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Les Sleeth
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At another science forum site someone asked about the speed of gravity. I posted a link to a news article about Kopeikin's experiment and published results: http://www.nrao.edu/pr/2003/gravity/
Some excerpts are:
I’d thought this was all but accepted by scientists, until another member there posted this link to a paper rebutting Kopeikin's results: http://www.metaresearch.org/media%20and%20links/press/SOG-Kopeikin.asp
Here are some relevant quotes from that paper:
I have a few questions. Is there general agreement now that Kopeikin’s team failed to measure the speed of gravity? Is it generally agreed that the speed of gravitational force is virtually instantaneous? In the article above they cited the following thought experiment which seems to make sense:
“A common thought experiment asks: ‘What would happen to the Earth's orbit if the Sun suddenly ceased to exist?’ The answer is now clear. The usual relationship ‘force is the gradient of the potential’ would instantly end. The Sun's potential field would then begin to dissipate, taking 8.3 minutes to dissipate out to the distance of the Earth's orbit; so effects such as light-bending and clock-slowing would persist for that long. But the Newtonian component of gravitational force, the force that keeps Earth in its orbit, would cease almost instantly, and Earth would fly off along a straight line like a weight on a spinning merry-go-round that broke free from its moorings.”
Mainly I wanted to ask this. If the speed of gravity is virtually instantaneous, what are people’s thoughts about what gravity is doing to space that would cause that? For example, would it be improper to see mass as having a “constricting effect” on space?
In that case, the constricting effect would simultaneously affect every place the force extends, and then disappear concurrently everywhere if, as in the example above, the Sun suddenly ceased to exists.
Some excerpts are:
“’We have determined that gravity's propagation speed is equal to the speed of light within an accuracy of 20 percent,’ said Ed Fomalont, an astronomer at the National Radio Astronomy Observatory (NRAO) in Charlottesville, VA. The scientists used the National Science Foundation's Very Long Baseline Array (VLBA), a continent-wide radio-telescope system, along with the 100-meter radio telescope in Effelsberg, Germany, to make an extremely precise observation when the planet Jupiter passed nearly in front of a bright quasar on September 8, 2002.
“The observation recorded a very slight ‘bending’ of the radio waves coming from the background quasar by the gravitational effect of Jupiter. The bending resulted in a small change in the quasar's apparent position in the sky.
“‘Because Jupiter is moving around the Sun, the precise amount of the bending depends slightly on the speed at which gravity propagates from Jupiter,’ Kopeikin said.
“‘Our main goal was to rule out an infinite speed for gravity, and we did even better. 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,’ Fomalont said.”
I’d thought this was all but accepted by scientists, until another member there posted this link to a paper rebutting Kopeikin's results: http://www.metaresearch.org/media%20and%20links/press/SOG-Kopeikin.asp
Here are some relevant quotes from that paper:
“Abstract. New findings were announced on 2003/01/08 by S. Kopeikin, claiming to have measured the ‘speed of gravity’ and finding it essentially equal to the speed of light. These findings are invalid by both experimental and theoretical standards because the quantity measured was already known to propagate at the speed of light. The hyped claims therefore 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. Several mainstream relativists have also stated their disagreement that the experiment really measured what it claimed to measure.
“Kopeikin's latest paper on the internet, giving the basis for his findings announced at the AAS meeting, contains some egregious errors. The following claims appear therein: ‘… a moving gravitating body deflects light not instantaneously but with retardation caused by the finite speed of gravity propagating from the body to the light ray. … We calculated this correction for Jupiter by making use of the post-Minkowskian approximation based on the retarded Lienard-Wiechert solutions of the Einstein equations. … Speed of gravity cg must enter the left side of the Einstein equations (2) … This will lead to the wave operator depending explicitly on the speed of gravity cg.’
“None of these statements is correct even in GR, provided only that ‘the speed of gravity’ retains its classical meaning for the past two centuries of force propagation speed. The Einstein equations require the potential field of all bodies to act from the body's instantaneous direction, not its retarded direction, because they set propagation delay for the gradient to zero. But Kopeikin adopts the Sun acting from its instantaneous position and Jupiter acting from its retarded position, which is inconsistent. In fact, although the Sun moves 1000 times more slowly than Jupiter, it is 1000 times more massive, making any hypothetical retardation effects comparably important. The Lienard-Wiechert equations consider retardation in mutual distance, but not in direction – the latter being a much larger effect of propagation delay. And the parameter on the left side of the Einstein equations is c2, and therefore has nothing to do with the speed of gravity, as we noted above. This does not prevent Kopeikin from calling it ‘cg’ and solving for this parameter as if it were the speed of gravity, which is what he has done.”
I have a few questions. Is there general agreement now that Kopeikin’s team failed to measure the speed of gravity? Is it generally agreed that the speed of gravitational force is virtually instantaneous? In the article above they cited the following thought experiment which seems to make sense:
“A common thought experiment asks: ‘What would happen to the Earth's orbit if the Sun suddenly ceased to exist?’ The answer is now clear. The usual relationship ‘force is the gradient of the potential’ would instantly end. The Sun's potential field would then begin to dissipate, taking 8.3 minutes to dissipate out to the distance of the Earth's orbit; so effects such as light-bending and clock-slowing would persist for that long. But the Newtonian component of gravitational force, the force that keeps Earth in its orbit, would cease almost instantly, and Earth would fly off along a straight line like a weight on a spinning merry-go-round that broke free from its moorings.”
Mainly I wanted to ask this. If the speed of gravity is virtually instantaneous, what are people’s thoughts about what gravity is doing to space that would cause that? For example, would it be improper to see mass as having a “constricting effect” on space?
In that case, the constricting effect would simultaneously affect every place the force extends, and then disappear concurrently everywhere if, as in the example above, the Sun suddenly ceased to exists.
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