Posted on 01/07/2003 6:23:34 PM PST by forsnax5
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.
You can read Fomalont and Kopeikin's account of their unique experiment in an exclusive, full-length feature in the next issue of New Scientist print edition, on sale from 9 January.
Isaac Newton thought the influence of gravity was instantaneous, but Einstein assumed it travelled at the speed of light and built this into his 1915 general theory of relativity.
Light-speed gravity means that if the Sun suddenly disappeared from the centre of the Solar System, the Earth would remain in orbit for about 8.3 minutes - the time it takes light to travel from the Sun to the Earth. Then, suddenly feeling no gravity, Earth would shoot off into space in a straight line.
But the assumption of light-speed gravity has come under pressure from brane world theories, which suggest there are extra spatial dimensions rolled up very small. Gravity could take a short cut through these extra dimensions and so appear to travel faster than the speed of light - without violating the equations of general relativity.
But how can you measure the speed of gravity? One way would be to detect gravitational waves, little ripples in space-time that propagate out from accelerating masses. But no one has yet managed to do this.
Kopeikin found another way. He reworked the equations of general relativity to express the gravitational field of a moving body in terms of its mass, velocity and the speed of gravity. If you could measure the gravitational field of Jupiter, while knowing its mass and velocity, you could work out the speed of gravity.
The opportunity to do this arose in September 2002, when Jupiter passed in front of a quasar that emits bright radio waves. Fomalont and Kopeikin combined observations from a series of radio telescopes across the Earth to measure the apparent change in the quasar's position as the gravitational field of Jupiter bent the passing radio waves.
From that they worked out that gravity does move at the same speed as light. Their actual figure was 0.95 times light speed, but with a large error margin of plus or minus 0.25.
Their result, announced on Tuesday at a meeting of the American Astronomical Society meeting in Seattle, should help narrow down the possible number of extra dimensions and their sizes.
But experts say the indirect evidence that gravity propagates at the speed of light was already overwhelming. "It would be revolutionary if gravity were measured not to propagate at the speed of light - we were virtually certain that it must," says Lawrence Krauss of Case Western Reserve University in Cleveland, Ohio.
Also, there is no relationship between the amount of spaghetti that spilled and the extent of the stain. The stain will spread to a surface area of 2304 square-inches regardless. :^)
ROFL! These guys just love to out-science each other. As long as your feet stick to the floor, don't worry about it (assuming they are not stuck in a pile of spaghetti).
LOL. As I wrote my post, I wondered whether some lawyer was going to come along and say that acceleration is not relative. (That doesn't make it absolute, either, but that's a longer story.) The poster wasn't talking about acceleration, but about velocity.
Abstract. New findings announced today by S. Kopeikin are invalid by both experimental and theoretical standards. They do a disservice to science in general and the advancement of physics in particular because the announced findings do not represent the meaning of the actual experimental results and cannot possibly represent the physical quantity heretofore called "the speed of gravity", which has already been proved by six experiments to propagate much faster than light, perhaps billions of times faster.
Abstract. New findings announced today by S. Kopeikin are invalid by both experimental and theoretical standards. They do a disservice to science in general and the advancement of physics in particular because the announced findings do not represent the meaning of the actual experimental results and cannot possibly represent the physical quantity heretofore called "the speed of gravity", which has already been proved by six experiments to propagate much faster than light, perhaps billions of times faster.
space.com notes that the article is still in the peer review process because of problems from the reviewer.
On the other hand, if it is shot down, it is a vindication of the peer review process, something that Aruanan claimed was part of the corrupt scientific establishment just the other day.
Whoa!!!! Multimode attack!!!! Shields up!!!!
If there is a quantum of space and a quantum of time this could be the soucre of the uncertainties of quantum mechanics: since a particle would have to jump from one point on some invisible grid to another, there is uncertainty about it's position when it is jumping from one point to the other.
The bad news is that if we find out that space and time is quantized, it could be because we are all part of some very sophisticated "first-person shooter" game driven by a computer with a fixed clock speed (the time quanta) and a fixed resolution (the space quanta)!
Where's my missile launcher?
Then, how would one modulate the baseband? Or would we have to use CW?
Mass has to move. Perhaps a rotating double star would give off CW strong enough to detect. Perhaps Jupiter is massive enough and close enough for the instrument to pick up something.
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