# Thread: Speculations on the speeds of gravity and light

1. ## Speculations on the speeds of gravity and light

When it comes to the speed of gravity, it appears we are in a quandary. Relativity says that nothing can travel faster than the speed of light. But if this is the case, orbits would decay very rapidly. They could never be as stable as they are observed to be.This is because if it takes time for the information that a body has moved to reach another through gravitation, a body will not be pulled to where the other is now (in its current position), but to where it was when the gravitational waves started out.

According to Newtonian gravity, the transmission is instantaneous. According to relativity, it appears to depend upon the situation, which is iffy at best. It says that gravitational waves travel at the speed of light, but that the effects of gravity are felt instantaneously. In other words, the warping of space-time moves with the body at all times, as if it were physically adhered to it. But then, how is the information transferred through such a permanent fixture to another when the body is in motion? And if this is the case, what is the meaning of gravitational waves (implying change of state through transmission)? This is the "scissors paradox".

I have determined (although some might disagree) that this is very similar to the effect that promoted relativity to begin with. That is, the Michelson-Morley experiment. In this, a light beam which was split, directed at perpendicular directions to each other, one in the direction of the motion of the Earth (through the ether) and the other perpendicular to this, and then realigned should have produced interference with each other which could be measured. However, no such interference could be found, just as no aberration is found with gravity. The underlying concepts are virtually the same.

Special relativity does very well when explaining the absence of interference in terms of time dilation and the contraction of distances in the line of motion, and has even resulted in the famous E=mc2. But when it comes to the aberration of gravity, it is a different matter. The time dilation necessary in order to explain it is on the order of billions of times greater, and vise versa for the distance contraction, so this is out of the question. And a non-Euclidean geometry would only serve to make matters worse, as a curved path only increases the time necessary for the interaction.

As far as the Michelson-Morley experiment is concerned, however, I believe I have found a flaw in the experiment. I have recreated it geometrically on paper and found that in any frame of reference other than at rest, it is in fact impossible to exactly realign the beams. That is to say, the two beams, once split, cannot be redirected by the mirrors so that they meet at the same point at final reflection and then travel in the same direction. The angles will instead diverge. The best we can do is to adjust the mirrors slightly so that the beams travel in the same final direction, but they won't meet at the same point at final reflection, and will travel parallel to each other as separate beams with a distance between them that increases with increased speed for Earth through the ether. We cannot even be sure that the angle of incidence equals the angle of reflection for all frames of reference.

What we need, then, is a way to measure the discrepencies of light for motion through the ether without the use of mirrors, the splitting of beams, or a measure of interference. How would we do that, you ask? Simple. No matter what the frame of refence, the Earth must travel with at least 1/10000 of the speed of light at some point in its orbit because of its revolutions around the sun. Let's consider this to be its velocity through the ether at the moment. If we were to direct a light beam down a ten meter long pole, that is directed perpendicularly to the motion through the ether, then according to the original expectations of the Michelson-Morley experiment and classical physics, the light would fall back away from the line of motion as it travels this distance since the Earth is moving forward during this time. When the pole is directed opposite this, the light will fall back the other way. The distance between these two points for this velocity as seen on a screen at the end of the pole will be 1/5 cm.

Of course, we would not originally know the velocity and direction of the Earth through the ether, but directing the pole at all possible angles will create a filled in circle on the screen at the end of the pole if all of the points are marked. The ratio of the radius of the circle to the length of the pole will equal the ratio of the velocity of the Earth through the ether to the speed of light. If the pole is then turned to where the light is pointed to the center of the circle and the light moves in the same direction as the pole when the pole is then turned away from the center, then the pole will be pointing in the direction of the Earth's direction of travel.

This experiment is so simple that it has probably already been tried (as at least 99% of what I propose seems to have already been thought of, but at least that shows I'm on the right track), but I have never heard of anything other than the Michelson-Morley experiment. With relativity being as successful as it seems to be, and with the aberration of gravity necessarily cancelling itself out, this probably will too (but it would still be an advantage to know for sure). But if it didn't, well, that would just be a whole different bag of tomatoes, wouldn't it? If it cancels itself out, then we must consider how gravity would do the same thing (time dilation and contraction aren't enough with gravity). If it doesn't, then we must show how the distance between two parallel beams of light cancel the interference that would otherwise be observed if they were aligned, and then somehow apply that to gravity.

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Grav,

No, we are not in any quandy with the speed of gravity. Start reading this thread here:

http://www.bautforum.com/showpost.ph...7&postcount=24

The math of GR has quite a few little tricks up its sleeve. Short answer is GR gravity is not simple central inverse square. It has components that depend on velocity and even acceleration in addition to position. If you've been reading Van Flandern, well, he's just being stubborn about this.

-Richard

3. I have read Tom Van Flandern's website and have come up with transmission velocities similar to his for different binary systems, billions of times greater than the speed of light. The differences in specific binary systems, however, change with their specifics but still remain about the same order. I thought at first that the rate of transmission might vary with those specific details but then decided that the rate of transmission should probably be the same in each case and also equal to the speed of light or at least close to it.

In your referred post, you mention that the fields should foretell the future position of a body in linear motion. I thought about that earlier today, since this seems to be the only way that gravity could appear instantaneous and in accordance to relativity. But I dismissed the idea as ridiculous. Perhaps I wasn't too far off after all. But I have trouble envisioning how this would apply to a constantly changing orbit. To find the implied vectors at each turn and incorporate them would be a tremendous task in itself. Do you have any suggestions?

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See the paper referenced in this post in the same thread:

http://www.bautforum.com/showpost.ph...0&postcount=50

The math of GR's tensors and metrics gets complicated, but Steve Carlip, the author and GR expert shows how this works. Myself, I don't understand the "high powered" tensor math enough to follow the derivation. He compares this to the EM case, which I understand better, although he uses the more elegant 4-vector and potential method of doing, while I think of EM in the 3-vector/1-time form, but I can follow it enough to see.

Basically, EM forces being to "miss" due to the propagation delay when there is acceleration, or the velocity changes significantly during the light-time propagation delay between charges. The missing energy and momentum goes into radiation, and in fact, radiation can be seen as the direct consequence of propagation delay in the forces. Acceleration corresponds to dipole radiation, that is a changing dipole moment produces radation.

GR gravity takes this one derivate higher, and anticipates acceleration as well as velocity. Gravity only misses due to changes in acceleration (da/dt= "jerk" )during the light-time delay. And this corresponds to quadropole radiation. That is it takes a time-varying quadropole moment, not simply a dipole moment to cause gravitational radiation.

In our solar system, the "jerk" is very small and there is very little radiation. In fact, it would take something like 10^20 years or something ridiculous like that for the orbit of Jupiter to decay due to radiation and propagation delay "missing". But in those binaries, the "jerk" or quadropole moment variation is enough to cause significant "missing" and losses to radiation.

And these agree with the predictions of GR within experimental error.

-Richard

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This topic has been discussed at least once more before, here in BAUT (in addition to the posts publius mentions)

Ashby's few short paras here are as good a succinct summary as I could find on the web.

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Grav, TVF makes a living promoting this nonsense. He is just plain wrong.

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## Gravity

I don't know if what I perceive to be gravity supports or disproves the spacetime of general relativity but I think that gravity is transmitted by gravitons and at the speed of light.

These gravitons carry a tiny packet of momentum from the originating object.

When emitted: the leftward momentums reduce the likelihood that the object will move left while the rightward momentums reduce the likelihood that the object will move right.

The gravitons are capable of "colliding" or cancelling out and so between two objects part of the "repulsive" momentum from the other object is lost to these collisions which produces a net affect of attraction.

Spacetime, if I were to construct such a mathematical beast, would consist of the interference patterns of the gravitons and the movements of bodies would be along such interference patterns.

The gravitons are able to "predict" the movement of objects because they are emitted in all directions away from the bodies and so the ones emitted in the forward direction reinforce with the ones from the central body which results in a predetermination of the "path of least resistence".

To visualize such a scenario just create a circle (mine was a 5 mm radius) and then construct offsets of 1 mm outward from that circle until you have constructed a circular "path" (my largest was 114 mm radius). This represents your "sun".

My "planet" is a 5 mm radius circle at an "orbit" of 57 mm with 1 mm offsets until its outer circle is 57 mm.

My sun is green and the planet is blue.

I can immediately see an area of interference in the display between the two objects and another area radiating outward from the planet which represents low interference.

Towards the front and back are interference patterns that represent the path of least resistence for the moving planet.

I did this all with a Unigraphics program (another graphics program could be used).

In conclusion, gravity in the above description is just the sum of momentums of two bodies.
Last edited by Squashed; 2006-Jun-09 at 05:12 PM.

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It just seems to me that the problem with TVF is in his particular concept of push gravity. In a push gravity where mass is vacumming the gravitons generating inverse square hydrondynamic effect, the velocity that causes the "drag" behind it would inversely create a wake in front of it with the bumps being accounted for by the "jerks" as explained by the GR math.

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My view of gravity is very similar to Squashed's, but it also has a component of grav's, the Le Sage component. Tom VF has a Le Sage component too, but I think he's offtrack with his FTL gravitons.

Here's what I would say. There is a background of em waves (let's not worry about their frequency for the moment). These waves are randomly oriented in phase, etc. When they contact masses they are organized into coherent waves, which I call gravitons. These gravitons interfere with other such gravitons emitted by other masses to form an interference pattern like Squashed says. The motions of masses are then guided by this interference pattern. The random waves are akin to the Le Sage particles or waves, which do the pushing. Basically, the 'pushing' waves push objects into the 'shadow' waves formed by gravitons. Later on, the coherent waves degrade to random waves once more to restore the system.

How then does gravitational aberration fit in? Taking the Earth and the Sun as an example, the interference pattern determining their gravitation is composed of gravitons emitted by each. The gravitons emitted by the Earth which hit the Sun are ones that are 'aimed' behind the Sun's current position. (Think of how a running hunter would have to aim to hit a stationary target.) The recoil momentum of these gravitons tend to advance the Earth in its orbit. However, the gravitons that are emitted by the Sun which hit the Earth had to have been ones 'aimed' ahead of the Earth's position. These gravitons tend to slow the Earth down. The momentum transfers thus cancel out and the Earth's orbit is stable.

I don't mean to be hijacking the thread or anything - just thought I'd pipe up since I saw some of my own ideas out here!

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## Pictures

Originally Posted by Squashed
I did this all with a Unigraphics program (another graphics program could be used).
Here is a picture of my display.

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Nice graphic, Squashed. I need something like that for my own paper!

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Originally Posted by publius
The math of GR's tensors and metrics gets complicated, but Steve Carlip, the author and GR expert shows how this works. Myself, I don't understand the "high powered" tensor math enough to follow the derivation. He compares this to the EM case, which I understand better, although he uses the more elegant 4-vector and potential method of doing, while I think of EM in the 3-vector/1-time form, but I can follow it enough to see.

Basically, EM forces being to "miss" due to the propagation delay when there is acceleration, or the velocity changes significantly during the light-time propagation delay between charges. The missing energy and momentum goes into radiation, and in fact, radiation can be seen as the direct consequence of propagation delay in the forces. Acceleration corresponds to dipole radiation, that is a changing dipole moment produces radation.
If EM forces are clear of aberration problems and if gravity is electromagnetic in nature, could we just say gravity too is clear of problems or would we still need some part of Carlip's GR arguments?

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## Here's Another One

Originally Posted by ExpErdMann
Nice graphic, Squashed. I need something like that for my own paper!
I tried another graphic using radial lines separated by 2.5 degrees (since the gravitons are supposed to be emitted straight outward according to my description).

Both the sun and the planet appear as 4-leafed clovers for some reason. It looks kinda kool on my monitor.

This representation does not show the interference patterns of gravitons as well as the first.

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Originally Posted by ExpErdMann
If EM forces are clear of aberration problems and if gravity is electromagnetic in nature, could we just say gravity too is clear of problems or would we still need some part of Carlip's GR arguments?

This can get confusing. EM is not free of aberration problems, EM forces do miss. Gravity "misses" as well, but it doesn't miss as much as EM by a long shot.

Netwonian gravity is modelled as simple central inverse square. The basic Coulomb force (electric) is also simple inverse square. However, you have the magnetic field when charges get in motion and the relativistic transforms as well. The result is the EM forces between two charges in motion have non-central, velocity dependent terms. The way it works it out is EM antipicates velocity. If the charges are constrained to move at constant velocity, then the EM forces will not miss, and will be exactly equal and opposite. Momentum is conserved. Put in another way, the EM field of a charge contains information about both position and velocity of the source. The force on a test charge will point in a direction r + v*(r/c), were r is the position vector of the soruce and v is it's velocity. The information is retarded, that is r and v are that of a time (r/c) in the past, the time it tooks for the fields to propagate to the test charge.

We can say that the EM field "extrapolates" motion to first order. Now, since the charges have forces on them, unless otherwise constrained, they will acclerate in the meantime, and the above direction will miss. From this you see that accelerating charges radiate, and that radiation carries away momentum and energy preserving momentum and energy conservation.

Now, GR gravity "extrapolates" to second order, taking acceleration into account as well as velocity. Or IOW, the gravitational field contains information about the acceleration of the source in addition to its position and velocity.

As Carlip shows in that paper I linked to, the gravitational force points in a direction r + v*(r/c) + 1/2a(r/c)^2, extrapolating acceleration as well.

So, for gravity to miss and radiate, there must a change in acceleration in the light-meantime. A uniformaly accelerating mass does not radiate. But a "jerking" mass does.

Another way this can be expressed is in terms of the ratio v/c, imagining two charges or two masses "orbiting" each other at some relative speed v. Propagation delay "miss" and radiation goes as (v/c)^3 for EM, but for GR gravity it is a whopping 5th power, (v/c)^5.

The aberration of EM orbits would be significant, and you couldn't have a stable solar system orbit with EM forces. However, because of that 5th power, you can with gravity.

-Richard

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Gravity is not electromagnetic in nature. No observational evidence to date suggests gravity is the least bit affected by EM fields. There is, however, considerable evidence EM fields are affected by gravity.

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Originally Posted by Thanatos
Gravity is not electromagnetic in nature. No observational evidence to date suggests gravity is the least bit affected by EM fields. There is, however, considerable evidence EM fields are affected by gravity.
Well, perhaps when we have a better understanding of EM. As things stand, g. is little more than a mathematical abstraction, and the math provides no meaningful insight on the mechanism.

Both EM and g. fall away with the square of the distance, of course.

17. Okay. A question for the experts. If gravity runs a little bit ahead of a body when it changes direction, then wouldn't the waves have to continue with the original velocity of the body plus c in order to be in the position the body would have been? If this is the case, then it travels with the additional velocity of the source and then so does light. Furthermore, this might cancel out the delay of interaction from the source, but the body that receives the waves would still observe an aberration due to its own velocity. It must therefore receive the waves ahead of its own position as well. Do the separate fields of each somehow interact before the receiving body catches up with it?
Last edited by grav; 2006-Jun-10 at 10:21 PM.

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Originally Posted by Thanatos
Gravity is not electromagnetic in nature. No observational evidence to date suggests gravity is the least bit affected by EM fields. There is, however, considerable evidence EM fields are affected by gravity.

Actually, EM does "make gravity", and if Hawking-Unruh radiation is real, then that is gravity making EM radiation, completing the coupling. But these effects are so weak that can be ignored for all practical purposes and may not even measurable.

Take a gander at Einstein's big bad GR field equation. A big non-linear tensor partial differential equation involving the metric of space-time. The source term on the right is called the "stress-energy" tensor. Mass and energy are equivalent (E=mc^2), so an energy density in space makes gravity just like a mass density. This energy density is the 0,0 component of the source tensor, the lower 3x3 part of the matrix is the "stress" part and contains the momentum transport. The other (0,i) (j,0) components are the power, or energy transport terms. Just a moving charge makes a magnetic field, so GR gravity has a "gravitomagnetic" component that depends on momentum.

Now, EM fields contain energy and if you have E and B together, momentum and power as well. You can construct an EM stress energy tensor. 00 is the energy density (E^2 + B^2 terms). The energy transport part is the Poynting vector, and the momentum part is the 3x3 Maxwell Stress Tensor.

When you have EM in a region of space-time, that EM stress-energy tensor adds right to the regular mass and its momentum stress-energy. EM curves space just like any other form of energy and momentum, but fortunately the effect is so small we can consider space to be flat for all practical EM purposes. But that effect is there, and technically since EM curves space-time and "makes gravity", you don't really have any truly inertial Lorentz frames. So you then would have to solve for Maxwell in curved space-time, or non-inertial frames, which is absolute complicated mess that will make your head spin.

Now, going the other way, a black hole is supposed to make Hawking radiation, which is EM radiation due to the event horizon. Unruh radiation is EM radiation an accelerating observer would see, which means the Equivalence Principle is sastified even for this as well.

However, there is no classical explanation for Hawking-Unruh radiation, it is a purely quantum effect. Classically, EM makes gravity, but gravity doesn't make EM. So these seems to suggest that a quantum theory of gravity would fill in the gaps. This may be the resolution of vexing Equivalence Principle conundrum of the question if charges actually radiate or not at rest in a gravitational field, and do freely falling charges really radiate or only apparently radiate.

-Richard

19. publius,

Your responses in the general science section on the theory of electricity and capacitance I posted have got me thinking about the relation to gravity. Now, as of yet, I am not convinced that the Lorentz conctractions are necessary for an explanation of the magnetic forces produced by an electric current (it would seem that Newtonian physics is enough), although I do see how this might be necessary to explain the motions of an individual charge through a magnetic field. This, then, would be the same for two point charges moving in relation to each other, which is the same for gravity. As far as the theory of the gravitational field continuing in straight lines while the bodies change directions, although interesting, this is not too appealling to me for a few reasons. One, if it keeps moving in a straight line, at what point does it dissipate and change direction (although I know you would probably say it is the total of all of the potential vectors). Two, the center of mass would be displaced, but not in the way necessary for what you describe. And three, how would they meet back up ahead of the receiving body in order to cancel its aberration. There are more, but this is enough to start with. I suppose you might say that I just don't understand the theories well enough, and this might be true to some degree, but I consider it my duty to pick apart every formula and concept I can get my hands on, refine them into their most basic components, and then build them back up again into something comprehensible and that can also be applied to other fields. That is what I am trying to do here.

I have (had) a couple of alternative scenarios to the "fields moving ahead of the body in straight lines" scenario. I have forgotten one of them but I'm sure it'll come back to me. I do a lot of jumping around when I get stuck on something for too long. Anyway, how about this? If a body were actually moving through a neutrino medium, the gravitational pressure might be effected by a body in motion. This would provide an extra push on the gravitational waves in front of the body and less in the back, creating a sort of Doppler effect (blueshifted in the front, redshifted in back). The waves would literally be pushed closer together in front of the body and enlongated behind it. Then they wouldn't have to travel separately or at different speeds, just different energies depending on the line of motion, the same as light. Now this may seem the same as relativity, and in fact it may be. Again, I am not arguing against it, I am simply trying to place it in the right perspective where the mechanisms make sense. In fact, Lorentz transformations would probably still apply with this scenario. Please let me know what you think.

EDIT: I'm sorry. The other scenario was the Lorentz contraction, where apparent distances would shrink in the line of motion, so that each body would seem to be a little further ahead than it really is, although now that I think about it, this seems about as tricky as the fields scenario.
Last edited by grav; 2006-Jun-12 at 05:28 AM.

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Originally Posted by publius
This can get confusing. EM is not free of aberration problems, EM forces do miss. Gravity "misses" as well, but it doesn't miss as much as EM by a long shot.
<>
Another way this can be expressed is in terms of the ratio v/c, imagining two charges or two masses "orbiting" each other at some relative speed v. Propagation delay "miss" and radiation goes as (v/c)^3 for EM, but for GR gravity it is a whopping 5th power, (v/c)^5.

The aberration of EM orbits would be significant, and you couldn't have a stable solar system orbit with EM forces. However, because of that 5th power, you can with gravity.

-Richard
Thanks for the very detailed reply! There must indeed be a lot of confusion on this, or Tom VF's paper on the speed of gravity would never have made it past review and Carlip would not have felt a need to reply. Not having much background on this, I wonder why Carlip had to make what look like new arguments concerning questions which one would think should have been solved long ago.

Now another question. You conclude that EM forces can't do it and Thanatos also made the same point. But the mechanism I'm thinking of, which seems similar in some respects to Squashed's, does not suppose that it is the electromagnetic forces between moving charges which is driving gravity. I'm just saying that background fields of em radiation are interacting with matter such that a portion of the em waves are being absorbed by matter. (To be more precise, they are being converted into coherent waves of em radiation, which have the effect, as Squashed states, of creating 'tracks' for particle motion). It is not a totally electromagnetic interaction per se because even neutral particles must also be part of this process. If we cast things in this light, would your conclusions change?

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Originally Posted by grav
publius,

Your responses in the general science section on the theory of electricity and capacitance I posted have got me thinking about the relation to gravity. Now, as of yet, I am not convinced that the Lorentz conctractions are necessary for an explanation of the magnetic forces produced by an electric current (it would seem that Newtonian physics is enough), although I do see how this might be necessary to explain the motions of an individual charge through a magnetic field. This, then, would be the same for two point charges moving in relation to each other, which is the same for gravity. As far as the theory of the gravitational field continuing in straight lines while the bodies change directions, although interesting, this is not too appealling to me for a few reasons. One, if it keeps moving in a straight line, at what point does it dissipate and change direction (although I know you would probably say it is the total of all of the potential vectors). Two, the center of mass would be displaced, but not in the way necessary for what you describe. And three, how would they meet back up ahead of the receiving body in order to cancel its aberration. There are more, but this is enough to start with. I suppose you might say that I just don't understand the theories well enough, and this might be true to some degree, but I consider it my duty to pick apart every formula and concept I can get my hands on, refine them into their most basic components, and then build them back up again into something comprehensible and that can also be applied to other fields. That is what I am trying to do here.

I have (had) a couple of alternative scenarios to the "fields moving ahead of the body in straight lines" scenario. I have forgotten one of them but I'm sure it'll come back to me. I do a lot of jumping around when I get stuck on something for to long. Anyway, how about this? If a body were actually moving through a neutrino medium, the gravitational pressure might be effected by a body in motion. This would provide an extra push on the gravitational waves in front of the body and less in the back, creating a sort of Doppler effect (blueshifted in the front, redshifted in back). The waves would literally be pushed closer together in front of the body and enlongated behind it. Then they wouldn't have to travel separately or at different speeds, just different energies depending on the line of motion, the same as light. Now this may seem the same as relativity, and in fact it may be. Again, I am not arguing against it, I am simply trying to place it in the right perspective where the mechanisms make sense. In fact, Lorentz transformations would probably still apply with this scenario. Please let me know what you think.

EDIT: I'm sorry. The other scenario was the Lorentz contraction, where apparent distances would shrink in the line of motion, so that each body would seem to be a little further ahead than it really is, although now that I think about it, this seems about as tricky as the fields scenario.
This scenario obviously increases the relative mass of the body. Now for math sake....and this scares me y'all. This is my crazy mind running wild again. Let's freeze frame the body in motion and mark it with a direction/velocity vector. Using the inverse square law project forward to where the strength of g is equal to the g of that mass if it were at rest. That is how much further ahead the body seems.

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The speed of gravity has been measured in a series of experiments executed by Kopeikin (see references). Contrary to what Tom Van Flandern says, it was found that the speed of gravity is approx. c.

http://en.wikipedia.org/wiki/Speed_of_gravity

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Originally Posted by aaaa
The speed of gravity has been measured in a series of experiments executed by Kopeikin (see references). Contrary to what Tom Van Flandern says, it was found that the speed of gravity is approx. c.

http://en.wikipedia.org/wiki/Speed_of_gravity
I must caution that there is a lot of controversy of Kopeikin's measurements. Kopeikin vigorously claims he did indeed measure the speed of gravitational propagation. But other GR experts, including Steve Carlip, strongly dispute it, saying all Kopeikin actually did was measure the speed of light in a very convoluted way, essentially comparing it to itself. The Wiki article mentions this, as it should.

As far as know, the question has not been conclusively resolved, and we can only hope the GR experts will get it sorted out and decide. Until then, we cannot say that the speed of gravity has been measured.

All observations to date are completely consistent with GR's predictions, which are based on the the speed of gravity being c. That's all we can say. We cannot say the speed of gravity has been measured at all.

-Richard

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Originally Posted by publius
I must caution that there is a lot of controversy of Kopeikin's measurements. Kopeikin vigorously claims he did indeed measure the speed of gravitational propagation. But other GR experts, including Steve Carlip, strongly dispute it, saying all Kopeikin actually did was measure the speed of light in a very convoluted way, essentially comparing it to itself. The Wiki article mentions this, as it should.

As far as know, the question has not been conclusively resolved, and we can only hope the GR experts will get it sorted out and decide. Until then, we cannot say that the speed of gravity has been measured.

All observations to date are completely consistent with GR's predictions, which are based on the the speed of gravity being c. That's all we can say. We cannot say the speed of gravity has been measured at all.

-Richard

Correct. We need to wait for LIGO's results.
In the meanwhile, it looks like Kopeikin is publishing in peer reviewed journals, so it is worthwhile to read his papers (especially since they can be read for free in arxiv)

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Originally Posted by publius
Actually, EM does "make gravity", and if Hawking-Unruh radiation is real, then that is gravity making EM radiation, completing the coupling. But these effects are so weak that can be ignored for all practical purposes and may not even measurable.

Now, EM fields contain energy and if you have E and B together, momentum and power as well. You can construct an EM stress energy tensor. 00 is the energy density (E^2 + B^2 terms). The energy transport part is the Poynting vector, and the momentum part is the 3x3 Maxwell Stress Tensor.

When you have EM in a region of space-time, that EM stress-energy tensor adds right to the regular mass and its momentum stress-energy. EM curves space just like any other form of energy and momentum, but fortunately the effect is so small we can consider space to be flat for all practical EM purposes. But that effect is there, and technically since EM curves space-time and "makes gravity", you don't really have any truly inertial Lorentz frames. So you then would have to solve for Maxwell in curved space-time, or non-inertial frames, which is absolute complicated mess that will make your head spin.

Now, going the other way, a black hole is supposed to make Hawking radiation, which is EM radiation due to the event horizon. Unruh radiation is EM radiation an accelerating observer would see, which means the Equivalence Principle is sastified even for this as well.

However, there is no classical explanation for Hawking-Unruh radiation, it is a purely quantum effect. Classically, EM makes gravity, but gravity doesn't make EM. So these seems to suggest that a quantum theory of gravity would fill in the gaps. This may be the resolution of vexing Equivalence Principle conundrum of the question if charges actually radiate or not at rest in a gravitational field, and do freely falling charges really radiate or only apparently radiate.

-Richard
That is right.
The EM field are virtual particles exchanged between (+) and (-) charge. That way the EM field has its energy.
Gravity is distortion (warping) of the space.
The energy is just an inward distortion of the space and this way EM field produces gravity.

Particle with a rest mass (baryon) is a localised energy, a local space-time vibrations. This vibrations are affecting the surrounding space as the gravitational field. So the gravitational field is any space inward distortion and it is propagating like EM field.

Gravitational field radiates an energy but 10^39 less then EM field.
Though this radiation is so tiny , the existence of the baryons matter needs an energetic field. That way baryon matter exists in the closed systems like Black Hole or our Universe where the space distortions are exchanged.
Some people called it gravitons but it is just every space distortion.

In closed system of the Universe our Sun is in gravitational balance with the rest of the Univerce's mass (Machian inertia) and does not radiate out its mass by the gravity.

In binary Black Holes is possible the energy outflow by the gravitational field.
Czeslaw

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Dec 2004
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Kopeikin, as publius pointed out, is not confirmed. LIGO will be the litmus test which IMO. has already been done:

http://www.arxiv.org/abs/astro-ph/0508050
Title: A 2.1 Solar Mass Pulsar Measured by Relativistic Orbital Decay
Authors: David J. Nice, Eric M. Splaver (Princeton), Ingrid H. Stairs (UBC), Oliver Loehmer, Axel Jessner (MPIfR), Michael Kramer (Jodrell Bank), James M. Cordes (Cornell)

PSR J0751+1807 is a millisecond pulsar in a circular 6 hr binary system with a helium white dwarf secondary. Through high precision pulse timing measurements with the Arecibo and Effelsberg radio telescopes, we have detected the decay of its orbit due to emission of gravitational radiation . . . . Interpreted in the context of general relativity, and combined with measurement of Shapiro delay, it implies a pulsar mass of 2.1+-0.2 solar masses, the most massive pulsar measured.

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11
Originally Posted by Thanatos
Kopeikin, as publius pointed out, is not confirmed. LIGO will be the litmus test which IMO. has already been done:

http://www.arxiv.org/abs/astro-ph/0508050
Title: A 2.1 Solar Mass Pulsar Measured by Relativistic Orbital Decay
Authors: David J. Nice, Eric M. Splaver (Princeton), Ingrid H. Stairs (UBC), Oliver Loehmer, Axel Jessner (MPIfR), Michael Kramer (Jodrell Bank), James M. Cordes (Cornell)

PSR J0751+1807 is a millisecond pulsar in a circular 6 hr binary system with a helium white dwarf secondary. Through high precision pulse timing measurements with the Arecibo and Effelsberg radio telescopes, we have detected the decay of its orbit due to emission of gravitational radiation . . . . Interpreted in the context of general relativity, and combined with measurement of Shapiro delay, it implies a pulsar mass of 2.1+-0.2 solar masses, the most massive pulsar measured.

Hmm.