January 7, 2003
REAL SCIENCE:
First speed of gravity measurement revealed (NewScientist.com, 07 January 03)The speed of gravity has been measured for the first time. The landmark experiment shows that it travels at the speed of light, meaning that Einstein's general theory of relativity has passed another test with flying colours.Ed Fomalont of the National Radio Astronomy Observatory in Charlottesville, Virginia, and Sergei Kopeikin of the University of Missouri in Columbia made the measurement, with the help of the planet Jupiter.
"We became the first two people to know the speed of gravity, one of the fundamental constants of nature," the scientists say, in an article in New Scientist print edition. One important consequence of the result is that it places constraints on theories of "brane worlds", which suggest the Universe has more spatial dimensions than the familiar three.
John Baez, a physicist from the University of California at Riverside, comments: "Einstein wins yet again." He adds that any other result would have come as a shock.
Relativity rankles, but unlike some other theories it is subject to experimentation and keeps passing the tests.. Posted by Orrin Judd at January 7, 2003 11:59 PM
Bear with me: A college physics text for a class I took mentioned an experiment to demonstrate the speed of light that measured the time it took a light signal to pass back and forth between two mountain tops (bounced back to point of origin by a mirror). How did they determine the distance to be travelled in advance, to plug into the equation? They used an electronic distance-finder (a device using EMR, or basically light, itself calibrated to the generally accepted speed of light)! The point is, the experiment proved nothing because its outcome was was also its input. Every time I am tempted to give some weight to some announced physics finding, I remember that textbook example and shrug.
Posted by: Paula R. McIntyre Robinson at January 8, 2003 5:40 AMI am no physicist, but this old Tom Bethell article
seems to hint at some doubt.
Paula -
I'll also note that in a related subject that there is some (admittedly sketchy) evidence that the speed-of-light has been decreasing, pace Barry Setterfield. He notes that since 1960 all speed-of-light experiments have been conducted using cesium atom oscillation clocks which would also be affected by a light decay, thus cancelling out any measurable effects - a redux of your complaint!
Didn't some scientists also slow down light in a lab a couple years ago?
Posted by: oj at January 8, 2003 8:14 AMStopped it cold. But you can do the same
thing with a 10-cent mirror.
You need to distinguish between speed of
light in a vacuum and speed of light
elsewhere.
Orrin, you should read up on Neopilina.
AUTHOR: mike earl
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DATE: 01/08/2003 12:50:00 PM
AUTHOR: mike earl
DATE: 1/08/2003 12:50:00 PM
Mike, I should have made clear that I was using the word "demonstrate" in the way it is ordinarily used in the jargon of the experimental sciences, as a synonym for "prove". Thanks for the tip.
Posted by: Paula R. McIntyre Robinson at January 10, 2003 5:35 AM