March 18, 2025 • 20 mins
Daniel and Kelly answer a question about whether the Earth might survive the Sun's ejection from the galaxy.
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Speaker 1 (00:07):
Daniel, it's been like forever. How are things good?
Speaker 2 (00:11):
Good?
Speaker 3 (00:12):
You know, same stuff in my world? Do big updates.
Speaker 1 (00:14):
So you guys didn't like move across the planet again?
Speaker 3 (00:18):
Oh no, we are done with those trans continental moves.
I hate moving.
Speaker 1 (00:23):
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?
Speaker 3 (00:43):
Then I think that's a billion dollar idea. You shouldn't
be sharing it on the podcast. You should be starting
that company.
Speaker 1 (00:50):
Delete delete now. I have no business acumen, so somebody
else can go ahead and make a billion dollars on that.
You're welcome.
Speaker 2 (01:14):
Hi.
Speaker 3 (01:14):
I'm Daniel, I'm a particle physicist, a professor at UC Irvine,
and I've never started a billion dollar company.
Speaker 1 (01:21):
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.
Speaker 3 (01:39):
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.
Speaker 1 (01:50):
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.
Speaker 3 (02:07):
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.
Speaker 1 (02:22):
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.
Speaker 3 (02:34):
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
(02:55):
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.
Speaker 1 (03:04):
Right, or to give you a headache wondering wondering how
this all works.
Speaker 3 (03:10):
Sometimes no pain, no gain, right, Kelly. That doesn't just
apply to lifting weights. It also applies to understanding the universe.
Speaker 1 (03:16):
Yeah no. And there's a lot of pain in physics.
Speaker 3 (03:20):
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
(03:41):
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
(04:02):
it was time to come back and fill your ears
with answers to physics questions.
Speaker 1 (04:07):
About the universe because missing you.
Speaker 3 (04:10):
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.
Speaker 2 (04:27):
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
(04:49):
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
(05:10):
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,
(05:31):
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.
Speaker 1 (05:47):
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?
Speaker 3 (06:07):
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
(06:28):
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
(06:50):
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.
Speaker 1 (07:04):
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.
Speaker 2 (07:12):
Right.
Speaker 3 (07:13):
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.
(07:35):
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.
Speaker 1 (07:47):
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
(08:07):
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.
Speaker 3 (08:14):
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
(08:38):
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,
(08:59):
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.
Speaker 1 (09:08):
Okay, And so does the answer to this question then
depend on how close does Jupiter need to be to
Earth when this happens.
Speaker 3 (09:16):
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
(09:37):
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
(09:59):
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,
(10:28):
and we're talking about what might happen if our star
is ejected from the galaxy and whether it's likely.
Speaker 1 (10:35):
Do we think this could happen? Probably not in our lifetimes.
Speaker 3 (10:38):
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
(10:59):
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
(11:20):
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.
Speaker 1 (11:31):
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.
Speaker 3 (11:39):
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
(12:00):
so that makes Earth like twenty galactic years old. Earth
is just grown up. It's like entering its adult phase.
Speaker 1 (12:07):
It can't even drink yet.
Speaker 3 (12:11):
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.
Speaker 1 (12:17):
Oh oh man, wait till you hit your thirties.
Speaker 2 (12:19):
Earth.
Speaker 1 (12:20):
It's all downhill after that.
Speaker 3 (12:23):
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
(12:46):
and down as it circles around.
Speaker 1 (12:48):
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.
Speaker 3 (13:00):
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,
(13:20):
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.
Speaker 1 (13:32):
Oh that's how close, Daniel, How close?
Speaker 3 (13:37):
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
(13:57):
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.
Speaker 1 (14:13):
Will it still be brighter than the other stars.
Speaker 3 (14:16):
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.
Speaker 1 (14:25):
Yeah, yeah, I guess I'm gonna miss it. Oh well,
this is important.
Speaker 3 (14:29):
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
(14:52):
out of the galaxy.
Speaker 1 (14:54):
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.
Speaker 3 (15:14):
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
(15:35):
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
(15:56):
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.
Speaker 1 (16:15):
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
(16:35):
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.
Speaker 3 (16:43):
Yeah, well, you're talking about a three body problem, and
this is known to be very chaotic.
Speaker 2 (16:48):
Right.
Speaker 3 (16:48):
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
(17:09):
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
(17:31):
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.
Speaker 1 (17:52):
What's that.
Speaker 3 (17:54):
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.
Speaker 1 (18:03):
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.
Speaker 3 (18:18):
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.
Speaker 2 (18:25):
You know.
Speaker 1 (18:25):
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.
Speaker 3 (18:35):
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
(18:57):
pen to paper and write me that story and make
it happy ending for Kelly.
Speaker 1 (19:01):
And that's your billion dollar idea. There we go. We
just keep throwing them out there.
Speaker 3 (19:09):
That's basically the next Harry Potter, I'm sure. Yeah, Harry
Potter and the Adventure of the Alternate Earth.
Speaker 1 (19:17):
There you go.
Speaker 3 (19:19):
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
(19:41):
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.
Speaker 1 (19:52):
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.
Speaker 3 (20:03):
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
(20:25):
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.
Daniel, it's been like forever. How are things good?
Speaker 2 (00:11):
Good?
Speaker 3 (00:12):
You know, same stuff in my world? Do big updates.
Speaker 1 (00:14):
So you guys didn't like move across the planet again?
Speaker 3 (00:18):
Oh no, we are done with those trans continental moves.
I hate moving.
Speaker 1 (00:23):
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?
Speaker 3 (00:43):
Then I think that's a billion dollar idea. You shouldn't
be sharing it on the podcast. You should be starting
that company.
Speaker 1 (00:50):
Delete delete now. I have no business acumen, so somebody
else can go ahead and make a billion dollars on that.
You're welcome.
Speaker 2 (01:14):
Hi.
Speaker 3 (01:14):
I'm Daniel, I'm a particle physicist, a professor at UC Irvine,
and I've never started a billion dollar company.
Speaker 1 (01:21):
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.
Speaker 3 (01:39):
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.
Speaker 1 (01:50):
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.
Speaker 3 (02:07):
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.
Speaker 1 (02:22):
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.
Speaker 3 (02:34):
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
(02:55):
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.
Speaker 1 (03:04):
Right, or to give you a headache wondering wondering how
this all works.
Speaker 3 (03:10):
Sometimes no pain, no gain, right, Kelly. That doesn't just
apply to lifting weights. It also applies to understanding the universe.
Speaker 1 (03:16):
Yeah no. And there's a lot of pain in physics.
Speaker 3 (03:20):
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
(03:41):
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
(04:02):
it was time to come back and fill your ears
with answers to physics questions.
Speaker 1 (04:07):
About the universe because missing you.
Speaker 3 (04:10):
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.
Speaker 2 (04:27):
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
(04:49):
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
(05:10):
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,
(05:31):
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.
Speaker 1 (05:47):
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?
Speaker 3 (06:07):
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
(06:28):
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
(06:50):
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.
Speaker 1 (07:04):
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.
Speaker 2 (07:12):
Right.
Speaker 3 (07:13):
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.
(07:35):
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.
Speaker 1 (07:47):
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
(08:07):
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.
Speaker 3 (08:14):
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
(08:38):
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,
(08:59):
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.
Speaker 1 (09:08):
Okay, And so does the answer to this question then
depend on how close does Jupiter need to be to
Earth when this happens.
Speaker 3 (09:16):
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
(09:37):
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
(09:59):
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,
(10:28):
and we're talking about what might happen if our star
is ejected from the galaxy and whether it's likely.
Speaker 1 (10:35):
Do we think this could happen? Probably not in our lifetimes.
Speaker 3 (10:38):
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
(10:59):
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
(11:20):
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.
Speaker 1 (11:31):
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.
Speaker 3 (11:39):
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
(12:00):
so that makes Earth like twenty galactic years old. Earth
is just grown up. It's like entering its adult phase.
Speaker 1 (12:07):
It can't even drink yet.
Speaker 3 (12:11):
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.
Speaker 1 (12:17):
Oh oh man, wait till you hit your thirties.
Speaker 2 (12:19):
Earth.
Speaker 1 (12:20):
It's all downhill after that.
Speaker 3 (12:23):
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
(12:46):
and down as it circles around.
Speaker 1 (12:48):
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.
Speaker 3 (13:00):
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,
(13:20):
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.
Speaker 1 (13:32):
Oh that's how close, Daniel, How close?
Speaker 3 (13:37):
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
(13:57):
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.
Speaker 1 (14:13):
Will it still be brighter than the other stars.
Speaker 3 (14:16):
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.
Speaker 1 (14:25):
Yeah, yeah, I guess I'm gonna miss it. Oh well,
this is important.
Speaker 3 (14:29):
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
(14:52):
out of the galaxy.
Speaker 1 (14:54):
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.
Speaker 3 (15:14):
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
(15:35):
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
(15:56):
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.
Speaker 1 (16:15):
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
(16:35):
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.
Speaker 3 (16:43):
Yeah, well, you're talking about a three body problem, and
this is known to be very chaotic.
Speaker 2 (16:48):
Right.
Speaker 3 (16:48):
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
(17:09):
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
(17:31):
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.
Speaker 1 (17:52):
What's that.
Speaker 3 (17:54):
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.
Speaker 1 (18:03):
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.
Speaker 3 (18:18):
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.
Speaker 2 (18:25):
You know.
Speaker 1 (18:25):
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.
Speaker 3 (18:35):
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
(18:57):
pen to paper and write me that story and make
it happy ending for Kelly.
Speaker 1 (19:01):
And that's your billion dollar idea. There we go. We
just keep throwing them out there.
Speaker 3 (19:09):
That's basically the next Harry Potter, I'm sure. Yeah, Harry
Potter and the Adventure of the Alternate Earth.
Speaker 1 (19:17):
There you go.
Speaker 3 (19:19):
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
(19:41):
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.
Speaker 1 (19:52):
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.
Speaker 3 (20:03):
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
(20:25):
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.
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