Quoth TVF:
Clifford Will's abstract:

Will's criticism is not of the actual experiment which was not a time delay at all but a spatial distortion and clearly measurable. The paper should be out on astro-ph within a few months and so it should be clearer then. However, the gist is Will's criticism is a criticism of a different test.

AB: Those "desired conditions" are imposed by their scheme limitations and by the fact that their first intention was to measure the phase velocity.

Not a chance. It makes no difference at all whether you are dealing with a mass on a spring or a vibrating crystal. They are both simple harmonic oscillators. The equation presented on page 11 is general, and not at all tied to the experimental setup. This should be obvious. I stand uncorrected, and stand by what I said before. The low mass & high frequency setup you propose is less efficient & less productive than a system with lower frequency & higher mass.

AB: You really should read somewhat deeper into the details of their experiment and my proposed modification before you start casting your superficial opinions.

You should try following your own advice someday.

LJ: I think you have this backward. ...

Well, at least I was right when I said that we should know the difference!

Agora: "DStahl, I believe Dunash commented on the thread subject and the earlier discussion that's before our W/D issue."

D'oh! Of course you are correct--I must have had blinders on. Dunash, with Agora's help I understand now, and I do tend to agree. The math both supporting and attacking the observation as a test of gravitational propagation is too many for me.

Wiley--You're welcome!

JS,
You must be very sure of what you say here... I'm not yet through the details, but from general considerations I'd say that differential time delays do appear as a spatial distortion to the "observer".

This is worse than wrong! The U*w^2, where U - amplitude and w - frequency, is a constant defined by transmitter material strength (since it's acceleration -> force), thus that dependence of 1/w^2 in amplitude is a phantom and U*w^2 is a direct linear measurable. Furthermore, it's quite obvious that the phase shift caused by signal delay t goes as t*w, i.e. phase-shift sensitivity goes up with frequency, page 10 of the preprint states it clearly as well.

Now on to their scheme specifics - they use transverse oscillations of long heavy bars of quartz. Mechanical strength of those bars against such kind of load is very low compared to quartz's ability to withstand direct longitudinal compression, stress forces at maximum amplitudes are simply incomparable for those types of oscillation - difference of many orders of magnitude. Thus their only hope was to read out the amplitude at lowest frequency thus using up the material strength to the max. Hence your erroneous interpretation.

Now, Tim, you are thoroughly proven wrong. It's the second time I tell you - you are dead wrong on those particular issues. All because you simply refused to think it over. Your move?

<font size=-1>[ This Message was edited by: AgoraBasta on 2003-01-12 09:58 ]</font>

<font size=-1>[ This Message was edited by: AgoraBasta on 2003-01-12 10:52 ]</font>

Well, all I know is that at the talk at AAS this very issue was addressed. The team did not observe a time delay which was another proposed experiment, rather a distinct angular distortion of the image. This is to be expected from any tensor model of GR, but his specific result can only be true if there gravity with finite speed.

Guess we just have to wait for the full report, too many questions and too much open for speculations.

The Walker-Dual thought plickens! Here's the abstract from a paper by William D. Walker, posted to the archive Sept. 2000:

"A simple experiment is presented which indicates that electromagnetic fields propagate superluminally in the near-field next to an oscillating electric dipole source. A high frequency 437MHz, 2 watt sinusoidal electrical signal is transmitted from a dipole antenna to a parallel near-field dipole detecting antenna. The phase difference between the two antenna signals is monitored with an oscilloscope as the distance between the antennas is increased. Analysis of the phase vs distance curve indicates that superluminal transverse electric field waves (phase and group) are generated approximately one-quarter wavelength outside the source and propagate toward and away from the source. Upon creation, the transverse waves travel with infinite speed. The outgoing transverse waves reduce to the speed of light after they propagate about one wavelength away from the source. The inward propagating transverse fields rapidly reduce to the speed of light and then rapidly increase to infinite speed as they travel into the source. The results are shown to be consistent with standard electrodynamic theory." [emphasis added]

Interesting, huh? Here are links to the abstract in html format and to the full paper in pdf format.

At the end of this paper Walker suggests that equivalent physics should hold for oscillating magnetic and gravitational fields. This wouldn't seem to be a big deal--the physics he is investigating fall within one wavelength of the source, and according to his analysis neither SR nor causality are violated by the superluminal propagation he describes (incidentally, he has published one other paper in which he shows this in detail). However, Walker also echoes some of Van Flandern's arguments:

"Light from the sun is not observed to be collinear with the sun's gravitational force. Astronomical studies indicate that the earth's acceleration is toward the gravitational center of the sun even though it is moving around the sun, whereas light from the sun is observed to be aberated (sic). If the gravitational force between the sun and the earth were aberated then gravitational forces tangent to the earth's orbit would result, causing the earth to spiral away from the sun, due to conservation of angular momentum. Current astronomical observations estimate the phase speed of gravity to be greater than 2X10¹⁰ c. Arguments against the superluminal interpretation have appeared in the literature [9, 10]." (emphasis added)

(The last sentence has references to Steve Carlip's paper (abstract in html, full paper in pdf and "The Speed of Gravity Revisited" by Ibison, Puthoff, and Little (abstract in html, full paper in pdf).

Very interesting! This is literally the first time I have read a physicist of any stripe who agrees with Van Flandern. (Incidentally, in my browsing I note that there are at least three William D. Walkers who do research in the general realm of physics, so if anyone wishes to contact the author of the paper quoted above, make sure you get the one teaching at the Kungl Tekniska Hogskolan (Royal Institute of Technology) at Stockholm Sweden and not the professor emeritus at Duke University!)

<font size=-1>[ This Message was edited by: DStahl on 2003-01-11 20:34 ]</font>

There's a neat animated demonstration of superluminal phase velocity at one of Greg Egan's pages.

<a name=""> page= aka
On 2003-01-11 22:25, DStahl wrote:
There's a neat animated demonstration of superluminal phase velocity at one of Greg Egan's pages.
------------------
I sure wish you'D put the direct(downloadable) link to the?
.jpg, .mov, .mpg, .map {whatever its called}
I cant seam to find what you've refered to..
{although I did try} (for 2 mili.S) 10:15 A.M.
now where was I? oh yeah / : __ ? ~-_
my guess the form may be ?.....?....?...?..?.

Sorry HUb', in this case it looks like there's no link because it's an imbedded java applet. There's nothing to download.

__________________
...And that, my liege, is how we know the Earth to be banana-shaped. --Sir Bedevere

Darn it HUb', Davic's right--the demo just can't be displayed outside a Java-enabled browser like Netscape, Internet Explorer, Mozilla, or the like. Sorry about that.

What it shows is a rectangle with a dozen or so colored sine waves sliding along the top, each moving at a slightly different speed. (I guess that was easier than making them co-moving and slightly different wavelengths, but it doesn't matter.) At the bottom of the rectangle is a compound wave built by summing all the waves. As the small series of sine waves slide slowly across the top of the screen you see that the coincidence of peaks and troughs creates periodic forms in the summed wave, forms which move much faster than any of the small sine waves.

Hub', try loading this .jpg image: http://frogshop.hypermart.net/phase1.jpg. It isn't animated, but it shows a still-shot of the demo.

<font size=-1>[ This Message was edited by: DStahl on 2003-01-12 17:35 ]</font>

It appears that Will's critique is aimed specifically at this Kopeikin's preprint. BTW, Will literally tears Kopeikin apart...

So do you, JS, say that they had yet another "spare" interpretation ready to fight back?

Will's critique is not valid, according to Kopeikin, because of an error in experimental set-up analysis on the part of Will. In effect, Will doesn't believe that the experiment is sensitive enough. Indeed, the experiment needs to be sensitive to the microarcsecond level. This is pretty ridiculous, but was, in fact, done.

I just got a Nature Science update on this topic. Maybe nothing new but I'm throwing it in anyway. [img]/phpBB/images/smiles/icon_smile.gif[/img]

http://www.nature.com/nsu/030106/030106-8.html

__________________
...And that, my liege, is how we know the Earth to be banana-shaped. --Sir Bedevere

"If the speed of gravity were infinite, Kopeikin predicted that the quasar should have traced a perfect circle in the sky as Jupiter passed. If gravity had some finite speed, this circle would distort into an ellipse."

And, one assumes, the deviation of the shape of the ellipse from a perfect circle would reveal something about the amount by which the speed of gravitational propagation falls short of instantaneousosity?

If one imagines the momentum of Jupiter distorting its gravitational field--its "spacetime dimple"--in a manner consistent with retarded-field theory, then one can get a feel for how the perfectly symmetrical circular figure produced by deflection of the quasar's light under a non-retarded-field regime would be transformed into an ellipse. Or so my mind's eye insists.

Reference: Propagation Speed of Longitudinally Oscillating Gravitational and Electrical Fields. Anyone trying to follow will have to download the paper to see the equations. If the paper was ever published, I can find no record of it.

AgoraBasta: This is worse than wrong! The U*w^2, where U - amplitude and w - frequency, is a constant defined by transmitter material strength (since it's acceleration -> force), ...

I would say that your description here is indeed worse than wrong. You really should try not to be so belligerent, when you present such poorly considered arguments.

I'm not at all sure what you are talking about, but I am talking about the only equation (itself un-numbered) on page 11 of the previously referenced paper. The diagram on the previous page presents the physical model, a damped spring, simple harmonic oscillator.

One of the first things you learn in your first course in physics is that all simple harmonic oscillators obey what is called the "simple harmonic oscillator equation". How they are built does not affect the form of the equation, but will affect the values assigned to factors in the equation.

So, since that equation is derived directly from a simple harmonic model, and since all simple harmonic models obey the same equation, then the equation I reference is always true for all simple harmonic systems, regardless of how they are built.

Now, since that equation has the transmitter frequency (w_tx) in the denominator, we realize that making w_tx smaller will make the term larger. And since the transmitter mass (m_tx) is in the numerator, we realize that making m_tx larger will make the term larger.

Hence, by dint of first year physics & grade school arithmetic, we come to the conclusion that making m_tx larger, and/or w_tx smaller, both work to make the amplitude of the receiver mass vibration (u_ac) larger, since it's on the other side of the equation. And this conclusion is explicitly delivered on page 11 of the referenced paper, in the paragraph immediately following the equation.

Agorabasta: ... thus that dependence of 1/w^2 in amplitude is a phantom and U*w^2 is a direct linear measurable.

So, having thoroughly misunderstood the physics involved, now you are tellng the authors of the paper that they have "phantoms" in their equation? Perhaps you would care to write your own paper and model the system "correctly"? You are allowed to do that, you know.

Agorabasta: Furthermore, it's quite obvious that the phase shift caused by signal delay t goes as t*w, i.e. phase-shift sensitivity goes up with frequency, page 10 of the preprint states it clearly as well.

I can see no such statement, clear or otherwise on page 10. Feel free to be more specific. But even if you are right, you are only looking at half the problem. If the receiver amplitude is too small to measure, you won't see the phase shift at all, regradless of how favorable the frequency is.

And keep in mind that the equation I am referencing is for the amplitude of the receiver vibration, not its frequency.

AgoraBasta: Now on to their scheme specifics - they use transverse oscillations of long heavy bars of quartz. Mechanical strength of those bars against such kind of load is very low compared to quartz's ability to withstand direct longitudinal compression, stress forces at maximum amplitudes are simply incomparable for those types of oscillation - difference of many orders of magnitude. Thus their only hope was to read out the amplitude at lowest frequency thus using up the material strength to the max. Hence your erroneous interpretation.

The erroneous interpretation is yours, not mine. You have erroneously decided that the transmitter frequency should be high, when in fact it should be low (if you want to increase receiver amplitude). So the entire discussion in this paragraph is irrelevant, since it is basd on your initial misinterpretation.

And in any case, I have no idea what the mention of mechanical strength has to do with anything.

AgoraBasta: Now, Tim, you are thoroughly proven wrong. It's the second time I tell you - you are dead wrong on those particular issues. All because you simply refused to think it over. Your move?

I have in fact thought it over quite a lot, and even gave a short talk on the subject a few days ago. I may even do another one. You are the one who is dead wrong. Maybe you just are in over your head. It certainly looks like you don't understand the basic physics, and are simply confusing yourself over irrelevant details, and issues divorced from the fundamentals of the problem.

It would appear that you are hung up on the receiver frequency. You want to maximize the frequency, perhaps to maximaze the phase shift. But that won't help if you can't se the amplitude. You have to find a happy medium, where the amplitude & phase shift are both above the noise at a detectable level. If that is indeed the case, you might have said so earlier.

Exactly the physics you don't understand.
Let A be amplitude of position, then
amplitude of velocity is Aw,
amplitude of accelerations is Aw^2,
amplitude of force mAw^2.
Hence sensitivity depends on quantity you measure. So I pick up the force since it's as direct an observable as is position.

In the W/D scheme they bend a long piece of quartz. Think for yourself, how would you destroy a long stick of quartz - by bending it or by compressing it axially? <- These two processes require very different values of force to destroy the sample, difference is of many orders of magnitude. And don't you forget that we need to push the transmitter to the max stress to get a sizable readout, so it's the max force it can stand that really limits us here.

Now on to the bandwidth and noise and phaseshift sensitivity - noise goes with bandwidth as w^1/2 in linear values(counting from zero Hz), phaseshift sensitivity goes as w, so their common effect goes as w/(w^1/2) = w^1/2 <- it's better with frequency.

So, Tim, how much longer are you going to stubbornly deny the obvious?

<font size=-1>[ This Message was edited by: AgoraBasta on 2003-01-17 10:25 ]</font>

http://www.space.com/scienceastronom...ed_030116.html
This link speaks for itself.