Listener Questions #36

This is an iHeart podcast. Guaranteed human. Spring is here and it's time to get out in the garden. British Garden Centers have all you need to make your garden bloom. Whether you're new to growing or already know your way around the garden, we've got the plants, tools and expert advice to help transform your outdoor space. And when your shopping is done, relax and refuel in our restaurants. Find your nearest center at BritishGardenCenters.com. For every gardener, for every garden, for everyone. Make it bloom with British Garden Centers. 8 p.m. Search UCSCollegeGroup.ac.uk. The otteron pops up when protons collide and bounce. A three-gluon ghost, too quick to announce. When microbes invade and our skin begins to swell, the immune system calls upon the Langerhans cell. If our universe sits in a black hole's embrace, do our own black holes nest like a matryoshka in space? Whatever questions keep you up at night, Daniel and Kelly's answers will make it right. Welcome to Daniel and Kelly's Extraordinary Universe of Listener Questions, episode number 36. Hello, I'm Kelly Wienersmith. I study parasites and space, and I think that this was one of our better rhyming starts to the show. Hi, I'm Daniel. I'm a particle physicist, and my goal is to write a rhyme that Zach Wienersmith doesn't skip. Well, I mean, I think you're violating the era of time with that, because, you know, he's just, he's not going to listen to you. Because, you know, he's just, he's not going to listen to any of them. No, he's listening to this part right now, and he's thinking, hmm, maybe I should go back and listen to the rhymes. See? Okay, well, so here, he's going to have to listen, because here's what I was thinking we could do today. All right. So I asked ChatGPT to write a two-line poem about each of the topics that we're talking about today, and I thought that after we answered each question, we could revisit our poem and then compare the ChatGPT poem, and one, see, we could have people like weigh in on which one they thought was better. Yes. And we could see if ChatGPT was like accurate at all. All part of our scheme to force Zach to listen to our terrible poetry. That's right. That's right. And, you know, if we're going to force him, it should be on a day when we did like pretty okay. So. And since you can rewind podcasts, we can break the podcast era of time. We can. For background for anyone who's wondering, Zach is my husband who has a degree in literature who cringes whenever Daniel and I make any attempts at poetry. So Zach. But today we're not just here to needle Kelly's husband. We're here to answer your questions, because you're curious about the universe from the stuff inside your body to the vast celestial bodies that make up our universe. You want to understand that you want to fit it all in your mind and make it make sense. But sometimes it doesn't play along. There's something that sticks out and doesn't click together. And we are here to make it all work. Yes. We are putting together the puzzles for you. And let's start with the puzzle presented to us by Tammy from Denver. Hi, Daniel and Kelly. This is Tammy from Denver. I recently heard about the Otter on Particle on another podcast, basically that it exists, and would love to learn more about it. I have just a few questions. How was the Otter on discovered? Does it exist naturally or is it created? And if it's created, then how? Is the particle stable or does it decay? And if it decays, what is the half life? Does the Otter on interact with other particles? And if so, how? Would it combine with them, repel them or would it just ignore them? If combined, would the resulting particle be stable? Thank you for answering my questions. And I really enjoy the show. All right, I'll be honest. I have never heard of the Otter on Particle. So I'm excited. Otter on. Yeah, there's two D's in it. It's an odd name, but it doesn't smell bad. The Otter on sounds like a really stinky particle. We'd have to get a smell expert back on the show to talk about the Otter on particle, but all right, I guess this one is in your wheelhouse. So tell us about the Otter on Particle. The Otter on Particle is not a particle in the sense that you are probably thinking. You're imagining the universe is made up of little bits and bobs and they come together to build apples and dinosaurs and all sorts of stuff. And you can think of them as like tiny little marbles or little bits of matter and ask questions like how much mass does it have? How long does it live? How does it interact? But physicists are very generous with the term particle. It can mean lots and lots of different things. And here the short answer is that the Otter on is not a little bit of stuff. It's actually just kind of a pattern seen among gluons when protons or anti protons collide. All right. So what does that mean? What does a pattern indicate? So to understand what's going on here, we really have to understand some crucial details of the strong force, which is who's in charge when protons collide. So often we smash protons together, right? Like at the Large Hadron Collider, we have a beam of protons going one way and another beam of protons going the other way. We smash them into each other. Sometimes they just bounce off each other like the way two billiard balls would. There's no internal structure at play there. They just bounce off each other. And we call this an elastic collision. Sometimes they smash and like what's going on inside the protons interacts. And we call this an inelastic collision. And then you get like new particles, etc. But if the protons are just bouncing off of each other in an elastic way, right? Not breaking open, just being treated as if they were their own particles. Then how does that interaction happen? Right. The protons get close to each other. How do they bounce off exactly? Well, they do that by exchanging virtual particles. Like we can talk about how electrons repel each other by exchanging a virtual photon. Or if you prefer the field picture by having ripples in the electromagnetic field between them. When protons bounce off each other, it's similar, except that they exchange gluons. Because gluons are the field that mediates the strong force. It's the analogy of the photon for electromagnetism. Still with me? Still with you. In my head, I can imagine what a photon is, but I'm having trouble remembering what a gluon is. Yeah. So a gluon is just like a photon for a different force, right? Photons we have for light and electromagnetism. Gluons are for the strong force. Remember, we have sort of four fundamental forces. There's the strong force, the weak force, electromagnetism and gravity. Well, the photon is for electromagnetism. The weak force is the W and Z particles. And the strong force has the gluons. OK, right. OK. So we have two protons coming together and the exchanging gluons to bounce off of each other. But gluons are really, really weird. OK, I'm still feeling like you don't get to judge me for using Latin names with all the terms that you're throwing around now, but I'm I'm still following you. I'm still following you. Well, unfortunately, a lot of the terms we use are not Latin names. They're just adopted from English. And then we give them totally different meanings to be massively confusing. Right, which seems even worse than what we do. But totally agrees even worse. For example, we talk about gluons as having color, even though it's not like you can look at them and see colors. But color for gluons is an analogy to charge for electrons. Electrons have a negative charge, protons have a positive charge. That's the electromagnetic charge. The strong force has its own charge, but we call it color because there are three varieties, red, green and blue. But there's a crucial difference between the strong force and electromagnetism. While the photon has no charge, right, it interacts with charged particles, but the photon itself is neutral. Gluons do have charge, and that's going to turn out to be crucial for forming this interaction among gluons that we call the otteron. So the gluon itself interacts with all particles that have strong charge or color, but it also itself has color. It is a colored particle. It's like if the photon was positive or negative in charge. OK, so when we say that a gluon has a charge, but we call it a color instead. Should I think of it as having a charge, but we're just calling it a color, but it actually is like has a charge that you can think of. Why don't we just call it a charge? We do sometimes call it a charge if you're thinking charge more generally, not just electromagnetic charge. So you can think of strong charge. Every time we say the word color, you can just think strong charge, and that totally works. OK, just realize that it's not electromagnetic charge. You're not talking about positives and negatives here. OK, so then this is going to be a real basic Kelly's and Barry's question. So then what does charge mean in a much more general sense? Oh, yeah, I think we have a whole episode about that. But charge means the two fields are coupled together. So the electromagnetic charge couples the photon field to any other kind of field. So any field that has a charge the photon interacts with really, that's a coupling between those two fields. It means energy can slosh back and forth from the electron field to the photon field or from the gluon field to the cork field. So a charge is just like a coupling between two fields that says energy can transfer between them. OK, got it. All right. So back to the gluon. Why are we talking about the gluon having color or having strong charge? Because it has to in order to form this order on. And it's really fascinating. I think this is super cool why the gluon has colors. One more detail we need to understand before we get to the order on, which is why you have to have multiple gluons. When two electrons come together, they can exchange just a single photon and they're done. And that's because the photon doesn't carry any charge. Right. So the electron comes in with negative charge, leaves with negative charge. It's all good. But because the gluon is charged, protons cannot just exchange one gluon because protons have to have no color charge. Any object that's out there in the universe can't have a color charge all by itself. And so if a proton comes in and it's one gluon, because that gluon carries away some color charge, then the proton itself would be color charged and the proton that received the gluon would be color charged. So the protons have to exchange two gluons, one going each direction so that the total color charge is canceled out, but they can still exchange momentum and bounce off of each other. So let's recap. We're talking about what's happening when two protons bounce off of each other without destroying each other. They're just exchanging some momentum and they do that by exchanging gluons. But because gluons are charged and protons are not charged under the strong force, then the gluons have to balance in charge. And so you have to have one going one way and one going the other way. OK. And that's where the auteron comes in. The auteron is like an interaction, a pattern between those two gluons. While the gluons are between these two protons, they can also interact because they both have color charge. And that's what an auteron is. It's like a compound of gluons that are sort of bound together very briefly while two protons are interacting. OK, so I should think of it as two gluons that are bound or they just kind of hang out near each other like awkward teenagers. Yeah, it's very short lived. It's not stable. It's really on the edge of whether you should call this thing a particle. It's more like a mathematical observation. And it turns out that you can exchange more than two gluons. You can exchange three or four or nineteen. And if you take all the exchanges, which have an odd number of gluons, three, five, seven, nine, eleven, and you add them all together mathematically, then the movement of that thing, the way the momentum gets exchanged between the protons is exactly as if there was a single particle exchange. So take all the odd number of gluon exchanges with the gluons are doing weird stuff and interacting along the way. Add them all together. You got a big, ugly mess of mathematics, but then it collapses. It simplifies into a very simple equation. The same equation you would write if you had a single particle mediating this exchange, and that's what the other on is. It's like this abstraction of all of these complicated interactions, which happens to come together into a very simple equation. And that's why they call it the odd Iran, because it's all the odd number of gluon exchanges, three, five, seven, nine, etc. I think I don't follow why it has to be odd numbers of exchanges. This mathematical simplification to take a bunch of terms and put it together into one particle works for the odd terms. It also works for the even terms. Even term has a different name. So we call these the other one and the other ones, I think we call the pomeran. Oh, come on, they need to be the even or on or something. Why are they the potter? I was embarrassed to even tell you, I know it's crazy. It's unforgivable the way we've named these things. It is. Yeah, I'm upset. I'm getting worked up over here. Yeah, so this is a really interesting bit of physics, Tammy. And I'm glad you asked about it. Apologies that it turned out to be so complicated. There's lots of little details that you have to put together here to understand what an odd Iran is. I'll try to recap it again one more time, just to make sure it's all coming together. When two protons bounce off of each other, they have to exchange gluons. It has to be more than one gluon because the gluons themselves carry charge, but the protons cannot. And they can also do three, five or seven or nineteen. And if you add up all the odd terms together, it looks mathematically equivalent to exchanging a particle. That doesn't mean that particle is there and real and you could like look at it and say, oh, there's an auto on. It means that we see this pattern in the universe and we wonder, hmm, that's cool. Let's treat it as if it was a particle. And this is a really subtle effect. It was predicted in 1973 and it took 50 years for us to find evidence of it. And we had to compare proton, proton collisions with proton, anti proton collisions, because those have a small difference in how many odds would be made. And finally, 50 years after it was predicted, they saw evidence for this in those collisions. So you asked how is it created? And the answer is in proton, proton interactions. You also asked if it decays. Well, it only exists very, very briefly. It doesn't exist on its own and then turn into other stuff. So in that sense, it always decays. It's more like a transient exchange object. It's not like a building block that you can use to make other stuff with. OK, so that was a great explanation before we hear what Tammy thinks, because maybe we can also get Tammy's input on the poem thing we're going to get to. All right, so here's what chat GPT had to say. Of the Otteron, chat GPT says, in quantum shadows, the Otteron leaves its subtle trace. An asymmetry of gluons shaping matters, hidden face. So is that is that correct, Daniel? It's not wrong. It's a little heavy, the vague symbolism. OK, all right. And then you said. The Otteron pops up when protons collide and bounce, a three gluon ghost, too quick to announce. Yeah, so Tammy, let us know what you think of the physics explanation and whose poetry you prefer. Oh, putting Tammy on the spot. All right, that's what we're going to do to all the listeners today. All right, throwing it to Tammy. Hi, Daniel and Kelly. Thanks for answering my questions and correcting the assumption that the Otteron is a particle and for explaining how it's created. You do a great job of explaining complicated concepts in an accessible way. And I learned new and interesting facts and concepts from both you and Kelly every episode. Thanks so much. And I'll see you next time. Thanks. All right, we're back and we're answering questions from listeners today. We are satisfying your curiosity. Up next is a fun question from Jude from Washington State. Hi, I just heard of Langer Hand cells. The explanation described very generally what they do, but it didn't describe how they work. Can you explain what Langer Hand cells are and how they work to help the skin respond to new stimuli? Thanks for helping us understand the universe. Jude from Washington State. All right, so after I reread this question, I thought to myself, oh, this is one of those that kind of feels like maybe I'm being asked to do someone's homework. And then I thought, well, unfortunately for Jude, if that's the case, it takes me about three months to answer someone's question. So it's no longer helpful. And also I'm sure Jude is just genuinely curious about Langer Hand cells. We always assume good faith. That's right. And I'm being totally unfair. So Langer Hand cells. Actually, I did not know about Langer Hand cells. So I really enjoyed getting a chance to read about them. They were first described by Paul Langer Hans in 1868. Did he name them after himself? Oh, gosh, I don't know. I know that for a while there, people were naming things after other people. And so this could be somebody being nice and naming something after someone else. I don't know. Maybe he did name them after, you know, I would name something of the Wienersmith cell if I could. So I can't judge too harshly, frankly. So this guy was just looking through a microscope and saw something new and weird. Yeah. Yeah. And so actually, as I understand it, he thought that it was a projection of a neuron going into your skin. So you find these cells in like your epidermis, which is the outer layer of skin. And they looked, you know, when you imagine a neuron in your head, they sort of end with like sort of like a circle with that then has all of these projections sort of coming out from it. Well, it kind of looks like that circle with a bunch of projections. And so he thought like, oh, this is kind of neuron like. And so maybe it's part of the nervous system. But then a lot later, we realized, no, it's actually part of the immune system. And so the Langerhans cells are like a line of attack from the immune system that is acting in your skin. OK. And so you find them again in your epidermis. And so this is the outer layer of skin. And in particular, they're sort of like moving around inside of your keratinocytes. Keratinocytes are like. So if you look at your fingers, you've got this like thick layer that is impermeable. And those are your keratinocytes. And so I learned about, you know, I'm going to try to not throw too many words at you. I know I can see Daniel's face already starting to roll his eyes. But but I didn't know this and I'm excited, right? OK, so the deeper you go into the top layer of skin, yeah, your keratinocytes are alive and they're fed by your blood vessels. But the closer you get to your surface of your skin, they essentially start suffocating and dying and then getting like cemented and smushed together to produce the like layer that protects you. And so I didn't realize that, like, just, you know, the closer you get, the more like dead they are. And over time, they kind of like slough off. And that also helps protect you from stuff because, like, you know, if you've got like a bad microbon there, eventually they kind of like fall off with your dead skin cells and they're like, no, I was trying to get in there. And now they're gone. This gives me the mental impression that our skin is like a slow motion waterfall just sort of like cascading off of our body. It is kind of like that. Yeah. I mean, you're you're like turning over your skin cells, you know, pretty regularly, they're getting like sort of sloughed off and water fall off. Wow, crazy. The waterfalls are more beautiful to think of than your skin cells falling off, but anyway. And so these Langer hand cells are part of these keratinocytes. They are living amongst your keratinocytes. And so they're a different kind of cell, as I mentioned, they kind of look like the end of like neurons. So they've got all of these like long projections that are sort of weaving amongst the keratinocytes. And so that lets them sort of like feel around for invaders. And then they're unique immune cells in that they do two pretty different jobs. So one thing that they do is that they're macro phage like and macro phage means big eater. And so when they encounter an invader, they essentially engulf it and consume it. Oh, wow. So that it, you know, can't do any damage. But what if there's more? The other thing that they do is they take it to your lymph nodes so that they can present it to other parts of your immune system. So other parts of your immune system can start mounting a defense in case it turns out that there's more and you need to mount a bigger defense. So they're moving around, right? I'm imagining these keratinocytes is like squishy squares squeezed together. But these Langerhands cells can like go between them, like in the alleyways. Yeah. So again, they're not really like squares. They're like cut, they're like circles, but out coming out from the circles are all of these long filaments. They're think more like an octopus, but the arms are sort of like weaving amongst the cells, the keratinocytes, like the cells in your skin so that they can like explore all around to try to find invaders. Wow. And so there's security guards, they like attack them if they can. And if they have too much to handle, they like bring them back to the lymph node and say, book them. So they, they definitely attack them. And then once they've eaten them, they can like still take a piece of what they've eaten and bring it to your lymph nodes and be like, OK, guys, look what I found, keep your eye out for this and like maybe get ready to mount an immune response. Oh, I see. And so in that sense, they're they're dendritic cells, which is another kind of immune cell. So they do two different jobs. They eat it and then they alert the immune system to the presence of invaders in case a bigger attack needs to be mounted. Wow. Fascinating. Yeah, it's pretty cool. And so they can come from bone marrow. So like say you've got a massive infection in your finger and it's like you've got a lot of inflammation. Your Langer hand cells will start moving towards that inflammation to like, you know, help deal with the invaders to help eat them and sort of figure out what needs to go on. And then at that point, your body might not have a lot of Langer hand cells to replenish after they've all sort of gone to do this job. And so your bone marrow will make more Langer hand cells and they'll sort of move up into the skin to replace the ones that have been lost. But during normal periods, your Langer hand cells will just sort of like divide and replicate on their own. And part of how we know that your Langer hand cells divide and sort of self-renew is that when we've done human limb transplants, we've looked at Langer hand cells over time and the donor's Langer hand cells are still there over long periods of time. So they must be replicating on their own as opposed to coming from the patient's own bone marrow. Yeah. I thought that was kind of interesting. That that's how we sort of figured that out. So Jude asks how they work to help the skin respond to new stimuli, but it sounds like they're more involved in the immune response. Yeah, that's right. They're not like helping you feel things like the, if the stimuli is a bacterial invader, the way they help you respond is they eat it and then they tell the immune system that this is something that you need to prepare to attack. Another thing that they regularly do, like if you aren't encountering anything bad, every once in a while, the Langer hand cells will leave and just go to your lymph nodes and be like, Hey, this is what you look like. And so they've got two modes. They've got a like what's called an activated mode where essentially they're like, I am bringing you something bad. I am worked up. I am activated. But they also have a mode where they're just like, Hey, I'm just telling you what you look like. This is something you don't need to attack. And so they're just sort of like trying to give you a heads up that like, here's what you look like. Don't freak out about you. And, you know, anyone who has an autoimmune disease will know it's important to not freak out at your own body. And so this regular reminder of what you look like is important. And so that's, that's another thing that they do. Unfortunately, sometimes things go wrong. And when things go wrong with these cells, you can get Langer hands cell histiocytosis. That doesn't sound good. No, it's not good. This is a kind of cancer that can be kind of hard to diagnose because it can be in your skin, but it can also end up in places like your bones or your lungs or your central nervous system or your lymph nodes. Basically, they get like lodged somewhere and they start replicating. And we don't really understand very well why this happens. And it can give you lots of very different symptoms. So sometimes it can be a little bit hard to diagnose. And I was listening to a podcast with a pediatric oncologist who was saying that this is sort of an understudied kind of cancer because we don't understand Langer hand cells particularly well. And so he was, you know, just like every other scientist arguing that we need more research and more money. And this is something you hear Daniel and I say all the time. Anyway, so yes, sometimes things go wrong with these cells. And this is unfortunately another cause of cancer. It's also incredible to me that this ever works. And this whole system seems so baroque, so complicated, so easy to break down that I'm amazed that people are just like walking around all day with everything going normally. The immune system in particular just seems incredibly complicated. And the more we study it, the more complicated it seems to get. And so, yeah, it is it is kind of amazing that we're not all just sort of shambling and falling apart every moment of every day. So speak for yourself. I kind of am over here. I'm rounding up to 100 these days. Don't forget. Oh, I'm not. I'm not. I'm I'm happy with my my actual age of 40, 40. I'm rounding down, actually. It's also incredible to me that there's so much in biology that someone like you who's been doing biology for decades will be like, oh, I don't know anything about this. And they still like so much to learn. I know. I mean, I like, yeah, as as we've discussed, like when I was at UC Davis, they were just so many biology departments. Yeah, yeah, there's I could spend my whole life, literally my whole life reading biology papers and somebody could still be like, oh, hey, have you heard about this cell in the human body? And I'd be like, no, nope, nope, that's new. But today I'm learning. But yes. And thank you to, you know, the listener questions. One of my favorite things is that quite often it's like, oh, haven't heard of that. But today, today I will be able to explain it, which is awesome. So should we go to the chat? G.P.T. poem? Yes. So what a chat G.P.T. compose about Langerhams cells. Sentinels in the skin, they quietly stand guard. Langerhams cells catch whispers of danger before it hits hard. I don't know if it's just your delivery, but I think chat G.P.T. is like a little overdramatic on the poetry. Yeah, yeah, no, I do think they're overdoing it a bit. They were super dramatic. I was a bit, I mean, I guess maybe I was a little overdramatic, too, but in like a superhero funny way, you know. So I said, when microbes invade and our skin begins to swell, the immune system calls upon the Langerhams cell. Langerhams. Anyway, so I think mine was way more fun. All right, Jude, well, we want you to weigh in. Let us know if we answered your question and also which poem you prefer. Hi, Kelly. That was great. I'm a librarian, not in school. No homework here. Genuine curiosity. I'd never heard of Langerhams cells until they were mentioned in another podcast. The description piqued my curiosity. My further reading was either too vague or too complicated. Your explanation made sense even to my non-science brain. As a bonus, I have a better understanding for how skin works. I didn't realize that Langerhams cells were so adaptive, identifying both friend and foe. Amazing biology, which gets to the Kelly versus Chat GPT poetry slam. Kelly's poem was more apt and vivid. You conveyed the superhero in the everyday that fits the Langerhams cell. Thanks. All right, we are back and we're answering questions from you today. We want to know what you are curious about, what part of the universe doesn't make sense right to us. Two questions at dandleandkelly.org and you'll get an answer. Up next, we're talking about black holes and the universe. Here's a question from Philip. Hi, Daniel. I'm Daniel. I'm a writer, not a librarian. I'm a writer, not a writer. I'm a writer, not a writer. Let's start with the question from Philip. Hi, Daniel and Kelly. This is Philip from Bucharest. With the hypothesis of the universe in a black hole doing the rounds lately in certain corners of the press, and which I might say you've debunked rather nicely in past episodes, I found myself wondering how would such a situation influence what we already see around us. For example, it seems that we already have black holes in our universe. Is physics as we know it even allowing for black holes inside black holes? Would the infinities be compounded? Or would that suggest that the singularities do not actually contain infinities? Thank you for the great podcast and can't wait to hear your answer. I can't wait to hear chat-chipi-tee's poem about this. I can imagine black holes within black holes is going to give a particularly epic and overblown poem. Also, I'll note that I'm always excited when we have a listener from another country. It still kind of amazes me that we have this technology that allows us to reach out to people from all over the world. Philip is from Bucharest. That's pretty cool to me. That is very cool. Super fun question. Thank you, Philip. Love this. First, let's remind people why our universe is not a black hole. I mean, you hear this a lot in popular science. It's really fun. But it glosses over a lot of really important details. So on the surface, the universe seems like it has something in common with a black hole. I mean, a black hole has an event horizon beyond which nothing can emerge. Well, our universe has a cosmic horizon. It's a place past which we cannot see because the universe has a finite age and the light has finite speed. So something that's far enough away, an event that happened a long, long time ago, far, far away, life from it will not have reached us yet. So there's parts of the universe that are just invisible to us. Teach the controversy. So both of those things have the word horizon in them. But that's really the end of the similarity. Event horizon means nothing will ever escape the cosmic horizon. We will eventually see those things if we wait long enough. So it's sort of a statement of what we can see right now. Whereas an event horizon says you will never see this stuff. In fact, the definition of an event horizon requires you to wait till the end of the universe to know for sure that nothing came out. It's defined as the place from which nothing ever emerged even at infinite time. So that's really very superficial. The other similarity between black holes in our universe is singularities. General relativity predicts that black holes have singularities at their heart, these points of infinite density. But we know that's not real anyway because quantum mechanics says that can't happen and that's a general relativity only extrapolation. So it's fun to think about but unlikely to be real. In the same way, if you wind the universe back in time, it gets denser and denser as you reverse the expansion by cranking that clock backwards. And if you keep going and again ignore quantum mechanics and just use general relativity, then you get to a moment when the universe had infinite density. So that sounds similar to the black hole singularity but it's really quite different. Black hole singularity is a location in space, a point of infinite density. Whereas the Big Bang singularity is a moment in time that occurred everywhere. If the universe is infinite, then it always was infinite and then that singularity was everywhere. So they both contain the word singularity and have infinities, but they're very, very different kind of beasts. Okay, but so here's the thing. I kind of zoned out and what I heard was that both of them have horizons and both of them have singularities and so I'm pretty convinced. I'm kidding. So we're the listeners who have been zoning out. Here's one more argument, which is there's a fascinating coincidence in our universe. We can calculate the radius of a black hole's event horizon based only on the mass of the black hole and also the speed of light and the gravitational constant. But the thing that changes from black hole to black hole is the mass and that's what controls the radius. Very simple calculations called the Schwarzschild radius. Now, if you put into that equation the mass of the observable universe, you get out a radius. And what does that radius mean? It means if you had a black hole, the mass of the observable universe, what would be the radius of the event horizon of that black hole? It's fascinating that that turns out to be the same size as our cosmic horizon. That means that if you had all of the mass of the universe in a singularity, it would be a black hole whose size is the universe. And so that's kind of cool. It sounds like it means that our universe could be a black hole because anyway, it has the mass and radius of a black hole, right? But of course, here comes Daniel to ruin that fun party. That calculation assumes a whole bunch of stuff. It only works in an empty universe where you only have a black hole and there's no expansion. In our universe, we don't think it is empty past the cosmic horizon and it is expanding. So the calculation does not apply even though it's a fun coincidence. All right, so that's the warm up. As Philip says, the universe unlikely to be a black hole, even though that would be more fun if it were. His question is, could you have black holes within black holes? Like if the universe was a black hole, could you have a black hole in our universe? Because we see one at the center of the galaxy and we've observed them in the universe. Is it possible if we're in a black hole to have black holes or more generally, can black holes exist within black holes? Super fun question. And the first thing you might think about is, well, merging black holes. Like what happens when two black holes come together? Is there a moment there when you have like two singularities within the event horizon and could you call that like a black hole within a black hole? Kind of, yeah, but it's temporary. What happens here is that the black holes approach each other and then they form a common horizon from their common energy. So they still have their own horizons, right? The original event horizon, you would calculate just for that black hole. But because of their combined gravitational power, they now have a larger combined horizon. So in that sense, they're kind of black holes within a common black hole, though it's not going to last because eventually they will radiate energy and they will orbit each other and they'll ring down to form one singularity within the event horizon. And then you're just going to get one bigger black hole. So it eventually becomes one event horizon. But temporarily you can have cool stuff like two singularities orbiting each other within the event horizon. Just to try to remember from a previous episode, but when we talked about when black holes get together, it is more likely that one throws the other one out, right? Or is it more likely that they merge? It depends a lot on the dynamics. If two galaxies merge, then you can get their central black holes merging. Or you can get one of them kicked out and that definitely has happened. It's a more complicated situation there because you have more than two objects. You have like the whole galaxy and the black hole. And so three body systems are much more chaotic than two body systems. Got it. And so that seems cool. And then you might try to engineer a situation where one black hole is much bigger than the other. Like imagine a tiny baby black hole being shot into a mega black hole. And then you can ask like, how long can it survive within that mega black hole? Because that feels like a little black hole inside a bigger black hole, right? Well, that's basically the same scenario we just talked about. It's again the merger of two black holes, except one of them is really big and one of them is really, really small. Same thing is going to happen is they're going to form a common horizon. They're going to orbit each other and then they're going to merge. It's going to look a lot more like one eats the other just because the center of gravity is closer to the bigger one. But fundamentally, it's the same physics. Two black holes merging and one big one eating the other one. Just sort of a change of reference frame. So so far, we have a temporary black hole within the other black hole. But if you've been listening to the show, we talked last time about Cauchy horizons and complicated structure inside black holes. So if you take your big black hole and you spin it, then you have an event horizon still. But now within the black hole, you have another horizon. It's called the Cauchy horizon. Outside the Cauchy horizon, things fall in just like they do in normal black holes. But inside the Cauchy horizon, the structure of space time is very different. And the singularity is no longer inevitable. Like you can have stable orbits around the singularity. You don't have to fall into it. For GR nerds, the singularity becomes time like. It's no longer true that every path through space leads to this singularity. And so it's possible, though it's very, very difficult because life inside the Cauchy horizon is extraordinarily unstable and unpredictable. As we talked about last time, it's not actually deterministic because now you have a singularity that can appear in your past life cone. But in principle, for the purposes of sounding like cool pop scientists, you can potentially exist within the Cauchy horizon of a spinning black hole for quite a long time, saying it's stable is maybe a bit much. But in that sense, you can have a mini black hole within a bigger spinning black hole and have it hanging out there for quite a while. So is that a yes to that? What was the actual question? Would the infinities be compounded or would that suggest that the singularities do not actually contain infinities? So the infinities here are densities, right? Not masses. Each black hole has a finite mass and that mass controls its vent horizon. The singularity is the density saying that that mass has been compacted to essentially zero space. So yes, you can add two masses together and you're going to get a bigger mass, a larger but still finite mass, and it's still going to have an infinite density. Of course, all of this is just ignoring quantum mechanics and quantum gravity and assuming general relativity is the law of the land, which we don't think it is. But for the purposes of this question. So yeah, you're going to get compounded infinities in that sense. Okay. All right. Are we ready for the poem? Bring on Shakespeare GPT. Okay, here we go. A black hole nested where no light can ever flee. An abyss within abyss folding infinity. Now's a little bit tortured. All right. Oh, we got to give him your poem again. All right, do it. If our universe sits in a black hole's embrace, do our own black holes nest like a matrushka doll in space? Don't know if I said matrushka correctly, but he knows. I'm sure he knows what we're going for. Let's hear from Philip if we answered his question and if he likes chat GPT poetry better than mine. Hello again, Daniel and Kelly. Wow, it's like they say, come for the black holes in science, stay for the poetry slam with AI. Thank you for the thoughtful answer to my question. I guess it sits firmly in the yes, but category along with many other physics topics. So based on the fine print of the theory, the singularities could technically nest inside one another, but that remains in no way relevant to the universe we observe. Imagining that is a fascinating thought experiment, but still leaves us no way to deduce something about what is really happening inside the event horizon. Well, I'll try to do better next time, and thank you for now. Well, Daniel, I feel like what we've learned today is that what we laughed at the fact that chat GPT's poems are sort of like a, you know, overly emotional teenagers poems. To be honest, I'm not sure they're that much worse than ours. So chat GPT is at like Daniel and Kelly level of poetry right now, which is, you know, not Emily Dickinson. Maybe we should feed it all of Zach's books and ask it to write Zach style poetry. I still imagine Zach would do better, but Zach and I did have Sunish scraped by AI. Oh. Were any of your books scraped by AI and were they part of that? Yes, absolutely. Part of that big case settlement thing? Well, maybe we should get the real Zach to write our poetry one week. I asked him and he politely declined. Maybe it's better we keep some parts of our lives separate. Yeah, that's good. All right. Well, thank you very much, everybody for listening and for sharing your curiosity. It's your desire to understand the universe that powers our podcast. Please send your questions to questions at Daniel and Kelly.org. We answer every question and some of the questions end up on the show and we look forward to hearing from you. We really do. Thanks everybody for listening. Please go and do us a favor and rate the show on whatever podcast app you're using. It really helps people find us. Daniel and Kelly's extraordinary universe is edited by the amazing Matt Kesselman. He really is a wizard. You can also find us online on Blue Sky Instagram and X, the end K universe. Come engage with us. You can email us at questions at Daniel and Kelly.org. We really do want to hear from you. And you can find our website www.DanielandKelly.org where you'll also find an invitation to join our Discord where everybody comes and talks about the amazing universe. And we also have the most amazing moderators. This is an iHeart podcast. Thanks for joining us. What are you getting? Like a great night's sleep and a tasty breakfast. You know what you're getting the premiere in. This is an iHeart podcast. Guaranteed human.