Do gravitational waves propagate faster than light waves?

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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.

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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]

 
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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.
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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 »

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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 »
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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 »

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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.

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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 »

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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.

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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?

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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)

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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?

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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)


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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.)

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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

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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.

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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.)
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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?
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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.

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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.

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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.
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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 :)

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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.
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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? 
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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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Offline JP

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Re: Do gravitational waves propagate faster than light waves?
« Reply #75 on: 11/01/2011 05:36:10 »
3. Causing and maintaining this distortion, in spite of spacetime's natural tendency to resist it, requires no energy.

This is where the rubber sheet analogy breaks down.  A rubber sheet is naturally flat because there is a resistive force keeping it that way.  To bend it, you need to provide a force to overcome this.  Just putting something on the sheet isn't enough--you have to push it into the sheet with force to get the sheet to bend.

Space-time and gravity isn't like this.  Just having mass there is enough to bend space-time.  There is no additional force required to create or maintain the bending.  To use a mechanical engineering term, things are in static equilibrium, so no additional energy is required to keep them this way.

Causing the distortion in the first place would require energy, but this is accounted for by mass-energy equivalence.  The mass has energy associated with it, and it is this energy that accounts for creating the curvature in the first place.

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Offline Foolosophy

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Re: Do gravitational waves propagate faster than light waves?
« Reply #76 on: 11/01/2011 05:38:05 »
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.

QED is not a deterministic theory that is based on first principles

Quantum behaviour that is explained using probability is a temporary approach that offers non-sensical irrational approximations and estimates of what is really going on in the atomic and sub-atomic worlds

Although QED generates accurate predictions, its conclusions are insane and should not be taken literally.

QED is on its last legs. It will be superceded in the next 2 or 3 centuries by a deterministic theory that can be validated using first principles and basic logic and rationale
« Last Edit: 11/01/2011 05:41:58 by Foolosophy »

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Offline yor_on

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Re: Do gravitational waves propagate faster than light waves?
« Reply #77 on: 11/01/2011 15:54:14 »
Maybe you are right in a way Foolosophy. I read somewhere that the Eskimos had 2-300 word describing snow. that's what I expect to happen in QM too. We will find new descriptions that suddenly will make a new sense to us. But I expect us to need to modify what we call a 'linear' behavior to fit this new paradigm.
==

Still, I don't see the beef you have with it. Do you accept Heisenberg uncertainty principle? Why? If you want to find a deterministic logic built on Newtonian principles you will have to refute it. Starting to think of it I'm sure I can find a lot examples like that. Indeterminacy as we see it Foolosophy is only as we see it. That's what the Feigenbaum constant tells me.

(Sorry, used the wrong name. Slept overlong, again, corrected now though:)
« Last Edit: 11/01/2011 16:07:11 by yor_on »
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Offline imatfaal

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Re: Do gravitational waves propagate faster than light waves?
« Reply #78 on: 11/01/2011 18:16:28 »
2. If the mass were suddenly removed, spacetime would revert to its undistorted state.

Not sure this is a valid statement at all Bill. Even a gedanken needs to follow some rules - masses do not suddenly disappear.  If one postulates a complete transfer to energy, then this energy will cause exactly the same distortion in spacetime as its corresponding mass did (although some it will then radiate away).  With the conservation of energy there is just no way you can correctly ask/answer that question.  If you change the rules to ask the question then you cannot use the rules to answer it.   
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Offline Bill S

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Re: Do gravitational waves propagate faster than light waves?
« Reply #79 on: 11/01/2011 19:21:01 »
Quote from: Bill
If the mass were suddenly removed, spacetime would revert to its undistorted state.

I read in a P S book (don't remember which one)an account of what the Earth would experience if the sun suddenly vanished.  The author was not suggesting that this was a physical possibility, it was more in the nature of a thought experiment (OK,gedanken, if you will).  My intention was simply to impute an elasticity to spacetime, not to suggest magical effects. 

Quote from: JP
This is where the rubber sheet analogy breaks down.  A rubber sheet is naturally flat because there is a resistive force keeping it that way.  To bend it, you need to provide a force to overcome this.

I was trying to avoid the rubber sheet, but since you mention it, I agree that "To bend it, you need to provide a force".  If I sit on a trampoline I cause an indentation, the "force" causing and maintaining this is gravity, but gravity is not a force and expends no energy. (?) 
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Offline Bill S

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Re: Do gravitational waves propagate faster than light waves?
« Reply #80 on: 11/01/2011 19:30:48 »
Quote from: JP
“There is no additional force required to create or maintain the bending”……… “Causing the distortion in the first place would require energy”.

Is it me, or is there a contradiction here?   [???]
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Offline Geezer

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Re: Do gravitational waves propagate faster than light waves?
« Reply #81 on: 11/01/2011 21:47:48 »
Quote from: JP
“There is no additional force required to create or maintain the bending”……… “Causing the distortion in the first place would require energy”.

Is it me, or is there a contradiction here?   [???]

I don't see a contrdiction.  For example, it required energy to put the Moon in orbit around the Earth (possibly as the result of a collision with another large object) but once the Moon began to orbit the Earth, regardless of the model you choose, no additional energy or force is required.

The graviational effect is similar to a piece of string that connects the two objects.

There ain'ta no sanity clause, and there ain'ta no centrifugal force ćther.

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Offline Bill S

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Do gravitational waves propagate faster than light waves?
« Reply #82 on: 12/01/2011 01:38:54 »
Let's focus in a little.

"no additional force required to create...the bending"

"Causing the distortion in the first place would require energy"

Still no contradiction?   It's late at night, I might not be thinking straight.   [:P
There never was nothing.

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Offline JP

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Do gravitational waves propagate faster than light waves?
« Reply #83 on: 12/01/2011 02:02:01 »
My point was this:

You need to put a mass there to create the bending initially.  E=mc2, so that matter is energy.  Therefore you need energy to create the bending.  But that mass is all the energy you need (if we assume you somehow created the mass from energy at that point, so you didn't need to push it there).

Once the mass is there no further energy needs to be put in and the bending will stay forever.