Posted on 01/17/2003 5:28:59 AM PST by NukeMan
Physicists leveled heavy criticism Thursday on a report from last week that claimed the speed of gravity had been determined by observation and was equal to the speed of light.
One physicist called the interpretation of the finding "nonsense". Others were more diplomatic, suggesting that the experiment, involving observations of the bending of light from a distant galaxy as the light sped by the planet Jupiter, had instead measured other phenomena.
The brewing controversy, which illustrates the fits and spurts with which science sometimes grudgingly moves forward, appears to have ground to a stalemate for now as the two scientists who conducted the experiment categorically defended their work.
"The claim that they've measured the speed of gravity is simply incorrect," said Clifford Will, a physicist at Washington University in St Louis, Missouri, and an expert in the field.
Interestingly, Will is friends with one of the researchers whose work he knocks.
In a telephone interview this morning, Will hailed the intricate observations as possibly "a great achievement" but said the interpretation of the data "clouded what would otherwise have been a really cool result."
Defending the claim
Ed Fomalont of the National Radio Astronomy Observatory and Sergei Kopeikin from the University of Missouri in Columbia, performed the experiment. They watched light from a faraway galaxy bend as the planet Jupiter passed almost directly between the galaxy and Earth. Their theory stated that the bending would occur due to the gravitational influence of Jupiter.
By noting the extent of the bending, the researchers claimed to have measured whether gravity acted instantly or somewhat more slowly, at light-speed.
Proving that gravity works at the speed of light would add support to Einstein's General Theory of Relativity and place limits on fringe theories in cosmology. Most physicists are confident that this is the case, but no one has ever confirmed it by direct measurement.
Isaac Newton long ago argued that gravity instead propagates instantaneously. The suggestion has not died. If it were true, a big door would open to wild theories of how the universe might work on the grandest scales, including its possible interaction with other universes or other dimensions. Even a slight difference in the speeds of light and gravity would give theorists nifty wiggle room to craft bizarre ideas about the mechanics of the unseen universe.
Fomalont, an observational astronomer, calmly refuted the criticisms one-by-one this morning.
"We're really confident that we've measured the speed of gravity and that our interpretation of the results of our experiment are as stated," Fomalont told SPACE.com.
Behind the scenes
The finding, announced Jan. 7 at a meeting of the American Astronomical Society (AAS), was controversial well before it was reported to the general public. Two papers on the work had in prior weeks been submitted for peer review and possible publication in the Astrophysical Journal Letters. One describes the technique, another details the results. Both are still being reviewed.
Will, the Washington University physicist and a self-proclaimed longtime colleague and friend of Kopeikin, was asked to review the theoretical paper for the journal. Will recommended it not be published. The paper has since been sent to another referee.
Will explained his reasoning: A moving body, like Jupiter, produces additional gravitational effects that Kopeikin did not take into account in his theoretical calculations. Will was surprised that the findings were announced last week, before the papers had been accepted for publication.
It is not uncommon for discoveries to be presented to reporters at AAS meetings prior to having been through peer review. Numerous other findings, by NASA scientists and others, are announced in press releases every year prior to any formal peer review. Scientists are sometimes critical of this so-called "science by press release" process. Others see it as a natural and inevitable flow of information into scientific and public hands.
Ultimately, Will said, the scientific community will sort out the truth in this case.
"Will is one of the giants in this field," Fomalont said. He added that Kopeikin and Will have gone politely back and forth on their differing interpretations of subtleties in what might be observed in the experiment, and are simply at loggerheads over which approach is correct.
Kopeikin said he has found a mistake hidden deep in Will's calculations, and that other mathematicians concur. "He does not agree," Kopeikin said of Will today. "But mathematics is against him."
Kopeikin, too, said the review process would ultimately reveal the truth.
Long-running debate
Kopeikin began circulating his theoretical idea for the experiment more than two years ago, and criticisms began well before the observational work was carried out last September.
Japanese physicist Hideki Asada published a paper, also in the Astrophysical Journal Letters, about a year ago arguing that Fomalont and Kopeikin would actually be measuring the speed of light, not gravity. That paper has been a thorn in Kopeikin's side ever since. During the AAS press conference last week, when questioned about Asada's work, Kopeikin was visibly frustrated and said Asada had made a mathematical mistake.
Fomalont said this morning that Asada's paper was "not valid." But because it was published, however, it had been given "a standing which it does not deserve." Today, also in the Nature Science Update article, Peter van Nieuwenhuizen, a physicist at Stony Brook University in New York, called the interpretation of the results by Fomalont and Kopeikin "compete nonsense," but the comment was not expanded upon.
Fomalont chose not to respond to van Nieuwenhuizen's choice of words. He also said he had no regrets over announcing the results prior to peer-reviewed acceptance in a journal.
The whole issue seems to have caught many physicists by surprise.
Fomalont notes that during the two or three years that scientists had to review the idea, most did not think the measurements could even be made (regardless of what was being measured) so few spoke up about the potential interpretation of the results (that the speed of gravity could be determined).
"Then they see that we can measure it, and that fostered a lot of bubbling up of criticism," Fomalont said.
There remains little doubt that something was measured last September when the largest planet in our solar system fortuitously passed in front of a bright galaxy some 9 billion light-years away. What remains is for physicists to agree on what was seen.
I read their results in "New Scientist" magazine. Perhaps the establishment is a bit miffed that they went ahead and "published" in a non-technical weekly such as that one?
I also wonder how much this has to do with the work by Kopeikin. To quote New Scientist:
"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".Is Kopeikins work generally regarded as valid? I admit I dont keep up on physics.
OK, so if the speed of gravity equals the speed of light and according to Albert E. to attain the speed of light you would go back in time. Then when I fall down I should get younger ...
Correct?
Ouch. Bump.
Physicist, I haven't had time to read up on this and I can't handle any General Relativity content. However, I have a perhaps simplistic view of what might be observable here.
Einstein's prediction that light would be affected by gravity predicts that light from a distant star will not follow a straight line when passing close to our sun but will be slightly bent toward the sun. Thus, the apparent position of a star which appears near the sun during an eclipse can be different than it would be without the effect of the sun's gravity.
I am imagining that Jupiter's gravity would have the same effect on the light from a distant star ( or galaxy ), and thus the light coming from the star would bend toward Jupiter if it passed through the stronger gravity near its surface.
Since the measurement of time has become so accurate with cesium beam clocks and such, it would be possible to chart the apparent position of the star versus time.
If gravity was instantaneous, then the symmetry of Jupiter's shape would result in equal bending of light on either side as Jupiter passes in front of the star. For the sake of my description, imagine that Jupiter is passing from right to left.
As Jupiter nears the path of light from the star, the light is bent such that the star would seem to shift toward our left as Jupiter nears it. The light would be travelling on a more and more curved path which would pass closer and closer to Jupiter's surface, until it would finally have to pass through Jupiter to get to us. At that instant, the star would disappear behind Jupiter.
As Jupiter moves further to the left, the star will appear on the right of Jupiter. Its position will be shifted to the right from where it would be without the presence of Jupiter. As Jupiter continues to pass to our left, the apparent position of the star will move to the left until it once again occupies the position in the sky expected in the absence of Jupiter.
Since the travel times to earth are virtually the same for all of these light rays, and assuming that gravity is instantaneous, I would predict that the apparent movements of the position of the distant star would be symmetrical with respect to both time and position of Jupiter. Or, in other words, if a movie of this event were filmed and run backwards, the events would be just as if we were viewing the original event in a mirror.
Now, finally, for my question. Is the experiment alluded to here one of measuring asymmetry in the apparent shifting of the position of the star? I can imagine that this event might have an asymmetrical appearance in both time and space if the gravitational field being generated by Jupiter was slight lower in the direction in which Jupiter is advancing because of a finite propogation speed for "gravity waves" or "gravitons" or whatever is interacting with the photons from the distant star.
Is this roughly what is happening? I am trying to save myself the disappointment of looking up the source materials and finding that I can't follow it.
Thanks for any tutoring.
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