http://www.space.com/scienceastronomy/gravity_speed_030107.html
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. You may or may not have ever considered whether gravity has speed. It is of great concern to scientists. Newton thought gravity's force worked instantaneously. Einstein thought it took effect at light speed. Here's a way to think of the difference: 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 work 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. xponent Silver Sliver Maru rob ________________________________ You are a fluke of the universe. You have no right to be here. And whether you can hear it or not, the universe is laughing behind your back. _______________________________________________ http://www.mccmedia.com/mailman/listinfo/brin-l
