What is the speed of gravity?
(Credit: NASA, produced by USGS)
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I have always heard about the speed of light. But I was wondering if there is such a thing as the speed of gravity. How long would it take for one planet to feel the attraction of another planet?
Isaac Newton was the first to explain gravity as a force between two objects – that was in the late 1600s. He thought that gravity traveled instantaneously across space – that, for example, Earth immediately “felt” the sun’s pull, and that, if the sun disappeared, Earth would instantly fly out of orbit into the void of space.
But when Albert Einstein developed his special theory of relativity in 1905, he concluded that no signal in the universe can travel faster than the speed of light – about 300 thousand kilometers, or 186 thousand miles, per second. Not even the tug of gravity can outrace light. Gravity, in Einstein’s view, is not a force that travels out from a massive object to tug instantly on everything around it. Instead, Einstein described gravity as a “field” that bends space and time.
Today’s scientists theorize that gravity travels in space as a particle, called a “graviton.” According to this theory, the graviton also travels at the speed of light. So as far as we know, if the sun disappeared, Earth – at eight light-minutes away – wouldn’t know it until eight minutes later.
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