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How fast is gravity?

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guess what, the spin of the graviton is 2

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I am proposing Two ways of measuring the speed of gravity.

 

Are they possible in theory and practice ?

 

1. Very precise equipment for measuring weight, calibrated to zero with a heavy weight.

The equipment is placed so the Moon, Earth and weight will center in a line.

The gravity from the Moon will "pull" on the weight when it passes over.

If the "pull" is strongest when light from the Moon centers -> Gravity speed is c.

If the peak is before light then gravity speed is higher - after then slower.

 

2. The orbits of the planets should be affected differently depending of the speed of gravity.

If speed of gravity = light speed then the gravity from the Sun is "pulling" Earth in the direction where the Sun was Eight minutes ago.

Further out the effect of this increases and since the Sun is rushing through space at high speed, measuring the orbit of Neptune with high precision should at least put some limits of the speed.

(Neptune is a heavy gas giant a long way out so the effects should be largest there.)

 

If the speed of gravity was so low that it took a Year to reach Earth from the Sun then Earth wouldn't orbit around the Sun, Earth would follow an 'S' -pattern behind like a tail.

:cool:

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I'm not an expert in this by any means, but I think the retardation effects are a little more subtle than that. I think the "lining up" argument is used by Van Flandern, and that has been discounted by other people. It doesn't work that way.

 

There is the notion that the curvature caused by GR does not have retardation in it - space is curved here now, not eight minutes from now, by the sun.

 

My guess is that measurable retardation would require that the sun be moving, so that the GR curvature is changing in position with time, and this requires more massive partner(s) in orbit.

 

Kopeikin's experiment was to look at gravitational lensing of a quasar by Jupiter. The amount of deflection depends on how quickly gravity acts. He measured it to be c within some margin. (In light of my above comment, it works, I think, because Jupiter is moving within the center-of-mass frame of the solar system)

 

The binary pulsar experiments also fit the condition of both objects be moving in the COM frame, and these exhibit orbital decay consistent with gravity acting at c.

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I think the "lining up" argument is used by Van Flandern, and that has been discounted by other people. It doesn't work that way.

For me it seems to work that way if the total eclipses of the Sun by the Moon reach maximum eclipse about 40 seconds before the Sun and Moon's gravitational forces align.

 

There is the notion that the curvature caused by GR does not have retardation in it - space is curved here now, not eight minutes from now, by the sun.

Is not the speed of gravity how long time it takes for the space curve to travel from object to object, eg: the Sun to Earth ?

(Either it is instant or takes time = speed)

 

My guess is that measurable retardation would require that the sun be moving, so that the GR curvature is changing in position with time, and this requires more massive partner(s) in orbit.

The Sun is moving, and very fast to !

Photons from the Sun travels in directions that are not parallel to the direction of Earth's gravitational acceleration toward the Sun.

(Without more massive partner(s) in orbit)

 

Kopeikin's experiment was to look at gravitational lensing of a quasar by Jupiter. The amount of deflection depends on how quickly gravity acts. He measured it to be c within some margin. (In light of my above comment, it works, I think, because Jupiter is moving within the center-of-mass frame of the solar system)

Kopeikin's experiment ended up just measuring the speed of light !

(And guess what, the speed of light was equal to c.) :)

 

The binary pulsar experiments also fit the condition of both objects be moving in the COM frame, and these exhibit orbital decay consistent with gravity acting at c.

Didn't the binary pulsar experiment measure the speed of waves, (riplets), travelling on the gravity, not the speed of gravity itself ?

Or maybe it is the same thing ??? :confused:

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The Sun is moving' date=' and very fast to !

Photons from the Sun travels in directions that are not parallel to the direction of Earth's gravitational acceleration toward the Sun.

(Without more massive partner(s) in orbit)

 

 

Kopeikin's experiment ended up just measuring the speed of light !

(And guess what, the speed of light was equal to c.) :)

 

 

Didn't the binary pulsar experiment measure the speed of waves, (riplets), travelling on the gravity, not the speed of gravity itself ?

Or maybe it is the same thing ??? :confused:[/quote']

 

The sun is not moving much in the center of mass frame, which I am speculating is the key.

 

I attend a talk by Kopeikin not long ago, and he explained the expected results if the speed of gravity were c or infinite, and they were distinctly different. So at my level of understanding he was not measuring the speed of light.

 

AFAIK the pulsar experiments were measuring the speed of gravity.

 

I'm not calling in to question the data about gravity alignment vs photon alignment - I'm not addressing that at all. What I'm saying is there is reason to think that those are the wrong ways to measure it. Gravitation and EM are not identical with the exception of the name, and can't automatically be treated in an interchangeable manner. I think the problem is the expectation that a graviton (in a quantum model) will behave exactly like a photon in all respects other than the type of the particle with which it interacts.

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The sun is not moving much in the center of mass frame' date=' which I am speculating is the key.

 

I attend a talk by Kopeikin not long ago, and he explained the expected results if the speed of gravity were c or infinite, and they were distinctly different. So at my level of understanding he was not measuring the speed of light.

 

AKAIK the pulsar experiments were measuring the speed of gravity.

 

I'm not calling in to question the data about gravity alignment vs photon alignment - I'm not addressing that at all. What I'm saying is there is reason to think that those are the wrong ways to measure it. Gravitation and EM are not identical with the exception of the name, and can't automatically be treated in an interchangeable manner. I think the problem is the expectation that a graviton (in a quantum model) will behave exactly like a photon in all respects other than the type of the particle with which it interacts.[/quote']

 

Well my toughts are if gravity has a speed and if the Sun is moving then gravity should reatch us from another point than were the Sun actually is, even if "the Sun is not moving much in the center of mass frame". Like when You hear an aeroplane and it is far in front of where the sound comes from. If then the speed of gravity is the same as light they should come from the same place or very close.

(If sound and light had the same speed You would hear the aeroplane from the same place You could see it.)

 

According to all of the experiments made I don't have enough knowledge to evaluate them.

And basically I think Kopeikin could be correct in theory but most scientist seem to refute his result and claims his measurments where not accurate enough. One Japanese event predicted Kopeikin should measure the speed of light - thus my joke.

 

The pulsar experiments were measuring the speed of gravity with electromagnetic radiation...

 

I'm not claiming or questioning the data about gravity alignment vs photon alignment either.

I just want to know why and how this could be, if correct and speed of gravity is c ?

(Also it's a good example of that scientist actually has tried it like I proposed, just better.)

 

Could You give a more explained version how "those are the wrong ways to measure it" ?

 

If I can't understand it - then I can't learn from it, neither belive it !

:)

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Well my toughts are if gravity has a speed and if the Sun is moving then gravity should reatch us from another point than were the Sun actually is' date=' even if "the Sun is not moving much in the center of mass frame". Like when You hear an aeroplane and it is far in front of where the sound comes from. If then the speed of gravity is the same as light they should come from the same place or very close.

(If sound and light had the same speed You would hear the aeroplane from the same place You could see it.)

 

[/quote']

 

Well, sound from an aeroplane and light from an aeroplane do not behave in the same way. Physicists a hundred years ago learned that assuming they behaved the same to be a mistake. Assuming that gravity and light behave the same may also be a mistake.

 

Gravity already exists at a place where the earth has yet to reach. To expect it to behave the same way as light behaves is an assumption about how gravity behaves.

 

One problem here is that we know light propagates in a certain way, and you can turn it on and off. You can't turn gravity off. From my limited understanding of GR, to generate gravity waves you have to accelerate the object. The basic curvature is static. That's why there is no aberration as with light.

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Well, sound from an aeroplane and light from an aeroplane do not behave in the same way. Physicists a hundred years ago learned that assuming they behaved the same to be a mistake. Assuming that gravity and light behave the same may also be a mistake.

I agree that it's most likely that gravity and light behaves differently.

However speed is still speed = time taken to travel a distance.

Thus if a moving object emits anything with a speed it will arrive from a past location.

 

Gravity already exists at a place where the earth has yet to reach. To expect it to behave the same way as light behaves is an assumption about how gravity behaves.

It's most likely that gravity already exists everywhere there is space-time.

But the force and direction of gravity must change in the place where Earth has yet to reach if the Sun is moving.

(I am assuming that the correct gravity is not sent there beforehand and reaches the same time as Earth.)

 

One problem here is that we know light propagates in a certain way, and you can turn it on and off. You can't turn gravity off.

It certainly is a problem, I would really, really enjoy turning it off ! ;)

 

From my limited understanding of GR, to generate gravity waves you have to accelerate the object. The basic curvature is static. That's why there is no aberration as with light.

You must have written something like this, "to generate gravity waves you have to accelerate the object", at least Three times now and I still don't get it, huh ? :embarass:

Well maybe finally I got your point ? :)

 

I will give an example to try it out:

Imagine you are standing inside a cargo wagon, there are no windows and it is silent outside.

You have an small object tied to a rope, which you swing around you.

Lets say the wagon is the frame of our solar system, your hand is the Sun, the object is Earth and the rope is gravity.

Then there is no way to measure if the wagon is at standstill or moving with constant speed, by measuring the forces on the rope !

If the wagon suddenly "bumps" on the road then we would get a stretching force, vibration, moving along the rope, a gravity wave.

 

The problem arrives when the rope is removed - the gravity must be sent there beforehand and reach the same time as Earth.

(Of course the Sun can't calculate where the Earth is going and target that place with gravity beforehand.)

Thus gravity from several of the Suns past locations must somehow "add up" to the correct force here on Earth.

(And everywhere else inside the Suns frame as long as the Suns speed is constant.)

Since we can't, yet, observe from where the gravity comes, only where it is directed, it differs from the light.

(The direction is just not the same as the source.)

:D

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It's most likely that gravity already exists everywhere there is space-time.

But the force and direction of gravity must change in the place where Earth has yet to reach if the Sun is moving.

(I am assuming that the correct gravity is not sent there beforehand and reaches the same time as Earth.)

 

But is the sun moving very much, relative to the earth's orbit? Why isn't the gravity sent beforehand - are you thinking that gravity doesn't exist at a point until you are there to measure it?

 

In your example, and elsewhere, you keep referring to the sun's speed. Relative to what? The system can be viewed as being at rest, and the laws of physics will be the same no matter what the speed is relative to some other non-accelerated observer.

 

A flaw with your example, if I understand your argument properly, is that it would seem that you have a preferred rest frame.

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You must have written something like this' date=' "to generate gravity waves you have to accelerate the object", at least Three times now and I still don't get it, huh ? :embarass:

[/quote']

 

This might help:

Newtonian gravity is a radial force. You don't do net work on an object in orbit (no work at all in a circular orbit), and can't exert a torque on it. So there should be no energy loss under those conditions. I.e. you can't have gravity waves bleeding energy from the system. And, as I alluded to before, this can't change if the system is moving with a constant velocity, since the laws have to work just the same under those conditions. AFAIK, GR is going to be consistent with that view under similar orbital conditions.

 

It's only when you accelerate an object that any possible retardation of the gravity comes into play, and you radiate energy, and cause a torque. That's why the binary pulsars have been studied - they have lost energy at the rate predicted by GR. Because they orbit the center-of-mass and are thus accelerating, they radiate.

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But is the sun moving very much, relative to the earth's orbit? Why isn't the gravity sent beforehand - are you thinking that gravity doesn't exist at a point until you are there to measure it?

Maybe you should read my post once more...

 

In your example, and elsewhere, you keep referring to the sun's speed. Relative to what? The system can be viewed as being at rest, and the laws of physics will be the same no matter what the speed is relative to some other non-accelerated observer.

If I am not misstaken, then that is exactly what I tried to prove with my example !

(Relative to standstill = not moving.)

 

A flaw with your example, if I understand your argument properly, is that it would seem that you have a preferred rest frame.

The wagon moves on the ground which is at standstill.

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And, as I alluded to before, this can't change if the system is moving with a constant velocity, since the laws have to work just the same under those conditions.
Then there is no way to measure if the wagon is at standstill or moving with constant speed' date=' by measuring the forces on the rope ![/quote']

Where is the difference in those Two statements above ?

 

 

It's only when you accelerate an object that any possible retardation of the gravity comes into play, and you radiate energy, and cause a torque. That's why the binary pulsars have been studied - they have lost energy at the rate predicted by GR. Because they orbit the center-of-mass and are thus accelerating, they radiate.
If the wagon suddenly "bumps" on the road then we would get a stretching force' date=' vibration, moving along the rope, a gravity wave.[/quote']

If the Sun should suddenly "bump" wouldn't it accelerate, release gravity waves and lose energy ?

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If I am not misstaken' date=' then that is exactly what I tried to prove with my example !

(Relative to standstill = not moving.)

 

 

The wagon moves on the ground which is at standstill.[/quote']

 

You still talk about the sun moving, though. Why do you keep saying that the sun is moving? Relative to what is it moving?

 

What does the ground represent in your example?

 

As far as the "bump" goes, what causes the bump? As an analogy to gravity, it seems to me that a bump is unphysical, and expecting physics to gve an explanation for it is unreasonable.

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You still talk about the sun moving' date=' though. Why do you keep saying that the sun is moving? Relative to what is it moving?

 

What does the ground represent in your example?

 

As far as the "bump" goes, what causes the bump? As an analogy to gravity, it seems to me that a bump is unphysical, and expecting physics to gve an explanation for it is unreasonable.[/quote']

Are you suggesting that the Sun is at standstill = not moving ?

(And the rest of the universe is revolving around it.)

 

According to wikipedia the Sun have an orbital speed of 217 km/s around the center of the Milky way.

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

 

I belive the Sun is moving relative to space, stars, the Milky way, other galaxies, the local group and so on...

 

The ground represent a fixed position, (or area if preferred), in space.

 

The example with the "bump" may not have been the best, I admit that. Still it could be caused by a close encounter or collision with an object with enough mass.

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Are you suggesting that the Sun is at standstill = not moving ?

(And the rest of the universe is revolving around it.)

 

According to wikipedia the Sun have an orbital speed of 217 km/s around the center of the Milky way.

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

 

I belive the Sun is moving relative to space' date=' stars, the Milky way, other galaxies, the local group and so on...

 

The ground represent a fixed position, (or area if preferred), in space.

 

The example with the "bump" may not have been the best, I admit that. Still it could be caused by a close encounter or collision with an object with enough mass.[/quote']

 

I'm saying whether the sun is moving or not is irrelevant. The only matter, AFAIK, is the motion of the sun with respect to the center of mass of the solar system.

 

If you think space has a preferred reference system you need to provide evidence that this is true. Thus far we have none.

 

Any encounter the sun has with a large mass is going to do far more than "bump" the sun.

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I'm saying whether the sun is moving or not is irrelevant. The only matter' date=' AFAIK, is the motion of the sun with respect to the center of mass of the solar system.

 

If you think space has a preferred reference system you need to provide evidence that this is true. Thus far we have none.

 

Any encounter the sun has with a large mass is going to do far more than "bump" the sun.[/quote']

If it is irrelevant that the Sun is moving then explain for me how the gravity alignment vs photon alignment can be different.

 

I don't think space has a preferred reference system, but it has dimensions which we measures in length and time. Thus it is possible to image a 3D-frame with a scale which can be used to calculate the Suns positions over time.

 

The outcome of an encounter with the Sun is highly dependent of how large the mass is and also the circumstances for the encounter. It doesn't matter how big the "bump" is, and what more that happens. The "bump" will cause the Sun to accelerate and release gravity waves, (or not). I have already admitted that the example was not the best, do you whish an apologize to ?

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If it is irrelevant that the Sun is moving then explain for me how the gravity alignment vs photon alignment can be different.

 

If gravity didn't behave the same way that the EM interaction does.

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Thanks for your responses and I'm sure you're right, but please indulge ..

 

 

Thanks very much

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If gravity is an instataneous force then blackholes can exist.If gravity propels at C then a blackhole would collapse into nothingness,disappear and have no influence.

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If gravity didn't behave the same way that the EM interaction does.

Thats right, but thats not what I ment, maybe it's a translation problem...

 

What would happen to the differents in alignment if the Sun was not moving ?

 

I think the differents would disappear, and thus it is important if the Sun is moving or not.

The differents gives us a clue about how gravity behave.

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If gravity is an instataneous force then blackholes can exist.If gravity propels at C then a blackhole would collapse into nothingness,disappear and have no influence.

 

why?

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Thats right' date=' but thats not what I ment, maybe it's a translation problem...

 

What would happen to the differents in alignment if the Sun was not moving ?

 

I think the differents would disappear, and thus it is important if the Sun is moving or not.

The differents gives us a clue about how gravity behave.[/quote']

 

Your hypothesis implies that the aberration should be different when the earth's motion is along the direction of the sun's motion as opposed to six month later, when it's moving in the opposite direction (and different still at 90 degrees to those points). Is that the case?

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Your hypothesis implies that the aberration should be different when the earth's motion is along the direction of the sun's motion as opposed to six month later, when it's moving in the opposite direction (and different still at 90 degrees to those points). Is that the case?

swansont are You teasing me ?

 

Please just answere my question what You think would happen to the differents in alignment if the Sun was not moving ?

 

Later on we can continue the discussion with what both our hypothesis implies...

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swansont are You teasing me ?

 

Please just answere my question what You think would happen to the differents in alignment if the Sun was not moving ?

 

Later on we can continue the discussion with what both our hypothesis implies...

 

I think there is no difference. As I said before the linear motion (or linear to first approximation) of the sun should be irrelevant.

 

Your contention that the motion of the sun makes a difference implies a testable prediction. What does the actual data say? Is the relative aberration between gravity and light dependent on the relative position of the earth to the sun?

 

If the answer is yes, then your hypothesis has some merit, and should be investigated further. If the answer is no, it's dead in the water.

 

BTW I don't have a hypothesis. All I am saying is that yours makes certain assumptions. If the assumptions are wrong, the hypothesis is most certainly incorrect. I am merely attempting to demonstrate that this is the case.

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Guest Pizer

semi OT, Do the gravitational waves produced by objects between the event horizon and singularity of black holes escape out of the black hole, and if so, doesn't that mean information escapes?

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