Gravity's speed of propagation

[ianke]

I believe that GR predicts that c is the speed at which gravity propagation occurs, but has it been pinned down yet?
In other words does gravity only effect things at the speed of light?

[Boris_Badenov]

Speed of gravity (wiki)
In the context of classical theories of gravitation, the speed of gravity refers to the speed at which a gravitational field propagates. This is the speed at which changes in the distribution of energy and momentum result in noticeable changes in the gravitational field which they produce.

The speed of gravity, and of all disturbances, is more often called the speed of light c. Within the well accepted theory of special relativity, the parameter c is not about light, it is a unit conversion factor for changing the units of time to the units of space in a Lorentz transformation. It is then also the only speed which does not depend on the motion of the observer, and equals the speed of gravity and of light and of any other massless particle.

The Speed of Gravity What the Experiments Say
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.

[ianke]

Thanks for the link!

[centsworth_II]

Thanks for the link!

The Meta Research site also posts the following paper:
PROOF THAT THE CYDONIA FACE ON MARS IS ARTIFICIAL

If you are content to be informed by such "research", you should go ask your questions about gravity in the Unexplained forum.

[ArcCentral]

The general consensus is the the propagation speed of gravity is the speed of light, and I would agree here, but disagree that gravity is a curvature of space. I prefer to consider it to be wave originating from matter.

Some might say that if you removed the sun, that the earth would continue to orbit the suns old location for eight and a half minutes, but I say that if you were to remove the sun, that the wave goes with it, as the gravitational wave of the sun is a part of the sun, thusly the earth would know toot sweet.

Some might say that if gavity propogates at the speed of light, orbits would get all out of wack, and that would be true, so with either the curvature of space, or gravitational waves, with a speed of light limit, it's screwed up, but there is a way around this, at least with the gravitational waves. In other words, the earth and sun know each others location almost instanly, but the distance between them has a delay. To be more precise, lateral motion between two bodies is known the second it happens, and motion toward or away has a delayed effect

[ianke]

Thanks for the link!

The Meta Research site also posts the following paper:
PROOF THAT THE CYDONIA FACE ON MARS IS ARTIFICIAL

If you are content to be informed by such "research", you should go ask your questions about gravity in the Unexplained forum.

Umm... Thank you for such a productive Post? This is a legitimate question. Just because Boris_Badinov sent a paper that shows another view, and I thank him for it doesn't mean that I buy into the theory. I asked for evidence, and at least he stayed on topic instead of spewing vitriol, Why don't you go play elsewhere.

Now, if you have something constructive to say then please stick around. Is there undisputed empirical evidence to show that gravity's speed of propagation is limited to c?

[ianke]

The general consensus is the the propagation speed of gravity is the speed of light, and I would agree here, but disagree that gravity is a curvature of space. I prefer to consider it to be wave originating from matter.

Some might say that if you removed the sun, that the earth would continue to orbit the suns old location for eight and a half minutes, but I say that if you were to remove the sun, that the wave goes with it, as the gravitational wave of the sun is a part of the sun, thusly the earth would know toot sweet.

Some might say that if gavity propogates at the speed of light, orbits would get all out of wack, and that would be true, so with either the curvature of space, or gravitational waves, with a speed of light limit, it's screwed up, but there is a way around this, at least with the gravitational waves. In other words, the earth and sun know each others location almost instanly, but the distance between them has a delay. To be more precise, lateral motion between two bodies is known the second it happens, and motion toward or away has a delayed effect

This is an interesting thought, but I have a question though. Isn't this akin to if you remove a light source then the already emitted light would be removed with it? I don't know exactly how this would work, but if you could elaborate on it I would appreciate it. And I really do mean thanks for the post.

[ramparts]

Thanks for the link!

The Meta Research site also posts the following paper:
PROOF THAT THE CYDONIA FACE ON MARS IS ARTIFICIAL

If you are content to be informed by such "research", you should go ask your questions about gravity in the Unexplained forum.

Umm... Thank you for such a productive Post? This is a legitimate question. Just because Boris_Badinov sent a paper that shows another view, and I thank him for it doesn't mean that I buy into the theory. I asked for evidence, and at least he stayed on topic instead of spewing vitriol, Why don't you go play elsewhere.

Now, if you have something constructive to say then please stick around. Is there undisputed empirical evidence to show that gravity's speed of propagation is limited to c?

Well, it's certainly limited to c, in the sense that it can't exceed c. If gravity (or any signal) travelled faster than the speed of light, it would (in some reference frames) go back in time, and then you have the possibility of feeling a change in gravity before the source itself changes! That's a violation of cause-and-effect, so we like to exclude that as a logical possibility

As for gravity propagating at a speed less than that of light, it's a possibility, but currently one without any observational support or theoretical motivation. It essentially corresponds to the mass of the graviton, the hypothetical particle that carries the gravitational force. If the graviton is massless, then its speed is the speed of light. This will be testable in the future with, I believe, gravitational wave detectors.

[ianke]

Hello ramparts,
Thankes for the input. This is what I have always thought. but lately I have run into a few things that are making me scratch my head. I want to know if there is any imperical data out there to confirm this. (test data)

Here is just one reason why:
I ran into this article. http://www.sciencedaily.com/releases/20 ... 104410.htm

I realize this is not a respectable journal. It is just an article, but in it they postulate that something beyond the known univerve is drawing A large number of Galaxies towards that direction. Hmmm? I then asked myself if this is even possible. If something is pulling on these then by definition it would need to be in this universe. Yes?

Or.. If this "whatever it is" is in our universe but beyond the limit of our ability to see. (Perhaps because light has not existed this long due to the age of the universe?) This also causes a dilema in my thinking because if gravity is subject to c then we could not be seing the effects of some thing that we can not see. Something to do with being outside of our lightcone so we cannot know. (if I recall the terminology)

Now I realize that there may be a large number of reasons why this article may prove to be bogus, or the postulate incorect, but for the sake of argument if soimething is pulling on a large mass of Galaxies from outside our ability to see, how would this be possible?

Can you see why the question I had about gravity fits this? Perhaps their are other explainations, but I imediately thought to look and see if gravity was maybe propagating faster that c. Unfortunately I haven't run into a lot of data that supports c as its upper limit. In fact I find about as many that propose that gravity is much faster than c. I do not subscribe to the big journals as I can not aford to. This is why I bring my question here.

So if anyone can point me to some data (not the rational mind experiment) that would support the propagation of G =c I would greatly appreciate it. I don't wish to sound like the tin foil hat type, and I still think that c is the limit, but when I started looking for proof I find arguments both ways. Test data anybody?
Thanks in advance to all of you.

[yevaud]

The Measurement of the Light Deflection from Jupiter: Experimental Results, E. B. Fomalont, S. M. Kopeikin, Astrophys. J. 598 (2003) 704 (astro-ph/0302294)

That's about as close as you're going to find on the subject. There's a great deal of controversy about Kopeikin and the observational results.

[ianke]

Hello yevaud,
Long time no see!
I have seen this, but I have seen statements that his experiment was flawed an only confirming the speed of light in his data. Most of the ones that I saw were not disputing the speed of G propagating, but think that his test was flawed.

Unfortunately for the amateur like myself, I will have to wait and see. I really thought that there was more consensus on the subject than I am finding.

[yevaud]

Ah, I've been around, merely lurking a lot.

[centsworth_II]

...Just because Boris_Badinov sent a paper that shows another view, and I thank him for it doesn't mean that I buy into the theory...

I didn't know whether you would buy into it or not but I thought it would be useful to you or anyone else reading that link to consider the source.

[ramparts]

Hello ramparts,
Thankes for the input. This is what I have always thought. but lately I have run into a few things that are making me scratch my head. I want to know if there is any imperical data out there to confirm this. (test data)

Here is just one reason why:
I ran into this article. http://www.sciencedaily.com/releases/20 ... 104410.htm

I realize this is not a respectable journal. It is just an article, but in it they postulate that something beyond the known univerve is drawing A large number of Galaxies towards that direction. Hmmm? I then asked myself if this is even possible. If something is pulling on these then by definition it would need to be in this universe. Yes?

Oh, that paper. Yes, that's a very interesting one. In fact, it's one I'm hoping to take a look at in my own research right now. I'll let you know if I find anything If there is such a gravitational source, it's not beyond our known universe - it's beyond our visible universe. There's a big difference. We know there's a lot of Universe out there that we can't see, but the stuff we can see makes up the visible universe.

Or.. If this "whatever it is" is in our universe but beyond the limit of our ability to see. (Perhaps because light has not existed this long due to the age of the universe?) This also causes a dilema in my thinking because if gravity is subject to c then we could not be seing the effects of some thing that we can not see. Something to do with being outside of our lightcone so we cannot know. (if I recall the terminology)

Recall that we're not feeling the gravity - we're seeing objects which are. Erm, I mean, I think it's possible we feel it too, but it's so minor as to be negligible here. Not sure. So this is a very good question, and I had a similar one when this paper came out (about a year ago). Here's the answer, in a nutshell: gravity is the curvature of spacetime, so if you take spacetime, curve it, and then expand it, then the curvature is still there (if you want to think of spacetime as a rubber sheet, the analogy works fine in this case). So this curvature would have been caused by something with which we were once in causal contact - that is, something which was once visible to us - but has now gotten so far away that we can no longer see it. The curvature it caused remains, and so the gravity is there as well.

Now I realize that there may be a large number of reasons why this article may prove to be bogus, or the postulate incorect, but for the sake of argument if soimething is pulling on a large mass of Galaxies from outside our ability to see, how would this be possible?

Can you see why the question I had about gravity fits this? Perhaps their are other explainations, but I imediately thought to look and see if gravity was maybe propagating faster that c. Unfortunately I haven't run into a lot of data that supports c as its upper limit. In fact I find about as many that propose that gravity is much faster than c. I do not subscribe to the big journals as I can not aford to. This is why I bring my question here.

Well, you can access almost any paper that gets published in a "big journal" for free at arxiv.org, as almost all scientists put papers there, but a non-expert shouldn't be perusing those too much, it's simply an inefficient way of learning things. Ask away here!

So if anyone can point me to some data (not the rational mind experiment) that would support the propagation of G =c I would greatly appreciate it. I don't wish to sound like the tin foil hat type, and I still think that c is the limit, but when I started looking for proof I find arguments both ways. Test data anybody?
Thanks in advance to all of you.

Whoa, whoa. The experimental data does exist (the paper posted a couple of posts up is a nice example), but don't just throw away "rational mind experiments." Things that violate well-established physics are things we should naturally be very, very suspicious of, and that's much more rigorous than a mere "rational thought experiment."

[ianke]

Recall that we're not feeling the gravity - we're seeing objects which are. Erm, I mean, I think it's possible we feel it too, but it's so minor as to be negligible here. Not sure.

To see the effect of the gravity before you see the light emitted from its source sounds problematic to me.

A----->B----->C

Let A be the source of gravity (unknown in the above paper)
Let B be the object being acted upon by A (hunderds, perhaps thousands of galaxies)
Let C be the observer (us)

If Gravity propagates at c then the image of A must reach B at the same time Right?
So.... If C (the observer) sees the action of A s gravitational field on B then A must also be visible to C because the observation comes to the observer at the speed of light..

The only way A is not visible to C and yet we observe A s gravitational influence on B is if gravity propagates faster than c.
Ce senior? (not my prefered thought, but....)

Unless: 1) this observation is flawed, or 2)there is the possibility of a super duper truly humungous mother of all black holes, I would expect that A s region of space should be visible if the GR prediction of the speed at which gravity propagates = c stands solid.

This is a bit of a canundrum to me. Does anyone wish to pick an option? Is my reasoning pertaining to this sound?

[ianke]

Ah, I've been around, merely lurking a lot.

It is me that hadn't posted here in quite a while.

[ArcCentral]

I'm gonna try to explain what I was getting at from my first post.

Imagine the pond analogy with the rock tossed in, wherein waves emanate outward, now imagine that pattern with a little twist, wherein the pattern is spiralled (not shown in picture). The spiral pattern makes the connection. I.E. The entire pattern is the particle,so when I say, if the sun were removed from existence, the gravitational field goes with it.

Now when a body moves through space like the earth, the gravitational waves (field lines) get compressed in the forward direction, decompressed in the rearward direction, and varying degrees of compression decompression to the sides, depending on forward and rearward direction of view. All field lines travel at c ... no exceptions, and those field lines will follow any moving body through space, like the earth for instance, wherein the field lines will distort in such a way to point in the direction of the current location of the moving body (not necessarily depicted in this pic.

Wish I had more time to give this justice, but i need to go to work today.

[ianke]

I'd like to keep up with this as well. When you have time of course.

[ramparts]

Recall that we're not feeling the gravity - we're seeing objects which are. Erm, I mean, I think it's possible we feel it too, but it's so minor as to be negligible here. Not sure.

To see the effect of the gravity before you see the light emitted from its source sounds problematic to me.

A----->B----->C

Let A be the source of gravity (unknown in the above paper)
Let B be the object being acted upon by A (hunderds, perhaps thousands of galaxies)
Let C be the observer (us)

If Gravity propagates at c then the image of A must reach B at the same time Right?
So.... If C (the observer) sees the action of A s gravitational field on B then A must also be visible to C because the observation comes to the observer at the speed of light..

The only way A is not visible to C and yet we observe A s gravitational influence on B is if gravity propagates faster than c.
Ce senior? (not my prefered thought, but....)

Unless: 1) this observation is flawed, or 2)there is the possibility of a super duper truly humungous mother of all black holes, I would expect that A s region of space should be visible if the GR prediction of the speed at which gravity propagates = c stands solid.

This is a bit of a canundrum to me. Does anyone wish to pick an option? Is my reasoning pertaining to this sound?

Yeah, that sounds right. But I think I answered that in my last post (in fact, the same one you're quoting). Gravity is a manifestation of spacetime curvature - so if we were able to feel an object's gravity at one point, then even though the object has since receded from our view, we still feel its gravity, since the curvature is still there.

[ianke]

Then perhaps this is where I need straightening out. I always assumed that the visually known universe was expanding at at c. Could it be the expansion of spacetime at our visual limit is expanding faster than c when added to it? Even then one would expect gravity to undergo the same limitations as the light.