We all consider that gravity travels at the speed of light. Light travels at the speed of light except when it is in a medium ,say glass, where it travels slower. What happens when gravity passes through a distributed mass. Will it still travel at the speed of light or will each atom absorb and emit gravity as it passes. I realize this is not the way anyone would like to think about gravity, but an answer to this question may be interesting.
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1I think that the implied particle interpretation might be a little bit dangerous as quantum electro dynamics works very well with those while not taking too much care about $c$ as limit. The Question would be it the propagation of a gravitational wave due to a first massive object would be effected by the gravitational field of a second massive object. – mikuszefski Apr 18 '15 at 13:27
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I've been wondering is the gravitational field continuously regenerate or is it static? can anyone please shed some light on this after answer the OP thanks. – user6760 Apr 18 '15 at 13:52
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A gravitational field does not propagate. It is static and extends to infinity. If a massive object rotates and wobbles, the center of the gravitational field may seem to move with regard to a distant observer, but the field itself does not change and no information is transmitted. This link also discusses gravity waves: http://en.wikipedia.org/wiki/Speed_of_gravity – Ernie Apr 18 '15 at 16:16
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In principle a gravitational wave will travel slower than $c$ when passing through matter, but in practice the reduction in speed is absurdly small.
Consider first a light wave passing through a dielectric. You can explain what happens using either classical or quantum approaches, but we'll use a classical description since that's all we have available for gravity. The oscillating electric field associated with the light wave makes the electrons in the dielectric oscillate, and those oscillating electrons reradiate an electromagnetic wave. In most cases the frequency will not match a natural oscillation frequency of the dielectric, so the phase of the reradiated wave lags the incident light wave. When you sum up the incident and reradiated wave the result is a wave travelling slower than $c$. (If you're interested, the process is discussed in detail in the answers to Why do prisms work (why is refraction frequency dependent)?.)
Now consider the gravitational wave. The gravitational wave will induce a quadrupolar oscillation in the matter it is passing through (this quadrupolar oscillation is what LIGO has been looking for). The oscillation in the matter will then reradiate a gravitational wave, and as with light there will usually be a phase lag so summing the incident and reradiated waves will give a wave travelling slower than $c$.
But gravitational waves interact much, much less strongly with matter than light does with a dielectric. The induced oscillation of the matter is so small that no-one has ever managed to measure it, and the gravitational wave reradiated by this undetectably small oscillation will be vastly smaller again. So while in principle the interaction with matter will slow down the gravitational wave, in practice any reduction in speed is utterly negligable.
John Rennie
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Does this mean that refraction of gravitational waves by matter is also not detectable? – asmaier Feb 11 '16 at 23:05
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@asmaier: I think it's extremely unlikely we'll ever observe refraction of gravitational waves. If we had enough mass for refraction to be detectable it would be swamped by gravitational lensing. – John Rennie Feb 12 '16 at 06:29
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The acceleration of gravity is that itself. The bigger the mass the more gravity pulls on the object. Especially with a force. This could be simplified into an equation we learned in Intro-Physics, F=ma or f=mg
