Does Gravity Act Faster Than the Speed of Light?

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Discussion Overview

The discussion revolves around the nature of gravity and whether it acts faster than the speed of light, exploring concepts from relativity, Newtonian gravity, and potential experimental evidence. Participants delve into theoretical implications, the relationship between gravity and particles, and the challenges of formulating a quantum theory of gravity.

Discussion Character

  • Debate/contested
  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant questions whether gravity acts instantaneously, suggesting that gravitational interactions between distant massive objects occur without delay.
  • Another participant argues that if gravity were to propagate faster than light, it could lead to paradoxes such as time travel, complicating the theoretical framework.
  • Some participants reference the implications of Newtonian gravity and its limitations in explaining phenomena like GPS, which relies on relativistic effects.
  • There is a proposal about gravity being a fundamental property of all particles, with a later reply emphasizing that all particles with mass or energy exert gravitational influence.
  • Discussion includes skepticism about the graviton, with participants expressing doubt about its existence and the theoretical framework surrounding it.
  • One participant highlights the difficulties in developing a quantum theory of gravity, noting that attempts to treat gravity similarly to electromagnetism lead to mathematical inconsistencies.
  • Another participant mentions the Higgs mechanism and its implications for understanding gravity, while also acknowledging that the current understanding may be flawed.
  • Some participants express uncertainty about the existence of experimental evidence that definitively supports or refutes the speed of gravity.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether gravity acts faster than light, with multiple competing views presented. There is significant debate regarding the nature of gravity, the validity of the graviton, and the implications of current theories.

Contextual Notes

Participants note limitations in current theories and the need for further experimental evidence to clarify the speed of gravity and its fundamental nature. The discussion reflects a variety of assumptions and interpretations of gravitational theory.

Who May Find This Useful

This discussion may be of interest to those exploring theoretical physics, particularly in the realms of gravity, relativity, and quantum mechanics, as well as individuals curious about the ongoing debates in these fields.

mintparasol
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Hi folks,
Just a quick question:-

Relativity says that nothing, even the gravitational impulse can travel faster than the speed of light. Is there any experimental evidence available online that proves that gravity's 'pull' or 'force' acts thru space at the speed of light?
I believe it's faster, that gravity is an instantaneous interaction. But I'm just a lay nut so I might be imagining things! I believe that if 2 supermassive objects at great distance from each other start to interact gravitationally, that it's an instantaneous reaction, it doesn't take the time it would take for light or other radiation to cross the distance, it's instant.

How wrong am I? Am I seriously misunderstanding relativity/spacetime/gravitation?

Thanks in advance,
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The basic problem is that if you can send information faster than light, then you can send information back in time, and this is bad. This is not to say that it's impossible, but a) we don't know of any cases in which you can send information back in time and b) if we could then there would be a lot of explaining.

If you assume that gravity is purely Newtonian with an infinite velocity then this is clearly wrong since you end up with spacecraft motions that are clearly wrong. You can change your theory to fit current observations, but that does take a bit of doing.

Science works by process of elimination. I'm pretty sure that if you have a theory of gravity in which the gravity moves instantly, that there are experiments that you can use to disprove that. I'm also pretty sure that if you have a theory in which gravity moves 0.0001 m/s faster than light, that our measurements aren't good enough to exclude that. Whether there are experiments that rule out that gravity moves say 10% faster than the speed of light, I don't know, but I'm sure there is some review article out there.

I don't think it's possible to *prove* that gravity doesn't move faster than light. It is possible to that if gravity behaved in X manner, that it would be inconsistent with experiment.
 
Ok, there's some material here to get me learning, thanks!

What if gravity were a fundamental property of ALL particles?
 
What do you mean? As far as I know, gravity influences all particles. You can't "escape" from a gravitational field like you could "escape" from an electromagnetic field by putting your charge to 0. Everything which has energy or mass is influenced by gravity and exerts gravity. And that means [itex]\emph{everything}[\itex]: neutrino's, light, electromagnetic fields, elektrons, stars, etc. etc.[/itex]
 
What experimental evidence do you suggest that supports this hypothesis? GR predicts weird effects like frame dragging. Gravity Probe B tested and confirmed these effects with great precision. What is left to be tested?
 
haushofer said:
What do you mean? As far as I know, gravity influences all particles. You can't "escape" from a gravitational field like you could "escape" from an electromagnetic field by putting your charge to 0. Everything which has energy or mass is influenced by gravity and exerts gravity. And that means [itex]\emph{everything}[\itex]: neutrino's, light, electromagnetic fields, elektrons, stars, etc. etc.[/itex]
[itex] <br /> Ok, well what if just one particle was responsible for gravity? Say for argument's sake this particle is the neutrino but it could be any particle in the standard model or some particle yet to be discovered. It exerts gravity over all other particles and therefore <i>is</i> the cause of all gravitational fields. How would the math work then?<br /> <br /> BTW, I'm just a lay nut trying to learn by throwing stuff out there!<br /> I don't believe in the graviton. Show me one. I've no problem with broken symmetry and the demonstrable parts of the standard model but I think gravity is something else entirely and while the math of relativity seems to work perfectly with respect to gravity, I believe it's not understood at all on a quantum level, at least by me in any case!<br /> Thanks in advance for any replies,<br /> ad[/itex]
 
I don't believe in the graviton. Show me one...I think gravity is something else entirely

reasons? Have you ever seen a photon? How about a quark?

Skepticism is always reasonable, but unless you have some facts to support you, it's unlikely anything here will be specific enough to satisfy you.
 
  • #10
Naty1 said:
reasons? Have you ever seen a photon? How about a quark?

Never seen a photon but the mathematical theory behind them owes much to observation, the theory behind gravitons is pretty hypothetical in comparison is it not? It would be more of a mathematical extrapolation than anything approaching a law, no?

Have quarks not been detected in particle accelerators by now? I thought they had...

My bad, maybe
 
  • #11
mintparasol said:
It exerts gravity over all other particles and therefore is the cause of all gravitational fields. How would the math work then?

It works very badly, and you've hit at the reason why it's been so difficult to get a quantum theory of gravity.

The quantum theory of electromagnetism involves electrons tossing photons back and forth, and those photons are mathematically treated as a "small correction" to the vacuum.

The problem with doing the same trick to gravity is that you assume that gravity occurs by exchanging "gravitons" you run into the problem that since everything produces gravity, then gravitons produce gravitons which produce more gravitons, and when you add everything up, you get infinities all over the place.

One reason that people are interested in string theory is that when you get to high enough energies, the gravitons become strings that presumably don't produce more gravitons, and so by cutting things off, you get finite answers. However, you run into a problem in that you can cut things off any which way, so instead of getting finite answers, you get any answer that you want, which is also bad.

I don't believe in the graviton.

Nature doesn't care what you believe. :-) :-)

Show me one. I've no problem with broken symmetry and the demonstrable parts of the standard model but I think gravity is something else entirely and while the math of relativity seems to work perfectly with respect to gravity.

The trouble is that you really can't have two completely separate theories of the universe, because you run into situations in which both theories are active.
 
  • #12
mintparasol said:
Never seen a photon but the mathematical theory behind them owes much to observation, the theory behind gravitons is pretty hypothetical in comparison is it not? It would be more of a mathematical extrapolation than anything approaching a law, no?

Well... No one has ever gotten a theory involving gravitons to actually work. Now you could say at that point "why bother?" and just say that things are run by GR. The trouble is that in some situations that we can imagine, GR just stops working. Unfortunately, those situations are extreme enough so that we just can do something like make a black hole and see what happens.

Have quarks not been detected in particle accelerators by now? I thought they had...

We have seen things for which quarks is the most straightforward explanation that anyone has come up with.
 
  • #13
research the higgs mechanism, gravity is not a force with infinite speed
 
  • #14
ZacharyFino said:
research the higgs mechanism, gravity is not a force with infinite speed

The higgs mechanism might be totally wrong.

The current situation is

1) we have no observations that indicate that gravity travels at faster than light (and people have tried to explain that to Tom Van Flattern without success, but that's his problem)

2) if gravity did travel faster than light, then there would be a lot of theoretical problems
 
  • #15
twofish-quant said:
We have seen things for which quarks is the most straightforward explanation that anyone has come up with.

OK, thanks. Quarks would still have a firmer basis in observable reality than the graviton, then, no?
 
  • #16
Planetary motion studies rule out superluminal gravity. See also:

Aberration and the Speed of Gravity
http://xxx.lanl.gov/abs/gr-qc/9909087
"The observed absence of gravitational aberration requires that ``Newtonian'' gravity propagate at a speed $c_g>2\times10^{10}c$. By evaluating the gravitational effect of an accelerating mass, I show that aberration in general relativity is almost exactly canceled by velocity-dependent interactions, permitting $c_g=c$. This cancellation is dictated by conservation laws and the quadrupole nature of gravitational radiation."
 
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