How fast is Gravity? How fast does it travel through space?

[Hawkgirl]

I've read that it is much faster than light but I didn't understand some of the article so does anyone have any answers that won't give me a headache? And how did they calcualate the speed?

[astro_uk]

As far as I understand it, in General relativity gravity moves at the speed of light. People always seem to give the example that if you could magically remove the sun, the Earth would continue in its orbit as normal for the 8 minutes it would take for influence of its gravity to be removed, the 8 minutes being the time taken for light to travel from the Sun to the Earth.

Another objection I would guess is that if gravity moved faster than light, it would be theoretically (but practically probably impossible) possible to transmit signals faster than light, simply by moving something back and forth. Anything of this nature is a big no no in relativity in general.

If you have read that gravity travels faster than light I would guess it is some speculative new theory.

[harry]

Hello All

On Gravity

Propagation Speed of Gravity and the Relativistic Time Delay
http://arxiv.org/abs/astro-ph/0301145

The Confrontation between General Relativity and Experiment
http://arxiv.org/abs/gr-qc/0510072

The status of experimental tests of general relativity and of theoretical frameworks for analysing them is reviewed. Einstein's equivalence principle (EEP) is well supported by experiments such as the Eotvos experiment, tests of special relativity, and the gravitational redshift experiment. Future tests of EEP and of the inverse square law are searching for new interactions arising from unification or quantum gravity. Tests of general relativity at the post-Newtonian level have reached high precision, including the light deflection, the Shapiro time delay, the perihelion advance of Mercury, and the Nordtvedt effect in lunar motion. Gravitational-wave damping has been detected in an amount that agrees with general relativity to better than half a percent using the Hulse-Taylor binary pulsar, and other binary pulsar systems have yielded other tests, especially of strong-field effects. When direct observation of gravitational radiation from astrophysical sources begins, new tests of general relativity will be possible.

Does Gravity Travel at the Speed of Light?
http://math.ucr.edu/home/baez/physics/R ... speed.html

In the simple Newtonian model, gravity propagates instantaneously: the force exerted by a massive object points directly toward that object's present position. For example, even though the Sun is 500 light seconds from the Earth, Newtonian gravity describes a force on Earth directed towards the Sun's position "now," not its position 500 seconds ago. Putting a "light travel delay" (technically called "retardation") into Newtonian gravity would make orbits unstable, leading to predictions that clearly contradict Solar System observations

In general relativity, on the other hand, gravity propagates at the speed of light; that is, the motion of a massive object creates a distortion in the curvature of spacetime that moves outward at light speed. This might seem to contradict the Solar System observations described above, but remember that general relativity is conceptually very different from Newtonian gravity, so a direct comparison is not so simple. Strictly speaking, gravity is not a "force" in general relativity, and a description in terms of speed and direction can be tricky. For weak fields, though, one can describe the theory in a sort of Newtonian language. In that case, one finds that the "force" in GR is not quite central--it does not point directly towards the source of the gravitational field--and that it depends on velocity as well as position. The net result is that the effect of propagation delay is almost exactly cancelled, and general relativity very nearly reproduces the Newtonian result.

While current observations do not yet provide a direct model-independent measurement of the speed of gravity, a test within the framework of general relativity can be made by observing the binary pulsar PSR 1913+16. The orbit of this binary system is gradually decaying, and this behavior is attributed to the loss of energy due to escaping gravitational radiation. But in any field theory, radiation is intimately related to the finite velocity of field propagation, and the orbital changes due to gravitational radiation can equivalently be viewed as damping caused by the finite propagation speed. (In the discussion above, this damping represents a failure of the "retardation" and "noncentral, velocity-dependent" effects to completely cancel.)

Speed of Gravity Measured for First Time
http://www.nrao.edu/pr/2003/gravity/

POSSIBLE NEW PROPERTIES OF GRAVITY
http://metaresearch.org/cosmology/gravi ... ravity.asp

Abstract. Gravity has no aberration, and propagation delays cannot be used without destroying angular momentum conservation at an unacceptable rate. Even the curved spacetime explanation (“gravity is just geometry”) breaks down when masses and speeds are large, as in binary pulsars. But if gravity or spacetime curvature information is carried by classical propagating particles or waves, a modern Laplace experiment places a lower limit on their speed of 1010 c. The so-called Lorentzian modification of special relativity permits such speeds without need of tachyons. But there are other consequences. If ordinary gravity is carried by particles with finite collision cross-section, such collisions would progressively diminish its inverse square character. Gravity would gradually convert to inverse linear behavior on the largest scales. Curiously, at all scales greater than about 2 kiloparsecs, gravity can be modeled without need for dark matter by an inverse linear law. The orbital motions of Mercury and Earth may also show traces of this effect. Moreover, if gravity were carried by particles, a collapsed ultra-dense mass between two bodies could shield each of them from the gravity of the other. Anomalies are seen in the motions of certain artificial Earth satellites during eclipse seasons that behave like shielding of the Sun’s gravity. Certain types of radiation pressure might cause a similar behavior, but require far more free parameters to model. Each of these effects of particle-gravity models has the potential to lead to a breakthrough in our post-Einsteinian understanding of gravitation. This would also change our views of the nature of time in relativity theory.

The Speed of Gravity – What the Experiments Say
http://metaresearch.org/cosmology/speed_of_gravity.asp

Abstract. Standard experimental techniques exist to determine the propagation speed of forces. When we apply these techniques to gravity, they all yield propagation speeds too great to measure, substantially faster than lightspeed. This is because gravity, in contrast to light, has no detectable aberration or propagation delay for its action, even for cases (such as binary pulsars) where sources of gravity accelerate significantly during the light time from source to target. By contrast, the finite propagation speed of light causes radiation pressure forces to have a non-radial component causing orbits to decay (the “Poynting-Robertson effect”); but gravity has no counterpart force proportional to to first order. General relativity (GR) explains these features by suggesting that gravitation (unlike electromagnetic forces) is a pure geometric effect of curved space-time, not a force of nature that propagates. Gravitational radiation, which surely does propagate at lightspeed but is a fifth order effect in , is too small to play a role in explaining this difference in behavior between gravity and ordinary forces of nature. Problems with the causality principle also exist for GR in this connection, such as explaining how the external fields between binary black holes manage to continually update without benefit of communication with the masses hidden behind event horizons. These causality problems would be solved without any change to the mathematical formalism of GR, but only to its interpretation, if gravity is once again taken to be a propagating force of nature in flat space-time with the propagation speed indicated by observational evidence and experiments: not less than 2x1010 c. Such a change of perspective requires no change in the assumed character of gravitational radiation or its lightspeed propagation. Although faster-than-light force propagation speeds do violate Einstein special relativity (SR), they are in accord with Lorentzian relativity, which has never been experimentally distinguished from SR—at least, not in favor of SR. Indeed, far from upsetting much of current physics, the main changes induced by this new perspective are beneficial to areas where physics has been struggling, such as explaining experimental evidence for non-locality in quantum physics, the dark matter issue in cosmology, and the possible unification of forces. Recognition of a faster-than-lightspeed propagation of gravity, as indicated by all existing experimental evidence, may be the key to taking conventional physics to the next plateau.

[Nereid]

For what it's worth Hawkgirl (and a belated welcome!), the material harry has posted, from metaresearch, is not science.

In fact, the author, in these pages harry cites, makes a rather gross error, based on his misunderstanding of GR (General Relativity). However, it's a rather technical mistake, so explaining it without lots of math is not easy (if you're interested, his mistake is that the propogation of gravity, in GR, has some similarities with the propogation of light, under Maxwell's equations; however, there are also differences, and failure to appreciate the differences leads to inconsistent conclusions).

[harry]

Hello All

Nereid maybe right in what he says.

In both cases there is inconsistent proof of the speed of gravity.