Pushkin from Pushkin Industries. This is Deep Background, the show where we explored the stories behind the stories in the news. I'm Noah Feldman. The world has recently been gripped by the extraordinary and extraordinarily beautiful image of a black hole, a thing which we know allows no information or light to escape, and of which we therefore, strictly speaking, shouldn't have an image at all to make sense of this. At the level of logic, at the level of physics, and at the level of deeper meaning, we're thrilled to have with us today. Andy Strominger one of the leading theoretical physicists in the world who's made fundamental contributions to quantum gravity theory, to string theory, and has also worked extensively on black holes. Don't take my word for it that and he's the right person to talk to. He's one of every prize there is to win in the space of theoretical physics. And Andy is also a director of the Center for Fundamental Laws of Nature at Harvard. On top of that, he's also one of the co directors of the black Hole Initiative here at Harvard University where I'm speaking to Andy today. Andy, thank you so much for coming and joining great to be here. Ah. So, Andy, let's just start with the image, which is a great headline grabber and something that is extraordinarily beautiful, but which strictly speaking, isn't a classic photographic image, whatever the world may imagine. So say a word, if you will, about what we are seeing, what it is, and then from there we can move on to what it tells us. Okay, well, I'd like to back up a little bit. It was a hundred years ago that Einstein predicted with his equations that there would be black holes, and people have been arguing about them for most of the time, not believing that they exist. Einstein wrote a paper nineteen thirty eight saying black holes don't exist. Most people thought they didn't exist until probably the seventies. And how they behave, what's inside them, why they're there, has been a central debate in physics for the last one hundred years. I have spent the majority of my scientific career thinking about them, trying to understand them, along with hundreds of other people, and then all of a sudden to see it, to see a picture of it, like Wow, that thing is real, it's really it's really it's not. We're not the only ones who have that. You could be the deepest specialist and you're moved by it. I promise you that we have a bunch bore. It rocked our worlds to like see this thing that we've been talking about our whole lives. So there it is, you know, even though you knew it was there. We knew it was there. But there is a big difference between knowing something's there and seeing it. You know, maybe there was still that tidy bagging about I don't know, but it really is great to see it. It's a great thing actually to hear that from a physicist, because when non physicists like me, mere lay people, we instinctively have the feeling if we don't see something, maybe it's not there. And then the physicists tell us it's all equations, it's all logic, there are experiments that validate these things. Take it on faith, you know, like you'll never fully understand those things, but we know. And so to hear that you too, or even you like to actually see stuff as a kind of I don't know, there's like some epistemological relief to me. And hearing that, yeah, yeah, so what is it that we are in fact seeing a black hole, by definition, is a region of space and time from which no light escapes. So we're not seeing light from the black hole. What we're really seeing is light emitted by gases swirling around the black hole, things that we don't understand very well. And we're seeing the shadow of the black hole. So that dark spot in the middle of that picture, the absence in the middle of the breast, the absence in the middle of the picture is where the black hole is. One of the ways that was central too, or the main thing that was central to making this telescope able to see something so extraordinarily far away, was to turn the whole Earth into a telescope. How does that work? We get to the size of the Earth because we take about eight different telescopes located at different points around the Earth and we synchronize them and so it's of course not a complete lens covering the entire Earth, but it's still gives you a lot of resolving power if you can just grab the light at those separate points. And as an accomplishment, the creation of the image with all of its coolness is scientifically significant. Why for several reasons. First of all, it is in and of itself a spectacular technical accomplishment, one that would not have been possible ten years ago. It required many things. It required amazing improvements in the accuracy of atomic clocks, um, it required uh, bigger hard drives, bigger data processing capabilities, it recovered. I read at one point that the data was so much that it actually had to be flown from one place. Yeah, because the Internet couldn't accommodated. Right at Sheep himself, I saw lugging around these you know, discs with the you know, he would go down to Mexico, go up to the top of the mountain and lug lug it back. Of course, the whole team was working on it. But Shep is the director of is the direct and your your co director at the black the director of this event Horizon project at a great great scientist and uh, and the algorithm has also gotten some attention and deserves some attention. I take it produced by Katie Bowman, a recent post doc. Right, Yes, there were of course, the whole there's there's a big team of one hundred to two hundred people, and you know, all this kind of big science is done in a big teams and big teams now and it's it's the only way it could can be done. But number one of the big technical accomplishment. Number Two, there is the importance of having seen these objects you know, that should be shouldn't be underestimated. Number three, it's only the beginning. Um. One of the things that struck me when I saw the papers was, which I was not privy too before the the general release, was how little actual observing time they had when I first met Chapter ten fifteen years ago. This project was you know, it was it was a dark horse. It was it was not, you know, the center of astronomical efforts. Um. And it was a funny idea, but one that the more you thought about it, the more since it made Why was it Why was that just panenthetically? Why why wasn't it at the centerpiece of as you say, black hole so crucial, so important and seeing it would be a big deal, you know, because it wasn't. There many ways it could have failed, right, They had to increase their observational precision by many orders of magnitude over whatever what anybody had ever seen. What they did. It's like standing in Boston and reading the data on a quarter in Los Angeles. That is, that is the precision that they had to have to image this black hole. The general public tends to forget, I tend to forget that the funding of scientific projects is always a kind of a bet or a gamble. It's a beat, and when the odds of the success are relatively low, the funders are skeptical about putting too much money on that gamble. When people thought about it ten or fifteen years ago, did they think, well, if we get enough computing power, this is one of the things will fix. And it's a question of whether we'll ever get enough computing power, or was it rather a question of other aspects of the technical difficulty of doing it. He wasn't dismissed, and the thing was funded in it and it did happen, but it was not obvious. It was not obvious. You know, the Earth is just barely big enough to image this thing. It's also very important that the wavelength that they could access with this large collator array is one in which there isn't a lot of absorption between us and the black hole. You know that there isn't a lot of dust that blocks the light at that that wavelength. Right, So there were some coincidence that you know, Luck smiled on the project. It might not have been possible. I don't I doubt if you get cheppy, you could ask him, but I doubt he would have been certain you ten fifteen years go that it would work. But I was going on to say, they didn't get all that much observing time. Now clearly they'll get more, right, there will be better resolution, more observing time, they'll set one up out in space. So there we are entering an era. So this is the opening of that era of precision black hole astronomy. So let's talk about now what we can see and what we will see when we get more time, more observations, and the emergence of what you described as a new a new science really of precision black hole astronomy. You with some collaborators have been actually making predictions the way theoretical physicists like to do. You know, a theoretical physicist makes predictions and sometimes they can be tested in his or her lifetime. Sometimes it takes generations. In this instance, you've made a series of observational predictions the things that you expect can be picked up, and now that will turn to whether they will in fact be be picked up, which is dramatic and exciting. What kinds of predictions have you already been making and when can we expect to see results. I've been working with Alex Sasa, Delilah Gates, and Dan Coppetts, and we are very interested in what happens very near the horizon of of the black hole, right at the edge of that inner shadow, and remind people, just because it's never bad, to redefine it the event horizon. Yeah. So the event horizon is the boundary of the region of space time from which light rays connects escape. So in practical terms, it's the edge of that you're inside the event horizon, you're in the black holiness of the black hole. Yeah. Once you go inside the event horizon, you can never come out, and so your predictions relate to what's happening at that edge, right. And one of the things that we are very interesting in is that black holes can spin around like a top and it's believed that the M eighty seven, the black hole that we've just seen, is spinning at light speed or very near light speed. So there has been claims of this from other kinds of measurements in the literature, and a black hole which spins at light speed does some incredibly peculiar things. Is you get near the edge of the black hole, a long sort of funnel or wormhole forms. It's kind of like a tornado with a long spout. And as the black hole spins faster and faster, that's spout. It sounds like I'm talking about sub sides fiction stuff. But everything with respected black holes though, so go on sounds like I'm talking about sizes fiction stuff. But we maybe seeing this kind of black hole. Now the spout or the wormhole that goes to the horizon, the black hole actually becomes an infinitely long tube protruding out of the out of space doot, and that will lead to about to ask you where where the wormhole leads. But if it's infinitely long, the answer is, yeah, it leads to infinity. It goes, it leads to infinity. But before it gets infinitely long where the wormhole leads it goes into the rise of black hole, and once it crosses there, we don't know. We don't know what's inside a black hole. So the part of the wormhole is in the very edge of the wormhole is at the event horizon, right as it were, and then it extends infinitely away from the black hole and connects on to the space time that you and I live in, and that so we're seeing into what does sound like science fiction. It does sound like science fiction, but we're seeing it, you know, And how would that be seen? I mean, what would that as it were look like? We in our paper gave some very specific predictions about what the polarization of the light coming out will be. It's known that it's polarized. Not that's coming from the black hole, but the lights, sorry, the light and the halo. Yes, it's known that it's polar polarized, but the distribution hasn't been extracted from the data yet. I think they've already seen it. They have these mountains of hard drives the data they need to process, and they haven't extracted from that what the polarization is. Luck will have to shine on us for Are there measurements to be sufficient to prove what you've predicted? Yeah? Right, because they weren't there looking for what you predicted. Well, that's right, and also might not be this round might not be a precise enough measurement for our prediction to be verified or not. But I'd stress that our prediction is a prediction of the Einstein equation. It's just the Einstein equation in a very unusual circumstance, not like the predictions that Einstein made, where the effects of general relativity on the bending of light or in the Solar system they were small effects. Yes here, it's huge effect. Here it changes dramatically the nature of space and time, everything that we really have to to somebody even reimagine what we are, what we mean in ordinary language term. Yeah. So we think that if you were to go in a spaceship to near the horizon of M eighty seven, you would be forced to whirl around it. You couldn't just approach it straight on. There would be a force by the warping of space time that would drag you around like a tornado and pull you down this down the drain into the down drain at the speed of light through the wormhole. Yeah, bow the wormhole to the Yeah, and it would grab you well before you got to the event horizon. So, in practical terms, though it's outside the event horizon, you're descent into the black hole would begin a lot sooner than it. Otherwise it would be if it were really spitting all the way at the speed of light, it would grab you when you were infinitely far away from the event horizon, but suck you there in a finite amount of time by pulling you up to the speed of light. But when you say we grab you when so I'm just trying to get my mind around this and not so much succeeding when you say would grab you the reason you're infinitely far away is that sounds as though, well, we're infinitely we're at some distance less than infinitely far away from M eighty seven right now. Why doesn't it grab up? Oh, we don't know that, because we're not infinitely far away from the edge of the wormhole, and the wormhole could be infinitely long. I don't think it is. You'd have to be going absolutely at the speed of light for it to be infinitely long. But it could be very very long, and so we could be much farther away than it seems. I mean, the rest of the universe exists. The rest of the universe is not presently I take it currently captured by the wormhole right and spinning at some very rapid speed around the black hole, and on the way to the event horizon, we're not headed all headed that way, I take it right. So my question is why, Well, because we're far away week, but when you get to some critical point instance, all of a sudden it's a spinning black hole is surrounded by a science fiction region which was discovered in the sixties called the ergosphere. And life inside the ergosphere is very different than life in this room, and existence rather than life, because nothing's living once you get into the ergosphere. Anyone who enters the ergosphere, which is still outside the black holes, you you are forced to spin around in the in the tornado vortex outside the black hole, and the wormhole is a big extension of that. The wormhole is the is the vortex going Yeah, it is the vortex going down to the black hole. So we what we know really is our distance from the mouth of the wormhole, not how long the wormhole is. Now nobody thinks it's infinitely long, but it could be long enough to be in testing and long enough to make a signal. And how how will the observation of the polarization of the light that presently is visible at the edge of the black hole get you to some better understanding of the of the wormhole. Well, the worm it will verify the existence of of the wormhole, I say. And the polarization is not the only thing um. There are other things that you might try to to to measure. Now I stress it there. We're just one of and not even the most important, what of many groups who are in the vent Horizon telescope themselves are making predictions. Of course, they had to compare their their theory to the theoretical predictions to their observation to get their estimate that they published of the mass. We are especially interested in some of these novel aspects because first of all, because they're weird and interesting and they're there and we're seeing them, and also because they tie in with ideas about the quantum structure of black holes and what's inside a black hole in a very intricate way. And that question of what's inside is hugely controversial and fascinating. So the question of what's inside also philosophical, if I yeah, I venture to use that word. There are philosophical aspects to it, but there is a very sharp meaning to it because, as Stephen Hawking showed, if you wait long enough and even the you know, event Horizon team won't have this much patience. I'd be like a very very long time, the black hole will evaporate and what's inside using quantum effects will come out. And then the question is would the thing that came out, would what was inside to come out and have some information? And then there is an inside that we would ultimately see if we could wait long enough, which I think, yeah, more than billions moves it from philosophy to physics because there would because it's not an unanswerable question. Well, it's a question people could argue about. That's a separate, interesting question. What makes something a physics question as opposed to philosopher ques I was using a shorthand of imagining that physicists only like questions that, in principle could be answered. It's a question which can be answered with a goadoncan experiment when you're do in your mind? Yes, I thought, you can't get the funding to do it? Okay, right, So some people would say infinite time, Well, you don't have infinite time. Some people would say that physics is the study of questions you could answer with real experiments that could be funded. That's a pretty cramp though, view if it wouldn't cover a lot of your your earlier work, wouldn't cover wouldn't cover a lot of my work, right, And I think, to be fair, I don't think that's what most non physicists think. I think it's that would be a very hard nosed, predictive, pragmatist view, and it's not physics if I can't test it, you know, and get funding to test it. Yea. The laws of nature presumably should be resistant to being cabined by what we can fund. But what's exciting to me here is that this observation is touching the edge, possibly touching the edge of the things that bearing on the issues of people that people think about who want to understand what's really inside a black hole. So you mentioned your friend Stephen Hawking, also your collaborator who died not so long ago and with whom you did a lot of work over the years, but most recently you had been working on some pretty major projects with him, also connected to black holes. Yeah, tell us a little bit about that. Yes, Stephen, in his most famous work in the Seven Daies, showed that with an argument that is so simple and elegant that it has never been seriously questioned that when you include quantum effects, black holes are not completely black. That quantum effects allow a sort of the uncertainty principle about where the horizon of the black hole is allows a small amount of light and matter to slowly trickle out of the of a black hole a very slow rate. So those are big things, and let me try a very very lay person's attempt to make sense of that. If we imagined determinative locations and laws of physics, then nothing escapes the black hole. That's what makes it a black hole. But one of the key points of quantum theory is it precisely you can't pin down the exact location of every quantum phenomenon. And since you can't pin it down exactly, that puts enough wiggle room, if you will, into the equation that there is some information in the black hole that might be capable of being discovered. How's that for a first order? That's right. So quantum mechanics says that the horizon and the black hole must fluctuate around a little bit, according must be slightly uncertain, and so that gives just enough wiggle room for a few quantum particles to escape from inside the black hole at a slow rate, so that you began with describing Hawking's famous nineteen seventies that was forty years ago, yep. And he gave an argument that the information about how the black hole was made would not escape, would not come out with this leak of energy and particles and so on. Things would come out, but not the information about how the black black hole came to be made. He claimed, the present does not determine the future and cannot, even in principle, be used to reconstruct the past. Bad news for historians, bad news for hystories for people who like free will in the future maybe, but bad news for physicists because it's equivalent to saying there aren't absolute laws of physics, because a law of physics is supposed to predict the future from the present. It was a very simple argument, and people didn't like the conclusion. It had been questioned in many different ways, but none of the ways in which it was questioned really stuck. So a few years ago I found, while investigating other problems in physics, I came across what seemed to be an error in the original flawed assumption in his original reasoning. Moreover, the nature of the flaw suggested a research program for understanding what really did happen. And I explained this to Stephen and he was very excited about it, and I just say, this is also it's a great model of what scientific collaboration can be and isn't always You find a flaw in an important claim by another famous physicist and you call him up and you say, hey, there's a problem, and that's collegial of you, and then he responds positively, and that's collegial of him. This is the way it's supposed to work in the textbooks. Yeah, and it really does work this way for the for the most part. Yeah, it's heartwarming. It's not like this in my end of the academy. I promise you that. Well, it may be related to the fact that there's no money in my branch of science. I know there's a there's a there's a money in those prizes. But go on. So he and I and his colleague Malcolm Perry, he had some ideas about how to proceed on this and to make sense of it, and so we began a very active and productive collaboration which went on for the last three years with life and we're pushing forward in that direction. It's looking promising, but we haven't delivered the goods, right. We don't know yet that there isn't some reason this is a technical issue rather than the fundamental right. When you were describing how you came up with the original thought that led to this collaboration, my reaction was you were describing how you were thinking about something else in physics, and then you hit upon reason to think that one of Hawking's original assumptions was inaccurate. And it's struck me that's a very andy way to go about things. One of the key features of your contributions across the whole range of areas where you've worked is that you find and see correspondences between different areas of thought physics, math that other people have never hit upon before. That's like the Andy move, as it were, and it's quite a move. So well, I don't think I have a pattern on this move. But it's the structure of the field the physics is. You know, there's many It's interconnected in surprising ways, and it often happens. Maybe I'm lucky enough that it happens to enough times that I'm not sure it looks like a coincidence, but maybe coincidental in nature, but it's not coincidental in you. But anyway, go on, and you know, maybe one could say, you know, our creator didn't have so many ideas that he kept using the same one over overget and you solve a problem in one area and it has a translation into another area. So that hints at a kind of set of structures of unity. I mean, you're sort of kidding about reusing the same idea. What you really mean is that there is an underlying unity and we are describing different parts of reality in different ways. We've got these mathematical tools or these physics tools to describe something, but we're actually describing a more unified underlying phenomenon. Yeah, we have many ideas and we often don't realize that they're the same idea. And is it your belief that there is some directionality here? I mean, now I'm aiming for something bigger, as it were, even bigger than you know, than the wormhole and the black hole? Are you a believer in direction in physics towards more and more unification of our theoretical knowledge? Sometimes people talk about a grand unified theory string theory, to which you've made fundamental contributions. Is sometimes described as a step in the direction of a grand unified theory or an aspiration in that direction. I'm asking you to put it along the line here. You know, the honest answer to that question is, I don't know. People work in different ways. Some people have beliefs that they think that that is how nature works, and they relentlessly pursue demonstrating the physical reality of their beliefs. Others just take the mathematical equations and follow them and see where they lead. And you see yourself in the latter camp. I'm somewhere in between. I have things I believe in, but I pride myself in being ready to drop my beliefs when they don't measure up to the equation. The equations are the final arbiters. The equations and the experiments are the final arbiters of truth in our field, and many people have, including you know Einstein. Einstein had very strong beliefs about how things should be should be, and that got him through special relativity, general relativity, and the beginnings of quantum mechanics. But then he had beliefs about the way the world should be that were being countermanded that we're being own by his own equations, and then the experiments that were validating those equations, and that reduced his his his productivity. M He did pretty well, He did pretty well. Then he did pretty well. But at some point he believed things that weren't true. He believed that quantum mechanics was wrong. He believed their word black holes, he believed their word gravity weight. You know, he had some raw beef, wrong beliefs that he got stuck on. So it interfered with his being able to move on to make the next set of He might have come up with even more fundamental things if he had been able to keep on pushing. That's right, that's right. So that's an argument that you may need some beliefs to get you started. Yeah, but there needs to be some kind of a reflective equilibrium where at some point you have to start believing your equations. Yeah, you know, it's always a conflict between sticking with what you believe in and not giving up, and being too stubborn and not being flexible enough. The real truth is it takes all types. You know, there's some people who have an idea and pursue it in the face of unreasonable hardship and difficulty, and everybody's saying no, and everybody's saying no, and some of those people turn out to be right. Now people turn out to be right, but most of them fall by the way side. Yeah, you need some of You need people with unreasonable beliefs. You need people who are ready to drop their beliefs. You know, it takes a village. Let me ask a final question about how these different pathways to understanding the world are going to play out in the black hole context. Yea. When you started working on black holes, as you said, there was still a view among lots of people that there were no such things right, and now we're in a very different place. We've seen one. Yeah, does that take some of the thrill out of it? Does it seem you know? I mean, it's nice to be right, But there seems like there's a stage of, as you said, great observational astronomy in the space of black holes, which is important and will expand our knowledge and maybe give us radically new ideas about the world. But somehow seems to be confirmatory of what you and others predicted and what is actually now believed to be true. Is there some it takes. I mean it's thrilling now, but ten years from now, will some of the thrill will be gone in working on something which everyone acknowledges exists. No, I think it's only getting more interesting. We can think of this. The last few years, or this observation even is kind of a historical marker. You know, a hundred years ago the existence of black holes was predicted. Now they've been seen in the most straightforward way. So going forward there will be better and better observations. But we still have this huge puzzle. Yeah, the godon Can experient. What is the result of the Godonkan experiment? What's coming out of the black hole? Or equivalently, what is inside the black hole? Then you know there's a fundamental contradiction in the laws of physics as we currently understand them. So that's what makes it so exciting. Something has to give. It's that the thought experiment poses a contradiction between different things that we're we are committed to. All the things that we believe to be true. Can't all be true. Something which we are completely at this moment unwilling to give up as a truth about the universe must actually be wrong, and the fact that that contradictions was recognized forty years ago by Hawking and has sat there. As the years have gone by, the longer it's sat there, the more that we've realized what central importance it is. So somehow the observational astronomy world and the theoretical physics worlds have converged on black holes as the most interesting and things around and it is. I'm pretty confident that well, first of all, I there's no reason we can't ultimately solve this problem. And the fact that it has sat there for so long, I think there is a consensus in the community that we can't solve the problem without a fundamental new insight into the structure of the universe at the same revolutionary level as quantum mechanics or relativity. That it's not a technical problem that we missed a factor of two somewhere. So that's the holy grail. That is the holy grail. It's an exciting thing that black holes have become come to center stage and observational astronomy at the same time as in theoretical physics. We don't have a roadmap how we're going to talk to each other and close that gap. But we're thinking here on a hundred year time scale, we might not even have found the city where the whole grail is hidden, but we've maybe found the continent, and now we're gonna have to keep exploring. But it's a pretty big deal to have found the continent. That's a big deal to have found the kind we know where we're looking and now. And I think you know, Although I'm loath to draw too many non physics metaphoric conclusion from physics, the idea that sometimes we're in the grips of contradictory views and something's got to give, we need some new account to make it work out is about as good a lesson to take away from black Holes as I can imagine. Andy, thank you so so much for your for your brilliant thoughts in your time. Thank you Eddie, thank you Noah. When I see an image like the image of the black hole, I'm filled with wonderment. The mere accomplishment of human beings, to be able to see something so far away, to conceive of it, to make sense of it. That's the kind of thing that really hits me where I live. It makes me believe that being human is actually worth something. After all, we can actually know things and achieve connection. But you know what, when I listen to Andy, somebody who actually understands at the most profound level what these discoveries are, I'm even more struck by the wonderment that he feels than the wonderment that I feel. He's not jaded at all. He spent a lifetime working on black holes, and to him, where at the crossroads of excitement where things are only going to keep on getting better. That's genuine scientific exploration. That's genuine scientific collegiality and collaboration like the kind that Andy has done with Stephen Hawking. And it makes you think not just that the universe is an amazing place, but maybe we at our best when we're not fighting and we're searching for the truth. Are in such bad people? After all? Deep Background is brought to you by Pushkin Industries. Our producer is Lydia Geane Coott, with engineering by Jason Gambrell and Jasonstkowski. Our showrunner is Sophie mckibbon. Our theme music is composed by Luis GERA special thanks to the Pushkin Brass Malcolm Gladwell, Jacob Weisberg and Mia Lobel. I'm Noah Feldman. You can follow me on Twitter at Noah R. Feldman. This is deep background

Pushkin from Pushkin Industries. This is Deep Background, the show where we explored the stories behind the stories in the news. I'm Noah Feldman. The world has recently been gripped by the extraordinary and extraordinarily beautiful image of a black hole, a thing which we know allows no information or light to escape, and of which we therefore, strictly speaking, shouldn't have an image at all to make sense of this. At the level of logic, at the level of physics, and at the level of deeper meaning, we're thrilled to have with us today. Andy Strominger one of the leading theoretical physicists in the world who's made fundamental contributions to quantum gravity theory, to string theory, and has also worked extensively on black holes. Don't take my word for it that and he's the right person to talk to. He's one of every prize there is to win in the space of theoretical physics. And Andy is also a director of the Center for Fundamental Laws of Nature at Harvard. On top of that, he's also one of the co directors of the black Hole Initiative here at Harvard University where I'm speaking to Andy today. Andy, thank you so much for coming and joining great to be here. Ah. So, Andy, let's just start with the image, which is a great headline grabber and something that is extraordinarily beautiful, but which strictly speaking, isn't a classic photographic image, whatever the world may imagine. So say a word, if you will, about what we are seeing, what it is, and then from there we can move on to what it tells us. Okay, well, I'd like to back up a little bit. It was a hundred years ago that Einstein predicted with his equations that there would be black holes, and people have been arguing about them for most of the time, not believing that they exist. Einstein wrote a paper nineteen thirty eight saying black holes don't exist. Most people thought they didn't exist until probably the seventies. And how they behave, what's inside them, why they're there, has been a central debate in physics for the last one hundred years. I have spent the majority of my scientific career thinking about them, trying to understand them, along with hundreds of other people, and then all of a sudden to see it, to see a picture of it, like Wow, that thing is real, it's really it's really it's not. We're not the only ones who have that. You could be the deepest specialist and you're moved by it. I promise you that we have a bunch bore. It rocked our worlds to like see this thing that we've been talking about our whole lives. So there it is, you know, even though you knew it was there. We knew it was there. But there is a big difference between knowing something's there and seeing it. You know, maybe there was still that tidy bagging about I don't know, but it really is great to see it. It's a great thing actually to hear that from a physicist, because when non physicists like me, mere lay people, we instinctively have the feeling if we don't see something, maybe it's not there. And then the physicists tell us it's all equations, it's all logic, there are experiments that validate these things. Take it on faith, you know, like you'll never fully understand those things, but we know. And so to hear that you too, or even you like to actually see stuff as a kind of I don't know, there's like some epistemological relief to me. And hearing that, yeah, yeah, so what is it that we are in fact seeing a black hole, by definition, is a region of space and time from which no light escapes. So we're not seeing light from the black hole. What we're really seeing is light emitted by gases swirling around the black hole, things that we don't understand very well. And we're seeing the shadow of the black hole. So that dark spot in the middle of that picture, the absence in the middle of the breast, the absence in the middle of the picture is where the black hole is. One of the ways that was central too, or the main thing that was central to making this telescope able to see something so extraordinarily far away, was to turn the whole Earth into a telescope. How does that work? We get to the size of the Earth because we take about eight different telescopes located at different points around the Earth and we synchronize them and so it's of course not a complete lens covering the entire Earth, but it's still gives you a lot of resolving power if you can just grab the light at those separate points. And as an accomplishment, the creation of the image with all of its coolness is scientifically significant. Why for several reasons. First of all, it is in and of itself a spectacular technical accomplishment, one that would not have been possible ten years ago. It required many things. It required amazing improvements in the accuracy of atomic clocks, um, it required uh, bigger hard drives, bigger data processing capabilities, it recovered. I read at one point that the data was so much that it actually had to be flown from one place. Yeah, because the Internet couldn't accommodated. Right at Sheep himself, I saw lugging around these you know, discs with the you know, he would go down to Mexico, go up to the top of the mountain and lug lug it back. Of course, the whole team was working on it. But Shep is the director of is the direct and your your co director at the black the director of this event Horizon project at a great great scientist and uh, and the algorithm has also gotten some attention and deserves some attention. I take it produced by Katie Bowman, a recent post doc. Right, Yes, there were of course, the whole there's there's a big team of one hundred to two hundred people, and you know, all this kind of big science is done in a big teams and big teams now and it's it's the only way it could can be done. But number one of the big technical accomplishment. Number Two, there is the importance of having seen these objects you know, that should be shouldn't be underestimated. Number three, it's only the beginning. Um. One of the things that struck me when I saw the papers was, which I was not privy too before the the general release, was how little actual observing time they had when I first met Chapter ten fifteen years ago. This project was you know, it was it was a dark horse. It was it was not, you know, the center of astronomical efforts. Um. And it was a funny idea, but one that the more you thought about it, the more since it made Why was it Why was that just panenthetically? Why why wasn't it at the centerpiece of as you say, black hole so crucial, so important and seeing it would be a big deal, you know, because it wasn't. There many ways it could have failed, right, They had to increase their observational precision by many orders of magnitude over whatever what anybody had ever seen. What they did. It's like standing in Boston and reading the data on a quarter in Los Angeles. That is, that is the precision that they had to have to image this black hole. The general public tends to forget, I tend to forget that the funding of scientific projects is always a kind of a bet or a gamble. It's a beat, and when the odds of the success are relatively low, the funders are skeptical about putting too much money on that gamble. When people thought about it ten or fifteen years ago, did they think, well, if we get enough computing power, this is one of the things will fix. And it's a question of whether we'll ever get enough computing power, or was it rather a question of other aspects of the technical difficulty of doing it. He wasn't dismissed, and the thing was funded in it and it did happen, but it was not obvious. It was not obvious. You know, the Earth is just barely big enough to image this thing. It's also very important that the wavelength that they could access with this large collator array is one in which there isn't a lot of absorption between us and the black hole. You know that there isn't a lot of dust that blocks the light at that that wavelength. Right, So there were some coincidence that you know, Luck smiled on the project. It might not have been possible. I don't I doubt if you get cheppy, you could ask him, but I doubt he would have been certain you ten fifteen years go that it would work. But I was going on to say, they didn't get all that much observing time. Now clearly they'll get more, right, there will be better resolution, more observing time, they'll set one up out in space. So there we are entering an era. So this is the opening of that era of precision black hole astronomy. So let's talk about now what we can see and what we will see when we get more time, more observations, and the emergence of what you described as a new a new science really of precision black hole astronomy. You with some collaborators have been actually making predictions the way theoretical physicists like to do. You know, a theoretical physicist makes predictions and sometimes they can be tested in his or her lifetime. Sometimes it takes generations. In this instance, you've made a series of observational predictions the things that you expect can be picked up, and now that will turn to whether they will in fact be be picked up, which is dramatic and exciting. What kinds of predictions have you already been making and when can we expect to see results. I've been working with Alex Sasa, Delilah Gates, and Dan Coppetts, and we are very interested in what happens very near the horizon of of the black hole, right at the edge of that inner shadow, and remind people, just because it's never bad, to redefine it the event horizon. Yeah. So the event horizon is the boundary of the region of space time from which light rays connects escape. So in practical terms, it's the edge of that you're inside the event horizon, you're in the black holiness of the black hole. Yeah. Once you go inside the event horizon, you can never come out, and so your predictions relate to what's happening at that edge, right. And one of the things that we are very interesting in is that black holes can spin around like a top and it's believed that the M eighty seven, the black hole that we've just seen, is spinning at light speed or very near light speed. So there has been claims of this from other kinds of measurements in the literature, and a black hole which spins at light speed does some incredibly peculiar things. Is you get near the edge of the black hole, a long sort of funnel or wormhole forms. It's kind of like a tornado with a long spout. And as the black hole spins faster and faster, that's spout. It sounds like I'm talking about sub sides fiction stuff. But everything with respected black holes though, so go on sounds like I'm talking about sizes fiction stuff. But we maybe seeing this kind of black hole. Now the spout or the wormhole that goes to the horizon, the black hole actually becomes an infinitely long tube protruding out of the out of space doot, and that will lead to about to ask you where where the wormhole leads. But if it's infinitely long, the answer is, yeah, it leads to infinity. It goes, it leads to infinity. But before it gets infinitely long where the wormhole leads it goes into the rise of black hole, and once it crosses there, we don't know. We don't know what's inside a black hole. So the part of the wormhole is in the very edge of the wormhole is at the event horizon, right as it were, and then it extends infinitely away from the black hole and connects on to the space time that you and I live in, and that so we're seeing into what does sound like science fiction. It does sound like science fiction, but we're seeing it, you know, And how would that be seen? I mean, what would that as it were look like? We in our paper gave some very specific predictions about what the polarization of the light coming out will be. It's known that it's polarized. Not that's coming from the black hole, but the lights, sorry, the light and the halo. Yes, it's known that it's polar polarized, but the distribution hasn't been extracted from the data yet. I think they've already seen it. They have these mountains of hard drives the data they need to process, and they haven't extracted from that what the polarization is. Luck will have to shine on us for Are there measurements to be sufficient to prove what you've predicted? Yeah? Right, because they weren't there looking for what you predicted. Well, that's right, and also might not be this round might not be a precise enough measurement for our prediction to be verified or not. But I'd stress that our prediction is a prediction of the Einstein equation. It's just the Einstein equation in a very unusual circumstance, not like the predictions that Einstein made, where the effects of general relativity on the bending of light or in the Solar system they were small effects. Yes here, it's huge effect. Here it changes dramatically the nature of space and time, everything that we really have to to somebody even reimagine what we are, what we mean in ordinary language term. Yeah. So we think that if you were to go in a spaceship to near the horizon of M eighty seven, you would be forced to whirl around it. You couldn't just approach it straight on. There would be a force by the warping of space time that would drag you around like a tornado and pull you down this down the drain into the down drain at the speed of light through the wormhole. Yeah, bow the wormhole to the Yeah, and it would grab you well before you got to the event horizon. So, in practical terms, though it's outside the event horizon, you're descent into the black hole would begin a lot sooner than it. Otherwise it would be if it were really spitting all the way at the speed of light, it would grab you when you were infinitely far away from the event horizon, but suck you there in a finite amount of time by pulling you up to the speed of light. But when you say we grab you when so I'm just trying to get my mind around this and not so much succeeding when you say would grab you the reason you're infinitely far away is that sounds as though, well, we're infinitely we're at some distance less than infinitely far away from M eighty seven right now. Why doesn't it grab up? Oh, we don't know that, because we're not infinitely far away from the edge of the wormhole, and the wormhole could be infinitely long. I don't think it is. You'd have to be going absolutely at the speed of light for it to be infinitely long. But it could be very very long, and so we could be much farther away than it seems. I mean, the rest of the universe exists. The rest of the universe is not presently I take it currently captured by the wormhole right and spinning at some very rapid speed around the black hole, and on the way to the event horizon, we're not headed all headed that way, I take it right. So my question is why, Well, because we're far away week, but when you get to some critical point instance, all of a sudden it's a spinning black hole is surrounded by a science fiction region which was discovered in the sixties called the ergosphere. And life inside the ergosphere is very different than life in this room, and existence rather than life, because nothing's living once you get into the ergosphere. Anyone who enters the ergosphere, which is still outside the black holes, you you are forced to spin around in the in the tornado vortex outside the black hole, and the wormhole is a big extension of that. The wormhole is the is the vortex going Yeah, it is the vortex going down to the black hole. So we what we know really is our distance from the mouth of the wormhole, not how long the wormhole is. Now nobody thinks it's infinitely long, but it could be long enough to be in testing and long enough to make a signal. And how how will the observation of the polarization of the light that presently is visible at the edge of the black hole get you to some better understanding of the of the wormhole. Well, the worm it will verify the existence of of the wormhole, I say. And the polarization is not the only thing um. There are other things that you might try to to to measure. Now I stress it there. We're just one of and not even the most important, what of many groups who are in the vent Horizon telescope themselves are making predictions. Of course, they had to compare their their theory to the theoretical predictions to their observation to get their estimate that they published of the mass. We are especially interested in some of these novel aspects because first of all, because they're weird and interesting and they're there and we're seeing them, and also because they tie in with ideas about the quantum structure of black holes and what's inside a black hole in a very intricate way. And that question of what's inside is hugely controversial and fascinating. So the question of what's inside also philosophical, if I yeah, I venture to use that word. There are philosophical aspects to it, but there is a very sharp meaning to it because, as Stephen Hawking showed, if you wait long enough and even the you know, event Horizon team won't have this much patience. I'd be like a very very long time, the black hole will evaporate and what's inside using quantum effects will come out. And then the question is would the thing that came out, would what was inside to come out and have some information? And then there is an inside that we would ultimately see if we could wait long enough, which I think, yeah, more than billions moves it from philosophy to physics because there would because it's not an unanswerable question. Well, it's a question people could argue about. That's a separate, interesting question. What makes something a physics question as opposed to philosopher ques I was using a shorthand of imagining that physicists only like questions that, in principle could be answered. It's a question which can be answered with a goadoncan experiment when you're do in your mind? Yes, I thought, you can't get the funding to do it? Okay, right, So some people would say infinite time, Well, you don't have infinite time. Some people would say that physics is the study of questions you could answer with real experiments that could be funded. That's a pretty cramp though, view if it wouldn't cover a lot of your your earlier work, wouldn't cover wouldn't cover a lot of my work, right, And I think, to be fair, I don't think that's what most non physicists think. I think it's that would be a very hard nosed, predictive, pragmatist view, and it's not physics if I can't test it, you know, and get funding to test it. Yea. The laws of nature presumably should be resistant to being cabined by what we can fund. But what's exciting to me here is that this observation is touching the edge, possibly touching the edge of the things that bearing on the issues of people that people think about who want to understand what's really inside a black hole. So you mentioned your friend Stephen Hawking, also your collaborator who died not so long ago and with whom you did a lot of work over the years, but most recently you had been working on some pretty major projects with him, also connected to black holes. Yeah, tell us a little bit about that. Yes, Stephen, in his most famous work in the Seven Daies, showed that with an argument that is so simple and elegant that it has never been seriously questioned that when you include quantum effects, black holes are not completely black. That quantum effects allow a sort of the uncertainty principle about where the horizon of the black hole is allows a small amount of light and matter to slowly trickle out of the of a black hole a very slow rate. So those are big things, and let me try a very very lay person's attempt to make sense of that. If we imagined determinative locations and laws of physics, then nothing escapes the black hole. That's what makes it a black hole. But one of the key points of quantum theory is it precisely you can't pin down the exact location of every quantum phenomenon. And since you can't pin it down exactly, that puts enough wiggle room, if you will, into the equation that there is some information in the black hole that might be capable of being discovered. How's that for a first order? That's right. So quantum mechanics says that the horizon and the black hole must fluctuate around a little bit, according must be slightly uncertain, and so that gives just enough wiggle room for a few quantum particles to escape from inside the black hole at a slow rate, so that you began with describing Hawking's famous nineteen seventies that was forty years ago, yep. And he gave an argument that the information about how the black hole was made would not escape, would not come out with this leak of energy and particles and so on. Things would come out, but not the information about how the black black hole came to be made. He claimed, the present does not determine the future and cannot, even in principle, be used to reconstruct the past. Bad news for historians, bad news for hystories for people who like free will in the future maybe, but bad news for physicists because it's equivalent to saying there aren't absolute laws of physics, because a law of physics is supposed to predict the future from the present. It was a very simple argument, and people didn't like the conclusion. It had been questioned in many different ways, but none of the ways in which it was questioned really stuck. So a few years ago I found, while investigating other problems in physics, I came across what seemed to be an error in the original flawed assumption in his original reasoning. Moreover, the nature of the flaw suggested a research program for understanding what really did happen. And I explained this to Stephen and he was very excited about it, and I just say, this is also it's a great model of what scientific collaboration can be and isn't always You find a flaw in an important claim by another famous physicist and you call him up and you say, hey, there's a problem, and that's collegial of you, and then he responds positively, and that's collegial of him. This is the way it's supposed to work in the textbooks. Yeah, and it really does work this way for the for the most part. Yeah, it's heartwarming. It's not like this in my end of the academy. I promise you that. Well, it may be related to the fact that there's no money in my branch of science. I know there's a there's a there's a money in those prizes. But go on. So he and I and his colleague Malcolm Perry, he had some ideas about how to proceed on this and to make sense of it, and so we began a very active and productive collaboration which went on for the last three years with life and we're pushing forward in that direction. It's looking promising, but we haven't delivered the goods, right. We don't know yet that there isn't some reason this is a technical issue rather than the fundamental right. When you were describing how you came up with the original thought that led to this collaboration, my reaction was you were describing how you were thinking about something else in physics, and then you hit upon reason to think that one of Hawking's original assumptions was inaccurate. And it's struck me that's a very andy way to go about things. One of the key features of your contributions across the whole range of areas where you've worked is that you find and see correspondences between different areas of thought physics, math that other people have never hit upon before. That's like the Andy move, as it were, and it's quite a move. So well, I don't think I have a pattern on this move. But it's the structure of the field the physics is. You know, there's many It's interconnected in surprising ways, and it often happens. Maybe I'm lucky enough that it happens to enough times that I'm not sure it looks like a coincidence, but maybe coincidental in nature, but it's not coincidental in you. But anyway, go on, and you know, maybe one could say, you know, our creator didn't have so many ideas that he kept using the same one over overget and you solve a problem in one area and it has a translation into another area. So that hints at a kind of set of structures of unity. I mean, you're sort of kidding about reusing the same idea. What you really mean is that there is an underlying unity and we are describing different parts of reality in different ways. We've got these mathematical tools or these physics tools to describe something, but we're actually describing a more unified underlying phenomenon. Yeah, we have many ideas and we often don't realize that they're the same idea. And is it your belief that there is some directionality here? I mean, now I'm aiming for something bigger, as it were, even bigger than you know, than the wormhole and the black hole? Are you a believer in direction in physics towards more and more unification of our theoretical knowledge? Sometimes people talk about a grand unified theory string theory, to which you've made fundamental contributions. Is sometimes described as a step in the direction of a grand unified theory or an aspiration in that direction. I'm asking you to put it along the line here. You know, the honest answer to that question is, I don't know. People work in different ways. Some people have beliefs that they think that that is how nature works, and they relentlessly pursue demonstrating the physical reality of their beliefs. Others just take the mathematical equations and follow them and see where they lead. And you see yourself in the latter camp. I'm somewhere in between. I have things I believe in, but I pride myself in being ready to drop my beliefs when they don't measure up to the equation. The equations are the final arbiters. The equations and the experiments are the final arbiters of truth in our field, and many people have, including you know Einstein. Einstein had very strong beliefs about how things should be should be, and that got him through special relativity, general relativity, and the beginnings of quantum mechanics. But then he had beliefs about the way the world should be that were being countermanded that we're being own by his own equations, and then the experiments that were validating those equations, and that reduced his his his productivity. M He did pretty well, He did pretty well. Then he did pretty well. But at some point he believed things that weren't true. He believed that quantum mechanics was wrong. He believed their word black holes, he believed their word gravity weight. You know, he had some raw beef, wrong beliefs that he got stuck on. So it interfered with his being able to move on to make the next set of He might have come up with even more fundamental things if he had been able to keep on pushing. That's right, that's right. So that's an argument that you may need some beliefs to get you started. Yeah, but there needs to be some kind of a reflective equilibrium where at some point you have to start believing your equations. Yeah, you know, it's always a conflict between sticking with what you believe in and not giving up, and being too stubborn and not being flexible enough. The real truth is it takes all types. You know, there's some people who have an idea and pursue it in the face of unreasonable hardship and difficulty, and everybody's saying no, and everybody's saying no, and some of those people turn out to be right. Now people turn out to be right, but most of them fall by the way side. Yeah, you need some of You need people with unreasonable beliefs. You need people who are ready to drop their beliefs. You know, it takes a village. Let me ask a final question about how these different pathways to understanding the world are going to play out in the black hole context. Yea. When you started working on black holes, as you said, there was still a view among lots of people that there were no such things right, and now we're in a very different place. We've seen one. Yeah, does that take some of the thrill out of it? Does it seem you know? I mean, it's nice to be right, But there seems like there's a stage of, as you said, great observational astronomy in the space of black holes, which is important and will expand our knowledge and maybe give us radically new ideas about the world. But somehow seems to be confirmatory of what you and others predicted and what is actually now believed to be true. Is there some it takes. I mean it's thrilling now, but ten years from now, will some of the thrill will be gone in working on something which everyone acknowledges exists. No, I think it's only getting more interesting. We can think of this. The last few years, or this observation even is kind of a historical marker. You know, a hundred years ago the existence of black holes was predicted. Now they've been seen in the most straightforward way. So going forward there will be better and better observations. But we still have this huge puzzle. Yeah, the godon Can experient. What is the result of the Godonkan experiment? What's coming out of the black hole? Or equivalently, what is inside the black hole? Then you know there's a fundamental contradiction in the laws of physics as we currently understand them. So that's what makes it so exciting. Something has to give. It's that the thought experiment poses a contradiction between different things that we're we are committed to. All the things that we believe to be true. Can't all be true. Something which we are completely at this moment unwilling to give up as a truth about the universe must actually be wrong, and the fact that that contradictions was recognized forty years ago by Hawking and has sat there. As the years have gone by, the longer it's sat there, the more that we've realized what central importance it is. So somehow the observational astronomy world and the theoretical physics worlds have converged on black holes as the most interesting and things around and it is. I'm pretty confident that well, first of all, I there's no reason we can't ultimately solve this problem. And the fact that it has sat there for so long, I think there is a consensus in the community that we can't solve the problem without a fundamental new insight into the structure of the universe at the same revolutionary level as quantum mechanics or relativity. That it's not a technical problem that we missed a factor of two somewhere. So that's the holy grail. That is the holy grail. It's an exciting thing that black holes have become come to center stage and observational astronomy at the same time as in theoretical physics. We don't have a roadmap how we're going to talk to each other and close that gap. But we're thinking here on a hundred year time scale, we might not even have found the city where the whole grail is hidden, but we've maybe found the continent, and now we're gonna have to keep exploring. But it's a pretty big deal to have found the continent. That's a big deal to have found the kind we know where we're looking and now. And I think you know, Although I'm loath to draw too many non physics metaphoric conclusion from physics, the idea that sometimes we're in the grips of contradictory views and something's got to give, we need some new account to make it work out is about as good a lesson to take away from black Holes as I can imagine. Andy, thank you so so much for your for your brilliant thoughts in your time. Thank you Eddie, thank you Noah. When I see an image like the image of the black hole, I'm filled with wonderment. The mere accomplishment of human beings, to be able to see something so far away, to conceive of it, to make sense of it. That's the kind of thing that really hits me where I live. It makes me believe that being human is actually worth something. After all, we can actually know things and achieve connection. But you know what, when I listen to Andy, somebody who actually understands at the most profound level what these discoveries are, I'm even more struck by the wonderment that he feels than the wonderment that I feel. He's not jaded at all. He spent a lifetime working on black holes, and to him, where at the crossroads of excitement where things are only going to keep on getting better. That's genuine scientific exploration. That's genuine scientific collegiality and collaboration like the kind that Andy has done with Stephen Hawking. And it makes you think not just that the universe is an amazing place, but maybe we at our best when we're not fighting and we're searching for the truth. Are in such bad people? After all? Deep Background is brought to you by Pushkin Industries. Our producer is Lydia Geane Coott, with engineering by Jason Gambrell and Jasonstkowski. Our showrunner is Sophie mckibbon. Our theme music is composed by Luis GERA special thanks to the Pushkin Brass Malcolm Gladwell, Jacob Weisberg and Mia Lobel. I'm Noah Feldman. You can follow me on Twitter at Noah R. Feldman. This is deep background