For the sake of arguement, let's assume that gravity is the result of curved spacetime. Let's also assume that length contraction is a physical property that occurs in a moving observer's frame of reference.

Wouldn't that mean that gravity should be influenced by length contraction because curved spacetime is being contracted? It appears that as a mass goes faster, its gravitational field parallel to the axis of motion should decrease, while its gravitational field that is perpendicular to the axis of motion should remain constant. Is this a correct assumption?

Tom

<i>Wouldn't that mean that gravity should be influenced by length contraction because curved spacetime is being contracted?</i>

Spacetime doesn't contract in GR. It only curves. The effect on objects viewed from a distance looks like contraction. Locally, objects aren't contracted.

<i>It appears that as a mass goes faster, its gravitational field parallel to the axis of motion should decrease, while its gravitational field that is perpendicular to the axis of motion should remain constant. Is this a correct assumption?</i>

No.

James,

Spacetime doesn't contract in GR. It only curves. The effect on objects viewed from a distance looks like contraction. Locally, objects aren't contracted.

Spacetime contracts in SR, but it curves in GR. How does the contraction of spacetime in SR effect the rate of curvature in GR?

If an object is moving at a relativistic speed, doesn't its curved spacetime contract in the same amount as the object itself? If so, does the gravitational field of the object still follow the 1/r^2 rule to a stationairy observer?

Tom

Tom:

<i>Spacetime contracts in SR, but it curves in GR.</i>

No it doesn't. It doesn't contract in either. SR is a subset of GR, remember.

<i>If an object is moving at a relativistic speed, doesn't its curved spacetime contract in the same amount as the object itself?</i>

What did I just say, in my previous post?

<i>If so, does the gravitational field of the object still follow the 1/r^2 rule to a stationairy observer?</i>

Gravity is not a force in GR. The description is completely different.

James,

If spacetime doesn't contract in SR, what does contract in SR?

Space and time. Field equations must me invariant under lorentz transformations!

Measured distances contract for some observers. Measured times dilate for some observers.

ryans,

Space and time. Field equations must me invariant under lorentz transformations!

Let me ask you the same question I asked James: If mass curves spacetime, and a mass in motion contracts space, then how is the curvature of spacetime influenced by the contraction of space?

Tom

James,

Measured distances contract for some observers. Measured times dilate for some observers.

What do you mean by "measured distance" and "measured time"? Is the length contraction and time dilation in SR less real than the spacetime curvature in GR? Isn't length contraction in a moving frame of reference just as physical as curved spacetime, and therefore, shouldn't length contraction influence curved spacetime?

Tom

Invariance of the lorentz 4-vector gives an equation relating the 2 frames of reference via the metric tensor.

Prosoothus, don't forget that in relativity, measurements make up reality! What you can measure, is what scientific "is". The rest is philosophical talk ... which we had a lot in the past :)

Tom:

<i>What do you mean by "measured distance" and "measured time"?</i>

What I said. They are things measured by some observer.

<i>Is the length contraction and time dilation in SR less real than the spacetime curvature in GR?</i>

SR is just GR in flat spacetime. Whatever applies to GR applies equally to SR.

If you want to get philosophical about it, you can ask whether GR is just a <b>description</b> of space and time which reproduces the observations, or whether space and time <b>really</b> are curved. For a physicist, the answer makes no practical difference. All a physicist can do is measure things. They can't see the "ultimate reality", whatever that is. Nobody can.

<i>Isn't length contraction in a moving frame of reference just as physical as curved spacetime, and therefore, shouldn't length contraction influence curved spacetime?</i>

Yes, it is just as physical.

You seem to be failing to appreciate that curvature of spacetime accounts for length contraction. They are not separate things.

James,

You seem to be failing to appreciate that curvature of spacetime accounts for length contraction. They are not separate things.

Are you saying that the curvature of spacetime caused by a 1kg mass is identical to an observer regardless of the speed of the 1kg mass relative to the observer?

Tom

Yes this is what is saying (correct me if I am wrong James)Mass is invariant under lorentz transformations. You are getting confused with momentum. There is no mass dilation. The idea of increasing mass is continuallt misinterpreted. The equivalence principle gives inertial mass = gravitational mass.

ryans,

Let's say that you have 1kg of mass that is stationairy relative to an observer. GR states that this mass will curve spacetime around it, generating a gravitational field.

Now let's take that mass and accelerate it to .90c. SR states that length contraction should occur. I assume that this length contraction would also influence the curvature of spacetime caused by the mass. I don't see how length contraction can occur, while keeping the spacetime curvature unchanged. Does the length of the mass changes as a result of length contraction, but the length of the gravitational field does not? Is length contraction limited only to the object itself, and not its fields?

Tom

Tom:

<i>I don't see how length contraction can occur, while keeping the spacetime curvature unchanged.</i>

Why not? You're talking about two completely separate things. Length contraction is a property of an object. Curved spacetime is something an object causes.

<i>Does the length of the mass changes as a result of length contraction, but the length of the gravitational field does not?</i>

What on earth does "length of the gravitational field" mean?

<i>Is length contraction limited only to the object itself, and not its fields?</i>

Length contraction is something observed by an observer.

Again, gravitational field equations must be invariant under lorentz transformations. The theory is based on this axiom.

James,

Why not? You're talking about two completely separate things. Length contraction is a property of an object. Curved spacetime is something an object causes.

Correct me if I'm wrong, but doesn't length contraction occur in the entire frame of reference of the object, and not just in the object itself? Doesn't length contraction have the same effect on the space surrounding an object (curved spacetime) as it does on the object itself?

Length contraction is something observed by an observer.

But isn't length contraction real and physical to the observer? Isn't length contraction just as real to an observer as curved spacetime? If both curved spacetime and length contraction are physical to an observer, won't length contraction have an effect on the curved spacetime?

Tom

ryans,

Again, gravitational field equations must be invariant under lorentz transformations. The theory is based on this axiom.

I'm just trying to understand why.

Let's look at a simplified example:

Let's say you take a piece of paper and you apply a force to it to make it curve. Now, let's say you contract the length of the curved paper to half its size. Won't the curvature change due to the contraction? How do you contract the paper without influencing its curvature?

Tom

ryans & James R.,


My impression of what Prosoothus is trying to convey is a view that objects contract at one rate and space at another.

I will resist my temptation to say where a dicussion of this issue might be found. It is called "q" and indeed suggests that distance via Lorentz Contraction varies differently (different rate) for an object vs the space it traveling through.

The consequences of "q" is should an object achieve v=c it will cease to have dimension but distance will not have gone to zero. In that regard all observers views remain consistant. Simular to Relativity but slightly different.

If cosmological distance were zero at v=c then a photon is in instant contact with all points in it line of travel at the same time and there is no v=c delay in photons reaching distant points.

I'll stop here and hope not to have started another battle, since this is an unqualified scientific view.

Is this the problem you are seeing Tom?

MacM-

i had a dream last night that your grandson lived on my floor in my college dorm. his name was dan mccoin, and he had orange hair. i told him i thought you were a crackpot and he laughed.

i think i ve been hanging out on this message board way too often, if it s starting to creep into my dreams.

oh, me too had few dreams..

MacM and Tom holding a net by its ends and running all around the marsh to catch Albie fish...

ryans grand father pointing a gun at Einstein's temple and demanding him not to rest until declare some axiom..

chroot trying to push a rock while kicking MacM and the rock winks at Mac.. hey the rock looks like James R..

Persol and MacM were standing still in a gun dual waiting for the final draw..

yeah, have to reduce the hanging out time a bit little..

lethe & everneo,

MacM-

i had a dream last night that your grandson lived on my floor in my college dorm. his name was dan mccoin, and he had orange hair. i told him i thought you were a crackpot and he laughed.

i think i ve been hanging out on this message board way too often, if it s starting to creep into my dreams.


ANS: I don't want to scare you but I do have a grandson named after me.

But he is only two.:D

everneo

I think you need to get out more Hey :)

Originally posted by Prosoothus

Its gravitational field parallel to the axis of motion should decrease, while its gravitational field that is perpendicular to the axis of motion should remain constant. Is this a correct assumption?

Tom [/B]

Yes it is known as centrifugal force!

MacM,

Is this the problem you are seeing Tom?

Let's say an object is moving at a relative speed of .90c. According to GR, the mass of the object will curve the spacetime around the object. According to SR, the length of the object, and the space around it, will contract as a result of the relative speed of the object. In other words, there are two things influencing the space around the object: the curvature caused by the mass of the object and the length contraction caused by speed of the object.

I don't see how an objects gravitational field remains constant, when SR states that distance gets contracted. SR states that not only will the length of the object contract, but that the entire frame of reference is contracted. This would mean that the curved spacetime caused by the mass should be contracted as well, thereby changing the gravitational field of that object.

Tom

god-of-course,

Yes it is known as centrifugal force!

Centrifugal force is the inertial force resulting from a change in the direction of the motion of an object. I was referring to an object moving at a constant speed and direction.

Tom

Prosoothus,

If you hven't yet, let me suggest you have a read of the link in the following topic.

"H Lindner's flowing space substance theory "

See if that makes more sense to you.

MacM,

If you hven't yet, let me suggest you have a read of the link in the following topic.

"H Lindner's flowing space substance theory "

See if that makes more sense to you.

I already saved the webpage. I'll take a closer look at it later.

Tom