Speed of Gravity: Experts' Opinion

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Discussion Overview

The discussion revolves around the speed of gravity, exploring various claims and theories regarding its relationship to the speed of light. Participants examine concepts from general relativity, the implications of gravitational wave measurements, and the nature of gravitational interactions, with a focus on theoretical and experimental perspectives.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • Some participants assert that the speed of gravity is equal to the speed of light, referencing general relativity and the propagation of gravitational effects over time.
  • Others propose that gravity could potentially travel faster than light, citing various theoretical frameworks and interpretations of quantum mechanics.
  • A participant mentions that gravitational wave measurements have suggested a speed approximately equal to the speed of light, although they express skepticism about the detection of such waves.
  • There are discussions about the implications of a star's sudden disappearance and how gravitational effects would propagate to nearby objects, with examples illustrating the time delay in gravitational influence.
  • Some participants challenge the notion of gravitons traveling at the speed of light, suggesting alternative models involving higher-dimensional spaces.
  • Concerns are raised regarding the validity of faster-than-light communication claims, with participants questioning the sources of such information.
  • There is a debate about the conceptual understanding of gravitational forces and their effects on planetary motion, with some participants expressing confusion over the implications of speed and force balance.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the speed of gravity, with multiple competing views presented. Some support the idea that it equals the speed of light, while others argue for the possibility of faster-than-light propagation. The discussion remains unresolved with ongoing debates and differing interpretations.

Contextual Notes

Limitations include the dependence on theoretical interpretations of general relativity and quantum mechanics, as well as the unresolved status of experimental measurements of gravitational waves. The discussion also reflects varying levels of understanding regarding gravitational interactions and the nature of forces.

  • #31
NoTime said:
Ok, that seems to be a GR take on things.
Did you have a non-GR take in mind?
NoTime said:
As stated elsewhere in this thread gravity is not a force in GR.
Agreed, gravity is not a force in the usual sense under GR, so, what is your point?
NoTime said:
My problem is with the spin 2 graviton.

There seems to be a requirement that gravitons travel >> than the speed of light, being force carriers.
There is? By what?
NoTime said:
What am I missing here and how is this resolved? Are gravitons optional in quantum gravity theory?
Hard to say, it is not clear what you are assuming.
 
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  • #32
There seems to be a requirement that gravitons travel >> than the speed of light, being force carriers.

What on Earth makes you think that?

As far as spin 2 gravitons go, if you quantize gravity, that's what you'd get. I'd strongly suggest to anyone and everyone that getting a basic handle on non-quantized gravity is a Very Good Idea before one gets too worked up over quantized gravity and gravitons.
 
  • #33
Gravity does act like a magnet, there is no doubt about that!

It is just that it acts like a magnet to mass, and not to force.

Why do we not get pulled towards the Earth in space? there are many factors one is the inverse square law, the other one is the fact that you are also being pulled by the gravitational fields of other planets and stars.
 
  • #34
bayan said:
Gravity does act like a magnet, there is no doubt about that!

It is just that it acts like a magnet to mass, and not to force.
Being as respectful of your opinion as I can, it's extremely easy to demonstrate that gravity doesn't 'act like a magnet' at all - there's no 'repulsive' counterpart.
Why do we not get pulled towards the Earth in space? there are many factors one is the inverse square law, the other one is the fact that you are also being pulled by the gravitational fields of other planets and stars.
Are you joking? The motions of solar system bodies are predictable, to a very high degree of accuracy, under Newtonian physics, and if you add General Relativity, the only apparent inconsistencies are the motions of some comets (which are now well understood in terms of the 'rocket' effect of the jets).
 
  • #35
hah!

lets get sirous now.

i was kidding about the second part, but with the first part wouldn't they be attracted to each other? when i say "act like magnet" i do not mean that they have "+" & "-" ends. Rather what i meant was that they will get "pulled towars each other". If there is an explenation why it is not like that please post.
 
  • #36
Chronos said:
Did you have a non-GR take in mind?
Yes QFT, LQG.

Chronos said:
Agreed, gravity is not a force in the usual sense under GR, so, what is your point?
That I think I have some idea of how GR does its thing? :biggrin:

pervect said:
What on Earth makes you think that?
I don't. It's actually something I have read.
With a light speed graviton the force vector points in the wrong direction.

Also, it seems to be the reason for the question "What's the speed of gravity?" in the first place.

Does this question of the speed of gravity arise from some other source?
Am I supposed to accept that gravitons are not limited to the speed of light?
Is there some way, retaining the speed of light, to handle this?
Are these quantum gravity theories just plain wrong?
 
  • #37
bayan said:
hah!

lets get sirous now.

i was kidding about the second part, but with the first part wouldn't they be attracted to each other? when i say "act like magnet" i do not mean that they have "+" & "-" ends. Rather what i meant was that they will get "pulled towars each other". If there is an explenation why it is not like that please post.
As there are no magnetic monopoles (at least, no experimental evidence of such), one cannot ignore the 'dipole' nature of magnets and magnetism 'just because'. Further, since there are no monopoles, it's very easy to demonstrate that magnetic fields don't follow the inverse square law (gravity does). Finally, there are an awful lot of 'pulled towards each other' things out in the universe - gravity, electrostatic, magnetic, springs, surface tension, ... - one needs to go at least a tiny step further before sharing 'ideas before morning coffee' with others, especially in PF.

bayan 0, Einstein+Newton 2
 

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