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[ft-l] The Speed of Gravity



Zowie! Cross Products, Vectors, Differentials.....Eigenvalues in the woods!!
Actually thanks for sending this along I am interested in this very subject.
I can just about follow along with the preprints but its been a long time
since Relativistic Physics 603. I had no idea that this list was so
advanced.

Bryan

"Si vis pacem para bellum"

> Most of us have by now heard of the speed of gravity being
> "measured" a few
> weeks ago. As the synopsis below explains this was done by a
> gravity lensing
> experiment utilizing Jupiter and several quasars, an event which
> occurs only
> once every ten years or so.
>
> When I first read the report, I was skeptical, on first read I thought,
> "gee, all we have really measured is the speed of light after gravity has
> had its effect". Which of course is the same as the speed of light as we
> have all come to know and love it. I was tempted to post a message to the
> board then, but held my peace.
>
> I just received the latest installment of AIP News, which predictably,
> covers the experiment. I have appended the article below, but to
> summarize,
> it seems that a lot of other scientists agree with me. This may not be the
> definitive experiment it is being purported to be.
>
> Okay, I am done throwing oil on the waves, here is the article:
>
> CAN THE SPEED OF GRAVITY be measured directly through the observation of
> gravitational lensing effects? Two scientists who monitored the deflection
> of quasar light as it passed very near Jupiter argue that they
> have derived
> an experimental value for the speed of gravity equal to 1.06
> times the speed
> of light (with an uncertainty of 20%). But two other scientists claim that
> the lensing experiment only served as a crude measurement of the speed of
> light itself.
>
> Physicists have long taken for granted that the effect of gravitational
> force, like the effect of electromagnetic force, is not instantaneous but
> should travel at a finite velocity. A familiar example of this
> delay is the
> fact that when we see the sun, we see it as it was 8 minutes ago. Many
> believe that gravity also travels at the speed of light. The trouble is,
> while it is relatively easy to gauge the strength of gravity (one can
> measure gravity even near a black hole, where orbiting matter
> emits telltale
> x rays), it is difficult to study the propagation of gravity.
>
> Although not as heavy as a star, Jupiter still has considerable
> gravity, and
> when on September 8, 2002, it swept very near the position of
> quasar J0842 +
> 1835, the theory of general relativity suggests that the apparent quasar
> position on the sky would execute a small loop over the course of several
> days owing to the lensing of quasar light by the passing planet.
>
> Sergei Kopeiken (University of Missouri) and Ed Fomolont (National Radio
> Astronomy Observatory, or NRAO) have now seen just such a loop, as they
> reported this week at the meeting of the American Astronomical
> Society (AAS)
> in Seattle. For this purpose they employed the Very Long Baseline Array
> (VLBA) of radio telescopes, a configuration of dish detectors providing an
> angular resolution of 10 micro-arcseconds. Actually the observed lensing
> loop was slightly displaced from what one would expect if gravity
> propagated
> instantaneously. Kopeiken and Fomolont interpret this slight
> displacement as
> providing an experimental handle on the speed of gravity itself,
> and thereby
> calculate the value of 1.06 times c.
>
> Other scientists disagree with this interpretation, and say that the radio
> lensing data can do little more than provide a measurement of the speed of
> light, not gravity. Two such opinions, by scientists who did not report at
> the AAS meeting, are as follows: Clifford Will of Washington University in
> the US (preprint at (www.arxiv.org/abs/astro-ph/0301145 ) and Hideki Asada
> of Hirosaki University in Japan (www.arxiv.org/abs/astro-ph/0206266 )
>
> Lee
>
>
> --
> If cats had thumbs, they'd still expect us to open the canned food.
> If dogs had thumbs they'd cook for us, but not very well.
> Certain Maxims of Rufus
>
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