How can the speed of gravity be measured?

Question

Has the speed of gravity ever been measured or is it just assumed to equal the speed of light?

I'm talking about the speed of gravity not the speed of an object falling.
If for example, the sun disappeared, would the sudden removal of it's gravity be noticed on earth immediately or does gravity travel at a measurable speed.

I'm talking about the speed of gravity not the speed of an object falling.
If for example, the sun disappeared, would the sudden removal of it's gravity be noticed on earth immediately or does gravity travel at a measurable speed.

Dont forget, I'm not asking what is the speed of gravity ... I'm asking how can it me measured.

Answer 1

The first accurate measurement ever taken of the speed with which gravity propagates shows that it is equal to the speed of light, agreeing nicely with the General Theory of Relativity.


Though fast, light takes time to travel. If the Sun suddenly disappeared, it would take about 8.3 minutes before daylight on Earth would evaporate. With the Sun gone, gravity would cease to keep Earth in a circular orbit, and it would fly away.

If gravity works instantly, Earth would fly away the moment the Sun disappeared. If gravity works at light speed, Earth's course would not change until 8.3 minutes later.

Sergei Kopeikin of the University of Missouri, Columbia, and Ed Fomalont of the National Radio Astronomy Observatory devised a clever experiment to test which of the two assumptions is right. On several days last September, they observed a faraway galaxy as the planet Jupiter passed near it in the sky.

Jupiter's gravity would bend the light ever so slightly, they knew. The question was by how much. Theory predicted two separate circles, slightly offset from one another, that the galaxy should appear to describe on the sky as Jupiter got close, closer, and then moved away.

The results show, within a 20 percent margin of error, that gravity worked at the speed of light. The finding was announced here today at a meeting of the American Astronomical Society.

"We now know that the speed of gravity is probably equal to the speed of light," Fomalont said. "And we can confidently exclude any speed for gravity that is over twice that of light."

That gravity works instantaneously is almost impossible, according to the study.

The results have been submitted for publication in a peer-reviewed scientific journal, but the publication has been held up because of criticisms of the work leveled by some researchers. Today, Kopeikin dismissed the criticisms as unfounded.

Craig Hogan, an astronomer and physicist at the University of Washington, was not involved in the new research. He said the very high-precision measurement was the first to check whether Einstein's assumption about gravity was correct.

"Thankfully, it is," Hogan said, adding that were it not, theorists would have their hands full trying to explain the result.

Nonetheless the finding, if accurate, puts constraints on cosmological theories of multiple universes and so-called string theory, but it is too early to know how, the researchers said.

The observations were made with National Science Foundation's Very Long Baseline Array, a series of radio telescopes spread around the Earth and working in concert. A 100-meter telescope in Germany was also used. The combined effect allowed a precision 100 times that of the Hubble Space Telescope. The fine measurements were akin to seeing a silver dollar on the Moon, the researchers said.

Answer 2

YES, it is the speed of light. The question is most likely asking at what speed does the effect of gravity move. ie, if you suddenly added 10% to the mass of the sun, would the earth instantaneously be affected, or would it take the 8 minutes to reach earth, like light does. Scientists have calculated that it would equal the speed of light, and not be instant.

Answer 3

The sun bends space-time, so if it disappeared, the space-time warp would dissappear, and the "gravity wave" that would follow would travel at the speed of light, so in eight minutes, the earth would get out of orbit. To get a picture of this whole thing, imagine putting a bowling ball on a trampoline, when you take the ball out, the trampoline will start vibrating. this is all theory, none has been proven

Answer 4

That the propagation speed of gravity is the speed of light is not an assumption. It is obtained from Einstein's equations of General Relativity. Experimentally determining that this value is correct then becomes further confirmation of that theory.

Answer 5

First of all u need to know that light 'carries' gravity to earth. As such, the speed of gravity = the speed of light.
Now, we know that light takes 8 min (approx.) to reach the earth; so if light disappears, it'll take us 8 min. to be spun off frm earth. We'll not be spun off as soon as the light disappears.

Answer 6

The speed of something falling through the air due to the force of gravity is -9.8 ft/sec, accelerating that speed every second, not factoring in wind resistance and terminal velocity.

Answer 7

Great question. I didn't know myself, but a quick search found the answer. Apparently it has been measured but the measurements were only precise enough to show that it is "probably equal to the speed of light."

Answer 8

First of all, there is no such thing as the speed of gravity. I think you mean the speed of an object that falls to the ground right? Well, they are measured in miles/hour or km/hour.

Answer 9

Gravity is a force. Because it is a force, it is based off of variables. In this case, it is dependent of distance of the two interacting bodies and the masses of the bodies.

Answer 10

9.81 m/s not the speed of light. On earth atleast.