Speed of Gravity

[Spazzy-kins]

So let me get this strait.

 

This guy measures the bend in light and/or radio waves and determines the speed of gravity by this? How? I think I must be missing something, because if I'm not, Kopeiken has made a gross error in his interpretation of the data. I don't see how any of this would show a change in the gravitational force created by Jupiter.

 

Don't get me wrong. It makes sense to me that gravity's force travels at ~c. I just don't see how Kopeiken proved it. To me it's still an unknown.

[5614]

that is the whole point!!!!

 

if the experiment was correct then that is the speed of gravity... however many scientists around the world are saying that the mathematics was mucked up and that (as you said) "Kopeiken has made a gross error in his interpretation of the data."

[swansont]

So let me get this strait.

 

This guy measures the bend in light and/or radio waves and determines the speed of gravity by this? How? I think I must be missing something' date=' because if I'm not, Kopeiken has made a gross error in his interpretation of the data. I don't see how any of this would show a change in the gravitational force created by Jupiter.

 

Don't get me wrong. It makes sense to me that gravity's force travels at ~c. I just don't see how Kopeiken proved it. To me it's still an unknown.[/quote']

 

As I understand it:

If the gravity is retarded by travelling at c, the light gets bent by one angle as it passes by Jupiter, with an impact parameter of d. If gravity acts instantaneously, the impact parameter is different, and the angle is different as a result.

[goodyhi11]

under any circumstance, we still think that gravity is the thing that puts everything in order. the planets are in a specific orbit. Gravity travels at the speed of light ralative to what. Gravity travels at the speed of light ralative to you. This is a confusing point of view which confuses every body. NO, GRAVITY DOES NOT TRAVEL AT THE SPEED OF LIGHT.

[5614]

NO, GRAVITY DOES NOT TRAVEL AT THE SPEED OF LIGHT.

 

well that depends on your view of the mathematics mentioned in this:

http://curious.astro.cornell.edu/question.php?number=573

article... the majority of astronomers think it is rubbish calculations and agree with goodyhi11... however just remember some would think that gravity does travel at c

 

i think i will stick with the majority of scientists and what i think which is that gravity does NOT travel at c.

 

(by the way c = speed of light)

[Sayonara]

Putting something in block capitals is not a substitute for explaining how it works.

[Gilded]

"Putting something in block capitals is not a substitute for explaining how it works."

 

Lol. :> That should be included in the "read this before you post" section. )

[The Rebel]

Who's to say gravity has speed at all???

 

I believe that we shouldn't be seeing light and gravity as a travelling phenomenom, but merely an effect of energies.

 

To me gravity and light are very similar and I see no reason why light and gravity should not be considered as identical entities.

 

Why are we also quantifying our judgements against c??? We've become so engrossed in a constant speed of light it almost seems impossible to progress other ideas because they do not align with current theories on light.

[Les Sleeth]

i think i will stick with the majority of scientists and what i think which is that gravity does NOT travel at c.[/i]

 

Since I posted here, I've done some research. You are wrong about the "majority of scientists." The majority think the speed of gravity is c, just as Einstein predicted. Although there are some technical problems with Kopeikin's results which invalidate them, swansont seems right to suggest, "Van Flandern is a crackpot."

 

I am just an amateur myself, so I posted the issue brought up here at another science site where I participate (physicsforums.com). That site is moderated by working physicists, educators and grad students, so if you'd like to read the discussion that took off from my post about Kopeik and Van Flandern's challenge try here.

[5614]

indeed i was wrong... thanks for pointing it out.

 

however there is no physical proof of the speed of gravity as it is too weak to measure, therefore we have to do it mathematically.

 

Van Flandern's proof (according to the majority of scientists) is rubbish as gravity didnt ever come into the equation he used and so his proof was invalid.

 

in netwonian model gravity travels instanteneous, however in general relativity (GR) it travels at the speed of light.

 

again this cannot be measure and the proofs are only mathematical, however the majority of scientists DO think gravity travels at c.

[Asimov Pupil]

Einstien clearly stated with some fancy mathematics that gravity does travel at the speed of light

[JaKiri]

Einstien clearly stated with some fancy mathematics that gravity does travel at the speed of light

 

That doesn't matter in the slightest. Until it has been reliably tested, and found to travel at the speed of light, we don't know. Mathematics can be based on wrong assumptions, there is no dogma.

[Severian]

There are of course differences between direct and indirect measurements. Often in physics one is forced to assume particular things and then say, 'if this assumption is true, our measurement shows...'. I think this is quite reasonable, as long as one remembers that assumptions have been made.

 

This is true with gravity as well. In addition to the direct observations of the 'speed of gravity', one can show that gravity must travel at (or very very near to) the speed of light just by thinking what would happen if it didn't. As I pointed out earlier in this post, gravity must be mediated by a particle, which I call the 'graviton'. This graviton does not have to be fundamanetal - it could be a composition of other particles (or strings!) if you like - the important point is that this must exist in a low energy (ie. < Planck mass) effective theory.

 

Now, lets further as what would happen if the graviton did not travel at c? To do this, the graviton would have to have non-zero mass. How non-zero depends on how close to c it travels. Now, it is relatively easy to show in QFT that any force mediated by a massive particle will give a (classical) force-distance dependance of:

 

[math]F \propto \frac{1}{r^2} e^{-mr}[/math]

 

(where I am setting c=1, r is the distance from the source and m is the mass of the mediator). This was first shown by Yukawa. You can see that any mass causes an exponential fall-off of the force. In fact, this is what happens to the weak nuclear force. It is 'weak' because the particles mediating it are massive, so we end up with an exponential decline of the force with distance. Of course, one could imagine that m is so small that one can expand [math]e^{-mr} \approx 1-mr[/math] giving the Newtonian result plus a small correction, but one must remember that gravity has been tested on atronomical scales. The values of r at which gravity has been tested are huge, so m would need to be very small indeed to make m*r a small number.

 

So, it is reasonable to say that m must be very small and that gravity propagates at (very near to) the speed of light.

[swansont]

(where I am setting c=1' date=' r is the distance from the source and m is the mass of the mediator). This was first shown by Yukawa. You can see that any mass causes an exponential fall-off of the force. In fact, this is what happens to the weak nuclear force. It is 'weak' because the particles mediating it are massive, so we end up with an exponential decline of the force with distance. Of course, one could imagine that m is so small that one can expand [math']e^{-mr} \approx 1-mr[/math] giving the Newtonian result plus a small correction, but one must remember that gravity has been tested on atronomical scales. The values of r at which gravity has been tested are huge, so m would need to be very small indeed to make m*r a small number.

 

So, it is reasonable to say that m must be very small and that gravity propagates at (very near to) the speed of light.

 

But there are issues with e.g. galaxies not rotating at the right speed for their observed mass. This is why dark matter has been hypothesized. The problem, AFAIK, is that assuming mass for the exchange particle does not solve the problems, or introduces others.

 

(Math markups do not seem to be currently working)

[Severian]

But there are issues with e.g. galaxies not rotating at the right speed for their observed mass. This is why dark matter has been hypothesized. The problem' date=' AFAIK, is that assuming mass for the exchange particle does not solve the problems, or introduces others.

[/quote']

 

If a massive graviton could be used to describe the rotation of galaxies (actually it can't, since we would need more gravity, not less) it would then fail for the gravitational interaction between galaxies.

[RawThinkTank]

Did any one of U searched GravityScope on the net yet ?