Why didn't we evolve around a red dwarf star?

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Speaker 1: Hey, Daniel, do you believe in luck? Do you think you're a lucky person? I'm not sure. I guess I'm pretty happy with how things have turned out. Oh yeah, But was that luck or was it inevitable? I'm sure there was a lot of randomness involved. I guess I'd have to study the multiverse to see how often Daniel gets to be a physics professor. But wait, is that the lucky outcome. Wouldn't the lucky outcome be the one where you get to be a movie star or a billionaire or maybe a billionaire movie star physics professor. That's a lot of titles there. It might cause the universe to collapse on itself, physicists always ending the universe. We might have caused it, but it doesn't mean it's our fault. That sounds like a logical contradiction. Wouldn't that also collapse the universe into a puff of logic? Hi am Jorhanmay, cartoonists and the creator of PhD comics. Hi, I'm Daniel. I'm a particle physicist and a professor at UC Irvine, and I'm doing my best to understand the universe without collapsing it. You're doing your best. I feel like your best is not enough, like I guarantee is not enough. Maybe you should look into that before doing it. I'll check with my legal department. I'll do twice my best time of that still not enough. Ending the universe twice is still ending the universe. Maybe it's like negative signs. You know, if you do it twice, it comes back. But then are you going to be a physics professor again? Are we going to be that unlucky? Maybe when everything snaps back, that's when I get to be a billionaire. But anyways, welcome to our podcast, Daniel and Jorge Explain the Universe, a production of iHeartRadio, where we try our best to make sense of this crazy universe. When you look out there in the cosmos and try to understand the way things are, the way things might be, and how it all can possibly make sense. We do our best to cram this incredible, giant, fantastical universe into our tiny little primate brains and squish it all around until it makes sense to us and hopefully makes sense to you. Yeah, it is an amazing universe, or maybe an amazing multiverse, or might be more than one universe out there, But at least the one we're in. It seems pretty amazing, pretty awesome to explore and to ask questions about, and to wonder about the logic of it. Yeah, as we look out into the universe, we wonder why is it this way and not some other way? Why are we in this part of the universe and not some other part of the universe? Are we lucky that we ended up here? Was it just a fluke or is it pretty common our experience of the universe? Is the universe guaranteed to be logical? Daniel? Do you think is it logical that the universe is not logical? Yeah? A guarantee itself rests on logic, and so if the universe is illogical, then it cannot provide any kind of guarantees at all. Philosophically speaking, we don't know why the universe makes sense to us at all, Like, why is it even possible to describe it in terms of pretty simple mathematical stories. We don't know, But we do know that it seems to work, and it works really really well. Well, the universe is random, right at the quantum level, things are random? Is random the same as logical. Well, that's a really interesting point. Because even if quantum mechanics is random, it's still also logical, Like quantum mechanics makes very specific predictions for the probabilities of different things to happen, even if it doesn't actually pin down what will happen. So quantum mechanics being random doesn't mean it's like crazy, you're out of control. It still makes very specific predictions about what can and cannot happen and the probabilities of those things happening. Right although technically acquantic to quantum physics, like a pink unicorn could technically appear in front of me out of the boob right now, or in front of any of us right now, right and that would be logical. According to physicists, that would be logical, even though it would also be fantastical. And that's something we're always trying to understand about the universe. We see what happens to us, we wonder was that just a random, lucky fluke, or is that the kind of thing we expect to see in the universe. And there's this overriding principle in science called the Copernican principle, which argues that our experience is not weird, that everywhere in the universe is the same, and nothing is special anywhere, and so when we look out into the universe, we tend to try to explain what we see without resorting to lucky chances and random flukes. But lucky flukes is why we're here, Daniel, Lucky flukes are the best. Well, every individual person, of course, has an almost astronomically tiny chance of ever existing with all of their constituent details. But what we don't know is what are the chances of any person existing? You know, one of the deep questions in the universe is what are the chances for life evolving, for intelligent life to evolve? Are we unusual or are we common in the universe? And we'd like to be able to explain our existence here without resorting to a one in a trillion chance of all of this is happening. Well, it seems like there's a sort of a fine line between illogic and unlikeliness or as you said, improbability. Yeah, that's right, and often we can tell the difference, you know, we have just this one example of our lives and the part of the universe that we can see. And often we look out into the universe and we see stuff that seems weird, that seems like a weird coincidence, and we want to try to explain it. We don't want to just like brush it under the rug and say, hm, that's random, seems weird. I guess sometimes you just get lucky. We'd like to understand if there's something else going on, something deeper behind it. But you know, there isn't always an explanation, like, for example, the sun in the moon take up about exactly the same space in our sky, which allows for very dramatic eclipses, and that's just a coincidence. Sometimes coincidences happen, but sometimes they do have deeper explanations that we can look for. Yeah. So one way we try to explore the logic of the universe is by coming up with situations in our minds or that maybe we get hints at out there of events or things that seem to break the logic of the universe. And these are paradoxes. Yeah. One very famous paradox is the Fermi paradox, which says where are all the aliens? You know, if the galaxy is really really old and actually filled with stars and planets, then maybe it should also be filled with aliens, and why haven't we seen any of them yet? Why haven't they sent us messages? This is called the Fermi paradox because if you accept all of those assumptions, then we should have heard from aliens, and yet we haven't. So paradoxes are fun because they make you re examine those assumptions to say, well, we haven't heard from aliens, then which of those assumptions must be wrong? And what does that tell us about the universe. Well. Another famous paradox is the grandfather of paradox. Right, This idea that if you go back in time and you somehow prevent your grandfather from giving birth or making your father or mother haven't, then that creates an illogical consistency because then how could you have existed to them prevent your grandfather from doing that. That's one of the most famous logical paradoxes, right, And that's like something that doesn't make sense logically, but it could maybe happen. Well, we don't know if that could maybe happen exactly. That's one of the paradoxes inherent in time travel. It's the kind of thing that makes people wonder like, well, what are we overlooking? Is there something in time travel which would prevent that from happening. And there are various ideas about cosmic censorship that might prevent paradoxes from cropping up if you could actually achieve time travel. So you're right, it's a really interesting idea and it focuses your thinking on the issues to say, well, what can we do to prevent this paradox from happening, because, as you say, the universe seems logical, and so anything that creates a contradiction, a logical contradiction, we don't think that that could exist. The universe can't exist in two states that disagree with each other simultaneously. Yeah, so there is another interesting paradox out there. Then maybe the challenges the logic of us being here in the first place, or at least of our son being here in the first place. Yeah, asked the question basically of why we're not looking up into our sky and seeing a different kind of star than the one that we have, or stars plural. So today on the podcast, we'll be asking the question what is the Red Dwarf paradox? The real Red Dwarf paradox is why don't more people watch the show The Red Dwarf. Is that a show? I've never seen it? Is that a show? Oh my gosh, it's like one of the most hilarious can't be science fiction shows ever. I've never heard of it. Where does it er? I think it's on the BBC, but you can find it online. Is it really hilarious show? Sort of in the vein of Hitchhiker's Guide to the Galaxy. Definitely not hard science fiction. Well, the paradox maybe, is how come I've never shown I mean, I've seen several seasons of Doctor Who. There you go, Yeah, well, maybe it only exists in another multiverse, and that's proof that I came from another universe. You do seem out of this world, Daniel, you mean out of my mind. But so, the Red Dwarf paradox apparently is a thing. I had also never heard of this, the paradox or the show before coming into this episode. But it's sort of like a thing that physicists talk about, right. It is a thing that physicists and biologists and basically everybody who's curious about why we ended up on this rock around this star. Fundamentally, we're always asking the question, is our experience unusual? Do we have to resort to shrugging our shoulders and saying, well, I guess we were just lucky, or is there a reason that our experience is this way and not some other way? And in this particular case, we're wondering about why our star is one of these yellow stars instead of a red dwarf star. Well, this, like you said earlier, this sort of seems similar to the Fermi paradox, which is sort of this idea that we should have been contacted or seen aliens right now, but we haven't, given the size of the universe. But I feel like those are not really logical paradoxes, right Like, strictly speaking, it's not a logical there's no logical contradiction here. It's just like an unlikeliness. Yeah, that's true. I mean, the set of assumptions, when you combine them, suggest that it would be very unlikely for us to not be contacted by aliens. So either we're just unlucky or there's some other reason one of the assumptions that goes into it is wrong. And so you can always explain these things away and say, oh, well, maybe it's just one a million chance, and that's what it is. But you can also sometimes make progress by digging into those assumptions and saying, is one of those wrong, let's take another look. You mean, it's sort of like a tool to examine our assumptions about the universe, or as someone else might come complete guesses. Yeah, but it's a basic part of science. You know, anytime you think you have an understanding of the universe, you then think about what the consequences are. You know, if the universe is this way, then I should be able to prove it by seeing this thing. And if you don't see that thing happening, then you wonder, well, what's wrong with my idea of the universe? When we thought, oh, the universe would make more sense if it had Higgs Boson in it, let's go look for it, and we found it. Now, if we hadn't found it, then we would have to go back and re examine those assumptions that suggested it does exist and wonder which one of them were wrong. All right, Well, this red dwarf paradox basically just real quickly in a nutshell. It kind of asked the question that you asked earlier, which is, why isn't our star a red dwarf. Our son is a nice yellow or white I guess technically white ball of fire. It's not a red, it's not a dwarf, and so that's kind of what the paradox is about. Yeah, that's about it all right. Well, as usually, we were wondering how many people out there had asked themselves this question, why isn't our son different? Why isn't it a red dwarf? So thanks very much to everybody who participates in this segment of the podcast, and we would love to hear your voice out there. Those of you who have been listening for a while but haven't yet chimed in, please write to us to participate to questions at Daniel Horge dot com. So think about it for a second. Have you ever asked yourself on a nice sunny day, why our star isn't red? Here's what people had to say. I feel like thybe it's too big, big to be a red dwarf. That's it. I really don't know the answer to this one. I would just imagine that it doesn't have enough mass to either collapse into itself a form a black hole or become a red giant. I don't know all a son didn't follow his diet and has eaten a lot, so it's too big to become a red dwarf. I think the main reason our star isn't a red dwarf is just because it's something has to do with like the amount of mass it has in the beginning and when it begins, because some stars go supernova and some stars just white doors. I don't know, I get mixed up. Maybe our son is not old enough to be a red dwarf. Maybe it still has a lot of fool to be larger and right, dar, I don't think that our star is supposed to be a red dwarf. I think that it may someday be a red dwarf given enough time, But I think that it's not quite yet reached that phase of stellar evolution. All right, A lot of interesting answers here, I like the one about the Sun not following a diet, yeah, or the one about it not being old enough. But I am disappointed nobody brought off Superman. I mean these answers, what does Superman have to do with the Sun being yellow or red? You don't know. I don't know, Yeah, you don't know. Some basic mythology about Superman. I spent all my time watching the show Red Dwarf instead of reading Superman comics. Well, there you go. That's a multiverse I don't want to live in. So tell us what a Superman have to do with red stars. Yeah, it's a basic part of his mythology. So in the original comics, he grew up in a planet with the red sun, and so when he comes to Earth, he has all these superpowers because our son is not red, it's yellow, and somehow that gives him his superpowers somehow. Wow, you just yadda yadded over all the crucial elements of it. Yeah, somehow, you know, like how physicists do somehow the Higgs boson is created in architectors. That's exactly what I wrote in the paper. Yeah, that was it basically. I mean, you use more words and formulas, but there's not much difference between Action comics in the Journal of Physics. I'm sure that Action Comics hired some physics consultants to work out the details, and there's somewhere in there archives there are formulas explaining how the yellow sun gives Superman his special powers. What does that mean that Superman doesn't have those powers? In the dark. Well later on, it's sort of it's sort of like he acts like a battery, kind of like he needs to recharge, he needs to sunbathe they to get his superpowers. I see. So kryptonite isn't his kryptonite. It's sunscreen. That's his kryptonite in the long run. Yes, okay, fascinating. Well, let's dig into this red dwarf paradox and how it might affect Superman, I guess, or all of us, because it'd be great if we were all Superman and women. Well, actually, what the redware paradox suggests is that most of the universe is basically Superman, because one thing that's really interesting about the universe is that most of the stars out there in the universe are red stars, not yellow like ours. All Right, well, let's dig into this topic and this red dwarf paradox, and it's starts with the basics. What is a red dwarf star? Daniel, So, a red dwarf is just a kind of star. Remember that a star is a huge ball of gas and it's squeezed down by gravity, so at its core it's hot enough and dense enough for fusion to happen, which is where the light comes from and why the star burns at the temperature at the core, and therefore the temperature at the surface depends on the mass of the star. The more gas you have, the higher temperature and pressure you have at the core of the star, and so the higher the temperature at the surface, and so the different color of the star. Remember that everything in the universe glows, and how it glows depends on its temperature. Our sun is a surface temperature of five or six thousand degrees kelvin, and so it tends to glow in our visible spectrum. Bigger stars are hotter, and so they tend to be bluer. Smaller stars are colder, and so they tend to be redder, and so a red dwarf star is a smaller, colder star that tends to be redder than our star. M I guess maybe can you explain why smaller means lower temperature? Is it because when you're smaller, you don't have as much fusion, if at all, inside the core of the gas cloud. There's definitely a close connection between the size of the star and its internal temperature, and that's just because of gravity. Like more mass means more gravitational pressure, which means higher temperature. We once topped our way through that thought experiment of like taking a big blob of gas and squeezing it down. Squeezing it down heats it up because you're basically applying pressure which pushes on all those molecules, turning them around to focus them back towards the center. You imagine like a big box containing cold gas. As you can strict that box, you're pushing on all the molecules that would have otherwise escaped, so you're giving them more and more energy. So as you squeeze down harder and harder, you're speeding up all those molecules, you're making them hotter and hotter. So a bigger blob of stuff has more gravitational pressure, which means a higher temperature. Something like Jupiter, which is also a ball of gas. It does squeeze its gas in the middle, but it doesn't radiate light like this star of Sundust, did it. It does not. You're right, there's a minimum mass in order to create the conditions for fusion. Fusion is hard. Remember, what you're doing is squeezing together two protons which have a pretty powerful force repelling them. Right, they're both positively charged. You don't like to get together, So to get the protons close enough together to fuse to make helium, you have to overcome that. So you got to squeeze them really, really hard. And so if you don't have enough gravitational pressure, you haven't raised the temperature enough, then fusion just doesn't happen. So there's a minimum threshold above which fusion happens and below which it doesn't. So Jupiter is below that threshold by like a factor of ten. In order to get Jupiter to have fusion to ignite at its core, you'd have to add like nine more Jupiter's worth of mass to get it to that threshold. Red dwarfs are stars that are just above that minimum threshold, like eight percent of the mass of the Sun. It's like the minimum amount of stuff you need to get fusion going. So red dwarfs are like basically the smallest fusion reactor you can have. So red dwarf is a star in the sense that it has fusion inside of it. If you don't make it to the threshold fusion, like if you're like point ninety ninety nine below the fusion limit, would you still glow or did you just be like a giant gas planet like Jupiter. You'd be a giant gas planet like Jupiter. You wouldn't have fusion, but you would still be kind of hot. Even just having that much mass and that pressure makes you kind of hot. Like the core of Jupiter is not cool, right, it's very high density, high temperature, just not high enough to be fusion. Now, because you're pretty hot, you are going to glow. You're gonna glow very deep in the infrared, and you're not going to be nearly as bright as stars that actually have fusion happening in them. All right, well, I'll take being kind of hot, but not being hot, although being cool it's also pretty cool. These stars are really fascinating, these red dwarfs, and they're kind of cool. As we say, so, they tend to radiate in the red region, and they're also really really dim, Like these things are not nearly as bright as our sun. As a star gets bigger, it gets hotter, and then the fusion happens faster, and so they get brighter and brighter, which is why like really big massive stars starts like one hundred or two hundred times the mass of our sun burn really brightly, very blue, and don't last for very long. They can burn out just a few million years. Stars that are about the size of our sun last for billions of years. But if a star is smaller and cooler, it doesn't burn as bright, it's much dimmer. It can actually last much much longer. So a red dwarf can last for longer than the age of the universe, or even much longer. WHOA, I guess, because it's got like the heat on low basically right, it's like it's got just enough gravity to make fusion, but not enough to like burn a lot of it, So it's just burning a little bit in the center of it like a candle, more like a bonfire, and there's something else going on like the heart of these red dwarfs. Because they're cooler, the way the heat gets mixed around in their core is a little bit different than in our star. Like at our star, a lot of the heat transfer is what we call radiative transfer. Like fusion happens, and photons zoom out and the energy gets dispersed through the star towards the outside by radiation. Right these photons are flying out and so the outer parts of the star get hotter and hotter, and helium the fusion product tends to fall towards the core in our star, and that's actually a problem for our star because that helium tends to sort of put out the fusion, and so then fusion only happens on the outside of the star. But in a red dwarf it's a little bit different. Remember it's not as bright the outside of a star. What do you mean for a star like our sun near the end of its life, as it accumulates helium at its core, most of the fusion will not be happening at its core anymore. Instead, it'll be happening on the outer layers of the star, which is one reason why our sun will grow eventually become like a red giant. It'll puff out to have like a radius the size of Earth's orbit, because the fusion will be happening like in the outer layers, and the core will be the sort of cooler helium. But a red dwarf won't have that problem. A red dwarf mixes in a different way because there's not so much radiation produced at its core, so there tends to be more convection of the plasma like mixes more thoroughly, so you don't get this accumulation of helium at the core, and it can basically just sort of like burn steadily for a long time. This tends to prolong the fusion. It's another reason why these red dwarves last a really long time. And we don't know because the universe isn't old enough, but some calculations suggest that a small star like ten percent the mass of our sun could last for ten trillion years. WHOA, that's like ten thousand billion years, right, that's ten thousand billion years, or almost a thousand times the current age of the universe. Like some of these red dwarfs that were created very early on in the universe, they could be less than one one thousands of the way through their life cycles so far. By lasting, you mean like sustaining fusion at their core, yeah, exactly, because eventually they will burn through their fuel and these things will become blue dwarfs and then white dwarfs. Eventually, the life cycle of one of these red dwarves, we think ends with it basically becoming a cooler blob of heavier metals, probably helium. Sounds like the cosmic version of the tortoise in the hair there that's slow and steady kind of wins the race. Yeah, exactly. So really big stars burn really brightly but don't last for very long, and really small stars burn cooler, but they last forever almost And this is really useful when we're looking out into the universe trying to understand how recently stars were made. If you're looking at a part of the universe and you see blue stars, you see hot, bright young stars, that means stars must have been made recently. If all you're looking at our redder stars, then you know that it's pretty old because all the hot young blue stars have already burned out. So it's a really helpful lever for understanding what's going on out there in the universe. So they're like looking at TikTok only stars there. All right, Well, that's what a red dwarf is. Until the big question is why isn't our star a red dwarf? And would we all have superpowers if it were? So let's dig into that, But first let's take a quick break. All right, we're talking about the red dwarf paradox. Basically, why isn't our son a red dwarf. I feel like this is an insensitive question, Daniel. I mean, how would our son feel? Maybe we should have asked it the other way, to say, why is our star so special and wonderful? Yeah, there you go. That sounds better. Maybe it should be the yellow sun bonus situation. There you go straight from our pr department. But our son is kind of special. I mean, if you look out in the universe, our son is not the most common kind of son. Instead, like seventy five percent of the stars in the galaxy are red dwarves. These things like dominate the galaxy. Most of the stars out there are red dwarves, not yellow stars like ours. What do you mean dominate? What kind of numbers are we talking about? So three quarters of all stars in our galaxy are red dwarfs. It's like overwhelming. M Well, that's kind of interesting. So three quarters of the stars in our galaxy are red dwarves, but they don't look red when you look out into the night sky. Yeah, this is really fascinating. Most of the stars in the galaxy are red dwarves, but none of the stars you can see in the sky with the naked eye are red dwarfs. And The reason as that these red dwarfs are pretty dim. Remember they can be like ten thousand times less bright than our sun, and so they're all over the place. They're out there. But the stars we see in the sky are not red dwarves. We see the bright ones, the rare ones. MM. Interesting. So I guess if you looked at the sky with maybe like an infrared glasses, or if you could see into the lower frequency light spectrum, then you might see a whole bunch more stars when you look at the nice sky. Yeah. In fact, that the closest star to us, Proximus Centauri, is a red dwarf. It is like twelve point five percent the mass of the Sun. You can't see it with the naked eye, even though it's the closest star to Earth. Most of the stars so you're looking at in the sky are what we call like FK or G type stars instead of red dwarfs. Well, it's super interesting. So I guess animals I can see that have night vision, basically I can see infrared more that would they look out into the nice sky and see a totally different picture than we would. Wow, that's a super fascinating question. I don't know. I guess we'll have to have an animal on the podcast as a guest, our first animal astronomer, and ask them all about what they see. Yeah, sounds good. Which animal would that be? An anteater? Of course for Ucia. Now, but we have built infrared eyeballs, right, James Webb. Remember is an infrared telescope. It specializes in seeing in the infrared. And we have lots of other infrared facilities that can see these spectra, and so we have, of course observed these stars. We look out into the universe and notice them. That's how we know that they are there. But it's really interesting to me to think, like, not only is our star not a red dwarf, but none of the stars we see are red dwarfs, even though they dominate the universe. I guess maybe the first question I would have, and I imagine anyone would have, is why is the universe mostly made out of red dwarves? Why is it seventy stars in the galaxy are red dwars? Why isn't it more distributed? Yeah, it's a really cool question. There's this concept in astronomy called the initial mass function, which tries to describe basically how much stuff a star gets. You know, ask the question like, if you're forming a star, how much stuff are you likely to get? What's the distribution of the mass of stars, for example, and what turns out to be like a power law, You're much much less likely to make a big star than a small star. And you know, as gas clouds are sort of coming together and forming stars, you're just less likely to grab a bigger blob of stuff. You're more likely to form multiple smaller stars than a single larger star because it's just how gravity works out there in space in a gas cloud. Yeah, it's actually quite complicated because it involves not just gravity but also where metals are and how they're distributed. Imagine this big gas cloud where gravity pulls things together to make stars depends on where you have little bits of density to start with, and the universe is mostly hydrogen, but it's also sprinkled with a bunch of metals, right, the metals from previous stars that burned and fused these heavy things and then sprayed them out into the universe. So we think that also as time goes on and the universe gets more and more metallic, less hydrogen and more heavy stuff, that the size of stars decreased, like the first generation of stars will be weirdly call type three. We think these were all really really big, hugely massive stars, like three or four hundred times the mass of our sun, and they burned out really really quickly. But while they burned, they also made some heavier metals, So the next generation of stars got seated with more overdensities because you have this like spray of little dots of metal to start more stars and sort of collapsed more easily into these cold blobs. So it's a complicated interplay with like the temperature of these gas clouds and the distribution of where the metal seeds are to start these things, and there's a lot of uncertainty. People aren't really sure exactly what the shape of this initial mass function is, but we are sure of the overall trend that bigger stars tend to be more rare and smaller stars more common, and that's why we have more small stars than big stars. M Interesting. I wonder what that was like when we first discovered that effect that most of the stars in the universe are red dwarfs, Because I imagine we looked that into the sky and saw a bunch of starts and thought, oh, that's pretty neat. But then we looked at the universe at a different kind of line, and so I'm lean, boom, there's like a three times more stars than we thought there were. Yeah, exactly. It's one of my favorite things about a start, me that every time we build a new kind of instrument and look out into the universe, we discover, Wow, there's a lot more going on than we thought. It's like a whole other universe out there filled with these red dwarves. We've been looking mostly at the rare stuff and not at the common stuff, not at the typical stuff, and it turns out that our sun is not one of the usual ones. And that's sort of the core of the red dwarf paradox. It's like, if most of the stars out there are red dwarfs, and they live much much longer than our kind of star, then why did we happen to evolve around one of these rare, shorter lived stars instead of one of the more common, longer lived ones. So that's the basic red dwarf paradox. It's like, why didn't we get to evolved or come up in a star that's the red dwarf because there is three times more common than our kind of star, They're five times more common, and on average they outlast our star by twenty So like, either it's a one in one hundred chance, or maybe there's a reason, Maybe there's an explanation why life can't happen around red dwarves or it's less likely around red dwarves. One thing we do know is that red dwarves tend to have planets around them, just like our kind of star. And so it's a fun question, like is there life around red dwarves? Are we an unusual kind of life? Is everybody else out there in the universe? Superman? Are all their planets called Krypton? That is what does this day up at night wondering about. But this is an interesting scenario. You're saying that most red dwarfs are kind of just like our stars. They can have planets orbiting around them. What would their sun look like to someone living at a planet like that, Well, if you're at the same distance from that red dwarf as we are from our sun, then of course there'd be a lot dimmer, right and colder, right, Yeah, exactly, dimmer and colder. It'd be dark and chilly. Of course, you could be closer up and then you'd be brighter and warmer. But the star itself also would look different. The star itself is colder, which means it's light is redder. So you look in the sky, you wouldn't see like a yellow or white sun. You see like a pale orange or a red disc in the sky. It would be a very different experience. Well, I wonder if it would be different, you know, because you would have to be closer to the star to get the same warmth as us. So it is possible for there to be a planet I run, a red dwarf that feels like our situation here, and you'd be closer to it, so would be just as warm and maybe just as bright as our sun is to us, wouldn't it. Yeah, you could definitely have a planet in a habitable zone where water is liquid at the surface and it's about the same temperature as Earth. But it would look different in the sky, right, It would still be red instead of yellow. Though if you evolve on that planet, then who knows what your experience of red is. Yeah, that's what I mean, Like, it would only look red if a human went over there and landed on that planet. But to some species that evolved there, it would just look like white light, or it would be what they call white light, because they would maybe see a different, totally different spectrum of light. The visible spectrum would be you know, shifted it over, but they would call that white light, right. I don't know what they would call it, but you're totally right that it's very likely that their visible spectrum would be different from ours because ours evolved in response to the light that happens to be here on Earth. What we call visible is no coincidence. Peaks around the light that the sun puts out our sun, and so it makes a lot of sense, as you say, for aliens around a red dwarf, for their visible sensitivity to peek around the light emitted by their star instead of ours. Whether they would call that white or not, I'm not sure what they would experience it, what would their art be like? You know, I guess what I mean is like what we call white light is just light that has all the frequencies in our visible spectrum. Like that's our experience of white light. And so if you're growing up in that red dwarf planet, you know, your eyes would probably evolve to also interpret, you know, everything that's in your visible spectrum to be you know, the white or what we would call white. And so you know, they wouldn't know they're in a red planet. That's interesting. And if they tend to paint like all their walls white, we show up to visit, there would be like, why is everything painted red? You guys have like a red sun. It's not enough. You'll also have to paint all of your walls red, right, That's what I mean. Or if they came to our planet, they'd be like, why is everything blue? You guys are nuts. That's not blue. That's not white. That blue. We say, we just got the blues because we didn't get to grow up around a red dwarf. We got the yellow dwarf blues. Yeah, and so our star is not a red dwarf. It's a different kind of star. It's bigger. We have a G dwarf. Wait, it's still a dwarf. Well, you might not be surprised, but there's a lot of disagreement about what to call them. Some people call it a yellow dwarf or a G type or a G dwarf, but it's part of a category of stars F, G, and K, where those letters just indicate basically the mass of the star and therefore it's temperature. So every star that has a mass of our sun within about ten percent we call a G type or G dwarf. And then there are F type and K type that can be like a little bigger or a little hotter or whatever. Lots of famous stars like Alpha Centauri, for example, is also a G type star. Interesting, well, I like our star. It's pretty nice and sunny for us here. Maybe my next question is like, why is this a paradox? I feel like maybe you're stretching the definition of the work because it doesn't feel like a logical inconsistency. It just feels like a philosophical question, like why did we happen to live around a star that represents, you know, the fifteen percent of all the stars in the universe. I think it's called a paradox because it asks a basic question. It says, if it's true that these stars are just as likely to have life as ours, then it's much more likely that we would have evolved on a red dwarf instead of a G type star. And so you have to either say all right, something very unlikely happened, or there's a reason. This an explanation is to again just a tool to dig into all of those assumptions. In this case, it's not like ridiculously unlikely. We're talking about it's like a one in a hundred chance. If life is equally like need to evolve around G type, F type K type and red dwarfs, then it's like a one one hundred chance to not end up evolving around a red dwarf. And that's not crazy. You know, one and one hundred chances happen, But it's an invitation to dig deeper. And for those of us who want to understand the universe, these are opportunities. These are clues that say maybe there's something else going on. All right, well, let's dig into what could be going on there. What kinds of assumptions are we making about life here on Earth and what life could be like around a red dwarf planet. So let's tag into that. But first let's take another quick break. All right, we're talking about Superman. What's your favorite Superman storyline, Denny? The one where Daniel didn't know that Superman required sunlight to work. You didn't know Superman was big on solar energy. The one where Superman makes a crossover on my favorite TV show, Red Dwarf. That might happen. You never know, You know, all these companies keep getting bought out by other companies. That's right. If DC buys the BBC and we have the DC BBC extended Universe, maybe it'll happen. Right the DBC. We're talking about red dwarves, and apparently our star, the one we see during the day, is not the most common type of star in the universe. It's only maybe fifteen percent of all it's kind, It's only fifty percent of all the stars out there in the galleys in our galaxy. Most of the stars seventy stars in the galaxy are red dwarves, which are different, smaller, cooler, And so maybe a question you can ask is like, why isn't our star a red dwarf? I guess I'm wondering what we're really asking here. We're asking why our star is not a red dwarf? Or are we asking why we're not a species that grew up around a red dwarf? Yeah? The second one we're asking is it just chance that we haven't evolve not in the most likely situation, or is there a reason or we misunderstood where life is possible and likely. I guess that's a weird question to ask, because the answer could be both. Right. It could be that there's equal chances of a species growing up around any star, but we just happened to be one one of the ones that grew up around a yellow star. Yeah. Absolutely, it certainly could be both, and it could also just be chanced. Those coincidences do happen. But we've made a lot of progress in science just by pushing this basic principle. The Copernican principle is saying, let's never assume that there's something special or weird about our situation. Let's try to describe what we see under the assumption that no place is special. And that's been very useful. It's not a hard and fast rule, but it's guided our thinking and helped us make discoveries. All Right, Well, if you apply that principle, what would be some of the answers to the red poarf paradox. Well, one way you could reduce the unlikeliness of the paradox is to think about how fast life does evolve into intelligent life. One thing we're saying is that these red dwarfs is five times as many of them, and they last twenty times is long. It seems to suggest that you're like a hundred times more likely to revolve around a red dwarf than our kind of star. But that is actually making some assumptions. That's assuming, for example, that life might take a long time to evolve. You know, that's very unlikely, and so these Red Dwarfs, because they last longer and they're more of them, they're basically like buying more lottery tickets, and so they're more likely to win. But instead, if intelligent life evolves pretty rapidly, it doesn't take very long to evolve, then the fact that Red Dwarves happen to live longer, have longer lifespan doesn't necessarily help them. And so in that scenario, instead of being like one hundred to one, it's more like five to one odds. It's just basically the relative rates of occurrence that determines your likelihood of being around a Red dwarf or a yellow star. I guess maybe I'm not quite sure I understand that argument. If you are around longer, if a red Dwarf is around longer, which it is, As you say, can we get even less longer than the eight of the universe doesn't make it more likely that it has or at some point in its history will have life. Then let's say our star. If life is really unusual or it takes a long time to evolve, then yes, But say life happens really quickly when it does. Right, then the fact that the red Dwarf is going to last for trillions of years means that civilization gets to live longer around its star. But it doesn't mean that it's twenty times as likely to evolve around one of those Why not? I guess you know you're assuming that life is sort of a certainty if you have a certain set of conditions. But maybe it's a probability thing for life to occur, right like if you need to roll the die and get a certain number to get any kind of seed of life when you're around your star, then the longer you are, the more times you get to throw the die. You're assuming it's a certainty, but it's not right. It's maybe chance base it maybe is right. But what we're doing here is we're examining which assumptions could possibly explain. It's what assumptions will we have to change in order to explain what we're seeing. You're totally right that if it's like rolling the dice and it's very unlikely, then the more times you roll the dice, the more odds you have, and so then you would be much more likely to evolve around a red star. But if it's not, if it's basically certain it happens pretty quickly, then you would expect life to happen around red dwarfs only five times as often as around yellow stars, because that's the relative rate of their occurrence, and the time wouldn't be a factor. And that could be the case, right, it could be five times more Kryptonians and Earthlings out during the universe. There certainly could be. And we also don't really know, you know, how common is life? How long does it take to evolve? We think that on Earth, life itself evolved pretty quickly. There's like fossil records going billions of years back, so we think it didn't take very long for life itself to evolve, although intelligent life is much more recent development, and so it might be that life is very common in the universe and all those red dwarfs are teeming with little bacteria. But intelligent life, you know, people making podcasts and writing comic books and all that kind of stuff, is more rare. We just don't know the answer to those questions. Well, if it is more rreer, then having five times more stars and being around longer would make that so much more likely that they have intelligent life, right exactly. Yeah, so this isn't a great answer to the question, but it changes the probabilities, right, the likelihood and the time it takes for intelligent life to evolve does change how likely you are to evolve around a red star or a yellow dwarf. So then how does this resolve the paradox? I don't think it totally resolves the paradox, But if we did live in a universe where intelligent life emerged very, very rapidly, then our situation wouldn't be as unlikely. It'd be like a one in five chance instead of a one in one hundred chance. So it reduces the tension a little bit. I see, all right, it makes us less of a miracle, yeah exactly, We're less a little less weird. All right, Well, what are other possible resolutions to this paradox. Well, it might be that it's not as easy for life to evolve around red dwarfs, Like maybe red dwarfs are not as habitable as yellow stars. There are more differences between red dwarfs and yellow stars than just their brightness. Because they're so much smaller, they tend to have different sort of behaviors, which might make it harder for life to evolve around them. Like what kinds of behaviors? Well, for example, we talked earlier about how to be in the habitable zone, you would have to be much much closer to the star, right, because the star is much dimmer. In that scenario, you're more likely to be tidally locked to the star, which means that like one surface of the planet is always facing the star. Tidal forces are really just gravitational forces. Gravity hinds to tug on the closer bit harder than on the further bit. If you can elongate the planet a little bit, then it prevents the planet from spinning the way. For example, the same side of the Moon is always facing the Earth, and so if you're on a planet really close to your star, you might be tidally locked and That means that one half of the planet would be super duper hot and the other half would be super duper cold, and biologists disagree about whether that's more or likely or less likely to evolve life. Does that assume a planet the same size as Earth. What if you're a smaller planet or what if you have some spin to begin with? Yeah, smaller planet would be less likely to be tightly locked. That's true, And it's not guaranteed that all these planets would be tightly locked. You right, If you have a lot of spin, you might be able to avoid it. But more of these planets would be tightly locked than, for example, earthlike planets around a yellow dwarf, so it might complicate the evolution of life. Another issue with these stars is that a lot of red dwarfs tend to be what we call flare stars. Unlike the Sun, which burns pretty steadily and you know it has some flare ups and some deviations in its brightness, red dwarfs can sometimes vary dramatically in their brightness. A flare star is something that can be like two or five or one hundred times as bright as it normally is all of a sudden for a little while and then sort of calm back down. They don't tend to burn as steadily. Well, you're saying red dwarves tend to flare up more than our kind of start. Yeah, red dwarfs tend to be more variable than yellow stars. I thought they were more like moderate and steady. It's a subject of intense debate, and we're not sure we understand. But remember that a lot of stars out there are also binary stars, and so these red dwarves might be in binary systems, and interactions between the magnetic fields of the two stars can interfere with what's going on inside the star and like heat it up briefly and cause it to burn hotter for a short period. So it's not something we understand very well. But the stars that we have studied, most of the flare stars, tend to be these red dwarves, and that would be pretty unpleasant for life. If all of a sudden the Sun is like a hundred times hotter than it usually is. M you might have to leave that planet right or at least like put your son in a spaceship and send it to another planet. It's like a yellow sun. Perhaps that sounds like a great idea for a comic book. You should copyright that, like fifty years ago. Let's go back in time to your grandfather and tell him that idea. That's right, it's called the Superman I had the idea for Superman Paradox. So why are you wasting your time on this podcast? You just be counting your money because I'm stuck in this multiverse, Daniel. I could be a billionaire cartoonist instead, I'm just a cartoonist. Just a cartoonist. Yeah, so flare stars would make it harder for life to evolve for at least lifelike hours. You know, maybe that kind of environment would lead to totally different kinds of life that are less sensitive to radiation. Or maybe they'd have to burrow underground where it might be safer and they could still somehow tap into the heat of the sun. M right, because we don't like we assume that you need day and nighttime cycles to thrive like we do, right, Like you need a good night's sleep. Of course you need nighttime for that. But maybe not right, Like, maybe it could be even the opposite, Like maybe life flourishes better if there's no nighttime. Yeah maybe, and maybe it's great to have like super duper hot summers every few hundred years. You know, things get fried to a crisp, but the strong survive. Who knows. There's one more issue with life developing around these red dwarfs is that in the systems we have studied so far, we see fewer large gas giants, basically fewer Jupiters. So, you know, we are very happy to have Jupiter or solar system because it's big, and it's gravitational, and it tends to protect us from comments and asteroids. Sometimes it sweeps these things out of the inner Solar system, But in systems with red dwarf stars, we tend to see fewer of these jupiters, which might mean that they're not as protected from asteroids, so it might mean more big impacts like the ones that wiped out the dinosaurs. I see. We don't see Jupiter size planets around those other solar systems, But I wonder if they have their own version of Jupiter. Right, I feel like a red dwarf system would be very similar to ours, just kind of scaled down. So maybe you have to scale down your expectations for what a Jupiter would be like. Yeah, as long as they're being hit by mini asteroids and maybe it's cool. And remember, also, being hit by an asteroid isn't all bad. I mean, sure, lots of things die, but it also can make room for all sorts of new evolution like mammals and humans. Doesn't necessarily have to be a planet wide extinction event. But I guess you're saying that life around a red dwarf isn't necessarily rosier than or it might be less rosy than technically, both metaphorically and physically speaking than life around a yellow start. Yeah, you might be wearing rose colored glasses, but there might actually be fewer roses, or at least the situation would be different. And if we're making a simple argument about the likelihood for life to evolve, this sort of undermines sense as well. The conditions we know are quite different, and so life might be less likely to evolve in those scenarios. On the other hand, it could also be more likely. Right, maybe life in the universe prefers that situation to ours. We just don't know. All right, Well, then what's another or maybe the last possible resolution to this paradox? The last sort of idea people have to explain this is that maybe there aren't as many earthlike worlds around these red dwarfs as we think. Remember, the red dwarfs, they're hard to study because they're small and they're dim. Most of the ones that we study are like the really big versions of them, sort of on the upper edge of red dwarfs. A lot of the red dwarfs that are out there, most of them that are out there, are smaller. It's not just true that there are more red dwarfs than yellow stars. There are more small red dwarfs than bigger red dwarfs. So most of the red dwarfs out there are the ones that we have trouble seeing. So our calculations are estimates about like how often there's an earthlike planet inhabitable zone around these things. Those could just be wrong, and it might be that most of the red dwarves out there don't have planets the way our stars do. They're just sort of too hard to study. Right now, we're like extrapolating into the unknown, well beyond what we really have confidence in, I see, because we haven't. We don't actually know what the planets around those smaller red dwarves are, like yeah, or how many there even are right. So we're making these assumptions. We're extrapolating from our situation and from the few examples we have been able to study about red dwarfs. But that's an extrapolation, and that could be where we're going wrong. Maybe only the red dwarves have these kind of planets, and most of the ones out there, which are most of the stars in the galaxy, don't have them. M that would make it less weird that we exist around a yellow star. And fortunately we're going to learn more about this soon. In twenty thirty five, we hope to be launching a new space telescope called have X, which is going to specialize in studying planets around stars, even dimmer stars. It's going to be super awesome with this like four meter sized mirror enough star shade to block out the light from the stars, and it's going to help us understand where are the planets in the galaxy? Are they mostly around yellow stars? Are they also around red stars? Are they also around the smaller, more variable red stars. What's life like over there? That's pretty cool. So a big telescope just to look at planets might even looking at star. It's just totally dedicated to looking four aliens. Basically, it's really amazing technology. This thing it has a star shade. This thing that fits in front of it floats in space. It's bread from it. It's like a two component thing. The second piece is just there to block out light from stars. Right, Mostly telescopes are focused on stars. This one specifically has a blind spot for stars because it wants to see the planets. Cool. Well, that will go up in twenty thirty five, and I'm sure we'll do an episode when we get to that point. If we're still alive, if neither of us are billionaires by the end, if an asteroid hasn't hit us, or Superma's income, or other aliens wearing their rose colored glasses having come to tell us all the secrets of the universe. Well, wouldn't they need blue colored glasses. It's a blue flower, a violet violet. There you go, violet colored glasses. Let's just hope they bring violets and not violence. All right, Well, I think this is an interesting question to think about, you know. It against kind of makes you wonder how rare it is for us to be here, or maybe how common it is. Either way, it's kind of a fun question to think about. It's all part of this journey looking out into the universe and wondering why it is the way that it is, and is our corner of it weird or not? Yeah? Are we superman or are we just regular earth Links? They're never talking about what what happens if you go from the yellow sun to a red sun? Do you get weaker? Maybe they have a comic book where earth Links go to their planet and they're called Underman underwear Man. Maybe, well, I think no one's already taken Captain Underpants. Every idea is out there. Yeah, there you go. Maybe you can go back in time. All right, Well, we hope that made you think about your life and how likely it is for you to be here, and how appreciative we should be every time you go outside and feel the warm rays of our sun and wonder about those aliens out there. Are they also enjoying a yellow star? Or is everything on their planet red? Or is what they call red actually yellow? Thanks for joining us, See you next time. Thanks for listening, and remember that. Daniel and Jorge Explain the Universe is a production of iHeartRadio. For more podcasts from iHeartRadio, visit the iHeartRadio app, Apple podcasts, or wherever you listen to your favorite shows.