Sun Earth Light Gravity

[Bishop]

OK here's a puzzler

Turns out the Earth is 8 light minutes away from the Sun

So where we see the Sun in the sky is actually where it was 8 minutes ago

Now... say I have a 'compass' which is attracted to the Suns gravity

If I use this compass in my back garden, will it point directly in the same direction as I see the Sun this instant, or will it point to where the Sun actually is (where I'll see it 8 mins from now)?

:blackeye:

-B

caution: don't look directly into the Sun

 

[Artlav]

That's a big issue of modern physics.
Supposedly, it's resolved in GR somehow.
If you assume light speed delay of gravity in classic newton formula, the solar system will fly apart.

 

[Bishop]

Aha

If you assume light speed delay of gravity in classic newton formula, the solar system will fly apart.

Hi Artlav!

So my compass points to where the Sun actually is, rather than where I see it to be... :hmm:

Thanks!

- B

 

[Urwumpe]

Since the light of the sun also travels at the speed of light, the compass would point right where you see the sun, but not where the sun actually already is.

Artlav: Solar System simulations based on general relativity actually work better than Newtonian ones. I don't know where you have the claim of the solar system falling apart, unless there is a incorrect application of relativity.

 

[garyw]

I thought it was pretty much resolved that gravity waves are information and thefore travel at the speed of light?

Remove the sun and the suns gravity doesn't instantly disappear because the information that the gravity is gone will take 8 minutes to propogate to Earth?

 

[Artlav]

Artlav: Solar System simulations based on general relativity actually work better than Newtonian ones. I don't know where you have the claim of the solar system falling apart, unless there is a incorrect application of relativity.

I may not worded it correctly, the solar system will fly apart if the light delay of gravity is introduced into Newtonian calculations.

 

[Loru]

Like garyw said all information's (including gravity) max speed is C so if Sun dissapears in certain moment Earth would change its orbit 8 minutes after that event. So your compass will indicate directly the Sun.

 

[dgatsoulis]

Just recently, i watched a documentary about this.

[ame="http://www.youtube.com/watch?v=O-p8yZYxNGc"]YouTube- Gravity - From Newton to Einstein - The Elegant Universe[/ame]

The whole series was pretty interesting but this particular vid (especially after 4:00) contains information relative to the topic discussed here.

 

[Hartmann]

Gravity nature and speed is the holy grial of the modern physics :uhh:

 

[RisingFury]

If you assume light speed delay of gravity in classic newton formula, the solar system will fly apart.

No...

The reason Newton invoked God holding the solar system together is because he could not account for the solar system being stable, using the two body system he thought of.

He could stabilize Earth and Moon, then the Earth-Moon and Sun, but when you start adding other planets, stuff falls apart.

It takes another kind of math to account for many bodies.

After Euler and Lagrange failed, Laplace managed to stabilize the solar system, invoking perturbations.

 

[Bishop]

Excellent

YouTube- Gravity - From Newton to Einstein - The Elegant Universe The whole series was pretty interesting but this particular vid (especially after 4:00) contains information relative to the topic discussed here.

Hey dgatsoulis

Yep, that animation answered the question in an easy to understand way... that Einstien chap got around didn't he :lol:

Thanks all! :tiphat:

- B