Direct Measurement of Gravitational Wave Velocity

chill_factor

http://www.spacedaily.com/reports/Ch...avity_999.html

Done by the Institute of Geophysics at the Chinese Academy of Sciences using earth tide measurements. The conclusion is that it is the speed of light.

http://en.wikipedia.org/wiki/Earth_tide

I believe this is different from the previous measurements based on binary pulsars which were theory dependent.

Bill_K

Sorry, this is baloney.

chill_factor

can you explain? perhaps the original paper will be of more use, but it is not out yet i think.

Bill_K

Their idea is that during a total solar eclipse, at the precise moment when the moon covers the sun, there is a considerable fluctuation in the gravitational field. (There isn't!) Previously they have reported seeing this in geophysical measurements of the Earth tides, and now they have gone further and claimed their data shows an 8 minute delay.

Needless to say, the solar gravitational field is not affected when the moon's disk slides in front of the sun.

Mentz114

The article does not mention gravitational waves. They seem to be talking about changes in the tidal field caused by changes of configuration elsewhere.

[Edit]I just saw Bill's post - I didn't realize they made such an absurd claim.

K^2

Bill, could you link to the abstract?

chill_factor

from your explanation this seems like its bad science.

however I've found that there may be an analogous effect here that DOES cause an observable (and what some think is a gravitational) anomaly:

https://en.wikipedia.org/wiki/Allais_Effect

could these effects possibly be related in some way, or is this really just bad science that got through the filters? my background is not in this particular area of physics, so I hope you can explain.

Bill_K

I couldn't find a real paper, but here's another popular account of what the group headed by Tang Keyun aims to do.This does seem to be related to the "Allais Effect". My guess would be that thermal fluctuations due to passage of the moon's shadow are probably to blame for things like this.

Vanadium 50

Chill_factor, you're piling bad science on top of bad science - as well as demonstrating what's wrong with Wikipedia.

Some lines from the article: "subsequent attempts to replicate this experiment ... failed to observe any effect", "but his report was not published in a mainstream English-language scientific journal", " – but the article has not undergone any peer review."

DaleSpam

Don't blame Wikipedia for that, the article specifically mentions multiple times in multiple different ways that the effect is not confirmed. This is a simple case of mis-citation, i.e. citing a source that does not actually support the point being made.

D H

Here: http://link.springer.com/article/10....434-012-5603-3
This is an open access journal; the PDF is freely available.

And it's pure excrement, as Bill_K already said.

D H

Amongst the many things the authors did wrong:

• Not understanding general relativity.
  Merely adding a lag for the finite speed of light to Newton's law of gravitation results in an easily falsifiable model. Newtonian gravity, with no time lag at all, is much closer to being correct than is Newtonian gravity with a time lag. There's a whole lot more the GR than just a finite speed of gravitation. Other elements of the theory make that finite propagation time essentially unobservable for objects such as the Earth that orbit at small velocities (relative to c) and at large distances from a gravitating body (relative to the Schwartzchild radius).
• Using the apparent positions of the Sun and Moon to calculate Earth tides.
  Because gravitation from the Sun and the Moon on the Earth is nearly Newtonian, one needs to use the "true" positions of the Sun and Moon rather than their apparent positions to properly model the Earth tides.

If the bulk of the authors' work is correct (and that's a mighty big if), what they have accomplished is a fairly low accuracy measurement of the speed of light, not the speed of gravitation.

K^2

Bwahahahahahahahaha...

Sorry. I think I'm done... Nope... Bwahahaha.

Ok, now I'm done. Apologies, but I just can't hold it.

Their premise is, basically, that because there is an 8 minute and change lag between light being emitted and light reaching Earth, the Sun's apparent position in the sky lags by 8 minutes and change.

I'll let everyone think about that for a moment.

Furthermore, same lag should be expected for gravity (!!!) so they look at when the sun is at highest point, compare it to highest gravitational tide, and conclude that since they found no significant phase shift between the two, speed of light is equal to the speed of gravity.

Somebody needs to tell these people that Sun doesn't revolve around the Earth. They do not appear to realize that.

D H

You are being far too kind. This paper is far worse than just a couple of "bwahaha"s. It is 100% pure excrement.

Which is wrong. This is their erroneous equation (1).

Which is also wrong. This is their even more erroneous equation (2).

There's nothing wrong with looking at the Sun from the perspective of a fixed Earth. Regardless of how you look at at, you will get an annual aberration of the Sun of about 20.5" of arc. That's the difference between the true and apparent positions of the Sun as observed from the Earth.

The problem is that this pertains to light, not gravity.

The authors' equation (1), their so called "practical Newtonian formula of the solar tidal force", is flat out incorrect. Gravitation in Newtonian mechanics is instantaneous. Correcting for a finite transmission speed without incorporating all of the rest of general relativity is wrong. Their equation (2) is also flat out invalid. That's not how the Earth tides work.

Another minor problem: Their phase differences are all over the map. They don't have data. They have garbage.

Garbage in + garbage model = two piles of garbage out.

A.T.

We had that discussion here already:
http://www.physicsforums.com/showthr...90#post3594190

K^2

There is nothing wrong with it if your equations for linearized gravity include covariant derivative with respect to your accelerated frame of reference.

If you use Newtonian Gravity with retarded potentials to describe Earth-Sun system from perspective of fixed, static Earth, there is a lot wrong with it.
You don't need full-blown GR. Retarded potentials work in linearized gravity just as well as they do in electrodynamics. That part of their assumption isn't completely wrong in inertial frame of reference. In accelerated frame of reference, things get more complicated.

D H

We're talking at cross-purposes here. You left out a key part of my response to post #13. What you left out is "The problem is that this pertains to light, not gravity." The "this" to which I referred was the annual aberration of the Sun, not gravitation. Sorry if I wasn't clear on the context.


Agreed. Yet this is exactly what they did with their equation (1). They started out on a very wrong footing and got even more wrong as the paper progressed.