I came across this site a few days ago, and it got me to thinking.
In Relativity, gravity is a bend in the space time fabric of the universe caused by mass. It was also predicted by Einstien that it propogates at the speed of light. Correct? Well, this site says experiements prove that it travels at 2x10[sup]10[/sup] the speed of light(or more).
This got me thinking some more:
Light is effected by gravity, It bends it, slows it, stops it in some extreme cases, yet never seems to speed it up.
(it is said it takes the light from the center of the sun 40k years to get to the surface, mabey this is caused by the extreme gravity slowing down the light instead of just particle interaction)
Here comes the leap in logic (and don’t think I’m a crackpot, I’m just questioning to see if anybody has had this thought);
If Gravity can effect light so much, and it seems to be able to propigate faster than light by many millions of times, (something that einstien didn’t forsee) could light actually travel faster outside of the gravity well of the sun (i.e outside of the solar system) Could true c be “the speed of light in a vacuum outside the effects of a gravity well”?
I am probably missing some simple, obvious answer here, something I will no doubt slap myself in the forehead about.
Nope, not correct. Again, I’m no physicist, but gravity is supposed to be an instantaneous thing, a property of spacetime. To be honest though, I’m not sure if Einstein came up with that or if a gravity propagation speed was later disproven (by him or others).
Of course, I don’t have any citations for this, so feel free to continue this discussion anyway until something factual turns up.
Its the best I can find right now, but I have seen several others in the past, I shall try and find them perhaps tommorow afternoon when I get a chance, but I think I have even read something on this message board that said something about gravity traveling at the speed of light, I could be mistaken on that part though.
The effects of acceleration and the effects of gravity cannot be distinguished by experiments. We can counteract the effects of gravity by having our reference frame free falling.
The reason it takes light so long to get from the center of the sun to escape is that it bounces around in a random walk being absorbed and re-emitted by other particles.
Light travelling outward from a black hold is suspended at the horizon. So light can be stopped by a strong enough gravitational field. The light going toward the singularity will travel faster than Einstein’s constant.
In Newtonian physics gravity acted instantaneously at a distance. The “spooky action at a distance” is prohibited by relativity. If the effects of gravity (or the effects of anything, for that matter) were to travel faster than light, this would cause all sorts of problems with causality.
This is getting more towards IMHO as the theorists haven’t agreed on the exact interpretation of the experimental results yet.
One rest mass moving relative to another rest mass does appear to generate a wave/particle effect that drains energy from the system as predicted by Einstein. This wave appears to travel at ~ the speed of light.
A particle with 0 rest mass interacts with a field effect generated by a rest mass as though the rest mass had distorted the fabric of space time. The gradient of the distortion can be greater than |c|. Changes in the relative position of the rest mass to the 0-rest mass object appear to effect the 0 rest mass object instantaneously.
Now for the real IMHO part, the non 0 rest mass object can moves at speeds < c, the distortion itself moves at speeds < c, the movement of the distortion relative to another non 0 rest mass object causes ripples (waves) in the space time continuum that move at speeds = c. The distortion is a permanent effect on the structure of space-time and all objects within that space-time will always be subject to its effect.
So as well as the particle interaction of the photon on it’s way out of the sun, there is also a distortion in relative time and distance as it moves out of the gravity well. This will affect light emitted from the surface of the sun as well as light emitted from the centre.
A light wave always travels at the speed of light. It may propagate at slower speed due to particle interactions, or distortions in space-time but it is always moving at the speed of light.
This subject has been discussed before but the present discussion has a lot of misinformation in it.
In order to calculate planetary (and other) orbits it is necessary to assume that gravity propagates with no delay. In other words, if you calculate the force of one body on another you calculate it using the current positions of the two bodies. If gravity had a finite propagation delay you would have to account for that and use the positions of the bodies at an earlier time. In the case of two bodies orbiting each other, any delay would mean the forces between the two bodies are no longer central – no longer aligned along their common axis. The force between the bodies would then have a non-axial component which would disturb the orbit. These disturbances would be large enough to shift Solar System orbits substantially in a few hundred years.
The Solar System has been around longer than a few hundred years, with essentially the same orbits. Based on the motion of the Moon, Laplace calculated the speed of gravity (in 1805) to be more than a million times the speed of light. Later analysis of other systems have raised this limit. This is sometimes referred to as “the observed absence of gravitational aberration”. Aberration is the need to make adjustments based on finite travel times, etc.
These are moving bodies – that is, their gravitational field is constantly changing. In fact they are accelerating. This is not a situation where the effects of the motion have had a chance to propagate away at the speed of light. The gravity-as-curvature argument is not valid here – the curvature is constantly changing and, apparently, propagating at essentially infinite speed.
Some physicists, notably T. Van Flandern, have therefore concluded that gravity does have a faster than light propagation speed. This contradicts both special and general relativity, especially since general relativity is supposed to reduce to Newtonian gravitation under certain conditions. Van Flandern has proposed some alternatives, but hasn’t found a large body of followers yet. Relativity is supported by a large body of experimental data as well, some of it incredibly precise. It’s hard to imagine a major overhaul that handles this contradiction and still retains that precision.
WARNING: The following is based on a paper by S. Carlip, UC Davis, which I have read and mostly understood, but the math is beyond my ability to follow. I’m assuming he knows what he’s talking about.
All is not lost. There are assumptions in the calculations made by Laplace and others that do not hold for general relativity, or even for Maxwell’s electrodynamics.
For example – a moving charge exerts a force on a stationary charge with no aberration. The force behaves exactly as if the speed of electromagnetic interaction (i.e., the speed of light) were infinite. From Carlip: “This effect does not mean that the electric field propagates instantaneously; rather, the field of a moving charge has a velocity-dependent component that cancels the effect of propagation delay to first order.”
Similar velocity-dependent components exist for gravitational fields in general relativity. They are based on quadrupole moments, rather than dipole moments for electromagnetism, which are more complicated and lead to more complicated results. For instance, they lead to an apparent cancellation of gravitational aberration for orbiting bodies. The proof is left as an exercise to the reader. (No, it’s not – it’s in Carlip’s paper. I just can’t claim to follow it all.)
Thanks Pluto,
I don’t suppose you have got a link to the article handy, it seems that they may have made progress on establishing the cancellation effects of ‘quadrupole moments’ since I last looked at the area, looks like some more nasty math reading ahead.
Now if we can just work around that collapsing wave function, all will be right with the world
Wow, thanks for the replies. Some of it is digestable, most is a bit beyond me at the moment. It was all just speculation based off of incomplete information, I am in no way making claims many people whom reject relativity generally do. I accept the tenants of science, knowing that anybody that could prove it wrong would get a nice fat nobel prize. (hence a good chance if there were gaping holes in the logic of it, it would be jumped on by every physisict within light years.
What I don’t understand is this:
Is Gravity actually “moving” at billions of times the speed of c (I realize that its not just the speed at which light is moving, c being the speed at which light moves in a vaccum)? Or is it just a sort of mathmatical loophole that is necessary to complete some formulas(or whatnot) rather than an actual occurance. (sort of like the 11 “dimensions” idea, a mathmatical abstraction necessary for completing some formulas, but AFAIK, not a physical reality)
The electric field of a charged particle moving at constant velocity points directly towards the particle with no retardation. This is most easily explained using special relativity, and without this effect there would be no electromagnetic radiation. This also applies to gravity and gravitational radiation. However, retardation does apply to both types of the radiation itself.
However this does not mean that any information can propagate faster than light.
Maybe its just an illusion, with us in the third dimension trying to interpret phenomenae occuring in the fourth dimension.
Lets put it this way.
Say you’re in a parking lot at sunset, with your shadow five times as long as you are tall. You drop a ball, which accelerates to velocity X by the time it hits the ground, but the shadow’s velocity travels at 5X.
This occurs due to observing a 2D effect of a 3D phenomena.
Perhaps the apparent super-speed of gravity in our 3D universe is merely the “shadow” of the greater 4D reality we do not directly observe, one which c still is the ultimate speed limit.
Aha! I found the thread that has the link. It’s in the post by JonF. He’s got some other links so I’ll send you to the thread rather than copy all the links:
Thanks for that it appears that it appears I will be able to incorperate this work into my understanding of field theory, given some time with the maths.