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nebularain
2003-Jan-08, 06:30 PM
...the speed of light!

http://www.cnn.com/2003/TECH/space/01/08/gravity.speed.ap/index.html



Edward B. Fomalout of the National Radio Astronomy Observatory and Sergei Kopeikin of the University of Missouri measured the amount that light from a distant star was deflected by the gravity of Jupiter as the planet passed in front of the star.

Albert Einstein, who formulated basic theories about space, time and relativity, had assumed that gravity moved with the speed of light, about 186,000 miles (300,000 kilometers) per second, "but until now, no one had measured it," said Kopeikin.

"Einstein was right, of course," said Fomalout.

AgoraBasta
2003-Jan-08, 06:35 PM
Those guys were sufficiently debunked well before they "measured" that thing - http://metaresearch.org/media%20and%20links/press/SOG-Kopeikin.asp

Jim
2003-Jan-08, 07:29 PM
On 2003-01-08 13:35, AgoraBasta wrote:
Those guys were sufficiently debunked well before they "measured" that thing -


"Sufficiently debinked?" If you care to believe Van Flandern... who has also been "sufficiently debunked."
http://math.ucr.edu/home/baez/RelWWW/wrong.html#speed
http://www.arXiv.org/abs/gr-qc/9909087
http://www.arXiv.org/abs/physics/9910050

TVF, btw, needs to learn how to write a proper abstract for a science paper. This one reads more like the opening arguments by a prosecuter.

AgoraBasta
2003-Jan-08, 07:39 PM
On 2003-01-08 14:29, Jim wrote:
"Sufficiently debinked?" If you care to believe Van Flandern...Do you care to believe Kopeikin? And what about the Japanese guy TVF mentioned? And what you personally read about the issue in question?

Laser Jock
2003-Jan-08, 08:20 PM
On 2003-01-08 13:35, AgoraBasta wrote:
Those guys were sufficiently debunked well before they "measured" that thing - http://metaresearch.org/media%20and%20links/press/SOG-Kopeikin.asp


Maybe they were debunked, maybe they weren't. As far as TVF is concerned, anyone who thinks the "face" on Mars is real has "issues." /phpBB/images/smiles/icon_wink.gif

http://metaresearch.org/solar%20system/cydonia/proof_files/proof.asp

DStahl
2003-Jan-08, 09:05 PM
Agora, we had quite a thread involving Van Flandern and his superluminal gravitation hypothesis. I got bored with the exchange after a while, but every physicist I polled said that TVF's physics is wrong at a very basic level--specifically, his proposal eliminates the effect of a moving body on the vector of electrical or gravitational interaction. However, in the first half of the 20<sup>th</sup> century this effect was shown to be a necessary part of the conservation laws; superluminal gravity would, then, violate basic physics. TVF could not or would not provide any mathematical justification for his position, nor could he mathematically refute analyses which had shown him to be wrong.

However, neither would he admit that he could not offer a refutation--he retreated into obfuscation, which is when I lost interest in (and any remaining respect for) his work.

AgoraBasta
2003-Jan-08, 09:20 PM
On 2003-01-08 16:05, DStahl wrote:
Agora, we had quite a thread involving Van Flandern and his superluminal gravitation hypothesis.I also think that TVF hasn't yet got it exactly right, though I still haven't read his last attempt, the one written together with Vigier.
Still no-one yet provided a satisfactory explanation for Walker-Dual experiment. And what's worse, is that nobody ever measured the gravity speed directly in a simple laboratory experiment which is quite possible.

JS Princeton
2003-Jan-08, 10:39 PM
Once again Agora is parading his ignorance of the subject and engaging in the art of selective criticism rather than taking the time to actually come down from his throne of blind balking and actually learn for a change. I just attended the AAS talk (that can be looked up on NASA ADS search) on measuring the speed of gravity by using lensing of a quasar due to Jupiter by the very same S. Kopeikin (University of Missouri-Columbia) and E. B. Fomalont (NRAO). They do provide a beautifully conclusive upper-bound on the speed of gravity at 1.06+0.12 times the speed of light while the lower-bound has been suffienently proven to rest at "c". This is further confirmation of the binary pulsar observation that showed the existence of gravitational radiation that also must (assuming the correctness of Einstein's GR) travel at the velocity of the speed of light. Of course, this was not a direct measurement of the speed, so it is nice that Fomalont provided one. As far as I'm concerned, Agora's naysaying is just a temper-tantrum as the other "alternatives" have been sufficiently shown untrue or have been outright discarded. If Agora refuses to see that, it is his problem.

So basically, if the speed of gravity is not the speed of light it is tantalizingly close and nowhere NEAR infinity which is the model most often embraced by certain whackos who shall remain nameless.

I like the conclusion: Einstein was right!

<font size=-1>[ This Message was edited by: JS Princeton on 2003-01-08 17:46 ]</font>

AgoraBasta
2003-Jan-08, 11:48 PM
JS,

You may believe whatever you choose. But the speed of gravity may and must be measured directly in a laboratory. That would be far cheaper and totally unambiguous a result.

DStahl
2003-Jan-09, 12:57 AM
Agora, you write that the speed of gravity should be measured in a laboratory experiment (rather than inferred from astronomical observation) as it would be more direct and "cheaper."

Steve Carlip writes, "To begin with, the speed of gravity has not been measured directly in the laboratory---the gravitational interaction is too weak, and such an experiment is beyond present technological capabilities. The "speed of gravity" must therefore be deduced from astronomical observations, and the answer depends on what model of gravity one uses to describe those observations." Reference (http://math.ucr.edu/home/baez/physics/Relativity/GR/grav_speed.html) (Incidentally, there is a record of a forum exchange between Steve Carlip and TVF on the subject of gravitational propagation here. (http://users.pandora.be/nicvroom/speedgr.htm))

The proposal for and mathematical explanation of the recent experiment can be read (as a PDF document) at this page. (http://www.mpifr-bonn.mpg.de/div/vlbi/evn2002/book/SKopeikin.pdf) I note that even taking advantage of body with the mass of Jupiter the experiment still required measurements with "the precision of a few picoseconds."

I'm curious exactly what apparatus you would use to conduct a laboratory measurement of the speed of gravitational propagation, Agora.

Chip
2003-Jan-09, 01:12 AM
On 2003-01-08 18:48, AgoraBasta wrote:
"...the speed of gravity may and must be measured directly in a laboratory. That would be far cheaper and totally unambiguous a result."

Actually they did do the experiment in a "laboratory" on earth. They needed enough room, as its very difficult to construct something equivalent to Jupiter's gravity well on the workbench, so their "lab" consisted of 10 radio telescopes placed around the world, a powerful distant quasar light source, and the planet Jupiter "in the precise position for such a measurement only once a decade." The results, though very small were also "totally unambiguous." /phpBB/images/smiles/icon_wink.gif

2003-Jan-09, 02:04 AM
?
On 2003-01-08 16:05, DStahl wrote:
to? 6:14 P.M. PST





1
0

2003-Jan-09, 02:08 AM
<a name="JD2452648.G"> page JD2452648.G aka G
On 2003-01-08 16:20, AgoraBasta wrote:

On 2003-01-08 16:05, DStahl wrote:
Agora, we had quite a thread involving Van Flandern and his superluminal gravitation hypothesis.I also think that TVF hasn't yet got it exactly right, though I still haven't read his last attempt, the one written together with Vigier.
Still no-one yet provided a satisfactory explanation for Walker-Dual experiment. And what's worse, is that nobody ever measured the gravity speed directly in a simple laboratory experiment which is quite possible.
[/quote]
Sure I measured this.. more than once
My number was 50 hrs +/- 2 Sun to Earth
for X-Class flares {durring Max's}Mack
Next ? 6:19 P.M. PST get it strait

RickNZ
2003-Jan-09, 02:15 AM
Perhaps u gentlemen (or ladies?) could help me out. (an ignorant person)

Objects approaching C gain infinite mass therefor...
light has no mass (im assuming here, alternative in my mind was infinite mass *cough*)

How is it that light is effected by gravity which works on mass?

I realise im oversimplifying things but thats the level i work at /phpBB/images/smiles/icon_wink.gif So please set me straight.

[confused reader]

Tim Thompson
2003-Jan-09, 02:18 AM
AgoraBasta: You may believe whatever you choose. But the speed of gravity may and must be measured directly in a laboratory. That would be far cheaper and totally unambiguous a result.

A nice idea, but impractical. there is no existing technology for measuring the speed of gravity in a local laboratory environment. Indeed, the difficulties encountered in measuring the force of gravity (let alone the speed of same), is the reason why the gravitational constant (http://www.npl.washington.edu/eotwash/gconst.html) G is the most imprecisely known of the fundamental constants (http://physics.nist.gov/cuu/Constants/).

But there is nothing wrong with inferring the speed of gravity from astronomical observations, and it should be quite a robust means of doing so.

For instance, if the speed of gravity is finite, then there should be gravitational radiation (http://math.ucr.edu/home/baez/physics/Relativity/GR/grav_radiation.html), as predicted by general relativity (http://www-gap.dcs.st-and.ac.uk/~history/HistTopics/General_relativity.html). If, on the other hand, the speed of gravity is infinite (as TvF claims), then there should be no gravitational radiation and general relativity is wrong.

So, consider this.

Measurement of relativistic orbital decay in the PSR B1534+12 binary system
I.H. Stairs et al.
Astrophysical Journal 505(1): 352-357, Part 1, September 20, 1998
ABSTRACT: We have made timing observations of binary pulsar PSR B1534+12 with radio telescopes at Arecibo (http://www.naic.edu/), Green Bank (http://www.gb.nrao.edu/), and Jodrell Bank (http://www.jb.man.ac.uk/). By combining our new observations with data collected up to seven years earlier, we obtain a significantly improved solution for the astrometric, spin, and orbital parameters of the system. For the first time in any binary pulsar system, no fewer than five relativistic or "post-Keplerian" orbital parameters are measurable with useful accuracies in a theory-independent way. We find the orbital period of the system to be decreasing at a rate close to that expected from gravitational radiation damping according to general relativity, although the precision of this test is limited to about 15% by the otherwise poorly known distance to the pulsar. The remaining post-Keplerian parameters are all consistent with one another and all but one of them have fractional accuracies better than 1%. By assuming that general relativity is the correct theory of gravity, at least to the accuracy demanded by this experiment, we find the masses of the pulsar and companion star each to be 1.339 +/- 0.003 solar masses and the system's distance to be d = 1.1 +/- 0.2 kpc, marginally larger than the d approximate to 0.7 kpc estimated from the dispersion measure. The increased distance reduces estimates of the projected rate of coalescence of double neutron star systems in the universe, a quantity of considerable interest for experiments with terrestrial gravitational wave detectors such as the Laser Interferometer Gravitational-Wave Observatory. (This result was refined in a report to the AAS in January 2002).

Since gravitational wave damping in GR is a direct result of the finite propagation velocity of gravity, this observation implies that GR is correct and that gravitational waves are generated, and therefore that the speed of gravity is not infinite. Indeed, since GR predicts that the speed of gravity is c, and since the timing observations are as GR predicts, we can also infer not just a finite speed of gravity, but a speed of c. This result should bot be considered "weak" just because it is an astronomical observation, as opposed to a local laboratory measurement.

Now, as for the latest entry by Kopeikin & Fomalont, here is the abstract of their presentation, the AAS talk referenced by JS Princeton.

Abstract: On 2002 Sep 08, the position of the bright quasar, J0842+1835 (http://www.ras.ucalgary.ca/VLBApls/J0842+1835.htm), was deflected by the gravitational field of Jupiter (http://seds.lpl.arizona.edu/nineplanets/nineplanets/jupiter.html) as it passed within 3.7' of the quasar line-of-site. General relativity predicts that moving celestial objects like Jupiter deflect light differently than that by a static mass. We have estimated that the first-order gravitational deflection term is approximately 1000 micro-arcsec directed radially away from Jupiter. The second order (dynamic) term is associated with the motion of Jupiter, and depends on the ratio of its orbital speed with the speed of propagation of gravity from Jupiter, c<sub>g</sub>. The expected deflection difference between c<sub>g</sub> = infinity and c<sub>g</sub> = c (the speed of light) is approximately 50 micro-arcsec in the direction of motion of Jupiter. In order to measure the deflection of the quasar's apparent position, we observed with the VLBA (http://www.aoc.nrao.edu/vlba/html/) + Effelsberg (http://www.mpifr-bonn.mpg.de/div/effelsberg/index_e.html) at 8.4 GHz on five days: 2002 Sep 04, 07, 08, 09, 12. For ten hours on each day, one minute scans were alternated among J0842+1835, J0839+1802 (0.8 SW), and J0854+2006 (http://www.ras.ucalgary.ca/VLBApls/J0854+2006.htm) (3.3 NE) to measure the precise separation of the quasars as a function of time. By observing for five days, we can remove the effects of variable source structure and determine realistic error estimates. By observing with two calibrators on either side of J0842+1835, we can remove most of the tropospheric and instrumental instabilities. We hope to achieve a positional sensitivity of about 10 micro-arcsec on Sep 08, and anticipate the results that gravity propagates with the same speed as light.

It is unfortunate, I think, that the abstract does not include the result cited by JS Princeton (who attended the talk), that c<sub>g</sub> = 1.06+/-0.12c<sub>light</sub>. If they achieve the 10 micro-arcsec sensitivity anticipated in the abstract, then an effect as large as 50 micro-arcsec should be quite clear.

We can indeed believe as we like. I don't believe van Flandern, because he does a poor job, and makes many mistakes, in areas where I have enough of my own experience to see it. There are plenty of good reasons for thinking that the speed of gravity and the speed of light are the same, and until somebody comes up with a good reason for thinking otherwise, I see no reason to change my mind.

<font size=-1>[ This Message was edited by: Tim Thompson on 2003-01-08 21:23 ]</font>

RickNZ
2003-Jan-09, 02:19 AM
BTW measuring speed of gravity means..

A object traveling at known speed approaches a object of known gravity at a known distance.

Correct me if im wrong but isnt the measurement of the speed of gravity = how long the object takes to become effected?

Which of course has to take into account both objects produce gravity interaction.

Should scientists be noting speed of gravity before they know exactly wat gravity is and how it works?

2003-Jan-09, 10:15 AM
<a name="3-1-09.?G'"> page= 3-1-09.?G' aka ?G'
On 2003-01-08 21:19, RickNZ wrote:
BTW measuring speed of gravity means..
an "Enforced" mind set that has been prewired to assume
Gravity is a singualrity {monoFold ?OR? flux ?flex}
not like an electron which is genericly
shown to be Multi_particled and not Mono_Tune_Us
----- my view of course would be just the obverse
tail theres only one electron & its "FAST"
and there ar many MANY gravity flies filed here there
and everyWhen?where and move about just as slow or
even slower that there elected positions REMold4 {2:23 A.M.pst} it did take about four min to SUBmit this as the board reported it was unrreachable}( my guess its not the board at all 2:25 A.M.}

<font size=-1>[ This Message was edited by: HUb' on 2003-01-09 05:18 ]</font>

DStahl
2003-Jan-09, 11:06 AM
A Brief History of the Walker-Dual Experiment

In October of 1996 Jurg Dual, William D. Walker, and Thomas Chen of the Institute of Mechanics, Swiss Federal Institute of Technology, wrote a paper entitled "Gravitational Forces with Strongly Localized Retardation" in which they used GR equations to show that "the gravitational forces generated in this [proposed] extreme near-field experiment are retarded, which may be verifiable with modern technology." "Retarded" in this case means that the vector of interaction points in a direction determined by both the position and the momentum of the interacting body. The theory of retarded fields is a basic tool of physics; there's a short description with neat visuals at this page (http://webphysics.davidson.edu/Applets/Retard/Retard_FEL.html) by Wolfgang Christian. Retarded field theory applies to both electrical and gravitational interactions, though because the equations describing gravity are of a higher order than the equations describing electromagnetism the genesis and behavior of the radiation produced is somewhat different.

About a year after their first paper Walker and Dual (with GR analysis by Chen) wrote up the results of the experiment they had proposed, in a paper titled "Propagation Speed of Longitudinally Oscillating Gravitational and Electrical Fields."

Now, in this paper Walker and Dual again note that their experiments are specifically near-field experiments: "The near-field Lienard-Wiechert potential solution of a longitudinally oscillating electrical field produced by an oscillating charge is presented, and the results are compared to the R. P. Feynman multipole far-field solution." An explication of near-field versus far-field is given on this page (http://farside.ph.utexas.edu/~rfitzp/teaching/em1/lectures/node47.html) from the University of Texas:

In the near-field region..."It is clear that we are fairly safe just using Coulomb's law, Faraday's law, and the Biot-Savart law to analyze the fields generated by this type of circuit."

In the far-field region..."We conclude that accelerating electric charges emit electromagnetic waves. The wave fields...fall off like the inverse of the distance from the wave source. This behaviour should be contrasted with that of Coulomb or Biot-Savart fields which fall off like the inverse square of the distance from the source. The fact that wave fields attenuate fairly gently with increasing distance from the source is what makes astronomy possible. If wave fields obeyed an inverse square law then no appreciable radiation would reach us from the rest of the universe."

"In conclusion, electric and magnetic fields look simple in the near field region (they are just Coulomb fields, etc.) and also in the far field region (they are just electromagnetic waves). Only in the intermediate region, R approximately equal to R<sub>o</sub>, do things start getting really complicated (so we do not look in this region!)."

So what did Walker-Dual really find? "The results indicate that the phase speed of a longitudinally oscillating electrical field is much faster than the speed of light in the near field. A similar analysis is presented for a longitudinally oscillating gravitational field produced by a vibrating mass. The result also indicates that the phase speed of a longitudinally oscillating gravitational field is also much faster than the speed of light in the near-field."

"Phase speed?" From the Mathpages explanation (http://www.mathpages.com/home/kmath210/kmath210.htm) of phase, group, and signal velocities:

"The ambiguity in the definition of 'wave velocity' often leads to confusion, and we frequently read stories about experiments purporting to demonstrate 'superluminal' propagation of electromagnetic waves (for example). Invariably, after looking into the details of these experiments, we find the claims of 'superluminal communication' are simply due to a failure to recognize the differences between phase, group, and signal velocities."
...
"Since a general wave (or wavelike phenomenon) need not embody the causal flow of any physical effects, there is obviously there is no upper limit on the possible phase velocity of a wave. However, even for a 'genuine' physical wave, i.e., a chain of sequentially dependent events, the phase velocity does not necessarily correspond to the speed at which energy or information is propagating."

In other words, in the paragraph describing the results of their experiment Walker and Dual did not claim that energy or information was being transmitted superluminally. What they did is confirm a decades-old calculation by Feynman: "In 1963 R. P. Feynman published a general physics book in which he analysed the electric field of an oscillating charge. Feynman's conclusion was that the oscillating field propagates nearly instantaneously along the axis of vibration, much faster than the speed of light. Because of the similarity of the analogous oscillating mass problem, the physics community has since concluded that the phase speed of both a longitudinally oscillating gravitational field and a longitudinally oscillating electrical field are too fast to measure with a near-field laboratory equipment." So the main part of the Walker-Dual experiment confirmed conventional physics, and did not claim that gravity could propagate energy or information superluminally. In addition, it dealt specifically with near-field effects, not the long-range effects that Van Flandern is interested in.

According to Walker and Dual it is not the phase velocity of electromagnetic and gravitational radiation which is taken to be c but the group velocity: "The possibility of measuring the group speed of a longitudinally oscillating gravitational field, which is commonly thought to be equal to the speed of light, is now being considered." [Emphasis added]

Near the end of their paper Walker and Dual write a somewhat enigmatic paragraph:

"The analysis of the group speed of a longitudinally oscillating electrical field is currently inconclusive. The group speed is commonly thought to be equal to the speed of light, but preliminary analysis indicates that the group speed is much faster than light which is not thought possible due to causality violation."

This "preliminary analysis" of a "currently inconclusive" part of the experiment is the only place the authors suggest that they have found anything that challenges conventional theory. As noted, the paper was written in 1997. I don't know if the authors have firmed up their preliminary analysis or come to any solid conclusions about this segment of the work. I'll see if they care to answer an email on the subject.

<font size=-1>[ This Message was edited by: DStahl on 2003-01-09 06:20 ]</font>

Chip
2003-Jan-09, 11:18 AM
On 2003-01-08 21:19, RickNZ wrote:
"Should scientists be noting speed of gravity before they know exactly wat gravity is and how it works?"

Sure. There are many instances in science where portions of a system or process are known, yet basic unknowns remain. (Like having enough pieces of a puzzle to infer what the subject of the picture is.) Black Holes are but one example. They were predicted by physics before actually being detected or recognized, yet many mysteries remain.

AgoraBasta
2003-Jan-09, 11:30 AM
On 2003-01-08 21:18, Tim Thompson wrote:
A nice idea, but impractical. there is no existing technology for measuring the speed of gravity in a local laboratory environment.I have proposed and discussed one here - http://www.badastronomy.com/phpBB/viewtopic.php?topic=2219&forum=1 - perfectly doable and cheaper than dirt.

WHarris
2003-Jan-09, 12:44 PM
If it's so doable, and so cheap, why don't you do it?

AgoraBasta
2003-Jan-09, 12:55 PM
On 2003-01-09 07:44, WHarris wrote:
If it's so doable, and so cheap, why don't you do it?And who's gonna believe me?

JS Princeton
2003-Jan-09, 06:01 PM
Agora, that's just preposterous. Do the experiment and stop complaining about being persecuted. Science doesn't care about your pet "beliefs". Just witness how much Arp gets published. He does good science even if he's sometimes wrong. Your whining is ridiculously arrogant and frankly crankish.

AgoraBasta
2003-Jan-09, 06:23 PM
On 2003-01-09 13:01, JS Princeton wrote:
Do the experiment and stop complaining about being persecuted. Science doesn't care about your pet "beliefs".So far it's been you who does all the complaining. All because your "pet beliefs" don't find the due respect as to your taste.
So keep your whining to yourself, would you...

Jim
2003-Jan-09, 06:48 PM
On 2003-01-08 14:39, AgoraBasta wrote:

On 2003-01-08 14:29, Jim wrote:
"Sufficiently debunked?" If you care to believe Van Flandern...Do you care to believe Kopeikin? And what about the Japanese guy TVF mentioned? And what you personally read about the issue in question?


You responded to the original post by what is basically an Argument from Authority. "Look! TVF has sufficiently debunked this already!"

So, I responded in kind... with three Authorities that debunk TVF.

I thought those were the rules... all posturing and no real discussion.

My take? I have to go along with Tim's comments. Van Flandern makes many, obvious mistakes. There are a sufficient number of good reasons for thinking that the speed of gravity and the speed of light are the same. I see nothing in Van Flandern's paper to cause me to think otherwise.

And I still think he needs lessons in writing abstracts for technical papers.

WHarris
2003-Jan-09, 08:05 PM
On 2003-01-09 07:55, AgoraBasta wrote:

On 2003-01-09 07:44, WHarris wrote:
If it's so doable, and so cheap, why don't you do it?And who's gonna believe me?


I had a feeling your response would be something along these lines.

AgoraBasta
2003-Jan-09, 09:46 PM
On 2003-01-09 15:05, WHarris wrote:
I had a feeling your response would be something along these lines.I bet you didn't even think of reading the thread I linked. So who's more predictable?

DStahl
2003-Jan-09, 09:59 PM
Agora Basta: "I have proposed and discussed one here - http://www.badastronomy.com/phpBB/viewtopic.php?topic=2219&forum=1 - perfectly doable and cheaper than dirt."

Excellent! Here's what I strongly recommend: write this proposal up soberly and carefully--and succinctly!--and email it to at least half a dozen good experimental physicists. Try to find researchers who work in gravitation theory and who have experience with the kind of apparatus you propose.

Expect some to brush you off--these guys have regular jobs and some of them work 60 or more hours a week at them--but with luck and perseverence you'll get some insightful comments back from others. After all, if there really is a chance that the experimental setup you propose could be made to work in the hands of a clever experimenter, and if there is a chance that it could be a first ever desktop measurement of the propagation speed of gravity (and not just the phase speed), then just about any researcher would jump at the chance to perform the experiment.

Especially if there's even a remote chance of finding a genuine refutation of conventional theory! Nothing---<U>nothing!</U>--boosts a researcher's career more than starting a revolution. (Even being mistaken in a revolutionary finding is OK as long as the researcher cops to the mistake; the real career-killer is being conclusively proven wrong and never accepting it--the mistake of Fleischmann and Pons, and I suspect the reason Tom Van Flandern is no longer taken seriously by many.)

Personally, I've a great deal of respect for the inventiveness of my fellow humans. I would be surprised if someone, somewhere, hasn't already thought of and perhaps even tried to build a detector like the one you propose. In fact, I would be inclined to email William D. Walker, Jurg Dual, and Thomas Chen and ask them if they know of such an attempt. It's obviously right up their alley.

AgoraBasta
2003-Jan-09, 10:42 PM
On 2003-01-09 16:59, DStahl wrote:
Excellent! Here's what I strongly recommend: write this proposal up soberly and carefully--and succinctly!--and email it to at least half a dozen good experimental physicists.
I happen to have a rather direct path to the top people in Russian Academy of Sciences, so I'm hardly unaware of what/how/when could be done and what would be the final "vote". Nothing pretty...

In fact, I would be inclined to email William D. Walker, Jurg Dual, and Thomas Chen and ask them if they know of such an attempt. It's obviously right up their alley.
That would be an unbelievably positive outcome from my mere posting in this forum. If you email them on that matter, please let me have a cc.

DStahl
2003-Jan-09, 11:52 PM
Agora Basta: "...I'm hardly unaware of what/how/when could be done and what would be the final 'vote'. Nothing pretty..."

In emailing experts I've never gotten anything but constructive responses (or, sometimes, pleas of overwork--too many student papers to read and not enough time to respond to unsolicited questions). I've already emailed Walker, Dual, and Chen on the subject of their vibrating-field experiments and the "inconclusive" result given for the group propagation speed of an electrical field, and I'll mention their responses when and if I get them.

Am I right in thinking from your post that you believe a controversial experiment would be somehow blackballed by the physics community, or am I reading something into it that is not there?

Tim Thompson
2003-Jan-10, 02:43 AM
TT: A nice idea, but impractical. There is no existing technology for measuring the speed of gravity in a local laboratory environment.

AB: I have proposed and discussed one here - http://www.badastronomy.com/phpBB/viewtopic.php?topic=2219&forum=1 - perfectly doable and cheaper than dirt.

While it appears that the "no existing technology" part of my reply was wrong, or at least may have been wrong, I still think your proposed experiment is quite inferior to the experiment designed by Walker & Dual.

Consider the Walker-Dual paper "Propagation Speed of Longitudinally Oscillating Gravitational and Electrical Fields (http://cul.arXiv.org/abs/gr-qc/9706082)", especially the discussion on page 11, in the section "Experimental Gravitationally Vibrating System". The authors note that, to make the experiment more effective, the mass of the transmitter and the amplitude of the transmitter's vibration should be maximzed, while the oscillation frequency of the transmitter should be minimized. The quartz crystals in your propsed setup are far less massive than the masses in the Walker-Dual set up, and the vibration frequencies will be quite high, both contrary to the desired conditions.

So, while your experiment might in principle work, it is far less likely to produce viable results. It is also, I think, rather more difficult to do than you anticipate. Specifically, environmental noise is a major problem, since the effect you are looking for is very small. Such an experiment requires someone with experience in paying attention to the details of doing this kind of work.

The Walker-Dual and Chen-Walker-Dual ("Gravitational Forces with Strongly Localized Retardation (http://cul.arXiv.org/abs/gr-qc/9610049)") papers appear to have not been published, except in the archives. The latter was evidently submitted to Physical Review D in 1996 (the archive reads To appear in Phys. Rev. D, but I can find no sign of its having made it to the journal (see the Physical Review Online Archive (http://prola.aps.org/)).

Why the papers were never published I don't know. But it is evident that Dual is still working on this problem (Experimental Studies on Gravitationally Vibrating Systems (http://www.rereth.ethz.ch/mavt/mechanik/dual/pj.03.html)). I think it's clear that the Walker-Dual approach is the correct one, but it appears to be a technological challenge.

Reader's should also take care to understand that phase velocity and group velocity are significantly different. It is already "standard" physics that the phase velocity of an electromagnetic wave, or a gravitational wave, can be arbitrarily large compared to c without a problem. However, this is not true, or so I think, for the group velocity, which should be the velocity of energy propagation, and a real issue for causality. This means that the Walker-Dual conclusion that the phase velocity of a gravitational wave might be much larger than c is not surprising.

<font size=-1>[ This Message was edited by: Tim Thompson on 2003-01-09 21:45 ]</font>

AgoraBasta
2003-Jan-10, 09:15 AM
On 2003-01-09 18:52, DStahl wrote:
Am I right in thinking from your post that you believe a controversial experiment would be somehow blackballed by the physics community, or am I reading something into it that is not there?The real problem is that only the most expensive and complex experiments can pass when sensitive issues are about to be measured.

On 2003-01-09 21:43, Tim Thompson wrote:
The authors note that, to make the experiment more effective, the mass of the transmitter and the amplitude of the transmitter's vibration should be maximzed, while the oscillation frequency of the transmitter should be minimized. The quartz crystals in your propsed setup are far less massive than the masses in the Walker-Dual set up, and the vibration frequencies will be quite high, both contrary to the desired conditions.Those "desired conditions" are imposed by their scheme limitations and by the fact that their first intention was to measure the phase velocity. Now we need to modulate the signal with "information", so highest possible frequencies and sensitivities are absolutely required.

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

Dunash
2003-Jan-10, 10:16 AM
I understand that Tom Van Flandern claims that this experiment does not measure the rate at which the gravitational force travels, but only the speed of the
graviton. He claims that these are two different things, with the graviton travelling at the speed of light. I refer you to his web page
and the Meta Research Bulletin. I am ambivalent and prepared to wait and see how the matter develops. We need more information and insight before a "final" pronouncement can be made.

DStahl
2003-Jan-10, 10:56 AM
Hi, Dunash. The only discussion of the Walker-Dual experiment I could find on Van Flandern's website was his #2 paper on repealing the lightspeed limit, and it contains very little discussion of Walker-Dual.

Here's a direct link to TVF's paper: The Speed of Gravity - Repeal of the Speed Limit II (http://www.metaresearch.org/cosmology/gravity/speed_limit.asp)

He quotes several experiments which he believes disprove either SR, the geometrical interpretation of GR, or both. Here's what I gleaned on Walker-Dual from his paper (direct quotes in blue).

<font color=#0000ff>"(6) the Walker-Dual experiment, showing in theory that changes in both gravitational and electrostatic fields propagate faster than the speed of light, c, a result reportedly given preliminary confirmation in a laboratory experiment."</font>

That's the only time the document mentions Walker-Dual. The following is a general comment:

<font color=#0000ff>"Understanding the very meaning of the 'speed of gravity' requires resolving any confusion that may remain between these two unrelated concepts. The 'speed of gravity' refers to whatever causally links the source of gravity to the 3-space acceleration of a target body."</font>

This is quite important in relationship to Walker-Dual, because they themselves say their experiment measured the phase speed of both gravitational and electrical propagation and found them in excess of c, and it is quite clear from their own words as well as from other sources that the phase propagation speed most emphatically cannot be what Van Flandern refers to when he writes "The 'speed of gravity' refers to whatever causally links the source of gravity to the 3-space acceleration of a target body."

If Van Flandern discusses Walker-Dual in greater depth somewhere, please give us a pointer to a specific web page so's we can read it too! Thanks!

<font size=-1>[ This Message was edited by: DStahl on 2003-01-10 05:58 ]</font>

AgoraBasta
2003-Jan-10, 11:28 AM
DStahl,

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

GrapesOfWrath
2003-Jan-10, 02:20 PM
On 2003-01-10 05:16, Dunash wrote:
I understand that Tom Van Flandern claims that this experiment does not measure the rate at which the gravitational force travels, but only the speed of the
graviton.
I thought the graviton was supposed to be the exchange particle for the gravity force. Why the distinction?

Laser Jock
2003-Jan-10, 03:17 PM
On 2003-01-09 21:43, Tim Thompson wrote:
Reader's should also take care to understand that phase velocity and group velocity are significantly different. It is already "standard" physics that the phase velocity of an electromagnetic wave, or a gravitational wave, can be arbitrarily large compared to c without a problem. However, this is not true, or so I think, for the group velocity, which should be the velocity of energy propagation, and a real issue for causality. This means that the Walker-Dual conclusion that the phase velocity of a gravitational wave might be much larger than c is not surprising.



I think you have this backward. The phase velocity, defined as v_p = omega/k = c/n, is "the speed at which each of the cophasal surfaces [of a electromagnetic wave] advances."[1] To say this quantity can be arbitrarily large is misleading. Only in very rare cases can you get the refractive index (n) to be less than unity.

The group velocity, on the other hand, can be much different than c. The group velocity, defined as v_g = d(omega)/d(k), can be much less than c [2], or even negative (superluminal) [3]. It is the velocity at which the superposition of multiple frequencies propagate (ie. the interference pattern). However, the energy of the signal will not necessarily propagate at the group velocity in a medium with large dispersion.

References:

[1] M. Born and E. Wolf, Principles of Optics, 7th Edition, p. 19.

[2] See for instance L. V. Hau et al., Nature 397, 594 (1999).

[3] L. J. Wang, A. Kuzmich, and A. Dogariu, Nature 406, 277 (2000).

AgoraBasta
2003-Jan-10, 03:49 PM
On 2003-01-10 10:17, Laser Jock wrote:
I think you have this backward.Nope, you both got it right. /phpBB/images/smiles/icon_smile.gif

Wiley
2003-Jan-10, 05:35 PM
On 2003-01-10 10:17, Laser Jock wrote:
I think you have this backward. The phase velocity, defined as v_p = omega/k = c/n, is "the speed at which each of the cophasal surfaces [of a electromagnetic wave] advances."[1] To say this quantity can be arbitrarily large is misleading. Only in very rare cases can you get the refractive index (n) to be less than unity.

You're neglecting the source. For a simple source, the formula you present is correct. However for a more complicated source, e.g. a longitudinally oscillating charge as in the W/D paper, the phase speed is different. For the longitudinally oscillating charge, the phase speed is v_ph = c + c^3/( omega * r )^2. Note in the far field (as r goes to infinity) that it reduces to your formula.



The group velocity, on the other hand, can be much different than c. The group velocity, defined as v_g = d(omega)/d(k), can be much less than c [2], or even negative (superluminal) [3]. It is the velocity at which the superposition of multiple frequencies propagate (ie. the interference pattern). However, the energy of the signal will not necessarily propagate at the group velocity in a medium with large dispersion.

Exactly. For 99.9% of the time group velocity is equivalent to signal velocity. If there is no dispersion, group velocity and signal velocity are equal. Vacuum has no dispersion, and air has almost none. And in communication systems, dispersion is avoided like the plague. Dispersion causes signals that look like pulses at the input to look like blobs at the output. Rarely is there a significant difference between the group and signal velocities, and I think this has caused much confusion, even among scientists and engineers.

Wiley
2003-Jan-10, 05:48 PM
DStahl,

Thanks for linking to the math pages (http://www.mathpages.com/home/index.htm). This is really good stuff.

Two section in particular are important for this discussion:
Phase, Group, and Signal Velocity. (http://www.mathpages.com/home/kmath210/kmath210.htm)
Lead-Lag Frequency Response (http://www.mathpages.com/home/kmath249/kmath249.htm)

If you want to understand why TVF is wrong, read these pages. The section on numerator dynamics (about half way down in the lead-lag section) explains most of TVF's errors.

Good stuff. Thanks again, DStahl.

AgoraBasta
2003-Jan-10, 11:04 PM
Quoth TVF:

The latest news on the Kopeikin fiasco:

Respected relativist Clifford Will has just joined those insisting that Kopeikin has not measured the "speed of gravity" at all, but only the speed of light. See his preprint "Propagation speed of gravity and the relativistic time delay", http://www.arxiv.org/abs/astro-ph/0301145. -|Tom|-

Clifford Will's abstract:

We calculate the delay in the propagation of a light signal past a massive body that moves with speed v, under the assumption that the speed of propagation of the gravitational interaction c_g differs from that of light. Using the post-Newtonian approximation, we consider an expansion in powers of v/c beyond the leading ``Shapiro'' time delay effect, while working to first order only in Gm/c^2, and show that the altered propagation speed of the gravitational signal has no effect whatsoever on the time delay to first order in v/c beyond the leading term, although it will have an effect to second and higher order. We show that the only other possible effects of an altered speed c_g at this order arise from a modification of the parametrized post-Newtonian (PPN) coefficient alpha_1 of the metric from the value zero predicted by general relativity. Current solar-system measurements already provide tight bounds on such a modification. We conclude that recent measurements of the propagation of radio signals past Jupiter are sensitive to alpha_1, but are not directly sensitive to the speed of propagation of gravity.

JS Princeton
2003-Jan-11, 01:49 AM
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.

Tim Thompson
2003-Jan-11, 02:11 AM
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!

DStahl
2003-Jan-11, 03:32 AM
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!

AgoraBasta
2003-Jan-11, 09:23 AM
On 2003-01-10 20:49, JS Princeton wrote:
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.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".

AgoraBasta
2003-Jan-11, 05:07 PM
On 2003-01-10 21:11, Tim Thompson wrote:
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. 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>

JS Princeton
2003-Jan-11, 05:47 PM
On 2003-01-11 04:23, AgoraBasta wrote:
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".



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.

AgoraBasta
2003-Jan-11, 06:15 PM
On 2003-01-11 12:47, JS Princeton wrote:
The team did not observe a time delay which was another proposed experiment, rather a distinct angular distortion of the image.Guess we just have to wait for the full report, too many questions and too much open for speculations.

DStahl
2003-Jan-12, 01:28 AM
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 (http://arxiv.org/abs/physics/0009023) and to the full paper in pdf format. (http://arxiv.org/ftp/physics/papers/0009/0009023.pdf)

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 2X10<sup>10</sup> 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 (http://xxx.lanl.gov/abs/gr-qc/9909087), full paper in pdf (http://xxx.lanl.gov/PS_cache/gr-qc/pdf/9909/9909087.pdf) and "The Speed of Gravity Revisited" by Ibison, Puthoff, and Little (abstract in html (http://arxiv.org/abs/physics/9910050), full paper in pdf (http://arxiv.org/ftp/physics/papers/9910/9910050.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>

DStahl
2003-Jan-12, 03:25 AM
There's a neat animated demonstration of superluminal phase velocity at one of Greg Egan's (http://www.netspace.net.au/~gregegan/APPLETS/20/20.html) pages.

2003-Jan-12, 06:11 PM
<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 (http://www.netspace.net.au/~gregegan/APPLETS/20/20.html) 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 ?.....?....?...?..?.

David Hall
2003-Jan-12, 09:44 PM
On 2003-01-12 13:11, HUb' wrote:

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..


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

DStahl
2003-Jan-12, 10:13 PM
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>

AgoraBasta
2003-Jan-12, 11:27 PM
On 2003-01-11 12:47, JS Princeton wrote:
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.It appears that Will's critique (http://www.arxiv.org/abs/astro-ph/0301145) is aimed specifically at this Kopeikin's preprint (http://xxx.lanl.gov/abs/gr-qc/0212121). BTW, Will literally tears Kopeikin apart...

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

JS Princeton
2003-Jan-13, 08:32 AM
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.

David Hall
2003-Jan-14, 08:22 AM
I just got a Nature Science update on this topic. Maybe nothing new but I'm throwing it in anyway. /phpBB/images/smiles/icon_smile.gif

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

DStahl
2003-Jan-14, 09:00 AM
"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.

Tim Thompson
2003-Jan-17, 03:17 AM
Reference: Propagation Speed of Longitudinally Oscillating Gravitational and Electrical Fields (http://cul.arXiv.org/abs/gr-qc/9706082). 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 (http://www.m-w.com/cgi-bin/dictionary?va=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<sub>tx</sub>) in the denominator, we realize that making w<sub>tx</sub> smaller will make the term larger. And since the transmitter mass (m<sub>tx</sub>) is in the numerator, we realize that making m<sub>tx</sub> larger will make the term larger.

Hence, by dint of first year physics & grade school arithmetic, we come to the conclusion that making m<sub>tx</sub> larger, and/or w<sub>tx</sub> smaller, both work to make the amplitude of the receiver mass vibration (u<sub>ac</sub>) 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.

AgoraBasta
2003-Jan-17, 09:11 AM
On 2003-01-16 22:17, Tim Thompson wrote:
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". 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>

John Kierein
2003-Jan-17, 01:39 PM
http://www.space.com/scienceastronomy/gravity_speed_030116.html
This link speaks for itself.

David Hall
2003-Jan-17, 02:07 PM
That's not Jupiter, that's a ROD (http://www.badastronomy.com/phpBB/viewtopic.php?topic=3000&forum=1)! It must have flown in front of the VLBA antennae just as the image was being taken. /phpBB/images/smiles/icon_razz.gif

nebularain
2003-Jan-17, 04:51 PM
On 2003-01-17 08:39, John Kierein wrote:
http://www.space.com/scienceastronomy/gravity_speed_030116.html
This link speaks for itself.

Quote from the link above

"It is not uncommon for discoveries to be presented to reporters at AAS meetings prior to having been through peer review. Numerous other findings, by NASA scientists and others, are announced in press releases every year prior to any formal peer review. Scientists are sometimes critical of this so-called "science by press release" process. Others see it as a natural and inevitable flow of information into scientific and public hands."

Well, that's a great way to screw everybody up.

Today - "Hey, we've got this great discovery."

Tomorrow - "Psyche!"

I guess we'll have to see what the peer review determines.

JS Princeton
2003-Jan-17, 09:55 PM
But the discovery in question was not presented to reporters but to other scientists in a special session. The whole point of these sessions is to present your findings and in-process papers to fellow scientists. Then those interested come to talk to you afterwards and ask for preprints, etc.

It seems to me that one must be pretty scared of the results to criticize this person who has been working on this project out in the open for a few years now.

If you care to read his technical papers and criticize them, check it out here:

http://lanl.arXiv.org/find/astro-ph/1/au:+Kopeikin/0/1/0/past/0/1

And please, criticize away. It seems to me extremely legit: not a publicity stunt.

Zathras
2003-Jan-17, 10:12 PM
On 2003-01-17 16:55, JS Princeton wrote:
. . .
It seems to me extremely legit: not a publicity stunt.


But why can't it be both? This work certainly looks like solid, legitimate research, even if it does turn out to be wrong at the end. Just because he is doing legitimate work does not mean he isn't out to seek publicity. Publicity is a great way to get the research funding; many groups in various pockets of science have become very good at it. If the NSF or another public group decides to fund a project, and they have a choice between one that is well-publicized and one that is not (all other things being equal), they are more likely to fund the one with the publicity. It allows them to tell Congress during the next budget cycle that they are funding X, when some people in Congress (or at least some of their staff) have heard about the project.

Publicity begets the money. Unfortunately, legitimate research always needs the money. Therefore, many will seek the publicity to get the money.

JS Princeton
2003-Jan-17, 10:46 PM
Zathras, you have a point, but as I attended the talk I don't think he was really grubbing for publicity. That was just my personal opinion of him. He only gave a five minute talk and didn't hold a press conference. It was buried at the end of a gravitational cosmology session that was in one of the break-out rooms. It's a monumental finding, in my thinking, but the venue wasn't all that spectacular.

If you wanted to do a publicity stunt, wouldn't you call the press? I don't know... just my feeling I guess.

Tim Thompson
2003-Jan-23, 02:14 AM
And the speed of gravity marches on ...

AB: Exactly the physics you don't understand. Let A be amplitude of position, ...

I guess I don't. I never heard of "amplitude of position" before. What does that mean?

AB: ... then amplitude of velocity is Aw, ...

I never heard of "amplitude of velocity" either. But I do know that the velocity of a wave is the frequency times the wavelength. So, if "w" is the frequency, do you mean wavelength times frequency? Is "amplitude of position" supposed to mean "wavelength"? It can't very well be the amplitude of the wave (as in A*sin(wt)), because (so far as I know) the product of the amplitude & velocity does not mean anything physical.

AB: ... amplitude of accelerations is Aw^2, amplitude of force mAw^2.

I confess that I have no idea what the words "amplitude of acceleration" and "amplitude of force" are supposed to mean. I have absolutely no idea what you are trying to talk about.

AB: Hence sensitivity depends on quantity you measure.

Well, duh. Of course it depends on the quantity you measure, that's why experimentalists are always so picky about what they choose to measure. Is that all you are trying to get at?

AB: So I pick up the force since it's as direct an observable as is position.

I disagree. Position is a more direct observable than force. Position can be measured directly, but force can never be measured directly, it can only be inferred from other measurements (acceleration, mass, deflection, bending angle, & etc.)

AB: In the W/D scheme they bend a long piece of quartz.

According to figure 5, the transmitter beam (the one that's bent) is brass, not quartz. It's 11.0 mm wide, 12.0 mm high, and 95.90 cm long. The receiver is a quartz bar, but it is not bent, it hangs from rubber bands as a pendulum and vibrates freely. The transmitter bar is vibrated by a non-contact mechanism (a cobolt magnet attached to the bar, and in proximity to a electromagnet coil). The frequency of vibration for the transmitter is 40 Hz, the first resonant mode of the bar.

AB: 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.

I intend to forget it, since it is not true. You only assume it to be true, because you want to maximze the frequency. But that's a bad strategy for this kind of experiment. Much better to minimize the frequency, and maximize the transmitter amplitude. That eliminates any concern over mechanical strength.

AB: 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.

There are a couple of problems here. First, phaseshift sensitivity does not mean sqaut, if you don't have a measureable amplitude at the receiver. You simply can't ignore the receiver amplitude, as if it does not exist. It's part of the experiment, it's something you have to be able to measure. You're trying to drive the experiment into a regime where the receiver amplitude is unmeasureable, and the experiment undoable.

Also keep in mind that the phase shift is a time delay. Relatively long time delays are easier to measure than relatively short time delays, although I admit that the technology for measuring time delays and phaseshifts is well advanced, and probably is not challenged by this experiment no matter which way it's done.

But you have the noise wrong. It does not look like w<sup></sup> if the signal is sent through a bandpass filter (which eliminates frequency noise), and I believe it will not look like w<sup></sup> if the noise source is nonthermal (though I am weak here and open to correction). By using pure tones (like the resonant frequency of the bar), and keeping the amplitude signal clean, one should be able to do much better on the noise than you allow for.

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

I sort of figured I would ask you the same question.



<font size=-1>[ This Message was edited by: Tim Thompson on 2003-01-22 21:18 ]</font>

AgoraBasta
2003-Jan-23, 02:18 PM
On 2003-01-22 21:14, Tim Thompson wrote:
I never heard of "amplitude of velocity" either. But I do know that the velocity of a wave is the frequency times the wavelength. So, if "w" is the frequency, do you mean wavelength times frequency?
You obviously do not know certain basics. No problem, I can help -

Let there be a simplest mechanical oscillator:
x = A*sin(wt)
Then velocity of oscillating motion is:
v = dx/dt = A*w*cos(w*t) -> amplitude of v is V = A*w.
Acceleration of oscillating motion:
a = dv/dt = -A*w^2*sin(w*t) -> amplitude of a is A*w^2.
Stress force in the oscillator is then:
f = -m*A*w^2*sin(w*t) (instead of "=" we'd better use the "~", but it doesn't matter here).
Thus the amplitude of force, i.e. max stress force, is F~m*A*w^2.
Since max stress is limited by the material strength, the max value of the m*A*w^2 is a constant defined by the material used and by the design geometry.
Assuming linear transmission efficiency in A, and using A ~ m/w^2 from W/D, we get const = (m*w^2)*m/w^2 = m^2, i.e. tautology.
Force is a direct observable, and its electric analogue is voltage, so we move on.

I disagree. Position is a more direct observable than force. Position can be measured directly, but force can never be measured directly, it can only be inferred from other measurements (acceleration, mass, deflection, bending angle, & etc.)
Not true. A force of a kick in the rear is the most direct of observables.
There are plenty of ways to convert force into voltage.

According to figure 5, the transmitter beam (the one that's bent) is brass, not quartz. It's 11.0 mm wide, 12.0 mm high, and 95.90 cm long.
Brass or quartz - doesn't matter. The material can stand many orders of magnitude greater stress while compressed than while bent. That thin stick of brass would hardly stand some 100N bending force, while can easily stand about 10000N of axial compression stress.

AB: 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.
I intend to forget it, since it is not true.That's an obvious deliberate lie on your part.

But you have the noise wrong. It does not look like w<sup></sup> if the signal is sent through a bandpass filter (which eliminates frequency noise), and I believe it will not look like w<sup></sup> if the noise source is nonthermal (though I am weak here and open to correction).
So you get your correction. For the white noise, you get noise voltage ~ (delta w)<sup>1/2</sup>. At low freq's you also get flicker with power spectral density 1/w, and that's above the white.

By using pure tones (like the resonant frequency of the bar), and keeping the amplitude signal clean, one should be able to do much better on the noise than you allow for.
By using pure tone one cannot transmit info, so bandwidth is must.

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

I sort of figured I would ask you the same question.
Your ability to figure the stuff out appears badly challenged, so you better don't embarrass yourself any further...

<font size=-1>[ This Message was edited by: AgoraBasta on 2003-01-23 10:18 ]</font>

Zathras
2003-Jan-23, 02:59 PM
On 2003-01-17 17:46, JS Princeton wrote:
Zathras, you have a point, but as I attended the talk I don't think he was really grubbing for publicity. That was just my personal opinion of him. He only gave a five minute talk and didn't hold a press conference. It was buried at the end of a gravitational cosmology session that was in one of the break-out rooms. It's a monumental finding, in my thinking, but the venue wasn't all that spectacular.

If you wanted to do a publicity stunt, wouldn't you call the press? I don't know... just my feeling I guess.


Of course you would call the press, but you wouldn't necessarily call them to a paper presentation at a scientific conference. In fact, it would be better not to, because at a conference, there is the potential that questions would be asked that would make the findings appear more ambiguous. It would be better strategy to issue a press release, because in this way the press gets exactly what you want them to get.

It is clear that he did issue a press release of some sort. How else would the popular science news sources have received the information? Even more telling, how else would the cranks disputing the theory have gotten hold of it so quickly--it's not like they'd be caught asking questions in a scientific conference, where they'd just be laughed away.

Again, I am not belittling the actual science here. It certainly looks legitimate. The method of publicizing the results, however is subject to criticism, because the next guy who puts forth press releases before peer review might not have a legitimate theory. Once the popular press gets ahold of the information, they are unlikely to understand what is good science and what is junk science.

This is exactly what happened with cold fusion in 1988. Pons and Fleishmann gave the press their tailored release, and the press ate it up. It took scientists months to show that the results could not be duplicated, and the damage to the public's understanding of science has not been completely repaired (many people believe that cold fusion works, but that scientists and the government are covering it up to protect oil interests).

I believe that scientists have a duty to protect the public by not publicizing their findings before peer review. If they do otherwise, the amount of junk science in the public sphere will undoubtedly increase.

Tim Thompson
2003-Jan-24, 01:52 AM
AB: That's an obvious deliberate lie on your part.

End of discussion.

AgoraBasta
2003-Jan-24, 07:57 AM
On 2003-01-23 20:52, Tim Thompson wrote:
End of discussion.Sure. You lose. But you knew that. Now everybody knows.

JS Princeton
2003-Jan-24, 02:46 PM
On 2003-01-23 09:59, Zathras wrote:
The method of publicizing the results, however is subject to criticism, because the next guy who puts forth press releases before peer review might not have a legitimate theory.


Well, you the experiment has been on astro-ph for a few months now and the papers were already accepted by ApJ and PRL before the talk was given. Is it necessary to wait the four to six months for the hardbound publication to come out before you talk about your results?

ToSeek
2003-Jun-19, 07:40 PM
Speed of gravity claim challenged (http://www.sciencedaily.com/releases/2003/06/030619075759.htm)