A question for you physics guys

[mike wightman]

The gravity wave travels at light speed doesn't it?

 

[RainOfSteel]

Originally posted by Sigg Oddra:
The gravity wave travels at light speed doesn't it?

Yes.

 

[Ptah]

Originally posted by Sigg Oddra:
The gravity wave travels at light speed doesn't it?

Another yes. Brian Green's book "The Fabric of the Cosmos" is a nice semi-lay person read on such things.

 

[travlar]

Originally posted by Sigg Oddra:
The gravity wave travels at light speed doesn't it?

As far as we know, yes.

 

[aramis]

Originally posted by Kaale Dasar:
</font><blockquote>quote:</font><hr />Originally posted by Sigg Oddra:
The gravity wave travels at light speed doesn't it?

As far as we know, yes. </font>[/QUOTE]Given the speeds of natural objects, being able to tell if there is lightspeed lag on the objects requires more precision than we currently can put over a longer time than is practical.

So it's not reasonably testable at present. And unless/until FTL or Near-C vehicular speeds are attainable, we really don't need to know from an engineering standpoint.

The other problem is that a lot of recent theoretical physics is just that: pure theory beyond direct test.

And Dalton, Don't bother with any more physics than you absolutely need to make verisimilitude. Better to be vague, than to be wrong...

Personally, I believe the arguments for light-speed, but not enough to be certain, and not enough to object when a GM uses instant propagation.

I use light-speed to make gravitics no more valuable than opticals for detections. But I don't do it for orbits; the precision levels needed for it to matter other than for detection of FTL-Shipping arrivals/departures are beyond the precision to which I can find out real orbits.

 

[Gnusam Netor]

Originally posted by Sigg Oddra:
The gravity wave travels at light speed doesn't it?

I asked a "smart guy", (a professor in space physics) this very question some time ago. He said:
"Information cannot travel faster than speed of light in vacuum, so yes."

It is an assumption, a strong (but uncomfirmed) assumption.

 

[Dunryc]

http://www.seti.nl/article.php?id=418

First speed of gravity measurement revealed

20:30 07 January 03
NewScientist.com news service


The speed of gravity has been measured for the first time. The landmark experiment shows that it travels at the speed of light, meaning that Einstein's general theory of relativity has passed another test with flying colours.

Ed Fomalont of the National Radio Astronomy Observatory in Charlottesville, Virginia, and Sergei Kopeikin of the University of Missouri in Columbia made the measurement, with the help of the planet Jupiter.

"We became the first two people to know the speed of gravity, one of the fundamental constants of nature," the scientists say, in an article in New Scientist print edition. One important consequence of the result is that it places constraints on theories of "brane worlds", which suggest the Universe has more spatial dimensions than the familiar three.

John Baez, a physicist from the University of California at Riverside, comments: "Einstein wins yet again." He adds that any other result would have come as a shock.

You can read Fomalont and Kopeikin's account of their unique experiment in an exclusive, full-length feature in the next issue of New Scientist print edition, on sale from 9 January.

Isaac Newton thought the influence of gravity was instantaneous, but Einstein assumed it travelled at the speed of light and built this into his 1915 general theory of relativity.

Light-speed gravity means that if the Sun suddenly disappeared from the centre of the Solar System, the Earth would remain in orbit for about 8.3 minutes - the time it takes light to travel from the Sun to the Earth. Then, suddenly feeling no gravity, Earth would shoot off into space in a straight line.

But the assumption of light-speed gravity has come under pressure from brane world theories, which suggest there are extra spatial dimensions rolled up very small. Gravity could take a short cut through these extra dimensions and so appear to travel faster than the speed of light - without violating the equations of general relativity.

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.

Bending waves

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.

From that they worked out that gravity does move at the same speed as light. Their actual figure was 0.95 times light speed, but with a large error margin of plus or minus 0.25.

Their result, announced on Tuesday at a meeting of the American Astronomical Society meeting in Seattle, should help narrow down the possible number of extra dimensions and their sizes.

But experts say the indirect evidence that gravity propagates at the speed of light was already overwhelming. "It would be revolutionary if gravity were measured not to propagate at the speed of light - we were virtually certain that it must," says Lawrence Krauss of Case Western Reserve University in Cleveland, Ohio.

Hazel Muir

 

[TheEngineer]

Hi !

Well, the story developed further (Kopeikin & Co. made some errors in their derivations..):

http://metaresearch.org/media%20and%20links/press/SOG-Kopeikin.asp
http://www.arxiv.org/pdf/astro-ph/0304006

Regards,

TE

 

[Dunryc]

Quite interesting ...

 

[aramis]

Thanks, TE... Gravity as FTL, measured by angle of incidence versus angle of pull. Spiffy! (Kokeikin, 2006.)

 

[Richard Saunders]

Hello.
Just a though, if gravity travels at the speed of light how do's it get out of a black hole.

Now back to traveller.
If you surmise that jump space is a part of our universe then you must surmise that anything (with a jump drive or the equivelent) can travel FTL.
If gravity travels FTL then FTL coms is possible and should have been discovered thousands of years ago(traveller).
If on the other hand gravity dosn't travel FTL then the universe would be picking up a nasty harmonic from all the jumping and loss of material in jump space.
100000 tons jumps out and starts a ripple in gravity waves a week latter the same 10000 tons arives 3 light years away and another ripple starts (yes minus the fuel) now multiply this by several thousand every week think of the ripples (the highs and lows) AR a job for the Imperial Science Academy.
NASTY THOUGHT.
If you timed the ripples just right and used large enough ships you could probably send a sun nova (grav ripples combining to raise the gravity inside a sun BOOM, or offset the ripple and a solar flare (where have i heard this before) clears a planet for you.
Bye

 

[mike wightman]

I think I like your grav ripples effect to explain the Darrian Star Trigger more than the official version.

 

[aramis]

Lionel: Gravity doesn't affect gravity...

 

[Anthony]

No, gravity would probably affect gravity waves just fine. Gravity doesn't prevent the transmission of field effects via virtual particles -- a black hole's magnetic field can also get out.

 

[mike wightman]

Here's a link that may help to answer some of these questions.

And many thanks to Malenfant for providing the link

 

[mike wightman]

And here's one all about "Does Gravity Travel at the Speed of Light?"

http://math.ucr.edu/home/baez/physics/Relativity/GR/grav_speed.html

Thanks again Mal.

 

[aramis]

Interesting that Carlip, Wiener & Landis is 1998 dated, Sigg.

Elegant Universe is ©2003.

It would seem, Malenfant's ghost appearance aside, that the issue is STILL debated.

Kopekein is 2003.
Van Flanderm is 2004
Samuels is 2003, post Kopelein

So, in typical fasion, Mal argues there "is no debate", cites old works, and ignores the current papers, but this time with Mike (Sigg) as mouthpiece...

BTW, kepekein works out just a hair OVER C...

And I can't follow the math, but I can follow the non-math arguments wrapped around it.

It boils down to:
</font>

• It can't be tested with current instruments (Samuels, Van Flanders)</font>
• Our theories break down if it isn't (GR based arguments)</font>
• If gravity isn't instant, orbital dynamics fails (Van Flanders)</font>
• Kopeikin only tested one case in the observation, but the answer is different based upon frame of reference. (Samuels)</font>
• there has been debate for the last decade (samuels)</font>

now the Carlip, Wiener and Landis paper was interesting, and provides a decent basis for grasping the materials in the later works.

In short, neither side has proven much of anything, other than it is still debatable.

 

[mike wightman]

He posted them to the T5 and the Avenger websites, and I thought they'd be of interest here

AFAIK the physics jury is still a long way from accepting string theory as anything more than a theory, and there have been noises made in physics circles that it may not work out after all, and that new theories are going to be needed.

 

[mike wightman]

The Chronicle of Higher Education has this intro:

Two new books have cast a hot, critical light on the validity of string theory. Lee Smolin and Peter Woit both argue that string theorists have never generated any empirical evidence verified by expeimentation. Furthermore, Smolin and Woit lament that the dominance of string theory in physics departments has led to intellectual stagnation, stifling progress in other research areas. Not surprisingly, string-theory advocates have been busy rebutting this tide of anti-string sentiment.

I remember when string theory itself was a fringe theory...

Here's a link to the Observer/Guardian article on the subject of the new books:

http://observer.guardian.co.uk/uk_news/story/0,,1890340,00.html

 

[aramis]

In many ways, it still is a fringe theory. More recent films (2004, 2005) have shown that several major departments do not have strong support for string theory, and never have. Further, it's still debated just how many dimensions are needed to make it work... (Based upon a 2005 Discovery program on String Theory.)

It has, however, been a media darling... as the popular media was used to get the scientific media to even consider it.