Speaker 1: Daniel, it's been like forever. How are things good?
Speaker 2: Good?
Speaker 3: You know, same stuff in my world? Do big updates.
Speaker 1: So you guys didn't like move across the planet again?
Speaker 3: Oh no, we are done with those trans continental moves.
Speaker 3: I hate moving.
Speaker 1: Oh my gosh, I hate moving too, But you know,
Speaker 1: I think what I hate the most about moving is
Speaker 1: needing to like pack everything up and then not only unpacked,
Speaker 1: but then you discover like, oh I need new curtains,
Speaker 1: and like, oh we forgot the plunger, we need to
Speaker 1: get a new one, and like all of that stuff.
Speaker 1: So what if you could move and stay in the
Speaker 1: same house, like lift it up and move it. Would
Speaker 1: you move across the country?
Speaker 3: Then I think that's a billion dollar idea. You shouldn't
Speaker 3: be sharing it on the podcast. You should be starting
Speaker 3: that company.
Speaker 1: Delete delete now. I have no business acumen, so somebody
Speaker 1: else can go ahead and make a billion dollars on that.
Speaker 1: You're welcome.
Speaker 2: Hi.
Speaker 3: I'm Daniel, I'm a particle physicist, a professor at UC Irvine,
Speaker 3: and I've never started a billion dollar company.
Speaker 1: I'm Kelly Wiener Smith. I'm a parasitologist at Race University.
Speaker 1: I also have never started a billion dollar company. But
Speaker 1: I did move my husband across the country something like
Speaker 1: three or four times. But he made me promise we'd
Speaker 1: never move again, which is good because we can't move
Speaker 1: our farm.
Speaker 3: There's something about moving. It's sort of like having kids.
Speaker 3: It's horrible, it's painful. You swear you'll never do it again,
Speaker 3: and then a few years later you sort of forget
Speaker 3: how bad it was, and you're like, actually, that sounds
Speaker 3: kind of fun.
Speaker 1: I don't think my husband ever forgot how bad it was.
Speaker 1: He was always I'd be like, let's move again, and
Speaker 1: he'd always be like, no, don't you remember, And I'd
Speaker 1: be like, no, no, it's fine, fine, fine, But anyway,
Speaker 1: we're done moving and we're done having kids. So there
Speaker 1: you go. Everything about our life is standing still.
Speaker 3: Well, there was a period in our lives when we
Speaker 3: went back and forth from California to Geneva, I think
Speaker 3: ten times over a five or six year period, with
Speaker 3: tiny kids. Oh my gosh, I don't know how our
Speaker 3: sanity or our marriage survived.
Speaker 1: Oh okay, that is way more intense than what I did.
Speaker 1: That's incredible. Yes, I am also amazed that your sanity
Speaker 1: and marriage survived you too. It must be a very
Speaker 1: strong family.
Speaker 3: I think you should be less impressed and more doubting
Speaker 3: our judgment. But anyway, Welcome to the podcast Daniel and
Speaker 3: Jorge Explain the Universe, a production of iHeartRadio in which
Speaker 3: we try to move you to a place of deep
Speaker 3: understanding about the universe. We want to transport your brain
Speaker 3: to that mysterious location where everything makes sense. We're it
Speaker 3: all clicked together in your mind to give you a
Speaker 3: harmonious understanding of the deep knee of the universe, at
Speaker 3: least as far as we understand it.
Speaker 1: Right, or to give you a headache wondering wondering how
Speaker 1: this all works.
Speaker 3: Sometimes no pain, no gain, right, Kelly. That doesn't just
Speaker 3: apply to lifting weights. It also applies to understanding the universe.
Speaker 1: Yeah no. And there's a lot of pain in physics.
Speaker 3: And we want to help you with that pain. So
Speaker 3: if you are thinking about things and they don't quite
Speaker 3: click together in your mind, or if you have a
Speaker 3: physics question and you've tried googling it but haven't found
Speaker 3: any answers, we want to help you out. This is
Speaker 3: not just a one direction a lecture from us to you.
Speaker 3: We want this to be a conversation and we miss
Speaker 3: hearing from you, so please write to us two questions
Speaker 3: at Daniel iinhorge dot com. You'll always get an answer back.
Speaker 3: And on today's podcast, we're going to be doing just that,
Speaker 3: answering questions from a listener. So today on the podcast,
Speaker 3: we'll be answering listener questions. Bring Equinox edition. We thought
Speaker 3: it was time to come back and fill your ears
Speaker 3: with answers to physics questions.
Speaker 1: About the universe because missing you.
Speaker 3: And we hope you've been missing us. And today we
Speaker 3: have a really fun question about transportation or about moving,
Speaker 3: not just moving yourself, not just moving your house and family,
Speaker 3: but moving the entire solar system. So here's a great
Speaker 3: question from John in Kansas.
Speaker 2: Hello, Daniel, this is John and I listened to your
Speaker 2: show from south central Kansas near the Oklahoma border, and
Speaker 2: I love it. Anyway, my question is I've heard you
Speaker 2: discussed many times that occasionally stars get ejected from their systems,
Speaker 2: perhaps due to the pull of a passing star, and
Speaker 2: I remember you once even speculated that we ourselves may
Speaker 2: have started out as a binary system and our son's
Speaker 2: own twin brother got ejected ago. But my question is
Speaker 2: this Suppose this did happen and our Sun did get
Speaker 2: flung out of our galaxy. Would it be violently ripped
Speaker 2: away from its own planets? Or would the event be
Speaker 2: so gradual that we wouldn't even notice it? And if
Speaker 2: that happened, would be be towed with it along with
Speaker 2: the other planets, asteroids, the asteroid belt, the Kuiper Belt,
Speaker 2: the Oort Cloud, and all of the celestial bodies, all
Speaker 2: remaining nicely tucked away in their own orbits as we
Speaker 2: follow the Sun into oblivion. Thank you for answering.
Speaker 1: Oh fantastic. Another question that inspires existential dread what would
Speaker 1: happen if the Sun would would it rip apart our
Speaker 1: solar system? Or would our planets go with it? And anyway,
Speaker 1: it's okay, I don't need to sleep, so let's go
Speaker 1: ahead and dig right in, Daniel, how stable is our
Speaker 1: solar system?
Speaker 3: Yeah, this is a really fun question thinking about what
Speaker 3: might happen if our Sun got ejected from the galaxy.
Speaker 3: And you're right. The first part of the question is understanding,
Speaker 3: like how well are we latched onto the Sun? If
Speaker 3: the Sun gets thrown out somewhere, how likely are we
Speaker 3: to go along? For the ride, and this depends on
Speaker 3: the stability of the whole Sun Earth system, right, So
Speaker 3: good news is that mostly things are stable, Like the
Speaker 3: Earth is orbiting the Sun, and even if the Earth
Speaker 3: got like a little bit of a push, it would
Speaker 3: slide right back into its orbit. That's what we usually
Speaker 3: mean by stable. You know, if you have, for example,
Speaker 3: like a ball inside a cup and you push it
Speaker 3: a little bit, it's gonna roll right back down to
Speaker 3: the bottom. Whereas if you have like the ball sitting
Speaker 3: on top of another ball, or on top of a rock,
Speaker 3: or on top of a hill or something, and you
Speaker 3: give it a push, it's gonna roll away and not
Speaker 3: come back. That's an unstable configuration. So we call the
Speaker 3: Earth's orbit stable because it's pretty resistant to these kinds
Speaker 3: of pushes.
Speaker 1: So even though it's resistant to a kind of push,
Speaker 1: anything that could push Earth away from the Sun would
Speaker 1: have to be catastrophic.
Speaker 2: Right.
Speaker 3: Well, there's lots of little pushes that the Earth could survive,
Speaker 3: and the Earth is getting tugged on and pushed in
Speaker 3: lots of different ways. So the Earth's orbit would be
Speaker 3: perfectly stable if it was just the Earth and the
Speaker 3: Sun in totally empty space with nothing happening in classical mechanics,
Speaker 3: that could go forever. But you know, the situation is
Speaker 3: a little bit more complex. For example, like the Sun
Speaker 3: is pushing on the Earth. It's not just pulling on it.
Speaker 3: The radiation from the Sun, the wind, and the photons
Speaker 3: are actually applying a momentum pushing the Earth away from
Speaker 3: the Sun. But the Earth's orbit is stable enough that
Speaker 3: it can overcome that. It's like accommodates that.
Speaker 1: So I've read proposals. I don't know how serious any
Speaker 1: of them were, but like to deal with climate change
Speaker 1: by like putting like a big screen out that would
Speaker 1: block some of the photons from hitting the Earth. If
Speaker 1: you blocked enough photons, could the Earth move closer to
Speaker 1: the Sun because we're not getting pushed back and like
Speaker 1: not much. I know you said it's a small effect,
Speaker 1: but when we move like a couple feet closer if
Speaker 1: you blocked enough photons, well.
Speaker 3: That depends a little bit on where you put that shield.
Speaker 3: Like if it's connected to the Earth, then it's basically
Speaker 3: just part of the Earth and it doesn't change how
Speaker 3: we're getting pushed. If it's somehow floating separated from the
Speaker 3: Earth and absorbing that momentum itself by like firing rockets
Speaker 3: or something. Then yeah, that would relieve a little bit
Speaker 3: of the pressure on the Earth. But this is really
Speaker 3: a tiny, tiny effect on the Earth's orbit. Much more
Speaker 3: substantial are tugs by like Jupiter and Saturn, because the
Speaker 3: Solar System is not just the Earth and the Sun.
Speaker 3: There are other big players out there, and Jupiter is
Speaker 3: much more massive than the Earth. So if you want
Speaker 3: to model the Earth's orbit and its stability really accurately,
Speaker 3: you got to think about what the big boys do
Speaker 3: as they move around the Solar System, and they're constantly
Speaker 3: tugging on the Earth giving it little nudges here and there,
Speaker 3: and that the Earth is pretty stable towards like the
Speaker 3: Earth can tolerate a push from Jupiter, push from Saturn
Speaker 3: and then slide right back into its orbit.
Speaker 1: Okay, And so does the answer to this question then
Speaker 1: depend on how close does Jupiter need to be to
Speaker 1: Earth when this happens.
Speaker 3: Yeah, so Jupiter and Saturn are basically irrelevant to this question,
Speaker 3: is the good news. The bad news is that there
Speaker 3: are other things that can also perturb the Earth's orbit,
Speaker 3: And the biggest, number one thing to worry about are
Speaker 3: other stars because where the Sun is in the galaxy
Speaker 3: is not fixed relative to the other stars. Like all
Speaker 3: the stars in the galaxy are rotating around the center
Speaker 3: of the galaxy, but they're not all rotating together, so
Speaker 3: our distance to other stars changes as time goes on.
Speaker 3: So even if we don't get ejected from the galaxy,
Speaker 3: there is a danger that sometime in the future, another
Speaker 3: star will come close to us and that could perturb
Speaker 3: the Earth's orbit. It could provide enough of a gravitational
Speaker 3: nudge to knock us out of our orbit, or even
Speaker 3: a doesn't, it could disturb all the frozen objects out
Speaker 3: in the deep Solar System and rain down a bunch
Speaker 3: of comments on us, both of which would be bad.
Speaker 3: I know that doesn't sound like a lot of fun,
Speaker 3: but it might actually be spectacular. Well, dig into what
Speaker 3: it means just after this short break. Okay, we're back,
Speaker 3: and we're talking about what might happen if our star
Speaker 3: is ejected from the galaxy and whether it's likely.
Speaker 1: Do we think this could happen? Probably not in our lifetimes.
Speaker 3: Right, probably not in our lifetimes. But we do understand
Speaker 3: the Sun's path through the galaxy pretty well. It's actually
Speaker 3: pretty awesome to think about it, because you imagine space,
Speaker 3: you probably think about the Sun primarily as the center
Speaker 3: of our galactic coordinates, right, everything else is relative to that.
Speaker 3: But you know, the Sun is in motion relative to
Speaker 3: this center of the galaxy. And this is sort of
Speaker 3: a big conceptual step because remember that all motion is relative.
Speaker 3: So some people say, oh, you know, the Sun is
Speaker 3: moving through space, but everything is moving through space, it's
Speaker 3: just relative to what. So when you talk about like
Speaker 3: the earth velocity is relative to the Sun, you talk
Speaker 3: about the Sun's velocity is relative to the center of
Speaker 3: the galaxy. And the Sun, like everything else, is swirling
Speaker 3: around the center, and it takes about two hundred and
Speaker 3: fifty million years to orbit. It's like a really huge
Speaker 3: amount of time.
Speaker 1: But that's happened a number of times since the planet started,
Speaker 1: like many times since the planet started, So it's moving.
Speaker 1: I don't know, that's kind of impressive.
Speaker 3: I think, yeah, Well, the Earth is like four and
Speaker 3: a half billion years old, which means in terms of
Speaker 3: galactic spins, right, how long it takes the Milky Way
Speaker 3: to cycle, which in many ways is like a very
Speaker 3: natural unit. You could call it like a galactic year.
Speaker 3: Instead of measuring time in terms of how many times
Speaker 3: the Earth goes around the Sun, measure in terms of
Speaker 3: how many times the Sun goes around the galaxy. And
Speaker 3: so that makes Earth like twenty galactic years old. Earth
Speaker 3: is just grown up. It's like entering its adult phase.
Speaker 1: It can't even drink yet.
Speaker 3: That's right. So, yeah, the Earth is kind of young
Speaker 3: and sprightly. Right, it's still probably the fittest it's ever
Speaker 3: gonna be.
Speaker 1: Oh oh man, wait till you hit your thirties.
Speaker 2: Earth.
Speaker 1: It's all downhill after that.
Speaker 3: But the other thing is that the Sun doesn't just
Speaker 3: orbit around the center of the galaxy. It also wiggles.
Speaker 3: It's above the galactic plane sometimes, and then it zooms
Speaker 3: down through the galactic plane and then past it, and
Speaker 3: then the gravity of the galactic plane pulls it back.
Speaker 3: So it's like oscillating up and down above the galactic plane.
Speaker 3: So it's not just going in a circle around the
Speaker 3: center of the galaxy. It's more like a zigzag up
Speaker 3: and down as it circles around.
Speaker 1: All right, So now I'm picturing my son when we
Speaker 1: walk around the track together. He's like jumping up and
Speaker 1: down the whole time that we're doing. Yes, So this
Speaker 1: young Earth is going up and down while it's making
Speaker 1: its laps.
Speaker 3: Exactly, and that cycle takes about thirty million years. So
Speaker 3: as we go around the galaxy, we go up and
Speaker 3: down like eightish times every galactic year, and that's different
Speaker 3: for different stars. And so now imagine this whole galaxy.
Speaker 3: It's a chaotic swarm of all these stars moving closer
Speaker 3: and farther away from each other. There's a real possibility,
Speaker 3: of course, over millions and billions of years, that we
Speaker 3: come pretty close to another star. We've actually predicted that
Speaker 3: there is going to be a close approach by the
Speaker 3: star Glease seven to ten in a few million years.
Speaker 1: Oh that's how close, Daniel, How close?
Speaker 3: It's not going to be that close. I mean it
Speaker 3: depends on the units. In one point three million years,
Speaker 3: it's going to pass within zero point one seven light years,
Speaker 3: so like a seventh of a light year. That doesn't
Speaker 3: sound very far, but it's like a twenty fifth of
Speaker 3: the distance to the nearest star. So it's going to
Speaker 3: mean that the closest star to Earth is a lot
Speaker 3: closer than it is currently, but it's still pretty far away.
Speaker 3: It's like ten thousand astronomical units ten thousand times the
Speaker 3: distance from the Sun to the Earth. So it's not
Speaker 3: like gonna appear in our sky as bright as the
Speaker 3: Sun or anything. It's just going to be something moving
Speaker 3: in the night sky.
Speaker 1: Will it still be brighter than the other stars.
Speaker 3: It'll be brighter than the other stars. Yeah, it'll be
Speaker 3: very visible. But you know, in one point three million years,
Speaker 3: so your super great grandkids have this to look forward to.
Speaker 1: Yeah, yeah, I guess I'm gonna miss it. Oh well,
Speaker 1: this is important.
Speaker 3: To answer John's question because this is how stars get
Speaker 3: thrown out of the galaxy. Like just left alone. The
Speaker 3: Sun's orbit is pretty stable, it's just going to keep
Speaker 3: going around the center of the galaxy. But the same
Speaker 3: way that, like Earth is nudged by Jupiter and Saturn,
Speaker 3: the Sun can be nudged by other stars, and so
Speaker 3: a close approach with another star could end up doing
Speaker 3: a gravitational slingshot on our star, so it gets sent
Speaker 3: out of the galaxy.
Speaker 1: Obviously, if you live on Earth, whether Earth stays put
Speaker 1: or not, you're dead without the Sun and the light
Speaker 1: that it provides. But what kind of factors would determine
Speaker 1: if Earth stays put or not? Would it depend on
Speaker 1: how fast the Sun moves, or if the Sun came
Speaker 1: close to us on its way out, Yeah, what would
Speaker 1: we have to worry about.
Speaker 3: It's basically all proximity. Like if that star comes by
Speaker 3: and it's not super close, and it just like gives
Speaker 3: our Sun a new direction. Even if that direction eventually
Speaker 3: takes us out of the Milky Way, we'll be fine
Speaker 3: because if it's gradual, then the Earth's orbit can respond
Speaker 3: to these things, respond to little nudges. It's just like
Speaker 3: another Jupiter effect or another Saturn effect, and it'll follow
Speaker 3: the Sun as it takes its new trajectory. But if
Speaker 3: it's dramatic enough so that like the Sun gets accelerated
Speaker 3: significantly and new direction comes on quickly, then the Earth's
Speaker 3: orbit can't adapt. Because the Earth's orbit is pretty stable,
Speaker 3: but it's not infinitely stable. If you gave it a
Speaker 3: really big kick relative to the Sun, or equivalently, you
Speaker 3: give the Sun a really big kick, the two are
Speaker 3: the same, then the Earth will not be able to
Speaker 3: follow the Sun. And so if for example, another star
Speaker 3: comes very close to our Solar system, so the Sun
Speaker 3: feels a very strong gravitational pull, the kind of thing
Speaker 3: that can and does kick stars out of our galaxy,
Speaker 3: then the Earth has almost no chance of following. Oh Man.
Speaker 1: So, in the scenario where something is big enough to
Speaker 1: move the Sun, but the Sun is moving slowly, when
Speaker 1: the Earth reached the part of its path around the
Speaker 1: Sun where it was between the Sun and this other
Speaker 1: sun that was big enough and close enough to move
Speaker 1: the Sun, would that push Earth towards the other gigantic
Speaker 1: sun object then we would go back. And so would
Speaker 1: that be like a wobble in our orbit or would
Speaker 1: we get pulled out to that other Sun.
Speaker 3: Yeah, well, you're talking about a three body problem, and
Speaker 3: this is known to be very chaotic.
Speaker 2: Right.
Speaker 3: If you have two stars and a planet, then it's
Speaker 3: very difficult for that planet to find a stable orbit.
Speaker 3: And if that system is changing because one star is
Speaker 3: like flying by the other one, then it's essentially impossible.
Speaker 3: So the details depend on exactly the angle and exactly
Speaker 3: the velocity. That's what we mean by chaos and physics.
Speaker 3: We mean that a very small change in the situation
Speaker 3: can result in a very big change in the outcome.
Speaker 3: Like if you're playing pool and you hit one ball
Speaker 3: against the other, a very small change in how you're
Speaker 3: hitting the cue ball can mean you win the game
Speaker 3: or lose the game. Right, So in this scenario, a
Speaker 3: very small change in the direction of that star, or
Speaker 3: the mass of that star, or the velocity of that
Speaker 3: star could result in a completely different outcome. Some like
Speaker 3: you and vision like, oh, we wobble towards the star
Speaker 3: and then we wabble away from it, and others where
Speaker 3: we just got we just get ejected into deep space
Speaker 3: on our own. So I think if the star comes
Speaker 3: close enough to eject our Sun from the Milky Way,
Speaker 3: it's going to also come close enough to perturb our
Speaker 3: orbit around that Sun. It's going to be very unlikely
Speaker 3: we are along for the ride. But you know, there's
Speaker 3: a possible bright outcome there.
Speaker 1: What's that.
Speaker 3: It might be that this new star comes along, messes
Speaker 3: up our happy orbit around the Sun, ejects the Sun
Speaker 3: from the Milky Way, and then steals the Earth. It
Speaker 3: might be that we get a new Sun.
Speaker 1: But like, that's got to be an extinction level event.
Speaker 1: Even if it works out like a you know, on
Speaker 1: par with taking out the dinosaurs, that couldn't work smooth.
Speaker 1: That wouldn't be good for us. I don't want my
Speaker 1: kids to experience that.
Speaker 3: You know I'm reaching for a sliver of positivity here Elly,
Speaker 3: in very dark times. I need you to work with me,
Speaker 3: work with me.
Speaker 2: You know.
Speaker 1: A friend asked me the other day why I'm so
Speaker 1: relentlessly depressing. So I think you just you picked the
Speaker 1: wrong person to have on your show. I'm sorry.
Speaker 3: Well, you know, if we knew about it far enough
Speaker 3: in advance, and we could build bunkers to survive the
Speaker 3: intervening period where things very bright or very cold, the
Speaker 3: seasons are totally wacko. Then there's a situation where in
Speaker 3: the far future the Earth is in the habitable zone
Speaker 3: of another star, which I think would be an amazing
Speaker 3: premise for a science fiction novel. And I haven't read
Speaker 3: it yet, and I want somebody out there to put
Speaker 3: pen to paper and write me that story and make
Speaker 3: it happy ending for Kelly.
Speaker 1: And that's your billion dollar idea. There we go. We
Speaker 1: just keep throwing them out there.
Speaker 3: That's basically the next Harry Potter, I'm sure. Yeah, Harry
Speaker 3: Potter and the Adventure of the Alternate Earth.
Speaker 1: There you go.
Speaker 3: All right, Well, thank you very much, John for thinking
Speaker 3: about the nature of the universe and how it affects
Speaker 3: life here on Earth and how our future might be
Speaker 3: impacted by visitations from other stars. I hope we answered
Speaker 3: your question, and I hope we inspired everybody out there
Speaker 3: to think about their own questions about the universe. What
Speaker 3: doesn't make sense to you? What physics scenario are you
Speaker 3: wondering about that you can't find the answer to. Please
Speaker 3: write to us. We want to hear from you. Send
Speaker 3: us a message to questions at Danielandjorge dot com. And
Speaker 3: thanks very much Kelly for bringing your relentless optimism to
Speaker 3: the podcast.
Speaker 1: Oh you're welcome. Yeah. I hope we get more questions
Speaker 1: so that our list of reasons to feel existential dread
Speaker 1: can grow and grow and grow and grow. But yeah,
Speaker 1: thanks for having me on the show. It's always a
Speaker 1: good time.
Speaker 3: Wonderful to be in your ear again everyone, and hope
Speaker 3: you hear from us soon. Thanks for tuning in for
Speaker 3: more science and curiosity. Come find us on social media
Speaker 3: where we answer questions and post videos. We're on Twitter, Discord, Insta,
Speaker 3: and now TikTok. Thanks for listening and remember that Daniel
Speaker 3: and Jorge Explain the Universe is a production of iHeartRadio.
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