Great, Big Questions about the Universe

00:00:08
Speaker 1: Hey, or hey, if you had to leave a Yelp rating or for the universe, what would you give it?

00:00:14
Speaker 2: Can I give it like a trillion trillion stars?

00:00:18
Speaker 1: I think that might break their database. But I'm guessing you're saying that the universe is pretty great.

00:00:24
Speaker 2: Yeah, it's pretty great in a lot of ways.

00:00:26
Speaker 1: Right, you mean great is in it's awesome.

00:00:28
Speaker 2: It's awesome, and it's also really big. It's a great big universe.

00:00:32
Speaker 1: Hey, that's a catchy phrase.

00:00:34
Speaker 2: Yeah, somebody should use it for the title of a new book.

00:00:38
Speaker 1: That's a great big idea.

00:00:55
Speaker 2: Hi am Poorham, a cartoonist and the author of the new book Oliver is Great, Big Universe.

00:01:00
Speaker 1: Hi. I'm Daniel. I'm a particle physicist, and I also think the universe is pretty great and big.

00:01:05
Speaker 2: It's a great big universe.

00:01:07
Speaker 1: Great also means big, doesn't it? Or isn't that part of the etymology of great?

00:01:11
Speaker 2: I think technically can mean several things, like it's great, like you like it, but also like it's great, like it's.

00:01:16
Speaker 1: Big, Yeah, like great Britain. Right, it's pretty great and also big and pretty British. But anyways, welcome to our podcast. Daniel and Jorge Explain the Universe, a production of iHeartRadio in which we try to accomplish a feat which sounds impossible, to download the entirety of this great, big universe into your mind, to summarize all of the whizzing and banging and frothing and tewing and frowing of the tiny little particles that make up this universe into a mathematical story that somehow makes sense to these grown up apes.

00:01:46
Speaker 2: That's right, because it is a great, big universe full of amazing facts that we like to talk about here on this podcast, and also rate I guess with stars.

00:01:54
Speaker 1: The universe is definitely filled with stars, big glowing stars and also you know, blowing up pop stars.

00:02:00
Speaker 2: Well, hopefully I'm not literally blowing up, but it is filled with stars, planets, asteroids, galaxies, dark matter, dark energy, and also people young and old. We're here to ask questions and also sometimes answer them about the universe.

00:02:14
Speaker 1: That's right. We think everybody should be curious about the universe. When you stare up at the night sky, we want to know what makes you wonder, What questions do you have about how it all works? Not just the earth that's under our feet, but the whole big, great universe out there.

00:02:28
Speaker 2: Yeah, and speaking of great big universe, we are here to celebrate the release of my new book called Oliver's Great Big Universe, which is out now and you can go out and buy it.

00:02:37
Speaker 1: Yeah, congratulations. Tell us a little bit about the book and why you wrote it.

00:02:41
Speaker 2: Yeah, it's an awesome book. It's maybe the only book that is endorsed by Jeff Kinney, the author of Diary of a Wimpy Kit, and also Carlo Rovelli, the theoretical physicists.

00:02:51
Speaker 1: That's quite a collection. Do you have to be a cartoonist or a theoretical physicist to read it?

00:02:54
Speaker 2: Absolutely not. I actually wrote the book for kids who wouldn't normally pick up a science book, and also for anyone out there who's interested about the universe. Yeah.

00:03:04
Speaker 1: Tell us a little bit about your approach. How do you attract people who aren't usually into science.

00:03:09
Speaker 2: Well, the book again is called Oliver's Great Big Universe, and it's about the story of this eleven year old kid named Oliver, who one day decides he wants to be an astrophysicist, but of course, being eleven years old, he doesn't quite know what that means, and so the whole story is about him trying to figure that out and also him explaining to other kids all of these amazing facts about the universe. So there's chapters about black holes, there's a chapter about dark matter and dark energy. There are chapters about the planets, and there are chapters about the time as well.

00:03:39
Speaker 1: And don't you, by coincidence, have an eleven year old named Oliver.

00:03:43
Speaker 2: Yes, it is not a big coincidence. So the whole book was kind of inspired by my son when he was in fifth grade. He came home one day and at the dinner table he announced he wanted to be an astrophysicist, and so we were like, do you know what that means? And he's like, I have no idea, and yeah, that of like confidence and shuitspa and curiosity is kind of what inspired the whole book.

00:04:05
Speaker 1: So what's it like when a cartoonist has his son saying I want to be a physicist. Is that like when a physicist has a son who says I want to be an artist?

00:04:12
Speaker 2: Yeah? Kinda? Are you gonna go no? No, it's cool. He's always been kind of a science kid. He's always been interested in science. He's in the math teams, in the Science Olympics team, and so it wasn't super surprising that he says that he wants to be an as a physicist. But it's pretty cool. Yeah, we try to encourage it, for sure.

00:04:29
Speaker 1: Awesome. Well, something we encourage in our podcast listeners and their kids is asking questions, is thinking about the universe, is wondering if they want to be an after a physicist when they grow up and what exactly that entails. And step number one of being an after physicist is just looking up at the night sky and wondering what's out there, how does it all work? What is in our great, big universe?

00:04:51
Speaker 2: Yeah, and so to celebrate the release of the new book, we are answering listener questions from kids today.

00:04:56
Speaker 1: That's right. I went out there and asked our listeners to ask their kid kids what questions they had about the universe. And so today we'll be tackling a few of those.

00:05:06
Speaker 2: That's always a risky thing to ask your kids what kind of questions they have or did you make it specific about the universe?

00:05:12
Speaker 1: I made it specific about the universe, which makes it totally generic.

00:05:16
Speaker 2: I guess the universe is everything, even the uncomfortable parts.

00:05:20
Speaker 1: Ask me a question, but only about anything in the universe.

00:05:24
Speaker 2: Right, So we have several questions here from kids about all kinds of things about the universe, from suns and black holes to the infinity of the universe. So the first question comes from Violet. The cause of sun is still a star until one day collapse like other stars and turn into a black hole. Mmmm. That is a deep question from a small mind.

00:05:46
Speaker 1: I love. Even in that brief question, you can hear her train of thought. She's connecting our star to other stars. She knows that other stars collapse into black holes, and then she was reflecting that knowledge back here and wondering about the fate of our star. All the connection she's making, all the physics you can hear happening in her brain.

00:06:03
Speaker 2: Yeah, it's pretty awesome. And the sun is something I think all kids can relate to, right, I mean, everyone sees it every day, maybe not directly, but we're all basking and its light.

00:06:12
Speaker 1: I don't know, she sounded like she had an accent. She might not see the sun that often out in Great Britain. It's pretty cloudy.

00:06:19
Speaker 2: M Well, some parts of it are, sonny, aren't they.

00:06:22
Speaker 1: Let's hope.

00:06:22
Speaker 2: So I do have a whole chapter in Oliver's Great Piginius about the Sun, which it's a nice coincidence. It's kind of fun to explain it in terms that kids can't understand. And so let's dig into violid question here. She wants to know if our sun is going to collapse into a black hole, because I guess she said that other stars collapse into a black hole.

00:06:40
Speaker 1: Yeah, there are a lot of black holes out there, sort of two varieties are the kind of the center of galaxies, which are called super massive black holes, really really big ones, and nobody really knows where those come from. It's kind of a mystery. But then there's lots of smaller black holes out there which come from stars at the end of their life. These stars have collapsed into a black hole. And so she's wondering about those. And black hole is the endpoint of some stars. Not every star is going to end up as a black hole. And to understand why some stars become black holes and others don't, you have to understand something about the balance of forces that are keeping a star burning in the first place.

00:07:17
Speaker 2: Yeah, I guess it's a big point to know that not all stars are the same. They're all different, and they mostly differ in size, right, and like the amount of stuff that's in them.

00:07:26
Speaker 1: Yeah, stars come from the collapse of a big cloud of dust and gas that forms a denser blob. But a cloud can sometimes make lots of stars, and you can get smaller stars or more massive stars. It depends a little bit on the configuration and whether there was like a supernova shockway that triggered it, and whether you had like a cluster of heavy metals in the center to gather stuff more rapidly. So there's a big variation. The bigger stars are less likely and they burn hotter and shorter, and the smaller stars are much more common and they can burn for a long time.

00:07:54
Speaker 2: And as you said, it's kind of a balance of fusion and gravity, Like there's stuff exploding in the middle, but there's also gravity trying to squeeze the whole thing down. Right.

00:08:03
Speaker 1: Gravity is what gets things started. You tug a little pebble here and a little bit of cosmic dust over there, and then you get this runaway effect where it gets stronger and stronger gathering stuff together. And if there was only gravity, then any accumulation of stuff would turn into a black hole because it'd be nothing stopping it from getting infinitely dense. But there are other things in the universe than just gravity, Like the Earth doesn't collapse into a black hole. You don't collapse into a black hole because your body or the Earth's structure is strong enough to push against that gravity. Gravity is a huge force in the universe, but it's not very powerful, so it's not actually that hard to overcome.

00:08:36
Speaker 2: Yeah, but on a sun, that what keeps the whole sun, the whole cloud of gas from collapsing, is fusion, right, it's the nuclear reactions that are happening in the middle exactly.

00:08:44
Speaker 1: We call it a radiation pressure. That fusion is like an explosion. It's shooting out photons, it's pushing out on all the stuff. And that balance is the gravity of the star. It's sort of amazing that those things can be in balance and be in balanced for so long. Stars can burn for millions or billions. We think some small ones might even burn for trillions of years. It's an incredible balancing act.

00:09:06
Speaker 2: Yeah, it's pretty wild now that I think about it, to think that it is stable, right, like it could have been the case that suns and stars are not stable. They could either fizzle out pretty easily, or maybe they could have blown up more easily, exactly.

00:09:17
Speaker 1: And if you get a star that's big enough, like more than three hundred times the mass of our sun, then it gets so hot and so intense at the core that it really does blow itself apart. They don't last very long. There's an interesting range of masses. As you say, the initial scoop of stuff that you get really determines the outcome. And I guess we're just kind of lucky that there are lots of stars that can burn long enough to make our universe bright.

00:09:40
Speaker 2: I guess they're sort of like candles, right, Like a candle burns for a long time because it has this kind of balance of that it can burn, but it can't burn too much or too fast exactly.

00:09:48
Speaker 1: That's why you like to build a candle instead of a bomb. Right.

00:09:52
Speaker 2: That'd be hard to light up your home with bombs, right.

00:09:56
Speaker 1: I don't recommend anybody reads Jorge's new book By the Light of Bombs, Please get can those if you don't have light bulbs?

00:10:01
Speaker 2: Yeah, yeah, or a flashlight as well.

00:10:03
Speaker 1: That works a little safer exactly. But it's not just radiation pressure that can keep something from collapsing into a black hole, because eventually that radiation pressure gives up when you've burned up all the fuel in your star, when you've turned all that hydrogen into helium or something heavier, then you're not fusing anymore. But even still, not every star that finishes all of its fusion will turn into a black.

00:10:24
Speaker 2: Hole, right Like, you need to have a certain amount of mass to your star for it to even have a chance at becoming a black hole.

00:10:32
Speaker 1: Exactly, because there are other forces that can push back against gravity, Like you can make something really really dense, like a neutron star, which you can have like the mass of the Sun with a small radius of just kilometers, and even that is very dense, has a lot of gravity, but there are nuclear forces there. The strong nuclear force is pushing back and preventing it from collapsing into a black hole. So even if you don't have fusion pressure from an active star, you can still avoid collapsing into a black hole just from the chemical forces or the strong nuclear forces.

00:11:01
Speaker 2: Right now, Violet's question was about our sun. She's wondering if our sun will one day collapse into a black hole, and so what's the answer, yes or no.

00:11:09
Speaker 1: The answer is almost certainly no, but there is still a lot of uncertainty in exactly how much mass you need. As you said, if you have enough mass, then you have enough gravity. You can overcome all of these forces eventually, the fusion force and the strong nuclear force, and you can collapse into a black hole. But we think that the threshold is somewhere around ten times the mass of the Sun, though it's not something we understand in great detail, and the sort of the consensus number has been moving around a lot.

00:11:36
Speaker 2: Wait, what you mean, We don't know for sure if our Sun is going to collapse into a black hole.

00:11:41
Speaker 1: We don't know absolutely for sure, but it's very very unlikely. The smallest black hole we've ever seen is just over three times the mass of the Sun, and it probably came from a star that was more like ten or fifteen times the mass of the Sun. Some calculations say you have to have twenty twenty five times the mass of the Sun. But by looking at black hole mergers, we learned a lot about the sort of minimum black hole mass. It's a lot of interesting stuff still to be learned about this question. But Violet, don't worry.

00:12:08
Speaker 2: We think our Sun is safe, which means we're safe and she's safe.

00:12:12
Speaker 1: Although, of course, even though the Sun won't turn into a black hole, that doesn't mean it'll be a fun place to live in about five billion years when it expands into a red super giant and fries the.

00:12:21
Speaker 2: Earth boy, wait to setter at ease. There, we we just ask her a question and she's like phew, and then you drop the bond.

00:12:30
Speaker 1: Well, you know, budding astrophysicists got to learn that the universe is a scary place.

00:12:35
Speaker 2: But the basic answer for Violet is that our Sun doesn't have enough mass, we think, to ever collapse into a black hole. So what's going to happen to our Sun is just going to keep burning forever.

00:12:43
Speaker 1: It's not going to burn forever. A lot of helium will accumulate its core, which will move the burning more to the exterior, which will puff up the Sun, so it'll grow to be a super giant, a big red star. Then will blow off its outer layers and they'll leave behind a hot core. So probably the Sun will become a white dwarf, which basically just means it leaves behind a big blob of hot metal.

00:13:05
Speaker 2: It'll just be sort of like a big ball of metal glowing in the dark.

00:13:09
Speaker 1: Yeah, exactly.

00:13:10
Speaker 2: Well, hopefully by then a Violet will have invented a warp drive or something, or a wormhole maybe, because Violet sounds pretty smart. And by then we'll be expanding into other solar systems.

00:13:22
Speaker 1: That's right. Our whole generation of astrophysicists inspired by your book will save humanity. Yeah.

00:13:28
Speaker 2: And then I'll get all the credit right.

00:13:31
Speaker 1: And the royalties, right, you get some of those patents right?

00:13:35
Speaker 2: Yes, I'm going to say yes, and then have the lawyers figure it out. All right. Well, let's get to more questions from kids about this great big universe. But first let's take a quick great or right. We're answering kids questions here today about the universe to celebrate the release of my new book, Oliver's Great Big Universe. Now, Daniel, what kinds of books did you read when you were a kid? Did you read any physics books?

00:14:10
Speaker 1: Hmmm, oh, great question. When I was eleven, I was definitely reading a lot of science fiction books, and I definitely watched a lot of like nova and documentaries on TV, and I gobbled up like big picture books with drawings with artists impressions of black holes and stuff like that.

00:14:26
Speaker 2: Yeah, and so today, to mark the release of the book, we're answering listener questions and specifically from kids. And so our next question comes from James and his dead.

00:14:35
Speaker 3: Hi, Daniel and Joge. This is Paul from Manchester in England. My son James likes thinking about the implications of an infinite universe. In particular, he has this idea that's in an infinite universe, anything that could possibly have happened must have happened an infinite number of times. He was talking to me about this recently and it led me to wonder whether we can say that if the universe is inf it must not be possible to make a machine to travel cosmic scale distances very quickly, because if it was possible to build such a machine, then in an infinite universe, an infinite number of alien civilizations would have done it, and our planet would inevitably have been colonized by aliens. James and I look forward to hearing your thoughts on this. Thanks very much.

00:15:23
Speaker 2: Oh my goodness, this kid, James should write his own book. What an awesome idea. Can we just give him a Nobel prize.

00:15:31
Speaker 1: A Nobel Prize for arguing that a breakthrough is not possible.

00:15:36
Speaker 2: And a Noble price just for blowing my mind? What an interesting question.

00:15:40
Speaker 1: Yeah, it is a really ingenious idea, all.

00:15:44
Speaker 2: Right, So let's break it down. So I think James is saying that if faster than light travel was possible and the universe is infinite, then by now some alien civilization with faster than light travel should have visited us.

00:15:58
Speaker 1: But by now, yeah, I think think that's the argument. It's sort of similar to saying, if time travel is possible, somebody in the future would have discovered it and then come back to visit us, and so since they haven't, therefore time travel is not possible. Except in this case, he's reflecting that argument into space and imagining somebody out there must have figured out faster than light travel and if they had, they would have come visited us, and they haven't, so therefore maybe it's impossible.

00:16:23
Speaker 2: Right. What do you call that kind of argument? Is there a name for it?

00:16:27
Speaker 1: Clever? Clever argument from desperation?

00:16:31
Speaker 2: I don't know, And I've heard this argument before, like there's no time travel because otherwise there would be time travelers visiting us right now. But I always feel like that's assuming we live in an interesting time.

00:16:44
Speaker 1: But if there's an infinite future for humanity, then somebody will find us interesting.

00:16:48
Speaker 2: Right well, I feel like it's sort of like if you're in a really bad place and you're like, there must not be any tourists in the world, because we never get tourists here. That's really just says something about where you live.

00:17:00
Speaker 1: But if there were an infinite number of tourists, somebody would think that your boring street was fascinating. I think that's the crux of his argument. It really relies on this idea of infinity. In the power of infinity.

00:17:12
Speaker 2: Right right, unless your plate you live in an infinitely boring place, in case it cancels out, what's infinitely divided by infinity.

00:17:19
Speaker 1: Theologians have been thinking about infinitely powerful forces and infinitely strong walls, but you're thinking about infinitely boring places and infinite numbers of tourists.

00:17:28
Speaker 2: Yeah, you know, that's what this podcast is all about, great big ideas.

00:17:33
Speaker 1: That's right. Well, there's a lot of really interesting ideas in James's argument. The first one is essentially that if the universe is infinite. Anything that can happen will happen, and that's how we get the idea that if fast and light travel is possible, somebody out there will develop it. And that's a subtle idea.

00:17:51
Speaker 2: Actually, it's pretty interesting, right to think there might be an infinite number of alien civilizations, and if it was possible, one of them must surely have invented war price.

00:18:00
Speaker 1: Yeah, and if you take it literally, it doesn't just imply an infinite number of alien civilizations and implies an infinite number of human civilizations, right, because if humanity can evolve, which obviously it can because it has and space is infinite, that would suggest that it's happening somewhere else actually an infinite number of times.

00:18:19
Speaker 2: But do they have to be humans? Couldn't they be like tentacled aliens that invent the warp drive?

00:18:24
Speaker 1: No, they don't have to be humans. I think it's actually weirder if there are more humans out there totally independently evolved than like weirdly tentacled aliens.

00:18:32
Speaker 2: Although technically, in an infinite universe, wouldn't you also get an infinite number of human civilizations?

00:18:38
Speaker 1: Yeah? Exactly, you get an infinite number of everything that's possible.

00:18:41
Speaker 2: And virtually possible because we're here.

00:18:43
Speaker 1: Yeah, exactly, So you would have an infinite number of James Is asking an infant number of questions on an infinite number of podcasts.

00:18:52
Speaker 2: All right, So then how would you answer that or how would you break down the infinity argument.

00:18:56
Speaker 1: I think it's a pretty strong argument, but there are some holes. Here's some nuances, and one is on the issue of infinity. It's true that anything with a finite probability will happen an infinite number of times if you get an infinite number of tries, Like if you have some huge die with a billion sides to it, it doesn't really matter how many billion sides there are. If you get to roll an infinite number of times, eventually every side will come up. So that part is true. But when you apply that to anything could happen in the universe, there's a little wrinkle there, which is that you need the right initial conditions. Imagine an infinite universe, for example, that's just smooth and has no features, no structure to it, no stars ever form, no galaxies ever form. That's an infinite universe. But you don't get every outcome, because the outcomes are determined by the initial conditions. You have to have like the right configuration for things to start from, which determines essentially what is possible.

00:19:49
Speaker 2: Yeah, I guess you have to assume that the rest of the infinite universe is just like the universe that we see around us, which may not be the case.

00:19:56
Speaker 1: Which may not be the case exactly, But you could also imagine that maybe in order to develop faster than like travel, some alien civilization needs a very different set of conditions than the kind we have here. You're much stronger curvature, So these aliens grow up with a native understanding of space time and can therefore manipulate it. Maybe they need to be like a planet inside a black hole. Right, It's possible inside super massive black holes to have stable orbits and people are speculated you could have life evolve inside of it. But a species that evolves inside a black hole, they couldn't even use their FTL travel to reach us.

00:20:31
Speaker 2: WHOA, But I think that doesn't affect James's question, right, Like we know that the conditions surround us are possible.

00:20:37
Speaker 1: I think it's true that if the universe is infinite and filled with infinite stuff. There's an infinite number of human civilizations and maybe also infinite alien civilizations. But it might be that FTL travel is possible, is allowed by the laws of physics, but that none of the infinite number of human civilizations discover it either, because the conditions in which we grow up, in which we evolve don't give us a sort of natural intuition to manipulate space time, because we're like not near enough black holes to experience that.

00:21:04
Speaker 2: Well, But isn't that a bit of a stretch of an argument. I mean, we can still discover it. We don't have to be living inside of a black hole for us right now to understand what it's like to live in a black hole.

00:21:14
Speaker 1: Yeah, that's right. It's possible that we could in the future discover FTL travel. My point is essentially that there's some limitations to the possible outcomes. You have an infinite number of roles that die, but the die might have some limitations on those possible outcomes based on the configuration of space. Not everything that is possible actually does happen, only things that are possible, and that our potential outcomes from the initial conditions of the universe, like For example, having the entire universe collapse into a black hole physically possible is something against the laws of physics from that configuration, but you can't get to that configuration from here. There's lots of things between you and that arrangement of stuff in the universe. So not every arrangement that's physically possible will actually be realized by our universe because we start from a certain configuration.

00:22:01
Speaker 2: But then in an infinite universe, don't you get all infinite possible starting conditions?

00:22:06
Speaker 1: Yes, great question. We don't know, right because we don't really understand the starting configurations of our universe. We know that we had a fairly smooth universe with some quantum fluctuations, we don't really know exactly where those came from and what came before that, so we don't know if we've like really explored the full range of possible initial configurations, or if we're only getting a little slice, or maybe elsewhere in the universe they got different initial configurations. We just don't know.

00:22:32
Speaker 2: I guess I think James is saying, if it is possible for humans at least to come up with faster than light travel, then if there are infinite number of humans out there, then they must have surely discovered it. Just because it's maybe more likely for black hole aliens to discover it doesn't mean that we can't discover it or that it's not possible, right, because it's the same loss of physics, isn't it.

00:22:51
Speaker 1: Yeah, that's right. If it's possible for humans to discover FTL travel, then I think you're right. In an infinite universe they will. But there's a difference between is FTL travel allowed by the laws of physics and is it possible for humans to discover it. Another possibility is the universe allows faster than light travel by some crazy warped technology, but humans are just not smart enough to figure it out. That it's not discoverable by us and any of our infinite brethren because it just requires like much more mental computing power than we're capable of.

00:23:22
Speaker 2: Hmm. But that's why we build the eyes.

00:23:26
Speaker 1: Yeah, that's a great point. So like machine augmented human intelligence might not have the same kind of limitations, So that's a way around that argument. So yeah, it's a really interesting, I think, quite powerful argument. There are a few nuances and subtleties there, but I think he's right that we can say a lot about the likelihood of FTL travel from the fact that we haven't been visited. Or maybe you're right and our corner of Earth is just.

00:23:49
Speaker 2: Too boring, infinitely boring. Well, I think the other big limitation is just time, Like, maybe you need more time for any of these infinitializations to come up faster than light travel, and maybe the universe is just not old enough. You sort of also need infinite time, right.

00:24:05
Speaker 1: You definitely need time, but how much time you need depends a little bit on like how fast this faster than light travel is. If you can go anywhere in the universe in a moment, like with a wormhole, then you're really visitable from anywhere in the infinite universe. And you know, the universe is pretty old. Fourteen billion years is a long time. We're sort of late in the era of the universe. Our solar system has only been around for a few billion years. So in an infinite universe, there will have been civilizations that started billions and billions of years ago and certainly have had time to reach us.

00:24:37
Speaker 2: Yeah, or maybe not right, Like, maybe you need more time, right, And the other thing I was thinking about is that if it is an infinite universe, that means there are an infinite number of places you can go, which means like the likelihood that some an alien civilization with faster than light travel would come to our planet is almost like infinitely small, too, isn't it.

00:24:56
Speaker 1: Yeah, there's a lot of infinities here. You tackle a lot of similar ideas when you think just about the more standard Fermi paradox, like the galaxy is pretty old and not that big, why haven't we been visited even without FTL travel? Because it only takes like a few tens of thousands of years to explore the whole galaxy, either with like self replicating probes or even a small fleet of ships. So I think the same math holds there that an infinite universe, you should have an infinite number of aliens with FTL travel, and eventually some of them should reach us. And given how old the universe is, it is a little odd that we haven't been visited.

00:25:30
Speaker 2: Yeah, And the other counter argument to James's idea here, I feel like it's like, how do you know we haven't been visited by aliens with faster than like travel? You know, like, how do you know I'm not a time traveler from the future.

00:25:41
Speaker 3: Mmm.

00:25:42
Speaker 1: Or maybe James is actually an alien and this is his way to sort of introduce subtly the concept into the zeitgeist.

00:25:49
Speaker 2: I see, maybe he's an alien and a time traveler. Maybe he's an alien from the future.

00:25:55
Speaker 1: James, if you're visiting alien or visiting human from somewhere else farw in the universe, I hope you don't find us too boring.

00:26:01
Speaker 2: Yeah, I hope he finds us only finitely. All right, Well, let's get to more questions from kid listeners. But first let's take another quick break. All right, we're answering questions from kids to celebrate the release of my new book, Oliver's Great Big Universe. Let's get to our last questions here from kid listeners. The next one comes from Ida hy.

00:26:33
Speaker 1: Daniel Josh, Would I had special pal inside of black hole?

00:26:42
Speaker 2: Awesome question. I'm going to say the answer is yes.

00:26:45
Speaker 1: Next question, you are the superhero science expert on the podcast. You know what kind of special powers would you get from being inside a black hole?

00:26:53
Speaker 2: Oh? Boy, I feel like I could write a whole other book about this idea.

00:26:59
Speaker 1: Sounds like you and Ida should write that book.

00:27:02
Speaker 2: Itida's great big black hole. Well, then let's see her question. Let's break it down. She asked, would she have special powers if she was inside a black hole?

00:27:12
Speaker 1: Do you think this is sort of like a bitten by a radioactive spider kind of situation?

00:27:16
Speaker 2: Or maybe I think she's saying like, if she lived inside of a black hole, would life be the same for her? Or would she be able to do things she couldn't do outside of the black hole?

00:27:25
Speaker 1: Yeah? I see, Well, there is one way in which being inside a black hole would be pretty different from living on Earth, and that has to do with the flow of time. Right. We know that time goes slower when space is curved, the same way that space is curved. Near mass's time is essentially also curved. Space and time curved together. What that means is, if you're near something really, really massive, your time goes slower. Like somebody far out in space, their time goes faster than somebody standing on Earth and near a black hole or inside a black hole, time goes super duper slow.

00:27:59
Speaker 2: How slow to zero.

00:28:00
Speaker 1: It depends a little on the observer. But if you're far away from a black hole and you see somebody falling into a black hole. You will see their time go slower and slower, so that you'll never actually even see them cross over into the black hole because their time will slow down so much. They'll sort of asymptotically approach the black hole from their point of view. They will fall in the black hole, and they will see your clocks speed up by how much depends on the mass of the black hole that you're falling into.

00:28:27
Speaker 2: I see. So the power you get by falling into a black hole is you get to fast forward the rest of the universe.

00:28:32
Speaker 1: Yeah, you get to fast forward the rest of the universe.

00:28:34
Speaker 2: Like if it's infinitely boring, you can just be like.

00:28:36
Speaker 1: Skip exactly that button that says like skip intro or skip.

00:28:42
Speaker 2: Recap, skip everything. I just want to see the credits.

00:28:47
Speaker 1: Exactly, skip forward to see the credits. And so you'll see the rest of the universe going in fast forward. You'll see like the end of our star. You'll see the collision of our galaxy with other galaxies. All this kind of stuff will happen. Now actually see it all through just a tiny little pinprick, because if you're actually within an event horizon of a black hole, all the light in the universe still comes to you, but it comes to you through this tiny little dot. Most of space is so bent that everything in front of you is just the singularity, but there'll be this tiny little dot behind you where photons can still make it to you and bring you news of the universe you fast forwarded.

00:29:22
Speaker 2: Well. First of all, as we've talked about it before, it is possible to go into a black hole, right Like, if a black hole is big enough, then its event horizon is at a point where you wouldn't necessarily get shredded by the gravitational forces. It is possible for someone like you and me to go into a black hole.

00:29:38
Speaker 1: Yeah, And as we talked about in our recent book, frequently asked questions about the universe, As you get closer and closer, the event horizon swells to take up a larger and larger portion of your view, eventually takes up like half of your view, and then it grows around you and then you can only see a tiny little dot.

00:29:53
Speaker 2: But then you could potentially still be conscious and be thinking about and experiencing this phenomenon, right like, you'd be oh my god, what's going on now? Ida's question is, would you have superpowers.

00:30:06
Speaker 1: I think fast forwarding to the end of the universe feels like a special power. It's not a superpower in the sense that it's not like supernatural doesn't break the laws of physics, But I think what physics can do is pretty special, so I think it counts as a special power even if it's not a superpower.

00:30:20
Speaker 2: I guess, like if you fell into a black hole, then you survive, your body wouldn't necessarily change, so you wouldn't get the superpowers necessarily. But I wonder if maybe Ida's wondering, like, you know, like if you go to the moon or moon here, you could jump really high, for example, because there's less gravity. Would there be any kind of things I could do in a black hole I couldn't normally do.

00:30:39
Speaker 1: I think in a black hole you'd never have to worry about cleaning up. You could just throw stuff into the singularity. You basically never have to take out the trash.

00:30:46
Speaker 2: Yeah, that's a superpower for sure. I'm not sure that they'll let you into any adventurous team or anything like that. Yeah, but you know, you said earlier that it is possible maybe for there to be planets inside of a black hole. You know, orbiting a star and stuff. Would life be different for them or would it be the same as it is for us.

00:31:06
Speaker 1: Life would certainly be different for them, and you could check out our podcast episode. I think Katie was our co host on that one, because they would see things very differently. Right, you wouldn't have any illumination, and your planet would be really hot on the inside it be squeezed by the tidal forces. It'd be more like living on the moon of Jupiter, you know, like Io, which is very volcanic, So it'd be a very different kind of experience. Kids on that planet wouldn't look up at the night sky and see the same things that we see. They would see a completely black night sky except for a tiny little dot through which they would see everything else in the universe.

00:31:37
Speaker 2: Could they see like the hand in front of them? Like if I put my hand in front of me inside of black hole? Could I see my hand?

00:31:43
Speaker 1: And the outskirts of a super massive black hole. Space is not so curved that you couldn't see anything, and so it is possible for light to still make some progress towards your eyeballs. And the outskirts of a super massive black.

00:31:55
Speaker 2: Hole, like you'd be inside, but you'd be near the edge. Mm hmm, so maybe you could. You would see your hand, but it would all be kind of weird and distorted.

00:32:03
Speaker 1: All of space would be very distorted, so the way time would flow would be different. People closer to the center of black hole would have their clocks slow down compared to people further from the center of the black hole. So it'd be pretty hard, for example, to have like a zoom session across the whole planet if you're living inside a black hole.

00:32:18
Speaker 2: Oh, thank goodness.

00:32:20
Speaker 1: Great, there's your superpower. You can say no to all online meetings.

00:32:25
Speaker 2: That's right, it'd be infinitely boring, just like a regular zoom meeting. All right. Well, to answer Ida's question, it sounds like she wouldn't gain any special powers except the ability to see the rest of the universe in fast.

00:32:38
Speaker 1: Forward and to never have to clean your room.

00:32:40
Speaker 2: Although I think if Ida ever makes it inside of a black hole and lists to tell about it, I think she would be a superhero in my book. All right. Our last question comes from Joey. What are the newest and the oldest black holes in the universe? What are the newest and oldest black holes? In the universe. Awesome question, A little we knowsy if.

00:33:01
Speaker 1: You ask me, you don't think he deserves to know.

00:33:07
Speaker 2: I'm saying, if you go around asking people's age, you know, you might get some curd answers.

00:33:13
Speaker 1: No. I think the biggest, oldest black holes in the universe are probably proud of their status. You know, they're like silver backs tramping around in the jungles at the hearts of galaxies.

00:33:23
Speaker 2: Mmmm. I see, Yeah, they're like the alpha black holes that we're.

00:33:27
Speaker 1: Saying, yeah, the ogs exactly.

00:33:29
Speaker 2: All right, Well, this is an interesting question because we know that black holes form very early on in the universe, and we know that black holes are forming all the time right now. So you know, I wonder if his question is what are the oldest and newest black holes we know about? Or what are the oldest and newest black holes that exist in the universe.

00:33:49
Speaker 1: Yeah, right, Both of those are good questions. In the case of the oldest black hole, we definitely don't know what is the oldest black hole, or theoretically what could be the oldest black hole, because there's one theory that black holes are as old as the universe itself, that they might even like be older than electrons, that black holes could have been formed during the Big Bang.

00:34:10
Speaker 2: Whoa wait, even before we had like quantum fields.

00:34:13
Speaker 1: Before we had matter, before those quantum fields settled down, so we could have things called electrons and protons and quarks when things were still so hot and so dense that talking about them in terms of those objects doesn't make a lot of sense, the way you wouldn't talk about a wave in terms of its drops. So there's this theory of primordial black holes that suggest that very hot patches of the universe might have collapsed into black holes even before matter was formed, and those black holes might still be around.

00:34:40
Speaker 2: Mm they wouldn't have evaporated by now or right because black holes that don't die very easily.

00:34:46
Speaker 1: Some of the black holes would definitely have evaporated. The bigger black holes evaporate more slowly, and smaller black holes evaporate quickly, so we would expect it some of them to have evaporated and some of them to still be around, and some of them to be evaporating right now. So if the scenari is true, we should be able to see these primordial black holes like evaporating all the time.

00:35:05
Speaker 2: So maybe the oldest black hole in the universe was there from the beginning, from the beginning of the universe.

00:35:10
Speaker 1: It's possible. It's even this fun theory that this impact inside Burea about one hundred years ago, which mysteriously left no crater, was actually a primordial black hole that took like a core sample of the Earth instead of an actual medior.

00:35:23
Speaker 2: WHOA, Well, we should do an episode about that.

00:35:28
Speaker 1: We should. The problem with primordial black holes is again, if they were created, we should see them evaporating all the time, and we haven't ever seen one. We've looked for evidence of black holes evaporating very bright flashes of Hawking radiation, but haven't seen any. So it's a possibility that there are black holes as old as the universe, but it's still just theoretical. But we have seen some very very old black holes, like actually seeing them.

00:35:51
Speaker 2: So then what's the oldest black hole we know about?

00:35:54
Speaker 1: The oldest black hole we've ever seen was formed around five hundred million years after the Big Bang. It was seen by the games web Space telescope. It's super duper far away, which is why we can see so far back in time. Remember, light takes time to get here and so the further things are, the further we're looking back in time. So we're seeing this black hole which formed just a few hundred million years after the Big Bang. It's called sears ceers one zero one nine.

00:36:21
Speaker 2: Well, what that means that it's like thirteen fourteen billion years old.

00:36:24
Speaker 1: That's exactly right. It's between thirteen and fourteen billion years old, which is pretty old. At the time the light left it, it only had about nine million solar masses, which is much smaller than some other super massive black holes which have grown to like billions of solar masses. In the meantime, of course, it might have grown the light we're seeing is very out of date.

00:36:43
Speaker 2: Or it might have disappeared. Right, we don't actually know it's the oldest black hole. We just know that it was around a long time ago. But by now it could have maybe disappeared or evaporated. Isn't it possible?

00:36:55
Speaker 1: It's possible. You're right that we're not getting new information about this very quickly. We'd have to waste billions if years for the updates. But it's unlikely that a massive black hole in a cluster of stars, which is where we've seen it, would evaporate into nothing. To evaporate, it really has to be isolated to not be fed at all. And a black hole with nine million solar masses is going to have very very faint Hawking radiation. The Hawking radiation goes like inversely proportional to the mass, so very low mass black holes evaporate more quickly than very high mass black holes.

00:37:25
Speaker 2: What if Ida went into that one and.

00:37:27
Speaker 1: Broke it up, that would be a superpower.

00:37:30
Speaker 2: Yeah, maybe that Maybe she didn't get superpowers when she went in. All right, So that's the oldest black hole we know about. What are the youngest black holes we know about?

00:37:38
Speaker 1: The youngest black hole in the universe is certainly one that was created right now, and then another one created right now. I mean, they're happening all the time. We know that supernovas, which are typical precursors for black holes, happen like every fifty years in our galaxy. But you know, there's trillions of galaxies out there, so there's almost certainly a black hole being formed as we speak. And by the time you listen to this podcast that will be out date, the'll be a new black hole formed that's even more recent. So the youngest black hole in the universe is definitely one that was just formed.

00:38:07
Speaker 2: They're probably forming all the time right now, right, especially if it's an infinite universe, there's an infinite number of black holes being born right now.

00:38:15
Speaker 1: Yeah, that's exactly right. So the youngest black hole is constantly being replaced by some new baby black hole.

00:38:21
Speaker 2: But what about the youngest one we know about?

00:38:23
Speaker 1: So the youngest black hole that we have seen is called W forty nine B. It's about twenty six thousand light years away from Earth, and we know it's about twenty seven thousand years old because the light from it indicates that what we're seeing is a black hole that's about a thousand years old. So we're looking at the remnants of a supernova collapse that formed a black hole about twenty seven thousand years ago twenty six thousand light years away. So to us, it looks a thousand years old.

00:38:49
Speaker 2: But wait, wait, wait, how do we know it's age. We can tell it's aged from the light we get from it, or we just saw the supernova and assume that a black hole formed inside of it.

00:38:57
Speaker 1: Yeah, great question this one. We can actually do the history of it just by running the clock backwards. We look at the distribution of iron and sulfur and silicon in the remnant, and we can tell what happened and how long it's been drifting. So we can run our clock backwards essentially and say, oh, this is about a thousand years old, the same way you could look at a mushroom cloud from a nuclear bomb. You could tell when it went off.

00:39:19
Speaker 2: And you can actually see the black hole in the middle. Like, but I thought we could only see black holes if there was like if it was like a quasar or something.

00:39:26
Speaker 1: Yeah, you're right. We can't see the black hole directly because the black hole is black. We're deducing the presence of the black hole from the mass of the whole system and the X rays from the hot gas that are nearby. And so according to our model, a black hole has formed. Like what we're seeing is consistent with a star that exploded and left behind a black hole.

00:39:46
Speaker 2: All right, So then the youngest black hole that we think we know about is about one thousand years old.

00:39:51
Speaker 1: It looks a thousand years old to us, but it happened twenty seven thousand years ago.

00:39:55
Speaker 2: Mm. I mean we caught it, like we took a picture of it when it was a thousand years old, but the picture was taken twenty six thousand years ago exactly.

00:40:03
Speaker 1: And to answer your other question, like, it's possible that we did see this thing go supernova that like Chinese astronomers a thousand years ago, we're looking up at the sky and side. We do have some examples of that where we see a supernova remnant, and we can find in the historical record Chinese or Persian or Indian astronomers writing about that supernova, which is pretty cool. Not in this case, but it's possible that humans did see this one blow up a thousand years ago.

00:40:27
Speaker 2: Whoa do you think kids ask questions about it back then?

00:40:31
Speaker 1: It's been a great, big universe for a great long time, so yeah, probably.

00:40:37
Speaker 2: All right, Well, I think that answer is Joey's question. Those black holes in the universe might be the ones that were formed with the universe, but we don't know for sure. There is one that's at least thirteen to fourteen billion years old that we know about, and there's one that was born about twenty seven thousand years ago that is the youngest one we know about. Although there are probably definitely black holes being born all the time right now, and.

00:40:58
Speaker 1: I hope that one of those blacks is being formed near some distant human civilization that's inspiring them to invent faster than light travel.

00:41:06
Speaker 2: And maybe better cleaning technology, because we could all use that.

00:41:11
Speaker 1: And maybe give Ida special powers so that our corner of the universe becomes less boring and we get more visitors.

00:41:16
Speaker 2: I think if you take all of these kids and put them into a team together to be like a superhero physics team. I mean, these kids are so curious and clever and smart.

00:41:24
Speaker 1: Yeah, well, I hope that they and all the kids inspired by your book do solve some of our problems and change the way we understand the universe.

00:41:31
Speaker 2: So thanks again to all of our kid question askers and to all of our listeners for sending in their questions.

00:41:37
Speaker 1: That's right, what's that website? One more time?

00:41:40
Speaker 2: Great Big Universe dot Net. We hope you enjoyed that. Thanks for joining us, See you next time.

00:41:54
Speaker 1: Thanks for listening, and remember that. Daniel and Jorge Explain the Universe is a production of iHeartRadio. More podcast from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows,