SatchFan 0 #1 January 7, 2003 Interesting article... SEATTLE, Jan. 7 — Albert Einstein can rest a little easier in his grave: The first effort to measure how quickly gravity exerts its influence indicates that it more or less matches the speed of light, scientists reported Tuesday. If the results had come out differently, it would have cast new doubt on Einstein’s view of general relativity — and in fact, some doubters contend that the latest measurement by no means closes the case. THE MEASUREMENT, presented at this week’s meeting of the American Astronomical Society in Seattle, was made by analyzing how radio waves from a quasar nearly 9 billion light-years from Earth were bent as they passed through Jupiter’s gravitational field on Sept. 8. Scientists have known for decades that gravity bends waves of electromagnetic radiation: The phenomenon played a key role in the first test of general relativity during a 1919 solar eclipse. But it’s only been in the last few years that astronomers have worked on putting a number to the propagation speed of gravity’s effect. This speed is distinct from the much better-known rate of acceleration caused by gravity on Earth, which clocks in at 32 feet per second per second. The classic illustration of the problem goes this way: Imagine that the sun were somehow snuffed out of existence in the blink of an eye. Would there be an instant disruption in Earth’s orbit, sending it careening out of the doomed solar system, or would Earth continue to orbit a nonexistent star for eight minutes while the gravitational disturbance traveled 93 million miles (150 million kilometers) at the speed of light? “Newton thought that gravity’s force was instantaneous,” Sergei Kopeikin, a physicist at the University of Missouri at Columbia, said in an written announcement of the results. “Einstein assumed that it moved at the speed of light, but until now, no one had measured it.” Kopeikin’s partner in the research, Ed Fomalont of the National Radio Astronomy Observatory, said the propagation speed was equal to the speed of light within an accuracy of 20 percent. That may sound like a wide error margin, but the researchers said they were pleased with the results. “Our main goal was to rule out an infinite speed of gravity, and we did even better,” Fomalont said in the announcement. “We now know that the speed of gravity is probably equal to the speed of light, and we can confidently exclude any speed for gravity that is over twice that of light.” If gravity does propagate even 20 percent faster than light, it would break a cosmic speed limit imposed by Einstein’s theories — and could hypothetically open the way to new methods of faster-than-light communication (hopefully on a smaller scale than snuffing out the sun). HOW IT WAS DONE The experiment was conducted by carefully charting how the light of the quasar, J0842+1835, was distorted in the night sky as Jupiter passed through the field of view. In 1999, Kopeikin laid out what Einstein’s theory should predict about the pattern of distortion — then found that September’s “once-in-a-decade” alignment should allow for a test of the theory. He turned to Fomalont, who enlisted the aid of the National Science Foundation’s Very Long Baseline Array, a continent-wide network of radio telescopes. A 330-foot (100-meter) radio telescope in Effelsberg, Germany, was added to the network to increase the accuracy of September’s observations. “We had to make a measurement with about three times more accuracy than anyone had ever done, but we knew in principle that it could be done,” Fomalont said. Sunspot activity during the observations gave the researchers some cause for concern, but in the end, the data achieved a precision equal to the width of a human hair seen from 250 miles (400 kilometers) away, the researchers said. WHAT IT ALL MEANS Kopeikin said the observation sheds light on one of the last unsettled fundamental constants of physics — and could play a role in the continuing quest to develop a "theory of everything” that unites gravitational theory and quantum mechanics. “Our measurement puts some strong limits on the theories that propose extra dimensions, such as superstring theory and brane theories,” he said. “Knowing the speed of gravity can provide an important test of the existence and compactness of these extra dimensions.” However, not all physicists are convinced that the results truly measured the propagation speed. In Astrophysical Journal Letters, Japanese physicist Hideki Asada argued that the experiment actually measured the speed of light rather than the speed of gravity — and that previous experiments have already provided confirmation for Einstein’s view of how gravity propagates. Astronomer Thomas Van Flandern, who has built up a following for his views outside the scientific mainstream, said in a September commentary that the experiment may have measured the speed of gravitational waves, but “can provide no information about the propagation speed of gravitational force, which is bounded by many experiments to be much faster than light.” On Tuesday, Van Flandern told MSNBC.com in an e-mail that Kopeikin may have revised the theoretical basis for the experiment’s results, and that the findings “no longer represent what his own experiment showed, much less the speed of gravity.” Quote Share this post Link to post Share on other sites
quatorze 1 #2 January 7, 2003 "Dum Spiro Spero" Yep, sounds like Latin to me too I'm not afriad of dying, I'm afraid of never really living- Erin Engle Quote Share this post Link to post Share on other sites
falxori 0 #3 January 7, 2003 hmmm yeah , what he said ! O "Carpe diem, quam minimum credula postero." Quote Share this post Link to post Share on other sites
Sebazz1 2 #4 January 7, 2003 So how would this knowledge affect my Gravity Bong? Quote Share this post Link to post Share on other sites
happythoughts 0 #5 January 7, 2003 You know that your post is giving BillVon wood right now, don't ya? Quote Share this post Link to post Share on other sites
SatchFan 0 #6 January 7, 2003 Quote You know that your post is giving BillVon wood right now, don't ya? Yeah, I knew he'd dig that sort of thing. Quote Share this post Link to post Share on other sites
freeflyz 0 #7 January 7, 2003 How do you know that?Did your GIRLFRIEND tell you!!! Quote Share this post Link to post Share on other sites
epiphany 0 #8 January 7, 2003 So how would this knowledge affect my Gravity Bong?*** This means that in exactly eight seconds you will see 20 percent more sunspot activity than before. At least that's what I hope :p Quote Share this post Link to post Share on other sites
kallend 2,127 #9 January 8, 2003 Do you happen to know if they measured the phase velocity or group velocity of gravity?... The only sure way to survive a canopy collision is not to have one. Quote Share this post Link to post Share on other sites
WFFC 1 #10 January 8, 2003 OUCH! OUCH! OUCH! That is just too much information for my brain today...----- ~~~Michael Quote Share this post Link to post Share on other sites
