Speed of Gravity
If the Sun were to suddenly wink out of existence, we wouldn't know for more than eight minutes. That's because the Sun is 93 million miles away, and it takes light more than eight minutes to cross that distance.
But scientists aren't positive just when we'd feel the loss of the Sun. Would Earth start flying off into space at the same time we saw the Sun vanish, or would it continue in its curved orbital path for a while longer?
The answer depends on the speed of gravity.
Like light, gravity may travel as both waves and as particles. The speed of gravity depends on whether these particles, called gravitons, have mass.
Until a century ago, scientists thought that gravity traveled at an infinite speed. So if the Sun winked out, Earth would instantly feel the loss of its gravitational pull. But Albert Einstein showed that nothing can travel faster than light. His equations predict that gravity should move through the universe at the speed of light.
Some new theories, though, suggest that gravitons have a tiny bit of mass. If so, then they could travel at almost the speed of light, but could never quite get there.
Astronomers hope to solve the issue in the next decade or two. They'll use gravity-wave observatories to compare the visible light and the gravity waves from binary star systems. If these waves are in sync, then gravity travels at the speed of light. If not, then gravity is a slowpoke, lagging just behind light.
Script by Damond Benningfield, Copyright 2005
For more skywatching tips, astronomy news, and much more, read StarDate magazine.
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