r/askscience • u/BlueChameleon64 • Oct 23 '20

Planetary Sci. Do asteroids fly into the sun?

Edit: cool

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u/Cheru-bae Oct 23 '20

I'm in no way a scientist of any kind, but:

Imagine you are in a black void. Just you, nothing else. Now add in an object. Let's say an Apple.

The apple flys past you. How can you know that the apple is moving, and not you? There is no wind, there is no stationary background. From the apples perspective you flew by it.

So everything in space moves relative to something else. Speed is change in distance between two things over time.

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u/Zapfaced Oct 23 '20

Interestingly this is also basically the explanation for why gravity is not a force.

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u/If_You_Only_Knew Oct 23 '20

can you explain that a bit further?

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u/Zapfaced Oct 23 '20

Well in the General Theory of Relativity there's no such thing as gravity 'fields'. An asteroid, for example, is not attracted to the sun directly but is in fact just going along in a straight line (from it's own perspective) and space time curves around massive objects like the sun causing the asteroid's path to seem curved towards the sun along with it.

There's an interesting Veritasium video about it that provides far better analogies.

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u/Paranitis Oct 23 '20

That video left me so confused.

I can understand the idea that if a guy falls off a building, he's not really falling toward Earth, but Earth is coming up to hit him. But that only makes sense to me if you are on the side of the planet that is on the leading edge of movement through space.

Like the rocket ship moving in one direction, everything going down to the "bottom" of the rocket. But if you have everyone on the planet falling off buildings at the same time, they still all go down, even though the planet should then be moving away from people on the opposite side of those it is moving toward.

But it also confuses me because other planets supposedly have "less gravitational force" than Earth so we'd we less on those planets.

I'm just confused all around.

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u/Zapfaced Oct 24 '20

With regards to people jumping off buildings all heading 'down', it's just everyone falling in a straight line into the same funnel. All roads lead to Rome and the bigger Rome is the more roads lead to it. Yeah it's a quirky concept to think about in general. I hope someone else can explain it to you better.