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

reply to post by avingard

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.

So, in regards to my thought experiment, you're of the opinion that even with the sun somehow removed, that the Earth would continue to orbit the point in space where the sun HAD been for approx 8 mins more ?

reply to post by afoolbyanyothername


A very interesting question indeed and one that even the experts aren't 100% sure about.

I always thought of Gravity as a constant, something operating outside the rules that was always constant and instantaneous. An object has mass so it has gravity and it exerts said Gravity on everything around it including space-time itself. I'm not sure whether it would have to follow the speed of light, depends on whether you believe the speed of light is the Universal speed limit of everything or not...

One things for sure, let's hope this question stays hypothetical, we're not going to have time to figure it out if the sun really does blink out of existence

reply to post by afoolbyanyothername


Yes that is correct, I have a background in physics, the earth will not feel the loss of gravitation until 8 minutes afterward.

reply to post by VitalOverdose

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

And unlike the other poster who thinks the earth would continue in it's orbit for a while longer after the sun had been removed, you're thinking along the lines that gravity would shut off immediately and that we would notice that change immediately ?
Interesting .... if that's so, then we'd have the contradiction of apparently still seeing the sun in the sky for approx 8 mins more as the last photons travel to us but that the Earth would immediately depart from it's orbit !!

The gravity will "blink out" at the same rate the Sun "blinked out" because they are linked together, inseparable.

The reason you will see the light from the Sun for 8 minutes after it "blinks out" is because the light is independent of the Sun. After it leaves the Sun it is not connected to the Sun, it is separated. So if the Sun disappeared, the light would still exist.

But the matter/mass that makes the Sun is what makes the gravity. So if the matter disappeared, the gravity disapear with it. No matter how fast you remove the matter, the gravity will not exist independent of the matter. So none of the gravity effects would exist if the Sun didn't.

Basically, you have to think of the gravity of the Sun as actually being a part of the Sun physically, as one object.

So the question is, how fast did the Sun "blink out"?

If it blinked out instantly, then so did the gravity. But, how fast is "instantly"? Faster than light?



[edit on 29-7-2009 by ALLis0NE]

The poetzel effect suggests that gravity is effect of limiting the frequencys of Aether between objects, while maintaining the diversity of the frequencys on the outside; causing an inward force between the objects.

Hence Gravity is the modulation of frequencys of Aether between objects by their distances from one another.

Move objects closer, and larger frequencys of ZPE cannot fit between them, progressively weakining the inner pressure.

This I think could be proven by running gravity tests in vacuum, like heavy objects in proximity released to see if they pull together.

The difference would be you repeat the test with shaped objects.
If gravity is not ZPE sheets on edge will be as strongly attracted.

If ZPE is gravity the edge to edge will not be as strongly attracted.

I am franky amazed that physicists do not debate where the poetzel effect begin and gravity ends.

Obviously they would both be elements of the experiment if the poetzel effect truly is different from gravity. Yet gravity is never considered in the experiment.



[edit on 29-7-2009 by Cyberbian]

reply to post by ALLis0NE

So the question is, how fast did the Sun "blink out"?

If it blinked out instantly, then so did the gravity. But, how fast is "instantly"? Faster than light?

Obviously (well, as far as we know), there is NO mechanism that we could even postulate that could make the sun instantaneously or even slowly disappear in a very short time. Even going nova will leave the majority of it's mass within the original vicinity and assumedly still generating a gravitational effect. And anyway, who really knows ... it could be possible as it's a VERY big universe with allsorts of undreamed of possibilties.

But for the sake of this thought experiment, let's allow the sun to disappear over a max period of say, 5 minutes ... which is obviously less than the transit time of the last photons emitted.

So, with this in mind, and IF your above statement assumed true that gravity "blinks" out with the sun, then that immediately implies that gravitational propogation must exceed light speed ... otherwise how could the effect of gravity disappear completely in tandem with the suns disappearance (even if the sun took 5 mins to disappear) as those last photons won't arrive for a further 3 mins yet and they're travelling at light speed ?

Obviously this sort of scenario could only take place in a thought experiment but still gives our minds a mental workout trying to come to grips with the possible outcomes relating to gravity.

reply to post by afoolbyanyothername


Gravity isn't traveling, that is your error in your question.

If you stick to Einstein's theories, gravity is the bending of space-time, usually caused by matter. Matter and gravity are linked together, so they are basically the same object. Matter can't exist without causing gravity.

Think about it like this.... Imagine you have a string that is 1 light year long. Then imagine you have a flashlight at one end of the string, and it is pointed in the direction of the other end of the string, parallel... Well, here is an image:

Basically, the string represents the Sun and it's gravity, as ONE object.

What you are asking is, "What happens if the string (Sun and it's gravity) disappears in 5 minutes?".

The answer: The string will disappear before the light reaches the end of the string. But this doesn't mean the string is going faster than light.

Does that make sense to you?

Hi, gravity fans.

To be a little more able to answer the question,
I would consider "entenglement", thinking of gravity.

To know about that entenglement, buy/see/rent the
DVDs I talk about, in the first line of my signature.

Entenglement is REALLY instantaneous, accross
the COMPLETE UNIVERSE ! ! !
Gravity could have some similar property. . .

Blue skies.

reply to post by ALLis0NE


Nice little diagram, simple and understandable

And yes, I do understand what you're hypothesizing that gravity is not a "force" as such but a result of the curvature of space being altered by a large mass. The implication of this is that the curvature of space is purely a "physical" effect.
Using your string analogy as representative of gravity, then we should be able to immediately notice the cessation of gravity long before seeing the sun "blinks" out in the sky above us. This would therefore indicate that the increased curvature of space originally due to the presence of the sun's mass would in effect reduce or "flatten out" and that this alteration ("flattening") of space curvature (a physical effect) would again, be propagating faster than light.

Just another thought ....

Let's assume you're correct (string analogy) and the entire length of the string blinks out IMMEDIATELY, then how does the "information" (for lack of a better term) reach the far end of the string to inform it that it's "blink out" time ?
I'm not really making myself clear with that but basically I'm looking at the increased curvature of space (gravity) from the sun to the Earth as being a physical effect. As such, there MUST be a time component involved as naturally WE can't cross the Earth-Sun distance in zero time ... which also must imply that to decrease the curvature of space (a physical effect) between the sun and earth must also take a non-zero amount of time. Otherwise the implication would be that ANY amount of space curvature due to a mass (e.g 8 light mins, 1 light year, 5 light years, etc) could be INSTANTLY negated by the simple act of removing the mass ... so some one on Pluto would know at the EXACT same moment as someone on Mercury that gravity had just been "turned off" ... so if nothing else, and again using your example, "information transfer" has also exceeded the speed of light !!!

Getting brain strain here !

Originally posted by harrytuttle
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?

Photons do not have mass.

In Einsteinian gravity it is not necessary to have mass in order to be affected by gravity. Gravity affects geometry of the space in which everything else moves so it affects photons.

This was confirmed by the early experimental results on starlight bent by the sun observed during a solar eclipse.

Interesting.

I think I know how to answer this question though experimentally: surely if gravity propagated at the speed of light, you'd see the effects of this in the interaction of orbiting bodies like the moon, or any fast-moving bodies passing each other.

For example a testable scenario would be to examining the moon's orbits for slight signs of reacting to an older gravitational field as would occur if it was trailing behind the earth slightly due to the limit of gravity propogating at speed of light since the earth is moving (think of pushing an object slowly across a pool of water and watching how the circular ripples are offset away from the leading edge of the object, then consider that the moon can only orbit based on these ripples).

A more extreme scenario from gravity being limited to light-speed would be (if I can explain this well) two massive bodies traveling near the speed of light, crossing each other's paths at a 90 degree angle, just far enough such that the speed of light limit makes it so that one of them is not effected by the other's gravitational field whatsoever, but the other is. I can give a diagram if this doesn't make sense.

[edit on 30-7-2009 by ac500]

This isn't completely on-topic, but another thought:

Does a signal from a probe take less time to propagate towards the sun than a message that's being sent away from the sun?

Does gravity assist or hinder the speed of the signal in anyway? Why or why not?

[edit on 30-7-2009 by an0maly33]

reply to post by an0maly33

Gravity does not affect the speed of light. Light appears to "bend" because of the curving of space-time but it is not accelerated.

Originally posted by afoolbyanyothername
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 !

I would think that since the galaxy holds it own gravitational pull which is only amplified by stars near planets that the earth would continue to oribit
the same galaxcial course but would change the way our days and nights and weather of course are until we came in contact with another star large enough to hold our planets mass creating a new night day weather cycle.
(WE MAY HAVE A NEW TYPE OF SOLAR SYSTEM WITH MORE OR LESS PLANETS OR CELESTIAL BODIES.) depending on the size of the new star or stars.

Originally posted by JimIrie
...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.

NO! Someones are tracking via search terms and page accesses? Say it isn't so!

Sorry - I had too.

Here's a diagram of what I tried to explain:


Notice how when the effects of gravity are limited to propagation at the speed of light, these two high-mass, high-speed objects passing each other create a condition where the blue object encounters ZERO (0) gravitational pull towards the other, even though they pass well within each others' gravitational ranges. The green object though is pulled towards the blue object even more than you would expect due to the trailing gravitational field being stronger behind the blue object than in front.

This results in object paths something like this:


Which seems kind of strange. It seems that if gravity is limited to the speed of light, then effects like this would be observable at least very slightly, as I said in the moons orbit as one example (where you would be able to determine whether or not it's reacting to a trailing gravitational field). With precise enough measurements and the proper mathematics I'm sure you could then derive the "speed of gravity", if any, simply by observing orbits. I would be surprised if this has not already been done.

[edit on 30-7-2009 by ac500]

Originally posted by afoolbyanyothername
reply to post by ALLis0NE

 

Using your string analogy as representative of gravity, then we should be able to immediately notice the cessation of gravity long before seeing the sun "blinks" out in the sky above us. This would therefore indicate that the increased curvature of space originally due to the presence of the sun's mass would in effect reduce or "flatten out" and that this alteration ("flattening") of space curvature (a physical effect) would again, be propagating faster than light.

It's not propagating faster than light.. The "flattening" will NOT start at one point and end at another point (inner to outer, or outer to inner). The entire outer and inner parts of the curve will flatten simultaneously (at the same time).

Even though the gravity effects will be noticed on Earth before the light reaches Earth, it doesn't mean the gravity propagated faster than light. It just means the gravity disappeared from two different locations at the same time, and the distance just happens to be further than light can travel in a certain amount of time.

Originally posted by afoolbyanyothername

Let's assume you're correct (string analogy) and the entire length of the string blinks out IMMEDIATELY, then how does the "information" (for lack of a better term) reach the far end of the string to inform it that it's "blink out" time ?

...so if nothing else, and again using your example, "information transfer" has also exceeded the speed of light !!!

Ok, look at my string image again...

Imagine that the string is stretched out tight, with no slack. Now imagine I pulled the string to the left, and, at the same exact time I turned the flash light on.

The end of the string on the right will then move near instantly, before the light reaches the end of the string.

In that case, the "information transfer" just traveled faster than light. But, really, nothing traveled.

I think I might make a topic about the above..

[edit on 30-7-2009 by ALLis0NE]

I have a rod 1 light year long, poised at the earth end over the on switch to a sign saying "Faster Than Light Travel Agency" I push the rod at the far end, turning on the sign instantly. I never bother to turn on the flashlight. Why waste a year waiting, it already lost the race.

[edit on 2-8-2009 by Cyberbian]

reply to post by ALLis0NE

It's not propagating faster than light.. The "flattening" will NOT start at one point and end at another point (inner to outer, or outer to inner). The entire outer and inner parts of the curve will flatten simultaneously (at the same time).

Even though the gravity effects will be noticed on Earth before the light reaches Earth, it doesn't mean the gravity propagated faster than light. It just means the gravity disappeared from two different locations at the same time, and the distance just happens to be further than light can travel in a certain amount of time.

But even using your string example and stating that pulling on one end of the string IMMEDIATELY causes the far end of the string to move simultaneously in my opinion is a flawed analogy.
To explain, let's 1st replace your string, which is composed of long and/or short chain molecules and use a simlpler substance. So, replace it with an equal length of copper wire, which is composed entirely of copper atoms only.

Now when you pull on your end of the copper wire, you're actually applying a force to the copper atoms that you're in contact with. Now, all these copper atoms are NOT physically joined or touching their neighbours but are in a crystalline matrix state. By pulling on your end of the wire, you're actually deforming the matrix in your vicinity which then applies a deforming force to its neighbouring atoms ... which then in turn apply a deforming force to THEIR neighbouring atoms, etc, etc, etc.
So in effect, when you pull on the wire, you're inititing a "pulse" that essentially propagates from atom to atom along the entire length of the wire. This propagating pulse MUST be time dependent as I simply cannot see how imparting a deforming force to the copper atoms in your vicinity can IMMEDIATELY cause an equivalent deforming force to be applied to the final copper atoms of the wire located say, 1 light year away. A small but measurable time period MUST elapse as each atom in the wire is sequentially acted on ... and the TOTAL time taken for the pulse to travel the length of the wire to be considerable. So you pull on one end of the wire and time passes before the opposite end of the wire moves.

Now this wire being a physical entity, therefore has inherent spatial properties i.e. it's length. But with no knowledge of the actual "structure" of space itself, I have to assume that the curvature imparted to the region of space between the sun and earth is likewise a "physical entity" because if space can be "curved" or "bent", there has to be an underlying physical substrate that's being acted upon to create the resulting curve. After all, if there is NO underlying physical substrate, then consequently there would be NOTHING available to curve or bend. I can't see anything wrong with my logic at this point ... unless someone has finally managed to come up with a definitive and testable explanation as to what space is "composed" of at the fundamental level ?

Therefore I would also expect any force or effect applied to the start of a region of curved space to take FINITE time to propagate to the end of that same region of curved space. So having a mass "instantly vanish" from within a region of curved space would also take FINITE time to propagate that physical change throughout the entire region of that curved space, the implication again being that the Earth would continue to orbit (for an uncertain amount of time), the sun that is no longer there.