Speed of gravity vs speed of light?

[Daecon]

Is there any way on knowing for certain the speed in which gravity acts, compared to the speed of light?

 

If gravity works at light speed, - considering no particle can move faster than light speed - that could be evidence suggesting there is a force carrier particle, the graviton, although it wouldn't be conclusive proof.

 

If gravity acts truly "instantly" then it would most likely rule out the existance of any force carrier particle, for the same reason as stated above.

 

I believe that gravity is nothing more than an inherent mathmatical value acting on the physical laws of the universe; that gravity is just a manifestation of a mathmatical attribute.

 

Has there been, or can there ever be, a way of determining the "speed" of gravity?

[danny8522003]

If gravity happened instantaneously would this not have to travel faster than light? Seeing as no info can travel ftl this must be impossible.

[PhDP]

It was instantaneous in newtonian physics but in general relativity, the distortion of spacetime is moving at the speed of light. And yes, it must be hard to prove, gravity is a very weak force.

[swansont]

The orbital decay of binary pulsars indicates retardation, which would not be present if gravity acted instantaneously. The data is consistent with gravity travelling at c.

 

 

There is also the Kopeikin experiment of the change in the Shapiro delay of a quasar as it passed by Jupiter. There is disagreement over whether this measured the speed of gravity. When I attended a colloquium given by Kopeikin, it sounded convincing, but I'm not an expert on GR.

[gib65]

If gravity happened instantaneously would this not have to travel faster than light? Seeing as no info can travel ftl this must be impossible.

 

Not necessarily. It depends on what you mean by "travel". If you mean to go from some point A to some point B and pass through all points in between, then yes, instantaneous travel would be impossible. But if you mean teleporting from A to B without ever having been to any of the points in between, then I think this could be possible. It sounds like the latter is what Transdecimal was talking about.

[imasmartgirl]

There was a question i once heard about. It was if the sun were to suddenly disappear would earth immediatly be thrown off course or would it take a while? The sun's rays take about 8 min to get to earth, so would we be thrown off course and still see the sun there for 8 min? The answer they came up with is that since gravity is warped space, and the sun were to disappear it would cause a ripple in space at the speed of light and would take about 8 min for us to feel it so there would be no time gap.

[Callipygous]

i dont have much (any) expertise in this area, but what i would think intuitively is that since movement is cause by energy, not mass (that is, when pool balls collide they transfer energy, not mass), that forces act instantly. mass cant be transferred instantly, but cant energy?

[Teotihuacan]

Davinci determined the same thing.

And, you are both right...

a billiard ball moves in fps.

For all intents & purposes, a 1.0E6 ratio, is "instant".

 

That's one thing so intriguing about the Theory of Everything.

In a way, harkens to a return to more humanistic systems of measurement, since it would have to apply in all instances to be "everything". Not simply a balance between macro & micro entities, laws or distortions.

 

The question, though, appears to be striking at the speed of the agent of gravity, which has been omitted from the Newtonian calculations and subsequent additions.

 

Granted, no difference in the eventual outcomes. As witnessed by the sucessful landing on an asteroid. The reason, however, that gravity is the "weakest" force remains a mystery.

 

Consider, a moment, that gravity may not be the base force... but merely a "side effect". An incidental force. Like the sunlight is a side effect of the strong force, or the wind as the actual power of the sun, as we know it today. Then there's reason to believe it's such a weak net force.

 

The gravitron may actually travel faster than the speed of light, although not in "body" of this dimension. We know (or theorize) that gravity is the only force that applies cross dimensionally. If so, then gravity itself may operate that way.

 

All very interesting questions

[Daecon]

i dont have much (any) expertise in this area, but what i would think intuitively is that since movement is cause by energy, not mass (that is, when pool balls collide they transfer energy, not mass), that forces act instantly. mass cant be transferred instantly, but cant energy?

I'm not talking about any knid of mass, but there's something that I just realised...

 

There are four types of energy and they're all "active" - electromagnetic, strong & weak forces and gravity? And they travel at c.

 

But gravity is a force, not a type of energy? That is, if there's any real difference...?

[danny8522003]

They are the four types of forces each with their own carrier particle that travels at c.

 

I read that the carrier particle for EM force is the photon, not sure i understand why. Maybe someone can help?

[swansont]

I'm not talking about any knid of mass' date=' but there's something that I just realised...

 

There are four types of energy and they're all "active" - electromagnetic, strong & weak forces and gravity? And they travel at [i']c[/i].

 

But gravity is a force, not a type of energy? That is, if there's any real difference...?

 

Force is the gradient of potential energy. Can't have one without the other.

[padren]

There is something I don't quite get, which may be due to my rather paltry lack of education.

 

The concept of a particle transmitting a force requires a balance of energy, such as you shine a light on a solar sail, and it pushes the sail. However, if you put another solar sail in the shadow of the first, no photon particles will hit it as they are fully obscured when colliding with the first.

 

With gravity, if you put two small masses near a large mass, they will both fall towards the larger mass at a speed dictated most largely by the large mass, even if one is behind the other.

 

If there is a graviton particle, either it has a huge amount of force but only a small amount of that is used as it flies through any mass, allowing it to work on many objects without being absorbed or impacted, or it radiates in some manner not consistent with 3 dimensional space, like a light source raised an inch over a flat 2D paper will shine on all objects drawn on the paper, even those behind the light source's 2D location.

 

How does modern physics explain these characteristics, and if these characteristics are outside normal particle transmission behavior, is it safe to assume speed is consistent with other means of transmission? Personally I think it travels at c for the reasons swansont mentioned, but I don't have any first hand understanding of the force so my view is purely based on what others have observed.

[Edtharan]

Also why do all forces have charges, except gravity?

[bascule]

If there is a graviton particle, either it has a huge amount of force

 

Why do you say this? Gravity is exceptionally weak.

 

If gravity were stronger than the electromagnetic force then matter would not exist. The structure of all matter depends on the electromagnetic force being greater (much, much greater) than the force of gravity. Otherwise electrons would be pulled into the atomic nucleus and the structure of all matter would collapse.

 

Look at how easy it is for you to overcome the force of gravity. You can stand up. You can pick objects up.

 

Gravity is weak.

[padren]

Why do you say this? Gravity is exceptionally weak.

 

If gravity were stronger than the electromagnetic force then matter would not exist. The structure of all matter depends on the electromagnetic force being greater (much' date=' much greater) than the force of gravity. Otherwise electrons would be pulled into the atomic nucleus and the structure of all matter would collapse.

 

Look at how easy it is for you to overcome the force of gravity. You can stand up. You can pick objects up.

 

Gravity is weak.[/quote']

 

I know the degree to which gravity acts on that which it encounters (from light to matter to space), I am not contending otherwise.

 

What I am saying is, don't other forms of transmitted effect, themselves be altered by that which they act on?

 

Refer to my example with photons. A photon can hit something and push it - it will act on that which it collides with. But whatever is behind the source of photons will not be bombarded with photons. Gravitons however, if they immet from a source, will act not only on the first object it runs into, but every object behind it too, decreasing in force at an exact rate regardless of how many or how few objects it applies force to.

 

Therefore, one suggestion I proposed (though its just an idea and not one I hold as very likely) is that perhaps gravity does have a lot of energy, but barely touches that which it passes through and thus barely applies any force at all during that contact. More like how a high powered X ray can pass through your foot and while the X ray is affected, the effect it may have on any given cell in your foot would be effectively near identical to the effect on the cell before it.

Only instead of doing what an xray does, it would convey the attractive force of gravity.

 

But that is just an odd suggestion - what I am curious about is if there are gravitons, how is it they would equally impart an attractive force on a nearby object as well as one directly behind it without decreasing the attractive potential of the source object on the second?

 

If you have a black hole, a sun will fall towards it at a fixed rate of acceleration. If there is another star on the other side of the black hole, then it will also attract the first sun (and visa versa) and increase that acceleration...no? Its not like the black hole will have "gobbled up" the attractive potential of the second star (as far as I know) so how would this be explained?

[Edtharan]

But that is just an odd suggestion - what I am curious about is if there are gravitons, how is it they would equally impart an attractive force on a nearby object as well as one directly behind it without decreasing the attractive potential of the source object on the second?

You are talking about something a gravitational shadow. As light (electromagnetic carrier particle) casts a shadow when it is blocked by an object, why dose gravity not do the same?

 

Is that what you are asking?

[padren]

You are talking about something a gravitational shadow. As light (electromagnetic carrier particle) casts a shadow when it is blocked by an object' date=' why dose gravity not do the same?

 

Is that what you are asking?[/quote']

 

Yep.

 

With light its only going to hit one thing before its deflected/absorbed etc, meaning the source has a maximum effect potential based on the total number of photons it is spitting out in every direction in any given second.

 

However, if I understand gravity correctly, there is no maximum effect potential for gravity or any shadow - no matter how many objects are stacked around a source of gravitons (a massive object) every new object will feel the gravitational pull regardless of how many other objects are "blocking/interacting with" the gravitons.

 

I am curious how this is explained.

[gagsrcool]

Hi,

 

There is nothing known as a gravitational shadow and neither can it exist.

In terms of Newtonian Physics, gravity is a force, in terms of general relativity it is a result of the matter all throught the Universe. Gravity is no entity. It is only a result of curvature of space-time and the spreading of matter all throughout the Universe.

How could a force have a shadow? In terms of relativity, how could something with no colour, shape,size anything or even frequency have a shadow? I think you have misunderstood something somewhere.

 

gagsrcool

[Daecon]

Hi' date='

 

There is nothing known as a gravitational shadow and neither can it exist.

In terms of Newtonian Physics, gravity is a force, in terms of general relativity it is a result of the matter all throught the Universe. Gravity is no entity. It is only a result of curvature of space-time and the spreading of matter all throughout the Universe.

 

gagsrcool[/quote']

So does this curvature propogate throughout the universe at an instantaneous rate?

 

Imagine a scenario - a new black hole appears out of nowhere (Yes I know - but this is hypothetical)

 

Would the entire reigion of space curve around to create gravity, all at once with the farthest regions curving a little bit at the same time as the closest regions practically collapse on themselves at the event horizon

 

Or would gravity extend out from the new black hole in a ripple, travelling at the speed of light until it runs out of power at the furthest reach of the black hole's gravity?

 

But then if it was a ripple, wouldn't it eventually dissipate after it's "rippled" already, like a ripple on a pond?

[padren]

Hi' date='

 

There is nothing known as a gravitational shadow and neither can it exist.

In terms of Newtonian Physics, gravity is a force, in terms of general relativity it is a result of the matter all throught the Universe. Gravity is no entity. It is only a result of curvature of space-time and the spreading of matter all throughout the Universe.

How could a force have a shadow? In terms of relativity, how could something with no colour, shape,size anything or even frequency have a shadow? I think you have misunderstood something somewhere.

 

gagsrcool[/quote']

 

My questioning is along the lines of "if there is such a thing as a graviton...." since gravitons are often mentioned, as the conveyor of the force of gravity.

 

Therefore, if there is a graviton, then it must follow some properties in common with other radiative things, yet, things that radiate out from a source, generally leave shadows on the far side of that which they collide with, and only affect what they collide with by being altered in some way (loosing energy, gaining energy, deflecting, being absorbed, changing wavelength, etc).

 

From what I hear, it really behaves a lot more like a topographical disturbance, the whole "if you had a rubber sheet and put tennis balls and bowling balls on it" analogy....but that doesn't describe anything involving gravitons radiating from sources nor is it consistant with it from my understanding.

 

I'll be the first to admit I "don't got something right" since I don't understand it.

[swansont]

So does this curvature propogate throughout the universe at an instantaneous rate?

 

 

No. According to GR it would propagate at c.

[swansont]

My questioning is along the lines of "if there is such a thing as a graviton...." since gravitons are often mentioned' date=' as the conveyor of the force of gravity.

 

Therefore, if there is a graviton, then it must follow some properties in common with other radiative things, yet, things that radiate out from a source, generally leave shadows on the far side of that which they collide with, and only affect what they collide with by being altered in some way (loosing energy, gaining energy, deflecting, being absorbed, changing wavelength, etc).[/quote']

 

 

You are proceding from a false observation. One can e.g. place certain items in a magnetic or electric field and not have it affect the field strength. You are making assumptions about how a graviton must behave that are leading to incorrect conclusions. Since we can see how nature behaves, one must conclude that your assumptions about the behavior of gravitons are incorrect.

 

From what I hear' date=' it really behaves a lot more like a topographical disturbance, the whole "if you had a rubber sheet and put tennis balls and bowling balls on it" analogy....but that doesn't describe anything involving gravitons radiating from sources nor is it consistant with it from my understanding.

 

I'll be the first to admit I "don't got something right" since I don't understand it.[/quote']

 

The "rubber sheet" analogy is a description of GR, which is not a quantum theory. That's why it doesn't involve gravitons.

[padren]

You are proceding from a false observation. One can e.g. place certain items in a magnetic or electric field and not have it affect the field strength. You are making assumptions about how a graviton must behave that are leading to incorrect conclusions. Since we can see how nature behaves' date=' one must conclude that your assumptions about the behavior of gravitons are incorrect.

[/quote']

The conclusion I came to was that my assumptions were incorrect, which is why I am trying to understand it better.

 

I am curious how gravitons are described to behave, since they are described as radiative in nature. I'll look into quantum electrodynamics and classical electromagnetism so I have a better basis of how to make sense of the simularities and differences that appear in gravity.

 

The "rubber sheet" analogy is a description of GR' date=' which is not a quantum theory. That's why it doesn't involve gravitons.[/quote']

 

Can you recommend any good books for someone who graduated highschool with high marks in the advanced physics classes, but hasn't done anything since? I'd like to get back into physics and get a better working knowledge of many of these theories.

[Daecon]

No. According to GR it would propagate at c.

The "rubber sheet" analogy is a description of GR, which is not a quantum theory. That's why it doesn't involve gravitons.

 

I'm a little confused (again). Aren't quantumn theory and GR incompatible?

 

I get the impression on one hand you're siding with GR and on the other, against it...

[mrblond5311]

I'm not an expert on this matter but how can gravity have a set "force" or "energy" when it's power is determined by the mass of the object creating it? If it had a set force how would satelittes orbit it & wouldn't outer planets sizes be proportionate to the set force of the suns gravity i.e. the planets would have to lose mass as you move farther from the sun? Like how earth orbits the sun & the planets & sun don't orbit each other. And to go back to the beginning of the thread - gravity is a weak force so how can it have the same speed of light? Wouldn't it have the same strength to move at the same speed? And wouldn't gravity be considered a negative force:confused: ? I'm failing to see any similarites between photons & gravitrons. I might be way off on this so fill me in, please. Thanks! One more thing....does anyone have any similarites between magnetism & gravity? Fill me in!