Space Fabric Causing Orbits

[antimatter]

I was always tought that all the planets in our solar system were orbiting the sun because of gravity, but after learning a bit more about the fabric of space from a book, I was thinking that maybe the planets are kept in orbit around the sun because of the enormous indent made by the sun's mass. Am I correct?

But if that were true, wouldn't all the planets eventually sort of slide down into the sun like a...flushing toilet...

[ajb]

Time to read up on the basic ideas of general relativity methinks...

[swansont]

Tomato, tomahto, potato, potahto.

[thedarkshade]

But if that were true, wouldn't all the planets eventually sort of slide down into the sun like a...flushing toilet...

It's funny that I thought of that too when I first saw a video that explained why planets move around the sun in orbits, and that this is due to curves that those planets cause in the space time fabric but not really, I remember back from my 7th grade that centripetal and centrifugal forces play a major role in the movements of planets.

[iNow]

antimatter,

 

Don't forget that each of the planets also make their own "indents" in spacetime, and those "indents" need to be considered, as the planets are not going to slide toward the sun as if on some flat smooth surface.

[ydoaPs]

It's funny that I thought of that too when I first saw a video that explained why planets move around the sun in orbits, and that this is due to curves that those planets cause in the space time fabric but not really, I remember back from my 7th grade that centripetal and centrifugal forces play a major role in the movements of planets.

 

GAH!!!! There's no such thing as centrifual force! The acceleration is clearly pointing toward the center of rotation, not outward.

[SkepticLance]

All planets are falling towards the sun. Fortunately for our continued existence, they are also all moving forward. The vector of the two movements is a circle. ie. an orbit.

[antimatter]

Thanks, that clears it up for me,

but just one annoying question, do you have a source? Just so I can quote it if need be...

[swansont]

All planets are falling towards the sun. Fortunately for our continued existence, they are also all moving forward. The vector of the two movements is a circle. ie. an orbit.

 

Exactly — they accelerate toward the sun but keep missing. (though the general form is an ellipse)

[antimatter]

What do you mean by missing? So they're being pulled one way towards the sun, and yet they're moving in the other direction which balances it all out?

[Klaynos]

What do you mean by missing? So they're being pulled one way towards the sun, and yet they're moving in the other direction which balances it all out?

 

Yeah pretty much. The 'other direction' is tangential to the orbit.

[antimatter]

Do the indents of the planets make much of a difference?

[Klaynos]

Do the indents of the planets make much of a difference?

 

They're the reason you can stand on the surface... it depends what you mean though, relative to what?

[SkepticLance]

Just a comment on ellipses versus circles. It is true that the orbits of planets around our sun are ellipses. However, they are ellipses that approach being circles.

 

You may say, so what? It actually makes a hell of a difference in terms of the probability of life. A strongly elliptical orbit means massive temperature changes at different parts of the orbit. A weakly elliptical orbit - almost a circle, means temperature changes are minimal. While we have no empirical evidence for this, it seems reasonable to assume that minimal temperature change makes it more likely for life to form and evolve.

 

This difference is important when we look at what is known of extra-solar planets. The vast majority of planets discovered around other suns have very elliptical orbits. This reduces the probability of life in those places.

[antimatter]

They're the reason you can stand on the surface... it depends what you mean though, relative to what?

 

When we're talking about orbits, the planet moves in a tangent to the pull of the sun, but does the indent the planet itself makes, doesn't that interfere in a way with the sun's indent?

[Klaynos]

When we're talking about orbits, the planet moves in a tangent to the pull of the sun, but does the indent the planet itself makes, doesn't that interfere in a way with the sun's indent?

 

mass of the sun = 1.98892 × 10³⁰ kg

mass of Earth = 5.9742 × 10²⁴ kg

 

So there's 6 orders of magnitude difference, so no not really.

[swansont]

What do you mean by missing? So they're being pulled one way towards the sun, and yet they're moving in the other direction which balances it all out?

 

"missing" as in we don't hit the sun.

[Riogho]

Remember all those lovely conservation laws you learned in General Science in the 7th year? That is where these come into play. Keeping the nice little planets in a cute little ellipse.

[antimatter]

Nice one Riogho, you came in with your patronizing comment only 5 posts too late...

[Riogho]

*sighs* Everything I post is misunderstood, it wasn't mean to be patronizing at all. I was pointing you in the direction of momentum.

[antimatter]

Righto, sorry,

the whole "lovely little conservation laws" and "cute little ellipses", threw me off.

 

Anyway, so the planets try and go in a tangent, but the indent of the Sun keeps them from doing that, and in the orbit?

[Klaynos]

Righto, sorry,

the whole "lovely little conservation laws" and "cute little ellipses", threw me off.

 

Anyway, so the planets try and go in a tangent, but the indent of the Sun keeps them from doing that, and in the orbit?

 

Yep.

[antimatter]

Okay thanks.

 

And is there a specific scientific term for the indents made by the planets/sun/etc.?

[iNow]

Curvature?

Warpage?

Dimpling (not to be confused with dumpling)?

 

Basically, any mathematical term which describes shapes and change in non-Euclidean geometry would be appropriate.

[abskebabs]

I know that I am multiple posts too late for this, but I thought you guys could have been a lot more succinct by just saying:

 

The planets can be thought of as having a tangential velocity and constant speed. Note the difference in terms here, because velocity is a vector quantity. The planets experience a central force (in this case their weight), causing the mass to experience an acceleration(both force and acceleration are vector quantities). The acceleration, however, due to a central force is orthogonal to the tangential velocity, and therefore has no effect on its magnitude, causing it only to change direction. The orbit produced is approximately circular, when the central object(like the sun) is much more massive than the object in orbit. Otherwise, the orbits are generally elliptical, and sometimes hyperbolic(in the case of comets, though correct me if I'm wrong).