he's right and this is his famous tombstone and you see that formula at the top of his tombstone and that's the formula that makes these statements accurate this is a formula you learn if you take a thermodynamic statistical mechanics course S stands for entropy K is Boltzmann's constant and the rest has to do with the configuration number of the ingredients of the particles that make up the system and the famous second law of thermodynamics makes use of this formula and again it is something we are quite familiar with in the culturestrings, so we string theorists were a little bit struggling, yeah, we have these six extra dimensions, it's a little embarrassing, it's small, you can't see it and then other people were like, sure, yeah, yeah, so this was it. latest in technology until the mid 90's and where we did it.

We didn't know what to do with these extra dimensions, they were just there to make the theory consistent and we hid it in little things and then came the question about black holes and the black hole had the opposite problem, the problem with the black hole gave us information was missing from the black holes where were they what was that information it turned out that these two problems canceled each other and this is the problem they were in where are the ingredients or the degrees of freedom? that constitutes a black hole ended up in internal space, little space things I was talking about so the extra dimensions were helpful to find the resolution and maybe we can see there yeah so can we skip the next one and go beyond where we can see?

The perfect thanks, as you can see here, the red donut-shaped object represents these little internal dimensions and the blue sheet that you see represents the three macroscopic macroscopic dimensions, so the idea is that if you take a rope or a membrane or one of these extended objects and wrap it around the cycles in these little external spaces like a torus or like a circle or donut or any other shape you have, it will create a mass at the point where you are wrapping that circle and the more it is wrapped, the more mass It will form there and further form and distort the geometry of the space around it and it is enough to create this warped space which is what we call the black hole.

The black hole itself can be seen as these strings or membranes wrapped around these additional cycles of this small space, so if the question is what explains the degrees of freedom of the black hole, these are precisely these strings or membranes wrapped. around these extra dimensions how many there are how many degrees of freedom there are what are the entropy translates into how many ways these extra ropes or membranes can wrap around these extra dimensions and there are many ways and that explains the entropy of the black hole so with anteye anteye meter of straw and I actually did a calculation of how much entropy there is in these wraps of the string around the outer dimensions around these inner dimensions from string theory and we found an exact match with the prediction that Pickens Stein and Hawking had made about entropy. of these black holes, so just to quickly unpack a little bit, you basically found a new way to describe black holes in string theory that makes use of the extra curved dimensions of the red part of this image that we found here. and you're saying that by wrapping these strings or ingredients of string theory around the extra dimensions you can create a warp in space that looks like the black hole we've been talking about for many years before string theory was in existence. someone's reach.

Note, but in this description you can do a direct recount of the amount of information needed to describe the situation and in fact it matches what Hawking said exactly yes, so this gives us an idea of ​​a possible way to Describe the internal structure of a black hole. which in many ways I think the community of uses is one of the most important pieces of information that string theory may be going in the right direction. We have no experimental support for these ideas, but there is experimental mathematical support here, so to speak. which coincides with ideas that have been on the table for 25 or 30 years, so this is not a key step forward, but now let's move on to some of the puzzles that still remain and part of the puzzles surround something that is closely related With what we've been talking about, which is something called Hawking radiation, if you tell us a little bit about what Hawking radiation is, Hawking, after discovering the properties of having information, return and entropy, also noticed that black holes are actually not completely black and what happens is if we go to the next one maybe still PowerPoint so if you get close, go to the next one if you get close to the event horizon of the black hole, yeah what happens is that you get pairs of particles. created from vacuum, these are quantum fluctuations, quantum fluctuation is always creating particles and antiparticles in pairs.

They usually come and go without doing anything, but if they are close to the event horizon, one of them could maybe go towards the inside the black hole and then another could come out and the mother that enters has no way to get out. It is so trapped there, but the one who leaves can leave and go very far away to infinity and that looks like radiation from the point of view of part of the outside, in other words, from the point of view of part of the outside, the black hole . it is actually radiating energy as it radiates energy it loses mass and shrinks and shrinks and shrinks until after a while the black hole completely disappears where there is no more energy left to emit so once the black hole disappears, the question is what happens to everyone.

That information that went into the black hole, what happened in that area, talked about where that information went, so this was a question that Hawking basically posed and this was probably the slide before this, yeah, we can go back if you wait. two. slides if you wanted if you saw those two slides you actually know further back sorry two is the wrong number go back to Hawking's court if you wanted then he had this amazing coat if maybe you remember the argument between Einstein and Bohr that Einstein didn't care he liked the probabilistic aspect of quantum mechanics and that's why he said God doesn't play dice and Niels Bohr responded by telling Einstein to stop telling God what to do and Hawking added his own wrinkle to this, he said well what. happens if you roll a dice inside the black hole and the black hole after the white disappears and we the dice disappeared then he said that not only God rolls the dice but sometimes he rolls them where they can't be seen and then you made a little cake so yes, we were lucky enough to have Stephen Hawking as our house guest a couple of years ago when he was visiting Harvard and we made the cake in the shape of a black hole with the dice and the book from his famous The Book which is actually made is a cake and it's actually gluten-free because he was allergic, so Steven had eaten his cake and he could make it.

Yes, in that image you can see that there are two dice hanging there floating. towards the black hole and it is entering and that is the problem of the information puzzle, the information of what the roll of dice is is lost and that is what is called the information puzzle because if the dice roll some number and the hole black evaporates and disappears, we did it. Here appears the information about what the role of the dice was and that is called the information puzzle that we are still struggling to understand even today. Now most people in the field have long anticipated that somehow information comes out with that radiation. that we saw coming out of the black hole for a while Stephen Hawking said that the information wouldn't come out and I mean that quote was pretty serious, he was saying that we have to rethink quantum mechanics because the information doesn't come out again. then he changed his mind that yes, so part of the reason for this is the discovery of a more detailed version of what is called holography, in other words, this started with work that was already done a long time ago, but it became more precise with the work of the war mother Senna, where it was discovered that a gravitational system can be described accurately using objects that are much simpler to understand and, in particular, in that system it can be demonstrated mathematically rigorously that there is no way to lose information, so indirectly there was proof that whatever happens with black holes, information should come to light, so that part was starting to be established using these kinds of arguments in the theory of strings, but the problem is that even though there is this mathematical proof that this should happen, we haven't done it yet.

I know exactly how and some people thought that maybe the information spreads with this radiation, as you were saying, very gradually and very little by little, but gradually it builds up to give you information and this is what I think Stephen agreed early on. that this is the resolution, but I still think and I think the community still believes that we haven't really understood how exactly this happens, so the information conundrum of how this information comes out is still one of the great mysteries of black holes and I don't really understand it, so do you think it is possible that one day we will come to the conclusion that Hawking's original opinion was correct and that the information does not spread?

In his opinion, that's still on the table. Well, I think that sounds a lot less likely given that we think we understand a dual description, another description of these black holes, so it seems like that seems a lot less likely now, but you know, we can never say we know everything about it, that it's our current understanding because of course it evolves, but even even. With that understanding, our understanding is not detailed enough to convince us of how it happens now. Much of our discussion here has focused on what happens at the edge of a black lot, the event horizon, or whatever black hole it may be.

Where information is stored may be where entropy is stored. We haven't said much about what happens in the center right. Can we spend a little time talking about that? Well, one of the things that happens at the center of the black hole is that there is this singularity, this infinity that Brian already discussed, this is this division by analogy with zero and we don't think it's physical, we think it's just the ghost of our equation, it's just a mathematical thing that comes out and that means our description falls apart. not that there is an infinity now quickly the infinity could be physically because you have all this mass squashed down to size zero and that size is not physically suitable for us there is nothing smaller than the length of the boards which is approximately 10 to less 33, which says that there is the notion of space breaks down anything smaller than that, so there can't be an infinity in physics, we don't believe that, so we don't understand what's happening in that, in that, in that, that way, and we do not understand the understanding of this singularity.

Nowhere close to understanding what is happening there, we know there should be a good description but we don't have it and why that is important is that we want to know what is happening inside black holes, of course we can send someone and discover it. what about that infinity but that wouldn't be a fair thing and even if we did that, even if we said well, we would send some creature, not us, that robot or something, the robot can't come back to tell us what happened or what I saw because nothing can escape from black holes so it won't be useful, so we have to figure out what's happening there without going into the black hole and even then we don't have, we just don't have observational data.

We don't have enough theoretical understanding and we think it's important not only for black holes, but it turns out that those infinities that we see, if you try to go through those infinities to the other side, so to speak, it turns out that they look very similar to infinities. that we see at the beginning of our own universe, it's as if our universe is emerging from the inside of one of these black holes in that sense and don't lose your train of thought, many times people think of the center of the black hole as a location in space the center is the right way no it's actually like at a certain time it happens at a certain time and that's because the nature of space in time changes as you enter the black hole but we need to cross the event. horizon of black, so one of the reasons you can't leave is because you can't stop time from moving forward exactly, so moving forward in time is like getting closer and closer to a different place at a certain time. hitting the singularity that is the moment at the given moment is that the singularity could be the end of time in some sense it could be, but we don't believe in that and then what would you say what comes after that and that is do you see a lot? like what could be a new universe or something, we are interested in understanding the resolution of the black hole singularity problem and I think it is very exciting to know that black holes, as we already discussed in this program, have a lots of evidence that they exist, so they are there, we can't say we are just imagining, so what is that?

What is that singularity? What are we learning from it? It is one of the most beautiful mysterious objects, I think, inthe universe and hopefully through some experiments and maybe. based on a theoretical understanding, we will have some progress on that, so what is your assumption? I mean, if we come back and we invite you to come back more. I don't know, the 2025 world science festival, can you give us the answer to what's happening at the center? from a black hole maybe you are inviting 20 55 million 20 50 okay, good prediction, a safe prediction, join me in thanking Qumran Vasa, thank you very much, fantastic, good evening everyone, thank you.