Into the Impossible With Brian Keating - Delilah Gates: Black Hole Basics! (#156)

Starting point is 00:00:03 Any sufficiently advanced technology is indistinguishable from magic. Welcome, everybody, to this episode of Into the Impossible with my guest, Dr. Delilah Gates. She is one of the world's experts in black hole physics and the mysteries of black holes of which there are many. Delilah, tell me, what is your favorite, most fascinating thing about black holes? I think my favorite thing is that black holes are the only object we know about around which light can travel in. in circular bound orbit. So there's this region around a black hole where if you could sit in it and aim a light rate just right, it would wind around the black hole and you would be able to then see

Starting point is 00:00:44 the back of your head. So I think that's pretty fascinating. In particular, this implies that there are actually, whenever you view a black hole, there are multiple images of the emission around it stacked on top of each other. That's just amazing. And who was the first person to really think about black holes that they could even, you know, possibly be conceived of, if not explored and studied? The first notion of a black hole actually came from way back in around 1783 when philosopher

Starting point is 00:01:14 John Mitchell posited, what if you had a star that had such strong gravitational pool that the escape velocity from its surface was the speed of light or greater. And today we, obviously, when we hear that, we think, oh, he's describing an event horizon. But of course, the idea didn't take off at the time. So everyone was just like, okay, what? Do people really think that dark matter could be made up of black holes? That's something I get asked about quite frequently. Probably not. I don't, I haven't followed literature in this specific topic, but I think the idea more so is black holes can be made of ordinary matter, but certainly if there is dark matter, that you could also have black holes made of that matter as well. So I don't,

Starting point is 00:02:01 think, at least in general relativity, as described by like Einstein, Schwartzschild and Kerr, and the black hole, it's kind of agnostic what matter made up the black hole. So certainly if you have particles that you want to describe which make up this dark matter, it could, of course, form black holes. Black holes could also be formed of just the ordinary luminous matter as well. Tell me, what is a Kerr metric, what is a Schwarzschild metric? What does it mean? What is a metric? Einstein's equations tell us that gravity is really the curvature of space time. And so in the equation, the mathematical object that describes the shape of the space time is what we call the metric. So really, the metric is just the mathematical object that describes the shape of the space time.

Starting point is 00:02:47 Of course, Einstein's equations are very general, and you can throw in different shapes and see if they satisfy the equation. And so if you find a solution that satisfies the equation, then it could describe gravity, in our world. There are particular solutions that describe different types of black holes that are often given the names of those who discovered them. So like you mentioned, Schwarzschild, the first solution to Einstein's equations, which Einstein never expected there to be any solutions that one could write in closed form. Schwartziel did it very quickly. He described a non-spinning black hole that had no charge. And then since then, we've also come to know that there are solutions that describe black holes that can be spinning as well as charged. Specifically, the case

Starting point is 00:03:31 of a non-charged but spinning black hole. This is the one we think describes the kinds of black holes that exist in our universe. You are moving from the venerable Harvard University down to Princeton University, where I understand that one of the predecessors there at Princeton, John Archibald Wheeler, coined the term black hole way back when. And he also said something that black holes have no hair. What does that mean? Black holes have no hair? The idea that black holes have no hair really means that regardless of the matter that went into making them, if they were formed, say, from gravitational collapse, that they're only described by a few parameters. And for the black holes, this could be the mass, the rate at which is rotating or spinning,

Starting point is 00:04:14 and if it has an electrical charge. And that's it. They really captivate the imagination. And in fact, they have more paradoxes associated with them than almost anything. one of which being the famous information paradox. I wonder, can you describe that? I know it's not something you necessarily work on, but people ask me about it all the time. Can you say, is it really that important,

Starting point is 00:04:36 this information loss paradox? And what is it, first of all? So in physics, even quantum mechanically, we believe that there's this idea of determinism, which means if you know what the physics are at one point of time, you can evolve forward or backwards in time and still have enough information to describe the whole situation. The thing about black holes, at least described classically, is that because there are so few details about them, you can't really say once you've thrown everything into a black hole, collapsed a black hole, you can't really say anything about what formed the black hole.

Starting point is 00:05:10 Further, in the 70s, Hawking came up with the idea that black holes should radiate, and this radiation is thermal radiation. And as the black hole radiates, it slowly loses mass. but because the radiation is just purely thermal, that means it carries no information about the mass that went about the stuff that went into making the black hole if it completely evaporates. And so this is the information paradox. How if a black hole eventually evaporates such that there's no, even behind the horizon that we couldn't access, but it's just it's not there anymore? What happened to that information? And we can't reconstruct it from a thermal distribution of radiation like Hawking originally described. There are a couple proposed

Starting point is 00:05:52 resolutions, it could be that black holes actually do have hair and there's fluctuations along the surfaces that you would need to use quantum gravity to describe. It could also be that instead of completely evaporating, the black holes will start to evaporate, but then they'll leave a remnant behind. And then finally, there are those people who say, maybe we should abandon the information, conservation altogether. Another kind of paradoxical aspect of black holes that I hear a lot about is the so-called holographic principle that somehow black holes, because of their mysterious ability to encode or encrypt their information via their surface area, what is the holographic principle? What does that mean?

Starting point is 00:06:36 The holographic principle, it can really most readily be thought about when you think about entropy. So in general, we're used to describing, say, the entropy of a bunch of particles in a box as having to do with the volume of that box. But for black holes, the entropy isn't described by the volume, but just the surface area of the horizon. So it's really proportional to the, not the volume that the horizon would take up or everything inside the horizon would take up,

Starting point is 00:07:05 but just the surface area of the horizon itself. And so this is the holographic principle, that really it's the idea that the physics, the entropy, the information is encoded, on a two-dimensional surface as opposed to in a volumetric way. So it's kind of a hologram. And this is a show for children, but that's friendly for children.

Starting point is 00:07:29 It's not necessarily for children. But I want you to describe what is a naked singularity? And keep it clean, Delilah. Please keep it clean. So despite the scandalous name, a naked singularity is nothing untoward, but still something very mysterious and questionable in its own right. So when we think about black holes, we think about this thing called an event horizon.

Starting point is 00:07:51 And this event horizon is this region from which we can no longer receive information. Once anything has passed the event horizon, it cannot escape back out to someone or send light, even, which is the fastest thing we know that can move. It cannot send any information via light or anything back outside the horizon to someone on the other side. And so in Black Hole Solutions described by General Relativity, behind the horizon, we have what's called the singularity. And this is a point where basically the curvature, at least described in general relativity, appears to blow up. And it could be that there are singularities behind Black Hole event horizons, or we need to then move to really using a different description of the, instead of just classical general relativity. basically as long as you have a horizon, you don't have to think too much about the singularity.

Starting point is 00:08:42 But what if you don't have an event horizon? Well, if you don't have an event horizon, there would be just this point that if general relativity is correct, everything goes to mayhem, curvature blows up, and all this stuff. Crazy stuff happens near as you approach. Can you create black holes in the laboratory and a particle accelerator? Is that a danger? Is that a reality? Are they different than cosmic black holes? So we don't, at least in the energies we have with like the LHC, the Large Hadron Collider, we cannot throw particles together with enough force to cause tiny black holes.

Starting point is 00:09:20 Thank goodness. So we can't make literal black holes that way, but I will say there is an interesting enterprise of trying to create analog black holes. These are tabletop systems using atoms or fluids that behave like black holes. such that you could create little event horizons from which information in one part of the system can't go back to a region on the other side of that horizon and things like this.

Starting point is 00:09:47 So there is a whole enterprise of trying to make tabletop, analog black holes that are tiny that we can see here on Earth and have a better handle on such that we can learn some things. For the moments that matter, choose Kyrad Naturals. Infused with aloeuvrea and vitamin E, Kiraad Natural's bandages protect your own. unexpected scrapes, cuts, and burns, while also moisturizing your skin. Find deeper relief with natural ingredients you can trust to start the healing. When life surprises call for the best,

Starting point is 00:10:19 choose Kyrad, a deeper level of care. Shop the full collection on Amazon or visit curad.com to learn more. Here's a question I asked Janelle Levin, who is one of my friends and heroes, and she answered it, but I'm not sure I understood it, so I'm going to ask you, what's a black hole made of? I thought you threw in all this matter, they eat it up, but they're just, you know, mass been in charge describe them. So what are they made of? Ah, so in general, in principle, in general relativity, they could be made of anything. Realistic black holes, though, are mostly made of the kind of matter that makes up our universe. They can come from gravitational collapse of a star, in which case they would really be made of the same stuff the star would have been made of. So really, they could

Starting point is 00:11:05 be made of any kind of matter we have in the universe. And those that result from supernovas are certainly made of the stuff that was making up the star before it blew up. Last kind of question, actually second to last question just about black holes is, is cosmic censorship? Is that related to this information loss paradox or is that something different? So cosmic censorship is related to the naked singularity I mentioned. So like I said, if we don't have an event horizon and we are still using general relativity to describe a space time that it has a singularity, at the singularity, the curvature would blow up and things like this. And so even though we can analytically with math, we can describe this kind of situation.

Starting point is 00:11:46 The cosmic censorship conjecture tells us that we suspect it's just a conjecture so that it's not a hard proof mathematically yet, but we suspect that any configuration that we could describe with general relativity that would include a singularity has to have that singularity behind an event horizon. Another question I get frequently is, is our universe sort of inside a black hole? Could we envision our universe either emerging from a white hole, a black hole? Yeah, we could be inside of a very large black hole. It could be everything in our universe is inside of the event horizon of a very, very, very big black hole that's bigger than our universe.

Starting point is 00:12:25 The reason for this is one of the things we worry about when we cross a event horizon, you probably have heard about is spaghettification. As you get close to the black hole, the change in the amount of gravity on the side of you closer to the black hole versus a side farther from the black hole would be so different that you would feel like you're being pulled apart. But it turns out the location of the event horizon depends on the size of the black hole. And if the black hole is very big, you can fall past the black hole without feeling very big tidal forces that would spaghettify you. So if our whole universe was just inside of a very big black hole, we wouldn't be seeing any weird spaghettification happening. universe. So technically we could be inside a very big black hole, but it would have to be so big that we might as well not model ourselves as being inside of one anyway. There's a possibility that black holes could have been primordial or can they only form from collapsed stars or gravitational

Starting point is 00:13:20 byproduct of the evolution of stellar life cycle? So this is not my area of expertise, but I certainly do think black holes, some subset of black holes have to be primordial or are most likely primordial. This means they didn't happen because of a star that was already a condensed bit of matter, blew up, it had gravitational collapse, and that's what compacted the matter tight enough

Starting point is 00:13:45 to form an event horizon. It could be that it wasn't stars formed, but just everything of earlier in the universe was kind of a soup, and it could have been, there are fluctuations in the density of the soup at different points, and some of these density, very dense regions could have become so dense

Starting point is 00:14:01 they formed black holes. And certainly, this is probably the case because if we look at the black holes at the center of all our galaxies, all the galaxies in the visible universe, there were called supermassive black holes. And these black holes are just so big. It would take a lot of sustained high energy accretion onto them if they first formed from a star collapse to then continue eating to get big enough to be as supermassive as they are if they hadn't been seated previously from just density fluctuations in the state. soup of matter earlier on in the universe. That reminds me of the new diet that I'm going on.

Starting point is 00:14:38 Have you heard of the black hole diet, Delilah? You know, it sounds like a, sounds like you can eat anything you want. You lose weight because you just, you just eat light. Oh my goodness, that's a really good one. I have to use that. That's an old one. That's an old one. I have more, if you want. Okay, now I'm going to go into some personal question. Would you like to go near a black hole's event horizon as a tourist? Only if it was a very big black hole and I wouldn't get spaghettified. Right, because if you get spaghettified, don't forget Delilah, you passed away. All right, that's another joke.

Starting point is 00:15:12 I can't help myself. No, I love them. I love tons. Keep them coming. You look like your dad. I want to talk about your dad in a bit. But next I want to talk about academia and being a graduate student. So you just finished up, your newly minted Ph.D.

Starting point is 00:15:26 You learn the secret handshake. We can do it now. You're going to be what's called a postdoc. Tell me about your academic world line. How did you get to work? you are. Your parents are both academics. Your mother's a well-known physician. Your father's a famous professor. He's my, I guess he's like kind of like my ultimate boss. He's the President of the American Physical Society. He's a big shot professor at my alma mater, Brown University.

Starting point is 00:15:51 So tell me, obviously they played a role, but you also took a very different tack in many ways. Tell me about your academic interest as a young person and then how you guided yourself. Yeah, so I also, I will say, I have a twin brother. He is a PhD student in my biology right now. And so when we were little, our parents never tried to convince us of what career we should take. They just wanted us to choose something where we would be able to support ourselves. But even so, in our household, given just what they study, there was always a lot of kind of math and exploration. But it happened through games. So we used to have fun counting games, adding and subtracting rubber ducks in the tub, or we learned to divide because we were twins and we wanted to divide everything evenly, so we would divide purposely my father or mother would put an odd number of breakfast sausages. And so we would have to think about how to divide them so that everyone who was eating could have equal amounts of food.

Starting point is 00:16:55 So from a young age, math was always kind of this fun kind of little game. And then we also used to play with different things like, I remember when we figured out you can bounce light off of mirrors by just shining flashlights and playing with the reflective toys we had in our rooms. And then we would be so excited we would call our parents over and show them what we'd figured out. So it started off as just fun in games. And I always enjoyed science and math, even in high school. But in high school, I wasn't exactly sure what I wanted to do. there was, I liked music as well, I played clarinet. And then of the kind of science and math, I really enjoyed chemistry. What I enjoyed about chemistry was when we would talk about the structure

Starting point is 00:17:39 of atoms. And when I learned that they weren't these, the just Newtonian model where the electrons are just on these toy little bound orbits, but instead had these clouds. People told me to understand that mathematically what you needed was quantum mechanics. And so it was at the end of high school that I decided chemistry slash physics or music. When I was trying to decide a major, I went with physics because I figured I was not an amazing musician and I could play music as a hobby, but I couldn't do the same with physics.

Starting point is 00:18:15 So that's kind of what I wanted to go into in college. And as I took my classes, it was really getting more and more into the world of the small and the structure of parts. and things like this that really got my interest. And so I really started to go down the root of particle physics, and I picked up a double major in math. And then I came to graduate school,

Starting point is 00:18:36 and I was kind of trying to figure out what I wanted to do. And I did a couple rotations. So I knew I wanted to kind of probably high energy theory, thinking about particles, and in fact, I do think about light, but I also think now about gravity and these giants, black holes. And so what led me to really that was, was I took a detour from just high energy physics and did a couple rotations. One I did in astrophysics and one I did in cosmology.

Starting point is 00:19:01 And it was really these that informed what I wanted to do within the high energy theory realm of study that led me to what I do now. It's a nice marriage between thinking about particles and using the really nitty-gritty of the analytical, mathematical to describe things that are relevant to observation in these giants of our universe. Yeah, it's kind of amazing that the smallest things in the universe influence the largest things in the universe. And conversely, you can learn about the smaller things in the universe from the largest things in the universe. Did you, besides your parents, obviously, one of whom I've had on the show, and I want to have your brother on the show, we've had on, I think I've had on, you know, six or seven parents of twins. I'm a parent of boy girl twins. I think you're the first twin that I've had on. Twins are great because you can do experiments with Einstein, you know, twin paradox, etc. But I do want to have on your brother at the same. I'm a friend. I'm a friend. I think you're a friend. some point. It's cool that you beat him to the PhD. You're older than him, I forgot. By one minute. Yeah, my son, my twin boy is older than my twin girl by 15 minutes, but a really brilliant man by the name of Sylvester James Gates told me once he said Einstein wasn't always Einstein.

Starting point is 00:20:15 And I used that line on a man by the name of Barry Barish, who knows a thing or two about black holes. And he told me an interesting story about Einstein. He said, when he, he said, when he went up to accept his Nobel Prize in 2017. You have to sign this register, this logbook that says, I got my Nobel Prize from the King of Sweden. And he said, I'm kind of curious. So he wanted to see who else signed the book. So he looked back and he saw Richard Feynman. Wow. Holy cow, there's Richard Feynman's name. He saw Marie Geppart Mayer. Her name is in there. Marie Kempart, Mayer. He saw Albert Einstein. And he said, I never felt like I had imposter syndrome more than that moment. And I said, that's amazing, you know, you probably felt, don't feel it anymore. He goes, no, I feel it even more than ever.

Starting point is 00:20:59 And I said, you win the Nobel Prize. You still feel that. He said, I didn't feel worthy. And, and I said, well, Barry, don't you feel like even Albert Einstein felt that way? And your dad even said that. Your dad said, you know, Einstein wasn't always Einstein. And if you make this notion that only Einstein's can do science, then we're going to eliminate the next Einstein's. And I think that would be a great tragedy. So I love this idea of self-care and actually just making time that we're not what we do. And despite these kind of notions that we're just like supposed to be these just like we get everything right. Everybody's got imposter syndrome. That's the dirty little secret.

Starting point is 00:21:38 And we have to recognize that we are unique and we all have a gift and we all have something to give. So speaking of your dad, speaking of Einstein, you know, he wrote a book, you know, proving Einstein right with his. co-author Kathy, Ed, we had him on the show for that and had him on also last summer. He's a frequent guest. I want to say he's been a huge influence on me and many scientists around the world. Father's Day is coming up. I wonder, do you have anything you'd like to say to him on this Father's Day occasion? Of course.

Starting point is 00:22:09 So we had a, my dad and I had a great time hanging out during the pandemic. So I just want to say, you know, thanks for taking me in during the pandemic, dad. It was so much fun to hang out with you. Happy Father's Day. And I can't wait until we can get together next. Well, as Newton said, the, you know, the apple doesn't fall far from the tree. The black holes don't orbit too far around from the event. I don't know.

Starting point is 00:22:31 I'm just making that up. You know, what they say about, you know, people that study black holes, they have to be pretty bright. I'm not that bright, so I couldn't study it. But Delilah, you are a delight, and I wish you such good luck. I hope I can see you again in person. We haven't been together in a couple of years since 2019, but I'll hopefully be in Princeton and see you on the East Coast many times in the future. I can't wait to see where your career goes. It's just so exciting to see someone so creative, inventive, and working

Starting point is 00:23:02 so hard on the forefront of the most important problems in science, in my opinion. So thank you so much for going into The Impossible with me today, Delilah. Have a wonderful rest of your summer, and good luck. And make sure you rejuvenate and recharge your batteries for what's to come. Thank you for having me. Any sufficiently advanced technology is indistinguishable from magic. Thanks for listening to End of the Impossible with Professor Brian Keating. Please support the show by rating, commenting, sharing, and leaving reviews. We appreciate hearing from you, and it really helps keep our universe expanding.

Starting point is 00:23:38 Watch our YouTube channel at Dr. Brian Keating. That's DR. Brian Keating and join our premieres Tuesdays at 8 a.m. Pacific Time. Follow Brian on Twitter and Medium and support us on Patreon at Dr. Brian Keating. exclusive content, visit Brian Keating's website and sign up for his informative newsletter at Brian Keating.com. Into The Impossible is produced with the Arthur C. Clark Center for Human Imagination in the Division of Physical Sciences at the University of California, San Diego. Produced by Stuart Volko and Brian Keating.

Into the Impossible With Brian Keating - Delilah Gates: Black Hole Basics! (#156)

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