What is the densest thing in the universe?

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Speaker 1: Hey, or Hey. You know how sometimes everybody thinks they know the answer to a question, but they're actually all wrong. You mean, like how you think everything weird in space is because of aliens. Well, that's not a good example. I think it probably is because of aliens. Or you mean, like, what why people think this guy is blue? Yeah, a lot of people think this guy is blue because of the ocean. Wait, it's not because of the ocean. Do you even listen to our podcast? We did a whole episode about that. I don't listen to our podcast. I'm too busy looking out for aliens. Well, if you did pay attention, sometimes you'd realize that sometimes there's a question in science that everybody assumes they know the answer to, but it turns out they don't. Hi. I'm or Hey. I'm a cartoonists and the creator of PhD comics. Hi I'm Daniel. I'm a podcast host and part time particle physicist. Have you been downgraded to part time? Now? I decided let's make this podcast thing my primary activity. That's right, it's two hours a week, but it's the most important and valuable two hours of my week. Two hours of work. Isn't that too much? For a physicist. Well, you know, you've got your naps in, you've got your coffee breaks, you got your scribbling nonsense on the board to look busy. So it's a pretty full day after a while, you mean a pretty full week, pretty for a week. Yeah, you know. But I modeled my work day after my um my cartooning role models. You know. Yeah, sleep in, never change out of your pajamas, this kind of stuff. Yeah, No, we should all look up to cartoonists as a nation. We would all be more productive if we follow the cartooning work week. We'd all be a lot more funny, that's right. We would do the low way to prosperity. But you are listeners are listening to our podcast, Daniel and Jorge Explain the Universe, a production of I Heart Radio, in which we take weird and funny and amazing and crazy things about the universe and try to doodle them into your brain with silly analogies and bad jokes. That's right. We try to take you to the corners, the far reaching corners of the universe, and to explore the heaviest things, the biggest things, the brightest things, the smallest things that are out there for us to discover that's right, And so we have this series of podcasts we've been really enjoying about the extreme Universe, Extreme Extreme, in which we look at all the weirdest, nastiest, hottest, wettest, craziest things in the universe, and we have actually done some of those. We did the hottest, we did the brightest, we did the biggest. What else did we do? You Ma, you make our podcast sound a little not safe for work there, Daniel. That's all in the minds of the listener. Okay, well, that's that's kind of the universe totally. The universe is not safe for work. Oh I thought you meant the universe is in the minds of the listener, which is also sort of true from a philosophical point of view. So today we're continuing our series of extreme Things in the universe, and in this episode we are going to explore what is the dnsest thing in the universe, the densest thing in the universe, that's right, Not the heaviest, not the biggest, not the smallest, but the most compact, the thing with the most stuffed stuffed into it, that's right, Not the sharpest thing, the densest thing, that's right, Not the brightest thing, but the densest things, right, Not the smartest thing in the universe, the dances, that's right. Yeah, the smartest thing in the universe. That would be an interesting discussion. I wonder what is the smartest thing in the universe. Do you think it's a human? Who? You think it's some super intelligent alien race? I think the universe is the smartest thing in the universe. Oh snap, we are the universe thinking? Is that what you're thinking? Where you're going? We are the brain of the universe. The universe is us. It's very holistic of you. I gotta get some of those banana peals you must have been smoking for today's episode. I am one with the universe, and the universe is me, and I am thinking the thoughts of the universe. Well, I but I don't. I don't smoke banana peals. I just I just eat them. Wrong, You eat them, you eat the flesh, and I smoked the peels. So we're a perfect team. Well, so, yeah, what is the densest thing you meaning? Like, what is the most compact crunched up think? Is you know, craziest most amount of stuff in a small amount of space. Thing that exists out there in the universe, that's right. And the point of this series, the Extreme Universe series, is to remind you that our little corner of the universe is fairly ho hum. It's not very fast, it's not very big, it's not very hot, it's not very cold. It's sort of just right. And what that means is that there is crazy stuff out there, this stuff out there that's bigger you than you can imagine, that's hotter than you can imagine, that's emptier than you can imagine. And one of my funniest extremes is density. To imagine how much stuff you can cram into the tiniest spot, get those atoms all crowded up into each other. Because when that happens, really weird things happen. Matter does all sorts of strange stuff when you squeeze it together. And so a lot of our listeners, a lot of you listening out there, might be thinking, Oh, I know the answer to this question. It's obviously a black hole. Hint, it's not a black hole. It's not a black hole. Maybe it is, maybe it isn't. There's a bit of a philosophical argument there at the end teaser, there's a plot twist. It is it isn't It is it isn't. Some people say it is, some people say it isn't. Those other people throw the other first people into a black hole, and the argument and at all just becomes a black hole of a mess exactly, it becomes a mental black hole. We all get a little denser. So hopefully that sucked you in into the topic of this podcast, and so stay tuned to see if it is or if it's not a black hole. Daniel says, maybe it is not, Maybe it is, maybe it's not. Exactly, But before we dive into that, I went around and I asked folks on campus that you see Irvine. I said, what do you think is the densest thing in the universe? Because I was curious, is everybody just going to say it's a black hole? To people have other ideas? Have people done the careful reading about the fundamental issues in the corners and the centers black holes? Or maybe people knew what the densest thing in the universe is. Maybe there it's it's something else and people knew about it. Yeah, that's right. Maybe it's the center of some weird kind of candy and you know, famously dance or something else weird people have read about. So I walked around I asked people. I said, what do you think is the densest thing in the universe? So think about it for a second, and if somebody asked you on the street, what is the denist thing in the universe, would you answer that it's a black hole. Here's what people had to say. A black hole. Oh, man, I hope it's chocolate black hole. Probably a black hole, a black hole, neutron stars, something like that. Black holes gets the anti matter black hole. I think I want to say the core, the core core of the Earth, okay, okay, or actually, so you know universe, probably the sun in the star, right, yeah, I would say a star al right. So most people answered black hole. A lot of people said it's a black hole. It's a good go to thing. I think people think what's the densest thing in the universe and their mind goes straight to a black hole because they imagine a black hole has a lot of stuff stuffed into it. But it wasn't the only answer. There was some pretty interesting ones here. I like the one that said it's chocolate exactly. I'm not sure that was a serious answer. Somebody out there really had a hanker and for some dark, dark chocolate. Right. The thing that interested me about these answers maybe they were thinking like richest, Like what's the richest thing you've ever tasted? Most? What's the most calorie dense thing in the universe? Maybe that's what they're thinking. There you go, is it still a black hole? Like what if you eat a black hole? That's a lot of calories technically, right, what if you ate a black hole? I think that's a physics question nobody has ever asked me before. While we are breaking new ground today. One of the things I liked about these answers is in contrast to someone the other extreme universe questions, where you you might have noticed people tended to answer in their local environment. They're like, thought about what is the brightest thing in our solar system? Or what is the biggest thing nearby here? People really went s at a universal They really cast their minds into the entire universe to find something really really dense. I mean like the person who said it was the core of the earth exactly, not that person, everybody, but that person yeah, all right, Well there were other answers here. Some people said neutron stars, other people said antimatter. Those are pretty a space physics the answers yeah, yeah, I think antimatters a would have stabbed there. You know, Um, antimatter is not anymore or less than the normal matter, right, it's just another kind of matter. It's at the opposite kind of matter. But a neutron star is a good answer. Um. I like the people who said, you know, I don't know something strange out there in space like that, you know, just conveys the whole idea we're trying to get across here, which is that space is filled with weird stuff, something crazy and strange and you probably can't even imagine. Well, that needs to be the answer to every single one of these extreme universe episodes. It's like, what's the brightest thing in the universe, some weird thing out there in space, something in space. I've noticed this trend that you seem to be trying to assemble a sort of universal list of answers to physics questions, Like how many physics questions can you just answer with the with the phrase the Big bang or space or you know, physics. Um, it's like you're trying to find shortcuts or something. Well, you know, I want to be ready when that physicist approaches me on the street wearing sandals and asking me strange questions about the universe. I want to be ready. You know, you want to be ready. I think we should do that someday. We should just flip your answers in and see if any listeners even noticed. Right, do I get to Google first? Nobody gets to Google first. There's no googling allowed in these questions. It's just what do you know? Now? What's in your mind? What answer can you construct? All right, well, let's launch into this discussion, Daniel. Let's figure out what is the dancest thing in the universe. But first let's maybe talk about what is density. I think we all have an intuitive sense of what density is, but you know, maybe there's a it's different from the physics definition. Yeah, and we talk a lot in this podcast about sort of the difference between technical physical definitions and sort of cultural definitions, and in this one case, I think they're pretty well aligned. But let's just go through the basics. Being people up to speed in case they haven't thought about density. Since you know high school chemistry or something um And so density is not a fundamental unit, it's a derived unit, which means it's a ratio of two other things. It's mass over volume. So mass is just like how much stuff is there. It's different from weight. Right, Wait, is how much force is there on you from from Earth's gravity. Mass is just like how much stuff is there in you? Right, And remember we talked about that another time. What is mass? And it comes from inertia and it's the property of an object to resist changes in its motion. Right, So that's what mass is. All the particles inside you and all their energy addupt to give you a certain amount of mass. And then on the bottom of that volume, right, So it's mass over a volume. And volume is just how much space do you take up? Right? How big are you? So something can be really dense if it has a lot of mass and not very much volume, or not very much mass but even less volume. Right. So it's not about being extremes in mass or extremes in volume. It's all about the ratio. It's having a lot of mass in a small space. I see. It's not about being the biggest thing or about having the most mass. It's about having the most mass in the smallest amount of space. Yeah, because you can think of things that are really really big and really really massive, but not very dense, like a blimp. Right. You know, a blimp is not that dense because it can float in the air. Right, It's filled with a gas that's less dense than air, even though it's really big and uh and and it has a huge amount of mass to it. A blimp is not actually that dense. But if the blimp was made out of rocks, that would be really really dense. That's right. That would be a terrible design for a blimp exactly. Um, I don't recommend you buy any stocks and your friends rock blimp startup. Well, it depends on what you're trying to float in, right, If you're trying to float into something that is denser than rock, then they would work. Yeah, that's true. I'm not sure where that exists, so you know, he's lava denser than rock, probably not right, So I'm not sure where your rock blimp would even work, but sure yeah, maybe you know, on the surface sid maybe in the liquid nitrogen oceans of Jupiter. There you go, there, there you go. There's a great reason to invest in your in that startup now. Yeah. But the point is, things can be really big and really massive without being very dense. Right. Dense requires a huge amount of mass compacted into a small space. So the densest thing in the universe doesn't have to be something big. It can be something small, that's right. And things can be very very dense without being that big. Right. You can have a really really small amount of something that's very dense as long as there's a huge amount of stuff crammed into it. But it could also be a really big thing, like you could you know, the densest thing in the universe could be like a star or a neutron star. It could be something that big. Yeah, exactly, it could be big, it could be small. It could be massive, it could be not that massive. The key is the ratio again between the mass and the volume, how much stuff is cramped into a certain amount of space exactly. And you know, that's physics density, And I think that matches pretty well with what people's intuition is for density. I don't think we have a pretty big disconnect like we usually do. So congratulation Physics Naming team. You picked a good one this time. Well, I guess intuitively, you know, it's kind of like, um, holding something in your hand. You know, like if you're holding a little rock that's dense and you know it's dnse because it feels heavy, but it still fits in your hand. But if you have you have like a ball of cotton in your hand, that's not very dense, that's right. And so one way to compare densities is to say, I'm going to compare different kinds of stuff and have the same volume, so the same amount of its same like physical space full of it, and then just compare the mass because it's the ratio of mass to volume. And if you fix the volume, then you can just compare the mass us. So you can compare like a handful of rock to a handful of cotton, to a handful of air to a handful of you know, hot lava or whatever. And don't actually try to get a handful of hot lava, but hand full of lava sounds like it sounds like a you know, a high school band name or something up next an extreme universe handful of lava. Anyway, Um, yeah, you if you fix the volume, then you can compare the mass. Okay, so you have a couple of great interesting numbers here for us, and they're all based on a fixed volume, which is a one teaspoon, right, that's right. I thought a teaspoon is like a macroscopic quantity. You know, you can imagine it's just like a normal kitchen spoonful of stuff. And then we can think about how heavy, how much mass is there in a teaspoon of this versus a teaspoon of that versus the teaspoon of something else. So if we fix the volume, then we can just think about how much mass there is, how much a teaspoon of something would Wait, that's right now. Wait, of course is slightly different from mass, but you know they're connected. And here Earth, something that has more mass has more weight. Um, you know, far away from the Earth, then you can still have mass even if you don't have weight. But they're the same if we're if we're doing this experiment on the surface of the Earth, then it's equivalent. So step us through here, Daniel. All right, so I thought we'd start really really light, all right, just sort of for scale, and imagine if you had, for example, um, a teaspoon of space right. I mean, I don't know how you would get that, but so you like scooped up a teaspoon of space, so you had, you know, stuff that had the same density of space. Like what do you mean space, like average space or like if you win out into space, grabbed the scoop of it and brought it back to Earth. Is that what you mean? Yeah? The average amount the average amount of stuff in space. And remember we did a whole podcast episode about how space he is space and it turns out that the answer is pretty different depending on where you get your scoop of space. But in all cases, as long as you're far away from the Earth's atmosphere, the answer is pretty pretty low. You know, you're gonna get less than one proton in your tea spoon. Okay, so this is like the average teaspoon of the universe. Yeah, exactly. The average density of a teaspoon in the universe is one times ten to the negative twenty seven kilograms, So that's zero point twenties seven. Zero's one. That's how much a proton. Ways, so you can have like a whole teaspoon with just a proton in it. That's about the average density of stuff out there, and a proton is pretty small, right, I mean it's it's pretty much. Uh, it's it's tiny. It's almost nothing, right, it's almost a fundamental unit of of mass. Right. Yeah, it's amazing because it's almost nothing. But then it makes up everything, right, And it's incredible how you can get big macroscopic stuff made out of super tiny stuff. Right. It boggles the mind how small a proton is, and then how many protons you need to make, Like you know, a cookie or whatever. There's so many protons in your cookie and you don't even think about them as you eat it. Wow. So that's the average density of the universe really, right, it's it's about one proton per teaspoon. And the reason is, you know, there's a lot of stuff out there in the universe, a lot of stars and they're big, and a lot of galaxies, but most of the universe is pretty empty, you know, the stuff between stars and between galaxies. There's not that much stuff there. And the biggest volume of the universe are these super voids, you know, between the sheets of superclusters. But there's really basically almost nothing. And so because density is mass over volume, and the volume of the universe is unbelievably gigantic. Then that's why the density is so small. I mean, it's amazing that it's even anywhere close to a proton. Frankly, Wow, that's pretty incredible to think that if you sort of, like if you shrank the entire universe into a teaspoon, like everything that's stuff, stars as planets, would just be about the size of a proton exactly. But but the next I thought, let's let's look at something sort of around here on the Earth, and and a good sort of normalization for like a standard for what density is is water, because water is one um gram per cubic centimeter, right, and a teaspoon is five cubic centimeters, So water is five grams per cubic centimeter. So you have a teaspoon of water, it weighs five grams, which is a whole lot more than a proton. What about a teaspoon of tea? A teaspoon of tea, that's a good question. It must be a little bit more dense, right because you put something into it, but it's about the same, Okay, So that's um. I think that's a pretty good anchor for people, maybe, you know, because we're all sort of familiar with how water feels and how much it wasgs. That's right, And if you're holding a teaspoon, you can tell the difference between having a full teaspoon and an empty teaspoon. Right, somebody pours water into your teaspoon with your eyes closed, you can tell the difference. Whereas if I put a single proton in your teaspoon, you're not gonna notice. So you can feel it, right, you can feel five grams. It's not it's not a lot, but it's also not nothing. That really kind of tells you how empty the universe is, right, Like, if our average experience of matter is a teaspoon of water, compare that to a teaspoon with one proton in it. That's that's really kind of the difference between our everyday experience and the actual whole other rest of the universe, exactly at the low extreme, most of the universe is really not very dense at all, So we live in a pretty dense place compared to most of the universe. But then again, as you'll hear, our surroundings are not very dense at all compared to the densest places in the universe, So The craziest thing about the universe is that it has this enormous range. Most of it's not very dense at all, and then there's these incredible pockets of total density. Well, let's keep scooping up more and more dens for things. But first let's take a quick break. All right, we're scooping things up indiscriminately here and measuring their density to find out the densest thing in the universe. And we we just scipped up some water. So some water is about five grams that's right, five grams per tea spoon. And then people, um, a lot of people said, oh, maybe the sun or a star. That seems like a dense thing, right, because it seems like it's trapped by gravity and the reason it's burning is that it's all this gasp and compressed. So people figure, well, it must be pretty dense, right, Well, it is dense, but it's surprisingly not that dense. I mean, the density of the sun is about seven grams per teaspoon, so only a little bit denser than water. Are you serious? Yeah, the sun is not that much denser than water. Yeah, the Sun is not that much denser than the water. Now, the sun is really big, and the Sun is really hot, but it's not actually that dense. So this is the average density of the Sun, because I imagine the Sun is dens or at the middle in the middle unless dense at the edges. Right, the Sun really doesn't like when you talk about its middle that way. It's been working on it for a few billion years um. But yes, the the density of the Sun does vary. So this is the average density exactly. And I think the reason that it's not more dense is that there's more than just gravity going on. Right. Gravity is the thing that made the Sun. It pulled all that stuff together, it starts that fire. But once you have that fire happening, it's like a constant explosion, and that explosion is making the Sun less dense. So the Sun is this constant balance, right, It's a trapped, ongoing nuclear explosion. The explosions are pushing things out and gravity is pulling things in. And so if it was just gravity, then you know, the Sun would collapse into a very very dense state. But the reason it doesn't collapse is because it's exploding, so that keeps it, you know, a little fluffy, So you're really only kind of measuring the density of the fuel of the sun, Like once it turns into fire and photons once it turns into light, you don't really count that as part of the density. That's right, we're measuring the matter density of the sun. But you know a lot of the photons produced in the sun never leave it because they're reabsorbed. You make a photon somewhere in the middle of the sun, it's going to get reabsorbed before it leaves the sun. But I think they did is that if you scooped up a teaspoon of the sun, it would it would sort of feel the same as this teaspoon of water. It might be a lot brighter, right, and hotter, but exactly. Yeah, that's the idea, right, Somebody out there is imagining being blindfolded, and you're saying, I'm either going to pour a teaspoon of water into your teaspoon or a teaspoon of the sun, and you won't be able to tell which. And you're thinking, yeah, I think I'll be able to tell. But you're right, you won't be able to tell from the from the heaviness of it, because it's not that much heavier than water, all right, And in fact, it seems like things are even denser here on Earth. Yeah, exactly. And you might be thinking, well, water is not that dense, and you're right, And if you just like bent down and scooped up a teaspoon of rocks, you know of like gravel or whatever, then you would have something denser. In fact, the density of the Earth, again averaging over everything in the Earth, is thirty grams per teaspoon. Remember waters five grams, the sun is seven grams. The Earth is thirty grams per teaspoon. That's a lot denser than the Sun. So the Sun is actually kind of fluffy, right, Yeah, it's like a big cozy pillow on fire. Yeah. And the reason is right, the Earth is not on fire. Right. If the Earth was more massive so that there was more gravity so we can press it more infusion would get started, then it would actually get bigger, right, and then it would be more fluffy. So Earth is more dense because we only have gravity going on. We have no outward pressure from fusion to make us fluffy. We're not living in an explosion. We are pretty compact. So but that's kind of the average density of the Earth. But there must be things on Earth that are denser than the average density. Big variation in density. You know, the core of the Earth is more dense than the rocks under your feet, for example. So there's a lot of variation. But if you look around on Earth, for like, what is the densest thing that occurs on Earth? There's this one element it's called osmy um, and osmium weighs a hundred ten grams per teaspoon a hundred and ten grams, so like, um, that's a lot. That's like, how much is that like fifteen scoops of the sun compressed down? Is how much osm that's right? Um, If you had a teaspoon of osmium, it would feel like you had like a half a cup of water in your teaspoon. The stuff is pretty dense. I've never seen ausman. I don't even know what it looks like or if you can pour it, if it's liquided room temperature or whatever. But it's the densest stuff on Earth. But that's at the on the surface of the Earth. Like maybe down in the center of the Earth, things are more compact because there's more pressure. Yeah, and you're right, the core of the Earth is more dense than the rest of the Earth or the Earth's crust for example, or the average density of the Earth, which is what we mentioned earlier. But sort of surprisingly, it's not that much more dense, Like it's twice as dense at the core of the Earth than it is at the Earth's crust, which is most of the Earth. But so it's not crazy. It's not like a jillion times denser or anything. I mean, twice as dance is a lot, but it's not. It's not shocking. Okay, So now take us out into space, Daniel, what are some of the densest things out there in space? Well, so, as we talked about, stars that are normally burning, are not actually that dense, right, and so in our solar they're pretty fluffy. In our Solar system, one of the densest things is just the Earth, right, It's a pretty concentrated blob of rock. So what you gotta do if you want something really dense is something I think one of our listeners on the street or one of our interviewees on the street actually mentioned what you need is a failed star or a star that has gone supernova and then collapsed, right. And sometimes when a star blows its load, and it's finished burning all of its fuel and it's expended all of its energy, and that it no longer has that radiation pressure to keep it fluffy. It collapses into a neutron star. It's called a neutron star because the the gravity is so intense that it forces all the protons to give off an electron and become neutrons. And it's just like a big ball of neutrons and they are really scrunched in together, right, because there's so many of them that the gravity really compresses things and makes it really, really really dense. That's it. It's ridiculously dense because again there's no process going on to counteract is, so all you have is gravity. Is just like packing these little neutrons and imagine like a huge bag of ping pong balls, right, and you squeeze it so that they find like every little gap of space gets squeezed out, and they all find exactly the tightest way they can all fit together. And the density of this thing is incredible. I mean, it's even hard to understand. You know, we're talking about a teaspoon. If you had a teaspoon of a neutron star, it would be fifty times ten to the eleven kilograms. That's a lot of eleven Yeah, exactly. I think that's five thousand billion kilograms per teaspoon. And you rode here, it's about seven hundred thousand Eiffel towers in a single tea spoon. Yeah. I was trying to find an understandable unit of of mass, like you know, what is comparable in mass to a teaspoon of a neutron star. And it turns out, you know, it's almost a million Eiffel towers boiled down into a tea spoon. Like, I mean, it's ridiculous, Like you couldn't hold up a sing the Eiffel Tower. I mean, I know you've been working out and you're pretty strong and everything, but an Eiffel tower weighs a lot. Now I take a million Eiffel towers and then condense them down into a tiny teaspoon, It's hard to even imagine what that kind of matter is. Like, what you know I am stronger in France is that because the Earth is not round, there's a difference in like the difference from the distance from the center of the Earth. It's probably just the French wines out there. You feel stronger in France. Exactly, But I think I see what you're saying is that, like a neutron start is really just a star that went out right, or that collapse, Yeah, exactly, it finished burning. And so you're saying that, like our son would be that dense, except that since it's exploding, it kind of keeps everything fluffy. But if you were to suddenly turn it off, all that stuff woulds crunched down into something like a neutron star. Right. And so to take the bomb analogy, you know, a nuclear bomb when it's exploded is not actually that dense. It's a huge fireball, right, But the fireball itself is not that dense. It's much more dense before it explodes, right, when it has all that fuel compacted into a small place. After it explodes, it's much less dense. So an exploding bomb is less dense than a non exploding bomb. Right. It's kind of like can candy. You know how can candy is big and fluffy, but if you like crunch it down, then you just get one really dense piece of candy. Yeah, you're making, uh, the sun sound really comfortable and cozy. It's like big and fluffy like cotton candy. You know, every pink pink? What is in the air over your house that you think the sun is pink? Well, you know that it depends on your If you're wearing a rose color glasses, you know, I'll give it to you. That's your cartoonist license, you know, that's your art um. Yeah, exactly. So a neutron star is actually one of the densest things in the universe. It's it's unbelievably dense. You know, I think isn't even denser than Thor's hammer. You're the Marvel Universe guy. I think it is. It is made from the heart of a dying neutron star. So I don't know if it's heavier, but it sounds like it's maybe in the same order of magnitude. Well, so then do the calculation. You know, if a teaspoon of neutron star is a million Eiffel towers, then Thor's hammer is what, I don't know, a hundred teaspoons, a thousand teaspoons. You know, you're talking a billion Eiffel towers. So every time Thorpe picks up that hammer, he's lifting a billion Eiffel towers. It's a calming book. Wait, we're doing the physics of comic books here today, folks. Um. Yeah, but you know, not only do you have to be strong, but you have to be worthy right to pick up Thor's hammer. So so that's pretty dense. If you scoop up some neutron star in a teaspoon, you would be picking up a million Eiffel towers. Yeah, so make sure you do your stretches before you try that, or you're gonna hurt yourself. Make sure you use a strong spoon. Boon made out of osmium, or a spoon made out of a billion Eiffel towers, that's right, or vibranium. You sort of give it away. You said a neutron star is one of the densest things in the universe. But maybe so you're saying it's not the densest thing. Well, it's it's a little bit unclear. Depends a little bit who's camp you're in. Are you an Einstein kind of person or are you a shorting Your kind of person, Because depending on what you think is going on inside a black hole, black holes are either the densest thing in the universe or not very dense at all. All right time to pick sides Einstein versus short Anger. But first let's take a quick break. All right, we're talking about the densest thing in the universe, and we got to we are now at um black holes. That's right, and we are right smack in the middle of the longest standing physics grudge match. It's general relativity versus quantum mechanics, Albert Einstein versus Schrodinger in Heisenberg and all those other smart folks. And so you might be thinking that there are Let's tell me how dance is a black hole, because a black hole is also something that happens after a star collapses. Right, Sometimes the star performs a neutron star. Sometimes it forms a black hole. And a black hole seems like it must be the densest thing in the universe because it has the strongest gravity. Right. The problem with the black hole is that how do you define the edge of the black hole? Remember that to talk about density, we have to talk about mass. Black holes have huge masses, but we also have to talk about volume. So what's the denominator? What's the edge of the black hole? And one very reasonable thing to say is that the edge of the black hole is the point of no return, you know, the point where if you're closer to the center of the black hole than that than light can't escape and nothing can never leave. Right, So you're sort of saying, how do you when what do you count as the black hole? Is the question exactly, because if you're gonna do density, you have to calculate mass over volume. So what volume are you including? So you're saying, one option is to use what they call the event horizon, right, right, the point where not even light can escape the vicinity of the black hole. That's right, And I think that's a reasonable definition because we can't see inside the event horizons. We have no idea what's going on inside the event horizon, so all we really can do is average over it. Right, we can say, well, we know how much mass there is, and we know how big it is, what's going on inside? You know, that's Einstein versus Shortinger. So if you don't want to be dependent on which physics genius is right about the universe, then you just need to calculate the mass the black hole divided by the volume includes enclosed by that event horizon. So I think you're saying that a black hole should be measured by when it's when it's black. Yeah, exactly when the black star like that where the black star and the whole holiness. That's right. And the issue with black holes then is that they are really really massive, right, which means it's a huge amount of gravity, which means the event horizon is really really big. So you say, you don't know what's going on inside a black hole, but there's a huge amount of mass in there. The event horizon grows linearly with mass. So for example, you have twice as much mass, the event horizon is twice as big. It's it's it's linear. It's like a it's like a one to one increase. I give you double the mass exactly. You double the radius of the of the black area exactly. You double the radius of the event horizon. Now, for those of you you know something about geometry, think about that sphere right now. If you double the radius of the sphere, how much does the volume go up? Well, it goes up like the radius cubed. Right. So, so you have some black hole and you double its mass somehow, then you've increased its mass by two, but you've increased its volume by eight. Right, two cubed, so the density actually goes down. So you double the mass of a black hole, it's density goes down by a factor of four, which means really really massive according to your definition of the of the black holes, if you count the black part as the black hole exactly, which seems like a reasonable definition though you know, we'll talk about another definition in a moment. And so what that means is that the bigger your black hole is, sorry, the more massive your black hole is, the less dense it actually is. But you know, I guess it's a your I see what you're saying, like that you should count the black as the black hole. But that's it's not like a physical boundary, you know, And it's not like it's not like a surface, do you know what I mean. It's just where the effect of the gravity starts to get crazy, but it's not really sort of like you can't really touch the surface of the black part, right. I wouldn't recommend it, um, but you know, it is a real physical boundary. You know, if you're a photon and you are pro do that and you don't turn, you're gonna fall in. You know. It's like saying, how big is the Grand Canyon. While you start the definition at the edge of the Grand Canyon, right, not at the not at the river at the bottom of it. That made that Grand canyon. Right, you fall in the Grand Canyon, you still fell in the Grand Canyon. It doesn't matter if you fall into the edge or if you jump out of a helicopter in the middle. So I think it's a pretty reasonable definition that you're you're putting the emphasis on the whole part. Well, that's what makes the black hole so cool, right, is the whole part, not the black part. So if you just think of it the black hole as a whole, then you have to measure where the whole starts. Yeah, so you're saying them the density of the black hole, not determined by how much mass is inside of the black hole, is just kind of like how big the hole is, which when it grows, it doesn't help the density, that's right, because it's a connection there. Right. The more mass, the bigger the hole, and the bigger the whole, the less dense, right, So you sort of trapped there. In fact, to get a really dense black hole, what you need to do is is have um a smaller black hole. Right, If you take half of the mass away from the black hole, which of course you can't do, right, Then the mass goes down by two, but the volume goes down by eight. And so now the density increases by a factor of four. Okay, so then the smaller the black hole, the denser it is. Yes, exactly, So start with like a really big black hole, right. I did some some calculations here. If you have a supermassive black hole that has like the mass of four billion sons, right, four billion times the mass of our Sun, would be really really big black hole. It's event horizon would be so big that the density of the black hole would be the same as water, be five grams per teaspoon of black hole. Oh, I see, because all the masses just concentrated inside of this really really big hole. Exactly. And again we're saying we don't know where stuff is inside the hole. You know, we'll talk about that in a moment. But if you have a really really dense blob of matter that forms a black hole, then it's event horizing is so big that it's really on average on it's not denser than the water. Do you see them unsatisfied by that? Well, I'm just confused a little bit. So you're saying it's it's you need a billion sons for this, right, four billion sons. Four billion sons. So if you stuck four billion sons inside of a sphere that big, it would be a black hole. It would be a black hole. It doesn't matter how those sons are arranged inside. It could be in a little point in the middle, or it could be in a you know, the form of unicorns spread all over the whole. It would still create the same black hole. They could spell out your name absolutely. So you're saying that we don't know what the mass, how the mass is distributed inside of that black sphere. It could be anything that's right, and we don't because we can't see inside black holes. So we don't know what the distribution of mass is. Is it all in one little point in the center. Is it a little fuzzier because the quantum mechanics is it's some broader distribution. We don't know because we can't see. That's why it's a reasonable definition to say, you know everything inside this sphere, because we can't see any deeper anyway. Anything beyond that requires speculation. I always thought black holes had to be like a point. Everything had to be inside of a little point. But you're saying that they don't. They could. They could really be like like a fluffy cloud of four billion sons. That's right. And another cool thing is that any amount of matter can become a black hole as long as you put it in the right density. Right. You take your teaspoon of earth or a teaspoon of water, you can make that into a black hole if you candense it down to a small enough area. Right, however small that event horizon has to be. But if you have enough mass, right then then it doesn't have to be that dense. That's the point. Right, So you take four billion sons, you can distribute them in a really big area and it will still be a black hole, a really huge black hole. So I don't recommend that if you are distributing sons around, please be careful not to make a black hole. It's easier than you think can be careful handling those sons. Yeah, So the point is for huge masses, it's easier to make a black hole because they don't have to be as dense for small masses, like you want to turn your teaspoon of water or tea into. A black hole has to be really dense to become a black hole. There is a number, right, you can calculate how small you have to compress that into. But it has to be really dense, all right. So then, so a super massive black hole that's a four billion times the mass of our Sun would actually not be that dense. It would be about us dance as a tea spoon of water, that's right. But if you made a black hole out of just one sun, right, then it would be really pretty dense. It would be about as dense as a neutron star. Oh, I see, huh about us dance, But but it could be denser. Well, smaller black holes in that could be denser than neutron stars. Yes, but the smallest black hole we've ever seen is about six times the mass of the Sun. So in terms of actual stuff we've we've observed in the universe, then the densest black hole we've observed is not as dense as neutron stars because we've never seen one smaller than six solar masses and I have to be smaller than that to be denser. But so why haven't we seen one? Could one exist? They certainly could exist. Yeah, there's no minimum size to a black hole. Remember, at the large Hadron Collider, we think we might create black holes and those black holes would be like particle sized, So there's no minimum size to a black hole. So they certainly could exist. There could be black holes out there that are the mass of the Sun, or half the mass of the Sun, or the mass of one Horge for example. They could exist, but they're harder to see, right. Smaller black holes are harder to see. So the densest thing in any of the universe is probably a black hole, but it would have to a be a small black hole less massive than our sun and be we haven't seen what. So technically the densest thing we've seen is a neutron star. But the densest thing that could exist is a small black hole unless you're willing to pierce the veil of the event horizon and talk about what's going on inside the black hole. What's inside a hole? Right, Well, then that's the thing we don't know right now. Originally, Einstein and general Relative they say, in the center of a black hole is a singularity is a point, and a singularity means a point of infinite density, right, at a point where there is a huge amount of mass in zero volume, which is pretty hard to get your mind around, like how do you have stuff in no space? But black holes are hard to get your mind around anyway, So that's what Einstein would say. I would say, Oh, the answer this question is obvious, it's the singularity inside a black hole. But but que quantum mechanics, and he wouldn't say that. His spokesperson would say that, I guess um Foundation, that's right, the estate of Albert Einstein Um. But the quantum mechanics folks would say, look, we know the universe is quantum mechanical, and quantum mechanics says, you can't have that much stuff in a well defined location, right. Quantum mechanics says, we know there can't be a singularity at the center of black holes. We don't know what's there, we don't know how it works, we don't know what's going on. And at that point gravity gets so strong that our theories of quantum mechanics don't work, and we don't have a theory of quantum mechanics that work when gravity is really really powerful um, So it's a big mess. We don't know what's going on inside a black hole. If it's if general relativity is correct, which we're pretty sure it's not, then there's an infinite density singularity. If quantum mechanics is correct, which we think it is, but it doesn't work inside a black hole, then we don't know. So what's the densest thing in the universe? Apparently it's the ignorance of physicists. We don't really know i'near these things. We have no idea, that's the answer. We have no idea what the densest thing in the universe is. It could be a neutron star. It could be a small black hole, It could be a singularity at the center of a black hole. It could be something else weird and quantum mechanical that's going on inside a black hole. We just don't know, all right. So that so that's the answer to what is the dnist thing at the universe is? We don't know exactly, and it kind of depends on what we've observed and what the true theory of physics is at these extreme situations. That's right. But the densest thing we've ever found is a neutrons are, which is plenty dance to impress you about extreme densities in the universe, right, it goes from like a proton in a teaspoon up to a million Eiffel towers in the teaspoon. So there's an enormous range of densities. You know. The universe is not just like uniform and spread out right, it's like mostly empty with these incrediblely tight packed pockets. And that works even in France. That works email in France, exactly all right. Thanks for joining us and another one of our Extreme Universe series. We hope you enjoyed that. Thanks for tuning in, and hey, if you have a question about the universe or or want us to talk about another extreme thing in the universe, let us know. If you still have a question after listening to all these explanations, please drop us a line. We'd love to hear from you. You can find us at Facebook, Twitter, and Instagram at Daniel and Jorge That's one word, or email us at Feedback Daniel and Jorge dot com. Thanks for listening and remember that Daniel and Jorge Explain the Universe is a production of I Heart Radio. For more podcast from my Heart Radio, visit the i Heart Radio app, Apple Podcasts or wherever you listen to your favorite shows,