<A HREF="http://www.newscientist.com/news/news.jsp?id=ns99993232">First speed of gravity measurement revealed</A> (Source: New Scientist)

The speed of gravity has been measured for the first time. The landmark experiment shows that it travels at the speed of light, meaning that Einstein's general theory of relativity has passed another test with flying colours.

gravity had no speed only momentem



tell me how did they mesure gravitys speed?

Originally posted by A Canadian
gravity had no speed only momentem
Wrong. It has speed, but no momentum.

tell me how did they mesure gravitys speed?
Uhh.. read the link.

- Warren

sorry was looking for the link in the wrong places

=)



"I train at 500 times gravity!" - Vegeta, Dragon Ball Z

Very nifty, thanks. :)

Crisp

The landmark experiment shows that it travels at the speed of light

Does that mean we can finally chuck Tom Van Flandern and his theoretical gravity nonsense into the trash bin ?

Oh, happy day!

:)

Crisp,

With all due respect, why would anyone assume that gravity travels slower or faster than c. Isn't it logical to assume that gravitons (or whatever you think causes the gravitational interaction) travel at the same speed as virtual and electromagnetic photons?

It seems that the fastest speed in the universe (at least currently) is c for all long distance interactions. This seems to be a fundamental rule in our universe, whether general relativity agrees with it or not.

Tom

Prosoothus

why would anyone assume that gravity travels slower or faster than c.

This guy does:


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 v/c, 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 spacetime with the propagation speed indicated by observational evidence and experiments: not less than 2 x 10^10 c.

http://www.ldolphin.org/vanFlandern/gravityspeed.html

If gravity traveled faster than light, it would be analogous to seeing a fast plane fly over at a high altitude, and then a minute later hearing the "image" of that plane, delayed. As we observe farther and farther away, we'd measure more and more difference in where we see an object and where the gravitational influence seems to be coming from, as if there were gravity "ghosts" preceding the visual real object. Since a measurement of a galaxy's or galactic cluster's gravitation affect would show immediately if it's matched to light or not, I can only assume we can't measure that accurately enough to be sure yet. I would have thought local stars' influence on others vs. their apparent positioning would have given some evidence though.

Originally posted by Prosoothus
With all due respect, why would anyone assume that gravity travels slower or faster than c.
Aren't you the one who is constantly pressuring us to take nothing for granted? Here you are, stating quite calmly that it's self-evident that gravity should propagate at c, and we shouldn't need to do any experiment to verify it.

You also state that there is an aether. We did lots of experiments to verify it, and found no evidence. Yet you refuse to accept the experimental evidence.

What's with the double-standard?

- Warren

Silly bystander must ask: What is the relationship of gravitons and the curvature of space? Maybe I don't know about message passing in this system.

Harold

chroot,


Aren't you the one who is constantly pressuring us to take nothing for granted? Here you are, stating quite calmly that it's self-evident that gravity should propagate at c, and we shouldn't need to do any experiment to verify it.

I'm not saying that the speed of gravity shouldn't be verified, I'm just disagreeing with Crisp's assumption that the speed of gravity being equal to c somehow gives validity to general relativity.

The only thing that I see from the fact that the speed of gravity is equal to c is that gravity appears to be even more related to the electromagnetic interaction than it was before. And as everyone knows, the electromagnetic interaction is NOT the result of curved spacetime. :)

Tom

Originally posted by Prosoothus
I'm not saying that the speed of gravity shouldn't be verified, I'm just disagreeing with Crisp's assumption that the speed of gravity being equal to c somehow gives validity to general relativity.
Well, you don't understand relativity -- so how would you know what would or wouldn't give validity to it?

The only thing that I see from the fact that the speed of gravity is equal to c is that gravity appears to be even more related to the electromagnetic interaction than it was before. And as everyone knows, the electromagnetic interaction is NOT the result of curved spacetime. :)
The mass cancels from both sides of

F = ma = GMm/r²

The mass does not cancel from both sides of

F = ma = q₁q₂/r²

It is surprising and not at all "natural" that gravitational mass and inertia should be identically the same.

This alone is the reason that electromagnetism and gravity are fundamentally different.

- Warren

chroot,


The mass cancels from both sides of

F = ma = GMm/r2

The mass does not cancel from both sides of

F = ma = q1q2/r2

It is surprising and not at all "natural" that gravitational mass and inertia should be identically the same.

I would be surprised if the mass from the inertial formula DID NOT cancel the mass from the gravitational formula.

Which formula is "surprising" to you, the inertial formula or the gravitational formula?? What would you have expected the inertial formula or the gravitational formula to be in order for it to not surprise you?? Does it shock you that mass is in both formulas?? :)

As for the electrostatic formula you showed, I'm sure that if "electrostatic inertia" existed, the charge in the formulas would cancel as well. :)

Well, at least now we know that the electrostatic and the gravitational interaction have TWO things in common.

1) They both obey the 1/r^2 law.

2) They both travel at the speed of light (thanks Crisp :))

Gee, now it looks as if they're more similiar than different. :)

Tom

Originally posted by Prosoothus
Which formula is "surprising" to you, the inertial formula or the gravitational formula??
The fact that the gravitational mass and the inertia are the same is surprising to me (and to every other person who really grasps the consequences of that statement). There's no reason that they would have to be the same, but they are. It's a very loaded statement. It has fundamental significance. I didn't expect you to really grasp the significance.

As for the electrostatic formula you showed, I'm sure that if "electrostatic inertia" existed, the charge in the formulas would cancel as well.
But electromagnetic inertia doesn't exist. Why not? This is what is suprising. Gravity has deeper significance than electromagnetism.

1) They both obey the 1/r^2 law.

2) They both travel at the speed of light (thanks Crisp :))

Gee, now it looks as if they're more similiar than different.
There are many place in physics where the same form of equation pops up for very different phenomema. It doesn't mean the phenomena are the same -- especially in this circumstance, with the "gravitational charge" = inertia difference, which is fundamental and extremely important.

- Warren

Originally posted by Prosoothus
Gee, now it looks as if they're more similiar than different. :)
Besides, I hope you realize that the physics community is now on a quest to show how gravity, electromagnetism, the weak interactions, and the colour force are all actually different representations of one unified force. We hope we can find a way to make gravity work just like the other known forces... but it hasn't happened yet.

- Warren

Harold:

<i>Silly bystander must ask: What is the relationship of gravitons and the curvature of space?</i>

Nobody knows yet. The graviton is so far a hypothetical particle of a quantum theory of gravity. Curved spacetime is a classical theory. We don't know how to make the two go together yet.

Hi Tom,

"I'm not saying that the speed of gravity shouldn't be verified, I'm just disagreeing with Crisp's assumption that the speed of gravity being equal to c somehow gives validity to general relativity."

:D ... Unfortunately it was not my experiment and it is not me who is claiming that this gives validity to GR --- I'm not that good :D ... (yet ;)).

But it is one of the predictions of GR that was previously unmeasured, if it where to be found different, then GR would have failed... now the results is consistent with GR, making the theory a bit more probable again.

Bye!

Crisp

Would someone answer a few questions that I have:

1. If the speed of gravity changed; would the effect be a change in the speed of light? if not: what physics relative to the speed of gravity would change, and would there be a chain of mathematical equation to other elements or theories in physics.

Crisp,


But it is one of the predictions of GR that was previously unmeasured, if it where to be found different, then GR would have failed... now the results is consistent with GR, making the theory a bit more probable again.

I would say that it makes GR just as probable as it was before the experiment. :)

I think it was going overboard to say:


Einstein's general theory of relativity has passed another test with flying colours.

However, I am pleased that Einstein got something right. :). But then, even a broken clock is right twice a day. :)

Tom

pfcgrogan,

Welcome to sciforums.


1. If the speed of gravity changed; would the effect be a change in the speed of light? if not: what physics relative to the speed of gravity would change, and would there be a chain of mathematical equation to other elements or theories in physics.

First, before I give my opinion, I just wanted to let you know that I'm the official crackpot on these forums. :) My opinions to not reflect the opinions of the general scientific community.

Now to your question. If the speed of gravity changed, the speed of all electromagnetic photons and virtual photons (particles that make up electric and magnetic fields) would change as well. My theory is that the photon is a gravitational dipole (one side is gravitational and the other side is antigravitational). This is what causes the photon to travel at the speed of light. When the photon is travelling at the speed of light, the force exerted on the photon is 0 because gravity can no longer "catch up" with the photon (since gravity travels at c). If you were to increase the speed of the gravity, the gravity would catch up with a photon that is travelling at c, and as a result it would "push" the photon to match the speed of the gravity. This would mean that the speed of light is always identical to the speed of gravity.

Tom

<i>1. If the speed of gravity changed; would the effect be a change in the speed of light?</i>

It's hard to say, but perhaps. Gravity and the speed of light seem to be tied together quite closely by general relativity. On the other hand, I can't think of anything which could cause the speed of either gravity or light to change.

Electrodynamic (Coulomb) forces propagate almost instantly, which is why the angular momentum of charges is unchanged by their encounters. By contrast, all electromagnetic phenomena propagate at speed c, and forces applied by these phenomena (e.g., radiation pressure) alter angular momentum.

In Zarkovian Spin Gravity, where the force pushing towards the centre of spin (spin gravity) is not a coulombic force, but is's manifestation of the force and the potential are intimately coupled.
To talk about this in relation to Zarkovian Spin Gravity see www.zarkscience.com
:cool:

<i>Electrodynamic (Coulomb) forces propagate almost instantly, which is why the angular momentum of charges is unchanged by their encounters. By contrast, all electromagnetic phenomena propagate at speed c, and forces applied by these phenomena (e.g., radiation pressure) alter angular momentum.</i>

This is false. Coulomb forces <b>are</b> electromagetic, and changes to the electric field propagate at the speed of light. Coulomb forces can alter angular momentum.