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Author Topic: Do gravitational waves propagate faster than light waves?  (Read 21640 times)

Offline QuantumClue

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Re: Do gravitational waves propagate faster than light waves?
« Reply #50 on: 08/01/2011 14:47:31 »
Quote
if photons can be captured and gravitons cannot, can we assume that gravity can and does travel faster than light?

Have I got this right: the graviton is a hypothetical particle, which might mediate the force of gravity, which is not really a force?

This force, that is not a force, might propagate at the speed of light, or 20,000,000,000 times faster, or perhaps instantaneously.

Then again, as CliffordK mentioned, it could be just a distortion of spacetime.

Surely it couldn't be that Mark McCutcheon is right and gravity is just an illusion brought about by the fact that everything in the Universe is expanding!

The gravitational attraction would be a hypothetical particle which mediates gravity and travels at lightspeed. As I stated The deAlembertian, a four dimensional wave equation will be represented as ▼. Not usual notation but box notation cannot be used here.

▼hμν=0

This is the same as saying

μμhμν=0

This means it will follow the speed of light since ▼∂t2 - c22x.


Saying the particle might be a distortion is an oxymoron by the way. By definition, particles are fluctuations in spacetime which are completely analogous to saying particles are distortions of spacetime itself.

But Mark is not right, and gravity is no illusion. It's a real force, more correctly said a psuedoforce, and may very well not require a graviton.
 

Offline Bill S

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Re: Do gravitational waves propagate faster than light waves?
« Reply #51 on: 09/01/2011 01:28:24 »
It is quite common to find in P S books the statement that "gravity is not a force". While I can see the argument that a spacetime distortion is not a force, as such, I find it difficult to understand how the distortion can be caused, or maintained without the application of a force, and the expenditure of energy.  Perhaps the idea that it is a pseudoforce might be a way round at least some of this.  I found the following definition of a pseudoforce: "The physically apparent but nonexistent force needed by an observer in a noninertial frame to make Newton's laws of motion hold true."  would this be your definition?

When is a force not a force?  ;D

 
 

Offline Geezer

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Re: Do gravitational waves propagate faster than light waves?
« Reply #52 on: 09/01/2011 04:54:20 »
It is quite common to find in P S books the statement that "gravity is not a force". While I can see the argument that a spacetime distortion is not a force, as such, I find it difficult to understand how the distortion can be caused, or maintained without the application of a force, and the expenditure of energy.  Perhaps the idea that it is a pseudoforce might be a way round at least some of this.  I found the following definition of a pseudoforce: "The physically apparent but nonexistent force needed by an observer in a noninertial frame to make Newton's laws of motion hold true."  would this be your definition?

When is a force not a force?  ;D

 

I have a similar difficulty, but I think it goes something like this:

The Earth seeems to be orbiting the Sun, but it isn't. It's really following a straight path through spacetime, so no force is required.

It strikes me that it's a bit "iffy" to talk about spacetime being curved (the old rubber sheet model), because if it is curved, that means there is a force being exerted on the Earth to keep it on its "tracks", so to speak, in which case the "non-force" argument sort of falls apart.

I'm confident that cleared things up a lot.
 

Offline Foolosophy

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Re: Do gravitational waves propagate faster than light waves?
« Reply #53 on: 09/01/2011 06:52:57 »
It is quite common to find in P S books the statement that "gravity is not a force". While I can see the argument that a spacetime distortion is not a force, as such, I find it difficult to understand how the distortion can be caused, or maintained without the application of a force, and the expenditure of energy.  Perhaps the idea that it is a pseudoforce might be a way round at least some of this.  I found the following definition of a pseudoforce: "The physically apparent but nonexistent force needed by an observer in a noninertial frame to make Newton's laws of motion hold true."  would this be your definition?

When is a force not a force?  ;D

 

Electricity is not a force either - and Magnetism

They are phenomena that can induce forces or effects upon other bodies

Gravity in the Relativity sense, is simply a distortion of space (time) by matter.

Its this curvature of space that can induce a force upon a body.

Semantics I suppose

Magnetism, Magnetic fields, Magnetic FORCE

Gravity, Gravitational fields, Gravitational FORCE
« Last Edit: 09/01/2011 06:54:42 by Foolosophy »
 

Offline Geezer

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Re: Do gravitational waves propagate faster than light waves?
« Reply #54 on: 09/01/2011 07:26:36 »
Electricity is not a force either - and Magnetism

They are phenomena that can induce forces or effects upon other bodies


Foolosophy,

Pardon me, but you appear to be waffling. Whoever said that electricity and magnetism are forces?

Not only that, but if the curvature of spacetime exerts a force, then gravity exerts a real force. If gravity does not exert any real force on a body, then spacetime cannot be curved. And, if it is not curved, we better come up with a better explanation for how gravity actually works.
« Last Edit: 09/01/2011 07:46:17 by Geezer »
 

Offline Foolosophy

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Re: Do gravitational waves propagate faster than light waves?
« Reply #55 on: 09/01/2011 09:43:41 »
Electricity is not a force either - and Magnetism

They are phenomena that can induce forces or effects upon other bodies


Foolosophy,

Pardon me, but you appear to be waffling. Whoever said that electricity and magnetism are forces?

Not only that, but if the curvature of spacetime exerts a force, then gravity exerts a real force. If gravity does not exert any real force on a body, then spacetime cannot be curved. And, if it is not curved, we better come up with a better explanation for how gravity actually works.


I certainly didnt say that - just highlighting the semantics involved in becoming confused as to whether gravity is a force.

Gravity is an end product of the curvature of space-time (on current theory)

The gravitational force experienced by a body is a direct result of there being a gravitational potential or field acting upon it.

Its all about terminology and semantics.

Magnetism is not a force, but a magnetic potential or field exerts a magnetic force (on a point charge for example).
« Last Edit: 09/01/2011 09:47:23 by Foolosophy »
 

Offline QuantumClue

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Re: Do gravitational waves propagate faster than light waves?
« Reply #56 on: 09/01/2011 12:39:49 »
It is quite common to find in P S books the statement that "gravity is not a force". While I can see the argument that a spacetime distortion is not a force, as such, I find it difficult to understand how the distortion can be caused, or maintained without the application of a force, and the expenditure of energy.  Perhaps the idea that it is a pseudoforce might be a way round at least some of this.  I found the following definition of a pseudoforce: "The physically apparent but nonexistent force needed by an observer in a noninertial frame to make Newton's laws of motion hold true."  would this be your definition?

When is a force not a force?  ;D

 

There are perhaps, many types of forces, so when stating ''when is a force not a force'' maybe an erreneous statement. More like ''when is a particular force not another force''.

For instance, do you accept the Coriolis effect is a force by definition? If so - the gravitational mechanism for it is identical to gravitation in the laws of motion we would find in GR. Both are by definition, psuedoforces.
 

Offline Foolosophy

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Re: Do gravitational waves propagate faster than light waves?
« Reply #57 on: 09/01/2011 17:04:34 »
It is quite common to find in P S books the statement that "gravity is not a force". While I can see the argument that a spacetime distortion is not a force, as such, I find it difficult to understand how the distortion can be caused, or maintained without the application of a force, and the expenditure of energy.  Perhaps the idea that it is a pseudoforce might be a way round at least some of this.  I found the following definition of a pseudoforce: "The physically apparent but nonexistent force needed by an observer in a noninertial frame to make Newton's laws of motion hold true."  would this be your definition?

When is a force not a force?  ;D

 

There are perhaps, many types of forces, so when stating ''when is a force not a force'' maybe an erreneous statement. More like ''when is a particular force not another force''.

For instance, do you accept the Coriolis effect is a force by definition? If so - the gravitational mechanism for it is identical to gravitation in the laws of motion we would find in GR. Both are by definition, psuedoforces.

....and so according to that rationale, the reaction to gravity is also fake?
« Last Edit: 09/01/2011 17:10:34 by Foolosophy »
 

Offline QuantumClue

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Re: Do gravitational waves propagate faster than light waves?
« Reply #58 on: 09/01/2011 19:25:49 »
It is quite common to find in P S books the statement that "gravity is not a force". While I can see the argument that a spacetime distortion is not a force, as such, I find it difficult to understand how the distortion can be caused, or maintained without the application of a force, and the expenditure of energy.  Perhaps the idea that it is a pseudoforce might be a way round at least some of this.  I found the following definition of a pseudoforce: "The physically apparent but nonexistent force needed by an observer in a noninertial frame to make Newton's laws of motion hold true."  would this be your definition?

When is a force not a force?  ;D

 

There are perhaps, many types of forces, so when stating ''when is a force not a force'' maybe an erreneous statement. More like ''when is a particular force not another force''.

For instance, do you accept the Coriolis effect is a force by definition? If so - the gravitational mechanism for it is identical to gravitation in the laws of motion we would find in GR. Both are by definition, psuedoforces.

....and so according to that rationale, the reaction to gravity is also fake?

It's not exactly fake, because psuedoforces have real effects in the world. They are real, just by standard definition a different type of force, or if you like, a different way to view a force.
 

Offline JP

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Re: Do gravitational waves propagate faster than light waves?
« Reply #59 on: 10/01/2011 01:32:45 »
Electricity is not a force either - and Magnetism

They are phenomena that can induce forces or effects upon other bodies


Foolosophy,

Pardon me, but you appear to be waffling. Whoever said that electricity and magnetism are forces?

Not only that, but if the curvature of spacetime exerts a force, then gravity exerts a real force. If gravity does not exert any real force on a body, then spacetime cannot be curved. And, if it is not curved, we better come up with a better explanation for how gravity actually works.

Well here's part of the problem.  I assume we all agree on what classical forces are.  In Newtonian mechanics (and including E&M), fundamental forces are actions-at-a-distance which cause acceleration according to F=ma.  If you replace Newtonian mechanics with another model, you give up this idea of forces.

With general relativity, you basically keep the idea of the electromagnetic force being action at a distance, but replace the idea of gravity as a similar action with gravity as a change in geometry of space-time.  Acceleration due to gravity is then modeled as motion along geodesics (the equivalent of straight lines).  Would you still call that a force since it's modeled differently from electromagnetic force?

If you go to QM, then forces are described differently again--as exchanges of particles.  But now you have a description of three fundamental forces in terms of particles, while gravity is still modeled in terms of geometry.  Is it still a force if it's described completely differently from other forces?

I think it just boils down to semantics, since we know perfectly well how the model of gravity differs from the other forces in GR.  If you call gravity a force, you're kind of lumping it together with the other forces, when it causes motion through completely a different model.  If you don't call it a force, then you're left with the oddity that in the Newtonian description, it is a force, and causes motion just like any other force--so why is it unique?
 

Offline Foolosophy

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Re: Do gravitational waves propagate faster than light waves?
« Reply #60 on: 10/01/2011 06:39:04 »
....String Theorists also define and describe "forces" in a different way

So the truth is where exactly?

It certainly cant be with the stochastic nuerosis that Quantum Physicists are inflicted by.

I think I will reserve my judgement until a deterministic theory surfaces that can describe the atomic and sub-atomic world. (most likey NOT in my lifetime)
 

Offline JP

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Re: Do gravitational waves propagate faster than light waves?
« Reply #61 on: 10/01/2011 07:23:26 »
It certainly cant be with the stochastic nuerosis that Quantum Physicists are inflicted by.

Why not?
 

Offline Foolosophy

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Re: Do gravitational waves propagate faster than light waves?
« Reply #62 on: 10/01/2011 10:37:45 »
It certainly cant be with the stochastic nuerosis that Quantum Physicists are inflicted by.

Why not?

,,,the fundamentals of QED are based upon the admission of "error" - that's why ridiculous counter intuitive conclusions are spawned. (the fact that QED has great predictive accuracy and is a useful mathematical tool is not relevant)

 

Offline JP

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Re: Do gravitational waves propagate faster than light waves?
« Reply #63 on: 10/01/2011 14:08:08 »
It certainly cant be with the stochastic nuerosis that Quantum Physicists are inflicted by.

Why not?

,,,the fundamentals of QED are based upon the admission of "error" - that's why ridiculous counter intuitive conclusions are spawned. (the fact that QED has great predictive accuracy and is a useful mathematical tool is not relevant)

How is it founded upon the admission of "errors"?  Can you give specific examples?  (I'm not saying you're wrong here--there are reasons not to think that QED is the full story, but these claims seem a bit strong from what I know of it.)
 

Offline Foolosophy

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Re: Do gravitational waves propagate faster than light waves?
« Reply #64 on: 10/01/2011 14:37:04 »
It certainly cant be with the stochastic nuerosis that Quantum Physicists are inflicted by.

Why not?

,,,the fundamentals of QED are based upon the admission of "error" - that's why ridiculous counter intuitive conclusions are spawned. (the fact that QED has great predictive accuracy and is a useful mathematical tool is not relevant)

How is it founded upon the admission of "errors"?  Can you give specific examples?  (I'm not saying you're wrong here--there are reasons not to think that QED is the full story, but these claims seem a bit strong from what I know of it.)

Stochastic methods are based on the quantification of errors

Thats what the statistical nature of QED is founded upon
 

Offline JP

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Re: Do gravitational waves propagate faster than light waves?
« Reply #65 on: 10/01/2011 15:06:34 »
It certainly cant be with the stochastic nuerosis that Quantum Physicists are inflicted by.

Why not?

,,,the fundamentals of QED are based upon the admission of "error" - that's why ridiculous counter intuitive conclusions are spawned. (the fact that QED has great predictive accuracy and is a useful mathematical tool is not relevant)

How is it founded upon the admission of "errors"?  Can you give specific examples?  (I'm not saying you're wrong here--there are reasons not to think that QED is the full story, but these claims seem a bit strong from what I know of it.)

Stochastic methods are based on the quantification of errors

Thats what the statistical nature of QED is founded upon

Ah.  That's the problem.  It isn't based on quantifying errors.  It's built on probability from the ground up, not on quantifying errors.
 

Offline Geezer

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Re: Do gravitational waves propagate faster than light waves?
« Reply #66 on: 10/01/2011 17:59:23 »
It isn't based on quantifying errors.  It's built on probability from the ground up, not on quantifying errors.

If it was based on errors, I'm sure I could make a fortune in Vegas (until they realized I'd cracked the system of course.)
 

Offline Bill S

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Re: Do gravitational waves propagate faster than light waves?
« Reply #67 on: 10/01/2011 20:15:04 »
We seem to have wandered some way from the OP, so let's not spoil the fun by getting back on track. ;)

One (almost on track) question that comes to mind is: if gravity is a distortion of spacetime, is energy expended in maintaining that distortion?
 

Offline QuantumClue

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Re: Do gravitational waves propagate faster than light waves?
« Reply #68 on: 10/01/2011 20:38:17 »
We seem to have wandered some way from the OP, so let's not spoil the fun by getting back on track. ;)

One (almost on track) question that comes to mind is: if gravity is a distortion of spacetime, is energy expended in maintaining that distortion?

If I understand your question, I do not believe energy or matter is physically expanded, only the space between particles expand.
 

Offline QuantumClue

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Re: Do gravitational waves propagate faster than light waves?
« Reply #69 on: 10/01/2011 20:51:51 »
Oh dear... i read expended as ''expanded''.

Forgive me, I don't have my glasses with me.
 

Offline Geezer

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Re: Do gravitational waves propagate faster than light waves?
« Reply #70 on: 10/01/2011 20:52:39 »
If I understand your question, I do not believe energy or matter is physically expanded, only the space between particles expand.

I believe Bill really did mean expended - as in "used up".

I would not think so Bill. If it was, where would the energy be coming from, and would it not tend to run out from time to time, in which case things might tend to "fly off the handle" and zoom off into outer space. I think we've got enough problems without having to worry about that scenario as well.
 

Offline QuantumClue

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Re: Do gravitational waves propagate faster than light waves?
« Reply #71 on: 10/01/2011 21:02:21 »
Yeah, I said in the post afterwards I seem to have made a critical reading error :)
 

Offline yor_on

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Re: Do gravitational waves propagate faster than light waves?
« Reply #72 on: 10/01/2011 21:22:46 »
My view is that forces is perfectly applicable. It's what we see after all, although when trying to define what's behind our perception of forces, then we may need to find new descriptions. We use what we find useful, don't we:) Like horsepower, not joule. so I agree with you all :) Heh ::))

When you discuss stochastic methods Foolosophy, can you give an example of how you think there? what I find questionable is not that some things are found to be undefinable, I expect much of what we find in QM to create a new way of seeing, and with it new ways to look at 'indeterminacy'. Although if it was the way we use 'renormalization' I see what you mean.

We use them where wee need a 'cut off' to make that equation give us a definite answer, don't we? So in that motto it's not the perfect tool, but it works, and it's also open for redefinition if we find better 'limits' as I see it.
 

Offline Bill S

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Re: Do gravitational waves propagate faster than light waves?
« Reply #73 on: 11/01/2011 02:55:02 »
Quote from: Geezer
I would not think so Bill. If it was, where would the energy be coming from, and would it not tend to run out from time to time,

What you, and numerous P S authors, seem to be saying is:

1. The presence of mass (ignore energy for the moment) causes a distortion of spacetime over an unbounded distance.

2. If the mass were suddenly removed, spacetime would revert to its undistorted state.

3. Causing and maintaining this distortion, in spite of spacetime's natural tendency to resist it, requires no energy.

If the Universe is not the ultimate "free meal", could this be? 
 

Offline Geezer

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Re: Do gravitational waves propagate faster than light waves?
« Reply #74 on: 11/01/2011 03:30:36 »
Pretty much. Of course, a lot of energy had to go into the orbiting systems in the first place, so it's not as if there really is a free lunch. All gravity (or distorted spacetime etc etc) does is provides a force, or a pseudo force or some other name of your own choosing, that captures the kinetic energy of the orbiting system so that it operates like an exceedingly large flywheel.
 

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Re: Do gravitational waves propagate faster than light waves?
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