How Fast Do Forces Like Gravity and Magnetism Act Compared to Light?

AI Thread Summary
Forces such as gravity and electromagnetism propagate at the speed of light, with massless bosons mediating these interactions. The weak force, however, is mediated by massive bosons, resulting in a slower propagation speed. There is ongoing debate regarding the speed of gravity, with some claims suggesting it could be faster than light, but these lack peer-reviewed support and are considered controversial. Experiments like those involving gravitational waves have yet to conclusively measure gravity's speed, reinforcing the current understanding that it aligns with the speed of light as described by general relativity. Overall, the consensus remains that all known fundamental forces travel at or below the speed of light.
quasi426
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I know light is the fastest thing in the universe. But what about forces, namely gravity, magnetism, strong and weak forces. Do these forces act instantaneously OR do they act as fast or slower than light, does the medium they are acting in matter or not?
 
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Nothing is instantaneous, that's for sure. All fundamental forces are described by bosons, gravity, electromagnetism and strong interactions are described by massless bosons, which means that they propagate wih "c". The weak interaction is mediated by massive bosons, whose velocity is obviously less than "c".

Daniel.
 
Are gluons massless?
 
gluons are "massless", but i don't know what "massless" means. maybe it is more tricky than that.
 
quasi426 said:
I know light is the fastest thing in the universe. But what about forces, namely gravity, magnetism, strong and weak forces. Do these forces act instantaneously OR do they act as fast or slower than light, does the medium they are acting in matter or not?
They all operate at the speed of light.
 
Can someone describe an experiment or simply give me a link where an experiment showed that these forces travel at the speed of light. (Does the medium the forces travel in matter?)
 
Sometime back, when I was actively reading material on astrophysics, I came across a paper which shows the speed of gravity much greater than light. The idea is that if the speed of gravity is equal to that of light, by Poynting-Robertson effect, the Earth would speed up and run away from the Sun. But no such evidences are perceived by the astronomists. The content of the paper seems plausible. It is worth reading http://www.metaresearch.org/cosmology/speed_of_gravity.asp

I don't know of any papers, as I am no expert in Physics, which negate the above theory but I hope experts of this forum may suggest something.

Regards,
 
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quark said:
The content of the paper seems plausible.

Here's a hint: If this "paper" only exists at this website and no references have been made to it appearing in any peer-reviewed journal, the "plausibility" degree drops WAAAAAY down.

Also, those people are called "astronomers", not "astronomists".

Zz.
 
OK, thanks for the correction. Can you let me know what is wrong with the paper? Not appearing in a peer reviewed journal may be one reason.
 
  • #10
quark said:
OK, thanks for the correction. Can you let me know what is wrong with the paper? Not appearing in a peer reviewed journal may be one reason.

I will deal with JUST the first few lines in the abstract, which already contain something weird

Standard experimental techniques exist to determine the propagation speed of forces. When we apply these techniques to gravity, they all yield propagation speeds too great to measure, substantially faster than lightspeed. This is because gravity, in contrast to light, has no detectable aberration or propagation delay for its action, even for cases (such as binary pulsars) where sources of gravity accelerate significantly during the light time from source to target

Where exactly are these measurements that "all yield propagation speeds too great to measure"? The speed of gravity requires the ability to measure gravity waves, either from a supernova, a binary star, etc.. i.e. something that is producing a fluctuating gravity as observed on earth. Now unless I've missed something, such gravitational waves have NOT been observed YET! LIGO still hasn't made any conclusive detection, and it is being upgraded further to be even more sensitive.

The only valid attempt so far as showing such measure was done a couple of years ago [http://arxiv.org/abs/gr-qc/0206022] . However, even this is still controversial, and people like Clifford Will has shown that the calculation/model is flawed [http://wugrav.wustl.edu/people/CMW/SpeedofGravity.html]

So judge for yourself.

Zz.
 
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  • #11
All known forces travel at the speed of light. All known particles travel at or under the speed of light. All massless particles travel at the speed of light. The neutrino, which is now thought to have mass, travels at the speed of light too. The existence of certain particles called "tachyons" have been theorized, which are supposed to have a minimas speed at the speed of light and maximum speed at infinity. They supposedly don't inetract with matter and get more massive as they get closer to the speed of light from the opposite direction of mater. However, they have never been observed and may turn out to be a mistake. There is one way of random information traveling faster than the speed of light called entanglement, which means that we can find out the spin of an electron at any distance from us immediately by observing it's partner electron.
 
  • #12
ZapperZ said:
The only valid attempt so far as showing such measure was done a couple of years ago [http://arxiv.org/abs/gr-qc/0206022] . However, even this is still controversial, and people like Clifford Will has shown that the calculation/model is flawed [http://wugrav.wustl.edu/people/CMW/SpeedofGravity.html]

A little background for interested readers. In late 2002, the measurement was performed by Fomalont and Kopeikin when a quasar passed behind Jupiter. Fomalont and Kopeikin claimed that this experiment showed that the speed of light and and the speed of gravity are the same. Cliffored Will disagreed, saying that Fomalont and Kopeikin's experiment didn't actually measure the speed of gravity.

In general relativity, the speed of gravity and the speed of light are the same, so an alternative to general relativity is needed to even talk about a difference. Steve Carlip has written a nice, thoughtful paper on this. According to his analysis, the interpretation of what was measured depends on the which class of alternatives to general relativity is used.

This is subtle stuff, and one of Carlip's conclusions is that for a certain class of models that have different speeds for gravity and light, measurements have yet to reach the sensitivity required to measure the difference.

Regards,
George
 
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  • #13
quark said:
Sometime back, when I was actively reading material on astrophysics, I came across a paper which shows the speed of gravity much greater than light. The idea is that if the speed of gravity is equal to that of light, by Poynting-Robertson effect, the Earth would speed up and run away from the Sun. But no such evidences are perceived by the astronomists. The content of the paper seems plausible. It is worth reading http://www.metaresearch.org/cosmology/speed_of_gravity.asp

I don't know of any papers, as I am no expert in Physics, which negate the above theory but I hope experts of this forum may suggest something.

Regards,

Meta Research is run by Tom Van Flandern, who is not a reputable source when it comes to such matters.
 
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  • #14
In Newtonian gravity, the speed of gravity is infinite. Otherwise, planetary orbits would not be stable. Since we are here to have this discussion, we can safely conclude either the speed of gravity is infinite or the Newtonian theory of gravity is incorrect. We have not yet actually measured the speed of gravity [as noted by other posters], but we do know the Newtonian theory of gravity is incorrect. It has been replaced by the much better theory of gravity called general relativity.

In Newtonian theory gravity is treated as a 'force'. In general relativity, gravity is treated as a field [technically speaking it is more precise to say gravity is the geometry of spacetime, but that needlessly complicates the explanation]. In a field, the attractive force exerted on a body is not directed squarely at the source of that field. It is instead offset by an amount that depends on both the velocity and position of the source and body being acted upon. This almost exactly cancels the effect of the apparent propogation delay predicted by Newtonian gravity. This nearly complete cancellation effect is directly predicted by the field equations.

Now for the rest of the story: the field equations allow us to predict the slight propogation delay that is not canceled out. When a body accelerates in a field, GR predicts it will radiate away a small amount of energy [i.e., gravity waves]. This would change the orbit of the body by a predictable amount. And the effect has been verified in the orbital decay of binary pulsars [which earned a Nobel prize]. The decaying orbit effect would not be observed if the speed of gravity was infinite. It was another stunning triumph for the much better [than Newtonian] theory of general relativity, and another resounding defeat for the meta-nonsense of Van Flandern.
 
  • #15
Thanks guys. Point well understood and I will look into the papers you suggested.
 
  • #16
Something more basic.

I'm a novice at all this, and I have a (perhaps) basic question.

If time slows as speed approaches the speed of light, shouldn't light (since it travels at the speed of light) get everywhere instantly (i.e. be infinitely fast)?

One plausible bit of reasoning is as follows:

1) To have infinite speed, a particle would have to have zero mass.
2) A particle with zero mass would not exist.
3) In order to exist, a photon has > zero mass, therefore travels at < infinite speed.

If so, doesn't the "speed of light" actually measure something just less than a perfect trade-off between speed and time?

Also, if 1), 2) and 3) are true, wouldn't this provide an easy way to measure the mass of a photon? Just calculate how much mass something would have to have to slow it down to the measured speed of light?

Anyway, thanks for any thoughts or answers.

SeaTea
 
  • #17
Would we be able to directly detect something moving faster than light or would it be invisible or "dark"? Might something moving faster than light be only detectable indirectly through an affect that cannot be explained?
 
  • #18
ZA said:
The neutrino, which is now thought to have mass, travels at the speed of light too.
No... just very close to it.

SeaTea said:
1) To have infinite speed, a particle would have to have zero mass.
2) A particle with zero mass would not exist.
3) In order to exist, a photon has > zero mass, therefore travels at < infinite speed.
1) Incorrect. To have a speed equal to that of light in vacuum, a particle has to have zero mass.
2) Incorrect. Mass is not a requirement for existence.
3) Incorrect. A photon has zero mass and thus travels at the speed of light (and light, of course, is photons).

reasonmclucus said:
Would we be able to directly detect something moving faster than light or would it be invisible or "dark"?
We detect things moving faster than light every day. The trick is that it has to be through a refractive medium rather than vacuum. 'Cherenkov radiation', for example, is the blue glow that is seen in uranium storage pools and is caused by massive particles exceeding the speed of light in water.
 
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  • #19
neutrino

Are you sure the neutrino travels at under the speed of light? Everywhere I erad, it said it travels at the speed of light. So could you please give me your source for that? thanks.
 
  • #20
Sorry, ZA... I can't cite a specific source. It's just something that's been around for decades. The reason that neutrinos were originally thought to travel at c was because they were believed to be massless. Once the Russians hypothosized that they had something like a 3eV rest mass, and it was experimentally verified, then their speed is of necessity known to be less than c.
 
  • #21
Check out this paper. It has practically all the references to experiments that have detected neutrino mixing/mass, from the first one at SuperK, to Kamland, to SNO experiments.

http://arxiv.org/abs/hep-ph/0503086

Zz.
 
  • #22
Thanks for the link, Zapper. Cool stuff.
 
  • #23
Chronos said:
the effect has been verified in the orbital decay of binary pulsars [which earned a Nobel prize]. The decaying orbit effect would not be observed if the speed of gravity was infinite. It was another stunning triumph for the much better [than Newtonian] theory of general relativity, and another resounding defeat for the meta-nonsense of Van Flandern.

Frictional aspects within a binary system, (individual stars) tidal forces within the non solid (plasma) system causes bodies to gradually lose orbital stability. Close binary stars would have a major contribution to each other. Like rolling a car with flat tires vs inflated tires. Tidal forces would be proportional to the mass/distance between bodies. Coronal/solar interactions would extend far out from the surface. There's also the electro/magnetic aspects. A rapidly spinning star would make one hell of a dynamo. Any comments?
 
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  • #24
GR predicts gravity travels at the speed of light. Why the speed of light? What is it traveling through? What is the current speculation as to the make up of space/time and why matter warps it? Is its speed some evidence of the graviton?

If anyone can answer, I thank you in advance!
 
  • #25
Just wanted to say i enjoy reading threads like this, really interesting stuff. I'm also a novice at this, and also have perhaps a very basic question...

Assuming that the universe is expanding below the speed of light (at the moment), what would happen if you were at the very edge traveling at the same speed and stuck your hand outside that boundary?
 
  • #26
There isn't an 'edge' to spacetime. It's finite, but unbounded. No matter where you are, you're in the 'centre'. Also, there is no 'outside'.
 
  • #27
Thanks Danger, that's really got me thinking such as along the lines of "how are you always at the centre?" the answer is probably somewhere on these forums. I could ask here but i feel i might be deterring the thread too much :redface:
 
  • #28
Think of it as a 4-dimensional analogue to a 3-D sphere. No matter where you are on the Earth, you're in the middle of the surface area. Keep going in one direction and you'll end up back where you started. I don't think that the human mind is capable of 'envisioning' it other than mathematically.
 
  • #29
Danger said:
...a 3-D sphere. No matter where you are on the Earth...

The surface of the Earth is a 2-sphere.
 
  • #30
That might be just a matter of definition, masudr. To my mind, a sphere is 3-D, a plane is 2-D, a line is 1-D, and the universe is 4-D. My apologies if this isn't proper topographic terminology; I've never studied that.
 
  • #31
Danger said:
'Cherenkov radiation', for example, is the blue glow that is seen in uranium storage pools and is caused by massive particles exceeding the speed of light in water.

True, however, the speed increase is relative to medium and NEVER exceeds the speed of light in a vacuum.
Therefore, the Cherenkov effects are superluminal with respect to the common mode within the medium, which IS LESS THAN C, but ARE NOT superluminal in a vacuum.
 
  • #32
In other words, the speed of light in a vacumm is approximately 299,792,458 meters per second. The Cherenkov effect DOES NOT exceed that. It only exceeds the speed of light common in that medium, which is about .75c.
 
  • #33
Absolutely, pallidin. That's why I specified that it can only occur within a refractive medium. Nothing—unless tachyons actually exist—can exceed c in vacuum. Even in a refractive medium such as water or glass, the individual photons still travel at vacuum-level c. The atomic interactions limit the propogation speed, which can be exceeded by other particles that suffer less interference. (Not a proper scientific explanation, but the best that I can summon right now.)
 
  • #34
A sphere embedded in \mathbb{R}^{3} is very much 2-dimensional.:wink:

Daniel.
 
  • #35
As Daniel correctly points out, the 3D sphere you speak of is embedded in \mathbb{R}^{3} but you only require 2 co-ordinates to describe any position on the surface (e.g. \theta, \phi form a common system). Since there are only 2 degrees of freedom in the tangent spaces of this system, there is no justification in calling the sphere 3D.
 
  • #36
masudr said:
\mathbb{R}^{3}(e.g. \theta, \phi
Okay, that makes sense. I have no idea what the above quoted symbols are, though. So if a sphere is 2-D even though it occupies 3 dimensions, how many D's are planes and lines worth?:confused:
 
  • #37
pallidin said:
In other words, the speed of light in a vacumm is approximately 299,792,458 meters per second.
Not approximately. Exactly.

(By the http://www.bipm.fr/en/si/base_units/" .)
 
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  • #38
In everyday informal discourse, the words "sphere" and "ball" are sometimes used interchangeably, but not in mathematics. For example, in R^3, a 2-sphere is the 2-dimensional surface of a 3-dimensional ball.

Regards,
George
 
  • #39
Oh... okay. Thanks George. It's probably time to repeat my oft-mentioned fact that I have a grade 9 math level (if that) and never finished high-school.:redface:
 
  • #40
I could be wrong, but isn't the speed of gravity only equal to 'c' in the perturbative regime.
In the full non-perturbative General Relativity its speed depends on local conditions and the observer's "position".

There is a quote between Einstein and Born (I think) about it.
 
  • #41
Help! I have a speed of light question

I just registered today! I am looking for a place to get some of my physics questions answered.

I am a complete novice (note to one who might reply), but I am fascinated with thinking about physics.

My question is - if nothing can go faster than the speed of light (and I know there is now some debate about that), how is it that we are able to SQUARE the speed of light in E= mcsquared? I know that we CAN because this equation is used all the time. But why is it that we can SQUARE something that we aren't supposed to be able to change?

Dumb question - I know - but I'd love for someone to tell me how I'm thinking about this wrong. THANKS!
 
  • #42
In the equation, only the numerical value of c is squared. It has nothing to do with altering its physical properties. You could also square the value of your bank balance, but it won't make you rich.:biggrin:
 
  • #43
Space/time can travel faster than the speed of light can't it? There is nothing in GR to say it can't. Isn't that the reason for hypothetical galaxies being beyond our viewing? This being true, then surely we can't feel their gravitation. How is this effect calculated when estimating the size of the universe?
 
  • #44
flotsam said:
Space/time can travel faster than the speed of light can't it? There is nothing in GR to say it can't. Isn't that the reason for hypothetical galaxies being beyond our viewing? This being true, then surely we can't feel their gravitation. How is this effect calculated when estimating the size of the universe?

First I would have to know what you mean by "space/time" moving!
 
  • #45
The expansion of space is not limited by c, only the passage *through* space is limitd by c.
 
  • #46
KY girl said:
I just registered today! I am looking for a place to get some of my physics questions answered.
I am a complete novice (note to one who might reply), but I am fascinated with thinking about physics.
My question is - if nothing can go faster than the speed of light (and I know there is now some debate about that), how is it that we are able to SQUARE the speed of light in E= mcsquared? I know that we CAN because this equation is used all the time. But why is it that we can SQUARE something that we aren't supposed to be able to change?
Dumb question - I know - but I'd love for someone to tell me how I'm thinking about this wrong. THANKS!

When you square something with physical units the answer will be in different units and you are not changing the original units.

Example, assume you have a room that has walls of 10 ft length each. If I square the length of the walls, I get an answer of 100 square feet, a measure of area. By squaring 10ft I have not changed the length of the walls, but instead converted length into a new measure, area.

With E=mc², you are doing the same thing; you are taking the speed of light, one form of measure, squaring it, and then multiplying by a mass, another form of measure to calculate a third form of measure, energy. In doing so, you do not change the speed of light, any more than you change the length of the walls of a room when you calculate its area.
 
  • #47
re: Dave's post
That's the basis of one theoretical approach to 'starship' design. If a ship can generate a bubble of artificial spacetime around itself, and remain sub-c relative to it, the bubble itself could be accelerated to superluminal speed within the 'real' spacetime. I'm not too confident about it ever being achieved, but at least it offers some hope for interstellar travel.
 
  • #48
Yes I mean the expansion of space.
 
  • #49
Danger said:
Okay, that makes sense. I have no idea what the above quoted symbols are, though. So if a sphere is 2-D even though it occupies 3 dimensions, how many D's are planes and lines worth?:confused:
Planes are 2 dimensional (you can describe every point on a plane using 2 co-ordinates); lines (and other curves) are 1 dimensional.
 
  • #50
Danger said:
Okay, that makes sense. I have no idea what the above quoted symbols are, though. So if a sphere is 2-D even though it occupies 3 dimensions, how many D's are planes and lines worth?:confused:
\mathbb{R} is the set of real numbers, \mathbb{R}^3 is a 3-dimensional vector space, the space represented by a list of 3 real numbers.
 

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