Science question: Does gravity propagate faster than the speed of light ?

I was having a discussion the other day with a friend on the effect on the Earth should the sun hypothetically instantly vanish. Obviously we agreed that we would still "see" the sun in the sky for approx 8 minutes as the last of the photons emitted by the sun before it "vanished" completed their journey to Earth.

But what had us really scratching our heads was the gravity side of the equation. If the sun miraculously winked out of existance, would the Earth continue to orbit as usual for a certain amount of time or would it immediately fly of into space ?

In other words, would gravity immediately and completely disappear the moment the sun disappeared ... or would the lingering effects of the vanished suns gravity still remain to hold the Earth in it's orbit for a while ? If it disappeared completely and immediately before the last photon reached us, wouldn't that imply a faster than light effect ? But if the suns gravity could still be felt even after the disappearance of the sun itself (even for just a few seconds or minutes), wouldn't that imply gravity propagates much slower than light and can also exist without the mass of the sun to generate it ?

The answer must surely be interesting in either case !

reply to post by afoolbyanyothername


Newton says yes (perhaps unknowingly), Einstein says no. His argument was that nothing could move faster than the speed of light. In other words, no type of universal information (such as gravity) could be transfered through the universe faster than the speed of light. We have since achieved trans-luminal speed with radio waves/particles (I think) and there's a thread in this very forum somewhere that explains that. While this has left the door open to types of information that CAN move faster than the speed of light, gravity has not been found to be one of them.

[edit on 23-7-2009 by Eitimzevinten]

reply to post by Eitimzevinten


So are you saying that gravity propagates at the speed of light or slower then the speed of light?
And does that therefore imply (n both cases) that gravity can exist (if only for a short time) without any mass to sustain it as would be the case in the hypothetical disappearance of the sun ?

reply to post by afoolbyanyothername


Its not so much being sustained as it is no longer being released from its source like the light. Just like the last of the light will take awhile to get here, so will the last of the gravity. If its slower than light, we may very well be orbiting nothing for a couple of seconds (a very cold couple of seconds) but this is not because the gravity is still being emitted, its just because it hasn't gone past us yet.

Once the suns gravity is gone, we'd fall into the orbit of the next strongest gravitational field effecting us. This field is also effecting us right now, but its simply overlapped with the much stronger local pull of the sun. We would probably start heading for jupiter unless there is a further away but much more massive object with a greater field to over take jupiters local field.

Yesterday i was looking for news or else about free energy and antigravity
While i was reading, someone posted me a message over icq i should have a look on this side

www.SK-Dynamics.com They builded a "Gravity motor"

at first i was thinkin it´s a spammail but when i noticed he knows what im looking for i got interested.

The foreign guy told me he´s in Chaos Comp. Club and my firewall was hacked by government cause of my "unusual" search terms. He decided - after checkin my dats...!-
That i´ma cool guy who needed to be informed about that.

so about this site:
It´s a indian page from a industrial Engineer who thinks, he got the answer of Gravity
on borderlands.de ( german site ) is a pdf about the work of this engineer and his theory
He claims that gravity is nothing else than an electromagnetic field which has a so high frequenzy we now can´t mess.
On this base he designed a "gravity motor" for use in satellites or else.
Also on his side is a "unmanned flying car drone" for security, remebers me to a skeleton prototype of the "Terminator" -Robots, nor?

Well. the speed of light is directly affected by gravity. So.. how different are the two? Are they not the same, just a different state. Light is electromagnetic and photon energy, gravity looks to be electromagnetic energy also. Look at rotating disc early experiments and other high field experiments involving propulsion and antigravity research.

So to the previous poster.. I'd agree

Which then leads to the question: has the speed of gravity been determined yet or is it assumed to be the same as light speed ?

Gravity is said to be real time and instantaneous and it is not at the speed of light. The gravity is also a particle-wave duality and the particle is called as graviton. The graviton has not been proved yet but it is theorized to exist

Originally posted by sunny_2008ny
Gravity is said to be real time and instantaneous and it is not at the speed of light. The gravity is also a particle-wave duality and the particle is called as graviton. The graviton has not been proved yet but it is theorized to exist

So if the sun were to be immediately removed, then if gravity was instantaneous as you state, that would mean we'd notice it's absence immediately which then would imply that it propagates faster than light as the last photons would still be in transit for 8 mins.

The correct answer is: "We don't yet know".

Gravitons (gravity waves) are yet to be detected and unless someone manages to disappear a rather large star and measure the immediate effects that's the only truthful answer. Theories are plenty, evidence scarce.

Kind regards, M.

Originally posted by Eitimzevinten
reply to post by afoolbyanyothername

 

Its not so much being sustained as it is no longer being released from its source like the light. Just like the last of the light will take awhile to get here, so will the last of the gravity.

...

Gravity is the effect of mass on space time, it isn't released. The question really is how fast space time can be reshaped given a sudden change in mass (like the sun disappearing).

I would suspect that the question is irrelevant. In the original question, saying that the sun suddenly disappeared is assuming that the speed of light has already been broken (the sun can't just disappear, and any other event would negate the question), so why not also assume that the absence of the sun's gravity field will have propagated faster than the speed of light?

reply to post by avingard


Following a space-time model removes the "force" factor of gravity. I don't believe in that model. I believe that it is infact a force of the electromagnetic spectrum emitted by mass. It's not a force that mass can run out of but you get the point. It's similar to how the shear energy that composes us manifests as solid objects. Part of that energy is directed towards having a gravitational pull.

Gravity must propagate at a speed faster than light or the Earth would not stay in its orbit around the Sun.

Einstein was wrong.

See Dr. Van Flandern's article here.
[as published in Physics Letters A 250:1-11 (1998)]

Plasma cosmology has the answers.


[edit on 28-7-2009 by mnemeth1]

reply to post by Eitimzevinten


If you believe that gravity is a part of the electromagnetic spectrum then there is only one answer to the original question: gravity travels at the speed of light.


My point was that we are comparing two entirely different entities (following traditional relativity). Light is part of the electromagnetic spectrum and travels at the speed of light; it is the result of a release of energy due to any number of processes. Gravity is the state of space time at any given location. Whereas light can only travel through space time at the speed of light, gravity is space time and so isn't constrained by the speed of light (because the speed of light is a restriction on all mass/data within space time).


I just googled it and the "official" answer is that gravity travels at the speed of light because gravity propagates as distortion waves in spacetime. So any change in gravity would cause a new distortion wave to propagate from the source, but it would only reach any affected bodies at the speed of light.



[edit on 29-7-2009 by avingard]

The prevailing consensus is that gravity travels at the speed of light (but like all things science, this is not without disagreement nor guaranteed to be the consensus for ever).

Another interesting question is this: If a black hole has so much gravity that even light can't escape, then a photon must have mass. Physics says that photons have zero mass, but if that's true, then how can the effects of gravity (even from a black hole) affect a photon???

To the contrary, any object with mass traveling at the speed of light will have INFINITE mass, therefore a photon can NOT have any mass (which agrees with physics).

So which is it? Does light (photons) have mass or not?

But what had us really scratching our heads was the gravity side of the equation. If the sun miraculously winked out of existance, would the Earth continue to orbit as usual for a certain amount of time or would it immediately fly of into space ?

Im pretty sure it would fly off into space imdediatley but id have to check.

In thinking about this i thought about a pebble being dropped into still water and how the ripples move outwards from the initial impact with the water. maybe the mass of the sun would create a ripple that would move out from it through space and time after it dissapeared much like the stone dropping in water.

The answer to this is no. If you for instance disrupt the sun, the earth will not feel rotation until 8 minutes later, gravitational waves travel at the speed of light.

reply to post by harrytuttle

The old saying of 'not even light can escape a black hole' is a bit mimisleading

When you shine a light across the width of a black hole the only reason the light seems to be sucked in is that thats the only available direction it has to go .Massive gravity fields distort and bend space time and light just follows the bent fabric of space.

reply to post by VitalOverdose

I was just thinking about that too.

Also, since space & time are intertwined, and gravity is the bending of space, time gets "bent" too. Could we bend time backwards (time machine)?? Is it possible to bend space in half?