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Speaker 1: Hey, Daniel, did you see the reason launch at tempt

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Speaker 1: by SpaceX.

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Speaker 2: Oh?

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Speaker 3: Yeah, I did. That massive rocket with so many engines attached.

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Speaker 3: Really awesome to watch.

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Speaker 4: Yeah, I hear.

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Speaker 1: The fireworks were great. It really popped. But the whole

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Speaker 1: thing kind of has me worried a little bit.

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

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Speaker 1: A little bit? I mean I live in my house.

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Speaker 1: That would be a problem. No, But I guess I'm

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Speaker 1: more worried about the effect it has on the Earth

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Speaker 1: than all those engines in the rocket also push on

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Speaker 1: the Earth.

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Speaker 3: Yeah. I guess it's kind of like putting a rocket

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Speaker 3: engine on the Earth itself.

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Speaker 1: A little bit, right, So we're letting elon Musk steer

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Speaker 1: our planet.

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Speaker 4: I mean, you can't even steer Twitter.

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Speaker 3: It would be pretty cool if a planet had a

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Speaker 3: steering wheel. I guess that'd be fun.

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Speaker 1: I would probably fall asleep, so maybe I shouldn't be

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Speaker 1: driving the Earth.

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Speaker 4: It probably flies into the sun.

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Speaker 5: Hi.

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

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Speaker 3: Hi I'm Daniel. I'm a particle physicist and a professor

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Speaker 3: at UC Irvine, and I don't want to fly into

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Speaker 3: the Sun.

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

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Speaker 3: I guess I want to look into the Sun. Of

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Speaker 3: all the verbs, I think that's the least destructive one.

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Speaker 4: I like hearing about the Sun and feeling the Sun.

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Speaker 2: I don't know.

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Speaker 4: I don't know if I want to look at it.

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Speaker 4: It isn't that dangerous.

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Speaker 3: I want us to build new scientific eyeballs that let

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Speaker 3: us peer into the Sun and understand the chaotic churning

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Speaker 3: inside of it.

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Speaker 4: You want to peer into the Sun?

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Speaker 3: Yeah, exactly, yes, I consider the Sun to be our

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Speaker 3: peer in the Solar system.

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

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Speaker 3: No, I'm saying we're ever accused of breaking a law

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Speaker 3: of physic that I want a jury of our peers,

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Speaker 3: which I guess would include the Sun.

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Speaker 1: M and who else? Who else do you consider your

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Speaker 1: peers in the cosmos?

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

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Speaker 1: Yeah, he would be a massive help on the jury.

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Speaker 1: But anyways, Welcome to our podcast, Daniel and Jorge Explain

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Speaker 1: the Universe, a production of iHeart Radio.

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Speaker 3: In which we try to thread the needle of understanding

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Speaker 3: the entire universe without pissing it off too much. We

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Speaker 3: try to pay attention to what's going on out there

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Speaker 3: in the universe, from the tiny little particles to the

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Speaker 3: very massive objects swirling around each other, to try to

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Speaker 3: deduce the laws that this universe follows as it moves

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Speaker 3: forward through time towards its eventual end, whatever that may be.

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Speaker 3: And we hope that before that end comes, we can

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Speaker 3: figure out how it all works.

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Speaker 1: That's right, because it is a massively cool universe, fools,

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Speaker 1: amazing and incredible laws and mechanism that seem to make

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Speaker 1: the whole thing work like a giant clock, it seems,

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Speaker 1: going around and around, taking away till the end of time.

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Speaker 3: A clock makes it seem like very organized and stable.

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Speaker 3: I see it more like a really complicated Rube Goldberg machine,

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Speaker 3: you know, like ball rolls down a wheel and hits

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Speaker 3: this lever which makes the cat jump, and then that

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Speaker 3: knocks something else over. Sometimes it feels like the mechanisms

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Speaker 3: on which our entire existence are based are very precarious.

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Speaker 1: Like it knocks a ball, the ball rolls sound a

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Speaker 1: ramp and then outcomes humans, and out of those humans,

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Speaker 1: one of them bumps into another, and you and I

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Speaker 1: are born, and this podcast is born exactly.

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Speaker 3: It seems like it could have gone a lot of

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Speaker 3: different ways, and in many of those ways we wouldn't

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Speaker 3: be here. So in some respects our existence here seems very,

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Speaker 3: very fortunate, and I wonder sometimes about the future of

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Speaker 3: our existence here. How long these special cozy conditions will continue.

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Speaker 1: I know, I feel pretty inevitable. I feel like r

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Speaker 1: cham was meant to be.

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Speaker 3: You feel like the whole project of the universe was

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Speaker 3: to bring you into existence?

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Speaker 1: Why not at least my universe now. I don't know

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Speaker 1: if my kids feel the same way. Over my spouse.

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Speaker 1: I'm an unfortunate byproduct. Sometimes it seems.

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Speaker 3: Well one of the joys of understanding the universe is

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Speaker 3: being able to predict its future, taking those laws of

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Speaker 3: physics that describe what we have seen and also applying

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Speaker 3: them to the future, and thinking what's going to happen,

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Speaker 3: what's likely to happen in the next one hundred years,

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Speaker 3: million years, or billion.

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Speaker 1: Years, m or the next hour. I mean, I don't

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Speaker 1: know where this conversation is going.

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Speaker 3: To be honest, the podcast does seem kind of unpredictable.

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Speaker 3: Doesn't seem to matter too much what I write any outline.

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Speaker 1: Well, I think that's what happens when you put two

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Speaker 1: unstable people and try to create a stable system here.

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Speaker 1: But it is kind of an interesting question how precarious

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Speaker 1: our existence is and how likely it was that we

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Speaker 1: are here in this place talking about the universe. It

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Speaker 1: seems like the universe kind of could go either way

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Speaker 1: at any moment.

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Speaker 3: Mm hmmm. And there's lots of ways that things could

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Speaker 3: go south for us. But on the podcast a few

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Speaker 3: times we've talked about one in particular, which is the

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Speaker 3: requirement that the Earth stay in orbit around the Sun

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Speaker 3: at just the right distance to keep water nice and

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Speaker 3: toasty on our surface but without bubbling it into steam

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Speaker 3: or dropping it into a deep freeze.

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Speaker 1: Yeah, the Earth is and what's called the Goldilock zone

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Speaker 1: of our solar system, where it's not too hot and

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Speaker 1: not too cold, which makes it just right for life

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Speaker 1: to flourish on it and for vicious birds, animals, and

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Speaker 1: humans which I guess are also animals for them to

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Speaker 1: come about.

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Speaker 3: So you might wonder how long this Goldilock situation can

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Speaker 3: continue before the bears come home and ask for their

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Speaker 3: porridge back, so to.

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Speaker 1: Be On the podcast, we'll be asking the question, how

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Speaker 1: stable is the Earth's orbit? Never thought about the stability

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Speaker 1: of our planet's orbit. I guess it seems so predictable

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Speaker 1: and regular, right, I mean, nobody questions whether the sun

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Speaker 1: will rise in the morning every day.

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Speaker 4: We just assume it is.

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Speaker 3: It's one of these really fun questions where the answer

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Speaker 3: depends a lot on the time frame your imagining. Nobody

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Speaker 3: suspects that the Earth will fall out of its orbit

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Speaker 3: tomorrow or next year, or in one hundred years, and

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Speaker 3: on the kind of time scales the humans are used

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Speaker 3: to thinking about. The Solar System is kind of static.

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Speaker 3: We imagine it's looked the same way for one hundred years,

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Speaker 3: a thousand years, probably a million years. But when you

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Speaker 3: look on longer time scales, hundreds of millions of years

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Speaker 3: or billions of years, you see the Solar System is

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Speaker 3: actually quite chaotic. Planets have been lost, they've changed their orbit,

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Speaker 3: they've moved from the outer Solar System to the Inner

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Speaker 3: Solar System and back. All sorts of crazy stuff has happened.

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Speaker 3: So then you can ask, like, well, how long will

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Speaker 3: this phase of our Solar system last?

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Speaker 1: Yeah, I guess the Solar system was just a giant

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Speaker 1: cloud of dust and gas at someone, right, and then

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Speaker 1: the Sun form, and then the planet's form. But even

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Speaker 1: after the planet's form, the Solar System kind of had

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Speaker 1: to find its groove kind of right, it's rhythm, it's orbits.

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Speaker 1: Things will crash into each other a lot before settling

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Speaker 1: into planets.

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Speaker 3: Right, Yeah, that's exactly right. And you look at the

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Speaker 3: surface of anything in the Solar System, like the Moon,

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Speaker 3: and you'll see lots of evidence for collisions. Basically, anything

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Speaker 3: that's out there is getting smacked into all the time.

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Speaker 3: The Earth doesn't have a surface filled with craters because

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Speaker 3: we have an atmosphere that mostly burns those things up

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Speaker 3: before they hit the ground, but of course sometimes they don't.

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Speaker 3: Sixty five million years ago or so, something really big

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Speaker 3: hit the Earth, and billions of years before that, the

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Speaker 3: Moon was formed in an even more giant collision.

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

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Speaker 3: And if we look at Jupiter, for example, there's a

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Speaker 3: lot of evidence that Jupiter and Saturn migrated to the

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Speaker 3: inner Solar System and then turned around and went back out,

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Speaker 3: returning to the depths of the outer Solar System. So

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Speaker 3: planetary orbits are not as fixed as you might imagine.

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Speaker 1: At least some large time scales. As you were saying, well,

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Speaker 1: as usually, we were wondering how many people out there

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Speaker 1: had thought about this question, about the stability of our orbit,

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Speaker 1: about how steady the Solar system is. So, as usual,

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Speaker 1: Daniel went out there into the Internet to ask people

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Speaker 1: how stable is the Earth's orbit.

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Speaker 3: I'm eternally grateful to everybody who answers these questions. If

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Speaker 3: you want to be part of this segment, please don't

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Speaker 3: be shy. Just write to me to question at Danielandjorge

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Speaker 3: dot com.

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Speaker 1: So think about it for a second. How stable do

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Speaker 1: you think our orbit is? Here's what people had to say.

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Speaker 6: So I would say that the Earth orbit is very

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Speaker 6: stable millions or maybe even billions of years. But perhaps

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Speaker 6: when the Sun turns into a ridge giant and expands,

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Speaker 6: maybe that will change things and throw that we're further

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Speaker 6: or closer.

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Speaker 7: In Well, I think earth orbit is quite stable, but

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Speaker 7: we are slowly drifting away from the Sun because of

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Speaker 7: the Moon, and we might get hit by asteroids in

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Speaker 7: the future. But otherwise I think the Earth's orbit is stable.

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

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Speaker 6: I think it looks pretty stable to us, because the

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Speaker 6: time scale of.

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Speaker 3: The universe, of the Solar System is pretty long.

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Speaker 6: I would say it's like a metastable state, and maybe

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Speaker 6: even an asteroid could kick the Earth out of orbit.

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Speaker 3: It's more like a castle of cards. Remove one and

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Speaker 3: everything falls apart.

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Speaker 4: It seems pretty stable to me.

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Speaker 8: If Hummans had long enough to you will, so hopefully

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Speaker 8: it'll hang in there a bit longer.

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Speaker 9: I know from your podcast about when stars collide that

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Speaker 9: any object that's accelerating gives off gravitational waves because of

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Speaker 9: its acceleration. So fundamentally the orbit is not stable, and

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Speaker 9: although it will take a really really long time, eventually

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Speaker 9: the Earth's orbit will fall into the Sun.

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Speaker 8: I think the Earth's orbit is very stable. I have

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Speaker 8: heard about studies that talk about Jupiter moving around in

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Speaker 8: the ancient Solar System, and studies of sensitivity of mercury

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Speaker 8: and Venus to subtle perturbations. But I just think that

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Speaker 8: the Earth's orbit is very stable.

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Speaker 1: I think it's stickaying just like you know might expect

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Speaker 1: it to, but you know, not going into the Sun

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Speaker 1: anytime soon.

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Speaker 2: I think the Earth's orbit about the Sun is very stable,

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Speaker 2: at least over the timeframes that we're concerned with long

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Speaker 2: term millions or billions of years. There might be some

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Speaker 2: drift in its position relative to the Sun, just like

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Speaker 2: there's some drift of the Moon relative to the Earth

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Speaker 2: over time.

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Speaker 5: I think it's bruey stable in a human time scale,

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Speaker 5: but on the long term I think that either gravity

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Speaker 5: or angular momentum will be more revalent.

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Speaker 1: All right, it seems like most people think it's kind

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Speaker 1: of stable. Only a few dissenters.

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Speaker 3: Not a lot of people worried about this out there,

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Speaker 3: although maybe they got more worried after they read this question.

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Speaker 4: Maybe they should be more worried.

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Speaker 1: That's what we're here for, to make people think about

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Speaker 1: all the different ways that the universe can kill them.

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Speaker 3: Mmm. Maybe we should be selling Earth orbit insurance somehow.

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Speaker 4: There you go.

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Speaker 3: If the Earth plunges into the Sun, we will pay

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Speaker 3: you any arbitrary amount of money.

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Speaker 1: A bazillion dollars exactly. Just give us a million dollars

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Speaker 1: a year.

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Speaker 3: That's right, submit request of this po box.

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Speaker 1: But yeah, it's kind of an interesting question. How stable

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Speaker 1: is the Earth's orbit? Because I guess we're going around

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Speaker 1: the Sun pretty steadily, right, is our orbit?

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Speaker 7: Like?

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Speaker 1: Do we always go through the same spot in the

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Speaker 1: Solar system or is our orbit kind of wobbling?

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Speaker 3: Well, our orbit around the Sun is not perfectly circular, right,

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Speaker 3: It's an ellipse, and that ellipse can process a little bit,

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Speaker 3: which means if you imagine an ellipse or like a

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Speaker 3: football or anything oblong, then that orbit itself can rotate. Right,

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Speaker 3: the path of the ellipse itself can rotate.

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Speaker 1: And is that the same for the whole Solar system?

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Speaker 1: Like there, everyone's orbits also kind of rotating.

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Speaker 3: There are some changes in the eccentricity of the Earth's

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Speaker 3: orbit that's deviation from it being circular over like one

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Speaker 3: hundred thousand year timescale, and these things actually can affect

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Speaker 3: like the climate. These are called Milankovich cycles. We talked

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Speaker 3: about it once in the podcast about ice ages. But

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Speaker 3: that doesn't make the Earth's orbit stable or unstable. An

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Speaker 3: elliptical orbit can be stable over very very long time periods.

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Speaker 3: Whether or not your circular or elliptical doesn't change whether

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Speaker 3: or not your stable.

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Speaker 1: M I see the orbit is changing a little bit.

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Speaker 1: But I think maybe what you mean by stable or

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Speaker 1: unstable is whether, like if you move the Earth a

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Speaker 1: little bit, is it gonna go back to its same orbit,

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Speaker 1: or is it gonna spin out of control and like

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Speaker 1: shoot out of the Solar System. That's kind of more

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Speaker 1: what you mean, right.

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Speaker 3: Yeah, my stability. We mean will it return to its

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Speaker 3: current configuration if it's pushed a little bit, Say, for example,

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Speaker 3: you jump. Every time you jump, you are pushing on

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Speaker 3: the Earth. Right, You're using your leg muscles to push

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Speaker 3: yourself away from the Earth, but you're also pushing the

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Speaker 3: Earth away from you. And Newton's laws tell us, you know,

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Speaker 3: every force is an equal and opposite reaction, and so

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Speaker 3: you're moving away from the Earth and the Earth is

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Speaker 3: also moving away from you. Now, of course, because the

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Speaker 3: Earth has so much mass, your push doesn't really affect

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Speaker 3: it as much as it affects yourself. It's sort of

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Speaker 3: like when you fire a rifle. The bullet gets going

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Speaker 3: really really fast, but the rifle itself also has a

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Speaker 3: little bit of recoil, and so when you jump, the

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Speaker 3: Earth recoil a little bit against you. And so if

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Speaker 3: the Earth's orbit is stable, then a little push like

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Speaker 3: that won't like send it spiraling into the Sun, it

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Speaker 3: like drift back to its original orbit. If the Earth

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Speaker 3: is unstable, then it's more like a pencil balancing on

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Speaker 3: its tip. Any tiny little touch will knock it out

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Speaker 3: of its configuration and it won't come back. So stability

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Speaker 3: tells you about whether you come back to your current

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Speaker 3: orbit when you're given a little push.

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Speaker 2: Hmmm.

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Speaker 1: First of all, it's cool that every time I take

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Speaker 1: a step, basically I'm sort of moving to Earth a

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Speaker 1: little bit. Right, every step I take is earth shattering,

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Speaker 1: Earth moving.

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Speaker 3: It sort of is, though. You return to the Earth

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Speaker 3: right and the Earth returns to you, So in the end,

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Speaker 3: the Earth's orbit isn't actually changed by that. To really

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Speaker 3: change the Earth's orbit, you need to like take a

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Speaker 3: rock and throw it into outer space and have it

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Speaker 3: escape from the Earth. So the rock and the Earth

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Speaker 3: are now like parting ways and going in opposite directions.

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Speaker 1: M yeah, I guess that's what I meant. It's like,

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Speaker 1: if I jump, I'm going to fall back down onto

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Speaker 1: the Earth unless I jump super duper high. But I'm

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Speaker 1: not that fit, I guess. But if I jump, but

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Speaker 1: the Earth pulls me back and then it sort of

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Speaker 1: recovers right, Like, as it's pulling me back down into Earth,

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Speaker 1: it's also moving a little bit towards me exactly.

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Speaker 3: You come back together, and so there's no effective change.

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Speaker 3: That's why I was talking about Elon Musk instead of

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Speaker 3: you and your ripped thighs jumping off the surface. You know,

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Speaker 3: if Elon Musk launches a rocket away from the Earth,

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Speaker 3: then it really is giving the Earth a push. Now,

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Speaker 3: if that rocket ends up in orbit, then it isn't

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Speaker 3: because it's still in the Earth's gravitational system. But if

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Speaker 3: he launches a rocket to Mars or a to deep

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Speaker 3: space or something like that, so it really leaves the

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Speaker 3: earth gravitational system, then it's given the Earth a push.

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Speaker 3: And if the Earth was in an unstable situation, like

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Speaker 3: a pencil balanced on its tip, then even a tiny

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Speaker 3: push would knock it out of orbit.

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Speaker 1: Yeah, I guess maybe an analogy is that sort of

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Speaker 1: like tossing a coin or like rolling a coin. That's

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Speaker 1: a system that's kind of unstable, right, Like if you

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Speaker 1: tip the coin just a little bit to the right,

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Speaker 1: it's the whole coin is going to veer off to

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Speaker 1: the ride a lot. Or if you tip it a

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Speaker 1: little bit to the left's going to veer off to

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Speaker 1: the left a lot. That's what you mean by sort

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Speaker 1: of unstable kind of sitting on the edge of something.

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Speaker 3: Mm hmm exactly. Or imagine you have a ball in

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Speaker 3: a glass, right, you shake the glass a little bit,

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Speaker 3: the ball moves from the bottom of the glass, but

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Speaker 3: it comes back to where it was. When it deviates

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Speaker 3: from its preferred location, there are forces to push it

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Speaker 3: back to where it was. Or if you have the

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Speaker 3: situation upside down, like ball balance on the top of

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Speaker 3: a hill, for example, if it's precariously balanced there and

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Speaker 3: you give it a push, then the forces are going

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Speaker 3: to pull it away from that configuration place. So another

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Speaker 3: way to think about stability is are there forces that

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Speaker 3: are restoring you back to your original location or are

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Speaker 3: there forces that are pushing you away. So in the

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Speaker 3: stable case, their forces restoring you to where you were,

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Speaker 3: and in the unstable case, their forces pushing you away.

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Speaker 1: Right, I guess it's kind of what you mean by

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Speaker 1: basing a pencil, or like if you take a long

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Speaker 1: rod or stick and you try to bous it on

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Speaker 1: the palm of your hand, like there is a way

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Speaker 1: for you to like move your hand around a lot

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Speaker 1: and not have this stick fall over. But that's sort

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Speaker 1: of an unstable situation, Like if you deviate a little

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Speaker 1: bit from that path, then the stick will fall exactly.

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Speaker 3: And in physics we call that equilibrium. Right, there is

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Speaker 3: a configuration for the stick to be balanced, for all

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Speaker 3: the forces to be equal, and for it to just

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Speaker 3: stay there, but it would be unstable. Like a tiny

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Speaker 3: fly lands on it pushes it in one direction. Now

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Speaker 3: the forces are going to keep it going in that

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Speaker 3: direction rather than pushing it back. Whereas if you have

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Speaker 3: a ball and a glass and a fly lands on

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Speaker 3: it and pushes it a tiny little bit up the glass,

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Speaker 3: the glass is going to return it back to the

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Speaker 3: equilibrium location. So you can have stable and unstable equilibrium.

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Speaker 3: And the difference really is whether you have forces pushing

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Speaker 3: you back towards the equilibrium or away.

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Speaker 1: From it, right, And so that's what we're talking about

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Speaker 1: here for the Earth, I mean, we're going around the

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Speaker 1: Sun in a circle or a semicircle sort of a circle,

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Speaker 1: and it seems stable, but it could be an unstable orbit,

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Speaker 1: meaning like we're going around this path and we just

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Speaker 1: got lucky to get into this groove.

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Speaker 4: But if we actually sort of step.

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Speaker 1: Away from the groove or fall a little bit to

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Speaker 1: the one side, then maybe it'll take us into a

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Speaker 1: completely different orbit or even away from the Solar System

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Speaker 1: or into the Sun.

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Speaker 3: I guess yeah, And you might be worried like that

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Speaker 3: if you jump too high you're going to push the

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Speaker 3: Earth out of orbit, because if you imagine that the

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Speaker 3: Earth like DV it's a little bit towards the Sun,

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Speaker 3: gravity gets stronger and it pulls on it harder. So

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Speaker 3: you might worry that, like if you jump on the

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Speaker 3: wrong side of the Earth, you could actually push the

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Speaker 3: Earth into the Sun like a fly toppling that balanced

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Speaker 3: pole on your hand.

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Speaker 1: Although I guess it would depend on which way you jump,

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Speaker 1: like you just said, like if I jump in the direct,

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Speaker 1: like if I jump off of the North pole, maybe

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Speaker 1: I'll just move the orbit up and down a little bit.

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Speaker 3: Right, Yeah, exactly.

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Speaker 1: Or if I jump sort of like trailing the Earth

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Speaker 1: in the direction where a bit behind the Earth, I

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Speaker 1: guess then I will give it a little boost. Or

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Speaker 1: if I jump in the front, I'll slow down to

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Speaker 1: Earth a little bit mm hm.

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Speaker 3: Or if you have a friend on the other side

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Speaker 3: of the Earth and you time your jumps together, then

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Speaker 3: it doesn't matter, right, So really this question is about

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Speaker 3: can you do exercise whenever you like, or do you

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Speaker 3: need to coordinate it with the rest of humanity.

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Speaker 4: That's right?

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Speaker 1: Or do we have any friends? All right, So that's

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Speaker 1: what stability means for an orbit and for our planet.

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Speaker 1: And now let's get into whether or not it is

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Speaker 1: a stable orbit or if it's a precariously balanced orbit

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Speaker 1: and we are just here at a sheer luck. But

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Speaker 1: first let's take a quick break.

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Speaker 4: All right.

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Speaker 1: We're asking the question how stable is the Earth's orbit?

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Speaker 1: And we talk about how we are in orbit around

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Speaker 1: the Sun. Right, the Earth is being pulled by gravity

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Speaker 1: towards the Sun, but we have a certain velocity which

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Speaker 1: makes the whole planet kind of go around in a circle.

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Speaker 3: Right, Yeah, that's right. We're moving in roughly circles essentially

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Speaker 3: in the lips. But we'll talk about the difference there

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Speaker 3: in a minute. And the question is, like, is the

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Speaker 3: orbit stable If we deviate from this situation a tiny

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Speaker 3: little bit, are we going to spiral into the Sun

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Speaker 3: or drift out into deep space?

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Speaker 1: Which makes you worry, not just for like everyone jumping

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Speaker 1: at the same time, is that going to knock the

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Speaker 1: Earth out of its orbit? But if something else comes

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Speaker 1: out from space and hits us, right.

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Speaker 3: Yeah, exactly, because we are hit all the time on

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Speaker 3: asteroids and meteors. Right, every time you see a meteor shower,

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Speaker 3: those are objects from other places in the Solar System

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Speaker 3: smashing into the Earth's atmosphere. And a minute ago we

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Speaker 3: talked about it in terms of forces. Are there forces

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Speaker 3: restoring you back to your orbit or are there forces

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Speaker 3: pulling you away from your equilibrium? And in this situation,

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Speaker 3: the only relevant force is gravity, right, gravity pulls us

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Speaker 3: towards the Sun. There's no electromagnetic force, there's no weak force,

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Speaker 3: there's no strong force. It's really just gravity here. And

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Speaker 3: so from that simple perspective, you might think, hm, the

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Speaker 3: only force is pushing us inwards. So if we got

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Speaker 3: hit like from just the right angle, like an asteroid

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Speaker 3: falling in from the outer Solar System and pushing us

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Speaker 3: towards the Sun, it might make you worried because the

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Speaker 3: force of gravity would get stronger as you get closer

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Speaker 3: and then pull you harder, plummeting the Earth into the Sun.

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Speaker 3: But it's a little bit more complicated.

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Speaker 1: And also made me think, like, if an asteroid falls

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Speaker 1: to Earth and it gets burned up in the atmosphere,

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Speaker 1: does it actually pushes or does it just get converted

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Speaker 1: into fire and smoke and light.

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Speaker 3: It definitely pushes us. It doesn't matter if it gets

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Speaker 3: burned up or not. It's sort of like a bullet

444
00:20:15,240 --> 00:20:17,320
Speaker 3: entering your body, right, It's still going to push you back,

445
00:20:17,400 --> 00:20:19,560
Speaker 3: even if it doesn't leave your body or if it

446
00:20:19,560 --> 00:20:22,399
Speaker 3: gets shredded inside you. It doesn't really matter whether it

447
00:20:22,440 --> 00:20:25,440
Speaker 3: turns into heat or not. You absorb the momentum.

448
00:20:25,080 --> 00:20:27,000
Speaker 1: Of that object, doesn't Some of the energy of an

449
00:20:27,040 --> 00:20:29,520
Speaker 1: asteroid also like leave maybe as light.

450
00:20:29,480 --> 00:20:31,320
Speaker 3: Yeah, a little bit, although that actually might have a

451
00:20:31,320 --> 00:20:34,800
Speaker 3: bigger impact because that's more like the asteroid bouncing off

452
00:20:34,840 --> 00:20:38,000
Speaker 3: of the Earth, which would be a larger momentum transfer.

453
00:20:38,359 --> 00:20:41,040
Speaker 1: Or doesn't some of it gets transferred into heat, like

454
00:20:41,080 --> 00:20:43,080
Speaker 1: it heats up the Earth, But that doesn't necessarily push

455
00:20:43,080 --> 00:20:43,719
Speaker 1: the Earth, does it.

456
00:20:43,760 --> 00:20:46,000
Speaker 3: If the Earth totally absorbs it, then it's going to

457
00:20:46,040 --> 00:20:49,240
Speaker 3: absorb all of its momentum. If it bounces off the atmosphere,

458
00:20:49,440 --> 00:20:51,880
Speaker 3: then it's going to get twice its momentum because it's

459
00:20:52,000 --> 00:20:55,159
Speaker 3: changing direction entirely. The way for it to actually minimally

460
00:20:55,200 --> 00:20:57,760
Speaker 3: affect the Earth would be like passed through the Earth

461
00:20:58,119 --> 00:21:00,800
Speaker 3: out the other side. To maintain its So if it

462
00:21:00,920 --> 00:21:04,359
Speaker 3: like grazed the atmosphere somehow, then it wouldn't affect the

463
00:21:04,400 --> 00:21:05,040
Speaker 3: Earth as much.

464
00:21:05,160 --> 00:21:07,680
Speaker 1: All right, Well, let's get into the stability of our orbit.

465
00:21:07,880 --> 00:21:10,560
Speaker 1: Maybe step us through the basics, like what makes an

466
00:21:10,640 --> 00:21:13,359
Speaker 1: orbit and what would make it stable or unstable?

467
00:21:13,560 --> 00:21:15,720
Speaker 3: Yeah, so there's only gravity at work here, which is

468
00:21:15,720 --> 00:21:18,240
Speaker 3: pulling us towards the Sun. And the first you might wonder, like,

469
00:21:18,240 --> 00:21:20,240
Speaker 3: how do you get equilibrium at all? How is it

470
00:21:20,320 --> 00:21:23,920
Speaker 3: possible to have an orbit where your radius is basically constant? Again,

471
00:21:24,040 --> 00:21:26,320
Speaker 3: just thinking about it in terms of circular orbits for now,

472
00:21:26,800 --> 00:21:28,639
Speaker 3: how is that even possible if all you have is

473
00:21:28,680 --> 00:21:31,080
Speaker 3: a force towards the center. Well, it's true you only

474
00:21:31,080 --> 00:21:33,720
Speaker 3: have one force, but it's a little bit more complicated

475
00:21:33,760 --> 00:21:37,160
Speaker 3: than that. There's another apparent force because we're talking about

476
00:21:37,240 --> 00:21:40,280
Speaker 3: circular motion, which is not inertial frames. Like there's an

477
00:21:40,280 --> 00:21:43,720
Speaker 3: acceleration here, then there's an effective force that appears. It's

478
00:21:43,720 --> 00:21:47,399
Speaker 3: not a fundamental force like gravity or electromagnetism or whatever.

479
00:21:47,560 --> 00:21:50,480
Speaker 3: The effect of working in a rotating frame of reference

480
00:21:50,600 --> 00:21:52,080
Speaker 3: the way, for example, if you're on a merry go

481
00:21:52,200 --> 00:21:55,480
Speaker 3: round and it spins, you feel a force pushing you

482
00:21:55,600 --> 00:21:58,600
Speaker 3: towards the edge of the merry go round. It's not gravity,

483
00:21:58,600 --> 00:22:02,000
Speaker 3: it's not an electromagnetism. It's an effective force due to

484
00:22:02,040 --> 00:22:02,640
Speaker 3: the rotation.

485
00:22:02,960 --> 00:22:04,879
Speaker 1: Right, It's not like a real force. It's more like

486
00:22:05,000 --> 00:22:07,040
Speaker 1: you feel like something is pushing you towards the middle

487
00:22:07,080 --> 00:22:08,639
Speaker 1: of the merry go round. But really it's just a

488
00:22:08,680 --> 00:22:11,199
Speaker 1: merry go around trying to make you go in a circle.

489
00:22:11,320 --> 00:22:14,960
Speaker 3: Right, Yeah, exactly, And so there really are two effective

490
00:22:14,960 --> 00:22:17,359
Speaker 3: forces to consider there. There's gravity pulling you in and

491
00:22:17,400 --> 00:22:20,400
Speaker 3: then there's this centripetal force pushing you out. So there

492
00:22:20,520 --> 00:22:22,480
Speaker 3: is the possibility to have a balance there. That's where

493
00:22:22,480 --> 00:22:25,200
Speaker 3: the equilibrium comes from. When those two things balance, then

494
00:22:25,240 --> 00:22:27,840
Speaker 3: you have an orbit. When the force of gravity pulling

495
00:22:27,880 --> 00:22:31,159
Speaker 3: in and the centripetal force pushing out balance, then you

496
00:22:31,280 --> 00:22:33,879
Speaker 3: have circular motion. So that's why you can have an

497
00:22:33,880 --> 00:22:37,560
Speaker 3: equilibrium at all. But equilibrium doesn't necessarily mean it's stable.

498
00:22:37,680 --> 00:22:41,159
Speaker 3: You can have stable or unstable equilibria. Like the example

499
00:22:41,160 --> 00:22:43,320
Speaker 3: of a pole balancing in your hand. All the forces

500
00:22:43,359 --> 00:22:46,400
Speaker 3: are balanced there, but as soon as you deviate from it,

501
00:22:46,400 --> 00:22:48,240
Speaker 3: it falls over, whereas a ball and a cup is

502
00:22:48,240 --> 00:22:51,320
Speaker 3: it's stable equilibrium because the forces are restoring. So now

503
00:22:51,359 --> 00:22:53,879
Speaker 3: we understand why the Earth can be an equilibrium in

504
00:22:53,920 --> 00:22:55,879
Speaker 3: an orbit, but we still have to answer the question

505
00:22:55,920 --> 00:22:57,760
Speaker 3: of whether that's stable or unstable.

506
00:22:57,880 --> 00:22:59,760
Speaker 1: Yeah, I guess I've always thought about it as like,

507
00:23:00,080 --> 00:23:02,720
Speaker 1: say I'm flying through space and I have a velocity

508
00:23:03,200 --> 00:23:06,640
Speaker 1: vector pointing in front of me. I'm going forward, and

509
00:23:06,800 --> 00:23:09,520
Speaker 1: the sun is too exactly to my right. Now, the

510
00:23:09,560 --> 00:23:12,440
Speaker 1: Sun is pulling me towards the right, but it's sort

511
00:23:12,480 --> 00:23:16,080
Speaker 1: of not affecting my velocity that I have going forward

512
00:23:16,359 --> 00:23:19,560
Speaker 1: because it's pulling me per pendicular to that velocity. So

513
00:23:19,600 --> 00:23:21,760
Speaker 1: it's going to kind of change the direction my velocity,

514
00:23:21,760 --> 00:23:23,720
Speaker 1: but it's not going to slow me down or speed

515
00:23:23,760 --> 00:23:26,560
Speaker 1: me up. And if you keep doing that, it traces

516
00:23:26,600 --> 00:23:27,200
Speaker 1: out a circle.

517
00:23:27,320 --> 00:23:29,200
Speaker 3: Right, Yeah, that's right. There's a couple of things going

518
00:23:29,240 --> 00:23:32,240
Speaker 3: on there. You have the constant total velocity, right, your

519
00:23:32,280 --> 00:23:36,040
Speaker 3: overall velocity, the overall magnitude of your velocity doesn't change,

520
00:23:36,160 --> 00:23:39,320
Speaker 3: but the direction of it does, and that confuses people sometimes.

521
00:23:39,400 --> 00:23:42,639
Speaker 3: That still counts as acceleration because you're changing like the

522
00:23:42,680 --> 00:23:46,760
Speaker 3: different components of your velocity. So moving in a circle,

523
00:23:46,800 --> 00:23:49,440
Speaker 3: You're right, it doesn't change your overall velocity. That can

524
00:23:49,480 --> 00:23:52,720
Speaker 3: be constant, but the direction of the velocity changes and

525
00:23:52,760 --> 00:23:55,400
Speaker 3: that requires acceleration. And that's what the force of gravity

526
00:23:55,440 --> 00:23:58,119
Speaker 3: is doing. It's changing the direction of your velocity, not

527
00:23:58,160 --> 00:23:59,879
Speaker 3: the overall value, right.

528
00:24:00,040 --> 00:24:02,080
Speaker 1: And I think you're saying that an orbit is when

529
00:24:02,320 --> 00:24:05,679
Speaker 1: that's perfectly balanced, like the force of gravity pushing you

530
00:24:05,720 --> 00:24:08,320
Speaker 1: towards the Sun. But then also you have enough velocity

531
00:24:08,440 --> 00:24:10,960
Speaker 1: to kind of resist that motion. That's when you get

532
00:24:11,000 --> 00:24:13,960
Speaker 1: an orbit, which is a circular kind of path around

533
00:24:13,960 --> 00:24:15,640
Speaker 1: the Sun. But there are I mean, there are many

534
00:24:15,640 --> 00:24:17,720
Speaker 1: other paths, right, Like, if I'm near a big object

535
00:24:17,800 --> 00:24:19,719
Speaker 1: like the Sun, I don't have to fall into an orbit, right,

536
00:24:19,760 --> 00:24:22,440
Speaker 1: I could just, for example, fall straight into the Sun

537
00:24:22,880 --> 00:24:24,080
Speaker 1: or spiral into the Sun.

538
00:24:24,160 --> 00:24:28,480
Speaker 3: Right, mm hmm exactly. There's also parabolic trajectories and hyperbolic trajectories, right.

539
00:24:28,760 --> 00:24:31,200
Speaker 3: Things that fall in from the outer Solar system can

540
00:24:31,240 --> 00:24:33,199
Speaker 3: get sling shotted by the Sun and then leave the

541
00:24:33,200 --> 00:24:36,240
Speaker 3: Solar System. So there's lots of different trajectories around the Sun.

542
00:24:36,280 --> 00:24:38,720
Speaker 3: This is sort of a very special arrangement. You have

543
00:24:38,760 --> 00:24:42,080
Speaker 3: the right direction and the right velocity at the right radius,

544
00:24:42,400 --> 00:24:45,359
Speaker 3: then everything settles in and you can just keep doing it.

545
00:24:45,359 --> 00:24:47,520
Speaker 1: Right, and it kind of seems lucky that we are

546
00:24:47,560 --> 00:24:50,000
Speaker 1: stuck in an orbit that does go around in a circle.

547
00:24:50,160 --> 00:24:53,280
Speaker 1: But that's because that's kind of how what survived the

548
00:24:53,359 --> 00:24:56,280
Speaker 1: chaos of the Solar system, right, Like, the Solar system

549
00:24:56,280 --> 00:24:58,480
Speaker 1: probably had a bunch of rocks flying all over the place,

550
00:24:59,200 --> 00:25:02,000
Speaker 1: and over the millions of years, maybe billions of years,

551
00:25:02,440 --> 00:25:05,040
Speaker 1: anything that wasn't in an orbit basically fell into the

552
00:25:05,040 --> 00:25:08,159
Speaker 1: Sun or got thrown out, and so anything that remains

553
00:25:08,160 --> 00:25:10,320
Speaker 1: after all that time, it should be in an orbit.

554
00:25:10,400 --> 00:25:12,280
Speaker 3: Right, Yeah, that's right. We only see the things that

555
00:25:12,359 --> 00:25:14,399
Speaker 3: didn't fall into the sun, and so we see the

556
00:25:14,440 --> 00:25:18,160
Speaker 3: bits that have the right radius and velocity match. Right,

557
00:25:18,200 --> 00:25:20,600
Speaker 3: at a given radius, you need a certain velocity to

558
00:25:20,640 --> 00:25:22,960
Speaker 3: have that orbit work. Or so in another way, if

559
00:25:23,040 --> 00:25:24,840
Speaker 3: you have a certain velocity, you have to be at

560
00:25:24,840 --> 00:25:27,880
Speaker 3: a specific radius, so you have to have those pair match.

561
00:25:27,920 --> 00:25:31,080
Speaker 3: You can't just have an arbitrary velocity and an arbitrary

562
00:25:31,160 --> 00:25:33,080
Speaker 3: radius and expect to be in an orbit for a

563
00:25:33,119 --> 00:25:35,520
Speaker 3: given radius. You have to have a very specific velocity

564
00:25:35,600 --> 00:25:38,439
Speaker 3: to be in an orbit. But that seems like almost impossible, right.

565
00:25:38,480 --> 00:25:41,199
Speaker 3: It seems like, well, if your velocity has to be

566
00:25:41,280 --> 00:25:45,359
Speaker 3: exactly some number, then how did anything end up in orbit,

567
00:25:45,400 --> 00:25:48,080
Speaker 3: because what are the chances that two like real valued

568
00:25:48,200 --> 00:25:50,080
Speaker 3: numbers exactly match.

569
00:25:49,880 --> 00:25:51,680
Speaker 1: Each other, right, Like, maybe I wonder if there could

570
00:25:51,680 --> 00:25:54,320
Speaker 1: have been a planet early in our Solar system's history

571
00:25:54,400 --> 00:25:57,159
Speaker 1: that there were, you know, flowing around the Sun and

572
00:25:57,200 --> 00:25:59,080
Speaker 1: they're like, oh, we're in an orbit. This is pretty cool.

573
00:25:59,119 --> 00:26:01,920
Speaker 1: But it turns out they weren't in a circular orbit.

574
00:26:01,960 --> 00:26:03,920
Speaker 1: They were in a spiraling orbit exactly.

575
00:26:03,960 --> 00:26:05,880
Speaker 3: But if you look at the energy dynamics of it,

576
00:26:05,880 --> 00:26:09,040
Speaker 3: it turns out that these orbits actually are stable, meaning

577
00:26:09,119 --> 00:26:12,200
Speaker 3: if you don't have exactly the right value, the physics

578
00:26:12,200 --> 00:26:15,080
Speaker 3: of it tends to push you towards having the right value.

579
00:26:15,280 --> 00:26:17,240
Speaker 3: Or if you have the right value and somebody gives

580
00:26:17,240 --> 00:26:20,040
Speaker 3: you a push, or hey jumps off the planet, or

581
00:26:20,080 --> 00:26:22,640
Speaker 3: an asteroid hits us or Elon Musk launches a super

582
00:26:22,680 --> 00:26:25,440
Speaker 3: heavy rocket. So we deviate a little bit from having

583
00:26:25,560 --> 00:26:29,159
Speaker 3: the right pair of velocity and radius, that actually the

584
00:26:29,240 --> 00:26:32,879
Speaker 3: forces will push us back towards having the right velocity

585
00:26:32,880 --> 00:26:35,680
Speaker 3: and radius. Turns out that just from a gravitational point

586
00:26:35,680 --> 00:26:38,840
Speaker 3: of view, using Newtonian physics, these orbits are stable.

587
00:26:39,480 --> 00:26:41,640
Speaker 1: Wait wait, wait, wait, are you basically answering the question

588
00:26:41,720 --> 00:26:43,879
Speaker 1: of the episode. So orbits are stable.

589
00:26:43,640 --> 00:26:46,320
Speaker 3: In the simplified universe that we don't live in, where

590
00:26:46,320 --> 00:26:48,600
Speaker 3: we have only one planet and the only thing happening

591
00:26:48,640 --> 00:26:51,840
Speaker 3: is Newton's gravity, then yes, these orbits are stable. But

592
00:26:51,880 --> 00:26:53,840
Speaker 3: of course there's lots of other things going on. The

593
00:26:53,880 --> 00:26:57,080
Speaker 3: Sun is losing its mass, the Earth feels the solar wind, etc. Etc.

594
00:26:57,280 --> 00:26:59,600
Speaker 3: There are other planets hugging on us, so it's a

595
00:26:59,600 --> 00:27:02,399
Speaker 3: little bit more complicated. But in the simplified view of

596
00:27:02,480 --> 00:27:05,640
Speaker 3: just a single planet orbiting a star, then yes, those

597
00:27:05,720 --> 00:27:06,680
Speaker 3: orbits are stable.

598
00:27:07,000 --> 00:27:09,399
Speaker 1: Oh I see way wait wait, So like if the

599
00:27:09,440 --> 00:27:13,040
Speaker 1: Solar System only had one planet, us, then no matter

600
00:27:13,080 --> 00:27:14,920
Speaker 1: what we do, we would be in an orbit.

601
00:27:15,080 --> 00:27:17,280
Speaker 3: If the Solar System had only one planet and the

602
00:27:17,320 --> 00:27:20,080
Speaker 3: Sun lasted forever and there was no solar wind and

603
00:27:20,119 --> 00:27:23,720
Speaker 3: no gravitational radiation and nothing else from outside the Solar

604
00:27:23,720 --> 00:27:26,239
Speaker 3: System affected us, then yes, we would be in an

605
00:27:26,320 --> 00:27:28,440
Speaker 3: orbit that would be stable basically forever.

606
00:27:28,640 --> 00:27:31,119
Speaker 1: But like it has to be one particular orbit, or

607
00:27:31,160 --> 00:27:33,720
Speaker 1: like let's say we're this single planet around the Sun.

608
00:27:33,960 --> 00:27:37,520
Speaker 1: There's nobody else, nothing changes in terms of how big

609
00:27:37,560 --> 00:27:39,320
Speaker 1: it is or what happens to the Sun. Where with

610
00:27:39,440 --> 00:27:42,680
Speaker 1: one planet in the Solar System, and you know, something

611
00:27:42,720 --> 00:27:45,639
Speaker 1: comes and knocks it or gives it some boost in

612
00:27:45,680 --> 00:27:48,399
Speaker 1: one direction, it's going to move out of the orbit

613
00:27:48,440 --> 00:27:50,600
Speaker 1: we're in. But is it going to then get into

614
00:27:50,680 --> 00:27:51,800
Speaker 1: another different orbit?

615
00:27:51,880 --> 00:27:53,880
Speaker 3: It depends a lot on how it gets hit. If

616
00:27:53,880 --> 00:27:55,680
Speaker 3: the Earth speeds up a lot, for example, it gets

617
00:27:55,720 --> 00:27:58,880
Speaker 3: hit from behind, then there's another radius that it needs

618
00:27:58,880 --> 00:28:01,159
Speaker 3: in order to have a stable orbit. But it's actually

619
00:28:01,240 --> 00:28:04,359
Speaker 3: likely to slide over into that radius because the energy

620
00:28:04,400 --> 00:28:07,680
Speaker 3: configuration is stable. If the Earth has too much velocity,

621
00:28:07,720 --> 00:28:09,600
Speaker 3: then the balance of the forces will tend to push

622
00:28:09,680 --> 00:28:12,800
Speaker 3: it towards the radius it needs for that velocity. On

623
00:28:12,840 --> 00:28:14,800
Speaker 3: the other hand, if it gets pushed like from the side,

624
00:28:14,840 --> 00:28:16,920
Speaker 3: that it gets kicked out a little bit, then it

625
00:28:17,000 --> 00:28:19,280
Speaker 3: might actually oscillate and move from a circular orbit to

626
00:28:19,280 --> 00:28:22,120
Speaker 3: an elliptical orbit, which is sort of like a circular orbit,

627
00:28:22,160 --> 00:28:24,440
Speaker 3: but you're like sloshing back and forth a little bit.

628
00:28:24,800 --> 00:28:27,720
Speaker 3: There's like a harmonic motion around a circular orbit.

629
00:28:28,480 --> 00:28:30,560
Speaker 1: So like, let's say I have the Earth and we're

630
00:28:30,600 --> 00:28:32,959
Speaker 1: the only planet in the Solar System, and I attach

631
00:28:33,040 --> 00:28:36,439
Speaker 1: some rockets to the back of the Earth and I

632
00:28:36,480 --> 00:28:38,200
Speaker 1: fire them up. I'm going to speed up is that

633
00:28:38,280 --> 00:28:40,840
Speaker 1: gonna get me into like an elliptical orbit then around

634
00:28:40,840 --> 00:28:42,840
Speaker 1: the Sun, or is it going to be like a

635
00:28:42,960 --> 00:28:46,680
Speaker 1: totally chaotic orbit, Like I feel like the only reason

636
00:28:46,720 --> 00:28:49,920
Speaker 1: we tend to think of orbits as stable is because.

637
00:28:49,680 --> 00:28:51,880
Speaker 4: They're pretty circular, right, But you can.

638
00:28:51,840 --> 00:28:54,280
Speaker 1: Also go around the Sun for a long time, going

639
00:28:54,320 --> 00:28:57,680
Speaker 1: around in like big ellipses, right, Like, you're really far

640
00:28:57,720 --> 00:28:59,760
Speaker 1: from the Sun, and then you fly towards the some

641
00:29:00,040 --> 00:29:01,800
Speaker 1: you get really close, but you fly really fast, and

642
00:29:01,800 --> 00:29:03,600
Speaker 1: then you shoot past the Sun, and then you come

643
00:29:03,640 --> 00:29:05,320
Speaker 1: back and you do the same thing over and over,

644
00:29:05,360 --> 00:29:08,440
Speaker 1: and maybe that big ellipse is not always the same.

645
00:29:08,480 --> 00:29:10,800
Speaker 1: You're sort of going around and around the Sun, but

646
00:29:10,840 --> 00:29:15,000
Speaker 1: you're still sort of you're not falling into the Sun exactly.

647
00:29:15,080 --> 00:29:18,280
Speaker 3: That ellipse can also be a stable orbit. It's not circular,

648
00:29:18,360 --> 00:29:20,080
Speaker 3: but it can be stable, and you can think of

649
00:29:20,120 --> 00:29:22,400
Speaker 3: it as having two components. You can think of it

650
00:29:22,400 --> 00:29:26,360
Speaker 3: as a circular orbit plus motion relative to that circular

651
00:29:26,480 --> 00:29:29,080
Speaker 3: orbit where you're slashing in and out and in and out,

652
00:29:29,280 --> 00:29:31,880
Speaker 3: and that whole arrangement can be stable. You can be

653
00:29:31,920 --> 00:29:35,440
Speaker 3: in a circular orbit forever around a star without ever

654
00:29:35,480 --> 00:29:37,720
Speaker 3: falling in. And the reason is something you just mentioned,

655
00:29:37,760 --> 00:29:40,400
Speaker 3: which is at your speed and your radius vary. Say

656
00:29:40,440 --> 00:29:43,360
Speaker 3: somebody comes along and pushes us towards the Sun, for example.

657
00:29:43,600 --> 00:29:45,600
Speaker 3: So now we fall in a little bit towards the

658
00:29:45,640 --> 00:29:48,520
Speaker 3: Sun and gravity is getting stronger. But we're now also

659
00:29:48,600 --> 00:29:51,280
Speaker 3: going to speed up. So when we come around the curve,

660
00:29:51,560 --> 00:29:53,680
Speaker 3: we're going to be going fast enough to go further

661
00:29:53,760 --> 00:29:55,840
Speaker 3: out than we used to. That's going to slow us down,

662
00:29:55,840 --> 00:29:57,800
Speaker 3: and gravity is going to pull on us slowing us down.

663
00:29:57,840 --> 00:29:59,880
Speaker 3: We're going to use up our energy climbing out of

664
00:29:59,880 --> 00:30:02,480
Speaker 3: the gravitational well, and then we're going to come back

665
00:30:02,520 --> 00:30:04,680
Speaker 3: and we're going to slosh back and forth around that

666
00:30:04,760 --> 00:30:07,080
Speaker 3: original circular orbit. That's what I mean when I say

667
00:30:07,080 --> 00:30:09,480
Speaker 3: that it's stable. There's forces of gravity pulling you back

668
00:30:09,520 --> 00:30:12,800
Speaker 3: towards it, and then there's this centripetal force effectively pushing

669
00:30:12,840 --> 00:30:15,800
Speaker 3: you back towards your orbit, and those two forces are

670
00:30:15,920 --> 00:30:18,120
Speaker 3: encouraging you to stay in that orbit to.

671
00:30:18,200 --> 00:30:19,760
Speaker 4: Then you elliptical orbit.

672
00:30:19,880 --> 00:30:22,880
Speaker 1: Right Like if I put some booster rockets on the Earth,

673
00:30:22,920 --> 00:30:25,480
Speaker 1: it's not gonna maybe make the Earth' spiral land. It's

674
00:30:25,520 --> 00:30:28,080
Speaker 1: going to make it just it's just going to change

675
00:30:28,080 --> 00:30:30,200
Speaker 1: the shape of the orbit, or is that true, or

676
00:30:30,280 --> 00:30:32,400
Speaker 1: is there a possibility for me to fall into the sun.

677
00:30:32,440 --> 00:30:34,720
Speaker 3: There's a possibility for you to fall into the sun, absolutely,

678
00:30:34,720 --> 00:30:37,200
Speaker 3: if you push hard enough, right, stability is always approximate.

679
00:30:37,240 --> 00:30:39,120
Speaker 3: It's always possible to get out of the orbit. If

680
00:30:39,160 --> 00:30:40,800
Speaker 3: you put in enough energy in that rocket, you can

681
00:30:40,920 --> 00:30:44,200
Speaker 3: escape the Sun's gravity, or if you turn really really hard,

682
00:30:44,240 --> 00:30:46,880
Speaker 3: you can drive right into the Sun. But small deviations

683
00:30:46,920 --> 00:30:48,960
Speaker 3: will return to the stable orbit, to a.

684
00:30:48,960 --> 00:30:51,800
Speaker 4: Stable orbit, right, not necessarily the one we're in right now.

685
00:30:51,960 --> 00:30:53,560
Speaker 3: Yeah, that's right, And it might be circular, and it

686
00:30:53,640 --> 00:30:56,240
Speaker 3: might be elliptical, depends exactly on the kick that you

687
00:30:56,280 --> 00:30:59,240
Speaker 3: give it. You can also change your circular orbit to

688
00:30:59,280 --> 00:31:03,600
Speaker 3: another circular orbit, So that's basically an ellipse with zero eccentricity,

689
00:31:03,600 --> 00:31:05,640
Speaker 3: and so that's a little bit less likely to happen.

690
00:31:05,720 --> 00:31:07,760
Speaker 3: So if you're in a perfectly circular orbit, I think

691
00:31:07,800 --> 00:31:09,880
Speaker 3: the most likely thing if you get a kick is

692
00:31:09,880 --> 00:31:11,680
Speaker 3: to end up in a slightly elliptical orbit.

693
00:31:11,960 --> 00:31:13,920
Speaker 1: Or if you're in a slightly elliptical orbit, if you

694
00:31:13,960 --> 00:31:16,360
Speaker 1: get a kick, then you're saying the most likely thing

695
00:31:16,440 --> 00:31:19,680
Speaker 1: is that they'll just change the shape of that lips right.

696
00:31:19,760 --> 00:31:22,920
Speaker 1: In my twist urn my turn, it might get rounder

697
00:31:23,000 --> 00:31:25,440
Speaker 1: or narrower, but will still be in an orbit that

698
00:31:25,760 --> 00:31:27,160
Speaker 1: the Earth will want to stay in.

699
00:31:27,400 --> 00:31:30,520
Speaker 3: Yeah, exactly, So there's lots of different stable configurations. Circular

700
00:31:30,600 --> 00:31:34,000
Speaker 3: orbits are like a special condition of elliptical orbits. Really,

701
00:31:34,000 --> 00:31:36,760
Speaker 3: circles are like a special kind of ellipse than ellipse

702
00:31:36,800 --> 00:31:40,240
Speaker 3: with zero eccentricity. So if you think about all orbits

703
00:31:40,240 --> 00:31:43,320
Speaker 3: as elliptical, and circular ones are like one particular kind

704
00:31:43,400 --> 00:31:46,800
Speaker 3: of elliptical orbit. But yes, elliptical orbits are a stable.

705
00:31:46,480 --> 00:31:48,840
Speaker 1: And I think a big reason we're here a lie

706
00:31:48,880 --> 00:31:51,160
Speaker 1: full of animals and plants around us is that our

707
00:31:51,280 --> 00:31:53,680
Speaker 1: orbit is pretty circular. Like if you look at a

708
00:31:53,680 --> 00:31:56,320
Speaker 1: picture of it, you couldn't probably tell that it's not

709
00:31:56,400 --> 00:31:57,160
Speaker 1: a perfect circle.

710
00:31:57,280 --> 00:31:59,520
Speaker 3: Yeah, the eccentricity is not huge, and you're right, if

711
00:31:59,520 --> 00:32:02,360
Speaker 3: it was much greater, we would have more dramatic seasons.

712
00:32:02,800 --> 00:32:05,800
Speaker 1: Yeah, Like, you know, you think about just how different

713
00:32:05,800 --> 00:32:08,240
Speaker 1: summer and winter are, and that's just because of our tilt.

714
00:32:08,560 --> 00:32:11,400
Speaker 1: But like, if our orbit was elliptical and we flew

715
00:32:12,080 --> 00:32:14,520
Speaker 1: a lot closer to the Sun in some parts of

716
00:32:14,560 --> 00:32:17,200
Speaker 1: the year, I mean we basically be toast right and

717
00:32:17,400 --> 00:32:18,880
Speaker 1: we would freeze the other parts of the year.

718
00:32:19,000 --> 00:32:21,480
Speaker 3: Yeah, that's right. And there are very elliptical orbits that

719
00:32:21,560 --> 00:32:24,480
Speaker 3: would in principle be stable but would not be survivable.

720
00:32:24,600 --> 00:32:26,760
Speaker 3: So stable and survivable are not the same thing.

721
00:32:27,040 --> 00:32:29,680
Speaker 1: So it's not just about the goldilocks soon right, being

722
00:32:29,720 --> 00:32:32,320
Speaker 1: at the right distance from the Sun. It's also about

723
00:32:32,360 --> 00:32:35,240
Speaker 1: having a pretty circular orbit, right, so that things are stable.

724
00:32:35,360 --> 00:32:36,680
Speaker 3: Mm hmm, yeah, that's important.

725
00:32:36,840 --> 00:32:37,160
Speaker 4: All right.

726
00:32:37,200 --> 00:32:40,520
Speaker 1: Well, as you said, this stability and this ability to

727
00:32:40,560 --> 00:32:42,680
Speaker 1: stay in orbit is only good if it's in a

728
00:32:42,720 --> 00:32:46,440
Speaker 1: perfect universe where we're the only planet in our solar system. Unfortunately,

729
00:32:46,480 --> 00:32:49,280
Speaker 1: as most kids know, having siblings is kind of a

730
00:32:49,320 --> 00:32:51,480
Speaker 1: hard thing to deal with. You can really throw your

731
00:32:51,560 --> 00:32:55,120
Speaker 1: household in this array. So let's get into what could

732
00:32:55,200 --> 00:32:58,040
Speaker 1: maybe knock us out of our orbit or at least

733
00:32:58,040 --> 00:33:01,160
Speaker 1: make that orbit unstable, and what we have any control

734
00:33:01,200 --> 00:33:04,400
Speaker 1: over those things. But first let's take another quick break.

735
00:33:17,000 --> 00:33:19,840
Speaker 1: All right, we're asking the question how stable is Earth's orbit,

736
00:33:20,000 --> 00:33:22,640
Speaker 1: and it sounds like in the perfect world, orbits are

737
00:33:22,680 --> 00:33:23,280
Speaker 1: pretty stable.

738
00:33:23,400 --> 00:33:26,480
Speaker 3: Yeah. Universes in which you have three directions of space

739
00:33:26,600 --> 00:33:30,959
Speaker 3: like XYZ have stable gravitational orbits if you have nothing

740
00:33:30,960 --> 00:33:33,400
Speaker 3: else going on. What's fascinating to think about is that

741
00:33:33,480 --> 00:33:37,000
Speaker 3: other universes with like two dimensional space or four dimensional

742
00:33:37,040 --> 00:33:39,920
Speaker 3: space don't actually have the same kind of balance. Is

743
00:33:40,000 --> 00:33:41,720
Speaker 3: balance you talked about where gravity pulls are you at

744
00:33:41,800 --> 00:33:44,280
Speaker 3: just the right strength to bend your velocity? That perfect

745
00:33:44,360 --> 00:33:48,000
Speaker 3: balance only happens in three dimensional space and four D

746
00:33:48,120 --> 00:33:51,720
Speaker 3: and two D space centrifugal force and gravity both change

747
00:33:51,800 --> 00:33:54,560
Speaker 3: and they don't balance each other. There aren't stable orbits

748
00:33:54,800 --> 00:33:56,479
Speaker 3: in two D or four D space.

749
00:33:56,840 --> 00:34:00,600
Speaker 1: Wait, what like isn't the Earth basically going around a

750
00:34:00,600 --> 00:34:02,840
Speaker 1: flat ellipse? Aren't we technically in two D?

751
00:34:03,080 --> 00:34:05,680
Speaker 3: We're not technically in two D because gravity gets dispersed

752
00:34:05,720 --> 00:34:08,799
Speaker 3: in three dimensions, right, So if there's only two dimensions

753
00:34:08,840 --> 00:34:11,920
Speaker 3: of space, then the dependence of gravity would be different.

754
00:34:12,160 --> 00:34:12,440
Speaker 4: Uh.

755
00:34:12,520 --> 00:34:14,960
Speaker 1: Interesting, All right, Well, as you said, this is only

756
00:34:14,960 --> 00:34:16,759
Speaker 1: in a perfect world, But we don't live in a

757
00:34:16,760 --> 00:34:19,640
Speaker 1: perfect world. There are other things in the Solar system

758
00:34:20,320 --> 00:34:22,879
Speaker 1: that things can change in the Solar system. So let's

759
00:34:22,960 --> 00:34:25,560
Speaker 1: talk about some of the things that could maybe knock

760
00:34:25,640 --> 00:34:27,120
Speaker 1: the Earth out of its orbit.

761
00:34:27,280 --> 00:34:29,320
Speaker 3: So, of course, the Sun is the source of our gravity,

762
00:34:29,360 --> 00:34:31,880
Speaker 3: and the gravity of the Sun comes from its mass.

763
00:34:32,239 --> 00:34:35,319
Speaker 3: But the Sun's mass is not actually constant. The way

764
00:34:35,360 --> 00:34:37,719
Speaker 3: that the Sun lights up our skies and heats up

765
00:34:37,760 --> 00:34:42,160
Speaker 3: our days is that it burns its fuel. It's converting

766
00:34:42,560 --> 00:34:45,200
Speaker 3: mass into energy in order to send it to us,

767
00:34:45,680 --> 00:34:48,200
Speaker 3: and so it's actually dropping its mass, which means the

768
00:34:48,239 --> 00:34:50,120
Speaker 3: Sun's gravity is actually fading.

769
00:34:50,320 --> 00:34:51,160
Speaker 4: It's burning up.

770
00:34:51,400 --> 00:34:54,600
Speaker 3: It is burning up because the fundamental process inside the

771
00:34:54,640 --> 00:34:58,680
Speaker 3: Sun that produces that light is fusion, which converts mass

772
00:34:58,680 --> 00:35:01,600
Speaker 3: into energy. Like if you take four protons and you

773
00:35:01,680 --> 00:35:04,719
Speaker 3: convert them into helium four, which is two protons and

774
00:35:04,760 --> 00:35:07,800
Speaker 3: two neutrons, they don't have the same amount of mass

775
00:35:07,880 --> 00:35:11,360
Speaker 3: as those four protons. Remember, mass is not a measure

776
00:35:11,360 --> 00:35:15,120
Speaker 3: the amount of stuff. It's actually measured the internal stored energy.

777
00:35:15,200 --> 00:35:17,240
Speaker 3: And that arrangement of all those quirks and a helium

778
00:35:17,239 --> 00:35:21,680
Speaker 3: four nucleus has less stored energy than four individual protons

779
00:35:22,080 --> 00:35:25,319
Speaker 3: by aboutzo point seven percent, which means that every time

780
00:35:25,480 --> 00:35:28,240
Speaker 3: fusion happens, the Sun loses mass.

781
00:35:28,560 --> 00:35:31,920
Speaker 1: Well, it's basically burning away it's itself, right like it's

782
00:35:32,120 --> 00:35:34,759
Speaker 1: it's sort of like a log eventually burns down into

783
00:35:34,800 --> 00:35:35,560
Speaker 1: a pile of ashes.

784
00:35:35,680 --> 00:35:38,239
Speaker 3: Yeah. No, of course, the Sun is really massive, and

785
00:35:38,400 --> 00:35:42,520
Speaker 3: even though it burns like four million tons of mass

786
00:35:42,600 --> 00:35:46,680
Speaker 3: every second, Right, every single second, the Sun loses four

787
00:35:46,880 --> 00:35:50,560
Speaker 3: million tons of its mass. That energy flies away in

788
00:35:50,680 --> 00:35:53,520
Speaker 3: photons and in the solar wind. But over the lifetime

789
00:35:53,560 --> 00:35:55,640
Speaker 3: of the Sun, that only adds up to like the

790
00:35:55,680 --> 00:35:59,239
Speaker 3: mass of Saturn, which is a tiny, tiny fraction of

791
00:35:59,280 --> 00:36:00,280
Speaker 3: the mass of the Sun.

792
00:36:00,520 --> 00:36:03,640
Speaker 1: Wait, over billions of years, the Sun is only going

793
00:36:03,719 --> 00:36:06,880
Speaker 1: to lose the equivalent of one Saturn' sports of mass.

794
00:36:07,160 --> 00:36:08,319
Speaker 3: Yeah, that's right.

795
00:36:08,400 --> 00:36:10,399
Speaker 1: That doesn't seem like a lot. I mean, Saturn is big,

796
00:36:10,400 --> 00:36:11,640
Speaker 1: but it's tiny compared to the Sun.

797
00:36:11,719 --> 00:36:13,919
Speaker 3: Yeah, that's right. Saturn is tiny compared to the Sun.

798
00:36:14,080 --> 00:36:16,560
Speaker 3: But of course it has an effect on the Sun's mass,

799
00:36:16,800 --> 00:36:19,560
Speaker 3: which has an effect on the Sun's gravity, And so

800
00:36:19,719 --> 00:36:23,120
Speaker 3: every year the Sun loses enough mass, so the Earth's

801
00:36:23,200 --> 00:36:26,320
Speaker 3: orbit gets larger by about a centimeter and a half

802
00:36:26,440 --> 00:36:29,400
Speaker 3: every year because the Sun's gravity is getting weaker.

803
00:36:29,520 --> 00:36:31,040
Speaker 4: Whoa, every year.

804
00:36:31,000 --> 00:36:33,480
Speaker 3: Every year we got a centimeter and a half further

805
00:36:33,560 --> 00:36:36,919
Speaker 3: from the Sun. We're like slowly spiraling out.

806
00:36:36,719 --> 00:36:39,640
Speaker 4: So is our orbit then it just getting bigger or orbit?

807
00:36:39,920 --> 00:36:42,399
Speaker 3: Yeah, that's right. Every time the Sun loses mass, there's

808
00:36:42,440 --> 00:36:44,920
Speaker 3: a new radius where we would have a stable orbit.

809
00:36:45,280 --> 00:36:47,160
Speaker 3: So if you took like a scoop of stuff out

810
00:36:47,160 --> 00:36:49,040
Speaker 3: of the Sun. And the Sun lost its mass, the

811
00:36:49,080 --> 00:36:51,839
Speaker 3: Earth would slide out a little bit into a new

812
00:36:51,880 --> 00:36:55,440
Speaker 3: stable orbit. And reality is happening on a continuous basis.

813
00:36:55,600 --> 00:36:57,640
Speaker 3: The Sun is losing its mass and the Earth is

814
00:36:57,680 --> 00:37:00,919
Speaker 3: sliding out, So at any moment it's in this stable orbit.

815
00:37:01,160 --> 00:37:04,200
Speaker 3: But the stable orbit is actually changing with time because

816
00:37:04,200 --> 00:37:06,520
Speaker 3: the Sun is losing mass over time.

817
00:37:07,320 --> 00:37:11,479
Speaker 1: But I think an average humanity is gaining weight in general, right,

818
00:37:12,280 --> 00:37:13,319
Speaker 1: So wouldn't that mean that.

819
00:37:13,360 --> 00:37:17,480
Speaker 4: Our gray stronger. I'm just thinking, like a five year old.

820
00:37:17,360 --> 00:37:19,880
Speaker 3: Deer, if you eat the Earth, you gain weight, But

821
00:37:19,960 --> 00:37:22,760
Speaker 3: the U plus Earth system doesn't get any more massive.

822
00:37:23,760 --> 00:37:26,640
Speaker 1: Although weaight, are we getting energy from the Sun And

823
00:37:27,040 --> 00:37:29,799
Speaker 1: isn't some of that energy being converted into I don't

824
00:37:29,800 --> 00:37:32,080
Speaker 1: know things and plants for us to eat.

825
00:37:32,239 --> 00:37:35,040
Speaker 3: Yeah, that actually does have an effect. All the photons

826
00:37:35,120 --> 00:37:37,560
Speaker 3: hitting the Earth and all the energy hitting the Earth

827
00:37:37,600 --> 00:37:39,840
Speaker 3: does have an effect on the Earth, and it actually

828
00:37:39,880 --> 00:37:43,040
Speaker 3: pushes it. Right, The Earth is like a big solar sail.

829
00:37:43,320 --> 00:37:45,719
Speaker 3: I remember we talked about how photons can push on

830
00:37:45,840 --> 00:37:48,440
Speaker 3: things even though they don't have mass, they have momentum

831
00:37:48,560 --> 00:37:50,640
Speaker 3: and you can like fly a spaceship if you have

832
00:37:50,680 --> 00:37:53,680
Speaker 3: a huge solar sail which catches those photons. So the

833
00:37:53,760 --> 00:37:56,120
Speaker 3: Earth is kind of like a big solar sail. And

834
00:37:56,200 --> 00:37:58,400
Speaker 3: that's another effect we didn't include when we thought about

835
00:37:58,400 --> 00:38:01,960
Speaker 3: just the simple Newtonian view. So all of photons hitting

836
00:38:02,000 --> 00:38:04,000
Speaker 3: the Earth do push it a little bit, but the

837
00:38:04,000 --> 00:38:07,120
Speaker 3: effect is super duper tiny because the Earth is pretty massive.

838
00:38:07,200 --> 00:38:10,640
Speaker 3: The calculation suggests that over a million years, that increases

839
00:38:10,680 --> 00:38:13,840
Speaker 3: the Earth's orbital radius by about the width of a proton.

840
00:38:14,200 --> 00:38:15,360
Speaker 4: Wow, that's tiny.

841
00:38:15,560 --> 00:38:17,600
Speaker 3: Yeah, that's basically something we can ignore.

842
00:38:17,719 --> 00:38:20,600
Speaker 1: But I wonder, like we've talked about how, like you know,

843
00:38:20,680 --> 00:38:24,280
Speaker 1: mass is really just energy, and that concentration of energy

844
00:38:24,400 --> 00:38:28,320
Speaker 1: is what affects your gravity and how you bend space

845
00:38:28,360 --> 00:38:30,239
Speaker 1: around them with that energy. So does that mean like

846
00:38:30,280 --> 00:38:33,440
Speaker 1: the horder the Earth gets, the more gravity we have.

847
00:38:33,719 --> 00:38:36,320
Speaker 3: Yeah, as the Earth heats up, you have more mass.

848
00:38:36,640 --> 00:38:38,200
Speaker 3: Like when you put a rock in the sun and

849
00:38:38,200 --> 00:38:41,160
Speaker 3: it absorbs photons, it doesn't just get hotter. It has

850
00:38:41,200 --> 00:38:43,919
Speaker 3: more internal stored energy, It has more mass, it has

851
00:38:44,040 --> 00:38:48,040
Speaker 3: more inertia, it bends space more. The same way like

852
00:38:48,040 --> 00:38:50,160
Speaker 3: if you take a box of mirrors and you shine

853
00:38:50,160 --> 00:38:52,160
Speaker 3: a flashlight in it, and then slam it closed. You've

854
00:38:52,239 --> 00:38:55,760
Speaker 3: trapped those photons inside that box gains mass.

855
00:38:56,080 --> 00:39:00,840
Speaker 1: Hmmm, interesting, I'm guessing it's not maybe not enough to

856
00:39:01,680 --> 00:39:04,719
Speaker 1: counteract or to change our orbit around the Sun, or

857
00:39:04,760 --> 00:39:05,000
Speaker 1: is it?

858
00:39:05,200 --> 00:39:08,160
Speaker 3: No, that's not enough. The overall effect from the Sun's

859
00:39:08,320 --> 00:39:10,840
Speaker 3: energy hitting the Earth is to push it to transfer

860
00:39:10,880 --> 00:39:14,480
Speaker 3: our momentum. But really these effects are totally negligible compared

861
00:39:14,520 --> 00:39:17,359
Speaker 3: to the Sun losing its mass. This is basically something

862
00:39:17,400 --> 00:39:18,040
Speaker 3: we can ignore.

863
00:39:18,280 --> 00:39:21,240
Speaker 1: Although it depends on how hot you make the Earth,

864
00:39:21,280 --> 00:39:23,319
Speaker 1: doesn't it by if you make it super duper hot,

865
00:39:23,440 --> 00:39:24,600
Speaker 1: it is going to be heavier.

866
00:39:24,760 --> 00:39:27,280
Speaker 3: Yeah, that's right, And the Sun actually is getting hotter

867
00:39:27,440 --> 00:39:30,160
Speaker 3: every year and it's growing. Something else to think about

868
00:39:30,239 --> 00:39:33,600
Speaker 3: over these very long times is whether the Earth is

869
00:39:33,600 --> 00:39:35,560
Speaker 3: going to get gobbled by the Sun. Right as the

870
00:39:35,560 --> 00:39:39,319
Speaker 3: Sun burns its fuel and gets a helium core, then

871
00:39:39,360 --> 00:39:41,560
Speaker 3: the fusion starts to happen the outer edges and it

872
00:39:41,560 --> 00:39:44,680
Speaker 3: puffs out and the radius of the Sun grows really,

873
00:39:44,719 --> 00:39:48,080
Speaker 3: really large. The estimates are that eventually the radius of

874
00:39:48,120 --> 00:39:51,560
Speaker 3: the Sun will be two hundred times its current radius,

875
00:39:51,680 --> 00:39:55,240
Speaker 3: which puts it right about where the Earth's orbit is today.

876
00:39:55,080 --> 00:39:58,919
Speaker 1: Mm, which will be bad news for anyone on Earth

877
00:39:58,960 --> 00:40:01,080
Speaker 1: at that time, right, it'll be way too hot.

878
00:40:01,120 --> 00:40:02,839
Speaker 3: It'll be way too hot. Though. It's actually a really

879
00:40:02,840 --> 00:40:05,840
Speaker 3: interesting and complicated calculation because the Sun gets larger, and

880
00:40:05,880 --> 00:40:08,120
Speaker 3: it would be very bad for the Earth obviously to

881
00:40:08,160 --> 00:40:10,719
Speaker 3: get enveloped by the outer layers to the Sun, because

882
00:40:10,760 --> 00:40:12,799
Speaker 3: not only would it be super hot, but it would

883
00:40:12,880 --> 00:40:14,719
Speaker 3: drag on us. It would tend to slow us down

884
00:40:14,760 --> 00:40:16,760
Speaker 3: and then we're very likely to fall into the Sun.

885
00:40:17,120 --> 00:40:19,840
Speaker 3: But at the same time, the Sun is losing mass,

886
00:40:20,200 --> 00:40:23,320
Speaker 3: so the Earth is spiraling out as the Sun grows,

887
00:40:23,880 --> 00:40:25,759
Speaker 3: So it's kind of a close race, like the Earth

888
00:40:25,800 --> 00:40:27,799
Speaker 3: is drifting away and the Sun is like trying to

889
00:40:27,880 --> 00:40:28,399
Speaker 3: catch us.

890
00:40:28,680 --> 00:40:31,319
Speaker 1: Wait, even if the Sun grows, as long as it

891
00:40:31,320 --> 00:40:34,240
Speaker 1: doesn't grow more than the orbit of the Earth, doesn't

892
00:40:34,280 --> 00:40:36,560
Speaker 1: it feel the same to the Earth, Like you know,

893
00:40:36,600 --> 00:40:38,239
Speaker 1: it feels like a point mass.

894
00:40:38,000 --> 00:40:40,359
Speaker 3: Exactly as long as the Sun is contained within the

895
00:40:40,400 --> 00:40:43,560
Speaker 3: Earth's orbit, then you're right. It doesn't matter how that's distributed,

896
00:40:43,560 --> 00:40:45,719
Speaker 3: big or small, a point mass, a black hole, the

897
00:40:45,760 --> 00:40:48,840
Speaker 3: current Sun, it's all the same gravitationally. But if it

898
00:40:48,840 --> 00:40:51,239
Speaker 3: does pass the Earth, then any parts of the Sun

899
00:40:51,239 --> 00:40:54,360
Speaker 3: that are outside of our orbit no longer contribute gravity

900
00:40:54,440 --> 00:40:57,280
Speaker 3: to pulling on us, and then we feel a drag

901
00:40:57,400 --> 00:41:00,400
Speaker 3: as because we're flying basically through the Sun's outer at sphere,

902
00:41:00,840 --> 00:41:02,959
Speaker 3: and that would just kill the stability of our orbit.

903
00:41:03,560 --> 00:41:06,239
Speaker 1: I feel like if we're flying through the Sun, we

904
00:41:06,320 --> 00:41:09,239
Speaker 1: have other things to worry about, exactly, or like if

905
00:41:09,239 --> 00:41:12,000
Speaker 1: we were still if we were still on Earth at

906
00:41:12,000 --> 00:41:14,319
Speaker 1: that time, it seems like it wouldn't matter if you're

907
00:41:14,360 --> 00:41:16,080
Speaker 1: going to fall into the Sun or not, like you're

908
00:41:16,080 --> 00:41:16,879
Speaker 1: already in the Sun.

909
00:41:16,960 --> 00:41:20,080
Speaker 3: Mm hmm. But because as the Sun gets bigger, it

910
00:41:20,120 --> 00:41:23,640
Speaker 3: also gets less massive, it's losing its mass. The Earth

911
00:41:23,680 --> 00:41:26,000
Speaker 3: is going to be sliding away from the Sun as

912
00:41:26,040 --> 00:41:28,239
Speaker 3: it gets puffy. So the estimates are like the Sun

913
00:41:28,280 --> 00:41:30,920
Speaker 3: will grow to a few hundred times its current radius

914
00:41:31,200 --> 00:41:33,360
Speaker 3: and the Earth will drift out to like a little

915
00:41:33,360 --> 00:41:36,680
Speaker 3: bit further than that. But the calculations are very uncertain,

916
00:41:36,960 --> 00:41:38,880
Speaker 3: and so it's not clear whether the Earth is going

917
00:41:38,960 --> 00:41:41,480
Speaker 3: to get engulfed by the outer atmosphere of the Sun

918
00:41:41,719 --> 00:41:43,640
Speaker 3: or if we're going to like escape that in orbit

919
00:41:43,680 --> 00:41:44,760
Speaker 3: at a new distance.

920
00:41:44,960 --> 00:41:47,719
Speaker 1: But I feel like maybe neither of those things is

921
00:41:47,760 --> 00:41:50,279
Speaker 1: making our orbit unstable, you know what I mean, Like,

922
00:41:50,360 --> 00:41:53,000
Speaker 1: neither of those things is enough to either make a

923
00:41:53,080 --> 00:41:55,000
Speaker 1: spiral into the Sun or kick us out of the

924
00:41:55,000 --> 00:41:55,640
Speaker 1: Solar System.

925
00:41:55,719 --> 00:41:57,680
Speaker 3: They won't kick us out of the Solar System if

926
00:41:57,719 --> 00:42:00,040
Speaker 3: we do enter the upper atmosphere of the Sun and

927
00:42:00,120 --> 00:42:02,160
Speaker 3: the orbit's unstable because the drag is just going to

928
00:42:02,239 --> 00:42:04,360
Speaker 3: serp all of our energy and it's like a satellite

929
00:42:04,480 --> 00:42:07,120
Speaker 3: orbiting in low Earth orbit, getting slowed down by the

930
00:42:07,160 --> 00:42:09,160
Speaker 3: atmosphere and eventually plummeting to Earth.

931
00:42:09,239 --> 00:42:12,080
Speaker 4: All right, what else can disturb our orbit in space?

932
00:42:12,160 --> 00:42:14,799
Speaker 3: Well, another big problem are the other planets, Right, It's

933
00:42:14,840 --> 00:42:17,960
Speaker 3: not just the Earth and the Sun. Jupiter and Saturn

934
00:42:18,040 --> 00:42:19,759
Speaker 3: are very tiny compared to the Sun, but they're not

935
00:42:19,800 --> 00:42:22,680
Speaker 3: something we can totally ignore. And the problem is that

936
00:42:22,760 --> 00:42:25,239
Speaker 3: while two objects can be in very stable orbits for

937
00:42:25,239 --> 00:42:28,960
Speaker 3: a very long time, three objects are chaotic. We talked

938
00:42:28,960 --> 00:42:31,440
Speaker 3: about this on our episode about the three body problem.

939
00:42:31,560 --> 00:42:33,960
Speaker 3: It's not just a cool science fiction novel. It's actually

940
00:42:33,960 --> 00:42:36,520
Speaker 3: a real thing in physics that three objects have a

941
00:42:36,560 --> 00:42:40,200
Speaker 3: hard time being stable for long periods of time, and

942
00:42:40,280 --> 00:42:43,440
Speaker 3: so as Jupiter and Saturn tug on us, they basically

943
00:42:43,480 --> 00:42:44,600
Speaker 3: disturb our orbit.

944
00:42:44,760 --> 00:42:49,280
Speaker 1: You sort of like romantic relationships, like two is barely

945
00:42:49,320 --> 00:42:51,520
Speaker 1: stable but three, that's just asking for trouble.

946
00:42:51,600 --> 00:42:53,400
Speaker 3: And if they push hard enough where they get lucky

947
00:42:53,480 --> 00:42:56,040
Speaker 3: or we get unlucky, then they can disturb our orbit

948
00:42:56,080 --> 00:42:58,720
Speaker 3: in a way that like ejects us from the Solar System.

949
00:42:59,040 --> 00:43:00,799
Speaker 3: And we think that this is happened. We think that

950
00:43:00,840 --> 00:43:03,640
Speaker 3: there have been planets in our Solar System which were

951
00:43:03,680 --> 00:43:05,280
Speaker 3: ejected by Jupiter and Saturn.

952
00:43:05,400 --> 00:43:08,640
Speaker 1: I guess it's kind of a wonder that it hasn't happened, right, Like,

953
00:43:08,920 --> 00:43:11,360
Speaker 1: Jupiter is there, Like, we're not just a three body

954
00:43:11,400 --> 00:43:14,040
Speaker 1: system in our Solar System. We're like a you know,

955
00:43:14,280 --> 00:43:18,719
Speaker 1: ten or ten million body problem because of all the asteroids.

956
00:43:18,800 --> 00:43:20,360
Speaker 1: Isn't it kind of a wonder that we are in

957
00:43:20,400 --> 00:43:24,040
Speaker 1: a stable orbit given everything that's flap flying out there.

958
00:43:24,160 --> 00:43:26,920
Speaker 3: Yeah, it is kind of amazing that we're left here, right.

959
00:43:26,960 --> 00:43:29,480
Speaker 3: We think that Jupiter traveled in towards the inner Solar

960
00:43:29,480 --> 00:43:31,720
Speaker 3: System and then back out. There might have been another

961
00:43:31,760 --> 00:43:34,799
Speaker 3: gas giant that got ejected. It's sort of amazing that

962
00:43:34,880 --> 00:43:38,960
Speaker 3: any planets survived that sort of chaotic motion. And especially

963
00:43:38,960 --> 00:43:41,560
Speaker 3: in the future, we think that as the Sun gets weaker,

964
00:43:41,719 --> 00:43:45,399
Speaker 3: Jupiter and Saturn's orbits will become more chaotic because they're

965
00:43:45,440 --> 00:43:47,600
Speaker 3: not going to be as tightly held, and then in

966
00:43:47,640 --> 00:43:50,360
Speaker 3: turn they will add more chaos to the rest of

967
00:43:50,360 --> 00:43:53,279
Speaker 3: the Solar System. So in some simulations I looked at,

968
00:43:53,480 --> 00:43:56,080
Speaker 3: Jupiter ends up being the only planet, like even if

969
00:43:56,080 --> 00:43:58,839
Speaker 3: the Earth escapes being engulfed by the Sun's atmosphere as

970
00:43:58,840 --> 00:44:01,600
Speaker 3: it grows, because it acted by Jupiter. And in the

971
00:44:01,640 --> 00:44:03,759
Speaker 3: long term future, the Solar system is just a big

972
00:44:03,800 --> 00:44:05,040
Speaker 3: puffy Sun and Jupiter.

973
00:44:05,280 --> 00:44:05,680
Speaker 1: Mmmm.

974
00:44:05,920 --> 00:44:08,080
Speaker 4: You see. And this is due to the Sun losing mass.

975
00:44:08,200 --> 00:44:10,399
Speaker 3: Yeah, the Sun loses mass and so it doesn't pull

976
00:44:10,440 --> 00:44:12,880
Speaker 3: on Jupiter as hard and it makes Jupiter more chaotic.

977
00:44:13,160 --> 00:44:15,600
Speaker 4: But again, this is in a few billion years, right.

978
00:44:15,440 --> 00:44:17,440
Speaker 3: This is in a few billion years exactly. So you

979
00:44:17,440 --> 00:44:20,040
Speaker 3: should buy your Earth stability insurance now and pay your

980
00:44:20,040 --> 00:44:22,200
Speaker 3: premiums every single year until then.

981
00:44:22,360 --> 00:44:23,959
Speaker 4: No, you should wait a few billion years.

982
00:44:24,600 --> 00:44:24,840
Speaker 6: You know.

983
00:44:25,560 --> 00:44:27,200
Speaker 1: You know, when something's gonna happen, you should buy it

984
00:44:27,280 --> 00:44:29,680
Speaker 1: right before it happens. That's how insurance works.

985
00:44:29,880 --> 00:44:31,919
Speaker 3: We're not gonna be offering this insurance in a billion years.

986
00:44:31,920 --> 00:44:33,919
Speaker 3: This is your one time offer.

987
00:44:34,400 --> 00:44:36,760
Speaker 1: To pay us a billion dollars for a billion years.

988
00:44:37,320 --> 00:44:39,080
Speaker 1: All right, What are some other things that could maybe

989
00:44:39,200 --> 00:44:41,000
Speaker 1: knock our orbit out of orbit.

990
00:44:41,160 --> 00:44:45,200
Speaker 3: Well, other sources of chaos are things outside the Solar System, right,

991
00:44:45,280 --> 00:44:48,200
Speaker 3: Like other stars can pass kind of nearby our Solar

992
00:44:48,239 --> 00:44:51,080
Speaker 3: system and give it a little kick, like a little perturbation.

993
00:44:51,440 --> 00:44:54,160
Speaker 3: This already happens, Like other stars come close enough that

994
00:44:54,200 --> 00:44:57,200
Speaker 3: they can like tweak stuff in the Org cloud, this

995
00:44:57,400 --> 00:45:00,600
Speaker 3: vast system of trillions of icy objects in the very

996
00:45:00,600 --> 00:45:03,200
Speaker 3: distant Solar System. Some of them then get knocked in

997
00:45:03,640 --> 00:45:05,919
Speaker 3: and become comets which burn their way into the Solar

998
00:45:05,920 --> 00:45:08,520
Speaker 3: System and whip around the Sun. But if other stars

999
00:45:08,560 --> 00:45:11,680
Speaker 3: come closer, for example, then they could perturb the orbits

1000
00:45:11,680 --> 00:45:14,080
Speaker 3: of planets themselves. Right.

1001
00:45:14,160 --> 00:45:17,520
Speaker 1: Yeah, we had that object, oh we uh right, come

1002
00:45:17,719 --> 00:45:20,759
Speaker 1: through our Solar System from out of space a few

1003
00:45:20,840 --> 00:45:21,200
Speaker 1: years ago.

1004
00:45:21,480 --> 00:45:23,320
Speaker 3: Yeah, that's right. Nobody really knows what.

1005
00:45:23,200 --> 00:45:27,319
Speaker 4: That thing was, or how to pronounce it correctly, or.

1006
00:45:27,239 --> 00:45:30,600
Speaker 3: If it was actually alien space junk. But it's a

1007
00:45:30,640 --> 00:45:32,920
Speaker 3: cool example of how we're not the only things out there. Right,

1008
00:45:32,920 --> 00:45:35,440
Speaker 3: We do bump into stuff from other Solar systems, and

1009
00:45:35,480 --> 00:45:37,759
Speaker 3: the galaxy is chaotic. You know, the stars are all

1010
00:45:37,760 --> 00:45:40,640
Speaker 3: moving in different velocities relative to each other, So we

1011
00:45:40,719 --> 00:45:43,919
Speaker 3: get further and closer to other stars. There's another star

1012
00:45:44,000 --> 00:45:46,920
Speaker 3: called Lease seven to ten, which is expected to pass

1013
00:45:47,040 --> 00:45:50,719
Speaker 3: near our solar system in about a million years, and

1014
00:45:50,840 --> 00:45:53,640
Speaker 3: that could have a gravitational impact on all the orbits.

1015
00:45:53,800 --> 00:45:55,920
Speaker 3: And remember, if it tugs on Jupiter, or Jupiter could

1016
00:45:55,960 --> 00:45:58,280
Speaker 3: then tug on us. It can all become very chaotic

1017
00:45:58,400 --> 00:45:58,920
Speaker 3: very quickly.

1018
00:45:58,960 --> 00:46:01,560
Speaker 1: But I guess stars are easy to see coming, Like

1019
00:46:01,640 --> 00:46:03,600
Speaker 1: you say, we know this one's going to fly by

1020
00:46:03,640 --> 00:46:04,359
Speaker 1: in a million years.

1021
00:46:04,440 --> 00:46:06,359
Speaker 3: Yeah, they're easier to see coming. They're harder to do

1022
00:46:06,400 --> 00:46:10,200
Speaker 3: something about. We talked once about building a star sized

1023
00:46:10,320 --> 00:46:12,280
Speaker 3: rocket ship, like flying in the Sun into a different

1024
00:46:12,280 --> 00:46:15,600
Speaker 3: spot in the galaxy to avoid oncoming stars. It might

1025
00:46:15,600 --> 00:46:17,480
Speaker 3: take us a million years to figure that out.

1026
00:46:17,480 --> 00:46:19,440
Speaker 4: Or just wait for the insurance premium to pay us.

1027
00:46:21,120 --> 00:46:22,920
Speaker 3: That's right, Sit back and relax.

1028
00:46:24,000 --> 00:46:27,239
Speaker 1: You're covered all right. Now, what's the last thing that

1029
00:46:27,280 --> 00:46:28,759
Speaker 1: could maybe push us out of orbit?

1030
00:46:28,840 --> 00:46:30,600
Speaker 3: So even if you don't worry about Jupiter, and you

1031
00:46:30,640 --> 00:46:32,960
Speaker 3: assume the Sun is going to be there forever and

1032
00:46:33,040 --> 00:46:35,400
Speaker 3: all sorts of chaotic things are not something to worry about,

1033
00:46:35,600 --> 00:46:38,799
Speaker 3: there's still a gravitational issue. The reason I said that

1034
00:46:38,840 --> 00:46:42,200
Speaker 3: a Newtonian system is stable over long periods of time

1035
00:46:42,800 --> 00:46:47,000
Speaker 3: is that Newtonian gravity ignores gravitational radiation. Anytime you have

1036
00:46:47,040 --> 00:46:49,640
Speaker 3: an object that's accelerating and moving in a circular orbit

1037
00:46:49,719 --> 00:46:53,920
Speaker 3: councils acceleration, it gives off gravitational waves because gravity is

1038
00:46:53,920 --> 00:46:56,320
Speaker 3: not actually a force, it's actually the curvature of space

1039
00:46:56,360 --> 00:46:59,640
Speaker 3: affecting how things move, and when things accelerate, they create

1040
00:46:59,719 --> 00:47:03,280
Speaker 3: ripple in that space. These are gravitational waves. We've seen

1041
00:47:03,320 --> 00:47:07,439
Speaker 3: gravitational waves from orbiting objects like black holes orbiting each

1042
00:47:07,440 --> 00:47:11,160
Speaker 3: other give us those gravitational waves. They radiate away energy,

1043
00:47:11,280 --> 00:47:13,239
Speaker 3: so that means that as the Earth is going around

1044
00:47:13,280 --> 00:47:17,680
Speaker 3: the Sun, it's also generating gravitational waves and losing energy.

1045
00:47:18,160 --> 00:47:20,640
Speaker 3: So in principle, over a very long amount of time,

1046
00:47:20,680 --> 00:47:23,560
Speaker 3: the Earth will radiate away its energy and fall into

1047
00:47:23,600 --> 00:47:24,000
Speaker 3: the Sun.

1048
00:47:24,280 --> 00:47:27,879
Speaker 1: WHOA, but that's not going to happen for a while, right, Yeah.

1049
00:47:27,920 --> 00:47:30,960
Speaker 3: We estimate that it loses about one proton with in

1050
00:47:31,080 --> 00:47:34,440
Speaker 3: radius every thousand years, So if you do the calculation,

1051
00:47:34,600 --> 00:47:37,640
Speaker 3: it's like ten to the twenty six years before the

1052
00:47:37,680 --> 00:47:41,399
Speaker 3: Earth spirals into the Sun, which is about ten quadrillion

1053
00:47:41,440 --> 00:47:44,200
Speaker 3: times the current age of the universe. So yeah, not

1054
00:47:44,320 --> 00:47:46,960
Speaker 3: something to worry about, but in principle, over a very

1055
00:47:47,040 --> 00:47:50,800
Speaker 3: very long times gravitational radiation will cause us to lose

1056
00:47:50,840 --> 00:47:52,439
Speaker 3: our energy and spiral into the Sun.

1057
00:47:52,719 --> 00:47:54,880
Speaker 1: All right, Well, it sounds like the message or the

1058
00:47:54,880 --> 00:47:57,600
Speaker 1: answer to the question is that the Earth's orbit is

1059
00:47:57,800 --> 00:48:01,719
Speaker 1: pretty stable, at least in the sh It sounds like

1060
00:48:02,080 --> 00:48:05,239
Speaker 1: most orbits are stable, and the fact that we are

1061
00:48:05,239 --> 00:48:08,320
Speaker 1: in a stable orbit probably means that we're going to

1062
00:48:08,360 --> 00:48:10,920
Speaker 1: be here for a while. But of course the universe

1063
00:48:11,000 --> 00:48:13,640
Speaker 1: has a lot of surprises, and we are in a

1064
00:48:13,760 --> 00:48:16,480
Speaker 1: sort of chaotic system with other planets in our Solar system,

1065
00:48:16,560 --> 00:48:20,799
Speaker 1: so something could happen in the near future, but it's unlikely.

1066
00:48:21,320 --> 00:48:26,080
Speaker 3: That's right. So in a Newtonian system, in principle, it's stable.

1067
00:48:26,400 --> 00:48:30,080
Speaker 3: An object orbiting the Sun can do that forever, but

1068
00:48:30,120 --> 00:48:33,960
Speaker 3: once you add gravitational radiation for Einsteini and gravity, then

1069
00:48:34,000 --> 00:48:35,920
Speaker 3: eventually it's going to fall into the Sun. And once

1070
00:48:35,960 --> 00:48:39,000
Speaker 3: you add other things in the Solar system, then you

1071
00:48:39,040 --> 00:48:42,000
Speaker 3: add chaos which are going to perturb those orbits. And

1072
00:48:42,040 --> 00:48:44,520
Speaker 3: once you consider the fact that the Sun itself is

1073
00:48:44,600 --> 00:48:48,160
Speaker 3: losing its mass and changing its gravitational pull on the Earth,

1074
00:48:48,440 --> 00:48:51,040
Speaker 3: then over those very long time scales, the Earth's orbit

1075
00:48:51,120 --> 00:48:53,480
Speaker 3: is not stable, but over short time scales, we don't

1076
00:48:53,480 --> 00:48:54,520
Speaker 3: have anything to worry about.

1077
00:48:54,920 --> 00:48:58,000
Speaker 1: So I guess maybe you don't need that insurance after all.

1078
00:48:58,200 --> 00:49:00,359
Speaker 1: So the next time you jump, feel free to jump

1079
00:49:00,360 --> 00:49:02,600
Speaker 1: as high as you can or want. The Earth is

1080
00:49:02,640 --> 00:49:05,640
Speaker 1: gonna stay where it is, going around the sun, and

1081
00:49:05,719 --> 00:49:08,799
Speaker 1: the sun will rise tomorrow most likely. All right, Well,

1082
00:49:08,800 --> 00:49:12,160
Speaker 1: we hope you enjoyed that. Thanks for joining us, see

1083
00:49:12,160 --> 00:49:12,719
Speaker 1: you next time.

1084
00:49:20,600 --> 00:49:23,400
Speaker 3: Thanks for listening, and remember that Daniel and Jorge explain

1085
00:49:23,440 --> 00:49:27,440
Speaker 3: the Universe is a production of iHeartRadio. For more podcasts

1086
00:49:27,440 --> 00:49:32,120
Speaker 3: from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever

1087
00:49:32,200 --> 00:49:33,920
Speaker 3: you listen to your favorite shows.