Re: OT: Gravity, Dark Energy, Universal expansion
 

Equal and opposite reactions.

If the sun was perfectly still there wouldn't be a problem. But earth (mostly jupiter, due to mass&distance) pull on the sun too.

If the sun's gravity appears to be coming from where it was 8 minutes ago, that would be slightly in front of us, rather than directly opposite the center of mass.
Accelerating forwards would spin us out into deep space.

Re: OT: Gravity, Dark Energy, Universal expansion
 

No, the earth must be moving at the same rate as the sun in order to even be in orbit. So there is no danger of 'slippage' of that orbit due to the sun's movement over time. Remember that (as far as we know) the earth formed from the same cloud of gas and dust as the sun. It has had the same basic motion/momentum from the beginning. And we orbit the center of mass of the whole solar system, not the sun itself. (Yes, that center is probably about 6 centimeters from the center of the sun... http://forum.shrapnelgames.com/images/smilies/happy.gif )While it's true that they have not yet figured out how to prove that gravity propagates at the speed of light, your supposed 'insight' is a misunderstanding of orbital mechanics, not any sort of proof that it propagates faster than light.

Re: OT: Gravity, Dark Energy, Universal expansion
 

Its not the angular speed, but a phase shift that I was talking about.

Measurements of Earth's acceleration show that we are accelerating towards the Sun's current position (to the precision of the instruments), not its position 8 minutes ago.
If the acceleration isn't directly in line with the center of mass, then there will be an an angular acceleration component, which is bad news.

PS:
The center of mass is not 6 cm from the center of the sun, but about 500km according to some quick math.
1 AU makes for a very long lever http://forum.shrapnelgames.com/images/smilies/wink.gif

Re: OT: Gravity, Dark Energy, Universal expansion
 

The current position of the sun according to what measurement? If it's the visible position of the sun, it's towards where the sun was 8 minutes ago. http://forum.shrapnelgames.com/image...ies/tongue.gif Have they somehow measured that the earth is moving relative to where the sun is -- 8 minutes travel from its visible position? That would be big news if so, because it would be proof that gravity propagates faster than light. I'm pretty sure I would have heard about this.

And I didn't do any math about where the system's center of gravity is, I was just tossing out a number. The planets do have about 98 percent of the system's angular momentum, but the sun has 99.5 percent of the system's mass.

Re: OT: Gravity, Dark Energy, Universal expansion
 

I thought that was obvious given the context.

Basically the Earth's acceleration is not in the same direction as the incident light from the sun.

Re: OT: Gravity, Dark Energy, Universal expansion
 

It wouldn't be that hard to predict the suns' position in eight minutes.

So. If gravity is found to travel at c and the earth orbits the suns' actual position...Could gravity be 'connected' to the object it came from?

Re: OT: Gravity, Dark Energy, Universal expansion
 

I'm confused. So there's both experiments that show that gravity is indeed travelling at the speed of light( or close to it ), and actual observations of the opposite?

Then that would indicate, as narf says, that there's some sort of connection to the object it came from. Perhaps gravity 'predicts' where the sun is going to be at the moment it reaches earth?

So if something was to suddenly push the sun out of its original and predictable path, it might take a while before gravity would catch up and start pulling us in the right direction again.

Re: OT: Gravity, Dark Energy, Universal expansion
 

That's what people are saying. I have little knowledge of the situation - Just trying to make sense of it.

Re: OT: Gravity, Dark Energy, Universal expansion
 

Because chaos theory gets involved, which I barely understand myself above the buzzword level. This astronomy abstract mentions chaotic orbits, but I'm already lost by the end of the first sentence. http://forum.shrapnelgames.com/image...s/confused.gif

Re: OT: Gravity, Dark Energy, Universal expansion
 

One of the most basic assumptions of relativity is that all inertial reference frames are equally valid. Simply choose your inertial reference frame to be one where the sun is motionless, and you can trivially show that the speed of gravity makes virtually no difference to the influence of the sun on any of its planets. Working out how this is compensated for in other reference frames is a bit more work, but the conclusion is guaranteed unless relativity is wrong.

For the speed of gravity to have a significant effect on gravitational interactions, both masses must be large enough to have significant effects on each other so that both have significant acceleration and no inertial reference frame exists where either body is reasonably close to at rest.

Re: OT: Gravity, Dark Energy, Universal expansion
 

That's a better description than I could find anywhere else http://forum.shrapnelgames.com/images/smilies/happy.gif

Re: OT: Gravity, Dark Energy, Universal expansion
 

...What about the inertial reference frame of one object being pulled by the other, which is pulled by the other one...

Sure, it's recursive. But some recursives do have solutions.

Re: OT: Gravity, Dark Energy, Universal expansion
 

By definition, inertial reference frames can not be accelerated. So, an object being accelerated does not have its own inertial reference frame.

Re: OT: Gravity, Dark Energy, Universal expansion
 

That falls under the "no such inertial reference frame exists" clause, and the speed of gravity does matter for such systems. Technically the Sun is accelerating so no inertial reference frame has it perfectly at rest either, but the difference is small enough on the scale of the solar system that it hardly matters.

Re: OT: Gravity, Dark Energy, Universal expansion
 

Even more to consider Link

Re: OT: Gravity, Dark Energy, Universal expansion
 

Acceleration is simply another factor. Just factor it out.

Re: OT: Gravity, Dark Energy, Universal expansion
 

The universe doesn't work that way... try throwing a ball on a merry-go-round sometime http://forum.shrapnelgames.com/images/smilies/happy.gif

Re: OT: Gravity, Dark Energy, Universal expansion
 

You could throw a fancy dress ball on a merry-go-round and it would be super-fun-cool. http://forum.shrapnelgames.com/images/smilies/wink.gif

Re: OT: Gravity, Dark Energy, Universal expansion
 

A ball on a merry-go-round would most likely be considerably more complex than two stellar objects moving towards each other - Ignoring all other stellar objects)