Speed of Gravity, part 2

[blike]

Someone pointed out this paper to me, what are your thoughts on it?

 

I've never taken any physics courses, so I can't really accurately assess his points...what do you guys think?

 

"Why do photons from the Sun travel in directions that are not parallel to the direction of Earth's gravitational acceleration toward the Sun? Why do total eclipses of the Sun by the Moon reach maximum eclipse about 40 seconds before the Sun and Moon's gravitational forces align? How do binary pulsars anticipate each other's future position, velocity, and acceleration faster than the light time between them would allow? How can black holes have gravity when nothing can get out because escape speed is greater than the speed of light?"

 

The Speed of Gravity - What the Experiments Say

 

Abstract

Standard experimental techniques exist to determine the propagation speed of forces. When we apply these techniques to gravity, they all yield propagation speeds too great to measure, substantially faster than lightspeed. This is because gravity, in contrast to light, has no detectable aberration or propagation delay for its action, even for cases (such as binary pulsars) where sources of gravity accelerate significantly during the light time from source to target By contrast, the finite propagation speed of light causes radiation pressure forces to have a non-radial component causing orbits to decay (the "Poynting-Robertson effect"); but gravity has no counterpart force proportional to v/c to first order. General relativity (GR) explains these features by suggesting that gravitation (unlike electromagnetic forces) is a pure geometric effect of curved space-time, not a force of nature that propagates. Gravitational radiation, which surely does propagate at lightspeed but is a fifth order effect in v/c, is too small to play a role in explaining this difference in behavior between gravity and ordinary forces of nature. Problems with the causality principle also exist for GR in this connection, such as explaining how the external fields between binary black holes manage to continually update without benefit of communication with the masses hidden behind event horizons. These causality problems would be solved without any change to the mathematical formalism of GR, but only to its interpretation, if gravity is once again taken to be a propagating force of nature in flat spacetime with the propagation speed indicated by observational evidence and experiments: not less than 2 x 1010 c. Such a change of perspective requires no change in the assumed character of gravitational radiation or its lightspeed propagation. Although faster-than-light force propagation speeds do violate Einstein special relativity (SR), they are in accord with Lorentzian relativity, which has never been experimentally distinguished from SR-at least, not if favor of SR. Indeed, far from upsetting much of current physics, the main changes induced by this new perspective are beneficial to areas where physics has been struggling, such as explaining experimental evidence for non-locality in quantum physics, the dark matter issue in cosmology, and the possible unification of forces. Recognition of a faster-than-lightspeed propagation of gravity, as indicated by all existing experimental evidence, may be the key to taking conventional physics to the next plateau.

[Giles]

That's really interesting.

 

Following the links, though, it looks like the author's personal hobby horse, which always inclines me to be skeptical.

[blike]

bump

[fafalone]

The recent measurement said c=v_g within 20%, and not only is that wildy inaccurate (since we can measure c to many decimal places), but it was published in New Scientist; why not in Science or Nature or an APS journal?

[JaKiri]

New Scientist's nice and politicy.

[Kedas]

from this article: http://www.spacedaily.com/news/gravity-03d.html

"With the correct formula, the effects of the motion of Jupiter on the quasar-signal time-delay are at least 100 times and perhaps even a thousand times smaller than could have been measured by the array of radio telescopes that Fomalont used," Samuel says.

 

Did they measered it with only 20% accuracy.

Then we know it's about the same as c. (and very likely equal)

 

But they also say their instruments weren't accuracy enough to measure it. so what is it ?

- about the speed of light. (but don't know exactly)

OR

- No idea ,we couldn't measure it because difference was to small.

 

And if second shouldn't they have know that before the experiment that they wouldn't be able to measure it.

They had two options c speed or infinite.

if the difference between the two assumtion can't be measured then why doing it?

 

P.S. administrator I don't receive email notifications although that they are enabled

(I know I should mail him/her but want to know if he/her reads this )

[Sayonara]

Originally posted by Kedas

P.S. administrator I don't receive email notifications although that they are enabled

(I know I should mail him/her but want to know if he/her reads this )

Obviously the first thing you should do is check that you have entered the correct e-mail address in your personal control panel.

 

Also bear in mind that sessions for this forum expire after 20 minutes with no activity, unless you log out when the session is terminated. So if you make a post then close your browser and go off and do something away from the PC, the forums still think you're logged in and will not bother sending out a mail for replies until after the 20 minute session expires (did that make sense?).

 

The third possibility is that your mail service automatically deletes mails they think are spam (a lot of automatically generated server mails get trapped this way - it depends if your mail service use reverse-DNS lookups to authenticate the source of an email).

 

I know e-mail notification is working because I get them for certain threads, along with other auto-generated mails.

[Kedas]

found some interesting things to read about it:

from http://www.metaresearch.org/media%20and%20links/press/SOG-Kopeikin.asp

 

n S. Kopeikin misquotes Van Flandern as predicting that cg (Kopeikin?s ?speed of gravity?) will be infinity. Van Flandern and Vigier are in print showing that six experiments better than Kopeikin?s already show that the speed of gravity is >> c (c = speed of light). But in posted discussions with Kopeikin and in USENET newsgroups, Van Flandern clearly states that Kopeikin?s ?cg? parameter cannot be the speed of gravity and will certainly come out near the value c, as it did.

it's an interesting site

 

So they did measure the speed of light and not the speed of gravity like they claimed. :lame:

 

BTW I like the idea of gravity being much faster than light.

 

[Dave]

Well it's like the guy said, we may not even have the technological capability yet to discover how fast the speed of gravity is - unless, of course, someone comes up with a viable method that is relatively easy to implement.

[Kedas]

Did some more reading:

they have two gravitational speeds:

 

1) The speed of gravitational radiation/waves is.

= speed of c (no one seems to doubt this)

 

2) gravitational force or acceleration.

>> c

 

anyone that can clearly explain this difference to me ?

 

edit:

found more or less the answer

 

http://archive.ncsa.uiuc.edu/Cyberia/NumRel/GravWaves.html

What are Gravitational Waves?

Predicted in Einstein's General Theory of Relativity , gravitational waves are disturbances in the curvature of spacetime caused by the motions of matter. Propagating at (or near) the speed of light, gravitational waves do not travel "through" spacetime as such -- the fabric of spacetime itself is oscillating. Though gravitational waves pass straight t hrough matter, their strength weakens proportionally to the distance traveled from the source. A gravitational wave arriving on Earth will alternately stretch and shrink distances, though on an incredibly small scale -- by a factor of 10e-21 for very strong sources. That's roughly equivalent to measuring a change the size of an atom in the distance from the Sun to Earth!