Scientists attempt to measure speed of gravity

spaceflightnow.com ^ | 5 SEP 02 | staff

[RightWhale]

Scientists attempt to measure speed of gravity

UNIVERSITY OF MISSOURI NEWS RELEASE

Posted: September 4, 2002

Ever since Albert Einstein proposed the general theory of relativity in 1916, physicists worldwide have tested the theory's underlying principles. Whil some principles - such as the speed of light is a constant - have been proven, others have enot. Now, through a combination of modern technology, the alignment of a unique group of celestial bodies on Sept. 8, and an experiment conceived by a University of Missouri-Columbia physicist, one more of those principles might soon be proven.

"According to Einstein's theory, the speed of gravity is assumed to be equal to the speed of light," said Sergei Kopeikin, MU associate professor of physics and astronomy. "While there is indirect evidence this is true, the speed has never been measured directly, and that's what we're attempting to do in an experiment that will not be possible again for another decade."

The experiment will involve precisely measuring the angular distances between several quasars, celestial objects in distant galaxies that resemble stars. On Sept. 8, Jupiter will pass very close to the primary quasar. When it does, its gravity will cause the quasar's position in the sky to shift by a distance that depends on the speed of gravity. Kopeikin and Ed Fomalont, a radio astronomer with the National Science Foundation's National Radio Astronomy Observatory (NRAO), will use an observational technique they developed to compare the position of the primary quasar to the position of other quasars unaffected by Jupiter. Using their data, they hope to confirm the accuracy of Einstein's theory further.

Measurements will be made using the NRAO's Very Long Baseline Array (VLBA), a series of 10, 25-meter radio telescopes located from the Virgin Islands to Hawaii, and the 100-meter radio telescope in Effelsberg, Germany, which is operated by the Max Planck Institute for Radio Astronomy. "Results from recent VLBA test observations indicate we can reach the accuracy necessary to determine the speed of gravity if the experiment goes well," Fomalont said.

"Japanese and NASA scientists also will conduct the experiment independently using other telescopes around the world, so we'll be able to compare our findings," Kopeikin said. "We believe the general theory of relativity is correct and that the speed of gravity is equal to the speed of light."

"The techniques we've employed for this experiment can also be used to more precisely determine the position of other objects in space," Fomalont said. "With more exact positioning of satellites, we could improve telecommunications. Unmanned space navigation could also be improved, allowing us to explore the solar system more deliberately."

The scientists said final results from the experiment should be available in mid-November.

[ATOMIC_PUNK]

Might you be referring to the difficult vortex theory of gravitation?

Thats the one its difficult indeed

[RightWhale]

its difficult indeed

It is so difficult that they were happy to have something relatively [!!!] simple like the general theory of relativity come along so they could work on that instead.

[apochromat]

That makes sense, but what should be made of the case where light is slowed down to a fraction of its vacuum speed, say for instance to 20 mph in a BEC medium? As far as I can guess, the speed of such light could be varied by moving the medium while it contains the light.

There would have to be some light speed reduction or medium (or something) that would define the regime of non-relativity, it seems.

[RightWhale]

the case where light is slowed down to a fraction of its vacuum speed, say for instance to 20 mph in a BEC medium?

The Bose-Einstein Condensate is not a place one would normally try to travel in or have a picnic. But perhaps when I am doing my doctoral studies, I will have the opportunity to measure the angle of Cerenkov radiation inside there.

[apochromat]

BECs are exotic, but they are what prompted my questions.

I was thinking about Cerenkov radiation for several minutes after I wrote my previous reply, while I was also muddling over whether "nonrelativistic" was the appropriate term for me to have used.

After thinking about it some more, I suppose that such exotic phenomena are relativistic, but their conditions are so complex that naively-applied relativistic transformations won't fit.

[RightWhale]

Bose-Einstein Condensates are exotic alright, but we don't have to use them to wonder about relativity inside non-vacuum conditions. The simple glass in your telescope lens allows light to pass right on through fairly easily, yet what kind of relativistic effects are going on inside there? You could shoot a nuclear particle into that region at over the speed of light in the medium until it collided with something. Light slows down instantly at the air-glass interface, but the alpha particle keeps on trucking, moving faster than light for a while. What happens to relativity there?

[capitan_refugio]

Are you saying, " E = M G squared "???

Great Scot, you could be right!

[apochromat]

What happens to relativity there?

I'll make an attempt at answering that, and you can correct me if you disagree. It seems that the non-uniformity of the medias involved is being made evident in such phenomena. In other words, the light-speed reduction defined for a medium is a macroscopic quantity based on averaged effects of all the atoms that make up the medium. Looking at it microscopically, the medium is a combination of vacuum and atoms, and light is normally induced by the atoms to meander about instead of taking the shortest path through the vacuum.

[RightWhale]

the medium is a combination of vacuum and atoms

It's the kind of thing we don't know and may never know. Even the deepest outer space between galaxies and between galactic filaments where there is really nothing contains photon radiation fields and and gravity fields and who knows what else criss-crossing in every direction everywhere. There may be no such thing as a perfect vacuum, and if there were it might be disastrous.

[SunkenCiv]

Vintage science topic.

[Stellar Dendrite]

lol!!!!!

[Age of Reason]

Too many exclamation points in your article.

So it must be B.S.

[FairOpinion]

Thanks for the science pings, in addition to the GGG ones.

I haven't had much time to spend on FR, so it helps to be pinged, to avoid missing interesting stuff.

[SunkenCiv]

You're most welcome. This one hadn't been posted to in nearly three years though. :')