Latest / Daniel and Kelly’s Extraordinary Universe / How stable is the Earth's orbit?

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How stable is the Earth's orbit? · Daniel and Kelly’s Extraordinary Universe

• 0:08
  Speaker 1: Hey, Daniel, did you see the reason launch at tempt
• 0:10
  Speaker 1: by SpaceX.
• 0:12
  Speaker 2: Oh?
• 0:12
  Speaker 3: Yeah, I did. That massive rocket with so many engines attached.
• 0:16
  Speaker 3: Really awesome to watch.
• 0:18
  Speaker 4: Yeah, I hear.
• 0:18
  Speaker 1: The fireworks were great. It really popped. But the whole
• 0:21
  Speaker 1: thing kind of has me worried a little bit.
• 0:23
  Speaker 3: You worried the rocket's going to crash into your house?
• 0:26
  Speaker 1: A little bit? I mean I live in my house.
• 0:30
  Speaker 1: That would be a problem. No, But I guess I'm
• 0:32
  Speaker 1: more worried about the effect it has on the Earth
• 0:34
  Speaker 1: than all those engines in the rocket also push on
• 0:36
  Speaker 1: the Earth.
• 0:37
  Speaker 3: Yeah. I guess it's kind of like putting a rocket
• 0:39
  Speaker 3: engine on the Earth itself.
• 0:41
  Speaker 1: A little bit, right, So we're letting elon Musk steer
• 0:44
  Speaker 1: our planet.
• 0:45
  Speaker 4: I mean, you can't even steer Twitter.
• 0:48
  Speaker 3: It would be pretty cool if a planet had a
• 0:50
  Speaker 3: steering wheel. I guess that'd be fun.
• 0:52
  Speaker 1: I would probably fall asleep, so maybe I shouldn't be
• 0:55
  Speaker 1: driving the Earth.
• 0:57
  Speaker 4: It probably flies into the sun.
• 1:14
  Speaker 5: Hi.
• 1:14
  Speaker 1: I'm Orham, a cartoonists and the creator of PhD comics.
• 1:17
  Speaker 3: Hi I'm Daniel. I'm a particle physicist and a professor
• 1:20
  Speaker 3: at UC Irvine, and I don't want to fly into
• 1:23
  Speaker 3: the Sun.
• 1:24
  Speaker 4: What do you want to do into the sun? Drive? Walk, fall, dive?
• 1:29
  Speaker 3: I guess I want to look into the Sun. Of
• 1:32
  Speaker 3: all the verbs, I think that's the least destructive one.
• 1:35
  Speaker 4: I like hearing about the Sun and feeling the Sun.
• 1:37
  Speaker 2: I don't know.
• 1:38
  Speaker 4: I don't know if I want to look at it.
• 1:39
  Speaker 4: It isn't that dangerous.
• 1:40
  Speaker 3: I want us to build new scientific eyeballs that let
• 1:42
  Speaker 3: us peer into the Sun and understand the chaotic churning
• 1:46
  Speaker 3: inside of it.
• 1:47
  Speaker 4: You want to peer into the Sun?
• 1:48
  Speaker 3: Yeah, exactly, yes, I consider the Sun to be our
• 1:51
  Speaker 3: peer in the Solar system.
• 1:53
  Speaker 4: I see. Are you saying you're like a sun god?
• 1:57
  Speaker 3: No, I'm saying we're ever accused of breaking a law
• 1:59
  Speaker 3: of physic that I want a jury of our peers,
• 2:01
  Speaker 3: which I guess would include the Sun.
• 2:03
  Speaker 1: M and who else? Who else do you consider your
• 2:06
  Speaker 1: peers in the cosmos?
• 2:08
  Speaker 3: Jupiter is pretty good. Yeah, it carries a lot of weight.
• 2:12
  Speaker 1: Yeah, he would be a massive help on the jury.
• 2:15
  Speaker 1: But anyways, Welcome to our podcast, Daniel and Jorge Explain
• 2:18
  Speaker 1: the Universe, a production of iHeart Radio.
• 2:20
  Speaker 3: In which we try to thread the needle of understanding
• 2:23
  Speaker 3: the entire universe without pissing it off too much. We
• 2:26
  Speaker 3: try to pay attention to what's going on out there
• 2:28
  Speaker 3: in the universe, from the tiny little particles to the
• 2:30
  Speaker 3: very massive objects swirling around each other, to try to
• 2:33
  Speaker 3: deduce the laws that this universe follows as it moves
• 2:37
  Speaker 3: forward through time towards its eventual end, whatever that may be.
• 2:40
  Speaker 3: And we hope that before that end comes, we can
• 2:43
  Speaker 3: figure out how it all works.
• 2:44
  Speaker 1: That's right, because it is a massively cool universe, fools,
• 2:47
  Speaker 1: amazing and incredible laws and mechanism that seem to make
• 2:51
  Speaker 1: the whole thing work like a giant clock, it seems,
• 2:54
  Speaker 1: going around and around, taking away till the end of time.
• 2:58
  Speaker 3: A clock makes it seem like very organized and stable.
• 3:01
  Speaker 3: I see it more like a really complicated Rube Goldberg machine,
• 3:04
  Speaker 3: you know, like ball rolls down a wheel and hits
• 3:06
  Speaker 3: this lever which makes the cat jump, and then that
• 3:09
  Speaker 3: knocks something else over. Sometimes it feels like the mechanisms
• 3:12
  Speaker 3: on which our entire existence are based are very precarious.
• 3:17
  Speaker 1: Like it knocks a ball, the ball rolls sound a
• 3:19
  Speaker 1: ramp and then outcomes humans, and out of those humans,
• 3:23
  Speaker 1: one of them bumps into another, and you and I
• 3:26
  Speaker 1: are born, and this podcast is born exactly.
• 3:30
  Speaker 3: It seems like it could have gone a lot of
• 3:31
  Speaker 3: different ways, and in many of those ways we wouldn't
• 3:34
  Speaker 3: be here. So in some respects our existence here seems very,
• 3:39
  Speaker 3: very fortunate, and I wonder sometimes about the future of
• 3:42
  Speaker 3: our existence here. How long these special cozy conditions will continue.
• 3:47
  Speaker 1: I know, I feel pretty inevitable. I feel like r
• 3:49
  Speaker 1: cham was meant to be.
• 3:51
  Speaker 3: You feel like the whole project of the universe was
• 3:52
  Speaker 3: to bring you into existence?
• 3:56
  Speaker 1: Why not at least my universe now. I don't know
• 3:59
  Speaker 1: if my kids feel the same way. Over my spouse.
• 4:03
  Speaker 1: I'm an unfortunate byproduct. Sometimes it seems.
• 4:05
  Speaker 3: Well one of the joys of understanding the universe is
• 4:08
  Speaker 3: being able to predict its future, taking those laws of
• 4:10
  Speaker 3: physics that describe what we have seen and also applying
• 4:13
  Speaker 3: them to the future, and thinking what's going to happen,
• 4:16
  Speaker 3: what's likely to happen in the next one hundred years,
• 4:18
  Speaker 3: million years, or billion.
• 4:20
  Speaker 1: Years, m or the next hour. I mean, I don't
• 4:23
  Speaker 1: know where this conversation is going.
• 4:24
  Speaker 3: To be honest, the podcast does seem kind of unpredictable.
• 4:28
  Speaker 3: Doesn't seem to matter too much what I write any outline.
• 4:31
  Speaker 1: Well, I think that's what happens when you put two
• 4:32
  Speaker 1: unstable people and try to create a stable system here.
• 4:38
  Speaker 1: But it is kind of an interesting question how precarious
• 4:40
  Speaker 1: our existence is and how likely it was that we
• 4:44
  Speaker 1: are here in this place talking about the universe. It
• 4:47
  Speaker 1: seems like the universe kind of could go either way
• 4:49
  Speaker 1: at any moment.
• 4:50
  Speaker 3: Mm hmmm. And there's lots of ways that things could
• 4:52
  Speaker 3: go south for us. But on the podcast a few
• 4:54
  Speaker 3: times we've talked about one in particular, which is the
• 4:57
  Speaker 3: requirement that the Earth stay in orbit around the Sun
• 5:00
  Speaker 3: at just the right distance to keep water nice and
• 5:03
  Speaker 3: toasty on our surface but without bubbling it into steam
• 5:07
  Speaker 3: or dropping it into a deep freeze.
• 5:09
  Speaker 1: Yeah, the Earth is and what's called the Goldilock zone
• 5:12
  Speaker 1: of our solar system, where it's not too hot and
• 5:14
  Speaker 1: not too cold, which makes it just right for life
• 5:17
  Speaker 1: to flourish on it and for vicious birds, animals, and
• 5:22
  Speaker 1: humans which I guess are also animals for them to
• 5:26
  Speaker 1: come about.
• 5:26
  Speaker 3: So you might wonder how long this Goldilock situation can
• 5:29
  Speaker 3: continue before the bears come home and ask for their
• 5:32
  Speaker 3: porridge back, so to.
• 5:33
  Speaker 1: Be On the podcast, we'll be asking the question, how
• 5:40
  Speaker 1: stable is the Earth's orbit? Never thought about the stability
• 5:44
  Speaker 1: of our planet's orbit. I guess it seems so predictable
• 5:47
  Speaker 1: and regular, right, I mean, nobody questions whether the sun
• 5:50
  Speaker 1: will rise in the morning every day.
• 5:53
  Speaker 4: We just assume it is.
• 5:55
  Speaker 3: It's one of these really fun questions where the answer
• 5:57
  Speaker 3: depends a lot on the time frame your imagining. Nobody
• 6:01
  Speaker 3: suspects that the Earth will fall out of its orbit
• 6:03
  Speaker 3: tomorrow or next year, or in one hundred years, and
• 6:05
  Speaker 3: on the kind of time scales the humans are used
• 6:08
  Speaker 3: to thinking about. The Solar System is kind of static.
• 6:11
  Speaker 3: We imagine it's looked the same way for one hundred years,
• 6:13
  Speaker 3: a thousand years, probably a million years. But when you
• 6:16
  Speaker 3: look on longer time scales, hundreds of millions of years
• 6:18
  Speaker 3: or billions of years, you see the Solar System is
• 6:21
  Speaker 3: actually quite chaotic. Planets have been lost, they've changed their orbit,
• 6:25
  Speaker 3: they've moved from the outer Solar System to the Inner
• 6:27
  Speaker 3: Solar System and back. All sorts of crazy stuff has happened.
• 6:30
  Speaker 3: So then you can ask, like, well, how long will
• 6:33
  Speaker 3: this phase of our Solar system last?
• 6:35
  Speaker 1: Yeah, I guess the Solar system was just a giant
• 6:38
  Speaker 1: cloud of dust and gas at someone, right, and then
• 6:40
  Speaker 1: the Sun form, and then the planet's form. But even
• 6:43
  Speaker 1: after the planet's form, the Solar System kind of had
• 6:45
  Speaker 1: to find its groove kind of right, it's rhythm, it's orbits.
• 6:48
  Speaker 1: Things will crash into each other a lot before settling
• 6:51
  Speaker 1: into planets.
• 6:52
  Speaker 3: Right, Yeah, that's exactly right. And you look at the
• 6:54
  Speaker 3: surface of anything in the Solar System, like the Moon,
• 6:57
  Speaker 3: and you'll see lots of evidence for collisions. Basically, anything
• 7:00
  Speaker 3: that's out there is getting smacked into all the time.
• 7:03
  Speaker 3: The Earth doesn't have a surface filled with craters because
• 7:05
  Speaker 3: we have an atmosphere that mostly burns those things up
• 7:08
  Speaker 3: before they hit the ground, but of course sometimes they don't.
• 7:10
  Speaker 3: Sixty five million years ago or so, something really big
• 7:14
  Speaker 3: hit the Earth, and billions of years before that, the
• 7:16
  Speaker 3: Moon was formed in an even more giant collision.
• 7:19
  Speaker 4: We've been hit around a lot, and yet we're still here.
• 7:21
  Speaker 3: And if we look at Jupiter, for example, there's a
• 7:23
  Speaker 3: lot of evidence that Jupiter and Saturn migrated to the
• 7:26
  Speaker 3: inner Solar System and then turned around and went back out,
• 7:29
  Speaker 3: returning to the depths of the outer Solar System. So
• 7:32
  Speaker 3: planetary orbits are not as fixed as you might imagine.
• 7:37
  Speaker 1: At least some large time scales. As you were saying, well,
• 7:39
  Speaker 1: as usually, we were wondering how many people out there
• 7:41
  Speaker 1: had thought about this question, about the stability of our orbit,
• 7:45
  Speaker 1: about how steady the Solar system is. So, as usual,
• 7:48
  Speaker 1: Daniel went out there into the Internet to ask people
• 7:51
  Speaker 1: how stable is the Earth's orbit.
• 7:53
  Speaker 3: I'm eternally grateful to everybody who answers these questions. If
• 7:56
  Speaker 3: you want to be part of this segment, please don't
• 7:58
  Speaker 3: be shy. Just write to me to question at Danielandjorge
• 8:01
  Speaker 3: dot com.
• 8:02
  Speaker 1: So think about it for a second. How stable do
• 8:04
  Speaker 1: you think our orbit is? Here's what people had to say.
• 8:08
  Speaker 6: So I would say that the Earth orbit is very
• 8:11
  Speaker 6: stable millions or maybe even billions of years. But perhaps
• 8:16
  Speaker 6: when the Sun turns into a ridge giant and expands,
• 8:19
  Speaker 6: maybe that will change things and throw that we're further
• 8:22
  Speaker 6: or closer.
• 8:22
  Speaker 7: In Well, I think earth orbit is quite stable, but
• 8:26
  Speaker 7: we are slowly drifting away from the Sun because of
• 8:29
  Speaker 7: the Moon, and we might get hit by asteroids in
• 8:32
  Speaker 7: the future. But otherwise I think the Earth's orbit is stable.
• 8:34
  Speaker 3: I don't think the Earth's orbit is stable forever.
• 8:38
  Speaker 6: I think it looks pretty stable to us, because the
• 8:41
  Speaker 6: time scale of.
• 8:42
  Speaker 3: The universe, of the Solar System is pretty long.
• 8:45
  Speaker 6: I would say it's like a metastable state, and maybe
• 8:47
  Speaker 6: even an asteroid could kick the Earth out of orbit.
• 8:50
  Speaker 3: It's more like a castle of cards. Remove one and
• 8:54
  Speaker 3: everything falls apart.
• 8:55
  Speaker 4: It seems pretty stable to me.
• 8:57
  Speaker 8: If Hummans had long enough to you will, so hopefully
• 9:03
  Speaker 8: it'll hang in there a bit longer.
• 9:05
  Speaker 9: I know from your podcast about when stars collide that
• 9:08
  Speaker 9: any object that's accelerating gives off gravitational waves because of
• 9:16
  Speaker 9: its acceleration. So fundamentally the orbit is not stable, and
• 9:23
  Speaker 9: although it will take a really really long time, eventually
• 9:28
  Speaker 9: the Earth's orbit will fall into the Sun.
• 9:32
  Speaker 8: I think the Earth's orbit is very stable. I have
• 9:34
  Speaker 8: heard about studies that talk about Jupiter moving around in
• 9:37
  Speaker 8: the ancient Solar System, and studies of sensitivity of mercury
• 9:42
  Speaker 8: and Venus to subtle perturbations. But I just think that
• 9:45
  Speaker 8: the Earth's orbit is very stable.
• 9:47
  Speaker 1: I think it's stickaying just like you know might expect
• 9:50
  Speaker 1: it to, but you know, not going into the Sun
• 9:53
  Speaker 1: anytime soon.
• 9:54
  Speaker 2: I think the Earth's orbit about the Sun is very stable,
• 9:58
  Speaker 2: at least over the timeframes that we're concerned with long
• 10:02
  Speaker 2: term millions or billions of years. There might be some
• 10:06
  Speaker 2: drift in its position relative to the Sun, just like
• 10:10
  Speaker 2: there's some drift of the Moon relative to the Earth
• 10:14
  Speaker 2: over time.
• 10:15
  Speaker 5: I think it's bruey stable in a human time scale,
• 10:18
  Speaker 5: but on the long term I think that either gravity
• 10:23
  Speaker 5: or angular momentum will be more revalent.
• 10:27
  Speaker 1: All right, it seems like most people think it's kind
• 10:29
  Speaker 1: of stable. Only a few dissenters.
• 10:31
  Speaker 3: Not a lot of people worried about this out there,
• 10:33
  Speaker 3: although maybe they got more worried after they read this question.
• 10:37
  Speaker 4: Maybe they should be more worried.
• 10:39
  Speaker 1: That's what we're here for, to make people think about
• 10:43
  Speaker 1: all the different ways that the universe can kill them.
• 10:45
  Speaker 3: Mmm. Maybe we should be selling Earth orbit insurance somehow.
• 10:48
  Speaker 4: There you go.
• 10:49
  Speaker 3: If the Earth plunges into the Sun, we will pay
• 10:51
  Speaker 3: you any arbitrary amount of money.
• 10:54
  Speaker 1: A bazillion dollars exactly. Just give us a million dollars
• 10:58
  Speaker 1: a year.
• 10:59
  Speaker 3: That's right, submit request of this po box.
• 11:01
  Speaker 1: But yeah, it's kind of an interesting question. How stable
• 11:03
  Speaker 1: is the Earth's orbit? Because I guess we're going around
• 11:06
  Speaker 1: the Sun pretty steadily, right, is our orbit?
• 11:09
  Speaker 7: Like?
• 11:10
  Speaker 1: Do we always go through the same spot in the
• 11:13
  Speaker 1: Solar system or is our orbit kind of wobbling?
• 11:16
  Speaker 3: Well, our orbit around the Sun is not perfectly circular, right,
• 11:18
  Speaker 3: It's an ellipse, and that ellipse can process a little bit,
• 11:22
  Speaker 3: which means if you imagine an ellipse or like a
• 11:23
  Speaker 3: football or anything oblong, then that orbit itself can rotate. Right,
• 11:28
  Speaker 3: the path of the ellipse itself can rotate.
• 11:31
  Speaker 1: And is that the same for the whole Solar system?
• 11:34
  Speaker 1: Like there, everyone's orbits also kind of rotating.
• 11:36
  Speaker 3: There are some changes in the eccentricity of the Earth's
• 11:39
  Speaker 3: orbit that's deviation from it being circular over like one
• 11:43
  Speaker 3: hundred thousand year timescale, and these things actually can affect
• 11:47
  Speaker 3: like the climate. These are called Milankovich cycles. We talked
• 11:49
  Speaker 3: about it once in the podcast about ice ages. But
• 11:52
  Speaker 3: that doesn't make the Earth's orbit stable or unstable. An
• 11:55
  Speaker 3: elliptical orbit can be stable over very very long time periods.
• 12:00
  Speaker 3: Whether or not your circular or elliptical doesn't change whether
• 12:02
  Speaker 3: or not your stable.
• 12:03
  Speaker 1: M I see the orbit is changing a little bit.
• 12:06
  Speaker 1: But I think maybe what you mean by stable or
• 12:08
  Speaker 1: unstable is whether, like if you move the Earth a
• 12:11
  Speaker 1: little bit, is it gonna go back to its same orbit,
• 12:14
  Speaker 1: or is it gonna spin out of control and like
• 12:16
  Speaker 1: shoot out of the Solar System. That's kind of more
• 12:19
  Speaker 1: what you mean, right.
• 12:20
  Speaker 3: Yeah, my stability. We mean will it return to its
• 12:22
  Speaker 3: current configuration if it's pushed a little bit, Say, for example,
• 12:26
  Speaker 3: you jump. Every time you jump, you are pushing on
• 12:30
  Speaker 3: the Earth. Right, You're using your leg muscles to push
• 12:32
  Speaker 3: yourself away from the Earth, but you're also pushing the
• 12:35
  Speaker 3: Earth away from you. And Newton's laws tell us, you know,
• 12:38
  Speaker 3: every force is an equal and opposite reaction, and so
• 12:41
  Speaker 3: you're moving away from the Earth and the Earth is
• 12:43
  Speaker 3: also moving away from you. Now, of course, because the
• 12:45
  Speaker 3: Earth has so much mass, your push doesn't really affect
• 12:49
  Speaker 3: it as much as it affects yourself. It's sort of
• 12:51
  Speaker 3: like when you fire a rifle. The bullet gets going
• 12:54
  Speaker 3: really really fast, but the rifle itself also has a
• 12:56
  Speaker 3: little bit of recoil, and so when you jump, the
• 12:59
  Speaker 3: Earth recoil a little bit against you. And so if
• 13:02
  Speaker 3: the Earth's orbit is stable, then a little push like
• 13:06
  Speaker 3: that won't like send it spiraling into the Sun, it
• 13:09
  Speaker 3: like drift back to its original orbit. If the Earth
• 13:11
  Speaker 3: is unstable, then it's more like a pencil balancing on
• 13:15
  Speaker 3: its tip. Any tiny little touch will knock it out
• 13:17
  Speaker 3: of its configuration and it won't come back. So stability
• 13:21
  Speaker 3: tells you about whether you come back to your current
• 13:23
  Speaker 3: orbit when you're given a little push.
• 13:25
  Speaker 2: Hmmm.
• 13:26
  Speaker 1: First of all, it's cool that every time I take
• 13:29
  Speaker 1: a step, basically I'm sort of moving to Earth a
• 13:31
  Speaker 1: little bit. Right, every step I take is earth shattering,
• 13:34
  Speaker 1: Earth moving.
• 13:35
  Speaker 3: It sort of is, though. You return to the Earth
• 13:37
  Speaker 3: right and the Earth returns to you, So in the end,
• 13:40
  Speaker 3: the Earth's orbit isn't actually changed by that. To really
• 13:43
  Speaker 3: change the Earth's orbit, you need to like take a
• 13:45
  Speaker 3: rock and throw it into outer space and have it
• 13:47
  Speaker 3: escape from the Earth. So the rock and the Earth
• 13:50
  Speaker 3: are now like parting ways and going in opposite directions.
• 13:53
  Speaker 1: M yeah, I guess that's what I meant. It's like,
• 13:55
  Speaker 1: if I jump, I'm going to fall back down onto
• 13:58
  Speaker 1: the Earth unless I jump super duper high. But I'm
• 14:01
  Speaker 1: not that fit, I guess. But if I jump, but
• 14:04
  Speaker 1: the Earth pulls me back and then it sort of
• 14:06
  Speaker 1: recovers right, Like, as it's pulling me back down into Earth,
• 14:09
  Speaker 1: it's also moving a little bit towards me exactly.
• 14:12
  Speaker 3: You come back together, and so there's no effective change.
• 14:14
  Speaker 3: That's why I was talking about Elon Musk instead of
• 14:16
  Speaker 3: you and your ripped thighs jumping off the surface. You know,
• 14:19
  Speaker 3: if Elon Musk launches a rocket away from the Earth,
• 14:22
  Speaker 3: then it really is giving the Earth a push. Now,
• 14:25
  Speaker 3: if that rocket ends up in orbit, then it isn't
• 14:27
  Speaker 3: because it's still in the Earth's gravitational system. But if
• 14:30
  Speaker 3: he launches a rocket to Mars or a to deep
• 14:32
  Speaker 3: space or something like that, so it really leaves the
• 14:34
  Speaker 3: earth gravitational system, then it's given the Earth a push.
• 14:37
  Speaker 3: And if the Earth was in an unstable situation, like
• 14:40
  Speaker 3: a pencil balanced on its tip, then even a tiny
• 14:43
  Speaker 3: push would knock it out of orbit.
• 14:45
  Speaker 1: Yeah, I guess maybe an analogy is that sort of
• 14:47
  Speaker 1: like tossing a coin or like rolling a coin. That's
• 14:51
  Speaker 1: a system that's kind of unstable, right, Like if you
• 14:53
  Speaker 1: tip the coin just a little bit to the right,
• 14:55
  Speaker 1: it's the whole coin is going to veer off to
• 14:57
  Speaker 1: the ride a lot. Or if you tip it a
• 14:59
  Speaker 1: little bit to the left's going to veer off to
• 15:01
  Speaker 1: the left a lot. That's what you mean by sort
• 15:03
  Speaker 1: of unstable kind of sitting on the edge of something.
• 15:06
  Speaker 3: Mm hmm exactly. Or imagine you have a ball in
• 15:09
  Speaker 3: a glass, right, you shake the glass a little bit,
• 15:12
  Speaker 3: the ball moves from the bottom of the glass, but
• 15:13
  Speaker 3: it comes back to where it was. When it deviates
• 15:16
  Speaker 3: from its preferred location, there are forces to push it
• 15:19
  Speaker 3: back to where it was. Or if you have the
• 15:20
  Speaker 3: situation upside down, like ball balance on the top of
• 15:24
  Speaker 3: a hill, for example, if it's precariously balanced there and
• 15:26
  Speaker 3: you give it a push, then the forces are going
• 15:28
  Speaker 3: to pull it away from that configuration place. So another
• 15:31
  Speaker 3: way to think about stability is are there forces that
• 15:34
  Speaker 3: are restoring you back to your original location or are
• 15:37
  Speaker 3: there forces that are pushing you away. So in the
• 15:39
  Speaker 3: stable case, their forces restoring you to where you were,
• 15:42
  Speaker 3: and in the unstable case, their forces pushing you away.
• 15:45
  Speaker 1: Right, I guess it's kind of what you mean by
• 15:47
  Speaker 1: basing a pencil, or like if you take a long
• 15:50
  Speaker 1: rod or stick and you try to bous it on
• 15:52
  Speaker 1: the palm of your hand, like there is a way
• 15:54
  Speaker 1: for you to like move your hand around a lot
• 15:57
  Speaker 1: and not have this stick fall over. But that's sort
• 16:00
  Speaker 1: of an unstable situation, Like if you deviate a little
• 16:03
  Speaker 1: bit from that path, then the stick will fall exactly.
• 16:05
  Speaker 3: And in physics we call that equilibrium. Right, there is
• 16:08
  Speaker 3: a configuration for the stick to be balanced, for all
• 16:10
  Speaker 3: the forces to be equal, and for it to just
• 16:13
  Speaker 3: stay there, but it would be unstable. Like a tiny
• 16:15
  Speaker 3: fly lands on it pushes it in one direction. Now
• 16:18
  Speaker 3: the forces are going to keep it going in that
• 16:20
  Speaker 3: direction rather than pushing it back. Whereas if you have
• 16:23
  Speaker 3: a ball and a glass and a fly lands on
• 16:25
  Speaker 3: it and pushes it a tiny little bit up the glass,
• 16:28
  Speaker 3: the glass is going to return it back to the
• 16:29
  Speaker 3: equilibrium location. So you can have stable and unstable equilibrium.
• 16:34
  Speaker 3: And the difference really is whether you have forces pushing
• 16:36
  Speaker 3: you back towards the equilibrium or away.
• 16:38
  Speaker 1: From it, right, And so that's what we're talking about
• 16:40
  Speaker 1: here for the Earth, I mean, we're going around the
• 16:42
  Speaker 1: Sun in a circle or a semicircle sort of a circle,
• 16:46
  Speaker 1: and it seems stable, but it could be an unstable orbit,
• 16:49
  Speaker 1: meaning like we're going around this path and we just
• 16:51
  Speaker 1: got lucky to get into this groove.
• 16:53
  Speaker 4: But if we actually sort of step.
• 16:55
  Speaker 1: Away from the groove or fall a little bit to
• 16:58
  Speaker 1: the one side, then maybe it'll take us into a
• 17:00
  Speaker 1: completely different orbit or even away from the Solar System
• 17:03
  Speaker 1: or into the Sun.
• 17:03
  Speaker 3: I guess yeah, And you might be worried like that
• 17:06
  Speaker 3: if you jump too high you're going to push the
• 17:08
  Speaker 3: Earth out of orbit, because if you imagine that the
• 17:10
  Speaker 3: Earth like DV it's a little bit towards the Sun,
• 17:13
  Speaker 3: gravity gets stronger and it pulls on it harder. So
• 17:16
  Speaker 3: you might worry that, like if you jump on the
• 17:18
  Speaker 3: wrong side of the Earth, you could actually push the
• 17:20
  Speaker 3: Earth into the Sun like a fly toppling that balanced
• 17:23
  Speaker 3: pole on your hand.
• 17:24
  Speaker 1: Although I guess it would depend on which way you jump,
• 17:26
  Speaker 1: like you just said, like if I jump in the direct,
• 17:29
  Speaker 1: like if I jump off of the North pole, maybe
• 17:31
  Speaker 1: I'll just move the orbit up and down a little bit.
• 17:33
  Speaker 3: Right, Yeah, exactly.
• 17:36
  Speaker 1: Or if I jump sort of like trailing the Earth
• 17:39
  Speaker 1: in the direction where a bit behind the Earth, I
• 17:42
  Speaker 1: guess then I will give it a little boost. Or
• 17:44
  Speaker 1: if I jump in the front, I'll slow down to
• 17:46
  Speaker 1: Earth a little bit mm hm.
• 17:48
  Speaker 3: Or if you have a friend on the other side
• 17:49
  Speaker 3: of the Earth and you time your jumps together, then
• 17:51
  Speaker 3: it doesn't matter, right, So really this question is about
• 17:54
  Speaker 3: can you do exercise whenever you like, or do you
• 17:56
  Speaker 3: need to coordinate it with the rest of humanity.
• 17:58
  Speaker 4: That's right?
• 17:59
  Speaker 1: Or do we have any friends? All right, So that's
• 18:03
  Speaker 1: what stability means for an orbit and for our planet.
• 18:06
  Speaker 1: And now let's get into whether or not it is
• 18:09
  Speaker 1: a stable orbit or if it's a precariously balanced orbit
• 18:12
  Speaker 1: and we are just here at a sheer luck. But
• 18:15
  Speaker 1: first let's take a quick break.
• 18:29
  Speaker 4: All right.
• 18:29
  Speaker 1: We're asking the question how stable is the Earth's orbit?
• 18:33
  Speaker 1: And we talk about how we are in orbit around
• 18:35
  Speaker 1: the Sun. Right, the Earth is being pulled by gravity
• 18:39
  Speaker 1: towards the Sun, but we have a certain velocity which
• 18:41
  Speaker 1: makes the whole planet kind of go around in a circle.
• 18:44
  Speaker 3: Right, Yeah, that's right. We're moving in roughly circles essentially
• 18:47
  Speaker 3: in the lips. But we'll talk about the difference there
• 18:49
  Speaker 3: in a minute. And the question is, like, is the
• 18:51
  Speaker 3: orbit stable If we deviate from this situation a tiny
• 18:54
  Speaker 3: little bit, are we going to spiral into the Sun
• 18:56
  Speaker 3: or drift out into deep space?
• 18:59
  Speaker 1: Which makes you worry, not just for like everyone jumping
• 19:01
  Speaker 1: at the same time, is that going to knock the
• 19:03
  Speaker 1: Earth out of its orbit? But if something else comes
• 19:06
  Speaker 1: out from space and hits us, right.
• 19:08
  Speaker 3: Yeah, exactly, because we are hit all the time on
• 19:11
  Speaker 3: asteroids and meteors. Right, every time you see a meteor shower,
• 19:13
  Speaker 3: those are objects from other places in the Solar System
• 19:17
  Speaker 3: smashing into the Earth's atmosphere. And a minute ago we
• 19:20
  Speaker 3: talked about it in terms of forces. Are there forces
• 19:22
  Speaker 3: restoring you back to your orbit or are there forces
• 19:25
  Speaker 3: pulling you away from your equilibrium? And in this situation,
• 19:28
  Speaker 3: the only relevant force is gravity, right, gravity pulls us
• 19:32
  Speaker 3: towards the Sun. There's no electromagnetic force, there's no weak force,
• 19:36
  Speaker 3: there's no strong force. It's really just gravity here. And
• 19:39
  Speaker 3: so from that simple perspective, you might think, hm, the
• 19:42
  Speaker 3: only force is pushing us inwards. So if we got
• 19:44
  Speaker 3: hit like from just the right angle, like an asteroid
• 19:46
  Speaker 3: falling in from the outer Solar System and pushing us
• 19:49
  Speaker 3: towards the Sun, it might make you worried because the
• 19:52
  Speaker 3: force of gravity would get stronger as you get closer
• 19:54
  Speaker 3: and then pull you harder, plummeting the Earth into the Sun.
• 19:57
  Speaker 3: But it's a little bit more complicated.
• 19:59
  Speaker 1: And also made me think, like, if an asteroid falls
• 20:01
  Speaker 1: to Earth and it gets burned up in the atmosphere,
• 20:05
  Speaker 1: does it actually pushes or does it just get converted
• 20:08
  Speaker 1: into fire and smoke and light.
• 20:11
  Speaker 3: It definitely pushes us. It doesn't matter if it gets
• 20:13
  Speaker 3: burned up or not. It's sort of like a bullet
• 20:15
  Speaker 3: entering your body, right, It's still going to push you back,
• 20:17
  Speaker 3: even if it doesn't leave your body or if it
• 20:19
  Speaker 3: gets shredded inside you. It doesn't really matter whether it
• 20:22
  Speaker 3: turns into heat or not. You absorb the momentum.
• 20:25
  Speaker 1: Of that object, doesn't Some of the energy of an
• 20:27
  Speaker 1: asteroid also like leave maybe as light.
• 20:29
  Speaker 3: Yeah, a little bit, although that actually might have a
• 20:31
  Speaker 3: bigger impact because that's more like the asteroid bouncing off
• 20:34
  Speaker 3: of the Earth, which would be a larger momentum transfer.
• 20:38
  Speaker 1: Or doesn't some of it gets transferred into heat, like
• 20:41
  Speaker 1: it heats up the Earth, But that doesn't necessarily push
• 20:43
  Speaker 1: the Earth, does it.
• 20:43
  Speaker 3: If the Earth totally absorbs it, then it's going to
• 20:46
  Speaker 3: absorb all of its momentum. If it bounces off the atmosphere,
• 20:49
  Speaker 3: then it's going to get twice its momentum because it's
• 20:52
  Speaker 3: changing direction entirely. The way for it to actually minimally
• 20:55
  Speaker 3: affect the Earth would be like passed through the Earth
• 20:58
  Speaker 3: out the other side. To maintain its So if it
• 21:00
  Speaker 3: like grazed the atmosphere somehow, then it wouldn't affect the
• 21:04
  Speaker 3: Earth as much.
• 21:05
  Speaker 1: All right, Well, let's get into the stability of our orbit.
• 21:07
  Speaker 1: Maybe step us through the basics, like what makes an
• 21:10
  Speaker 1: orbit and what would make it stable or unstable?
• 21:13
  Speaker 3: Yeah, so there's only gravity at work here, which is
• 21:15
  Speaker 3: pulling us towards the Sun. And the first you might wonder, like,
• 21:18
  Speaker 3: how do you get equilibrium at all? How is it
• 21:20
  Speaker 3: possible to have an orbit where your radius is basically constant? Again,
• 21:24
  Speaker 3: just thinking about it in terms of circular orbits for now,
• 21:26
  Speaker 3: how is that even possible if all you have is
• 21:28
  Speaker 3: a force towards the center. Well, it's true you only
• 21:31
  Speaker 3: have one force, but it's a little bit more complicated
• 21:33
  Speaker 3: than that. There's another apparent force because we're talking about
• 21:37
  Speaker 3: circular motion, which is not inertial frames. Like there's an
• 21:40
  Speaker 3: acceleration here, then there's an effective force that appears. It's
• 21:43
  Speaker 3: not a fundamental force like gravity or electromagnetism or whatever.
• 21:47
  Speaker 3: The effect of working in a rotating frame of reference
• 21:50
  Speaker 3: the way, for example, if you're on a merry go
• 21:52
  Speaker 3: round and it spins, you feel a force pushing you
• 21:55
  Speaker 3: towards the edge of the merry go round. It's not gravity,
• 21:58
  Speaker 3: it's not an electromagnetism. It's an effective force due to
• 22:02
  Speaker 3: the rotation.
• 22:02
  Speaker 1: Right, It's not like a real force. It's more like
• 22:05
  Speaker 1: you feel like something is pushing you towards the middle
• 22:07
  Speaker 1: of the merry go round. But really it's just a
• 22:08
  Speaker 1: merry go around trying to make you go in a circle.
• 22:11
  Speaker 3: Right, Yeah, exactly, And so there really are two effective
• 22:14
  Speaker 3: forces to consider there. There's gravity pulling you in and
• 22:17
  Speaker 3: then there's this centripetal force pushing you out. So there
• 22:20
  Speaker 3: is the possibility to have a balance there. That's where
• 22:22
  Speaker 3: the equilibrium comes from. When those two things balance, then
• 22:25
  Speaker 3: you have an orbit. When the force of gravity pulling
• 22:27
  Speaker 3: in and the centripetal force pushing out balance, then you
• 22:31
  Speaker 3: have circular motion. So that's why you can have an
• 22:33
  Speaker 3: equilibrium at all. But equilibrium doesn't necessarily mean it's stable.
• 22:37
  Speaker 3: You can have stable or unstable equilibria. Like the example
• 22:41
  Speaker 3: of a pole balancing in your hand. All the forces
• 22:43
  Speaker 3: are balanced there, but as soon as you deviate from it,
• 22:46
  Speaker 3: it falls over, whereas a ball and a cup is
• 22:48
  Speaker 3: it's stable equilibrium because the forces are restoring. So now
• 22:51
  Speaker 3: we understand why the Earth can be an equilibrium in
• 22:53
  Speaker 3: an orbit, but we still have to answer the question
• 22:55
  Speaker 3: of whether that's stable or unstable.
• 22:57
  Speaker 1: Yeah, I guess I've always thought about it as like,
• 23:00
  Speaker 1: say I'm flying through space and I have a velocity
• 23:03
  Speaker 1: vector pointing in front of me. I'm going forward, and
• 23:06
  Speaker 1: the sun is too exactly to my right. Now, the
• 23:09
  Speaker 1: Sun is pulling me towards the right, but it's sort
• 23:12
  Speaker 1: of not affecting my velocity that I have going forward
• 23:16
  Speaker 1: because it's pulling me per pendicular to that velocity. So
• 23:19
  Speaker 1: it's going to kind of change the direction my velocity,
• 23:21
  Speaker 1: but it's not going to slow me down or speed
• 23:23
  Speaker 1: me up. And if you keep doing that, it traces
• 23:26
  Speaker 1: out a circle.
• 23:27
  Speaker 3: Right, Yeah, that's right. There's a couple of things going
• 23:29
  Speaker 3: on there. You have the constant total velocity, right, your
• 23:32
  Speaker 3: overall velocity, the overall magnitude of your velocity doesn't change,
• 23:36
  Speaker 3: but the direction of it does, and that confuses people sometimes.
• 23:39
  Speaker 3: That still counts as acceleration because you're changing like the
• 23:42
  Speaker 3: different components of your velocity. So moving in a circle,
• 23:46
  Speaker 3: You're right, it doesn't change your overall velocity. That can
• 23:49
  Speaker 3: be constant, but the direction of the velocity changes and
• 23:52
  Speaker 3: that requires acceleration. And that's what the force of gravity
• 23:55
  Speaker 3: is doing. It's changing the direction of your velocity, not
• 23:58
  Speaker 3: the overall value, right.
• 24:00
  Speaker 1: And I think you're saying that an orbit is when
• 24:02
  Speaker 1: that's perfectly balanced, like the force of gravity pushing you
• 24:05
  Speaker 1: towards the Sun. But then also you have enough velocity
• 24:08
  Speaker 1: to kind of resist that motion. That's when you get
• 24:11
  Speaker 1: an orbit, which is a circular kind of path around
• 24:13
  Speaker 1: the Sun. But there are I mean, there are many
• 24:15
  Speaker 1: other paths, right, Like, if I'm near a big object
• 24:17
  Speaker 1: like the Sun, I don't have to fall into an orbit, right,
• 24:19
  Speaker 1: I could just, for example, fall straight into the Sun
• 24:22
  Speaker 1: or spiral into the Sun.
• 24:24
  Speaker 3: Right, mm hmm exactly. There's also parabolic trajectories and hyperbolic trajectories, right.
• 24:28
  Speaker 3: Things that fall in from the outer Solar system can
• 24:31
  Speaker 3: get sling shotted by the Sun and then leave the
• 24:33
  Speaker 3: Solar System. So there's lots of different trajectories around the Sun.
• 24:36
  Speaker 3: This is sort of a very special arrangement. You have
• 24:38
  Speaker 3: the right direction and the right velocity at the right radius,
• 24:42
  Speaker 3: then everything settles in and you can just keep doing it.
• 24:45
  Speaker 1: Right, and it kind of seems lucky that we are
• 24:47
  Speaker 1: stuck in an orbit that does go around in a circle.
• 24:50
  Speaker 1: But that's because that's kind of how what survived the
• 24:53
  Speaker 1: chaos of the Solar system, right, Like, the Solar system
• 24:56
  Speaker 1: probably had a bunch of rocks flying all over the place,
• 24:59
  Speaker 1: and over the millions of years, maybe billions of years,
• 25:02
  Speaker 1: anything that wasn't in an orbit basically fell into the
• 25:05
  Speaker 1: Sun or got thrown out, and so anything that remains
• 25:08
  Speaker 1: after all that time, it should be in an orbit.
• 25:10
  Speaker 3: Right, Yeah, that's right. We only see the things that
• 25:12
  Speaker 3: didn't fall into the sun, and so we see the
• 25:14
  Speaker 3: bits that have the right radius and velocity match. Right,
• 25:18
  Speaker 3: at a given radius, you need a certain velocity to
• 25:20
  Speaker 3: have that orbit work. Or so in another way, if
• 25:23
  Speaker 3: you have a certain velocity, you have to be at
• 25:24
  Speaker 3: a specific radius, so you have to have those pair match.
• 25:27
  Speaker 3: You can't just have an arbitrary velocity and an arbitrary
• 25:31
  Speaker 3: radius and expect to be in an orbit for a
• 25:33
  Speaker 3: given radius. You have to have a very specific velocity
• 25:35
  Speaker 3: to be in an orbit. But that seems like almost impossible, right.
• 25:38
  Speaker 3: It seems like, well, if your velocity has to be
• 25:41
  Speaker 3: exactly some number, then how did anything end up in orbit,
• 25:45
  Speaker 3: because what are the chances that two like real valued
• 25:48
  Speaker 3: numbers exactly match.
• 25:49
  Speaker 1: Each other, right, Like, maybe I wonder if there could
• 25:51
  Speaker 1: have been a planet early in our Solar system's history
• 25:54
  Speaker 1: that there were, you know, flowing around the Sun and
• 25:57
  Speaker 1: they're like, oh, we're in an orbit. This is pretty cool.
• 25:59
  Speaker 1: But it turns out they weren't in a circular orbit.
• 26:01
  Speaker 1: They were in a spiraling orbit exactly.
• 26:03
  Speaker 3: But if you look at the energy dynamics of it,
• 26:05
  Speaker 3: it turns out that these orbits actually are stable, meaning
• 26:09
  Speaker 3: if you don't have exactly the right value, the physics
• 26:12
  Speaker 3: of it tends to push you towards having the right value.
• 26:15
  Speaker 3: Or if you have the right value and somebody gives
• 26:17
  Speaker 3: you a push, or hey jumps off the planet, or
• 26:20
  Speaker 3: an asteroid hits us or Elon Musk launches a super
• 26:22
  Speaker 3: heavy rocket. So we deviate a little bit from having
• 26:25
  Speaker 3: the right pair of velocity and radius, that actually the
• 26:29
  Speaker 3: forces will push us back towards having the right velocity
• 26:32
  Speaker 3: and radius. Turns out that just from a gravitational point
• 26:35
  Speaker 3: of view, using Newtonian physics, these orbits are stable.
• 26:39
  Speaker 1: Wait wait, wait, wait, are you basically answering the question
• 26:41
  Speaker 1: of the episode. So orbits are stable.
• 26:43
  Speaker 3: In the simplified universe that we don't live in, where
• 26:46
  Speaker 3: we have only one planet and the only thing happening
• 26:48
  Speaker 3: is Newton's gravity, then yes, these orbits are stable. But
• 26:51
  Speaker 3: of course there's lots of other things going on. The
• 26:53
  Speaker 3: Sun is losing its mass, the Earth feels the solar wind, etc. Etc.
• 26:57
  Speaker 3: There are other planets hugging on us, so it's a
• 26:59
  Speaker 3: little bit more complicated. But in the simplified view of
• 27:02
  Speaker 3: just a single planet orbiting a star, then yes, those
• 27:05
  Speaker 3: orbits are stable.
• 27:07
  Speaker 1: Oh I see way wait wait, So like if the
• 27:09
  Speaker 1: Solar System only had one planet, us, then no matter
• 27:13
  Speaker 1: what we do, we would be in an orbit.
• 27:15
  Speaker 3: If the Solar System had only one planet and the
• 27:17
  Speaker 3: Sun lasted forever and there was no solar wind and
• 27:20
  Speaker 3: no gravitational radiation and nothing else from outside the Solar
• 27:23
  Speaker 3: System affected us, then yes, we would be in an
• 27:26
  Speaker 3: orbit that would be stable basically forever.
• 27:28
  Speaker 1: But like it has to be one particular orbit, or
• 27:31
  Speaker 1: like let's say we're this single planet around the Sun.
• 27:33
  Speaker 1: There's nobody else, nothing changes in terms of how big
• 27:37
  Speaker 1: it is or what happens to the Sun. Where with
• 27:39
  Speaker 1: one planet in the Solar System, and you know, something
• 27:42
  Speaker 1: comes and knocks it or gives it some boost in
• 27:45
  Speaker 1: one direction, it's going to move out of the orbit
• 27:48
  Speaker 1: we're in. But is it going to then get into
• 27:50
  Speaker 1: another different orbit?
• 27:51
  Speaker 3: It depends a lot on how it gets hit. If
• 27:53
  Speaker 3: the Earth speeds up a lot, for example, it gets
• 27:55
  Speaker 3: hit from behind, then there's another radius that it needs
• 27:58
  Speaker 3: in order to have a stable orbit. But it's actually
• 28:01
  Speaker 3: likely to slide over into that radius because the energy
• 28:04
  Speaker 3: configuration is stable. If the Earth has too much velocity,
• 28:07
  Speaker 3: then the balance of the forces will tend to push
• 28:09
  Speaker 3: it towards the radius it needs for that velocity. On
• 28:12
  Speaker 3: the other hand, if it gets pushed like from the side,
• 28:14
  Speaker 3: that it gets kicked out a little bit, then it
• 28:17
  Speaker 3: might actually oscillate and move from a circular orbit to
• 28:19
  Speaker 3: an elliptical orbit, which is sort of like a circular orbit,
• 28:22
  Speaker 3: but you're like sloshing back and forth a little bit.
• 28:24
  Speaker 3: There's like a harmonic motion around a circular orbit.
• 28:28
  Speaker 1: So like, let's say I have the Earth and we're
• 28:30
  Speaker 1: the only planet in the Solar System, and I attach
• 28:33
  Speaker 1: some rockets to the back of the Earth and I
• 28:36
  Speaker 1: fire them up. I'm going to speed up is that
• 28:38
  Speaker 1: gonna get me into like an elliptical orbit then around
• 28:40
  Speaker 1: the Sun, or is it going to be like a
• 28:42
  Speaker 1: totally chaotic orbit, Like I feel like the only reason
• 28:46
  Speaker 1: we tend to think of orbits as stable is because.
• 28:49
  Speaker 4: They're pretty circular, right, But you can.
• 28:51
  Speaker 1: Also go around the Sun for a long time, going
• 28:54
  Speaker 1: around in like big ellipses, right, Like, you're really far
• 28:57
  Speaker 1: from the Sun, and then you fly towards the some
• 29:00
  Speaker 1: you get really close, but you fly really fast, and
• 29:01
  Speaker 1: then you shoot past the Sun, and then you come
• 29:03
  Speaker 1: back and you do the same thing over and over,
• 29:05
  Speaker 1: and maybe that big ellipse is not always the same.
• 29:08
  Speaker 1: You're sort of going around and around the Sun, but
• 29:10
  Speaker 1: you're still sort of you're not falling into the Sun exactly.
• 29:15
  Speaker 3: That ellipse can also be a stable orbit. It's not circular,
• 29:18
  Speaker 3: but it can be stable, and you can think of
• 29:20
  Speaker 3: it as having two components. You can think of it
• 29:22
  Speaker 3: as a circular orbit plus motion relative to that circular
• 29:26
  Speaker 3: orbit where you're slashing in and out and in and out,
• 29:29
  Speaker 3: and that whole arrangement can be stable. You can be
• 29:31
  Speaker 3: in a circular orbit forever around a star without ever
• 29:35
  Speaker 3: falling in. And the reason is something you just mentioned,
• 29:37
  Speaker 3: which is at your speed and your radius vary. Say
• 29:40
  Speaker 3: somebody comes along and pushes us towards the Sun, for example.
• 29:43
  Speaker 3: So now we fall in a little bit towards the
• 29:45
  Speaker 3: Sun and gravity is getting stronger. But we're now also
• 29:48
  Speaker 3: going to speed up. So when we come around the curve,
• 29:51
  Speaker 3: we're going to be going fast enough to go further
• 29:53
  Speaker 3: out than we used to. That's going to slow us down,
• 29:55
  Speaker 3: and gravity is going to pull on us slowing us down.
• 29:57
  Speaker 3: We're going to use up our energy climbing out of
• 29:59
  Speaker 3: the gravitational well, and then we're going to come back
• 30:02
  Speaker 3: and we're going to slosh back and forth around that
• 30:04
  Speaker 3: original circular orbit. That's what I mean when I say
• 30:07
  Speaker 3: that it's stable. There's forces of gravity pulling you back
• 30:09
  Speaker 3: towards it, and then there's this centripetal force effectively pushing
• 30:12
  Speaker 3: you back towards your orbit, and those two forces are
• 30:15
  Speaker 3: encouraging you to stay in that orbit to.
• 30:18
  Speaker 4: Then you elliptical orbit.
• 30:19
  Speaker 1: Right Like if I put some booster rockets on the Earth,
• 30:22
  Speaker 1: it's not gonna maybe make the Earth' spiral land. It's
• 30:25
  Speaker 1: going to make it just it's just going to change
• 30:28
  Speaker 1: the shape of the orbit, or is that true, or
• 30:30
  Speaker 1: is there a possibility for me to fall into the sun.
• 30:32
  Speaker 3: There's a possibility for you to fall into the sun, absolutely,
• 30:34
  Speaker 3: if you push hard enough, right, stability is always approximate.
• 30:37
  Speaker 3: It's always possible to get out of the orbit. If
• 30:39
  Speaker 3: you put in enough energy in that rocket, you can
• 30:40
  Speaker 3: escape the Sun's gravity, or if you turn really really hard,
• 30:44
  Speaker 3: you can drive right into the Sun. But small deviations
• 30:46
  Speaker 3: will return to the stable orbit, to a.
• 30:48
  Speaker 4: Stable orbit, right, not necessarily the one we're in right now.
• 30:51
  Speaker 3: Yeah, that's right, And it might be circular, and it
• 30:53
  Speaker 3: might be elliptical, depends exactly on the kick that you
• 30:56
  Speaker 3: give it. You can also change your circular orbit to
• 30:59
  Speaker 3: another circular orbit, So that's basically an ellipse with zero eccentricity,
• 31:03
  Speaker 3: and so that's a little bit less likely to happen.
• 31:05
  Speaker 3: So if you're in a perfectly circular orbit, I think
• 31:07
  Speaker 3: the most likely thing if you get a kick is
• 31:09
  Speaker 3: to end up in a slightly elliptical orbit.
• 31:11
  Speaker 1: Or if you're in a slightly elliptical orbit, if you
• 31:13
  Speaker 1: get a kick, then you're saying the most likely thing
• 31:16
  Speaker 1: is that they'll just change the shape of that lips right.
• 31:19
  Speaker 1: In my twist urn my turn, it might get rounder
• 31:23
  Speaker 1: or narrower, but will still be in an orbit that
• 31:25
  Speaker 1: the Earth will want to stay in.
• 31:27
  Speaker 3: Yeah, exactly, So there's lots of different stable configurations. Circular
• 31:30
  Speaker 3: orbits are like a special condition of elliptical orbits. Really,
• 31:34
  Speaker 3: circles are like a special kind of ellipse than ellipse
• 31:36
  Speaker 3: with zero eccentricity. So if you think about all orbits
• 31:40
  Speaker 3: as elliptical, and circular ones are like one particular kind
• 31:43
  Speaker 3: of elliptical orbit. But yes, elliptical orbits are a stable.
• 31:46
  Speaker 1: And I think a big reason we're here a lie
• 31:48
  Speaker 1: full of animals and plants around us is that our
• 31:51
  Speaker 1: orbit is pretty circular. Like if you look at a
• 31:53
  Speaker 1: picture of it, you couldn't probably tell that it's not
• 31:56
  Speaker 1: a perfect circle.
• 31:57
  Speaker 3: Yeah, the eccentricity is not huge, and you're right, if
• 31:59
  Speaker 3: it was much greater, we would have more dramatic seasons.
• 32:02
  Speaker 1: Yeah, Like, you know, you think about just how different
• 32:05
  Speaker 1: summer and winter are, and that's just because of our tilt.
• 32:08
  Speaker 1: But like, if our orbit was elliptical and we flew
• 32:12
  Speaker 1: a lot closer to the Sun in some parts of
• 32:14
  Speaker 1: the year, I mean we basically be toast right and
• 32:17
  Speaker 1: we would freeze the other parts of the year.
• 32:19
  Speaker 3: Yeah, that's right. And there are very elliptical orbits that
• 32:21
  Speaker 3: would in principle be stable but would not be survivable.
• 32:24
  Speaker 3: So stable and survivable are not the same thing.
• 32:27
  Speaker 1: So it's not just about the goldilocks soon right, being
• 32:29
  Speaker 1: at the right distance from the Sun. It's also about
• 32:32
  Speaker 1: having a pretty circular orbit, right, so that things are stable.
• 32:35
  Speaker 3: Mm hmm, yeah, that's important.
• 32:36
  Speaker 4: All right.
• 32:37
  Speaker 1: Well, as you said, this stability and this ability to
• 32:40
  Speaker 1: stay in orbit is only good if it's in a
• 32:42
  Speaker 1: perfect universe where we're the only planet in our solar system. Unfortunately,
• 32:46
  Speaker 1: as most kids know, having siblings is kind of a
• 32:49
  Speaker 1: hard thing to deal with. You can really throw your
• 32:51
  Speaker 1: household in this array. So let's get into what could
• 32:55
  Speaker 1: maybe knock us out of our orbit or at least
• 32:58
  Speaker 1: make that orbit unstable, and what we have any control
• 33:01
  Speaker 1: over those things. But first let's take another quick break.
• 33:17
  Speaker 1: All right, we're asking the question how stable is Earth's orbit,
• 33:20
  Speaker 1: and it sounds like in the perfect world, orbits are
• 33:22
  Speaker 1: pretty stable.
• 33:23
  Speaker 3: Yeah. Universes in which you have three directions of space
• 33:26
  Speaker 3: like XYZ have stable gravitational orbits if you have nothing
• 33:30
  Speaker 3: else going on. What's fascinating to think about is that
• 33:33
  Speaker 3: other universes with like two dimensional space or four dimensional
• 33:37
  Speaker 3: space don't actually have the same kind of balance. Is
• 33:40
  Speaker 3: balance you talked about where gravity pulls are you at
• 33:41
  Speaker 3: just the right strength to bend your velocity? That perfect
• 33:44
  Speaker 3: balance only happens in three dimensional space and four D
• 33:48
  Speaker 3: and two D space centrifugal force and gravity both change
• 33:51
  Speaker 3: and they don't balance each other. There aren't stable orbits
• 33:54
  Speaker 3: in two D or four D space.
• 33:56
  Speaker 1: Wait, what like isn't the Earth basically going around a
• 34:00
  Speaker 1: flat ellipse? Aren't we technically in two D?
• 34:03
  Speaker 3: We're not technically in two D because gravity gets dispersed
• 34:05
  Speaker 3: in three dimensions, right, So if there's only two dimensions
• 34:08
  Speaker 3: of space, then the dependence of gravity would be different.
• 34:12
  Speaker 4: Uh.
• 34:12
  Speaker 1: Interesting, All right, Well, as you said, this is only
• 34:14
  Speaker 1: in a perfect world, But we don't live in a
• 34:16
  Speaker 1: perfect world. There are other things in the Solar system
• 34:20
  Speaker 1: that things can change in the Solar system. So let's
• 34:22
  Speaker 1: talk about some of the things that could maybe knock
• 34:25
  Speaker 1: the Earth out of its orbit.
• 34:27
  Speaker 3: So, of course, the Sun is the source of our gravity,
• 34:29
  Speaker 3: and the gravity of the Sun comes from its mass.
• 34:32
  Speaker 3: But the Sun's mass is not actually constant. The way
• 34:35
  Speaker 3: that the Sun lights up our skies and heats up
• 34:37
  Speaker 3: our days is that it burns its fuel. It's converting
• 34:42
  Speaker 3: mass into energy in order to send it to us,
• 34:45
  Speaker 3: and so it's actually dropping its mass, which means the
• 34:48
  Speaker 3: Sun's gravity is actually fading.
• 34:50
  Speaker 4: It's burning up.
• 34:51
  Speaker 3: It is burning up because the fundamental process inside the
• 34:54
  Speaker 3: Sun that produces that light is fusion, which converts mass
• 34:58
  Speaker 3: into energy. Like if you take four protons and you
• 35:01
  Speaker 3: convert them into helium four, which is two protons and
• 35:04
  Speaker 3: two neutrons, they don't have the same amount of mass
• 35:07
  Speaker 3: as those four protons. Remember, mass is not a measure
• 35:11
  Speaker 3: the amount of stuff. It's actually measured the internal stored energy.
• 35:15
  Speaker 3: And that arrangement of all those quirks and a helium
• 35:17
  Speaker 3: four nucleus has less stored energy than four individual protons
• 35:22
  Speaker 3: by aboutzo point seven percent, which means that every time
• 35:25
  Speaker 3: fusion happens, the Sun loses mass.
• 35:28
  Speaker 1: Well, it's basically burning away it's itself, right like it's
• 35:32
  Speaker 1: it's sort of like a log eventually burns down into
• 35:34
  Speaker 1: a pile of ashes.
• 35:35
  Speaker 3: Yeah. No, of course, the Sun is really massive, and
• 35:38
  Speaker 3: even though it burns like four million tons of mass
• 35:42
  Speaker 3: every second, Right, every single second, the Sun loses four
• 35:46
  Speaker 3: million tons of its mass. That energy flies away in
• 35:50
  Speaker 3: photons and in the solar wind. But over the lifetime
• 35:53
  Speaker 3: of the Sun, that only adds up to like the
• 35:55
  Speaker 3: mass of Saturn, which is a tiny, tiny fraction of
• 35:59
  Speaker 3: the mass of the Sun.
• 36:00
  Speaker 1: Wait, over billions of years, the Sun is only going
• 36:03
  Speaker 1: to lose the equivalent of one Saturn' sports of mass.
• 36:07
  Speaker 3: Yeah, that's right.
• 36:08
  Speaker 1: That doesn't seem like a lot. I mean, Saturn is big,
• 36:10
  Speaker 1: but it's tiny compared to the Sun.
• 36:11
  Speaker 3: Yeah, that's right. Saturn is tiny compared to the Sun.
• 36:14
  Speaker 3: But of course it has an effect on the Sun's mass,
• 36:16
  Speaker 3: which has an effect on the Sun's gravity, And so
• 36:19
  Speaker 3: every year the Sun loses enough mass, so the Earth's
• 36:23
  Speaker 3: orbit gets larger by about a centimeter and a half
• 36:26
  Speaker 3: every year because the Sun's gravity is getting weaker.
• 36:29
  Speaker 4: Whoa, every year.
• 36:31
  Speaker 3: Every year we got a centimeter and a half further
• 36:33
  Speaker 3: from the Sun. We're like slowly spiraling out.
• 36:36
  Speaker 4: So is our orbit then it just getting bigger or orbit?
• 36:39
  Speaker 3: Yeah, that's right. Every time the Sun loses mass, there's
• 36:42
  Speaker 3: a new radius where we would have a stable orbit.
• 36:45
  Speaker 3: So if you took like a scoop of stuff out
• 36:47
  Speaker 3: of the Sun. And the Sun lost its mass, the
• 36:49
  Speaker 3: Earth would slide out a little bit into a new
• 36:51
  Speaker 3: stable orbit. And reality is happening on a continuous basis.
• 36:55
  Speaker 3: The Sun is losing its mass and the Earth is
• 36:57
  Speaker 3: sliding out, So at any moment it's in this stable orbit.
• 37:01
  Speaker 3: But the stable orbit is actually changing with time because
• 37:04
  Speaker 3: the Sun is losing mass over time.
• 37:07
  Speaker 1: But I think an average humanity is gaining weight in general, right,
• 37:12
  Speaker 1: So wouldn't that mean that.
• 37:13
  Speaker 4: Our gray stronger. I'm just thinking, like a five year old.
• 37:17
  Speaker 3: Deer, if you eat the Earth, you gain weight, But
• 37:19
  Speaker 3: the U plus Earth system doesn't get any more massive.
• 37:23
  Speaker 1: Although weaight, are we getting energy from the Sun And
• 37:27
  Speaker 1: isn't some of that energy being converted into I don't
• 37:29
  Speaker 1: know things and plants for us to eat.
• 37:32
  Speaker 3: Yeah, that actually does have an effect. All the photons
• 37:35
  Speaker 3: hitting the Earth and all the energy hitting the Earth
• 37:37
  Speaker 3: does have an effect on the Earth, and it actually
• 37:39
  Speaker 3: pushes it. Right, The Earth is like a big solar sail.
• 37:43
  Speaker 3: I remember we talked about how photons can push on
• 37:45
  Speaker 3: things even though they don't have mass, they have momentum
• 37:48
  Speaker 3: and you can like fly a spaceship if you have
• 37:50
  Speaker 3: a huge solar sail which catches those photons. So the
• 37:53
  Speaker 3: Earth is kind of like a big solar sail. And
• 37:56
  Speaker 3: that's another effect we didn't include when we thought about
• 37:58
  Speaker 3: just the simple Newtonian view. So all of photons hitting
• 38:02
  Speaker 3: the Earth do push it a little bit, but the
• 38:04
  Speaker 3: effect is super duper tiny because the Earth is pretty massive.
• 38:07
  Speaker 3: The calculation suggests that over a million years, that increases
• 38:10
  Speaker 3: the Earth's orbital radius by about the width of a proton.
• 38:14
  Speaker 4: Wow, that's tiny.
• 38:15
  Speaker 3: Yeah, that's basically something we can ignore.
• 38:17
  Speaker 1: But I wonder, like we've talked about how, like you know,
• 38:20
  Speaker 1: mass is really just energy, and that concentration of energy
• 38:24
  Speaker 1: is what affects your gravity and how you bend space
• 38:28
  Speaker 1: around them with that energy. So does that mean like
• 38:30
  Speaker 1: the horder the Earth gets, the more gravity we have.
• 38:33
  Speaker 3: Yeah, as the Earth heats up, you have more mass.
• 38:36
  Speaker 3: Like when you put a rock in the sun and
• 38:38
  Speaker 3: it absorbs photons, it doesn't just get hotter. It has
• 38:41
  Speaker 3: more internal stored energy, It has more mass, it has
• 38:44
  Speaker 3: more inertia, it bends space more. The same way like
• 38:48
  Speaker 3: if you take a box of mirrors and you shine
• 38:50
  Speaker 3: a flashlight in it, and then slam it closed. You've
• 38:52
  Speaker 3: trapped those photons inside that box gains mass.
• 38:56
  Speaker 1: Hmmm, interesting, I'm guessing it's not maybe not enough to
• 39:01
  Speaker 1: counteract or to change our orbit around the Sun, or
• 39:04
  Speaker 1: is it?
• 39:05
  Speaker 3: No, that's not enough. The overall effect from the Sun's
• 39:08
  Speaker 3: energy hitting the Earth is to push it to transfer
• 39:10
  Speaker 3: our momentum. But really these effects are totally negligible compared
• 39:14
  Speaker 3: to the Sun losing its mass. This is basically something
• 39:17
  Speaker 3: we can ignore.
• 39:18
  Speaker 1: Although it depends on how hot you make the Earth,
• 39:21
  Speaker 1: doesn't it by if you make it super duper hot,
• 39:23
  Speaker 1: it is going to be heavier.
• 39:24
  Speaker 3: Yeah, that's right, And the Sun actually is getting hotter
• 39:27
  Speaker 3: every year and it's growing. Something else to think about
• 39:30
  Speaker 3: over these very long times is whether the Earth is
• 39:33
  Speaker 3: going to get gobbled by the Sun. Right as the
• 39:35
  Speaker 3: Sun burns its fuel and gets a helium core, then
• 39:39
  Speaker 3: the fusion starts to happen the outer edges and it
• 39:41
  Speaker 3: puffs out and the radius of the Sun grows really,
• 39:44
  Speaker 3: really large. The estimates are that eventually the radius of
• 39:48
  Speaker 3: the Sun will be two hundred times its current radius,
• 39:51
  Speaker 3: which puts it right about where the Earth's orbit is today.
• 39:55
  Speaker 1: Mm, which will be bad news for anyone on Earth
• 39:58
  Speaker 1: at that time, right, it'll be way too hot.
• 40:01
  Speaker 3: It'll be way too hot. Though. It's actually a really
• 40:02
  Speaker 3: interesting and complicated calculation because the Sun gets larger, and
• 40:05
  Speaker 3: it would be very bad for the Earth obviously to
• 40:08
  Speaker 3: get enveloped by the outer layers to the Sun, because
• 40:10
  Speaker 3: not only would it be super hot, but it would
• 40:12
  Speaker 3: drag on us. It would tend to slow us down
• 40:14
  Speaker 3: and then we're very likely to fall into the Sun.
• 40:17
  Speaker 3: But at the same time, the Sun is losing mass,
• 40:20
  Speaker 3: so the Earth is spiraling out as the Sun grows,
• 40:23
  Speaker 3: So it's kind of a close race, like the Earth
• 40:25
  Speaker 3: is drifting away and the Sun is like trying to
• 40:27
  Speaker 3: catch us.
• 40:28
  Speaker 1: Wait, even if the Sun grows, as long as it
• 40:31
  Speaker 1: doesn't grow more than the orbit of the Earth, doesn't
• 40:34
  Speaker 1: it feel the same to the Earth, Like you know,
• 40:36
  Speaker 1: it feels like a point mass.
• 40:38
  Speaker 3: Exactly as long as the Sun is contained within the
• 40:40
  Speaker 3: Earth's orbit, then you're right. It doesn't matter how that's distributed,
• 40:43
  Speaker 3: big or small, a point mass, a black hole, the
• 40:45
  Speaker 3: current Sun, it's all the same gravitationally. But if it
• 40:48
  Speaker 3: does pass the Earth, then any parts of the Sun
• 40:51
  Speaker 3: that are outside of our orbit no longer contribute gravity
• 40:54
  Speaker 3: to pulling on us, and then we feel a drag
• 40:57
  Speaker 3: as because we're flying basically through the Sun's outer at sphere,
• 41:00
  Speaker 3: and that would just kill the stability of our orbit.
• 41:03
  Speaker 1: I feel like if we're flying through the Sun, we
• 41:06
  Speaker 1: have other things to worry about, exactly, or like if
• 41:09
  Speaker 1: we were still if we were still on Earth at
• 41:12
  Speaker 1: that time, it seems like it wouldn't matter if you're
• 41:14
  Speaker 1: going to fall into the Sun or not, like you're
• 41:16
  Speaker 1: already in the Sun.
• 41:16
  Speaker 3: Mm hmm. But because as the Sun gets bigger, it
• 41:20
  Speaker 3: also gets less massive, it's losing its mass. The Earth
• 41:23
  Speaker 3: is going to be sliding away from the Sun as
• 41:26
  Speaker 3: it gets puffy. So the estimates are like the Sun
• 41:28
  Speaker 3: will grow to a few hundred times its current radius
• 41:31
  Speaker 3: and the Earth will drift out to like a little
• 41:33
  Speaker 3: bit further than that. But the calculations are very uncertain,
• 41:36
  Speaker 3: and so it's not clear whether the Earth is going
• 41:38
  Speaker 3: to get engulfed by the outer atmosphere of the Sun
• 41:41
  Speaker 3: or if we're going to like escape that in orbit
• 41:43
  Speaker 3: at a new distance.
• 41:44
  Speaker 1: But I feel like maybe neither of those things is
• 41:47
  Speaker 1: making our orbit unstable, you know what I mean, Like,
• 41:50
  Speaker 1: neither of those things is enough to either make a
• 41:53
  Speaker 1: spiral into the Sun or kick us out of the
• 41:55
  Speaker 1: Solar System.
• 41:55
  Speaker 3: They won't kick us out of the Solar System if
• 41:57
  Speaker 3: we do enter the upper atmosphere of the Sun and
• 42:00
  Speaker 3: the orbit's unstable because the drag is just going to
• 42:02
  Speaker 3: serp all of our energy and it's like a satellite
• 42:04
  Speaker 3: orbiting in low Earth orbit, getting slowed down by the
• 42:07
  Speaker 3: atmosphere and eventually plummeting to Earth.
• 42:09
  Speaker 4: All right, what else can disturb our orbit in space?
• 42:12
  Speaker 3: Well, another big problem are the other planets, Right, It's
• 42:14
  Speaker 3: not just the Earth and the Sun. Jupiter and Saturn
• 42:18
  Speaker 3: are very tiny compared to the Sun, but they're not
• 42:19
  Speaker 3: something we can totally ignore. And the problem is that
• 42:22
  Speaker 3: while two objects can be in very stable orbits for
• 42:25
  Speaker 3: a very long time, three objects are chaotic. We talked
• 42:28
  Speaker 3: about this on our episode about the three body problem.
• 42:31
  Speaker 3: It's not just a cool science fiction novel. It's actually
• 42:33
  Speaker 3: a real thing in physics that three objects have a
• 42:36
  Speaker 3: hard time being stable for long periods of time, and
• 42:40
  Speaker 3: so as Jupiter and Saturn tug on us, they basically
• 42:43
  Speaker 3: disturb our orbit.
• 42:44
  Speaker 1: You sort of like romantic relationships, like two is barely
• 42:49
  Speaker 1: stable but three, that's just asking for trouble.
• 42:51
  Speaker 3: And if they push hard enough where they get lucky
• 42:53
  Speaker 3: or we get unlucky, then they can disturb our orbit
• 42:56
  Speaker 3: in a way that like ejects us from the Solar System.
• 42:59
  Speaker 3: And we think that this is happened. We think that
• 43:00
  Speaker 3: there have been planets in our Solar System which were
• 43:03
  Speaker 3: ejected by Jupiter and Saturn.
• 43:05
  Speaker 1: I guess it's kind of a wonder that it hasn't happened, right, Like,
• 43:08
  Speaker 1: Jupiter is there, Like, we're not just a three body
• 43:11
  Speaker 1: system in our Solar System. We're like a you know,
• 43:14
  Speaker 1: ten or ten million body problem because of all the asteroids.
• 43:18
  Speaker 1: Isn't it kind of a wonder that we are in
• 43:20
  Speaker 1: a stable orbit given everything that's flap flying out there.
• 43:24
  Speaker 3: Yeah, it is kind of amazing that we're left here, right.
• 43:26
  Speaker 3: We think that Jupiter traveled in towards the inner Solar
• 43:29
  Speaker 3: System and then back out. There might have been another
• 43:31
  Speaker 3: gas giant that got ejected. It's sort of amazing that
• 43:34
  Speaker 3: any planets survived that sort of chaotic motion. And especially
• 43:38
  Speaker 3: in the future, we think that as the Sun gets weaker,
• 43:41
  Speaker 3: Jupiter and Saturn's orbits will become more chaotic because they're
• 43:45
  Speaker 3: not going to be as tightly held, and then in
• 43:47
  Speaker 3: turn they will add more chaos to the rest of
• 43:50
  Speaker 3: the Solar System. So in some simulations I looked at,
• 43:53
  Speaker 3: Jupiter ends up being the only planet, like even if
• 43:56
  Speaker 3: the Earth escapes being engulfed by the Sun's atmosphere as
• 43:58
  Speaker 3: it grows, because it acted by Jupiter. And in the
• 44:01
  Speaker 3: long term future, the Solar system is just a big
• 44:03
  Speaker 3: puffy Sun and Jupiter.
• 44:05
  Speaker 1: Mmmm.
• 44:05
  Speaker 4: You see. And this is due to the Sun losing mass.
• 44:08
  Speaker 3: Yeah, the Sun loses mass and so it doesn't pull
• 44:10
  Speaker 3: on Jupiter as hard and it makes Jupiter more chaotic.
• 44:13
  Speaker 4: But again, this is in a few billion years, right.
• 44:15
  Speaker 3: This is in a few billion years exactly. So you
• 44:17
  Speaker 3: should buy your Earth stability insurance now and pay your
• 44:20
  Speaker 3: premiums every single year until then.
• 44:22
  Speaker 4: No, you should wait a few billion years.
• 44:24
  Speaker 6: You know.
• 44:25
  Speaker 1: You know, when something's gonna happen, you should buy it
• 44:27
  Speaker 1: right before it happens. That's how insurance works.
• 44:29
  Speaker 3: We're not gonna be offering this insurance in a billion years.
• 44:31
  Speaker 3: This is your one time offer.
• 44:34
  Speaker 1: To pay us a billion dollars for a billion years.
• 44:37
  Speaker 1: All right, What are some other things that could maybe
• 44:39
  Speaker 1: knock our orbit out of orbit.
• 44:41
  Speaker 3: Well, other sources of chaos are things outside the Solar System, right,
• 44:45
  Speaker 3: Like other stars can pass kind of nearby our Solar
• 44:48
  Speaker 3: system and give it a little kick, like a little perturbation.
• 44:51
  Speaker 3: This already happens, Like other stars come close enough that
• 44:54
  Speaker 3: they can like tweak stuff in the Org cloud, this
• 44:57
  Speaker 3: vast system of trillions of icy objects in the very
• 45:00
  Speaker 3: distant Solar System. Some of them then get knocked in
• 45:03
  Speaker 3: and become comets which burn their way into the Solar
• 45:05
  Speaker 3: System and whip around the Sun. But if other stars
• 45:08
  Speaker 3: come closer, for example, then they could perturb the orbits
• 45:11
  Speaker 3: of planets themselves. Right.
• 45:14
  Speaker 1: Yeah, we had that object, oh we uh right, come
• 45:17
  Speaker 1: through our Solar System from out of space a few
• 45:20
  Speaker 1: years ago.
• 45:21
  Speaker 3: Yeah, that's right. Nobody really knows what.
• 45:23
  Speaker 4: That thing was, or how to pronounce it correctly, or.
• 45:27
  Speaker 3: If it was actually alien space junk. But it's a
• 45:30
  Speaker 3: cool example of how we're not the only things out there. Right,
• 45:32
  Speaker 3: We do bump into stuff from other Solar systems, and
• 45:35
  Speaker 3: the galaxy is chaotic. You know, the stars are all
• 45:37
  Speaker 3: moving in different velocities relative to each other, So we
• 45:40
  Speaker 3: get further and closer to other stars. There's another star
• 45:44
  Speaker 3: called Lease seven to ten, which is expected to pass
• 45:47
  Speaker 3: near our solar system in about a million years, and
• 45:50
  Speaker 3: that could have a gravitational impact on all the orbits.
• 45:53
  Speaker 3: And remember, if it tugs on Jupiter, or Jupiter could
• 45:55
  Speaker 3: then tug on us. It can all become very chaotic
• 45:58
  Speaker 3: very quickly.
• 45:58
  Speaker 1: But I guess stars are easy to see coming, Like
• 46:01
  Speaker 1: you say, we know this one's going to fly by
• 46:03
  Speaker 1: in a million years.
• 46:04
  Speaker 3: Yeah, they're easier to see coming. They're harder to do
• 46:06
  Speaker 3: something about. We talked once about building a star sized
• 46:10
  Speaker 3: rocket ship, like flying in the Sun into a different
• 46:12
  Speaker 3: spot in the galaxy to avoid oncoming stars. It might
• 46:15
  Speaker 3: take us a million years to figure that out.
• 46:17
  Speaker 4: Or just wait for the insurance premium to pay us.
• 46:21
  Speaker 3: That's right, Sit back and relax.
• 46:24
  Speaker 1: You're covered all right. Now, what's the last thing that
• 46:27
  Speaker 1: could maybe push us out of orbit?
• 46:28
  Speaker 3: So even if you don't worry about Jupiter, and you
• 46:30
  Speaker 3: assume the Sun is going to be there forever and
• 46:33
  Speaker 3: all sorts of chaotic things are not something to worry about,
• 46:35
  Speaker 3: there's still a gravitational issue. The reason I said that
• 46:38
  Speaker 3: a Newtonian system is stable over long periods of time
• 46:42
  Speaker 3: is that Newtonian gravity ignores gravitational radiation. Anytime you have
• 46:47
  Speaker 3: an object that's accelerating and moving in a circular orbit
• 46:49
  Speaker 3: councils acceleration, it gives off gravitational waves because gravity is
• 46:53
  Speaker 3: not actually a force, it's actually the curvature of space
• 46:56
  Speaker 3: affecting how things move, and when things accelerate, they create
• 46:59
  Speaker 3: ripple in that space. These are gravitational waves. We've seen
• 47:03
  Speaker 3: gravitational waves from orbiting objects like black holes orbiting each
• 47:07
  Speaker 3: other give us those gravitational waves. They radiate away energy,
• 47:11
  Speaker 3: so that means that as the Earth is going around
• 47:13
  Speaker 3: the Sun, it's also generating gravitational waves and losing energy.
• 47:18
  Speaker 3: So in principle, over a very long amount of time,
• 47:20
  Speaker 3: the Earth will radiate away its energy and fall into
• 47:23
  Speaker 3: the Sun.
• 47:24
  Speaker 1: WHOA, but that's not going to happen for a while, right, Yeah.
• 47:27
  Speaker 3: We estimate that it loses about one proton with in
• 47:31
  Speaker 3: radius every thousand years, So if you do the calculation,
• 47:34
  Speaker 3: it's like ten to the twenty six years before the
• 47:37
  Speaker 3: Earth spirals into the Sun, which is about ten quadrillion
• 47:41
  Speaker 3: times the current age of the universe. So yeah, not
• 47:44
  Speaker 3: something to worry about, but in principle, over a very
• 47:47
  Speaker 3: very long times gravitational radiation will cause us to lose
• 47:50
  Speaker 3: our energy and spiral into the Sun.
• 47:52
  Speaker 1: All right, Well, it sounds like the message or the
• 47:54
  Speaker 1: answer to the question is that the Earth's orbit is
• 47:57
  Speaker 1: pretty stable, at least in the sh It sounds like
• 48:02
  Speaker 1: most orbits are stable, and the fact that we are
• 48:05
  Speaker 1: in a stable orbit probably means that we're going to
• 48:08
  Speaker 1: be here for a while. But of course the universe
• 48:11
  Speaker 1: has a lot of surprises, and we are in a
• 48:13
  Speaker 1: sort of chaotic system with other planets in our Solar system,
• 48:16
  Speaker 1: so something could happen in the near future, but it's unlikely.
• 48:21
  Speaker 3: That's right. So in a Newtonian system, in principle, it's stable.
• 48:26
  Speaker 3: An object orbiting the Sun can do that forever, but
• 48:30
  Speaker 3: once you add gravitational radiation for Einsteini and gravity, then
• 48:34
  Speaker 3: eventually it's going to fall into the Sun. And once
• 48:35
  Speaker 3: you add other things in the Solar system, then you
• 48:39
  Speaker 3: add chaos which are going to perturb those orbits. And
• 48:42
  Speaker 3: once you consider the fact that the Sun itself is
• 48:44
  Speaker 3: losing its mass and changing its gravitational pull on the Earth,
• 48:48
  Speaker 3: then over those very long time scales, the Earth's orbit
• 48:51
  Speaker 3: is not stable, but over short time scales, we don't
• 48:53
  Speaker 3: have anything to worry about.
• 48:54
  Speaker 1: So I guess maybe you don't need that insurance after all.
• 48:58
  Speaker 1: So the next time you jump, feel free to jump
• 49:00
  Speaker 1: as high as you can or want. The Earth is
• 49:02
  Speaker 1: gonna stay where it is, going around the sun, and
• 49:05
  Speaker 1: the sun will rise tomorrow most likely. All right, Well,
• 49:08
  Speaker 1: we hope you enjoyed that. Thanks for joining us, see
• 49:12
  Speaker 1: you next time.
• 49:20
  Speaker 3: Thanks for listening, and remember that Daniel and Jorge explain
• 49:23
  Speaker 3: the Universe is a production of iHeartRadio. For more podcasts
• 49:27
  Speaker 3: from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever
• 49:32
  Speaker 3: you listen to your favorite shows.