Here are the public USENET messages relevant to Abhi's post above:
<BLOCKQUOTE id=quote><font size=2 face="Verdana, Arial, Helvetica" id=quote>quote:<hr height=1 noshade id=quote>From: "Stephen Speicher" <sjs@compbio.caltech.edu>
Subject: Agreement between Stephen Speicher and Abhijit Patil
Date: Tuesday, September 10, 2002 12:46 PM
It is a prediction of general relativity that finite changes in
the gravitational field propagate at c. See, for instance,
S. Carlip, "Aberration and the speed of gravity," _Physics
Letters A_, 267 (2-3): pp. 81-87 Mar 13 2000.
R.J. Low, "Speed limits in general relativity," _Classical and
Quantum Gravity_, 16 (2): pp. 543-549 FEB 1999.
Data related to this very prediction is currently being collected
in an experiment designed and supervised by Sergei Kopeikin, as
outlined in "Testing the relativistic effect of the propagation
of gravity by very long baseline interferometry," _Astrophysical
Journal_, 556 (1): L1-L5 Part 2, Jul 20 2001.
The results of the experiment are expected to be made public
within two to three months from now. I hereby agree that if these
results show that finite changes in the gravitational field are
measured to be instantaneous, I will publicly acknowledge that
there exists a serious flaw in general relativity, and I will
promise not to post to any sci.* groups for one year after the
results are made public.
On the other hand, if the finite changes in the gravitational
field are not measured to be instantaneous, then Abhijit Patil
will publicly acknowledge that his own view of relativity is
mistaken and, further, he will refrain from making any posts
to the sci.* groups for one year.
I would ask Abhijit Patil to confirm this agreement by responding
with an acknowledgement to this post.
--
Stephen
sjs@compbio.caltech.edu
Printed using 100% recycled electrons.
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<BLOCKQUOTE id=quote><font size=2 face="Verdana, Arial, Helvetica" id=quote>quote:<hr height=1 noshade id=quote>"Stephen Speicher" <sjs@compbio.caltech.edu> writes:
> Abhi wrote:
>> [Abhi]:They are going to measure that it is instantaneous. ... YES! I do have courage to make deal. If I am wrong, I will not give up just sci.*, but all my physics related work. It is a deal, a promise.
> [ss]: I will make a separate post with an appropriate subject line so that this can be easily found by all. When you see the post, please acknowledge your agreement by responding there.
I object to this wager because it is being conducted under deceptive conditions. Abhi is obviously wagering that the “speed of gravity” (meaning gravitational force, the man-on-the-street’s understanding of the term) will turn out to be near-instantaneous, about which he is almost certainly correct according to all six experiments already done, as well as in physically reasonable interpretations of GR. Speicher is obviously wagering that the Kopeikin experiment will yield a result that the “speed of gravity” (meaning changes in gravitational potential, the geometric-GR relativist’s understanding of the term) will be the speed of light, about which he is also almost certainly correct. But it is unfair to promote a “sucker bet” in which one of the parties already knows the outcome, but allows the other party to believe that it tests something different and still in doubt.
The reason that the two speeds (force and potential fields) are different, even though the fields are mathematically connected, is that gravitational acceleration is the gradient (a form of derivative) of the gravitational potential. In general, a function and its derivative do not have the same properties. In the particular case of gravity, gravitational potential (sometimes called the “space-time medium”) is analogous to an optical medium for which the wave speed is c, the speed of light; and as its density increases near masses, refraction in any optical medium of increasing density will bend light away from the normal, slow the propagation of waves, etc., just as GR predicts. Even though the gravitational potential might be rigorously constant at every point in the gravitational field of a non-moving source mass, its *gradient* as viewed from a moving target body will in general be a variable that depends on the speed and direction of the target body.
A gravitational potential field must continually regenerate to be able to produce acceleration at all because, in physics, changes of motion cannot arise from something with no moving parts. (Causality and momentum conservation apply.) But the speed of regeneration of the potential field (the speed of gravitational force) has no relation to the wave speed of the potential field (the speed of gravitational waves). The former is constrained by experiments to be much faster than lightspeed, while the latter is necessarily the speed of light to produce the correct light-bending, signal slowing, redshift, and perihelion advance.
My entire discussion of this subject with the experimenter, Sergei Kopeikin, is available at [url]
metaresearch.org/home/viewpoint/Kopeikin.asp
[/url]. And I am not the only one concluding Kopeikin has misrepresented the significance of his experiment. A rebuttal to Kopeikin’s ApJ paper titled "The light cone effect on the Shapiro time delay" by H. Asada has just appeared in ApJ Letters 574, L69-L70 (2002). Asada concludes: "S. Kopeikin argued that the excess time delay was due to the propagation speed of gravity. The present Letter shows that the excess comes from nothing but the propagation delay of light, namely, the light cone effect."
Sadly for science, Kopeikin has mentioned plans to announce his results to the world in October/November as the first measurement of the “speed of gravity”. Few media reporters will know any better, and will just run with the story they are fed, as happened (mostly) with last week’s press release. Yet these measurements refer only to an effect of gravity, much like light-binding, radar time delay, or redshift. They are sensitive to changes in the propagation speed of the quasar signals in Jupiter’s and the Sun’s gravitational potentials, but not at all to the propagation speed of gravitational force, which does not affect passing quasar signals. (Proof: Consider the interior of a uniform spherical shell. It has gravitational potential but everywhere-zero gravitational force, yet GR predicts the same delay of light signals passing through as would occur for that same potential near a large mass with an arbitrary gravitational force.)
If Abhi reads and understands this and still wants to take Speicher’s wager, then by all means proceed with the plucking. But more than Abhi’s plight, I’m concerned about what will happen with Sergei Kopeikin. If he goes ahead with his plan to style his result as the “speed of gravity” instead of “the speed of gravitational waves”, an altogether different concept, that will be a setback for the understanding of science by the public and subject Kopeikin to criticism for exaggeration and/or misrepresentation at the expense of objectivity about the more limited nature of his result. Because he does not read newsgroups, his friends should advise Kopeikin accordingly. -|Tom|-
Tom Van Flandern - Washington, DC – see our web site on replacement astronomy research at <
metaresearch.org
>
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