Is gravity faster than light?

[Daecon]

I was about to start a thread in the Speculations forum, but then I got to thinking, is it even going to be possible to discern whether Gravity is faster than Light?

[Spyman]

Speed of gravity

In the context of classical theories of gravitation, the speed of gravity is the speed at which changes in a gravitational field propagate. This is the speed at which a change in the distribution of energy and momentum of matter results in subsequent alteration, at a distance, of the gravitational field which it produces. In a more physically correct sense, the "speed of gravity" refers to the speed of a gravitational wave.

 

The speed of gravitational waves in the general theory of relativity is equal to the speed of light in vacuum, c. Within the theory of special relativity, the constant c is not exclusively about light; instead it is the highest possible speed for any physical interaction in nature. Formally, c is a conversion factor for changing the unit of time to the unit of space. This makes it the only speed which does not depend either on the motion of an observer or a source of light and/or gravity. Thus, the speed of "light" is also the speed of gravitational waves and any massless particle. Such particles include the gluon (carrier of the strong force), the photons that light waves consist of, and the theoretical gravitons which make up the associated field particles of gravity (a theory of the graviton requires a theory of quantum gravity, however).

http://en.wikipedia.org/wiki/Speed_of_gravity

[ajb]

Spyman's quote is how we generally understand this question.

 

If we image some body sat in space and we make small changes to, say its mass then this will course small perturbations to the background gravitational field. These ripples in space-time, known as gravitational waves, will propagate away from the source at the speed of light in vacuum.

 

Some other test body will not know about these small changes until the gravitational wave reaches it.

[swansont]

The speed of gravity can be deduced from the decay of binary pulsars, which will shed energy in the form of gravitational waves, and observations of binary pulsar PSR 1913+16 has shown that the results are consistent with gravity traveling at c.

[Daecon]

Ah, it didn't occur to me to check Wikipedia. Thanks for enlightening me, I guess there's no need to make that Speculations thread now.

[EMField]

ALL calculations for orbital maneuvers, orbital of planets, etc., use NO aberration and use the instantaneous speed of gravity, not the speed of c. You might want to do some research yourself before making the claim gravity travels at c. GR reduces to Newtonian gravity and Newtonian gravity uses the instantaneous speed for gravity, not c. Even the math of GR uses no aberration for gravity which is the same thing as saying it is instantaneous. You can SAY anything you like, but the math says it is instantaneous, contrary to the words they use.

[doG]

You can SAY anything you like, but the math says it is instantaneous, contrary to the words they use.

Can you support that with anything other than you-say-so? Please show us the math and the proof that it proves what you say.

[ajb]

The speed of gravity can be deduced from the decay of binary pulsars, which will shed energy in the form of gravitational waves, and observations of binary pulsar PSR 1913+16 has shown that the results are consistent with gravity traveling at c.

 

These measurements also give us high precision tests of general relativity, so far GR seems to be working okay.