How stable is the Earth's orbit?

Daniel and Jorge talk about whether we can expect the Earth to continue in its path forever, or if our days are numbered.

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Episode Transcript

Speaker 1 (00:08):
Hey, Daniel, did you see the reason launch at tempt
by SpaceX.

Speaker 2 (00:12):
Oh?

Speaker 3 (00:12):
Yeah, I did. That massive rocket with so many engines attached.
Really awesome to watch.

Speaker 4 (00:18):
Yeah, I hear.

Speaker 1 (00:18):
The fireworks were great. It really popped. But the whole
thing kind of has me worried a little bit.

Speaker 3 (00:23):
You worried the rocket's going to crash into your house?

Speaker 1 (00:26):
A little bit? I mean I live in my house.
That would be a problem. No, But I guess I'm
more worried about the effect it has on the Earth
than all those engines in the rocket also push on
the Earth.

Speaker 3 (00:37):
Yeah. I guess it's kind of like putting a rocket
engine on the Earth itself.

Speaker 1 (00:41):
A little bit, right, So we're letting elon Musk steer
our planet.

Speaker 4 (00:45):
I mean, you can't even steer Twitter.

Speaker 3 (00:48):
It would be pretty cool if a planet had a
steering wheel. I guess that'd be fun.

Speaker 1 (00:52):
I would probably fall asleep, so maybe I shouldn't be
driving the Earth.

Speaker 4 (00:57):
It probably flies into the sun.

Speaker 5 (01:14):
Hi.

Speaker 1 (01:14):
I'm Orham, a cartoonists and the creator of PhD comics.

Speaker 3 (01:17):
Hi I'm Daniel. I'm a particle physicist and a professor
at UC Irvine, and I don't want to fly into
the Sun.

Speaker 4 (01:24):
What do you want to do into the sun? Drive? Walk, fall, dive?

Speaker 3 (01:29):
I guess I want to look into the Sun. Of
all the verbs, I think that's the least destructive one.

Speaker 4 (01:35):
I like hearing about the Sun and feeling the Sun.

Speaker 2 (01:37):
I don't know.

Speaker 4 (01:38):
I don't know if I want to look at it.
It isn't that dangerous.

Speaker 3 (01:40):
I want us to build new scientific eyeballs that let
us peer into the Sun and understand the chaotic churning
inside of it.

Speaker 4 (01:47):
You want to peer into the Sun?

Speaker 3 (01:48):
Yeah, exactly, yes, I consider the Sun to be our
peer in the Solar system.

Speaker 4 (01:53):
I see. Are you saying you're like a sun god?

Speaker 3 (01:57):
No, I'm saying we're ever accused of breaking a law
of physic that I want a jury of our peers,
which I guess would include the Sun.

Speaker 1 (02:03):
M and who else? Who else do you consider your
peers in the cosmos?

Speaker 3 (02:08):
Jupiter is pretty good. Yeah, it carries a lot of weight.

Speaker 1 (02:12):
Yeah, he would be a massive help on the jury.
But anyways, Welcome to our podcast, Daniel and Jorge Explain
the Universe, a production of iHeart Radio.

Speaker 3 (02:20):
In which we try to thread the needle of understanding
the entire universe without pissing it off too much. We
try to pay attention to what's going on out there
in the universe, from the tiny little particles to the
very massive objects swirling around each other, to try to
deduce the laws that this universe follows as it moves
forward through time towards its eventual end, whatever that may be.

(02:40):
And we hope that before that end comes, we can
figure out how it all works.

Speaker 1 (02:44):
That's right, because it is a massively cool universe, fools,
amazing and incredible laws and mechanism that seem to make
the whole thing work like a giant clock, it seems,
going around and around, taking away till the end of time.

Speaker 3 (02:58):
A clock makes it seem like very organized and stable.
I see it more like a really complicated Rube Goldberg machine,
you know, like ball rolls down a wheel and hits
this lever which makes the cat jump, and then that
knocks something else over. Sometimes it feels like the mechanisms
on which our entire existence are based are very precarious.

Speaker 1 (03:17):
Like it knocks a ball, the ball rolls sound a
ramp and then outcomes humans, and out of those humans,
one of them bumps into another, and you and I
are born, and this podcast is born exactly.

Speaker 3 (03:30):
It seems like it could have gone a lot of
different ways, and in many of those ways we wouldn't
be here. So in some respects our existence here seems very,
very fortunate, and I wonder sometimes about the future of
our existence here. How long these special cozy conditions will continue.

Speaker 1 (03:47):
I know, I feel pretty inevitable. I feel like r
cham was meant to be.

Speaker 3 (03:51):
You feel like the whole project of the universe was
to bring you into existence?

Speaker 1 (03:56):
Why not at least my universe now. I don't know
if my kids feel the same way. Over my spouse.
I'm an unfortunate byproduct. Sometimes it seems.

Speaker 3 (04:05):
Well one of the joys of understanding the universe is
being able to predict its future, taking those laws of
physics that describe what we have seen and also applying
them to the future, and thinking what's going to happen,
what's likely to happen in the next one hundred years,
million years, or billion.

Speaker 1 (04:20):
Years, m or the next hour. I mean, I don't
know where this conversation is going.

Speaker 3 (04:24):
To be honest, the podcast does seem kind of unpredictable.
Doesn't seem to matter too much what I write any outline.

Speaker 1 (04:31):
Well, I think that's what happens when you put two
unstable people and try to create a stable system here.
But it is kind of an interesting question how precarious
our existence is and how likely it was that we
are here in this place talking about the universe. It
seems like the universe kind of could go either way
at any moment.

Speaker 3 (04:50):
Mm hmmm. And there's lots of ways that things could
go south for us. But on the podcast a few
times we've talked about one in particular, which is the
requirement that the Earth stay in orbit around the Sun
at just the right distance to keep water nice and
toasty on our surface but without bubbling it into steam
or dropping it into a deep freeze.

Speaker 1 (05:09):
Yeah, the Earth is and what's called the Goldilock zone
of our solar system, where it's not too hot and
not too cold, which makes it just right for life
to flourish on it and for vicious birds, animals, and
humans which I guess are also animals for them to
come about.

Speaker 3 (05:26):
So you might wonder how long this Goldilock situation can
continue before the bears come home and ask for their
porridge back, so to.

Speaker 1 (05:33):
Be On the podcast, we'll be asking the question, how
stable is the Earth's orbit? Never thought about the stability
of our planet's orbit. I guess it seems so predictable
and regular, right, I mean, nobody questions whether the sun
will rise in the morning every day.

Speaker 4 (05:53):
We just assume it is.

Speaker 3 (05:55):
It's one of these really fun questions where the answer
depends a lot on the time frame your imagining. Nobody
suspects that the Earth will fall out of its orbit
tomorrow or next year, or in one hundred years, and
on the kind of time scales the humans are used
to thinking about. The Solar System is kind of static.
We imagine it's looked the same way for one hundred years,
a thousand years, probably a million years. But when you

(06:16):
look on longer time scales, hundreds of millions of years
or billions of years, you see the Solar System is
actually quite chaotic. Planets have been lost, they've changed their orbit,
they've moved from the outer Solar System to the Inner
Solar System and back. All sorts of crazy stuff has happened.
So then you can ask, like, well, how long will
this phase of our Solar system last?

Speaker 1 (06:35):
Yeah, I guess the Solar system was just a giant
cloud of dust and gas at someone, right, and then
the Sun form, and then the planet's form. But even
after the planet's form, the Solar System kind of had
to find its groove kind of right, it's rhythm, it's orbits.
Things will crash into each other a lot before settling
into planets.

Speaker 3 (06:52):
Right, Yeah, that's exactly right. And you look at the
surface of anything in the Solar System, like the Moon,
and you'll see lots of evidence for collisions. Basically, anything
that's out there is getting smacked into all the time.
The Earth doesn't have a surface filled with craters because
we have an atmosphere that mostly burns those things up
before they hit the ground, but of course sometimes they don't.
Sixty five million years ago or so, something really big

(07:14):
hit the Earth, and billions of years before that, the
Moon was formed in an even more giant collision.

Speaker 4 (07:19):
We've been hit around a lot, and yet we're still here.

Speaker 3 (07:21):
And if we look at Jupiter, for example, there's a
lot of evidence that Jupiter and Saturn migrated to the
inner Solar System and then turned around and went back out,
returning to the depths of the outer Solar System. So
planetary orbits are not as fixed as you might imagine.

Speaker 1 (07:37):
At least some large time scales. As you were saying, well,
as usually, we were wondering how many people out there
had thought about this question, about the stability of our orbit,
about how steady the Solar system is. So, as usual,
Daniel went out there into the Internet to ask people
how stable is the Earth's orbit.

Speaker 3 (07:53):
I'm eternally grateful to everybody who answers these questions. If
you want to be part of this segment, please don't
be shy. Just write to me to question at Danielandjorge
dot com.

Speaker 1 (08:02):
So think about it for a second. How stable do
you think our orbit is? Here's what people had to say.

Speaker 6 (08:08):
So I would say that the Earth orbit is very
stable millions or maybe even billions of years. But perhaps
when the Sun turns into a ridge giant and expands,
maybe that will change things and throw that we're further
or closer.

Speaker 7 (08:22):
In Well, I think earth orbit is quite stable, but
we are slowly drifting away from the Sun because of
the Moon, and we might get hit by asteroids in
the future. But otherwise I think the Earth's orbit is stable.

Speaker 3 (08:34):
I don't think the Earth's orbit is stable forever.

Speaker 6 (08:38):
I think it looks pretty stable to us, because the
time scale of.

Speaker 3 (08:42):
The universe, of the Solar System is pretty long.

Speaker 6 (08:45):
I would say it's like a metastable state, and maybe
even an asteroid could kick the Earth out of orbit.

Speaker 3 (08:50):
It's more like a castle of cards. Remove one and
everything falls apart.

Speaker 4 (08:55):
It seems pretty stable to me.

Speaker 8 (08:57):
If Hummans had long enough to you will, so hopefully
it'll hang in there a bit longer.

Speaker 9 (09:05):
I know from your podcast about when stars collide that
any object that's accelerating gives off gravitational waves because of
its acceleration. So fundamentally the orbit is not stable, and
although it will take a really really long time, eventually

(09:28):
the Earth's orbit will fall into the Sun.

Speaker 8 (09:32):
I think the Earth's orbit is very stable. I have
heard about studies that talk about Jupiter moving around in
the ancient Solar System, and studies of sensitivity of mercury
and Venus to subtle perturbations. But I just think that
the Earth's orbit is very stable.

Speaker 1 (09:47):
I think it's stickaying just like you know might expect
it to, but you know, not going into the Sun
anytime soon.

Speaker 2 (09:54):
I think the Earth's orbit about the Sun is very stable,
at least over the timeframes that we're concerned with long
term millions or billions of years. There might be some
drift in its position relative to the Sun, just like
there's some drift of the Moon relative to the Earth

(10:14):
over time.

Speaker 5 (10:15):
I think it's bruey stable in a human time scale,
but on the long term I think that either gravity
or angular momentum will be more revalent.

Speaker 1 (10:27):
All right, it seems like most people think it's kind
of stable. Only a few dissenters.

Speaker 3 (10:31):
Not a lot of people worried about this out there,
although maybe they got more worried after they read this question.

Speaker 4 (10:37):
Maybe they should be more worried.

Speaker 1 (10:39):
That's what we're here for, to make people think about
all the different ways that the universe can kill them.

Speaker 3 (10:45):
Mmm. Maybe we should be selling Earth orbit insurance somehow.

Speaker 4 (10:48):
There you go.

Speaker 3 (10:49):
If the Earth plunges into the Sun, we will pay
you any arbitrary amount of money.

Speaker 1 (10:54):
A bazillion dollars exactly. Just give us a million dollars
a year.

Speaker 3 (10:59):
That's right, submit request of this po box.

Speaker 1 (11:01):
But yeah, it's kind of an interesting question. How stable
is the Earth's orbit? Because I guess we're going around
the Sun pretty steadily, right, is our orbit?

Speaker 7 (11:09):
Like?

Speaker 1 (11:10):
Do we always go through the same spot in the
Solar system or is our orbit kind of wobbling?

Speaker 3 (11:16):
Well, our orbit around the Sun is not perfectly circular, right,
It's an ellipse, and that ellipse can process a little bit,
which means if you imagine an ellipse or like a
football or anything oblong, then that orbit itself can rotate. Right,
the path of the ellipse itself can rotate.

Speaker 1 (11:31):
And is that the same for the whole Solar system?
Like there, everyone's orbits also kind of rotating.

Speaker 3 (11:36):
There are some changes in the eccentricity of the Earth's
orbit that's deviation from it being circular over like one
hundred thousand year timescale, and these things actually can affect
like the climate. These are called Milankovich cycles. We talked
about it once in the podcast about ice ages. But
that doesn't make the Earth's orbit stable or unstable. An
elliptical orbit can be stable over very very long time periods.

(12:00):
Whether or not your circular or elliptical doesn't change whether
or not your stable.

Speaker 1 (12:03):
M I see the orbit is changing a little bit.
But I think maybe what you mean by stable or
unstable is whether, like if you move the Earth a
little bit, is it gonna go back to its same orbit,
or is it gonna spin out of control and like
shoot out of the Solar System. That's kind of more
what you mean, right.

Speaker 3 (12:20):
Yeah, my stability. We mean will it return to its
current configuration if it's pushed a little bit, Say, for example,
you jump. Every time you jump, you are pushing on
the Earth. Right, You're using your leg muscles to push
yourself away from the Earth, but you're also pushing the
Earth away from you. And Newton's laws tell us, you know,
every force is an equal and opposite reaction, and so

(12:41):
you're moving away from the Earth and the Earth is
also moving away from you. Now, of course, because the
Earth has so much mass, your push doesn't really affect
it as much as it affects yourself. It's sort of
like when you fire a rifle. The bullet gets going
really really fast, but the rifle itself also has a
little bit of recoil, and so when you jump, the
Earth recoil a little bit against you. And so if

(13:02):
the Earth's orbit is stable, then a little push like
that won't like send it spiraling into the Sun, it
like drift back to its original orbit. If the Earth
is unstable, then it's more like a pencil balancing on
its tip. Any tiny little touch will knock it out
of its configuration and it won't come back. So stability
tells you about whether you come back to your current

(13:23):
orbit when you're given a little push.

Speaker 2 (13:25):
Hmmm.

Speaker 1 (13:26):
First of all, it's cool that every time I take
a step, basically I'm sort of moving to Earth a
little bit. Right, every step I take is earth shattering,
Earth moving.

Speaker 3 (13:35):
It sort of is, though. You return to the Earth
right and the Earth returns to you, So in the end,
the Earth's orbit isn't actually changed by that. To really
change the Earth's orbit, you need to like take a
rock and throw it into outer space and have it
escape from the Earth. So the rock and the Earth
are now like parting ways and going in opposite directions.

Speaker 1 (13:53):
M yeah, I guess that's what I meant. It's like,
if I jump, I'm going to fall back down onto
the Earth unless I jump super duper high. But I'm
not that fit, I guess. But if I jump, but
the Earth pulls me back and then it sort of
recovers right, Like, as it's pulling me back down into Earth,
it's also moving a little bit towards me exactly.

Speaker 3 (14:12):
You come back together, and so there's no effective change.
That's why I was talking about Elon Musk instead of
you and your ripped thighs jumping off the surface. You know,
if Elon Musk launches a rocket away from the Earth,
then it really is giving the Earth a push. Now,
if that rocket ends up in orbit, then it isn't
because it's still in the Earth's gravitational system. But if
he launches a rocket to Mars or a to deep

(14:32):
space or something like that, so it really leaves the
earth gravitational system, then it's given the Earth a push.
And if the Earth was in an unstable situation, like
a pencil balanced on its tip, then even a tiny
push would knock it out of orbit.

Speaker 1 (14:45):
Yeah, I guess maybe an analogy is that sort of
like tossing a coin or like rolling a coin. That's
a system that's kind of unstable, right, Like if you
tip the coin just a little bit to the right,
it's the whole coin is going to veer off to
the ride a lot. Or if you tip it a
little bit to the left's going to veer off to
the left a lot. That's what you mean by sort
of unstable kind of sitting on the edge of something.

Speaker 3 (15:06):
Mm hmm exactly. Or imagine you have a ball in
a glass, right, you shake the glass a little bit,
the ball moves from the bottom of the glass, but
it comes back to where it was. When it deviates
from its preferred location, there are forces to push it
back to where it was. Or if you have the
situation upside down, like ball balance on the top of
a hill, for example, if it's precariously balanced there and

(15:26):
you give it a push, then the forces are going
to pull it away from that configuration place. So another
way to think about stability is are there forces that
are restoring you back to your original location or are
there forces that are pushing you away. So in the
stable case, their forces restoring you to where you were,
and in the unstable case, their forces pushing you away.

Speaker 1 (15:45):
Right, I guess it's kind of what you mean by
basing a pencil, or like if you take a long
rod or stick and you try to bous it on
the palm of your hand, like there is a way
for you to like move your hand around a lot
and not have this stick fall over. But that's sort
of an unstable situation, Like if you deviate a little
bit from that path, then the stick will fall exactly.

Speaker 3 (16:05):
And in physics we call that equilibrium. Right, there is
a configuration for the stick to be balanced, for all
the forces to be equal, and for it to just
stay there, but it would be unstable. Like a tiny
fly lands on it pushes it in one direction. Now
the forces are going to keep it going in that
direction rather than pushing it back. Whereas if you have
a ball and a glass and a fly lands on
it and pushes it a tiny little bit up the glass,

(16:28):
the glass is going to return it back to the
equilibrium location. So you can have stable and unstable equilibrium.
And the difference really is whether you have forces pushing
you back towards the equilibrium or away.

Speaker 1 (16:38):
From it, right, And so that's what we're talking about
here for the Earth, I mean, we're going around the
Sun in a circle or a semicircle sort of a circle,
and it seems stable, but it could be an unstable orbit,
meaning like we're going around this path and we just
got lucky to get into this groove.

Speaker 4 (16:53):
But if we actually sort of step.

Speaker 1 (16:55):
Away from the groove or fall a little bit to
the one side, then maybe it'll take us into a
completely different orbit or even away from the Solar System
or into the Sun.

Speaker 3 (17:03):
I guess yeah, And you might be worried like that
if you jump too high you're going to push the
Earth out of orbit, because if you imagine that the
Earth like DV it's a little bit towards the Sun,
gravity gets stronger and it pulls on it harder. So
you might worry that, like if you jump on the
wrong side of the Earth, you could actually push the
Earth into the Sun like a fly toppling that balanced
pole on your hand.

Speaker 1 (17:24):
Although I guess it would depend on which way you jump,
like you just said, like if I jump in the direct,
like if I jump off of the North pole, maybe
I'll just move the orbit up and down a little bit.

Speaker 3 (17:33):
Right, Yeah, exactly.

Speaker 1 (17:36):
Or if I jump sort of like trailing the Earth
in the direction where a bit behind the Earth, I
guess then I will give it a little boost. Or
if I jump in the front, I'll slow down to
Earth a little bit mm hm.

Speaker 3 (17:48):
Or if you have a friend on the other side
of the Earth and you time your jumps together, then
it doesn't matter, right, So really this question is about
can you do exercise whenever you like, or do you
need to coordinate it with the rest of humanity.

Speaker 4 (17:58):
That's right?

Speaker 1 (17:59):
Or do we have any friends? All right, So that's
what stability means for an orbit and for our planet.
And now let's get into whether or not it is
a stable orbit or if it's a precariously balanced orbit
and we are just here at a sheer luck. But
first let's take a quick break.

Speaker 4 (18:29):
All right.

Speaker 1 (18:29):
We're asking the question how stable is the Earth's orbit?
And we talk about how we are in orbit around
the Sun. Right, the Earth is being pulled by gravity
towards the Sun, but we have a certain velocity which
makes the whole planet kind of go around in a circle.

Speaker 3 (18:44):
Right, Yeah, that's right. We're moving in roughly circles essentially
in the lips. But we'll talk about the difference there
in a minute. And the question is, like, is the
orbit stable If we deviate from this situation a tiny
little bit, are we going to spiral into the Sun
or drift out into deep space?

Speaker 1 (18:59):
Which makes you worry, not just for like everyone jumping
at the same time, is that going to knock the
Earth out of its orbit? But if something else comes
out from space and hits us, right.

Speaker 3 (19:08):
Yeah, exactly, because we are hit all the time on
asteroids and meteors. Right, every time you see a meteor shower,
those are objects from other places in the Solar System
smashing into the Earth's atmosphere. And a minute ago we
talked about it in terms of forces. Are there forces
restoring you back to your orbit or are there forces
pulling you away from your equilibrium? And in this situation,

(19:28):
the only relevant force is gravity, right, gravity pulls us
towards the Sun. There's no electromagnetic force, there's no weak force,
there's no strong force. It's really just gravity here. And
so from that simple perspective, you might think, hm, the
only force is pushing us inwards. So if we got
hit like from just the right angle, like an asteroid
falling in from the outer Solar System and pushing us

(19:49):
towards the Sun, it might make you worried because the
force of gravity would get stronger as you get closer
and then pull you harder, plummeting the Earth into the Sun.
But it's a little bit more complicated.

Speaker 1 (19:59):
And also made me think, like, if an asteroid falls
to Earth and it gets burned up in the atmosphere,
does it actually pushes or does it just get converted
into fire and smoke and light.

Speaker 3 (20:11):
It definitely pushes us. It doesn't matter if it gets
burned up or not. It's sort of like a bullet
entering your body, right, It's still going to push you back,
even if it doesn't leave your body or if it
gets shredded inside you. It doesn't really matter whether it
turns into heat or not. You absorb the momentum.

Speaker 1 (20:25):
Of that object, doesn't Some of the energy of an
asteroid also like leave maybe as light.

Speaker 3 (20:29):
Yeah, a little bit, although that actually might have a
bigger impact because that's more like the asteroid bouncing off
of the Earth, which would be a larger momentum transfer.

Speaker 1 (20:38):
Or doesn't some of it gets transferred into heat, like
it heats up the Earth, But that doesn't necessarily push
the Earth, does it.

Speaker 3 (20:43):
If the Earth totally absorbs it, then it's going to
absorb all of its momentum. If it bounces off the atmosphere,
then it's going to get twice its momentum because it's
changing direction entirely. The way for it to actually minimally
affect the Earth would be like passed through the Earth
out the other side. To maintain its So if it
like grazed the atmosphere somehow, then it wouldn't affect the

(21:04):
Earth as much.

Speaker 1 (21:05):
All right, Well, let's get into the stability of our orbit.
Maybe step us through the basics, like what makes an
orbit and what would make it stable or unstable?

Speaker 3 (21:13):
Yeah, so there's only gravity at work here, which is
pulling us towards the Sun. And the first you might wonder, like,
how do you get equilibrium at all? How is it
possible to have an orbit where your radius is basically constant? Again,
just thinking about it in terms of circular orbits for now,
how is that even possible if all you have is
a force towards the center. Well, it's true you only
have one force, but it's a little bit more complicated

(21:33):
than that. There's another apparent force because we're talking about
circular motion, which is not inertial frames. Like there's an
acceleration here, then there's an effective force that appears. It's
not a fundamental force like gravity or electromagnetism or whatever.
The effect of working in a rotating frame of reference
the way, for example, if you're on a merry go
round and it spins, you feel a force pushing you

(21:55):
towards the edge of the merry go round. It's not gravity,
it's not an electromagnetism. It's an effective force due to
the rotation.

Speaker 1 (22:02):
Right, It's not like a real force. It's more like
you feel like something is pushing you towards the middle
of the merry go round. But really it's just a
merry go around trying to make you go in a circle.

Speaker 3 (22:11):
Right, Yeah, exactly, And so there really are two effective
forces to consider there. There's gravity pulling you in and
then there's this centripetal force pushing you out. So there
is the possibility to have a balance there. That's where
the equilibrium comes from. When those two things balance, then
you have an orbit. When the force of gravity pulling
in and the centripetal force pushing out balance, then you
have circular motion. So that's why you can have an

(22:33):
equilibrium at all. But equilibrium doesn't necessarily mean it's stable.
You can have stable or unstable equilibria. Like the example
of a pole balancing in your hand. All the forces
are balanced there, but as soon as you deviate from it,
it falls over, whereas a ball and a cup is
it's stable equilibrium because the forces are restoring. So now
we understand why the Earth can be an equilibrium in

(22:53):
an orbit, but we still have to answer the question
of whether that's stable or unstable.

Speaker 1 (22:57):
Yeah, I guess I've always thought about it as like,
say I'm flying through space and I have a velocity
vector pointing in front of me. I'm going forward, and
the sun is too exactly to my right. Now, the
Sun is pulling me towards the right, but it's sort
of not affecting my velocity that I have going forward
because it's pulling me per pendicular to that velocity. So

(23:19):
it's going to kind of change the direction my velocity,
but it's not going to slow me down or speed
me up. And if you keep doing that, it traces
out a circle.

Speaker 3 (23:27):
Right, Yeah, that's right. There's a couple of things going
on there. You have the constant total velocity, right, your
overall velocity, the overall magnitude of your velocity doesn't change,
but the direction of it does, and that confuses people sometimes.
That still counts as acceleration because you're changing like the
different components of your velocity. So moving in a circle,
You're right, it doesn't change your overall velocity. That can

(23:49):
be constant, but the direction of the velocity changes and
that requires acceleration. And that's what the force of gravity
is doing. It's changing the direction of your velocity, not
the overall value, right.

Speaker 1 (24:00):
And I think you're saying that an orbit is when
that's perfectly balanced, like the force of gravity pushing you
towards the Sun. But then also you have enough velocity
to kind of resist that motion. That's when you get
an orbit, which is a circular kind of path around
the Sun. But there are I mean, there are many
other paths, right, Like, if I'm near a big object
like the Sun, I don't have to fall into an orbit, right,
I could just, for example, fall straight into the Sun

(24:22):
or spiral into the Sun.

Speaker 3 (24:24):
Right, mm hmm exactly. There's also parabolic trajectories and hyperbolic trajectories, right.
Things that fall in from the outer Solar system can
get sling shotted by the Sun and then leave the
Solar System. So there's lots of different trajectories around the Sun.
This is sort of a very special arrangement. You have
the right direction and the right velocity at the right radius,
then everything settles in and you can just keep doing it.

Speaker 1 (24:45):
Right, and it kind of seems lucky that we are
stuck in an orbit that does go around in a circle.
But that's because that's kind of how what survived the
chaos of the Solar system, right, Like, the Solar system
probably had a bunch of rocks flying all over the place,
and over the millions of years, maybe billions of years,
anything that wasn't in an orbit basically fell into the
Sun or got thrown out, and so anything that remains

(25:08):
after all that time, it should be in an orbit.

Speaker 3 (25:10):
Right, Yeah, that's right. We only see the things that
didn't fall into the sun, and so we see the
bits that have the right radius and velocity match. Right,
at a given radius, you need a certain velocity to
have that orbit work. Or so in another way, if
you have a certain velocity, you have to be at
a specific radius, so you have to have those pair match.
You can't just have an arbitrary velocity and an arbitrary

(25:31):
radius and expect to be in an orbit for a
given radius. You have to have a very specific velocity
to be in an orbit. But that seems like almost impossible, right.
It seems like, well, if your velocity has to be
exactly some number, then how did anything end up in orbit,
because what are the chances that two like real valued
numbers exactly match.

Speaker 1 (25:49):
Each other, right, Like, maybe I wonder if there could
have been a planet early in our Solar system's history
that there were, you know, flowing around the Sun and
they're like, oh, we're in an orbit. This is pretty cool.
But it turns out they weren't in a circular orbit.
They were in a spiraling orbit exactly.

Speaker 3 (26:03):
But if you look at the energy dynamics of it,
it turns out that these orbits actually are stable, meaning
if you don't have exactly the right value, the physics
of it tends to push you towards having the right value.
Or if you have the right value and somebody gives
you a push, or hey jumps off the planet, or
an asteroid hits us or Elon Musk launches a super
heavy rocket. So we deviate a little bit from having

(26:25):
the right pair of velocity and radius, that actually the
forces will push us back towards having the right velocity
and radius. Turns out that just from a gravitational point
of view, using Newtonian physics, these orbits are stable.

Speaker 1 (26:39):
Wait wait, wait, wait, are you basically answering the question
of the episode. So orbits are stable.

Speaker 3 (26:43):
In the simplified universe that we don't live in, where
we have only one planet and the only thing happening
is Newton's gravity, then yes, these orbits are stable. But
of course there's lots of other things going on. The
Sun is losing its mass, the Earth feels the solar wind, etc. Etc.
There are other planets hugging on us, so it's a
little bit more complicated. But in the simplified view of
just a single planet orbiting a star, then yes, those

(27:05):
orbits are stable.

Speaker 1 (27:07):
Oh I see way wait wait, So like if the
Solar System only had one planet, us, then no matter
what we do, we would be in an orbit.

Speaker 3 (27:15):
If the Solar System had only one planet and the
Sun lasted forever and there was no solar wind and
no gravitational radiation and nothing else from outside the Solar
System affected us, then yes, we would be in an
orbit that would be stable basically forever.

Speaker 1 (27:28):
But like it has to be one particular orbit, or
like let's say we're this single planet around the Sun.
There's nobody else, nothing changes in terms of how big
it is or what happens to the Sun. Where with
one planet in the Solar System, and you know, something
comes and knocks it or gives it some boost in
one direction, it's going to move out of the orbit
we're in. But is it going to then get into

(27:50):
another different orbit?

Speaker 3 (27:51):
It depends a lot on how it gets hit. If
the Earth speeds up a lot, for example, it gets
hit from behind, then there's another radius that it needs
in order to have a stable orbit. But it's actually
likely to slide over into that radius because the energy
configuration is stable. If the Earth has too much velocity,
then the balance of the forces will tend to push
it towards the radius it needs for that velocity. On

(28:12):
the other hand, if it gets pushed like from the side,
that it gets kicked out a little bit, then it
might actually oscillate and move from a circular orbit to
an elliptical orbit, which is sort of like a circular orbit,
but you're like sloshing back and forth a little bit.
There's like a harmonic motion around a circular orbit.

Speaker 1 (28:28):
So like, let's say I have the Earth and we're
the only planet in the Solar System, and I attach
some rockets to the back of the Earth and I
fire them up. I'm going to speed up is that
gonna get me into like an elliptical orbit then around
the Sun, or is it going to be like a
totally chaotic orbit, Like I feel like the only reason
we tend to think of orbits as stable is because.

Speaker 4 (28:49):
They're pretty circular, right, But you can.

Speaker 1 (28:51):
Also go around the Sun for a long time, going
around in like big ellipses, right, Like, you're really far
from the Sun, and then you fly towards the some
you get really close, but you fly really fast, and
then you shoot past the Sun, and then you come
back and you do the same thing over and over,
and maybe that big ellipse is not always the same.
You're sort of going around and around the Sun, but
you're still sort of you're not falling into the Sun exactly.

Speaker 3 (29:15):
That ellipse can also be a stable orbit. It's not circular,
but it can be stable, and you can think of
it as having two components. You can think of it
as a circular orbit plus motion relative to that circular
orbit where you're slashing in and out and in and out,
and that whole arrangement can be stable. You can be
in a circular orbit forever around a star without ever

(29:35):
falling in. And the reason is something you just mentioned,
which is at your speed and your radius vary. Say
somebody comes along and pushes us towards the Sun, for example.
So now we fall in a little bit towards the
Sun and gravity is getting stronger. But we're now also
going to speed up. So when we come around the curve,
we're going to be going fast enough to go further
out than we used to. That's going to slow us down,

(29:55):
and gravity is going to pull on us slowing us down.
We're going to use up our energy climbing out of
the gravitational well, and then we're going to come back
and we're going to slosh back and forth around that
original circular orbit. That's what I mean when I say
that it's stable. There's forces of gravity pulling you back
towards it, and then there's this centripetal force effectively pushing
you back towards your orbit, and those two forces are

(30:15):
encouraging you to stay in that orbit to.

Speaker 4 (30:18):
Then you elliptical orbit.

Speaker 1 (30:19):
Right Like if I put some booster rockets on the Earth,
it's not gonna maybe make the Earth' spiral land. It's
going to make it just it's just going to change
the shape of the orbit, or is that true, or
is there a possibility for me to fall into the sun.

Speaker 3 (30:32):
There's a possibility for you to fall into the sun, absolutely,
if you push hard enough, right, stability is always approximate.
It's always possible to get out of the orbit. If
you put in enough energy in that rocket, you can
escape the Sun's gravity, or if you turn really really hard,
you can drive right into the Sun. But small deviations
will return to the stable orbit, to a.

Speaker 4 (30:48):
Stable orbit, right, not necessarily the one we're in right now.

Speaker 3 (30:51):
Yeah, that's right, And it might be circular, and it
might be elliptical, depends exactly on the kick that you
give it. You can also change your circular orbit to
another circular orbit, So that's basically an ellipse with zero eccentricity,
and so that's a little bit less likely to happen.
So if you're in a perfectly circular orbit, I think
the most likely thing if you get a kick is
to end up in a slightly elliptical orbit.

Speaker 1 (31:11):
Or if you're in a slightly elliptical orbit, if you
get a kick, then you're saying the most likely thing
is that they'll just change the shape of that lips right.
In my twist urn my turn, it might get rounder
or narrower, but will still be in an orbit that
the Earth will want to stay in.

Speaker 3 (31:27):
Yeah, exactly, So there's lots of different stable configurations. Circular
orbits are like a special condition of elliptical orbits. Really,
circles are like a special kind of ellipse than ellipse
with zero eccentricity. So if you think about all orbits
as elliptical, and circular ones are like one particular kind
of elliptical orbit. But yes, elliptical orbits are a stable.

Speaker 1 (31:46):
And I think a big reason we're here a lie
full of animals and plants around us is that our
orbit is pretty circular. Like if you look at a
picture of it, you couldn't probably tell that it's not
a perfect circle.

Speaker 3 (31:57):
Yeah, the eccentricity is not huge, and you're right, if
it was much greater, we would have more dramatic seasons.

Speaker 1 (32:02):
Yeah, Like, you know, you think about just how different
summer and winter are, and that's just because of our tilt.
But like, if our orbit was elliptical and we flew
a lot closer to the Sun in some parts of
the year, I mean we basically be toast right and
we would freeze the other parts of the year.

Speaker 3 (32:19):
Yeah, that's right. And there are very elliptical orbits that
would in principle be stable but would not be survivable.
So stable and survivable are not the same thing.

Speaker 1 (32:27):
So it's not just about the goldilocks soon right, being
at the right distance from the Sun. It's also about
having a pretty circular orbit, right, so that things are stable.

Speaker 3 (32:35):
Mm hmm, yeah, that's important.

Speaker 4 (32:36):
All right.

Speaker 1 (32:37):
Well, as you said, this stability and this ability to
stay in orbit is only good if it's in a
perfect universe where we're the only planet in our solar system. Unfortunately,
as most kids know, having siblings is kind of a
hard thing to deal with. You can really throw your
household in this array. So let's get into what could
maybe knock us out of our orbit or at least

(32:58):
make that orbit unstable, and what we have any control
over those things. But first let's take another quick break.
All right, we're asking the question how stable is Earth's orbit,

(33:20):
and it sounds like in the perfect world, orbits are
pretty stable.

Speaker 3 (33:23):
Yeah. Universes in which you have three directions of space
like XYZ have stable gravitational orbits if you have nothing
else going on. What's fascinating to think about is that
other universes with like two dimensional space or four dimensional
space don't actually have the same kind of balance. Is
balance you talked about where gravity pulls are you at
just the right strength to bend your velocity? That perfect

(33:44):
balance only happens in three dimensional space and four D
and two D space centrifugal force and gravity both change
and they don't balance each other. There aren't stable orbits
in two D or four D space.

Speaker 1 (33:56):
Wait, what like isn't the Earth basically going around a
flat ellipse? Aren't we technically in two D?

Speaker 3 (34:03):
We're not technically in two D because gravity gets dispersed
in three dimensions, right, So if there's only two dimensions
of space, then the dependence of gravity would be different.

Speaker 4 (34:12):
Uh.

Speaker 1 (34:12):
Interesting, All right, Well, as you said, this is only
in a perfect world, But we don't live in a
perfect world. There are other things in the Solar system
that things can change in the Solar system. So let's
talk about some of the things that could maybe knock
the Earth out of its orbit.

Speaker 3 (34:27):
So, of course, the Sun is the source of our gravity,
and the gravity of the Sun comes from its mass.
But the Sun's mass is not actually constant. The way
that the Sun lights up our skies and heats up
our days is that it burns its fuel. It's converting
mass into energy in order to send it to us,
and so it's actually dropping its mass, which means the

(34:48):
Sun's gravity is actually fading.

Speaker 4 (34:50):
It's burning up.

Speaker 3 (34:51):
It is burning up because the fundamental process inside the
Sun that produces that light is fusion, which converts mass
into energy. Like if you take four protons and you
convert them into helium four, which is two protons and
two neutrons, they don't have the same amount of mass
as those four protons. Remember, mass is not a measure
the amount of stuff. It's actually measured the internal stored energy.

(35:15):
And that arrangement of all those quirks and a helium
four nucleus has less stored energy than four individual protons
by aboutzo point seven percent, which means that every time
fusion happens, the Sun loses mass.

Speaker 1 (35:28):
Well, it's basically burning away it's itself, right like it's
it's sort of like a log eventually burns down into
a pile of ashes.

Speaker 3 (35:35):
Yeah. No, of course, the Sun is really massive, and
even though it burns like four million tons of mass
every second, Right, every single second, the Sun loses four
million tons of its mass. That energy flies away in
photons and in the solar wind. But over the lifetime
of the Sun, that only adds up to like the
mass of Saturn, which is a tiny, tiny fraction of

(35:59):
the mass of the Sun.

Speaker 1 (36:00):
Wait, over billions of years, the Sun is only going
to lose the equivalent of one Saturn' sports of mass.

Speaker 3 (36:07):
Yeah, that's right.

Speaker 1 (36:08):
That doesn't seem like a lot. I mean, Saturn is big,
but it's tiny compared to the Sun.

Speaker 3 (36:11):
Yeah, that's right. Saturn is tiny compared to the Sun.
But of course it has an effect on the Sun's mass,
which has an effect on the Sun's gravity, And so
every year the Sun loses enough mass, so the Earth's
orbit gets larger by about a centimeter and a half
every year because the Sun's gravity is getting weaker.

Speaker 4 (36:29):
Whoa, every year.

Speaker 3 (36:31):
Every year we got a centimeter and a half further
from the Sun. We're like slowly spiraling out.

Speaker 4 (36:36):
So is our orbit then it just getting bigger or orbit?

Speaker 3 (36:39):
Yeah, that's right. Every time the Sun loses mass, there's
a new radius where we would have a stable orbit.
So if you took like a scoop of stuff out
of the Sun. And the Sun lost its mass, the
Earth would slide out a little bit into a new
stable orbit. And reality is happening on a continuous basis.
The Sun is losing its mass and the Earth is
sliding out, So at any moment it's in this stable orbit.

(37:01):
But the stable orbit is actually changing with time because
the Sun is losing mass over time.

Speaker 1 (37:07):
But I think an average humanity is gaining weight in general, right,
So wouldn't that mean that.

Speaker 4 (37:13):
Our gray stronger. I'm just thinking, like a five year old.

Speaker 3 (37:17):
Deer, if you eat the Earth, you gain weight, But
the U plus Earth system doesn't get any more massive.

Speaker 1 (37:23):
Although weaight, are we getting energy from the Sun And
isn't some of that energy being converted into I don't
know things and plants for us to eat.

Speaker 3 (37:32):
Yeah, that actually does have an effect. All the photons
hitting the Earth and all the energy hitting the Earth
does have an effect on the Earth, and it actually
pushes it. Right, The Earth is like a big solar sail.
I remember we talked about how photons can push on
things even though they don't have mass, they have momentum
and you can like fly a spaceship if you have
a huge solar sail which catches those photons. So the

(37:53):
Earth is kind of like a big solar sail. And
that's another effect we didn't include when we thought about
just the simple Newtonian view. So all of photons hitting
the Earth do push it a little bit, but the
effect is super duper tiny because the Earth is pretty massive.
The calculation suggests that over a million years, that increases
the Earth's orbital radius by about the width of a proton.

Speaker 4 (38:14):
Wow, that's tiny.

Speaker 3 (38:15):
Yeah, that's basically something we can ignore.

Speaker 1 (38:17):
But I wonder, like we've talked about how, like you know,
mass is really just energy, and that concentration of energy
is what affects your gravity and how you bend space
around them with that energy. So does that mean like
the horder the Earth gets, the more gravity we have.

Speaker 3 (38:33):
Yeah, as the Earth heats up, you have more mass.
Like when you put a rock in the sun and
it absorbs photons, it doesn't just get hotter. It has
more internal stored energy, It has more mass, it has
more inertia, it bends space more. The same way like
if you take a box of mirrors and you shine
a flashlight in it, and then slam it closed. You've
trapped those photons inside that box gains mass.

Speaker 1 (38:56):
Hmmm, interesting, I'm guessing it's not maybe not enough to
counteract or to change our orbit around the Sun, or
is it?

Speaker 3 (39:05):
No, that's not enough. The overall effect from the Sun's
energy hitting the Earth is to push it to transfer
our momentum. But really these effects are totally negligible compared
to the Sun losing its mass. This is basically something
we can ignore.

Speaker 1 (39:18):
Although it depends on how hot you make the Earth,
doesn't it by if you make it super duper hot,
it is going to be heavier.

Speaker 3 (39:24):
Yeah, that's right, And the Sun actually is getting hotter
every year and it's growing. Something else to think about
over these very long times is whether the Earth is
going to get gobbled by the Sun. Right as the
Sun burns its fuel and gets a helium core, then
the fusion starts to happen the outer edges and it
puffs out and the radius of the Sun grows really,
really large. The estimates are that eventually the radius of

(39:48):
the Sun will be two hundred times its current radius,
which puts it right about where the Earth's orbit is today.

Speaker 1 (39:55):
Mm, which will be bad news for anyone on Earth
at that time, right, it'll be way too hot.

Speaker 3 (40:01):
It'll be way too hot. Though. It's actually a really
interesting and complicated calculation because the Sun gets larger, and
it would be very bad for the Earth obviously to
get enveloped by the outer layers to the Sun, because
not only would it be super hot, but it would
drag on us. It would tend to slow us down
and then we're very likely to fall into the Sun.
But at the same time, the Sun is losing mass,
so the Earth is spiraling out as the Sun grows,

(40:23):
So it's kind of a close race, like the Earth
is drifting away and the Sun is like trying to
catch us.

Speaker 1 (40:28):
Wait, even if the Sun grows, as long as it
doesn't grow more than the orbit of the Earth, doesn't
it feel the same to the Earth, Like you know,
it feels like a point mass.

Speaker 3 (40:38):
Exactly as long as the Sun is contained within the
Earth's orbit, then you're right. It doesn't matter how that's distributed,
big or small, a point mass, a black hole, the
current Sun, it's all the same gravitationally. But if it
does pass the Earth, then any parts of the Sun
that are outside of our orbit no longer contribute gravity
to pulling on us, and then we feel a drag
as because we're flying basically through the Sun's outer at sphere,

(41:00):
and that would just kill the stability of our orbit.

Speaker 1 (41:03):
I feel like if we're flying through the Sun, we
have other things to worry about, exactly, or like if
we were still if we were still on Earth at
that time, it seems like it wouldn't matter if you're
going to fall into the Sun or not, like you're
already in the Sun.

Speaker 3 (41:16):
Mm hmm. But because as the Sun gets bigger, it
also gets less massive, it's losing its mass. The Earth
is going to be sliding away from the Sun as
it gets puffy. So the estimates are like the Sun
will grow to a few hundred times its current radius
and the Earth will drift out to like a little
bit further than that. But the calculations are very uncertain,
and so it's not clear whether the Earth is going

(41:38):
to get engulfed by the outer atmosphere of the Sun
or if we're going to like escape that in orbit
at a new distance.

Speaker 1 (41:44):
But I feel like maybe neither of those things is
making our orbit unstable, you know what I mean, Like,
neither of those things is enough to either make a
spiral into the Sun or kick us out of the
Solar System.

Speaker 3 (41:55):
They won't kick us out of the Solar System if
we do enter the upper atmosphere of the Sun and
the orbit's unstable because the drag is just going to
serp all of our energy and it's like a satellite
orbiting in low Earth orbit, getting slowed down by the
atmosphere and eventually plummeting to Earth.

Speaker 4 (42:09):
All right, what else can disturb our orbit in space?

Speaker 3 (42:12):
Well, another big problem are the other planets, Right, It's
not just the Earth and the Sun. Jupiter and Saturn
are very tiny compared to the Sun, but they're not
something we can totally ignore. And the problem is that
while two objects can be in very stable orbits for
a very long time, three objects are chaotic. We talked
about this on our episode about the three body problem.
It's not just a cool science fiction novel. It's actually

(42:33):
a real thing in physics that three objects have a
hard time being stable for long periods of time, and
so as Jupiter and Saturn tug on us, they basically
disturb our orbit.

Speaker 1 (42:44):
You sort of like romantic relationships, like two is barely
stable but three, that's just asking for trouble.

Speaker 3 (42:51):
And if they push hard enough where they get lucky
or we get unlucky, then they can disturb our orbit
in a way that like ejects us from the Solar System.
And we think that this is happened. We think that
there have been planets in our Solar System which were
ejected by Jupiter and Saturn.

Speaker 1 (43:05):
I guess it's kind of a wonder that it hasn't happened, right, Like,
Jupiter is there, Like, we're not just a three body
system in our Solar System. We're like a you know,
ten or ten million body problem because of all the asteroids.
Isn't it kind of a wonder that we are in
a stable orbit given everything that's flap flying out there.

Speaker 3 (43:24):
Yeah, it is kind of amazing that we're left here, right.
We think that Jupiter traveled in towards the inner Solar
System and then back out. There might have been another
gas giant that got ejected. It's sort of amazing that
any planets survived that sort of chaotic motion. And especially
in the future, we think that as the Sun gets weaker,
Jupiter and Saturn's orbits will become more chaotic because they're

(43:45):
not going to be as tightly held, and then in
turn they will add more chaos to the rest of
the Solar System. So in some simulations I looked at,
Jupiter ends up being the only planet, like even if
the Earth escapes being engulfed by the Sun's atmosphere as
it grows, because it acted by Jupiter. And in the
long term future, the Solar system is just a big
puffy Sun and Jupiter.

Speaker 1 (44:05):
Mmmm.

Speaker 4 (44:05):
You see. And this is due to the Sun losing mass.

Speaker 3 (44:08):
Yeah, the Sun loses mass and so it doesn't pull
on Jupiter as hard and it makes Jupiter more chaotic.

Speaker 4 (44:13):
But again, this is in a few billion years, right.

Speaker 3 (44:15):
This is in a few billion years exactly. So you
should buy your Earth stability insurance now and pay your
premiums every single year until then.

Speaker 4 (44:22):
No, you should wait a few billion years.

Speaker 6 (44:24):
You know.

Speaker 1 (44:25):
You know, when something's gonna happen, you should buy it
right before it happens. That's how insurance works.

Speaker 3 (44:29):
We're not gonna be offering this insurance in a billion years.
This is your one time offer.

Speaker 1 (44:34):
To pay us a billion dollars for a billion years.
All right, What are some other things that could maybe
knock our orbit out of orbit.

Speaker 3 (44:41):
Well, other sources of chaos are things outside the Solar System, right,
Like other stars can pass kind of nearby our Solar
system and give it a little kick, like a little perturbation.
This already happens, Like other stars come close enough that
they can like tweak stuff in the Org cloud, this
vast system of trillions of icy objects in the very
distant Solar System. Some of them then get knocked in

(45:03):
and become comets which burn their way into the Solar
System and whip around the Sun. But if other stars
come closer, for example, then they could perturb the orbits
of planets themselves. Right.

Speaker 1 (45:14):
Yeah, we had that object, oh we uh right, come
through our Solar System from out of space a few
years ago.

Speaker 3 (45:21):
Yeah, that's right. Nobody really knows what.

Speaker 4 (45:23):
That thing was, or how to pronounce it correctly, or.

Speaker 3 (45:27):
If it was actually alien space junk. But it's a
cool example of how we're not the only things out there. Right,
We do bump into stuff from other Solar systems, and
the galaxy is chaotic. You know, the stars are all
moving in different velocities relative to each other, So we
get further and closer to other stars. There's another star
called Lease seven to ten, which is expected to pass
near our solar system in about a million years, and

(45:50):
that could have a gravitational impact on all the orbits.
And remember, if it tugs on Jupiter, or Jupiter could
then tug on us. It can all become very chaotic
very quickly.

Speaker 1 (45:58):
But I guess stars are easy to see coming, Like
you say, we know this one's going to fly by
in a million years.

Speaker 3 (46:04):
Yeah, they're easier to see coming. They're harder to do
something about. We talked once about building a star sized
rocket ship, like flying in the Sun into a different
spot in the galaxy to avoid oncoming stars. It might
take us a million years to figure that out.

Speaker 4 (46:17):
Or just wait for the insurance premium to pay us.

Speaker 3 (46:21):
That's right, Sit back and relax.

Speaker 1 (46:24):
You're covered all right. Now, what's the last thing that
could maybe push us out of orbit?

Speaker 3 (46:28):
So even if you don't worry about Jupiter, and you
assume the Sun is going to be there forever and
all sorts of chaotic things are not something to worry about,
there's still a gravitational issue. The reason I said that
a Newtonian system is stable over long periods of time
is that Newtonian gravity ignores gravitational radiation. Anytime you have
an object that's accelerating and moving in a circular orbit

(46:49):
councils acceleration, it gives off gravitational waves because gravity is
not actually a force, it's actually the curvature of space
affecting how things move, and when things accelerate, they create
ripple in that space. These are gravitational waves. We've seen
gravitational waves from orbiting objects like black holes orbiting each
other give us those gravitational waves. They radiate away energy,

(47:11):
so that means that as the Earth is going around
the Sun, it's also generating gravitational waves and losing energy.
So in principle, over a very long amount of time,
the Earth will radiate away its energy and fall into
the Sun.

Speaker 1 (47:24):
WHOA, but that's not going to happen for a while, right, Yeah.

Speaker 3 (47:27):
We estimate that it loses about one proton with in
radius every thousand years, So if you do the calculation,
it's like ten to the twenty six years before the
Earth spirals into the Sun, which is about ten quadrillion
times the current age of the universe. So yeah, not
something to worry about, but in principle, over a very
very long times gravitational radiation will cause us to lose

(47:50):
our energy and spiral into the Sun.

Speaker 1 (47:52):
All right, Well, it sounds like the message or the
answer to the question is that the Earth's orbit is
pretty stable, at least in the sh It sounds like
most orbits are stable, and the fact that we are
in a stable orbit probably means that we're going to
be here for a while. But of course the universe
has a lot of surprises, and we are in a

(48:13):
sort of chaotic system with other planets in our Solar system,
so something could happen in the near future, but it's unlikely.

Speaker 3 (48:21):
That's right. So in a Newtonian system, in principle, it's stable.
An object orbiting the Sun can do that forever, but
once you add gravitational radiation for Einsteini and gravity, then
eventually it's going to fall into the Sun. And once
you add other things in the Solar system, then you
add chaos which are going to perturb those orbits. And

(48:42):
once you consider the fact that the Sun itself is
losing its mass and changing its gravitational pull on the Earth,
then over those very long time scales, the Earth's orbit
is not stable, but over short time scales, we don't
have anything to worry about.

Speaker 1 (48:54):
So I guess maybe you don't need that insurance after all.
So the next time you jump, feel free to jump
as high as you can or want. The Earth is
gonna stay where it is, going around the sun, and
the sun will rise tomorrow most likely. All right, Well,
we hope you enjoyed that. Thanks for joining us, see
you next time.

Speaker 3 (49:20):
Thanks for listening, and remember that Daniel and Jorge explain
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