Black Hole Questions!

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Speaker 1: Hey, it' Jorhan Daniel here, and we want to tell you about our new book. It's called Frequently Asked Questions about the Universe because you have questions about the universe, and so we decided to write a book all about them. We talk about your questions, we give some answers, we make a bunch of silly jokes as usual, and we tackle all kinds of questions, including what happens if I fall into a black hole? Or is there another version of you out there that's right? Like usual, we tackle the deepest, darkest, biggest, craziest questions about this incredible cosmos. If you want to support the podcast, please get the book and get a copy not just for yourself, but you know, for your nieces and nephews, cousins, friends, parents, dogs, hamsters, and for the aliens. So get your copy of Frequently Asked Questions about the Universe is available for pre order now, coming out November two. You can find more details at the book's website, Universe f a Q dot com. Thanks for your support, and if you have a hamster that can read, please let us know. We'd love to have them on the podcast. Hey, Jorge, why do you think we get so many questions about black holes. Well, you know, it's the mystery. You know, they're so inscrutable. They're like the reclusive celebrities of the universe exactly right, Like the more they avoid the paparazzi, the more people want to know about them. That could be true, but I was actually wondering if it might be the exact opposite. What do you mean, Well, what if black holes are like the car crash of the universe. They're like a cosmic disaster that you can't drive by without slowing down to check it out. Saying physicists are just rubber neckers, cosmic rubber neckers. That sounds kind of dangerous, like you might cause another accident by not watching where you were driving your spaceship. Exactly. That's the gravitational runaway effects of the black holes. Slow down to check it out, get sucked in, make a bigger black hole. That's how I feel about driving in Los Angeles. It's like an infinite black hole that you will never escape. I am Jorge made cartoonists and the creator of PhD comics. Hi, I'm Daniel. I'm a particle physicist and a professor at U C. Irvine, but I almost never go up to Los Angeles. Really do you avoid it like a black hole. If it was a black hole, it would suck me in. So yeah, I'm trying to stay in orbit around Los Angeles instead of falling into the singularity, yes, where time slows down through plastic surgery apparently. But yeah, I mean you're kind of famous now, Daniel. You don't get calls from Hollywood these days. I screened my calls, so if they're calling, I'm just not picking them up. You look for the aira code. If it's your local air code, it's ma'am. If it's three one oh, then it's someone from Hollywood, like Jorge, so you just hang up. Also, you know, there's famous and then there's Los Angeles famous. You can be like super famous in Orange County and be nobody in Los Angeles. But anyways, welcome to our podcast, Daniel and Jorge Explain the Universe, a production of I Heart Radio, in which we ask all the biggest and famous and most time dilated questions of the universe. We ask all of them about where it came from, where it's going, what it's made out of, and how it all works. We dive deep into the questions about black holes and neutron stars and galaxies and tiny particles and quaisars and everything in between, because we think it's possible to download all of that into your amazing brain and hold for a moment an understanding of the entire universe. Yeah, because it is a pretty famous universe. Everyone seems to know about it. Everyone's fan. I would hope, you know, it's everywhere he got. He can't get away from this universe, and it's pretty fascinating, even it's black sheep. You know, everyone wants to know about the black Sheep of the celebrities. Yes, have you been checking out the universe's reviews on yelp? Yes, I think it. It has about infinite stars and also infinite thumbs, but you know it's about fifty up and them. That's right, And you know nobody has any other are alternatives. It's not like people like, hey, I was in this other universe the other day and they have better chips. So you know, this is basically all we got learned to love at people. Maybe you just need to get out more than you You might find other universes if you just, you know, get out of your Orange County Bubble l A does seem like another universe sometimes, not just because it's weird, but because it takes forever to get there. Definitely an alternate reality for sure. But anyways, Yeah, people are curious not just about the universe but about the things in it, especially things that are extra mysterious, and those are the things that drive physics. We look around in the universe and we say, do we understand how this works? Does that bit over there makes sense? And if it doesn't, then we focus our brains on and try to understand how could that possibly work? How could that make sense? How could that be consistent with what we know about the nature of space and time and energy, And so the weirdest things are also the best opportunities to learn something about the universe. Yeah, because when you look around, I guess it's all pretty bright and beautiful and majestic and cosmic, but everyone's in a When you look at into the universe, there is a basically a big hole, like a big hole in our knowledge and also literally figuratively and in all the ways there there are actual holes in the universe. There are holes in the universe, and you know, to answer the question to our intro. I think one reason that they're fascinating is because they are so different from what we experience. You know, it's not just like, hey, there's a banana out there in space, like we know bananas, We bananas, were familiar with bananas. You know, it's something out there in space which is so different from our everyday experience, so bizarre that we just sort of like want to see it. Yeah, and so to be on the podcast, we'll be tackling unanswered questions about black holes. Now, Daniel, I assume it's not just bananas out there. We don't know, you know, maybe bananas are the fundamental element of the universe and it is just all bananas all the way down. That's a viable theory. It sounds like a slippery slope there. We just gotta peel back the layers of reality until we reveal the banana inside. But yeah, black holes. A lot of people have questions about black holes, and you're asking me earlier why they're so mysterious. Like everyone, you get a lot of questions about black holes, right, Yeah, I say like a third of all the questions we get are about black holes. What happens if you fall in them, What would they look like if you did this? What would happen if you shoot two black holes at each other? All sorts of questions people love to think about black holes. Interesting a third of the questions. That's amazing. It's like, it's some black hole in your It does make my inbox pretty dense. But I love it. I love thinking about black holes just as much as our listeners do for the same reasons, you know. And the cool thing about black holes is that we all understand them about as well, you know. I love that we can bring our listeners to the very forefront of knowledge, because in the case of black holes, it's not that far away. You know. We just don't understand very much about these weird, mysterious objects. I think that's why they're so fascinating to physicists, because they represent such a great opportunity to learn something new and shocking about the universe. Yeah, so today we're answering questions that we've gotten about black holes from listener. It's just like you, and we've got three pretty interesting questions, one of them about the mass of a black hole, about mini black holes, and also about whether or not black holes can explain dark matter. So let's jump into our first question right away here, and it comes from Levi from the Ukraine. I didn't know m Levi are Ukraine, and I had two questions about my favorite topic, which is black holes. First, how is the mass of a black hole calculated? And second? Is there anybody to know when an event horizon of a black hole begins? If I were to say, take a rocket ship to the black hole and this sene our galaxy, is there any way that I could know when I need to turn that thing around before I become spaghetti? Thank you? M M. Interesting question? Now? Was he allowed two questions? I feel like he's not good extra question in his question imploded into a black hole because of its density, he had it multiplied. It seems so you just can't stop asking questions. Once you start thinking about black holes, the questions just proliferate. What do you think it's captured the imagination of not just our listeners, but it seems like everyone out there has questions about black holes. I think it's just the opportunity to see something hidden, to learn something new. You know. The thing that captivates me about the black hole is knowing that one of the greatest mysteries in modern physics. How to reconcile crazy intense gravity and quantum little particles, how to bring those together into one idea is out there, and it's hidden inside a black hole. So if we could only peek inside, we could learn the very nature of space and time. There's so much we could know by the universe if only we could see inside a black hole. And yet he's hidden from us. So it's sort of like somebody saying, I have the secrets you want, and they're written on this envelope and I'm gonna burn it. I'm gonna throw in the fire instead of opening it to you. That would kill you. Oh man, if you's so frustrating to know the answers are out there and not be able to get them, that's very frustrating. These there a big red button into that envelope. That would drive doubly crazy. But all right, let's jump into Levi's questions here. The first one is how do you calculate the mass of a black hole? Now I'm guessing down or there are not gigantic scales we can use to measure the mass of a black hole, A sort of if we can Yeah, scales work by using gravity. Right, If you put something on a scale, you're measuring its weight, and its weight is the force of gravity on it, which is determined by its mass. And so to measure the mass of something you can use the strength of the gravitational pull on it, which depends on the object's mass. Now out there in space, You're right, there's not some like massive scale we can put it on. But we can see how the black hole tugs on things around it which are visible, and that's one way we can measure its mass, and so you can see the effects of its mass on the things around it. I guess kind of like our son, right, Like if our son with a different and mass, like if it was bigger or smaller than our orbit around it would be different. Right, Like you could tell what the mass of the Sun is maybe from our orbit. Yeah, if you measure just the velocity and location of the Earth as it moved around the Sun, you can deduce exactly the mass of the Sun because you can tell what gravitational force is necessary to move the Earth in that path, and that would tell you how much mass you need to provide that gravitational force. So, yeah, the Earth is like a little scale that's measuring the Sun all the time. But what do you need to know the mass of the Earth too, pretty accurately? Yes, absolutely, you need to know the mass of the Earth. And don't say you just use the sun, because then now we're in a circular argument. No, you need to use the mass of the Earth. Absolutely. The mass of the Earth you can get using like your knowledge of what it's made out of and it's volume. So if you know the radius of the Earth, like its size, and your understanding roughly what it's made out of, then you can tell its mass, or you can bootstrap. You can say, well, I'm gonna look at the moon and see how the moon moves around the Earth, and that's going to tell me the mass of the Earth if again you know the mass to the moon. Yeah, and so on and so on. I guess at some point, maybe the question is at some point when do you have to guess? Right, because something you have to guess what the moon is made out of, or even the Earth you cannot have to guess. I mean, we have some measurements, but we ultimately you're sort of guessing what's inside the Earth. Yeah, in the end, you do need to know the mass of one of the objects to measure the mass the other. But there's also some constraints. They're like, what you really need to know is the product of the two masses, right, mass one times mass too. So if you make enough measurements of pairs of objects and you can narrow that down, you get like enough systems of equations that you can constrain it. But yeah, you also do need to say something about what they are made out of to get some information about how much mass one of them has. You can also measure the mass of the Earth by flipping that around and saying, here, I have an object whose mass I know, and that can measure the gravitational effect on it, and from that I can measure the mass of the Earth. To build like a calibration object, like a test object, like a one kilogram pound of platinum or something. Yeah, you can see how much it pulls on like a known weight, and then that's how you would estimate the mass of the Earth. And that's just sort of definition. All you say, like, this is the definition of a kilogram this object, and from that you can measure essentially the ratio of its mass to the mass of the Earth. You can say how massive is the Earth in terms of this object I'm defining to be one kilogram, and then you can bootstrap your way up to the Sun and basically everything else in the universe. Right, you can strap your boot. You can boot your strap. But what about for like a black hole? I mean, they're so far away, we've barely seen one directly. You know, we can see the things flying around it, But how do we know what those things are? I mean, they're just like bright little pinpoints, right, yes, So one way we can see the black holes exist is by seeing their gravitational effect on stuff nearby. Because black holes, of course are black, they don't admit any radiation directly, or if they're emitting hawking radiation, then we can't see it. It's too faint. So you're right, we need to know the mass of the objects nearby. And so, for example, the black hole the center of our galaxy has some stars whizzing very close by to it, and we can measure the mass of those stars by looking at the light they emit, because we have a pretty good model for how the brightness of a star is related to its mass. So we did a whole episode on how you measure the mass of stars. And that's not perfect, it's not exact, but it's pretty good, right, it's based on like models and some observations, and so just from the light that you get from those stars around the black hole, you can say, well, that's a a stage so and so star weighs about they usually wait about this much and so there, and it's curving around the black hole this much. So therefore that black holes probably there's many kilograms exactly. And those models are pretty good, and we validate them using binary star systems where we can see two stars, we can measure their brightness, and we can see how they move around each other, and so we can really validate those models pretty well. I mean, there are uncertainties, but we can trust those because remember there are a lot of binary star systems out there in the universe, many more than you might expect. So that lets us measure the mass of the stars and from that deduced the mass of the black hole. Because remember, black holes don't emit any information from their inside except for the total mass of the black hole, which can be deduced by its gravitational effect. That's the only information that comes out other than the black holes spin and charge. And also do you have to account for like the camera adding ten pounds, like does the telescope at you know, ten million kims? No, the black holes agent is very particular by the cameras. We used to take their pictures nicely. These is doubles. When it's taking the naked pictures. I said, take a profile above the accretion disk. That's when it looks good, all right. And there's also sort of a different way to measure the mass of a black hole, which is by looking at its size. Like if we ever do get better pictures of a black hole, you might be able to tell how heavy it is by just seeing its size, right, Because the size of the event horizon depends on the mass of the black hole. Yeah, they're very closely connected. As the black hole eats more and gets more mass than it is gaining in size, the size the event horizon is growing, and so if you could measure the event horizon, then you could deduce its mass. Measuring the event horizon is tricky though, because you need to see photons like whizzing around it. So you need a direct picture and we've done that for one, maybe two black holes now. But it's much harder, obviously, And so that brings us to the second question leave I had, which is like, if I'm trying to check out a black hole, like, could I tell where the actual event horizon is? Like, at what point do you want to make sure you turn around before you get sucked in forever? Well, I would say turn around now, do not take that trip to the black hole. It's not a good idea. Don't even buy the ticket sets when you should turn around. Right, So it is a good idea to think about where a black hole begins, where it's event horizon is, so that if you are a billionaire scientist, entrepreneur and you do take that trip to the center of the Milky Way to study the black hole, you know when to turn around. And one thing you could do, if you know the mass of the black hole is, you could just calculate it. You could say, well, I know how massive it is, so I know the point of no return. I can calculate the event horizon. So, yeah, there's a point at a distance from the center of the black hole at which now even light can escape, right. I think maybe that's what LEVI is asking, Like, what's the point where not even light can escape. That's the event horizon, and from a distance you can sort of see it, right, Like, it's sort of where when you look at a black hole, and we've looked at one, it looks like a big black circle, and so that's generally where the event horizon is, although it's not exact right. That's right, the black circle you see when you look at a black hole is actually bigger than the event horizon because you can't see photons that like fly just above the event horizon from behind the black hole. Those we get curved and fall into the black hole. So there's the event horizon itself, and then there's like a shadow that the black hole makes that's even larger than the event horizon. You can get closer than the shadow, you see it looks bigger than it actually is. And as you get closer and closer to the black hole, that shadow grows and it grows to take over more and more of your view. So if you're very close to the black hole, for example, then it might appear to take up like half of your entire view. Right. That's kind of the tricky thing about black holes is that there's so much distortion around them that you know, from afar, they look like a nice clean circle, But as you get closer, everything gets distorted and kind of blown out of proportion, and so it's gonna be really hard to tell when you've reached the actual event horizon, right, because, like you're saying, the black hole is gonna start taking a bit more and more of your field of view, and you're gonna be like in my inn or am I out? I don't know, yeah exactly, And so this is very dangerous not to be recommended or endorsed. But as you get closer and closer to the black hole, the image of it grows larger and larger, and as you say, what you're seeing is not anymore a good representation of what's actually there. Like when you look around yourself in your room, the stuff you see is the stuff that's there, because the light is moving in a straight line from whatever it is to your eyes, and so you can look around and say, oh, that's over there and this is over here. But if there are like lenses around you that bend the light, then you get distorted images. Imagine you're in a fun house mirror. What you see is not what's actually there, and that's what's happening with the black hole. Light is no longer following straight lines, so what you see is a distortion. And it's really interesting. As you get closer and closer to the black hole than the shadow of the black hole, this big black image of the event horizon gets larger and larger eventually becomes more than just half of your view. It like takes up most of your view, and the rest of the universe is squeezed down into a smaller and smaller circle. And you can get a clue about when you're back to cross the event horizon, because when you cross the event horizon, that circle that there's the rest of the universe is now shrinking down to a tiny little dot. And once you fall inside the event horizon, then the rest of the universe is now exactly one tiny little point where light from the universe can still reach you. Yeah, it's a pretty trippy experience and pretty extreme and and actually, if you want to know more about this, it's conveniently a question we answer in our new book. Right Daniel frequently ask questions about the universe. That's right, This is a frequently asked question. What would it be like to fall into a black hole, and the book is a lot of fun. It's out on November two one. You can check it out at you reverse f a q dot com. It's filled with answers and a bunch of really awesome cartoons at or he drew. They give you a sense for what it would look like to fall into a black hole. Yeah, order a copy for yourself, for your nieces and nephews, uncles and best friends. But we do sort of go into a lot of details because there are a lot of details about going into the black hole, and I'm not sure we can cover all of them. So please check out the book if you are actually that curious, because there are a lot of complications, like not only does the black hole take up your whole field of view, but also like it's possible for you to get inside a black hole without getting stretched into spaghetti. It sort of all depends on these details about the mass of the black hole, right, And that's right. So if you're interested that, dig into that copy of that book and let us know if you have any follow up questions. All right, So, the basic answers for Levi is you can calculate the mess with a black hole by how the things around it are moving. And also when you need to turn around when you visit a black hole, before you visit a black hole, when you need to turn around right exactly before you start arching Airbnb for black hole opportunities. Yeah, don't believe those pictures. They distort the space inside of the airbnbs. All right, let's get into our two other listener questions about black holes. One of them is about mini black holes and the other one is about dark matter. But first, let's take a quick break. All right, we're answering questions about black holes from listeners, and you get a lot of questions about black holes. I do. I have a lot of questions for about black holes. I read a lot about black holes, and we get lots of questions from the listeners about black holes because everybody wants to know what's going on. I see, And what proportion of the questions you get do you actually know the answer? We'll have a wonderful backup, which is if I don't know the answer, I just send them a link to our book we have no idea and say that's the answer. Go buy a copy of the book. Oh boy, you're plugging away today. I'm plugging away. But also I think people like to hear that the question they've asked is not one that has an answer. Of course people would like to know the answer, but it's also satisfying to feel like, Oh, I'm at the forefront of human knowledge. I have questions, just like Kip Thorne has questions, or just like very Barish has questions. These Nobel Prize winners who also don't understand what's going on inside a black hole. Welcome to the club, the curious about black holes club. All right, so our second question is from Tim and he has a question about mini black holes. Hello, Daniel, Joaii, and Katie. I've got to question about many black holes. If you were to have some super large head dron collider and create miniature black holes that immediately disappear with Hawking radiation, how would you detect that Hawking radiation? And what would you learn since all the information other than the mass of the black hole is essentially destroyed? Curious about the answer? Shoots? Alright, awesome question here. There's a lot in this question. There's the idea of MENI black holes, there's the idea of Hawking radiation. And he asked about quantum information. I know so many good questions and so many fun opportunities to learn about black holes by creating them a particle colliders. All right, so let's dig into it, Daniel, What is a medi black hole? I guess it's just a small black hole. Are there's possible? How do you make them? Yeah? Black holes can come in almost any size. There is an absolute minimum size to a black hole, but it's pretty small. You can make a black hole that's the size of the galaxy. You can make a black hole that's like, you know, the size of a particle. Almost The crucial thing is not the mass, it's the density. If you compact enough stuff into a small enough space, then you can create a black hole. Is this combination of mass and radius. You know, for example, if you took the Earth, you could compact it into a peanut and that would be a black hole. So the mass of the Earth is enough to make a black hole, is just not dense enough. And so you can make many black holes by poor enough energy or enough mass into a small enough space. And that's what you do at the large Hadron collider. Right, you think you're making mini black holes, or you know you're making mini black holes. We hope we're making many black holes. We haven't yet seen any. But that is exactly what we do at the Hadron Collider and it Aeron Collider, is that we pour a lot of energy into a very small space and we let the universe decide what comes out. We take advantage of the quantum mechanical nature, the probabilistic nature of the rules of physics that say, if you have a little ball of energy there, it can basically turn into anything. It might turn into some new particle you haven't seen before, it might turn into a black hole, right, And so you sometimes you get enough energy pack into such a small space that you make a mini tiny black hole about the size of like a particle. And so those are actually black holes, just like the ones at the center of the galaxies. They're just really really small, and something special happens to them, right. They don't last very long, that's right. And so to be clear, we have not to our knowledge made any of these black holes. We have not seen any. It's hypothetical to fear radical idea that perhaps it's possible to make these black holes by colliding particles together. And so we are looking for them, and the thing you have to understand about many black holes is that they don't last very long. Like big black holes can last for billions of years as they keep eating stuff. But all black holes emit radiation. They don't actually keep all of their information is inside. They leak a little bit of mass all the time. It's called hawking radiation. And this happens faster if you're a small black hole. So a big black hole hardly emits any hawking radiation. It can last for a long time. A little black hole will very rapidly evaporate by giving away all of its mass in terms of hawking radiation. So the smaller the black hole is, the quicker it disappears, which is actually good because you want your black holes to evaporate rather than growing and gobbling up the earth. All right, So then the tiny black holes evaporate quickly. And the question I guess is can you detect that hawking radiation? And what would you learn from it? Yes, So these black holes, if you made them, they would basically explode almost instantaneously. The kind we're talking about making it the large Hadron collider would last like ten to the minus twenty seven seconds, and they would just admit a bunch of hawking radiation. But what is that hawking radiation? And how would you see it? The cool thing about black holes is that they couple gravitationally, right, They're connected to everything that has mass. They don't care about things electric charge or strong charge or weak charge, so there's sort of democratic. They turn into like all kinds of particles with basically equal probability, And so that means that what you would see is just a huge spray of a bunch of different particles, like a huge explosion at the center of your detector, with a lot more energy than you would typically seem I see, but you're eagually like to see like an electron or a proton or men kind of right. I mean, depending on how much energy they have, they might be more probable, but there's no constraint about what particular particles you'll see, that's what you're saying. Yeah, And because the particles that feel the strong force, like quarks and gluons, have so many more varieties, because for example, for the upcork, there's the red upcork, the green upcork, and the blue upcork, where the electron doesn't feel that, and so it only has one version. That means there are more versions of quirks and gluons, So you're more likely going to get quarks and gluons than electrons and muans, just because there are more of those, and black holes are democratic, So most likely what you're gonna see is a big spray of quarks and gluons that fly out, and quirks and gluons. We don't see those directly because quirks and gluons can't be by themselves, so instead each one turns into its own stream of particles. So what does a black hole look like? In our detector at CERN It looks like seven or ten streams of particles all coming out of the center of the collision. Well, I think the question that Tim had was like, could you learn or would you learn anything from that stream of particles? And it sort of seems like you wouldn't write because it just be a random spray of particles, right, Yeah, And this is a subtle point here, because you can't look at an individual collision that has like ten of these sprays of particles and say that's a smoking gun signature of a black hole, because there are other ways for that to happen. Sometimes two protons collide and you do get ten quarks flying out, which makes ten of these streams of particles. So that does happen. So we can't specifically say this was a black hole, that was a black hole. All we can do is say, look, we see more of these collisions that lead to ten or twelve sprays of particles than we expected from non black hole sources. So we can like statistically say we think we're making black holes because we see more of these weird kind of events than we can explain otherwise. And this weird kind of event is just what we expected to see from black holes. So we can't definitively say a black hole is created on Tuesday at four pm, but we can't say over the last year, we think we made ten of them. Well, I see, you can't study like a particular mini black hole. You can study kind of like a statistically what's going on in your collider. But I think Tim was sort of making the connection to this idea that we've talked about before, which is an inside of a black hole, quantum information is destroyed. So does that mean that when a mini black hole evaporates, there's no information in the Hawking radiation. Yeah, this is not something that we understand because we think that quantum information can't be stroids, and so we wonder if somehow that hockey information does have encoded in it the quantum information that went into the black hole. And we had recently a fun podcast episode where we talked about people who recently made a breakthrough about how this might work as super fascinating, but it's not something we understand very well. But the information is being destroyed in a black hole is just about the particles that went into it, which is like the two protons you smashed together. So you don't really care that much about that quantum information. It's not like useful or interesting. But if you do make black holes, you can learn something much more interesting about the universe. You can gain like contextual information because you can learn something about quantum gravity. If we make black holes with a large Hadron collider, it means that gravity is much stronger at very short distances than it is at long distances. Something weird and different is going on when two particles get really close together, their gravity gets different, and that's a clue about maybe the whole nature of space, about how many dimensions there are two space itself. Well, what do you mean, Like you would shoot things together, create many black goals, and then you would see how it interacts with the things around it. Like, can you actually get a sense of, you know, what happens as you get that close to mini black holes or is it maybe hidden in the fact that you do or do not get mini black holes. Yeah, it's the fact that you make black holes, and also their typical energy tells you something about how they are made. You can't study an individual black hole or like put things near it or anything like that. But one thing we are really curious about is why gravity seems to be so weak. You know, gravity is so much weaker than all of the other forces. Like we say, often you can defeat the entire gravity the Earth by using a simple kitchen magnet to pull on a screw, for example. So why is gravity so weak? It's not something we understand. One possible explanation is that maybe gravity is so weak because it's leaking out. It's like getting diluted. Because there are other ways that you can move through space other than the three were familiar with. So these are called extra dimensions, Like maybe space doesn't have just three dimensions, maybe it has eleven or twenty six, but only gravity can feel those, and so when you're far away from something, you're not really feeling it's true gravity because most of it's leaked out into these other dimensions. But these other dimensions might be really really small and compact, so if you get really close to something, you might feel it's like true strength of its gravity. So the idea is if you smash two protons together and you bring them really close together with enough energy, then they might feel that strong gravity enough to make a black hole. So the fact that you made the black hole would tap you off that gravity is getting strong at short distances and maybe reveal something about the existence of those other dimensions of space and time. So you're saying that if you do make black holes at the large Harding glider, then maybe that points to the existence of extra dimensions. Yes, exactly, so we can't learn that much from one black hole, but if we can prove that we have been making them, then that suggests that there must be extra dimensions space and time, and the pattern in which they appear, like the energy that they come with and how often we make them, can give us a clue to like how many dimensions are there and what radius do they have, because these aren't dimensions like the ones we're familiar with, like x, y, and z that we move around in. These are like a little looped dimensions. They're like moving a little circle, or they are only like a centimeter wide. They're really weird and strange dimensions. But lots of theories of physics actually insist on having more dimensions, like string theory. Yeah, and conveniently that's another topic we cover in our book. But it sort of sounds like the answer for tim here is that we haven't detected any mini black holes in you're in the colliders, but if you if you do create them, hey, you would see this big shower of sort of random particles, maybe mostly quirks, and be would point to the existence of extra dimensions. That's right, that's one explanation. There are other theories that also predict the creation of black holes, and so if we did see them, the theories would go crazy coming up with new ideas to explain our data. It would be very very exciting. And for those of you nervous about the safety aspect of this, don't worry. We've done all the calculations and we're confident we can't make black hole is big enough to eat. That's good to know, always reassuring that you've done the calculations and that you never make mistakes. Right, that's right. We've never ever made a mistake that destroyed the Earth. Right, that's a pretty good track record. Yeah, yeah, so far zero for zero. All right, well, let's get into our last question about black holes from a listener, and this one has to do with dark matter. But first let's take another quick break. All right, we're answering questions from listeners about black holes because they're so cool and mysterious and dark. And our last question comes from Jue, who has a question about whether black holes can explain a little bit of missing mass. If there's missing gravity in the galaxy, why can't we attribute it too the black hole in the center of it since we don't know it's mass. M interesting question, and first of all, we're missing mass, like did we misplace some mass in the galaxy? Oops? I thought you were going to bring it home? Where is it that the galaxy going a quick diet or something? In a go keto? You look in great these days, milky Way. Maybe it's like only two percent milky way or like low fat milky way skin milky way. All right, so there is some missing mass in the galaxy, right, I know this one. It's like, if you measure how the stars in the galaxy are spinning around, they are spinning around faster than they would be if there was only stars and planets in the galaxy. Right, there's something else missing from the mass of how we see the galaxy spinning exactly, just like we were talking about. You can deduce the mass that the Sun has to be to explain the Earth's motion. You can do the same thing with the whole galaxy. Measure the motion of the stars and from that deduce the mass of all the stuff that has to be pulling on those stars to keep them moving in a circle. It's exactly the same strategy, right, And this is kind of how people first started thinking about dark matter, which is that they saw that the galaxies were spinning faster than they would be if if the stars were to stay in the galaxy, and so they hypothesized like, hey, maybe there's some invisible mass. We'll call it dark matter, and that's what's keeping all the stars in the galaxy I usually think about it the other direction. They measure the velocity of the stars, and then they asked, how much gravity do you need to explain that motion to keep the stars from flying up? And then they couldn't find that much mass. They looked at all the stars and all the dust and all the things they could see, and it just didn't add up. It wasn't even close. So that was a big puzzle for decades, right, And so the idea of a lot of invisible mass out there in the universe is kind of crazy. So a lot of people are like, are you sure that sounds crazy? How do you know that maybe the black hole at the center of the galaxy isn't just heavier than you think it is. Maybe that would explain why the stars are not flying off into space. Yeah, it's a great question because it points to like our uncertainty, like how do you know how massive those stars are? And how do you know the other things in the galaxy? How well do you know their mass? And so it's just like pointing at you know, other places we could be making mistakes, which is a great scientific exercise, like to go back and think, maybe we just missestimated the number of stars, or maybe we missestimated their mass, or maybe it's all hiding at the center of the galaxy inside that black hole. Yeah, so the question is like, could a bigger black hole at the center of the galaxy explain how all the stars are moving around the galaxy or does it have to be something like dark matter. So there's sort of three answers, two knows, and then maybe yes. So the first know is that we actually kind of do know the mass of the black hole at the center of the galaxy. It's not just some huge cosmic noob that we can turn up and down and say nobody knows, So we can just set it to anything. As we talked about just a few minutes ago. We can measure the mass of black holes by looking at the movement of stars near it. And the one near the center of our Milky Way is actually super awesome because there's a star that gets really really close to it. It whizz is right by, It ends up going super fast and allows us to make a pretty precise measurement of the mass of the black hole at the center of the Milky Way. I see, so there isn't like a mysterious black hole at the center of the galaxy. There's one that we can measure. Yeah, we've measured its mass pretty well, and there's a bunch of stars moving around it. And this is this really awesome video you should watch. It took like decades to make of them observing the black hole and seeing the motion of the stars around it, and you can watch it in time lapse. You know, it took them twenty years, but you can watch the whole thing in twenty seconds, and you can see these stars moving around some obvious, invisible object, like they're bending their path around what seems to be nothing and therefore must be something. Right, And it's pretty massive, I imagine, right, it's a pretty massive black hole at the center of our galaxy. Yeah, it's pretty heavy. It has four point one million times the mass of our star, so it's pretty hefty. And I just want to make a plug for U. C. L a that won the Nobel Prize for these observations very recently. So go check out that video. It's pretty cool, but it's a pretty massive black hole hole, but it can't explain all of the dark matter. Number one, because we know it's mass, but number two also, it's in the wrong place to explain the dark matter, right, Like, even if we didn't know the mass of the black hole at the center of the galaxy, Like, even if we were wrong, one giant mass at the center of the galaxy wouldn't explain how the all the stars are moving. That's exactly right, because even if you increase the mass of the black hole to account for all the missing stuff, it wouldn't give you stars moving the way our stars are moving. And that's because we can look at the velocity of stars very close to the center of the galaxy and the velocity stars further away from the center of the galaxy. So what we need is dark matter to explain all of those different velocities stars closer to the center and stars further from the center, and every star it's motion tells you about how much mass is sort of in a sphere that's closer to the center of the galaxy. Event it like, stars are not affected by stuff that's further away from them, only by stuff that's closer to them. So as you look at stars as a function of their distance, you know is that you need a distribution of mass that's sort of spread out to the galaxy. If you only put a huge blob of mass at the very center. It would make the stars near the core of the galaxy move way too fast, for example, right, right, because that's kind of an interesting property of mass. It's like, you know, if you're really far away from it, you might as well treat it as a like a thought. But if you're really close to it, then it does matter whether or not it's like diffused in the little tiny ball in the middle or in a giant cloud that actually there is actually sort of engulfs you. Right, Yeah, if you're inside of it, then you're only sensitive to the parts of it that are closer to the center. Just like if you drill the whole inside the Earth and jumped inside, the force of gravity on you would decrease as you are closer and closer because a lot of the stuff would now be outside of your shell. You could ignore it, and when you get to the very center, there would be no force of gravity, so you can no longer treat and the Earth is like just a point particle. Was the mass of the Earth, and so it's the same thing with the galaxy. In order to explain the velocity of stars, we have to distribute be the mass in just the right way to make these stars go fast and these starts to go a little slower. So the cool thing about this velocity measurement is that we're not only sensitive to the overall amount of missing mass, but also how it's distributed through the galaxy. Right. I like that analogy about the Earth because like, if you fall to the center of the Earth, and you're at the center of the Earth, basically the Earth is all around you and it's pulling you in every direction, so you're basically weightless right in the middle of the Earth. Yeah, there's no force of gravity at the center of the Earth. Yeah, And so the same would be with a galaxy. Like if you're at the center of the galaxy and you would feel the dark matter pulling all around you, so you wouldn't feel this mass, but if you were out in the edge of the galaxy, you would feel the mass of the dark matter like it was a point in the middle. Yeah, exactly. So imagine now a star that's very close to the center of the galaxy. If you took all the dark matter and you put it inside the black hole, that would mean that that star is feeling all of that gravity, would be moving really really fast. If instead you took that dark matter, you spread it out through the galaxy, then most of it wouldn't affect that star near the core, because, as you say, it would all be balanced out, it will all be on the outside of it. It would be null. And so you can tell how it's distributed by looking at the velocity stars that are close to the center and then a little further away. In a little further away, a distributed mass of dark matter makes a very different prediction than dark matter concentrated all at the core of the galaxy. All right, So then that's the answer of the answer is that a black hole cannot explain the missing mass in the galaxies and the trajectory of stars. You kind of need something large and diffused like how we think dark matter is. But there's also a possible yes maybe to his answer, which is that we don't think that all of the dark matter is in the black hole the center of our galaxy. But remember that we don't know what dark matter is, and there's a possibility that dark matter, though it's spread out through the galaxy, might be a bunch of smaller black holes, right like primordial black holes. Right, Yes, black holes made in the very first few moments before there was and stuff and matter in the universe. They could still be around and they could account for the dark matter. It's one of the theories that are out there. It's maybe not the most common or highly voted theory of dark matter, but it's still possible. It's still plausible, and we haven't figured out what dark matter is, so it could just be a bunch of black holes spread out through the galaxy. Wow, that sounds a little horrifying to know then, Like if you were flying through space, it's like riddled with minds kind of right. You might be flying through space and there's a hole. You've flying through a cloud of little tiny black holes. That wouldn't be good for your spaceship, right, that would not be good for your spaceship. But you know, it's eaten zero earths so far, so it must be pretty safe so far. Zero. No, We've been flying through the galaxy for billions of years, right, and we have not yet run into a black hole. On the other hand, we don't know if there are other planets out there that have fallen into primordial black holes, because they've they had we wouldn't see them, so it's not really a great argument. All right. Well, then the answer is that a black hole at the center of the galaxy wouldn't explain dark matter. But maybe dark matter is explained by little, tiny black holes everywhere. But it's great thinking one to try to come up with some other explanation for dark matter in terms of like the things we do know and our uncertainties about them. It's a great way to exercise your brain and do physics and think about different hypotheses. So great idea. Cool. So those are three awesome questions about black holes than you do think. We've on our job here to fill the black hole of questions about black holes a little bit. Yeah. The problem is that the black hole questions just grow the more you feed them. The bigger gets, the stronger it's pulled, the more we want to know. It's just kind of like science that way. The more we ask questions and get answers, the more questions we have. Yeah, and hopefully we won't get stuck in them forever. At some point we'll get out of them or maybe Inside the black Hole is a really wonderful book, filled with the secrets of the universe and a cozy reading nook to enjoy it in Yeah, who doesn't love a good book about the universe? Titled Frequently Asked Questions about the un that's right Hypothetically at universe f a q dot com. You'll have to run an expair meant to see if it's a real website universe f a q dot com. You might find a black hole, or you might find a lot of interesting knowledge that's right and funny cartoon, and so go check it out, Go be a scientist. Those of you who write in asking how can we support the podcast, this is how you can support the podcast. Please go out there and check out our book. We put a lot of energy and a lot of fun and a lot of love into it, and we hope that you all enjoy it. Yeah. And more importantly, it's also those of you wondering, like how can I tell my friends or my cousin or my uncle or my mom, Like how cool all of this stuff is this book? I think it's a great way into these topics. You think it's going to convert the physics skeptics out there are an all physicists skeptics. I thought that was your thing, like that was your identifier. Yeah, but some people are skeptics about physicists, skeptic about skepticism, meta skeptics. All right, well, please go check it out and please send us more of your questions. Was really fun to get and really fun to answer on the podcast. That's right. Please don't hesitate right to us any questions you have about physics, except of course, homework problems to Westerns at Daniel and Jorge dot com. I hope you enjoyed that. Thanks for joining us, see you next time. Thanks for listening, and remember that Daniel and Jorge explained. The Universe is a production of I Heart Radio or more podcast for my heart Radio, visit the I Heart Radio app, Apple Podcasts, or wherever you listen to your favorite shows.