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# Is Gravity Faster Than Light?

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February 7, 2011 7:47:52 PM

I just got laughed off the leisure forums in computing.net but Ill let you guys have a go.

So lets say something happened to the Sun, aliens came by and zapped it into another dimension. So in an instant our Sun had just disappeared. We know that the speed of light is the universal speed limit. My question is (Simply for demonstrating this question), would the loss of the suns gravity tethering us to current orbit lead to an instantaneous "un-tethering", where would would fly off into space at the moment the sun disappeared and continue to see the light from the sun for 8 minutes while we slowly froze into a big ice ball. Or....... is gravity restricted to the speed of light, where the "un-tethering" and the loss of light would correspond (we would lose light and gravity at the same time). Because without the sun I think we know what that means.......Grues..........

Not an astrophysicist and not expecting any of you to be just looking for some input.....

More about : gravity faster light

February 7, 2011 8:15:52 PM

gravity travels at the speed of light afaik
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February 7, 2011 8:30:02 PM

Quote:
I just got laughed off the leisure forums in computing.net but Ill let you guys have a go.

So lets say something happened to the Sun, aliens came by and zapped it into another dimension. So in an instant our Sun had just disappeared. We know that the speed of light is the universal speed limit. My question is (Simply for demonstrating this question), would the loss of the suns gravity tethering us to current orbit lead to an instantaneous "un-tethering", where would would fly off into space at the moment the sun disappeared and continue to see the light from the sun for 8 minutes while we slowly froze into a big ice ball. Or....... is gravity restricted to the speed of light, where the "un-tethering" and the loss of light would correspond (we would lose light and gravity at the same time). Because without the sun I think we know what that means.......Grues..........

Not an astrophysicist and not expecting any of you to be just looking for some input.....
If you took off at the speed of light, you would continue seeing the sun forever even though it went dark...but that's not what you're asking. What would actually happen is that the earth's trajectory would become a vector at the same velocity (as its current arced path), so it would take a little longer for the sun to disappear.
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February 7, 2011 9:12:47 PM

The earth would no longer travel in an orbit ... it would seek an escape vector at the time the suns gravitational mass ceased.

You would receive solar radiation for another 5 - 9 minutes then the light would go out.

Earth would rapidly decrease in temp.

If the mass was removed by tesseract then you have a further problem not identified ... the shock wave caused by vacuum. That implosion and resultant shock wave would effect the planets vector around 16 minutes later ... and the remaining pieces of the planet would then travel outwards ...

I would be forced to get my spaceship out of the garage, top up the lithium fuel cell and pickup badge to return home.

Sadly we have enjoyed our time here.

I'll have to madly collect as much music as possible now ... most annoying.

crash ... do you want a lift back to Alpha Centauri ??
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February 7, 2011 9:28:51 PM

Don't forget the rest of the planets, especially the gas giants. They become the only gravitational players in the solar system. It will be a cosmic billiard game with gravitational interactions.
I believe there is a solar system simulator, actually a gravitational simulator, that you can download for free. You can input the mass and the velocity of the objects, along with other parameters, and watch them behave. You could easily program it to subtract the mass of one object, like it disappeared, and see what happens.
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February 7, 2011 9:36:33 PM

Quote:
The earth would no longer travel in an orbit ... it would seek an escape vector at the time the suns gravitational mass ceased.

You would receive solar radiation for another 5 - 9 minutes then the light would go out.

Earth would rapidly decrease in temp.

If the mass was removed by tesseract then you have a further problem not identified ... the shock wave caused by vacuum. That implosion and resultant shock wave would effect the planets vector around 16 minutes later ... and the remaining pieces of the planet would then travel outwards ...

I would be forced to get my spaceship out of the garage, top up the lithium fuel cell and pickup badge to return home.

Sadly we have enjoyed our time here.

I'll have to madly collect as much music as possible now ... most annoying.

crash ... do you want a lift back to Alpha Centauri ??
I'm wanted by the global government of the only habitable planet there...which probably explains my opinion of global governance.
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February 7, 2011 10:01:50 PM

Doesn't the assertion made that the speed of gravity is the speed of light assume that gravity is a substance that travels, rather than some sort of intrinsic, instantaneous, matterless force.
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February 9, 2011 12:47:27 AM

An object in motion tends to stay in motion unless another force acts on it. If the sun disappeared instantaneously, the earth would still try to continue in its orbit. It would no longer have the sun's gravitational force acting on it, however the other forces acting on it (The moon, other planets) would be miniscule in comparison to the gravitational force of the sun. It's orbit would deteriorate slowly because of the massive amount of inertia involved in its current motion.

This is not like a yoyo that suddenly gets released from your hand and flies off in one direction. If the earth suddenly disappeared would the moon go flying off on a tangent? Does that make sense to you?

No, we know it would continue to spin and continue in its arc, I think it would take some time before completely leaving its orbit. How much? I am sure this could be calculated, but I am not certain how long. Much like a satellite that cannot maintain its orbit any more, it doesn't come crashing into earth immediately. Its orbit decays over several days until the inertia of its movement is not enough to fight the earth's gravity. Then it will begin an ever increasing acceleration toward the surface.
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February 9, 2011 2:04:44 AM

Quote:
An object in motion tends to stay in motion unless another force acts on it. If the sun disappeared instantaneously, the earth would still try to continue in its orbit. It would no longer have the sun's gravitational force acting on it, however the other forces acting on it (The moon, other planets) would be miniscule in comparison to the gravitational force of the sun. It's orbit would deteriorate slowly because of the massive amount of inertia involved in its current motion.

This is not like a yoyo that suddenly gets released from your hand and flies off in one direction. If the earth suddenly disappeared would the moon go flying off on a tangent? Does that make sense to you?

No, we know it would continue to spin and continue in its arc, I think it would take some time before completely leaving its orbit. How much? I am sure this could be calculated, but I am not certain how long. Much like a satellite that cannot maintain its orbit any more, it doesn't come crashing into earth immediately. Its orbit decays over several days until the inertia of its movement is not enough to fight the earth's gravity. Then it will begin an ever increasing acceleration toward the surface.
Nope, the earth would fly off in a tangent, physics works the same for large objects as it does for "relatively small". With no gravitational force to continue its arc, what do you propose would cause it to arc?

Mythbusters even tried to arc a bullet, it can't be done.
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February 9, 2011 1:55:37 PM

I know (Theoretically) what would happen with the loss of gravity, our nice little planet would fly off in the most convenient trajectory and slowly become an ice ball of death, if it doesn't run into anything else..... But since Gravity is one of the four forces that keep our universe doing it thing is it also restricted by the speed of light. The story was an illustration asking if the loss of mass, in this case our sun, would be an instantaneous loss of gravity/orbit?

Neptune would be a better example, or Pluto if your one of "those" guys. But really how trippy would it be to lose the gravitational tether while still receiving light from your host star?

As a side note life would exist on our planet for several thousand years after the sun goes our from our own internal heat sources. The ice would be a mile thick and everything on the surface would be dead, but ocean life would thrive at the deepest parts of the ocean.
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February 10, 2011 12:43:07 PM

If the sun is missing the effect of gravity is missing ... no mass ... therefore no continuaton of orbit ... the effect would be instantaneous.
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March 8, 2011 12:51:11 PM

Yes but the question is then, if light is the fastest thing in the universe, are you saying gravity is faster that light?

This is what the OP wants to know. If you think gravity is faster than light and can prove it, you will receive a Nobel prize.
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March 8, 2011 12:51:25 PM

And lots of money, girls etc.
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July 15, 2011 12:38:25 AM

Quote:
I just got laughed off the leisure forums in computing.net but Ill let you guys have a go.

So lets say something happened to the Sun, aliens came by and zapped it into another dimension. So in an instant our Sun had just disappeared. We know that the speed of light is the universal speed limit. My question is (Simply for demonstrating this question), would the loss of the suns gravity tethering us to current orbit lead to an instantaneous "un-tethering", where would would fly off into space at the moment the sun disappeared and continue to see the light from the sun for 8 minutes while we slowly froze into a big ice ball. Or....... is gravity restricted to the speed of light, where the "un-tethering" and the loss of light would correspond (we would lose light and gravity at the same time). Because without the sun I think we know what that means.......Grues..........

Not an astrophysicist and not expecting any of you to be just looking for some input.....

Conclusion: The Speed of Gravity is ≥ 2x10¹º c
http://metaresearch.org/cosmology/speed_of_gravity.asp

The speed limit of light is merely the speed limit of time. Beyond that speed there is no time, but direction. A pseudo dimension gravity operates in.
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July 15, 2011 12:56:54 AM

Welcome Lancecraft to News and Leisure.

I hope you realise that time and space work differently here ... we booted Eistein and his gibberish writings in favour of a new math based on feelings.

The infinite (and often tautological truth) here is that is it feels right and there is general consensus ... then it is right.

However we currently have a disproportionate nember of republicans here at present ... so consensus is difficult.

This is the reason why the Chinese are taking over the world ... their mathematicians easily reach consensus.
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July 15, 2011 12:44:58 PM

Thank you lancecraft. At first I was like "Oh shite this thread again" But you understand the question and provided a more than satisfactory answer. Your prize is being shipped to you and will hopefully arrive before it dies.
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July 15, 2011 1:39:17 PM

I Shall grant him a best answer mingo ...
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July 15, 2011 1:41:13 PM

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July 15, 2011 4:08:50 PM

Hmm, sorry I didn't see this thread before now - very interesting link that Lancecraft posted. Certainly seems to be a lot of experimental evidence for gravity effects propagating faster than c (speed of light). I had previously wondered about how gravity itself managed to escape the infinite gravitational well that a black hole resides in.

General relativity says a mass in spacetime warps the latter to bend light and other propagating or moving objects (given the interpretation that light is both particle - photon - and wavelike in nature). So I would guess that the particle responsible for conveying the force of gravity - graviton - doesn't actually propagate in spacetime, but instead maybe in one or more of those 6 or 7 'curled up' dimensions that are popular in string theory (now called M theory I believe). Since these extra dimensions are on the order of the Planck length (10^-35 meters), then even if gravitational waves/gravitons are limited to the speed of light in those dimensions, corresponding to the special theory of relativity prohibiting anything traveling faster than c in spacetime, that would appear instantaneous in ordinary macro spacetime.

BTW, general relativity does not have a speed limit - it's only special relativity that does. That's why stuff like Star Trek's "warp" drive works by compressing space around the ship - effectively it shrinks the length of the space in front of the ship, allowing the ship to remain below c in the warped space, but considerably faster than c in the remainder of the universe.

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July 15, 2011 8:36:44 PM

Physics major here...

The gravitational force travels at the speed of light, not slower, not faster (lancecraft's figure is complete BS). Scientists are pretty sure about this. The gravitational force can be used as a means of communication and is thus prohibited (by special relativity) from traveling faster than the speed of light. Astronomical observations support this.
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July 16, 2011 1:14:54 AM

Psych / Ed / Statistics post grad here ... no laughing please sciency peoples !!

Had a spa last night with an Engineer (who kept playing with the spa controls till I beat him with a stick) and several plebs and we agreed with Lancecraft ... mind you after 3 hrs most were pretty intoxicated so would have agreed with anything I guess.

Take the Sun's gravitational effect on Earth ... knowing that light from the sun (travelling at C) takes minutes to reach us.

We are travelling at about 18.4 miles per second ... at an average distance of 92.93 (91 - 94.5) million miles from the sun (1 AU).

So light takes a different amount of time to reach earth depending on the time of year. Light travels at 186,282 miles per second, and the average distance is 92,957,000 miles. This means its light takes about 8 minutes and 20 seconds to get here.

If gravity travelled at the speed of light the 8 plus minutes lag would mean that the Earth would not travel in its elliptical orbit ... it would have been flung out into space.

either Gravity is instantaneous or something clos to the figure previously stated (bout 90 times C).

Attention science users ... please post.

I moved the previous thread (of this ilk) over here too ... it was very popular.

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July 16, 2011 4:32:50 PM

Quote:
Physics major here...

The gravitational force travels at the speed of light, not slower, not faster (lancecraft's figure is complete BS). Scientists are pretty sure about this. The gravitational force can be used as a means of communication and is thus prohibited (by special relativity) from traveling faster than the speed of light. Astronomical observations support this.

I dunno - has anybody ever actually detected gravity waves? Seems to me there was an experiment going on, using a couple of lasers bouncing off mirrors a kilometer or so away, each arm's laser oriented 90 degrees from each other. Supposedly a gravity wave impinging on the system would compress one arm more than another and thus be detectable. Last I heard (Scientific American article from ~ 10 years ago), no signal had been detected in several years of operation.

Anyway, according to Wiki:

Quote:
Newtonian gravitation

Isaac Newton's formulation of a gravitational force law requires that each particle with mass respond instantaneously to every other particle with mass irrespective of the distance between them. In modern terms, Newtonian gravitation is described by the Poisson equation, according to which, when the mass distribution of a system changes, its gravitational field instantaneously adjusts. Therefore the theory assumes the speed of gravity to be infinite. This assumption was adequate to account for all phenomena with the observational accuracy of that time. It was not until the 19th century that an anomaly in astronomical observations which could not be reconciled with the Newtonian gravitational model of instantaneous action was noted: the French astronomer Urbain Le Verrier determined in 1859 that the elliptical orbit of Mercury precesses at a significantly different rate than is predicted by Newtonian theory.[3]

Laplace

The first attempt to combine a finite gravitational speed with Newton's theory was made by Laplace in 1805. Based on Newton's force law he considered a model in which the gravitational field is defined as a radiation field or fluid. Changes in the motion of the attracting body are transmitted by some sort of waves.[4] Therefore, the movements of the celestial bodies should be modified in the order v/c, where v is the relative speed between the bodies and c is the speed of gravity. The effect of a finite speed of gravity goes to zero as c goes to infinity, but not as 1/c2 as it does in modern theories. This led Laplace to conclude that the speed of gravitational interactions is at least 7×106 times the speed of light. This velocity was used by many in the 19th century to criticize any model based on a finite speed of gravity, like electrical or mechanical explanations of gravitation.

From a modern point of view, Laplace's analysis is incorrect. Not knowing about Lorentz invariance of static fields, Laplace assumed that when an object like the Earth is moving around the Sun, the attraction of the Earth would not be toward the instantaneous position of the Sun, but toward where the Sun had been if its position was retarded using the relative velocity (this retardation actually does happen with the optical position of the Sun, and is called annual solar aberration). Putting the Sun immobile at the origin, when the Earth is moving in an orbit of radius R with velocity v presuming that the gravitational influence moves with velocity c, moves the Sun's true position ahead of its optical position, by an amount equal to vR/c, which is the travel time of gravity from the sun to the Earth times the relative velocity of the sun and the Earth. The pull of gravity (if it behaved like a wave, such as light) would then be always displaced in the direction of the Earth's velocity, so that the Earth would always be pulled toward the optical position of the Sun, rather than its actual position. This would cause a pull ahead of the Earth, which would cause the orbit of the Earth to spiral outward. Such an outspiral would be suppressed by an amount v/c compared to the force which keeps the Earth in orbit; and since the Earth's orbit is observed to be stable, Laplace's c must be very large. In fact, as is now known, it may be considered to be infinite, since as a static influence, it is instantaneous at distance, when seen by observers at constant transverse velocity.

In a field equation consistent with special relativity (i.e., a Lorentz invariant equation), the attraction between static charges is always toward the instantaneous position of the charge (in this case, the "gravitational charge" of the Sun), not the time-retarded position of the Sun. When an object is moving at a steady speed, the effect on the orbit is order v2/c2, and the effect preserves energy and angular momentum, so that orbits do not decay. The attraction toward an object moving with a steady velocity is towards its instantaneous position with no delay, for both gravity and electric charge.

So the explanation seems to be that in a static (pre-existing & unchanging) gravitational field between 2 masses, the field vectors are completely radial (point to the instantaneous centers of the 2 masses), vs. partly tangential as espoused in the article Lancecraft linked to. Of course the latter would also be correct if the speed of gravity was infinite. And it would also explain why the collapse of a star into a black hole doesn't remove the gravitational field emanating from it, despite the presence of an infinite gravitational well at the event horizon.

However if the Sun's mass were suddenly removed from existence, I'd think that "change" would propagate as a gravitational wave which would mean it's limited to c and thus the earth wouldn't find out about it (and continue to orbit the Sun's former position) until some 8.3 minutes later, in which case it would head off along the tangent. I'd also expect some small tsuanmi would occur, as the Sun's tidal force would disappear instantaneously as well, albeit much smaller than if the Moon would disappear (the Moon being 240 times closer and hence the gravitational gradient between the near & far sides of the Earth much larger than that of the Sun).

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July 16, 2011 4:47:21 PM

In a field equation consistent with special relativity (i.e., a Lorentz invariant equation), the attraction between static charges is always toward the instantaneous position of the charge (in this case, the "gravitational charge" of the Sun), not the time-retarded position of the Sun. When an object is moving at a steady speed, the effect on the orbit is order v2/c2, and the effect preserves energy and angular momentum, so that orbits do not decay. The attraction toward an object moving with a steady velocity is towards its instantaneous position with no delay, for both gravity and electric charge.

Bit convenient eh ... just make up a new rule to explain it.

I checked the equations and decided my brain was insufficient for the task ... humbling indeed.

Baa ... it desn't make sense.
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July 19, 2011 12:10:59 AM

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gravity travels at the speed of light afaik

Gravity travels greater than or equal to 2x10¹º times the speed of light = faster. If the sun spontaneously disappeared, the Earth would 'instantly' careen off into space while it would take more than 8.3 minutes for us on Earth to notice because we would still see the light arriving after it died.
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July 19, 2011 9:09:23 AM

We should be able to test this theory by sticking a nova bomb into the sun and taking careful measurments at the time of the explosion when the sun's mass is converted into energy.

Its a bit of a one shot deal but i am sure it is worth it ...

/dumb
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July 19, 2011 9:21:53 AM

Whats the make up of light?
If its trajectory is said to be known instantanaeously, why then does gravity have an impact on it, while not simply stopping it, as a solid object of course would?

I say Einsteins discovery of seeing light bend proves that gravity is more a constent in time than light
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September 12, 2011 2:07:10 PM

This topic has been moved from the section News & Leisure to section Toms Network by Reynod
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September 12, 2011 4:53:48 PM

This topic has been moved from the section Toms Network to section Tom's Guide by Reynod
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September 14, 2011 11:13:19 AM

bump
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February 25, 2012 7:33:18 PM

This topic has been closed by Mousemonkey
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