Speed of gravity

[Jay-qu]

according to relativity gravity couldnt go any faster that light, but this does mean it goes at the speed of light... any way the real point i wanted to make is that if there is matter at the other end of the universe receding from us at a rate faster than c than becuase gravity cant go faster than c, the gravity from that matter will never reach us and hence never effect us and pull us in, so then how could the universe ever stop expanding?

[infamous]

according to relativity gravity couldnt go any faster that light, but this does mean it goes at the speed of light... any way the real point i wanted to make is that if there is matter at the other end of the universe receding from us at a rate faster than c than becuase gravity cant go faster than c, the gravity from that matter will never reach us and hence never effect us and pull us in, so then how could the universe ever stop expanding?

You cosmologists help me out with this one if I'm wrong but, I believe they are referring to the speed with which space is expanding and not the relative speed of matter within space. It is assumed that matter cannot exceed this limit relative to any other matter within the universe.

[Erasmus00]

according to relativity gravity couldnt go any faster that light, but this does mean it goes at the speed of light...

 

Speed of gravity generally means how fast a gravitational wave would travel. If you start from Einstein's theory, and do a weak field approximation, but allow relativistic fields, you find that traveling solutions do indeed pop up, and that they do travel at a speed c.

-Will

[Aki]

Some other universes are indeed receeding from us faster than the speed of light, but this does not violate relavity because it is space itself that is stretching. Therefore the gravitational field of those universes may never reach us. Space will most likely going to continue to expand, and this expansion is due to dark energy.

[EWright]

Some other universes are indeed receeding from us faster than the speed of light, but this does not violate relavity because it is space itself that is stretching. Therefore the gravitational field of those universes may never reach us. Space will most likely going to continue to expand, and this expansion is due to dark energy.

 

:shrug: She did not just say that there are other universes speeding away from us faster than the speed of light!

 

There are GALAXIES at the edge of the observable universe that are speeding away at NEAR the speed of light! If something is speeding away faster than the speed of light, it's light can not reach us. And yes, relativity says that gravity travels at exactly the speed of light. And yes, space itself can expand at faster than c.

[Tormod]

Aki's post is a great leap of faith :shrug: but the apparent violation of the Hubble Limit was discussed a short while ago here:

 

http://hypography.com/forums/showthread.php?t=2361&highlight=hubble+limit

[Aki]

:shrug: She did not just say that there are other universes speeding away from us faster than the speed of light!

 

There are GALAXIES at the edge of the observable universe that are speeding away at NEAR the speed of light! If something is speeding away faster than the speed of light, it's light can not reach us. And yes, relativity says that gravity travels at exactly the speed of light. And yes, space itself can expand at faster than c.

 

 

oops, my mistake. I mean galaxies, not universes, lol. Thanks EWright.

[EWright]

If I drive fast enough at the red light, it'll appear green.

 

Because it will be blue-shifted?

[Jay-qu]

so gravity is loosing its grip over large distances.. is it fairly likely that the universe will keep expanding forever? and that there is no way gravity can stop or reverse the process?

[pgrmdave]

I believe it all depends on how much matter there is in the universe. If there is enough, then gravity will pull parts of the universe togeather, and slowly, but surely, the universe's expansion will slow, then stop, then reverse.

[UncleAl]

1) Gravitation propagates at lightspeed.

2) Gravitation waves propagate at lightspeed.

 

Both are necessary to avoid contradictions in causality and observation. Now, the fun stuff!

 

2) http://arXiv.org/abs/gr-qc/0212121

Sergei Kopeikin

http://arXiv.org/abs/astro-ph/0301145

Clifford Will

http://arXiv.org/abs/astro-ph/0302294

Kopeikin's results

http://arXiv.org/abs/astro-ph/0302462

Kopeikin's analysis of results

http://arXiv.org/abs/astro-ph/0303346

Faber's dissent re parameterized post-Newtonian (PPN) model

http://arXiv.org/abs/astro-ph/0304006

Stuart Samuel's invalid analysis of Kopeikin

http://arXiv.org/abs/astro-ph/0311063

More Kopeikin

http://arxiv.org/abs/gr-qc/0403060

More criticism of Kopeikin

[coldcreation]

1) Gravitation propagates at lightspeed.

2) Gravitation waves propagate at lightspeed.

 

Both are necessary to avoid contradictions in causality and observation. Now, the fun stuff!

 

Where do you see gravity propagating. Where is your empirical evidence. Gravitons have never been observed, neither have gravitational waves. You read somewhere on internet that gravity propagates at c. You have no qualifications to assert that gravity propagates at all. Don't believe everything you were taught in elementary school.

 

Sit down and read: The rigidity along the line connecting gravitating objects induces the apparent instantaneous propagation of the gravitational ‘force.’ In other words, the field acts in a similar manner as a frozen waterfall, as opposed to a flowing waterfall. The computations using instantaneous positions of say the Earth and Sun is the correct one, the retarded positions is in conflict with observation. Sir Arthur Eddington (UncleAls favorite astrophysicist) explicated this known fact in 1920: …”the two forces are in the same line and in balance…[if the forces propagate with a delayed gravitational interaction…] This couple will tend to increase the angular momentum of the system, and acting cumulatively, will soon cause an appreciable change of period, disagreeing with observations if the speed of propagation is at all comparable with that of light” (Eddington, 1920, p. 94, from Van Flandern, T., 1998, The Speed of Gravity – What the Experiments Say,

 

http://www.ldolphin.org/vanFlandern/gravityspeed.html (metaresearch.org).

 

Coldcreation

[lindagarrette]

Why would gravity have any speed. Until someone finds a graviton, I believe the best theory is that gravity is a result of the curvature of space. Nothing "has" gravity. How could black holes, for example, have gravity when nothing can get out because escape speed is greater than the speed of light?

[Erasmus00]

Where do you see gravity propagating. Where is your empirical evidence. Gravitons have never been observed, neither have gravitational waves. You read somewhere on internet that gravity propagates at c. You have no qualifications to assert that gravity propagates at all. Don't believe everything you were taught in elementary school.

 

Do the calculations in GR though, and you'll find that it predicts gravity, like light, propagates at c. Now, Van Flandern is of the opinion the gravity must travel at much faster than light speeds, but his argument is seriously flawed. This can be demonstrated by the formulation of GR, in GR moving bodies set up fields that effectively encode their motion into them. This is not something adhoc, it is built into the very fomrulation of GR. Van Flandern ignores this, and his argument doesn't make any sense in the context of GR.

-Will

[Boerseun]

With very precise measurement of the Earth/Sun system, we should see that the Earth is orbiting around a point that is eight minutes ahead of where the visible sun is, eight minutes ahead in the Sun's path around the galactic centre. This should be if gravity is a curvature in space. If gravity is propagated by gravitons at c, then the one focus of the orbit should be exactly where the visible sun is. Have this test been done, or can't we make such fine observations yet?

[lindagarrette]

Van Flandern doesn't try to explain GR in terms of gravity speed and I don't think it is ever presented that way. Here's what he says in very simple terms. "As viewed from the Earth's frame, light from the Sun has aberration. Light requires about 8.3 minutes to arrive from the Sun, during which time the Sun seems to move through an angle of 20 arc seconds. The arriving sunlight shows us where the Sun was 8.3 minutes ago. The true, instantaneous position of the Sun is about 20 arcs seconds east of its visible position, and we will see the Sun in its true present position about 8.3 minutes into the future. In the same way, star positions are displaced from their average position by up to 20 arcs seconds, depending on the relative direction of the Earth's motion around the Sun. This well-known phenomenon is classical aberration, and was discovered by the astronomer Bradley in 1728."

[EWright]

If gravity is propagated by gravitons at c, then the one focus of the orbit should be exactly where the visible sun is.QUOTE]

 

Can you explain this further please? It sounds like your saying one position of earth's orbit would run through the sun.

 

If gravity is a warpage of space, does it have to travel at all? At least in situation like the earth's orbit, as something travels through gravity's "trough", that trough would already be there; no need for travel time. We could think of the trough the earth travels through as a fixed trough in space related to its relationship to the sun, with no need for it to be constantly generated the way the light reaching the earth must be. I'm not saying this works, and it is not part of my theory, just food for thought.