Easy way to prove the speed of gravity?

Our whole solar system is moving through space. It takes eight minutes to get from the earth to the sun at the speed of light. So, shouldn't it be possible to check and see if the earth is rotating around where the sun "actually is" or where it appears to be based on observation of its light? Has anyone done this, or are our observational instruments not good enough?

 

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I'm not sure how you relate gravity to the solar system's motion through the galaxy (or universe?) Doesn't gravity travel along with the solar system? I have been wondering about what 'gravity' actually is. Gravity seems to have more that one component to me. It seems to be a type of 'field' that is concentrated within a system, with gravitational waves that travel through the gravitational field at the speed of light, as EM waves do. The gravitational waves are a disturbance in the field, in other words. Possibly the 'field' is a kind of 'ether', and 'dark matter' is actually concentrations of the ether. Needless to say, I haven't got it all worked out yet!

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Likely the effect is too small to measure. You would be looking for a difference between the optical position and the annual circle the center of the sun makes around the center of mass of the earth/sun system. Throw in the perturbations of the other planets and I wouldn't expect you would be able to arrive at any meanful result.

 

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I agree with kevinalm, its probably theoretically possible, but your error would likely be larger than what you would measure.

 

If gravity traveled at the speed of light then the orbital mechanics for the solar system would not work.

 

Why shouldn't they work?

 

Hi przyk

If gravity's speed equaled speed of light then the pull of mass A would be towards a point behind mass B (and visa versa) which would result in unstable orbits. Also aberration of gravity would be seen. To overcome this speed limit on gravity, mass A would have to know the future position of mass B (and visa versa).

This would require some sort of faster than light comunication or the ability to remember the past and compute the future.

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The same thing happens with electric charges, but it is more clear because you don't have to worry about curved spacetime and you know that the interaction is limited to light speed.

If you have one charge orbiting another and the central charge is moving with a constant velocity, then it is pretty easy to show that if the orbiting charge is attracted to where the object was then the orbit is unstable but if the orbiting charge is attracted to where the object is then the orbit is stable. Since it cannot be stable in one frame and unstable in another then the object must be always attracted to where the central charge is, not was.

So, does that imply FTL communication? The answer is, no. If you solve Maxwell's equations (clearly not FTL) for a moving charge you will find that the retarded potential naturally points to where the object will be if it maintains a constant velocity. So orbits around an inertial primary are stable, but orbits around an accelerating primary can be unstable.

-Dale

 

Actually the earth is not "rotating" (I suppose you mean orbiting) around the sun. They are both orbiting around a common center of gravity that is inside the sun do to it's overwhelming mass when compared to the Earth. But that's not to say the center of gravity is the center of the sun, it is not, so actually the sun wobbles as a result of being oribited by the Earth. Looking for this wobble is actually how stars are analyzed for orbiting planets.

This is very well understood, both long before now and especially now that we have instruments in space.

 

exactly. I agree. Physics act instantly. There are no gravity particles its not like light that is made of photons. If a sun was to be moved from its position the effect would be instantaneous on Earth...

 

And you oppinion is based on what?

 

Based on the fact that currently no so called gravity particles were discovered. And even though not finding something does not mean that it does not exist, currently since we havent found it, does mean it does not exist.

 

http://www.newscientist.com/article.ns?id=dn3232

http://www.nrao.edu/pr/2003/gravity/

 

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Whatahell? So you oppinion is based on the fact that we haven´t seen graviton?

Thank you Oli

 

draqon,

The best available theory (General Relativity) says otherwise. While no mention is made of gravity particles, gravitational effects do travel at the speed of light in GR. The explanation given by Dale is the correct one. Also, it is possible, though this is not widely known, to obtain GR from the dynamics of a spin 2 field propagating in a flat Minkowski background. This line of development highlights the many profound similarities between gravity and electromagnetism.

 

yeah what a strange occurance that no gravity particles are mentioned...

 

draqon,

I think you may have missed my point. The fact that GR can be obtained from a spin 2 field theory means that it can be described in terms of gravitions. Gravitons would be the quanta of the spin 2 field.

 

Photons travel at c as predicted by the Maxwell wave equation.

Gravitons travel at c based on which specific equation?

 

Agreed.

 

According to Einstein's equation.
When you take the einstein's equations for weak perturbations, the solutions are gravitational waves that travel at the speed of light