First speed of gravity measurement revealed

NewScientist.com ^ | 01/07/2003 | Ed Fomalont and Sergei Kopeikin

[forsnax5]

Ping for Gravity fans!

[Fiddlstix]

BTTT

[Excuse_My_Bellicosity]

Pretty wild. I always assumed that gravity was an instantaneous thing.

[aruanan]

Ping for Gravity fans!

Except that if gravity propagated at the speed of light, the earth would long ago have ceased to orbit the sun. The calculation of orbital trajectories, in order to work, have to be plotted treating the speed of gravity as virtually instantaneous.

[Southack]

"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.

Measuring the speed of gravity 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."

Then again, perhaps all that they really measured was the speed of the radio waves bending around Jupiter...

[Excuse_My_Bellicosity]

It's amazing that Einstein's theories, unprovable when he was alive, are still being shown to be right.

I remember in 1995 when they discovered that Einstein-Bose Condensate was just like Einstein (and Bose) predicted it would be in 1925.

[forsnax5]

I always assumed that gravity was an instantaneous thing.

You're in good company. So did Isaac Newton...

[blam]

Gravity particles bump.

[conservativemusician]

Fascinating stuff.

[MonroeDNA]

Geeze, we all knew that. It HAS to.

*burp*

[NEWwoman]

What Gravitas!

[Jhoffa_]

Ping for Gravity fans!

Of course you realize this ping is entirely redundant..

[aruanan]

You're in good company. So did Isaac Newton...

I would think that measurements of earth's acceleration toward the sun that show a direction that is 8.3 minutes ahead of the apparent position of the sun in the sky also demonstrate a propagation speed that is virtually (at these distances) instantaneous. That is, the earth is not accelerating toward where "gravity waves" are supposedly reaching the earth together with the photons that left the sun 8.3 minutes previously but toward where the sun actually is.

[supercat]

Pretty wild. I always assumed that gravity was an instantaneous thing.

What, then, would prevent the use of gravitational waves as a faster-than-light communications medium?

[Libertarianize the GOP]

http://www.freerepublic.com/perl/bump-list

[supercat]

[thoughts]: (1) Do photons interact gravitationally with each other? (2) Do gravity waves have mass?

[Nick Danger]

Perhaps there is a minimum distance -- a quantum of space -- and a minimum amount of time -- a quantum of time. There is a speed limit on light because it cannot take less than one quantum of time to travel across one quantum of space. Do I know what I'm talking about here? Absolutely not. But I don't think anyboody else does, either.

[VadeRetro]

You got it nonetheless. The "Planck" distance and the "Planck" time. Values very small in each case. Everything is grainy when you get small enough.

[rface]

I love gravity!

Columbia, Missouri (actually Ashland, Missouri)