Daniel and Jorge Explain the UniverseDaniel and Kelly answer a question about whether the Earth might survive the Sun's ejection from the galaxy.
Daniel, it's been like forever. How are things good?
Good?
You know, same stuff in my world? Do big updates.
So you guys didn't like move across the planet again?
Oh no, we are done with those trans continental moves. I hate moving.
Oh my gosh, I hate moving too, But you know, I think what I hate the most about moving is needing to like pack everything up and then not only unpacked, but then you discover like, oh I need new curtains, and like, oh we forgot the plunger, we need to get a new one, and like all of that stuff. So what if you could move and stay in the same house, like lift it up and move it. Would you move across the country?
Then I think that's a billion dollar idea. You shouldn't be sharing it on the podcast. You should be starting that company.
Delete delete now. I have no business acumen, so somebody else can go ahead and make a billion dollars on that. You're welcome.
Hi.
I'm Daniel, I'm a particle physicist, a professor at UC Irvine, and I've never started a billion dollar company.
I'm Kelly Wiener Smith. I'm a parasitologist at Race University. I also have never started a billion dollar company. But I did move my husband across the country something like three or four times. But he made me promise we'd never move again, which is good because we can't move our farm.
There's something about moving. It's sort of like having kids. It's horrible, it's painful. You swear you'll never do it again, and then a few years later you sort of forget how bad it was, and you're like, actually, that sounds kind of fun.
I don't think my husband ever forgot how bad it was. He was always I'd be like, let's move again, and he'd always be like, no, don't you remember, And I'd be like, no, no, it's fine, fine, fine, But anyway, we're done moving and we're done having kids. So there you go. Everything about our life is standing still.
Well, there was a period in our lives when we went back and forth from California to Geneva, I think ten times over a five or six year period, with tiny kids. Oh my gosh, I don't know how our sanity or our marriage survived.
Oh okay, that is way more intense than what I did. That's incredible. Yes, I am also amazed that your sanity and marriage survived you too. It must be a very strong family.
I think you should be less impressed and more doubting our judgment. But anyway, Welcome to the podcast Daniel and Jorge Explain the Universe, a production of iHeartRadio in which we try to move you to a place of deep understanding about the universe. We want to transport your brain to that mysterious location where everything makes sense. We're it all clicked together in your mind to give you a harmonious understanding of the deep knee of the universe, at least as far as we understand it.
Right, or to give you a headache wondering wondering how this all works.
Sometimes no pain, no gain, right, Kelly. That doesn't just apply to lifting weights. It also applies to understanding the universe.
Yeah no. And there's a lot of pain in physics.
And we want to help you with that pain. So if you are thinking about things and they don't quite click together in your mind, or if you have a physics question and you've tried googling it but haven't found any answers, we want to help you out. This is not just a one direction a lecture from us to you. We want this to be a conversation and we miss hearing from you, so please write to us two questions at Daniel iinhorge dot com. You'll always get an answer back. And on today's podcast, we're going to be doing just that, answering questions from a listener. So today on the podcast, we'll be answering listener questions. Bring Equinox edition. We thought it was time to come back and fill your ears with answers to physics questions.
About the universe because missing you.
And we hope you've been missing us. And today we have a really fun question about transportation or about moving, not just moving yourself, not just moving your house and family, but moving the entire solar system. So here's a great question from John in Kansas.
Hello, Daniel, this is John and I listened to your show from south central Kansas near the Oklahoma border, and I love it. Anyway, my question is I've heard you discussed many times that occasionally stars get ejected from their systems, perhaps due to the pull of a passing star, and I remember you once even speculated that we ourselves may have started out as a binary system and our son's own twin brother got ejected ago. But my question is this Suppose this did happen and our Sun did get flung out of our galaxy. Would it be violently ripped away from its own planets? Or would the event be so gradual that we wouldn't even notice it? And if that happened, would be be towed with it along with the other planets, asteroids, the asteroid belt, the Kuiper Belt, the Oort Cloud, and all of the celestial bodies, all remaining nicely tucked away in their own orbits as we follow the Sun into oblivion. Thank you for answering.
Oh fantastic. Another question that inspires existential dread what would happen if the Sun would would it rip apart our solar system? Or would our planets go with it? And anyway, it's okay, I don't need to sleep, so let's go ahead and dig right in, Daniel, how stable is our solar system?
Yeah, this is a really fun question thinking about what might happen if our Sun got ejected from the galaxy. And you're right. The first part of the question is understanding, like how well are we latched onto the Sun? If the Sun gets thrown out somewhere, how likely are we to go along? For the ride, and this depends on the stability of the whole Sun Earth system, right, So good news is that mostly things are stable, Like the Earth is orbiting the Sun, and even if the Earth got like a little bit of a push, it would slide right back into its orbit. That's what we usually mean by stable. You know, if you have, for example, like a ball inside a cup and you push it a little bit, it's gonna roll right back down to the bottom. Whereas if you have like the ball sitting on top of another ball, or on top of a rock, or on top of a hill or something, and you give it a push, it's gonna roll away and not come back. That's an unstable configuration. So we call the Earth's orbit stable because it's pretty resistant to these kinds of pushes.
So even though it's resistant to a kind of push, anything that could push Earth away from the Sun would have to be catastrophic.
Right.
Well, there's lots of little pushes that the Earth could survive, and the Earth is getting tugged on and pushed in lots of different ways. So the Earth's orbit would be perfectly stable if it was just the Earth and the Sun in totally empty space with nothing happening in classical mechanics, that could go forever. But you know, the situation is a little bit more complex. For example, like the Sun is pushing on the Earth. It's not just pulling on it. The radiation from the Sun, the wind, and the photons are actually applying a momentum pushing the Earth away from the Sun. But the Earth's orbit is stable enough that it can overcome that. It's like accommodates that.
So I've read proposals. I don't know how serious any of them were, but like to deal with climate change by like putting like a big screen out that would block some of the photons from hitting the Earth. If you blocked enough photons, could the Earth move closer to the Sun because we're not getting pushed back and like not much. I know you said it's a small effect, but when we move like a couple feet closer if you blocked enough photons, well.
That depends a little bit on where you put that shield. Like if it's connected to the Earth, then it's basically just part of the Earth and it doesn't change how we're getting pushed. If it's somehow floating separated from the Earth and absorbing that momentum itself by like firing rockets or something. Then yeah, that would relieve a little bit of the pressure on the Earth. But this is really a tiny, tiny effect on the Earth's orbit. Much more substantial are tugs by like Jupiter and Saturn, because the Solar System is not just the Earth and the Sun. There are other big players out there, and Jupiter is much more massive than the Earth. So if you want to model the Earth's orbit and its stability really accurately, you got to think about what the big boys do as they move around the Solar System, and they're constantly tugging on the Earth giving it little nudges here and there, and that the Earth is pretty stable towards like the Earth can tolerate a push from Jupiter, push from Saturn and then slide right back into its orbit.
Okay, And so does the answer to this question then depend on how close does Jupiter need to be to Earth when this happens.
Yeah, so Jupiter and Saturn are basically irrelevant to this question, is the good news. The bad news is that there are other things that can also perturb the Earth's orbit, And the biggest, number one thing to worry about are other stars because where the Sun is in the galaxy is not fixed relative to the other stars. Like all the stars in the galaxy are rotating around the center of the galaxy, but they're not all rotating together, so our distance to other stars changes as time goes on. So even if we don't get ejected from the galaxy, there is a danger that sometime in the future, another star will come close to us and that could perturb the Earth's orbit. It could provide enough of a gravitational nudge to knock us out of our orbit, or even a doesn't, it could disturb all the frozen objects out in the deep Solar System and rain down a bunch of comments on us, both of which would be bad. I know that doesn't sound like a lot of fun, but it might actually be spectacular. Well, dig into what it means just after this short break. Okay, we're back, and we're talking about what might happen if our star is ejected from the galaxy and whether it's likely.
Do we think this could happen? Probably not in our lifetimes.
Right, probably not in our lifetimes. But we do understand the Sun's path through the galaxy pretty well. It's actually pretty awesome to think about it, because you imagine space, you probably think about the Sun primarily as the center of our galactic coordinates, right, everything else is relative to that. But you know, the Sun is in motion relative to this center of the galaxy. And this is sort of a big conceptual step because remember that all motion is relative. So some people say, oh, you know, the Sun is moving through space, but everything is moving through space, it's just relative to what. So when you talk about like the earth velocity is relative to the Sun, you talk about the Sun's velocity is relative to the center of the galaxy. And the Sun, like everything else, is swirling around the center, and it takes about two hundred and fifty million years to orbit. It's like a really huge amount of time.
But that's happened a number of times since the planet started, like many times since the planet started, So it's moving. I don't know, that's kind of impressive.
I think, yeah, Well, the Earth is like four and a half billion years old, which means in terms of galactic spins, right, how long it takes the Milky Way to cycle, which in many ways is like a very natural unit. You could call it like a galactic year. Instead of measuring time in terms of how many times the Earth goes around the Sun, measure in terms of how many times the Sun goes around the galaxy. And so that makes Earth like twenty galactic years old. Earth is just grown up. It's like entering its adult phase.
It can't even drink yet.
That's right. So, yeah, the Earth is kind of young and sprightly. Right, it's still probably the fittest it's ever gonna be.
Oh oh man, wait till you hit your thirties.
Earth.
It's all downhill after that.
But the other thing is that the Sun doesn't just orbit around the center of the galaxy. It also wiggles. It's above the galactic plane sometimes, and then it zooms down through the galactic plane and then past it, and then the gravity of the galactic plane pulls it back. So it's like oscillating up and down above the galactic plane. So it's not just going in a circle around the center of the galaxy. It's more like a zigzag up and down as it circles around.
All right, So now I'm picturing my son when we walk around the track together. He's like jumping up and down the whole time that we're doing. Yes, So this young Earth is going up and down while it's making its laps.
Exactly, and that cycle takes about thirty million years. So as we go around the galaxy, we go up and down like eightish times every galactic year, and that's different for different stars. And so now imagine this whole galaxy. It's a chaotic swarm of all these stars moving closer and farther away from each other. There's a real possibility, of course, over millions and billions of years, that we come pretty close to another star. We've actually predicted that there is going to be a close approach by the star Glease seven to ten in a few million years.
Oh that's how close, Daniel, How close?
It's not going to be that close. I mean it depends on the units. In one point three million years, it's going to pass within zero point one seven light years, so like a seventh of a light year. That doesn't sound very far, but it's like a twenty fifth of the distance to the nearest star. So it's going to mean that the closest star to Earth is a lot closer than it is currently, but it's still pretty far away. It's like ten thousand astronomical units ten thousand times the distance from the Sun to the Earth. So it's not like gonna appear in our sky as bright as the Sun or anything. It's just going to be something moving in the night sky.
Will it still be brighter than the other stars.
It'll be brighter than the other stars. Yeah, it'll be very visible. But you know, in one point three million years, so your super great grandkids have this to look forward to.
Yeah, yeah, I guess I'm gonna miss it. Oh well, this is important.
To answer John's question because this is how stars get thrown out of the galaxy. Like just left alone. The Sun's orbit is pretty stable, it's just going to keep going around the center of the galaxy. But the same way that, like Earth is nudged by Jupiter and Saturn, the Sun can be nudged by other stars, and so a close approach with another star could end up doing a gravitational slingshot on our star, so it gets sent out of the galaxy.
Obviously, if you live on Earth, whether Earth stays put or not, you're dead without the Sun and the light that it provides. But what kind of factors would determine if Earth stays put or not? Would it depend on how fast the Sun moves, or if the Sun came close to us on its way out, Yeah, what would we have to worry about.
It's basically all proximity. Like if that star comes by and it's not super close, and it just like gives our Sun a new direction. Even if that direction eventually takes us out of the Milky Way, we'll be fine because if it's gradual, then the Earth's orbit can respond to these things, respond to little nudges. It's just like another Jupiter effect or another Saturn effect, and it'll follow the Sun as it takes its new trajectory. But if it's dramatic enough so that like the Sun gets accelerated significantly and new direction comes on quickly, then the Earth's orbit can't adapt. Because the Earth's orbit is pretty stable, but it's not infinitely stable. If you gave it a really big kick relative to the Sun, or equivalently, you give the Sun a really big kick, the two are the same, then the Earth will not be able to follow the Sun. And so if for example, another star comes very close to our Solar system, so the Sun feels a very strong gravitational pull, the kind of thing that can and does kick stars out of our galaxy, then the Earth has almost no chance of following. Oh Man.
So, in the scenario where something is big enough to move the Sun, but the Sun is moving slowly, when the Earth reached the part of its path around the Sun where it was between the Sun and this other sun that was big enough and close enough to move the Sun, would that push Earth towards the other gigantic sun object then we would go back. And so would that be like a wobble in our orbit or would we get pulled out to that other Sun.
Yeah, well, you're talking about a three body problem, and this is known to be very chaotic.
Right.
If you have two stars and a planet, then it's very difficult for that planet to find a stable orbit. And if that system is changing because one star is like flying by the other one, then it's essentially impossible. So the details depend on exactly the angle and exactly the velocity. That's what we mean by chaos and physics. We mean that a very small change in the situation can result in a very big change in the outcome. Like if you're playing pool and you hit one ball against the other, a very small change in how you're hitting the cue ball can mean you win the game or lose the game. Right, So in this scenario, a very small change in the direction of that star, or the mass of that star, or the velocity of that star could result in a completely different outcome. Some like you and vision like, oh, we wobble towards the star and then we wabble away from it, and others where we just got we just get ejected into deep space on our own. So I think if the star comes close enough to eject our Sun from the Milky Way, it's going to also come close enough to perturb our orbit around that Sun. It's going to be very unlikely we are along for the ride. But you know, there's a possible bright outcome there.
What's that.
It might be that this new star comes along, messes up our happy orbit around the Sun, ejects the Sun from the Milky Way, and then steals the Earth. It might be that we get a new Sun.
But like, that's got to be an extinction level event. Even if it works out like a you know, on par with taking out the dinosaurs, that couldn't work smooth. That wouldn't be good for us. I don't want my kids to experience that.
You know I'm reaching for a sliver of positivity here Elly, in very dark times. I need you to work with me, work with me.
You know.
A friend asked me the other day why I'm so relentlessly depressing. So I think you just you picked the wrong person to have on your show. I'm sorry.
Well, you know, if we knew about it far enough in advance, and we could build bunkers to survive the intervening period where things very bright or very cold, the seasons are totally wacko. Then there's a situation where in the far future the Earth is in the habitable zone of another star, which I think would be an amazing premise for a science fiction novel. And I haven't read it yet, and I want somebody out there to put pen to paper and write me that story and make it happy ending for Kelly.
And that's your billion dollar idea. There we go. We just keep throwing them out there.
That's basically the next Harry Potter, I'm sure. Yeah, Harry Potter and the Adventure of the Alternate Earth.
There you go.
All right, Well, thank you very much, John for thinking about the nature of the universe and how it affects life here on Earth and how our future might be impacted by visitations from other stars. I hope we answered your question, and I hope we inspired everybody out there to think about their own questions about the universe. What doesn't make sense to you? What physics scenario are you wondering about that you can't find the answer to. Please write to us. We want to hear from you. Send us a message to questions at Danielandjorge dot com. And thanks very much Kelly for bringing your relentless optimism to the podcast.
Oh you're welcome. Yeah. I hope we get more questions so that our list of reasons to feel existential dread can grow and grow and grow and grow. But yeah, thanks for having me on the show. It's always a good time.
Wonderful to be in your ear again everyone, and hope you hear from us soon. Thanks for tuning in for more science and curiosity. Come find us on social media where we answer questions and post videos. We're on Twitter, Discord, Insta, and now TikTok. 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.
