is gravity faster than light?

Question

I'm not sure if I've phrased the subject correctly, but I'm still unsure of the outcome of this classic contest.. Imagine that one day an alien comes and zap our moon, making it disappear.. Will we see the tide rises and falls before seeing the moon disappear? i.e. Will the influence of gravity be exerted faster than the speed of light? Of is C the ultimate speed limit of all things?

Answer 1

Yes and no! In September 2002, Sergei Kopeikin and Edward Fomalont announced in a conference in Seattle, Washington that they had made an indirect measurement of the speed of gravity, using their data from VLBI measurement of the retarded position of Jupiter on its orbit during Jupiter's transit across the line-of-sight of a bright radio source - quasar QSO J0842+1835. Kopeikin and Fomalont concluded that the speed of gravity is between 0.8 and 1.2 times the speed of light, which would be fully consistent with the theoretical prediction of general relativity that the speed of gravity is exactly the same as the speed of light.

Source:
http://en.wikipedia.org/wiki/Speed_of_gravity

There are experimental problems with resolving this;

http://math.ucr.edu/home/baez/physics/Relativity/GR/grav_speed.html

Good question, Shan. Truth is that no ones knows for sure yet, but the scientific speculation is that they likely both have the same velocity. That is important because there could be lots of bad implications if gravity is faster. Relativity states that nothing is faster than the speed of light, so this is a very important question.

Answer 2

According to relativity, gravity is transmitted at the speed of light, and as pointed out by a couple of others here, observational data seems to indicate that the theory of relativity is right--yet again. If the sun suddenly disappeared, the earth would contiunue to orbit for 8 seconds or so, then off we'd go. Of course then it would be lights out...

I would like to address the couple of people who said that it cannot.

Gravity DOES have a speed of transmission. It is NOT, I REPEAT NOT, instantaneous.

The surface gravity of an object, like 9.8 meters per second squared for the earth, IS NOT the speed of gravity, it is the acceleration of an object within the gravitational field. This is an important distinction. A bowling ball dropped from a building falls 9.8 m/s faster for every second that it falls--until it hits the ground (this doesn't factor wind resistance).

If the surface gravity WERE the speed of gravity, then the speed of gravity would vary, but it isn't, so it doesn't.

Further, there is a place where objects in a gravitational field could exceed the speed of light. Of course, by doing this, they would be completely destroyed, probably turned into electromagnetic radiation. This place, of course, is beyond the event horizon of a black hole--where the escape velocity of the black hole is faster than the speed of light.

Answer 3

Scientists have succeeded in measuring the speed of gravity for the first time. Sergei Kopeiken of the University of Missouri-Columbia and Ed Fomalont of the National Radio Astronomy Observatory in the US used a rare cosmic alignment to check that gravity and light travel at the same speed -- as predicted by Einstein. The astronomers presented their findings today at the American Astronomical Society meeting in Seattle.

On September 8 last year Jupiter passed almost directly between the Earth and the quasar J0842+1835. Kopeikin and Fomalont used the Very Long Baseline Array of radio telescopes in the US and a 100-metre radio telescope in Effelsberg, Germany, to measure how radio waves from the quasar were deflected by Jupiter. Previously they had shown that the size of the deflection depends on the speed at which gravity propagates from Jupiter. From their measurements Kopeikin and Fomalont calculated the speed of gravity to be 95% of the speed of light, with an error margin of plus or minus 25%.

Prior to this work, physicists had assumed that the only way to measure the speed of gravity was to detect gravitational waves. Kopeikin believes that this new result is the first of many observations of gravitation that will shed new light on the general theory of relativity.

Answer 4

I'm surprised at how many people got this wrong. It is quite true that the expansion of spacetime is not limited to the speed of light -- but that's irrelevant to this question. The general theory of relativity predicts that we WILL NOT detect the absence of the sun's gravity until 8.3 minutes have passed. If the sun vanished, it would produce a "gravity wave" -- an outwardly expanding ripple in spacetime. Once the rippple passes us, the sun's effect on us is effectively turned off -- but that ripple does not travel faster than light, according to relativity theory. One way to look at it is this: The theory of relativity says that no "signal" (no information) can travel through space faster than light. The loss of the sun's gravity is definitely a "signal." So it can't reach us faster than a light beam can.

Answer 5

There is no speed associated with gravity. Think of Gravity as a big rubber band pulling the earth and the moon together only the speed of the 2 planets keeps the rubber band taught. Now cut the rubber band or blow up a planet what happens and how fast.

Light is a wave/particle that constantly moves away from its source at a high speed. Similar to a bullet exiting a gun.

If the two are competing. Gravity can bend or slow light. Light does nothing to gravity.

Answer 6

Gravity, as far as anyone knows, is a static force of attraction between objects, greater or less, depending on the masses of the affected objects. Gravity itself has no "speed" or velocity itself, it only varies with the mass of an object; it is the ACCELERATION imparted between affected objects that gives its' "speed". This is why one only weighs 1/6 of weight on the Moon, or 1/3 on Mars. The greatest velocity that can be attained by anything in the natural universe, matter or energy, is in the vicinity of a black hole, which absorbs ANYTHING which crosses its' event horizon, which gravity will accelerate any captured object to EXACTLY the speed of light.
If, somehow, the Moon were destroyed, or forced out of its' Terran orbit, its' gravitational influence would cease, and so would the greater of the tidal influence, as tides are also caused by the Sun's gravity.
The only thing that exceeds the speed of light are tachyons, about which so little is known, that nobody understands them.

Answer 7

Interesing question no doubt? But it is hard to associate velocity to a force i,e gravity. Gravitation is a force acting on two bodies separated by a distance. If moon is to go away the gravitational interaction with moon will be null but it is not easy to define the amount of time it will take to perceive the change in tide conditions. But definitely you will be missing the moon before you are missing the tides.

Answer 8

Gravity is a force, while light is a particle propelled by force. Light can be affected by gravity. So, if this should happen, ignoring the fact that all life on Earth would be totally sc#$@ed, then we would probably see it happen just as the tides went completely bonkers.

Answer 9

Nothing can exceed the speed of light.
If the moon disappeared it would take more than one second before any gravitational effects would reach earth.

Answer 10

Its a perfectly good question and the answer is, since Einstein's general relativity that gravity propagates as a wave at the speed of light.