Einstein was right about the speed of gravity

  • Thread starter Rashid
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  • #1
[SOLVED] Einstein was right about the speed of gravity

Here's the link.
http://www.msnbc.com/news/856046.asp#BODY
I just read an article on MSNBC. I always thought gravity traveled at the speed of light anyways. Makes sense in soooo many different respects.
Anyway, thought I'd post that bit of info.
 

Answers and Replies

  • #2
Brad_Ad23
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There is still intense debate as to whether the expiriment really measured the speed of gravity.
 
  • #3
Loren Booda
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How would light speed gravity restrict possible universe topologies?
 
  • #4
Brad_Ad23
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Well, it would stop changes in the topology of the universe from changing instantly, and I would assume stop gravity from being the same strength everywhere originating from a body (after all, if it were to travel instantly, why should it get weaker with distance?). Not only that, it keeps information in accordance with SR.
 
  • #5
kyle_soule
240
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Originally posted by Rashid
Here's the link.
http://www.msnbc.com/news/856046.asp#BODY
I just read an article on MSNBC. I always thought gravity traveled at the speed of light anyways. Makes sense in soooo many different respects.
Anyway, thought I'd post that bit of info.

This is, in fact, under great scrutiny, while the author maintains the errors do not lie in his mathematics, but in ones who challenge.

First of all, Clifford Will published a paper in the Astrophysical Journal in which he explained that a "deflection caused by the finite speed of gravity should indeed occur, but that it is some 10,000 times smaller than the shift the radio team predicted and observed."

It is true that the effect exists, but the VLBA's 10-microarcsecond resolution just isn't enough resolution to see it.

A much better test is coming up though, when the LIGO is done. All the experiment with the VLBA did was indirectly measure the speed of light.

EDIT:
Well, it would stop changes in the topology of the universe from changing instantly, and I would assume stop gravity from being the same strength everywhere originating from a body (after all, if it were to travel instantly, why should it get weaker with distance?). Not only that, it keeps information in accordance with SR.

The actual effect that matter has on gravitational waves is very minimal, it could travel great distances with almost no dispersion or scattering. For example, if a GW propagated through the universe once, its dispersion would only be one [lamb]. Although, GW's can show redshifting and can be lensed, much like light. The only restriction, that I know of, on the topology of the universe and GW's is that the GW's [lamb] must be less than the radius of the curvature of space-time.
 
Last edited:
  • #6
Could this tie in with Wheyl Tensor?
 
  • #7
kyle_soule
240
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Originally posted by Rashid
Could this tie in with Wheyl Tensor?

I'm not sure what the Weyl Tensor is, but I do know that the curvature is described as a rank 4-Riemann tensor, R sub(abcd). I don't know if this actually helps or not though.

NOTE: ABCD being alpha, beta, gamma, and delta.
 
  • #8
Hurkyl
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How could GR look if speed of light was unequal to speed of gravity anyways?

Hurkyl
 
  • #9
Heres a link to describe Weyl Tensor

http://mathworld.pdox.net/math/w/w088.htm [Broken]
 
Last edited by a moderator:
  • #10
Brad_Ad23
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Well Hurkyl, I don't think it would be consistent with SR then (in other words, I don't think it would be internally consistent, with the ONLY exception being when Vgravity < c). Otherwise information could travel FTL. Where it slower than c, I would imagine then it might add a sort of dampening effect and allow one to better sheild gravity, perhaps even managing to be able to manipulate spacetime so that light would not bend around massive bodies.
 
  • #11
Mr. Robin Parsons
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Nice article, nice testing, Black Holes prove that gravity can exceed light, as no light escapes the gravitational pull of a Black Hole.

Hummmm, makes me wonder why?
 
  • #12
Brad_Ad23
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Don't confuse the magnitude of the force of gravity and its effect on the escape velocity with actual velocity of gravity. Gravity does not "come out" of a black hole, as it is the local curvature of spacetime around the hole.

edit: If I recall correctly, the black hole is a 90 degree 'rotation' of spacetime.
 
  • #13
Mr. Robin Parsons
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Originally posted by Brad_Ad23
Don't confuse the magnitude of the force of gravity and its effect on the escape velocity with actual velocity of gravity. Gravity does not "come out" of a black hole, as it is the local curvature of spacetime around the hole.

edit: If I recall correctly, the black hole is a 90 degree 'rotation' of spacetime.

Ahem, I haven't forgotten, that it goes in, as proven by matter falling across it's event horizon as evidenced by Hubble's film of that event, Broadcast imagery, on TV.

(Go Figure)
 
  • #14
Originally posted by Brad_Ad23
Well, it would stop changes in the topology of the universe from changing instantly, and I would assume stop gravity from being the same strength everywhere originating from a body (after all, if it were to travel instantly, why should it get weaker with distance?). Not only that, it keeps information in accordance with SR.

do you believe that quantum gravity could have an answer?
 
  • #15
Originally posted by Mr. Robin Parsons
Ahem, I haven't forgotten, that it goes in, as proven by matter falling across it's event horizon as evidenced by Hubble's film of that event, Broadcast imagery, on TV.

(Go Figure)

across the event horizon? not into the black hole/EH?
Do you mean to say that gravity goes into a black hole? it doesn't; its the cause of the going in of matter.
 
  • #16
how do you imagine gravity travels?
 
  • #17
Mr. Robin Parsons
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Originally posted by MajinVegeta
across the event horizon? not into the black hole/EH?
Do you mean to say that gravity goes into a black hole? it doesn't; its the cause of the going in of matter.

Please tell me the difference between something that crosses the Event Horizon of a Black Hole, and something the goes into a Black Holes 'environment', that is JUST behind the event horizon, that the object, going into it, crossed??

Gravity absents the space inside a Black Hole, (other side of the event Horizon!) of EMR! ...and it will 'suck in' matter, as well, quickly too!
 
  • #18
Mr. Robin Parsons
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Originally posted by dr-dock
how do you imagine gravity travels?

Frame shifting.
 
  • #19
Originally posted by Mr. Robin Parsons
Please tell me the difference between something that crosses the Event Horizon of a Black Hole, and something the goes into a Black Holes 'environment', that is JUST behind the event horizon, that the object, going into it, crossed??

Gravity absents the space inside a Black Hole, (other side of the event Horizon!) of EMR! ...and it will 'suck in' matter, as well, quickly too!

never mind what I said. I had an idea about it, but I guess its a little self-contradictory.
 
  • #20
Mr. Robin Parsons
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Originally posted by MajinVegeta
never mind what I said. I had an idea about it, but I guess its a little self-contradictory.

NOTHING wrong with having ideas, nothing wrong with having ideas that end up, once reflected against others, being not quite the right answer, cause, sometimes knowing/realizing (finding out it's...) the wrong way, leads you to the right one!

My Apologies if I came across, just a little bit to strong, sometimes I don't know my own strength, well. sort of do, but , you know, sometimes, well, HUH, I, Errrr, Ummmm, weillllll, you see, it's like this, (Insert "Yadda-Yadda-Yadda" here)


EDIT SP ERROR(S)
 
  • #21
Originally posted by Mr. Robin Parsons
Frame shifting.
i don't know how it answers my previous q:?

i meant in a sense of:

what is it "travel"?
what does it take for one thing to travel?
what kind of things do travel?
why "Gravity" would be such a thing(a traveling thing)?
 
  • #22
Are you familiar with wave mechanics, or should I just start from the beginning??

BTW, gravity is composed of theoretical/hypothetical particles called gravitons.
 
  • #23
Brad_Ad23
502
1
In response to several replies that quoted my previous post:

Gravity does not go in. It is an attractive force, best seen as a warping of spacetime. Imagine a 90 degree drop in spacetime occurring at the event horizon. With this we see it more of a distortion effect, as it should be.


And in all liklihood quantum gravity would indeed provide an answer, but we are a few years away from having a very nice quantum theory of gravity.
 
  • #24
I don't know a thing about quantum gravity. Can you tell me at least a few things??
 
  • #25
selfAdjoint
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Program: Develop a quantum approach to spacetime that is background free. Ordinary quantum physics has the physics happening on a fixed background space and time, or spacetime. This is just like Newton. But Einstein's General Relativity built the physics into spacetime, and the spacetime into physics. "The scenery got into the act".

Quantum gravity researchers are very strong on background indpendence.

There are several schools of quantum gravity research, but the one most famous in North America is Loop Quantum Gravity (LQG) which currently uses a concept of quantum foam, more or less the successor to the original loops. Names to google: Ashtekar, Baez, Perimeter Institute. Successes: proof that area and volume (but not length) are quantized in their theory. Also they can prove the Hawking-Beckenstein black hole entropy formula from (their) first principles, up to an undetermined parameter, the Immirzi parameter. Lots of recent discussion about whether they can get rid of the Immirzi parameter problem by doing some fairly major redefinitions of their quantum foam.

Quantum foam consists of quantized four dimensional triangular pyramids - simplexes - carrying spinor values and filling spacetime. where they cut into some surface (say a black hole event horizon) they give it a quantum of area. Smolin has some material on LQG in his book "Three Roads to Quantum Gravity". I don't know of any other popular presentation of it.
 
  • #26
Originally posted by Mr. Robin Parsons
NOTHING wrong with having ideas, nothing wrong with having ideas that end up, once reflected against others, being not quite the right answer, cause, sometimes knowing/realizing (finding out it's...) the wrong way, leads you to the right one!

My Apologies if I came across, just a little bit to strong, sometimes I don't know my own strength, well. sort of do, but , you know, sometimes, well, HUH, I, Errrr, Ummmm, weillllll, you see, it's like this, (Insert "Yadda-Yadda-Yadda" here)


EDIT SP ERROR(S)

Okay. Take a singularity. If the EH is infinitely small, then nothing can cross it. crossing over an EH that is infinitely small almost doesn't quite make sense to me.
 
  • #27
Mr. Robin Parsons
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Try it this way, a Singularity cannot be "infinitely" small, as an "infinity" is an inconcievable thing.

If you have something there, then you have something there, just because the math might be 'teeny', doesn't mean that there isn't something there.

If you can measure it, then it (should, if it follows the logic in reality) should be "accepted" as being there, whether or not anything can cross it, an EH at that level, probably, just you struggle to 'imagine' it.
 
  • #28
kyle_soule
240
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Originally posted by MajinVegeta
Okay. Take a singularity. If the EH is infinitely small, then nothing can cross it. crossing over an EH that is infinitely small almost doesn't quite make sense to me.

Wouldn't a singularity, such as BB, have a massive EH, in comparison to it's size? The size of the EH depends on the mass doesn't it?
 
  • #29
Eh
746
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Originally posted by selfAdjoint

...Successes: proof that area and volume (but not length) are quantized in their theory.

That one caught my attention. Are you sure length is not quantinized in LQG? In other words, can you take a fundamental loop and divide it infinitely?
 
  • #30
Mr. Robin Parsons
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Originally posted by kyle_soule
Wouldn't a singularity, such as BB, have a massive EH, in comparison to it's size? The size of the EH depends on the mass doesn't it?

You seem to be assuming that the BB was a 'Black Hole' with an EH, what if, because the rest of the "Universe", hadn't been let out yet, it was simply a BH without any EH, because spacetime hadn't propagated just yet?

Is that possible?/ or possibly, the answer?
 
  • #31
I don't see how effects of gravity, even if they do occur instananeously, would have any useful purpose whatsoever...besides throwing a few computations out of whack. Can someone suggest to me how FTL based on gravity would do anything useful?
 
  • #32
Mr. Robin Parsons
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Sure, it would "get us there"!
 

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