Can the Earth survive when the Sun expands?

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Speaker 1: Hey, Kelly, I've been thinking about something you said to me. Oh okay, what did I say? Well, when you moved to the Science Farm awhile ago, you said that I was welcome to come visit. But then last episode you officially retracted that invitation. Well, yeah I did because you said you were going to tell my kids that shooting stars might kill them. So I think I was justified. All right, Well, then it's now my official goal to earn back an invitation. Okay, but like it's not a super high bar. Just don't give my kids nightmares. Well do your kids want to hear about how the sun is going to explode one day? So you know, I'm thinking that maybe you should just wait until they grow up and move away, and then you can come visit, assuming they move away before the sun explodes, I hope. So. As much as we love our kids, we do want them to move away eventually, eventually. Yes, Hi, I'm Daniel. I'm a particle physicist and a professor at U C Irvine, and I don't like scaring children, but I do like telling them the truth. I'm Kelly Wayner Smith um an edgeunt professor at Rice University, and I prefer lying to them. What you lie to your kids. What if they ask you a science question you don't know the answer, you just make one up. No, in that case, I tell them the truth. That's important, you know. But one of them does still believe in Santa And now we'll not be listening to this episode. What if they ask you a science question that has a scary answer, It depends on it if I think they can handle it or not. And it depends on what I want to go to bed that night, because I might be up late doing the explaining. There's lots of things to consider. Well, then let's hope they don't ask you about when the sun is gonna But welcome to the podcast Daniel and Jorge Explain the Universe, in which we try to teach you everything about the universe, scary or not, the things that will keep you up at night, worried about whether you will survive, and the things that make you feel like the universe is a comfortable, cozy places all set up for you to have a good time. We talk about black holes, we talk about quirks. We talk about the future of the human race and whether it has a future or not. Dark stuff, My friend and co host Jorge can't be here today, so we are joined by Kelly Weener Smith, who is trying to teach you things without scaring your children. I feel like maybe I need to defend that decision, but I'm just gonna let it go. Sometimes kids don't need to be scared. You get to spend your whole adulthood being scared about stuff. You know you're right, And the thing I love about the universe is that it doesn't really care about our feelings. It's just crazy. It's just bonkers. It's just doing its thing, whether that means it's threatening to tear you apart and blow you away, or whether it's created this wonderful environment for you to relax in and sip your market riata while you listen to a podcast. The universe doesn't care either way. You know, it's really good that you went into physics and not like psychiatry or something. And how how are your kids turning out? My kids so far are not sociopaths, you know, but hey, we need to collect more data. No, my strategy has always been to answer their questions honestly, though I will admit if their questions bring up something awkward or uncomfortable or maybe age inappropriate. I'll try to deflect the question once or twice, but if they really insist, if they drill in for an answer, I'm giving it to them. Well, you know, we should both be trying to collect more systematic data, and we'll see if you were kids or my kids handle the future better. I see whose kids grew up weirder, like the children of a physicist or the children of a cartoonist and parasitologist. I don't know. Both sets have stiff odds overcoming their parents are doing to them, I think exactly. And it's a weird universe out there, and one that sort of defines the context of our lives. The more we learn about how the universe works and how our neighborhood has been put together, the more we understand how fragile our existence on this rock is. That's right, you know. The more we talk, the more I'm wondering if maybe you should be lying to me. Also, forget the kids. I'm not sure I can handle this, but alright, alright, let's see how I do today. All right, If this podcast keeps you, feel free to call me at two am and I'll tell you even scarier things about the universe. I'll pass. Thanks, you're like an anti friend. Well, something I think that people should be more worried about and more scared of is sort of the context of our situation here. You know. I think a lot of people think about the solar system as something old, something that's been there for a long time, like a mountain that's survived millions and millions of years. But the truth is that the solar system is actually a very chaotic and dynamic place. It hasn't a we've looked the way that it does today, and it will not always look the way that it does today. And in the future. Is it going to be less nice to us than it is right now? Because last time we talked to you told me that shooting stars were trying to kill us. It gets worse, I don't know about worse. It's going to get different, for sure, sort of in the science fiction movie plot twists sort of a way. I mean, I think there's something that people don't appreciate, which is that our solar system hasn't even existed for the whole length of the universe. The universe is like fourteen billion years old. Our solar systems only four and a half billion, which means the first nine billion years our Sun didn't even exist, Like there was nothing like our Solar system. So we're relative newcomers in the universe. We're not even middle aged, and we might just be here for a blip. And as you and I have talked about on the podcast a couple of times, the Solar system itself has seen a lot of transformations. People think that maybe Jupiter was formed closer to the Sun, or maybe it formed far out and then migrated in and then migrated back out the outer Solar system, ejecting some other planets along the way. Our Solar system might have had other planets which are now lost to us, like siblings that were rejected by our parents. But surely when the Sun realizes that humans are on the Earth, the whole Solar system is going to start behaving for us. Right. I don't think the Sun cares at all about us, and I think it's amazing that we have sort of evolved on this rock under these conditions which have been fairly stable over the last few billion years. But we're also very dependent on those conditions. If they change even just a little bit, then life on Earth could be very, very different. When is that going to happen? Do we know? It turns out that the conditions are constantly changing. The Sun is getting brighter and brighter every year. Originally for us, it's pretty slow, but as we think deep, deep into the future of humanity, conditions could change a lot over millions or billions of years. And I hope at least that our children and our children's children and our children's children's children's children's children are around in billions or billions of years to scare each other with crazy stories about the future. Me too, but probably they're gonna have to be pretty clever to stick around for that long. They are going to have to be pretty clever if we want to outlast our cosmic conditions, if we want a society that lasts for millions or billions of years, then the clock is ticking. We're going to have to figure this out before our conditions changed. I mean, we've only ever lived here on Earth under these circumstances, so we're gonna have to do some pretty clever engineering if we're going to figure out how to live in the future of our own solar system. Well, I sure hope we're smart to figure that out. It might depend on how long we have to figure it out. But I'm keeping my fingers crossed exactly, And that's precisely what we'll be talking about today. So on the podcast, we'll be asking the question can the Earth survive when the sun expands? How do you feel, Kelly about this sort of apocalyptic scenarios we've been imagining recently on the podcast, asteroid impacts, nuclear disasters. Yeah, well, you know, I gotta say I'm starting to have this feeling of anxiety when our monthly time to record together comes, you know, to what extent is my conversation with Daniel going to amp up the existential dread in my life? So here we go again for another roller coaster ride. Well, that's one way to look at it. The other way to look at it is like, what is physics going to do to save us? Right? We are constantly thinking about the deep future of humanity and wondering what we have to do today to make sure that we are prepared for those eventualities, to make sure that those humans living many many years from now can build on our work and survive. Yeah, I suppose I should be. I should be thanking the physicists for figuring out these problems way ahead of time, so we have a long lead time to try to do something about it. Exactly. The thing to really be scared about are the things business haven't yet figured out that we'll probably kill us all m This is why we need more money for the sciences, exactly. It's always the unknown unknowns that'd kill you that, right, I mean you well, you know, we we've also talked about how the nonns will kill you. So it sounds like there's a lot of things that can kill you. There are a lot of things that can kill you, but there are also a lot of things we can do, I think, to our physicist and engineers to maybe save our tissues. It's been a long time since I've heard the wood tushies. Is that what you said? That tusses? Yeah, I'm trying to be family friendly here. I'm hoping if kids are listening to the podcast, you know that we're not scarring them in multiple ways. We're just scaring them about extinction of humanity. Right, So we talk about death, but no foul words for hyenees. Got it. Hey, we're Americans were totally inconsistent about these things. Yeah, I'm not sure you understand your audience perfectly, but that's all right. Let's move forward. So today we're wondering how humanity will survive and whether we can preserve the Earth as a place for humanity to live on as the Sun's condition changes, as the Sun goes through its evolution to a larger and large or star and eventually collapses into a white dwarf. And as usual, I was wondering whether people are aware of this issue and whether they had thought about plans humanity might have to survive it. And so as usual, I called on our list of volunteers to answer random and difficult physics questions without any opportunity to do any research for googling. So if that sounds like a lot of fun to you, please don't be shy. We'd love if you've participated in the future. Just right to me. Two questions at Daniel and Jorge dot com. So let's hear what they had to say. I think it would probably survive um because it wouldn't necessarily change how the orbit is functioning. If the it's just kind of generally swallowed up. So would it survive well, not as a grain water filled planet. It maybe as a roasted lump of rock that Earth like an object, probably will survive like a rock, but no formal life probably would survive. Hopefully, by then we can develop the technology to move the Sun whenever we want, whenever it's good for it and for us, probably to a different solar system. So everybody go, study, study, study, study. We need to do something with the Sun. As far as I know, the Sun will eventually become a red giant, and I heard that when the Sun will expands, its diameter will encompass the current orbit of the Earth. So it doesn't seem to be any salvation for us unless we build some massive rocket boosters and steer the Earth away from from the expanding Sun. But maybe we will have blown ourselves up by then. I think it all depends on the ratio of the temperature loss to the size increase. I know red giants are cooler um, but I don't know if there is a set ratio in terms of the growth of the um Sun compared to the heat loss. So I think if it ends up being perfect, I mean, we can have a climate similar to what we're having now, where yeah, the Sun is closer, but it's given off less heat. Yeah, but we need some pretty big technology, you know. I think the person who said but we'll have blown ourselves up by then, so we don't need to worry has been listening to too much of your podcast. Maybe, but why is that something not to worry about, Like don't worry about the sun exploding, worry about us blowing ourselves up instead, or just like fatalistic, like, look, we're all gonna die anyway, so don't even worry about anything. Oh, I could see it either way, though. I think they have a point that there's a lot of things we should worry about maybe first, but I you know, I suppose we can divide and conquer. There's enough humans to address all these problems exactly. And I like that some people are hopeful, you know, that we'll have some good technology that maybe we'll figure it out. Yeah. I like that you have You've got a mix of optimists pessimists, and you know, maybe one of them is a realist thrown in there. So I guess we'll just have to see. So how about you give us a little bit more information on what the problem is and like how long we've got to solve it. Yeah, that's a great idea, Like people might be wondering, why won't the Sun just sit there burning forever? Right, It's always looked the same to you. It hasn't changed a lot over the ten fifty years that you've been alive and looking up at it. Why is it suddenly going to change? The answer is that the Sun is really a delicate balancing act. Like what's going on inside the sun? Why is it possible for you to get warmed by this ball of plasma that's ninety million miles away. Well, inside the Sun, there's incredible gravitational pressure. Gravity is pulling on all the molecules of the Sun, all that hydrogen, a little bit of helium and other stuff, and squeezing it down, and in doing so, it creates the conditions for fusion. Fusion squeezes two protons together, for example, the nuclei of hydrogen atoms. Those protons don't typically like to get together because they're both positively charged. But if it's enough gravitational pressure, they get squeezed together, and all of a sudden, boom, they fused together and you get helium. It's actually a little bit more complicated. Sometimes you have four protons involved, you get two helium atoms. But the upshot is that you make heavier elements out of lighter elements, and you also get energy in return, and that energy keeps the Sun from collapsing, right, Like, why doesn't the Sun just run away into a black hole? Because that energy from fusion is providing like a back pressure. So the Sun itself is in this balancing act as this tug of war between two dramatic forces in the universe, fusion pushing out and gravity pulling in. And so this is a fairly efficient way of doing things, isn't it. And that's why we're trying to make fusion power work on Earth, Like, so, what is it going to take a long time to burn up because of that? Or am I sort of not understanding? Yeah, fusion is very efficient and very clean and very nice, and if we could make that happen here on Earth, we would love to. There's a bunch of efforts to try to make that happen. Magnetized fusion we could create like a little mini star inside a magnetic bottle. And then there's laser fusion, where use zapp pellets with really high intensity lasers and hope that they implode and fuse so far, we haven't gotten any of those things working because these conditions are hard to establish. The Sun is doing a pretty good job of it, and it's steadily turning hydrogen into helium, but it's a really big ball of hydrogen, and so it's gonna take a long long time. The lifetime of a star depends a little bit on how much mass it has. The more massive it is, the hotter it is at the core, and the faster fusion happens. The smaller it is, the cooler it is at the core, and the slower fusion happens. So like a really really big star, like some of the earliest stars in the universe that were like three hundred times the mass of the Sun, might just burn for millions of years, and a really small star might burn for billions and billions or even trillions of years. Whoa, and so so where are we on that that spectrum? How long do we get to burn? So we think that our son is going to burn for about ten billion years total. So this is sort of like a light bulb. You know, you put it in the ceiling, you know it's gonna burn for weeks or months or years, depending on the kind that you have. Our sun is like a ten billion year light bulb, and we're about five billion years in, which means we've got about five billion more years of the Sun successfully balancing fusion and gravity. You know, the light bulbs in our house never last as long as they're supposed to, So I hope the physicists are doing a better job than the people who give the light bulb ratings. But okay, so we're about of the way there. That's that's a little bit scary. It is a little bit scary, right. It makes you feel like, oh my gosh, we're halfway done. What have we done with ourselves so far? Right? What if we accomplished? You know, I mean, we build the Golden gate Bridge and all some buildings, and we discovered a lot of the secrets of the universe. But there's so much left to do and not that much time. And one of the issues is that the next five billion years are not going to be exactly like the last five billion. It's not like a light bulb that just burns nicely and then one day it pops and goes out. The Sun is going to change steadily over the next few billion years. Oh so, like, how how long do we have to solve the problem or to like figure out what we're gonna do. Not the full four billion, maybe more like a billion years. One of the issues is that as the Sun burns, it makes more helium, and the helium is heavier than the hydrogen, so it sinks to the core of the Sun. This makes the core of the Sun more dense, which means more gravity and increases the temperature, which makes the Sun hotter. So the Sun is getting hotter Italy. Every hundred million years, the Sun gets about one percent brighter. You might think, well, one percent, what's the big deal? One percent can make a big difference in the overall energy deposited on the Earth and totally change our climate. And that compounds every hundred million years. It's one percent brighter, So like in a billion or two billion years, we think the surface of the Earth will be at a hundred C. That's like the boiling point of water. Oh my gosh, Okay, so we need we need to find a solution way before that. Is it just going to be hotter or is this I feel like I remember pictures of the Sun expanding while this happens, Or is I guess that's part of the whole process. So the Sun is like seven hundred thousand kilometers in radius, right, which seems pretty big, But as time goes on, it's going to expand to about two hundred times that radius. So the outer edges of the Sun are going to get pushed out by all this extra fusion energy. And that's about one au right, that's right about where the Earth orbits. Oh my gosh, So it's gonna oil or oceans off, and then it's going to engulf like all of the Earth. It sort of seems like it in a naive calculation. The radius of the Sun is now the same as the radius of the Earth's orbit, so we'll be like flying through the outer layers of the Sun. But it's actually a tiny bit more complicated than that, because as it gets larger, it also loses mass, Like some of its mass just gets blown out past the Solar system. So the Sun will lose some of this mass, right, Like the final white dwarf that's left over in the end doesn't have all the mass of the Sun. Some of it's been lost by getting blown out. So that means that as the Sun expands, it's gravity actually weakens a little bit, and so it's tug on the Earth weakens a little bit, so the Earth will actually drift out naturally to a larger radius. It's orbit will get enlarged because the Sun's gravity is getting weaker. So for a moment, I had this little glimmer of hope, thinking, like, you know, the Earth is going to move away, and maybe we'll move away fast enough that the oceans aren't going to burn up. But you, being you, you're gonna go ahead and squash that right and and tell me that even if the Earth keeps a little bit ahead of the Sun, we're still all going to be dead, right, because it's still going to boil off our oceans. Well, Kelly, I mean, do you want the truth or do you want to feel good about the universe? You can't always get both. Obviously I want to feel good about the but but you're going to give me the truth. So people have done some studies to try to understand what's going to happen here. It turns out that the sun expansion outpaces the sun losing mass, and so even though the Earth would start to drift out to a higher radius, it's going to get caught by the outer surfaces of the Sun before it can do that. And one of the issues is that once you are skimming over the surface of the Sun, you're not really in a simple orbit anymore because now there's drag. Right, You're like flying through plasma of the Sun that slows you down. In our current orbit, we don't really hit very much, right, and we don't lose a lot of kinetic energy as we go around. But this is gonna be like flying through the outer surfaces of the Sun, sort of like a spaceship experiencing drag. It flies in too low an orbit, it gets pulled down into the planet. So even a tiny little bit of getting engulfed by the Sun means the Earth eventually just plummets directly into the Sun. I shouldn't have asked, how is that for sleeping at night? Exactly all right, So now the Earth has been absorbed by the Sun. What happens after that? The Sun is non as red giant phase, it's very bright as a huge radius, and now it moves to the next stage, which is that it begins to fuse helium. So mostly at the core we have hydrogen that's fusing into helium. But if the Sun has enough mass, and Ours does. Eventually it will reach a temperature where helium itself can get fused into heavier stuff. Now, if we have an even more massive star tens or hundreds of times the mass of the Sun, this could go into the next stage where helium then fuses into something else, which then fuses into something else, and you get elements all the way up there, like iron in the heaviest of stars. Ours isn't big enough to do that. We can only achieve helium fusion. But when that happens, it's really awesome because the whole stage just lasts for a few seconds. It's like we fuse hydrogen for billions of years, accumulating all this helium ash, and then once the helium is ready to fuse, we burn through that in just a few seconds, creating this incredible helium flash. Oh my gosh. Is this where galactic cosmic radiation comes from in bigger stars where they make iron ions and then shoot them out or is that a different process? I think that's a different process. This helium flash turns out to me entirely internal to the star because the star is opaque to this radiation. So even though it releases like as much light as the entire Milky Way, like as much as billions of stars. It's all internally absorbed, so you can't actually see it from the outside. But it's very cool this helium flash which just last for seconds. I love the discrepancy there, and like how long we burn hydrogen, how long we burn helium? And in other stars where you continue, then these cycles get shorter and shorter, and so you're like fusing iron for a very very small amount of time before the star starts to go out. That is incredible. Yeah, and it's really fascinating. Okay, so we've we've lost the Earth, but there are proposals for going to other places. So I want to know is anything in the Solar System going to be left when this is done? The Solar System will probably be totally unrecognizable. I mean, remember that the Sun's weakening gravity also has impacts on other planets, right, So Jupiter and Saturn, for example, will get much larger orbits because the Sun's gravity it gets weaker as it loses a little bit of its mass, and this is going to create a lot of chaos for the Solar System. Anytime Jupiter does anything, it creates chaos, and now you're moving Jupiter and Saturn like two entirely new orbits. Probably they will eject all the other planets in the Solar System, bye by Neptune, by by Uranus, bye by Pluto, whether or not you call it a planet, they're all probably gone. And why it's always Jupiter. Jupiter is the big bully of the Solar System. And in some of these simulations I've seen, we're basically left with Jupiter right as the only planet now. And then after the Sun is done expanding, then it collapses into a white dwarf, and that's what's left behind. You have this hot lob of glowing helium fusion products. You have some helium, some carbon maybe, and that's all that's left. And the outer layers that were the red giant I'll get blown out. And so you have like Jupiter, solo planet orbiting this hot lump of helium and carbon. Does it just keep glowing for eternity? Does does something else happen to it after that? So it's not fusing anymore, but it's still really really hot. So I think about what happens to like a lump of hot stuff in space. It's glowing which means it's losing energy, so it's cooling down, but it happens really slowly. So scientists think that a white dwarf, eventually, after trillions of years, will cool down so it's not glowing anymore, and they call that a black dwarf. But our universe isn't old enough to have any black dwarfs in it. So we have a bunch of white dwarves, but none of them have cooled yet because our universe is still so young on that time, do we have an estimate for when we might find the first black dwarf? Trillions of years. These things can stay hot in space for a long long time. Remember, in space, it is actually harder to lose your energy, to lose your heat than it is here on Earth because there is no air. All you can do is radiated away. There's no like wind to come and cool you down. Got it. Okay, Well, now you have made it so it will be tough for me to sleep at night. But we still have some time left on this podcast, and so after this break, I'm going to ask you to tell me if there's any prospects for survival. Okay, we're back from the break. What kind of options do we have for being proactive about this problem? Because you know, if I was going to tell my kids about a problem, I'd want to make sure I had some strategies I can tell them about so they felt like they had so control over the situation. Yeah, there are a lot of clever people thinking deeply about these problems, and I think it's super fun to think about problems that you don't need to solve for millions or billions of years, because you know, the technology is going to be different in a million years and people will have better ideas. But that only happens if we start thinking about it now, right, we have to begin those explorations. You start with the bad ideas, and those generate the good ideas. That's sort of like the way my research happens. A student comes into my office and we sort of brainstorm bad ideas until one of them turns into a good idea. So it's important that we dig into this stuff now, and the ideas are sort of categorized by like what time scale we're talking about, you know, before, for example, the sun actually grows to have the radius of the orbit of the Earth, we still have to worry about things getting hotter right like before five billion years from now when we risk being engulfed, we still need to survive somehow without our oceans boiling. You know, it almost seems like we should start worrying about what your planet does when it gets hotter, like you know now anyway, Yeah, that's right. We have other reasons to worry about how to keep the Earth cool, like how do you build a planet wide cooling system? And so this is something people are thinking about, and it's something you could actually get started on, like tomorrow. Some of these strategies, like geo engineering, involves spraying things into the atmosphere to reflect more of the Sun's light. Basically, even though the Sun is going to get hotter and brighter, we just want less of that energy to fall on the Earth and we should be okay. These kinds of proposals always make me a little nervous because I feel like we still don't understand what causes climate. And if you do something like you know, spraying particles are blocking part of the sun, there's just as good a chance that you're going to mess something up. But here's hoping we figure this all out soon. So what kind of stuff are we thinking of trying to spray up there. It's definitely a Rube Goldberg device, right. We have no idea how these things are working, and we're like, huh, let's just add another gear over here and see what happens. One thing that people are thinking about is sulfur. Sulfur is very reflective and not that expensive, and we have a lot of it. So if you just like spread a bunch of sulfur into the upper atmosphere, that would effectively reflect a lot of the light that is hitting the earth and cool it down. This is something people are thinking about, like for climate change today, and what we're talking about today on the podcast is effectively climate change writ large the sun getting much much brighter and a lot more energy. So the same kinds of solutions are being considered, but this would have a lot of weird effects on the climate on the Earth, and would they stay where we put them? They would not necessarily stay where we put them, and there are currents up there right. Also, these things would eventually drift back down, so we need to continuously pump sulfur into the atmosphere to replace it. And it would also change a lot what it's like to be on the Earth. If we had this like diffuse shield, it would bounce the Sun's light around a lot, so you wouldn't necessarily like see a sun in the sky. It's like the whole sky would go from being blue with like a yellow sun in it just being like white glow. This honestly isn't sounding like a great idea to me so far. It's sort of like, you know on a cloudy day, how it can feel bright even though you can't see the sun. It would be a very different experience of being a human. And the other issue is that it wouldn't have a constant effect everywhere on the Earth. It would change the climate. Parts of the Earth would get hotter and other parts would get colder. So even though on average you might keep the same temperature, the tropics would be cooler and the high latitudes would be a little bit warmer. And that would have all sorts of crazy effects like flooding certain areas, making other areas drier. And I'm pretty sure that you know, different countries would have different opinions about like who gets a drought this year? Yeah, well, I mean, I suppose it's it's all better than the oceans boiling, But it doesn't sound ideal, and hopefully by then we're all getting along really well. So well refugees are fleeing around the planets, they'll be welcomed with open arms. Yeah. I don't have a lot of hope for us coming up with communal compromises to these big decisions. So, but you know, this is the kind of strategy people are thinking about for sort of short term geo engineering of preventing the Earth from getting toasted. All right, so that messing with our atmosphere is one method which sounds a little scary. Can we stop the Sun before it gets to our atmosphere? Yeah, some people are thinking about like building massive space mirrors to reflect the light. Right, so instead of geo engineering, like, let's have massive space engineering projects. And the idea is that all you need to do is counteract, Like currently two percent of the energy that comes to the Earth would solve our global warming problem. And then in the future you need more and more to protect ourselves from the growing sun. But you know, there are attractive places to put this in space. You've probably heard of the L two lagrange point, which is a gravitationally stable place where the James Web space telescope is it's like along the line between the Sun and the Earth. For example, it keeps the Earth between it and the Sun. So it's a stable place where the James Webb could stay in the shadow of the Earth. There's another one, the l one lagrange point, is between the Earth and the Sun and it's also stable, so you put something there and it will remain between the Earth and the Sun. So you could build like a shield and put it at the l one point and the Earth has like a little parasol. How cute and charming, But it would probably have to be huge. It sounds like a tough engineering problem. But we've got like a billion years. How how big would it need to be. The l One point is four times the distance from the Earth to the Moon, so it's pretty far away and that makes it a challenge, right because the further away it is from the Earth, the bigger it has to be. And imagine like a shield at the Earth. You could be the size of the Earth and totally block the Sun. But as that shield gets closer and closer to the Sun, it needs to get bigger and bigger to effectively shield the Earth. Like an earth size shield at the Sun would basically do nothing. So the l one point is four times the Earth Moon distance. So you need a shield that's like a million square kilometers, have to be basically as big as the Moon. And do you have to worry about like, you know, so there's stuff shooting around in space, you know, running into stuff and causing problems. Do you have to worry I guess you'd have to worry about it poking a hole or something big enough hitting it and moving it out of orbits or is there nothing big enough that could move something four times the moon? No, there is definitely something big enough, and that's the Sun. Like you build a big shield that is that wide, it's basically a solar sale and it'll just fly away, right, And so you have to worry about this somehow, right, Like if it's reflective, then it's going to get pushed away by the Sun, even if it's just like black, and then it's going to absorb all that energy. It's going to get overheated and it's still going to absorb all that momentum. And so people have really worried about how to design this thing. And there's a guy, Roger Angel, who has this idea instead of like a big sheets like make it a screen, and so instead of absorbing the light or reflecting the light, it's like just bend the light. So it's like a huge lens, but built out of these little rings, each of which deflects light away from the earth, so it doesn't get any momentum pressure or it just sort of like bends some of the light out of our path. That's pretty cool. And what would this change the amount of light that the whole Earth gets or would this be like, you know, the southern hemisphere gets as much light, Like is it going to be evenly distributed? That's a great question. Probably wouldn't be. I think you'd probably get most deflection at the center, and other places would get some of the light that would have gone to the equator we go to higher latitudes for example. That's a good question. But even this would still need to be really big, Like initial designs for this kind of shield would require twenty million tons of mass. Oh my gosh, I mean that's going to be incredibly expensive, but I guess all the world's governments would probably pitch in. Hopefully, Elon Musk and his generations of descendants have driven the cost down to like a penny per pound or something by that point, I don't know. There are ideas about building this thing on the moon and then launching it from there, but you know, we're talking about an incredible space industry, and you know, we are far far away from being able to build anything on the moon. Even getting people to the Moon right now is challenging for us. Another idea I read about, which is really cool, is to develop a new kind of launch technology, magnetic launch, when you basically have like an aluminum tube and a magnetic field rises up the tube and pushes a piece of metal up into space. It's sort of like a maglev version of a train, but vertical. So first you'd process the aluminum out of the regulars and then you'd shoot it. He's in one of these canons. Yeah, but this is technology that's like very speculative. People have like worked on the theory of it, but nobody's ever built one of these things before. But you know, this is like, how could we solve this one? Are the biggest problems involved? You know, this is passing it off to the engineers. Were like, in theory, if we put a shield in l one, that might work. Let's let the engineers figure out how to build it. So you said that L one is stable, Is it perfectly stable? Like if you put those rings there, are they really going to stay there forever? They are not. Unfortunately, these places are quasi stable, right. Stay Able technically means you get pushed away from it a little bit, then the force naturally restores you to the original location, whereas unstable at the opposite unstable means that as soon as you deviate from it a tiny little bit, then you get further away. Like a pencil balancing on its tip is unstable. It could balance there if a state exactly vertical, as soon as it leans over a little bit, then the game is over. So these things are quasi stable, which means some deviations get pushed back and some deviations don't get pushed back, and eventually we'll lose them all, so we'll need to continuously be shooting up new elements of it. And the good news is you don't just need like one big piece. It's okay to have like two thousand or two million small little lenses that each blur the sun's light a little bit, so it's okay to continuously lose them and then build more, but it means a continuing expense. Let's make sure we don't mess up those lenses and then all end up like ants under some kids, magnifying less. Al Right, So any of these methods that we've just talked about are just buying us time. So this is to try to reduce the temperature increase as the Sun is getting closer, but the Earth is still going to get engulfed. So we need some way to outrun the Sun, some bigger solutions. So we're gonna need something else. What are some of these longer term solutions. Yeah, you're right. Eventually we want to move the Earth somehow in order to avoid it getting engulfed and dropping into the Sun. And you know, this is a really fun idea, and it appears a lot of times in science fiction, which means a lot of people have thought about it. You know, science fiction authors really do contribute to these problems by thinking through the details. And here we really benefit from the fact that the Sun's intensity, the amount of light you get falls very quickly as you get further away. Right, it's not like twice as far away you get half the sunlight. Twice as far away you get a quarter of the sunlight. And so if you want to remove like one percent of the Sun's intensity of its lubidosity, you only need to move the Earth half a percent further away. And if you increase the radius less than ten percent, you like twenty or more reduction in the Sun's light. So the universe is against us, but for once, math and physics are kind of on our side exactly. Then the question is how do you get the Earth into another orbit? Right? This is complicated. The Earth is a big mass with a lot of kinetic energy. Moving it is not going to be something that you can do easily. So people have thought of a few different scenarios here. One of my favorites is to use a gravitational slingshot. Like you know how sometimes we send satellites around Jupiter to whizz around and change their direction or even change their speed. Well, that actually changes the flight path of Jupiter, right, It steals a little bit of energy from Jupiter. So the idea is to do sort of the opposite is to send a big asteroid near the Earth, send it around the Earth to sort of like push the Earth out right, to like change the orbit of the Earth. I can't imagine how that could go wrong. Tell that to your kids. I'm sure they'll believe it. Well. In this case, people have thought about an asteroid like a hundred kilometers y something weighing like ten to the nine, And if you have it like counterbalancing around the Earth, it could slowly get pulled out and use Jupiter's gravity a little bit also, and you get the Earth out to a larger radius. And of course you need a whole different set of physicists trying to figure out how you go about moving an asteroid carefully. But that sounds like a fun problem to solve. And I'm pretty sure that sixty two miles is more than an extinction level event. If you mess it up right, it is exactly. So that's danger number one is oops, you killed everybody. Danger number two is you miscalculated, and now the Earth doesn't have a larger radius. It's got no radius. It's just getting ejected from the Solar System and it's now flying free in dark dark space. That's failure mode number two, neither of which you can recover from. It's not like oops, let's try again or something right. These are one time only mistakes. Yeah, we should be investing in science more. But there's a cleverness I like that because instead of moving the Earth now you just have to move a hundred kilometer asteroid, which seems easier I guess than moving the entire Earth. But some folks are working on that, you know, they say, how could we actually move the whole earth further out? Like could you build engines like rocket engines and put them on the south pole and fire them up and like treat the whole earth as a spaceship move it out to a larger radius. Well, I guess that you also have to be pretty careful about not not messing up. How much of an increase in radius are we talking. Well, if you increase the radius by like four or something per cent, then the energy you receive drops by like ten percent. And you know, as the Sun gets larger and larger over the next few billion years, we could just like keep moving the Earth. One way to think about it is that right now the Earth is in the habitable region, right we have just about the right amount of energy falling on the surface so that we can survive. But as the Sun gets brighter and bigger, the habitable zone changes, and so we could just sort of cruise the Earth gradually, so we always stay in the sweet spot. And if global warming hasn't killed us by then, the amount of fossil fuels we're going to have to burn to move the entire planet will probably finish the job. Well, you know, people have talked about using like a solar array, building one that's like ten to the fifteen square meters, which captures a tiny fraction of the Sun's energy, but that's ten times the surface area of the Earth. And remember we talked about space based solar power and you were pretty skeptical that we could even like power Australia's refrigerators using space based technology. Now we're talking about building a space based solar power network that's ten times the surface area of the Earth, and so that seems a little ambitious. Well, you know, we've got some time. Are we just moving away or at some point are we moving back in again? Like, do we need to be able to go in both directions long term? We do, absolutely, because what happens in the very far future is that we just have that white dwarf, right, and then we need to get pretty close because the white dwarf is not going to be that hot and there are habitable regions around white dwarfs. In fact, astronomers found white dwarfs with planets before. In fact, recently they found one it's called w D ten fifty four to to six, that they think has a planet in its habitable zone where the surface of it could have like liquid water. So technically it is possible to have a planet in orbit around a white dwarf. But the plan would then be to have the Earth go further out as the Sun expands, and then when the Sun collapses again, to move the Earth back into the now shrinking habitable zone. So I really like my schedule, and I make three year plans and five year plans, and I'm feeling like, if we're changing how far the Earth is from the Sun, we're probably changing how long a year is, and that's really going to mess up my scheduling. Is this going to be a problem. This is gonna be a big problem. Absolutely. For example, we move the orbit of the Earth out by five percent or something, the year is going to be fifteen percent longer because our orbital speed is going to be slower. Remember that the further away you are from the Sun, the less the Sun pulls on you. And so the slower you need to be going to be in orbit. And so for example, in some of these scenarios, the year is now four hundred and eighteen days. That's when we're out at the larger radius, and then we bring the Earth back in the year could be very short, right, it could be several weeks long. So you could be having birthdays like all the time. Oh nice, Although I don't necessarily want to feel like I'm aging too much quicker. I think I prefer the four hundred and eighteen day version. I'll get much more done every year. I don't know. Then you could, like, you know, live to the year six hundred or something. Right, we could all have biblical ages. That sounds great. We should bring back biblical names too. They were more epic, although not more epic than waiters. And I just want to comment that there's an idea in a popular science fiction story called The Wandering Earth where people move the Earth out of the Solar system. They give up on the Sun entirely, and they're like, let's just move to a different star, and there they build these enormous engines, these plasma thrusters that pushed the Earth like out of the Solar System to another planet, like treat the whole Earth as a spaceship. And these are crazy, these plasma engines they build. I read an interview with a guy at JPL who works on these kind of thrusters, and he was skeptical because he said that it would require of the mass of the Earth to be used as fuel. So I think that would have some serious drawbacks. Yeah, I think maybe the math on that one is not in our favor. So you you told me that after we get to the point where the Earth has been enveloped, everything's gonna go crazy, and like, who knows what's going to survive, but probably Jupiter is gonna survive. So rather than trying to do these engineering solutions, which seemed like if you don't get perfect, there's a big chance you're going to fail, and we've never tried anything like this before, maybe we should just move to Jupiter. But that's not an option. Are Jupiter's moons still going to be around? Well, you know, it's a good idea because Jupiter is likely to stay in the habitable zone. Like in the new Sun, the habital zone will probably include Jupiter, So it's not a terrible idea. And you know, I know somebody who's writing a book on space settlements, and so I should ask you, for example, like could we build floating colonies in the clouds of Jupiter or could we settle on Io and use the like underground oceans and the underground tectonics to extract the energy? What do you think about all that? Well, so we are focusing on more near term, which we think is going to focus on the Moon or Mars or rotating space stations. So I haven't thought too much about the moons of Jupiter. There are some that have like nicer ish conditions, and couldn't you have some of the stuff that life needs. But at the end of the day, they don't seem so nice. But maybe they'll seem nice when we're in the habitable zone billions of years from now. What do you think I'm imagining you designing a pamphlet for people to move to these colonies and you call it nice ish better than death moons of Jupiter. I think it's pretty unlikely. And I think it comes back to something you often say, which is that people think about colonization, but they always assume that the Earth is going to be there as the core of the infrastructure. Like, yeah, maybe we could send people to Mars next year, but they're not going to be self sustaining for a long time to rely on shipments from Earth and technology from Earth for a long time. So it'd be hard to imagine sending up colonies on Io or something and having them be self sustaining in a way that could support like billions of people. So I think that scenario is like maybe dozens, hundreds thousands of people survive, but not the whole human race. I think most people are gonna lose out if we have to move to the moons of Jupiter. I think the space settlement advocates would tell you that that's why we need to start now working on these technologies. And also, if you can build rotating space stations, those are more movable, so you build those out of the stuff in the asteroids, and then that's easier to move closer or away from the Sun, depending on you know where the best places that at any particular moment, that'll be much easier than moving the entire Earth. Yeah, I agree, let's start building. Well. To me, you that still brings a whole new set of problems about what we'll be able to peacefully move out into space or what we kill ourselves before any of this becomes a problem. But you know, some people believe more in humans than I do, so so we'll see. So we have mostly been talking about trying to get away from the Sun as it expands. Next, we're gonna have to figure out how to survive when the Sun becomes a white dwarf. But let's chat about that after the break. Okay, So let's imagine that somehow humanity has managed to avoid having our oceans boiled off, We've managed to outrun the sun. What comes next the Sun becomes a white dwarf, and how do we eke out in existence then? So it would be cool if we were around to see the helium flash of the Sun, or send probes in there or something. It would be pretty awesome to study that. After that that, basically the Sun collapses. It's sort of like a mini supernova. You have this shock wave which blows out a lot of the layers of the Sun and then you're left with just this core, this hot lump of stuff, the white dwarf. So, as we talked about a little bit earlier, we need to then somehow move the Earth or our colonies or whatever we're living in closer, because it's gonna be a lot colder. If you're out in Jupiter's radius right now and the Sun becomes a white dwarf, you're gonna get almost no energy. So if you want to grow your space salads, for example, then you're gonna have to move everything much closer in. And the other technology is basically the same. You know, find another asteroid to gravitationally slingshot yourself closer to the Sun, or turn that rocket engine around that you build and pointed the other way and just fly the Earth towards the Sun. Though that seems pretty terrifying to me. Yeah, you gotta hope you don't overshoot, but you could fee ably get enough heat and sunlight if you managed to get close enough, You definitely could write. White dwarves are pretty hot. They do give off a lot of light. I mean there are regions near a white dwarf that are too hot for us to survive, which means that there is a habitable zone there. Right, You couldn't get just the right distance from a white dwarf, It is possible. The good news is white dwarfs last for a long, long time, right, trillions of years, and so that could be a pretty good long term scenario. All right, I'm like in this, but it also sounds like there's that complicated phase where we're sort of needing to do a lot of moving and we're hoping that all of that doesn't destroy the climate on Earth. Maybe at some point we should just like try a whole different system and move to a move near a different star. What do we need to do to make that happen? I think you're right, And if we're thinking very long term, then we have to think about other options and other stars. Currently, getting to another star is very tricky, right, We're talking about building like generation ships that move less than the speed of light to take tens or hundreds of years to get to proximate centauri. And they're still like, what fraction of the human race can you really fit onto ships? Thousands of people maybe millions of people? You have a lottery where like one in a thousand people gets to go and everybody else like stays behind to die. Sounds pretty sad. It's bleak. It's bleak, exactly. I think if we're talking about technology and millions and billions of years. Then we get to think about things that are theoretically allowed right now, but we haven't figured out how to do things we like to talk about in this podcast a lot like wormholes and warp drives. These are things that we think are allowed, that the physics of them says it's possible that we don't have a recipe for how to build a warp driver, how to construct or even find a wormhole, or to know if they're even traversible. But you know, fund basic physics for another thousand years and we'll probably figure a lot of that out. So you know, if we're talking about deep future and speculation, then physics could open a lot of in doors for how to get two other stars without actually having a fly there on a big fat ship. But I used to really like watching Doctor Who, and I'm pretty sure that on Doctor Who there was a point where time ends and at some point you're going to have the death of all stars, And so is there anything we can do? Can we make it until then? And then what happens? Right, if we're thinking about the really deep future, like all of the stars are burning and most of them have burned out, then we do think the universe will get darker, right Like, most of the university is hydrogen and that will continue to burn stars. But at some point the universe stops making stars, right Like, in order for stars to form, the gas that coalesces that builds a solar system has to be kind of cold, needs to be able to collapse. It can't be too hot. And we don't really understand, but we see that in galaxies when they get to a certain age, they just stop making stars. This is called quenching, and so we don't really understand it, but we do suspect that the universe is past its prime. In Star Make game, that like, the rate of new stars being formed is dropping. So as you say, that suggests that in the far far future we may not have any more stars. And some people imagine that what will be left with is just a bunch of black holes, right that used to be the centers of galaxies that have now swallowed up all those stars. And then dark energy is going to push those black holes apart. Remember that the universe is expanding, and that expansion is accelerating, and so the deep deep future is a bunch of black holes that are super duper far apart from each other, and no light in the universe at all. You know what, I want my kids to stay home living with us for a really long time so that you never come visit me either. But you know, there are possible ways to survive that future. We talked to the podcast recently about how to take energy from black holes. Black holes have this region around them called the ergosphere, which is ergo means work right, or ergs like an energy And turns out you can drop stuff into the ergo spheres outside the event horizon, so it'll come back to you and it will come back with more energy. So you can like drop rocks near a black hole and they'll whizz around and come back with more energy. So you can extract energy from black holes and use that to power you know, your underground salad farm or whatever you need to survive in the deep deep future. All right now, I want them to move out again. But you know, we're talking about something like a hundred trillion years from now, and the error bars on that are huge because it's always very difficult to predict far far in the future, and also because we just don't know what dark energy is going to do. Remember that we see the universe expanding We know that expansion is accelerating, but we don't understand it, which means that we can't accurately predict what it's going to do. So any speculation about the far far future comes with a huge galaxy sized asterisk and job security physicists. But you know, I think the lesson to take home is that while the future of our neighborhood is dynamic and changing and it won't always be the way that it is today, it's going to be different, and we have clever ways to maybe survive that human ingenuity might allow us to persist millions, billions, even trillions of years into the future. You know, human beings have done pretty amazing things that the fact that we have rovers going around studying Mars makes me optimistic about humanity in general. So I'm keeping my fingers crossed. We haven't died out yet, right, If you're listening to this podcast, that means that humans have still survived. Is that not hopeful enough for your Kelly? That's as hopeful as we can get on this show. So that's that's fine, alright. So remember that our time here on Earth is precious, and that the Earth's time around the Sun is also precious and short lived. And on this podcast, we're all hopeful that you folks out there, those young people thinking about signs and wanting to become business or engineers, will come up with the solutions to save us all. Otherwise we die. And somehow I became the optimist in this episode. So thanks for tuning in, everybody, and thank you Kelly very much for joining us, Thanks for having me. Have a nice week, everyone, alright, tune in next time. Thanks for listening, and remember that Daniel and Jorge explained. The Universe is a production of I Heart Radio. For more podcast For my heart Radio, visit the I heart Radio app, Apple Podcasts, or wherever you listen to your favorite shows.