>I forwarded David's response to Tom, who countered below.
> ...
Does anyone else find this habit of Bill's annoying where he sends the
posts of others to third parties without asking? Glenn asked me for my
take on a paper that he had been pointed to, and I gave him my
perspective. The reason that I answered Glenn on the list was that that
was how he had asked. If I had known that Bill would be circulating my
comments to others off the list, soliciting comments, and reposting
rebuttals, I would have answered Glenn privately. If I had wanted to
become embroiled in a debate with Tom Van Flandern I would have brought
him into the discussion myself. I prefer to not to have to deal with the
fallout of the services of an uninvited matchmaker when choosing my
discussion partners.
Now that Tom Van Flandern has been brought into this I feel his comments
may need a response (but I still am not in a mood for, nor have the time
for, and possibly not the expertise for a ongoing semi-interminable
debate about Van Flandern's paper).
Regarding:
> I've added a response below. Unfortunately, I can't follow up on any
>further discussion anytime soon because I leave within 24 jours for two
>weeks in Europe, and don't expect to have internet access. Best
>wishes. -|Tom|-
Bon voyage. Please don't think you need to keep the discussion going
after you get back.
> That material was removed only because of the length limitations for
>Letters in that journal. Major parts of it will now be published as a
>response to a critique by three relativists, who criticized my paper
>because it did not address certain issues. These were addressed in the
>omitted material.
Does anyone have a reference for this critique? Now that I've been drawn
into this can of worms I have begun to develop a curiosity about what
others may have said about Van Flandern's paper.
> My paper shows that the mathematics of general relativity (GR) is
>correct, but the common interpretation of GR now being taught to students is
>wrong. Specifically, the six experiments reported in the paper demonstrate
>that faster-than-light propagation and communication in forward time can and
>does take place.
I don't think so. I believe, rather that they *confirm* that the
retarded near field gravitational forces 'lead' the motions of the
masses (as predicted by GR) in such a way that smooth (not wildly jerky)
motions of the sources result in the gravitational forces pointing
essentially along the instantaneous positions of those sources because
the 'leading' effect tends to anticipate and cancel the effect of the
time delay in the propagation of the influences. For sufficiently
rapidly complicated motions, however, GR would predict that the direction
of the gravitational forces is not aligned with the sources and thus
betray the fact that causality actually does locally propagate at speed c
in GR. But the data shown in the paper do not, AFAIK, address that
particular case which would clearly demonstrate that effect.
>As for special relativity (SR), the paper demonstrates that
>Lorentz's version (Lorentzian relativity, LR) published a year before
>Einstein's is a better description of reality than SR.
I don't think so. I think the data shown in the paper confirm both
theories equally and do nothing to discriminate between them. Also,
I haven't heard that Lorentz ever developed a full-fleged theory of
gravitation to test against experiment anyway.
>The only known test
>that distinguishes the two theories is the existence of things propagating
>faster than light. And gravity now plays that role, showing that SR was
>wrong about the speed of light being an absolute speed limit, and LR was
>right about the universe apparently having no speed limit. ...
Van Flandern *claims* this but I don't think the evidence in the paper
*demonstrates* it at all.
>>What the Van Flandern paper actually shows is that a naive (but
>>understandably mistaken) understanding of relavity and gravitation
>>could easily lead an unsuspecting person to conclude that the
>>experimental evidence is against relativity.
>
> The experimental evidence supports the mathematical theory and refutes
>the interpretation now being taught, showing that the interpretation
>violates the causality principle.
The proper interpretation of any physical theory must be consistent with
its mathematics. If the math predicts something then the interpretation
must agree with the math about the prediction. Thus, since the
experimental evidence agrees with the math of conventional relavivity,
it also agrees with its proper interpretation.
> The Walker-Dual experiment is new, and shows that both electrostatic
>and gravitational fields propagate much faster than photons do.
>Accordingly, some relativists are upset.
I'm not familiar with this experiment. But if it also merely confirms
that electrostatic and gravitational near fields 'lead' the retarded
positions of the charges/masses then this does not show that they
propagate any faster than c either. To show what Tom claims they do they
would have to consider source motions that are so fast and complicated
that the 'leading' effect could in principle wrongly predict the actual
instantaneous locations of the sources--and yet the actual forces would
have to still be determined by those instantaneous positions.
>>For instance, in the slow speed limit of relativity the gravitational
>>force on an orbiting planet *should* be toward the instantaneous location
>>of the Sun (at least up to terms of order 1/c^2) rather than toward the
>>apparent direction toward it as seen by the aberrated image caused by the
>>time delay in the light propagating to the planet from the Sun, which is
>>merely a 1/c effect.
>
> That claim is made and taught by relativists. It cannot be justified.
Although I can not claim to be a relativist (as my field is statistical
mechanics), I believe it can be justified. I would invite anyone on the
list whose field of specialization is relativity to comment on this.
(Certainly Don Page would be more than qualified enough to comment, as
would George Murphy. Unfortunately, I think they don't participate in
this forum as possible casualties of the phenomenon that Glenn mentioned
about the loss of the "powerful thinkers".
I think my claim about aberration as being a 1/c effect can be seen by
inspection of the formula for the angle of aberration. The claim about
the direction pointed to by gravitational fields can, presumably, be
justified by looking at the appropriate post-Newtonian and
post-post-Newtonian approximation equations derived from GR and looking
at the order in 1/c to which they happen to be correct as agreeing with
full-blown GR.
>Forces that undisputably propagate at speed c (such as radiation pressure,
>the Compton effect, etc.) always act from the retarded position of the
>source, not its instantaneous position. The magic "cancellation" of
>retardation effects is a myth. Nothing actually cancels these effects in
>relativity. They simply never existed in the mathematical theory from the
>outset.
In the case of electostatics the cancellation effect is manifestly
present in the solution of Maxwell's equations and can be found by using
the retarded Lienard-Wiechert potentials. Van Flandern even gives a
reference to it in his paper, i.e. the Feynmann Lecture notes (v. II,
#21). In the case of gravitation I doubt that exact analogs to the
retarded Lienard-Wiechert potentials exist as closed form solutions to
Einstein's (nonlinear) equations of GR (but not being a GR expert I could
be wrong about this). However for slow speeds and weak fields their
solution can be expanded as a series of corrections in powers of 1/c^2 --
the first order correction being the post-Newtonian approximation. I
haven't studied this approximation in detail, but I expect that it does
predict that GR gravitation predicts motions based on future-predicted
extrapolation from the retarded positions of the sources (effectively
'leading' the retarded positions) and cancelling the retardation effects
to at least 1/c^2 (my guess is that the deviation may be to even a higher
power such as 1/c^3 or 1/c^4 than this though, and includes a 'leading'
extrapolation based on the position, velocity, and acceleration of the
sources at the retarded times).
>>*If* the Sun's gravitational force *had* been observed to align with
>the optical abberated image of the Sun, then the result *would*
>>contradict relativity, rather than its *straw man* version.
>
> The force of radiation pressure (e.g., sunlight pushing on a balloon
>satellite) does come from the retarded (optical) position of the Sun. Does
>that therefore contradict relativity?
Of course not.
>It seems to me you can't have it both
>ways. Why do all forces that propagate at speed c or slower clearly show
>retardation, whereas electrostatic and gravitational fields, which
>experimentally seem to propagate much faster than c, show no retardation?
Tom knows the answer to this question. Near-field electrostatics and
gravitation *anticipate* the non-retarded source positions based on the
conditions at the retarded times. They do not *propagate* faster than c.
Near-field configurations don't so much propagate at all, as they are
already pre-existently established, and any *changes* from their
anticipated/predicted/extrapolated behavior *do* propagate at speed c.
>>in the case of general relativity at low speeds, (AFAIK since I'm not
>>an expert) the behavior is similar *except* that the 'leading' action
>>effect is even more sophisticated. In this case if mass A is moving by
>>mass B then the gravitational force on mass B at time t points in the
>>direction mass A would be then *if* at time t - L/c it kept the same
>>velocity *and acceleration* it had then right up until time t.
>
> This is a reasonable statement about what might be true if the premise
>(that gravity propagates at speed c) were true. However, consider a binary
>pulsar. Whenever the two stars line up with a distant observer, the
>gravitational force on that observer is a maximum; and when the two stars
>are aligned perpendicular to the direction of the observer, the
>gravitational force is a minimum. So as the stars revolve, the gravitational
>field fluctuates too.
This would only be the case in the near-field regime where the observer
is much closer than cT where T is the orbital period of the binary
system. In this regime the 'leading' effect (the cancelling out most of
the retardation effects) would account for the results. But I don't
think this is the case for the gravitational field experienced by the
observer assuming the observer's distance from the system is very far
compared to cT since those fluctuations would then propagate at speed c
as the ordinary gravitational waves being broadcast by the oscillatory
mass quadrupole moment of the system.
> If the observer is far enough away, so that the stars make several
>revolutions during the light-time to the observer, then the observer sees
>the stars at some phase quite different from their actual phase at that
>instant. The question is, what does the gravitational field do? The answer,
>evident from either the field equations or the relativistic equations of
>motion (such as those on p. 1095 of "Gravitation" by Misner, Thorne and
>Wheeler), is that the gravitational field at the observer always agrees with
>the true, instantaneous positions of the source bodies, and not with their
>retarded (optical) positions, even if extrapolated forward using both
>velocity and acceleration.
I don't think the field equations predict this at all. The far-field
case you suggest here has the fluctuations in the gravitational effect
from the system propagate as ordinary gravitational waves at speed c.
As far as the equation given in MTW p.1095 goes, that is irrelevant for
(and that approximation breaks down for) this far-field problem. That
case (i.e. MTW p.1095) is the usual near-field post-Newtonian
approximation that is correct for terms through order 1/c^2. I think the
(post-post-Newtonian) corrections to this go as 1/c^4. In the near-field
where this post-Newtonian approximation applies it *includes* the
'leading' effect through the order in 1/c^2 considered. The corrections
to it due to the possibility of complicated motions that 'fool' the
'leading' effect go, I believe, as a higher order in 1/c^2. Because of
this the post-Newtonian approximation is too weak of an approximation to
discriminate between an theory with instantaneous interactions and a
causal one (with influences propagating at speed c) which does not have
them, but appropriately 'leads' the retarded positions.
>General relativity actually assumes instantaneous
>propagation of gravitational forces (but not "gravitational waves", which do
>propagate at speed c in all theories), which is why it agrees with Newtonian
>gravity in the low-velocity, weak-field limit. If GR had propagation delays,
>it wouldn't agree with either Newton or observations in that limit.
I disagree. I think changes in gravitational fields beyond those
predicted by the 'leading' effect *do* propagate at speed c in GR. The
Newtonian limit obtains because the 'leading' effect is so good in the
near field that the corrections due to its breakdown go as a higher power
of 1/c^2 which rapidly disappears as that (near-field) limit is taken.
I believe GR does have propagation delays at speed c, but it still agrees
with the Newtonian limit and the observations *because* of the 'leading'
effect that shows up and becomes most important in the near-field.
>>I suppose that the reason the Van Flandern was so coy about all of this
>>in his paper is that he had ulterior motives in publishing it. He heads
>>a fringe science (maybe pseudoscience) organization called Metaresearch
>>that advocates a bunch of wierd non-mainstream theories.
>
> Ah. Whenever you don't like the message, attack the messenger. Good
>science. :-)
I'm sorry if this sounded like an attack. It's just I had not been
very familiar with these theories until I visited the metaresearch web
site and they struck me as wierd and non-mainstream. I don't
particularly care if these theories are ultimately correct or not, so it
is not that I "don't like the message". I don't have any personal,
professional, philosophical, or religious stake in the correctness
mainstream physical theories, so I would not be very upset (other than
the nuisance of having to relearn most of my physics) if they were
someday overturned. OTOH, I have no prior metaphysical or religious need
to want to challenge the reigning physics paradigm either. It's just
that I haven't yet come across evidence that would seem to seriously
threaten that paradigm, and the theories described on that web site
struck me as "fringe" science.
> I suggest that we provide the URL, <http://metaresearch.org>, and let
>readers decide for themselves whether the organization (which does sharply
>criticize theories that conflict with experiments or observations) supports
>science or pseudoscience.
Fine. I would be interested in the opinions of others who have an
advanced knowlege of relativistic and planetary physics concening the
contents of this site. BTW, I didn't say Van Flandern's theories were
pseudoscience. I said they were 'fringe' science and parenthetically
said they *may be* pseudoscience. Admittedly, not all fringe science is
pseudoscience (and Van Flandern's theories may well be among those), but
all pseudoscience *is* on the fringe. To know one way or the other for
sure about this I would have to spend much more time studying these
theories than I am willing to invest.
> ...
>You seem to be arguing that experimental evidence favoring Lorentz over
>Einstein, or in general any argument that an accepted model may be incomplete
>or mistaken, even when published in a major, peer-reviewed journal (as is the
>case for all the examples you cite above), automatically qualifies as
>pseudoscience.
Not at all. I just do not think the evidence presented in Van Flandern's
Phys. Lett. A does anything to discriminate between Lorentz and Einstein.
I think it confirms both equally (at the SR level), and since Lorentz
doesn't even have (to my knowlege) a theory of gravitation that could
compete with GR anyway, it seems that the hegemony of Einstein is not
threatened by that evidence.
Again, regarding the pseudoscience aspect, a fringe theory does *not*
automatically qualify as pseudoscience, but it puts in a narrower
category of which all pseudoscience is a subset. It is entrirely
possible to be in that fringe category and not be pseudoscience though.
>IMO, such a view is too extremist. All of us should remain
>open to well-reasoned and tested challenges to all scientific
>theories at all times. That is how science continues to grow.
No quarrel from me about this. In fact, I believe that people like
Van Flandern working on fringe areas which challenge the reigning
paradigm perform an important service to science (assuming for now that
such fringe work doesn't actually qualify as pseudoscience). If there
*are* problems with mainstream theories, it will probably be easier for
them to be discovered and corrected if such people exist, than if the
only people working in a field are all yes-men to the status quo who have
been conditioned by their training to be blind to potential problems in
the mainstream theories. It's never bad for a theory to be critically
examined at it foundations. At worst it could only be a consumption of
time and effort that could more profitably be invested elsewhere.
However, in the specific case of the paper in question I have found
nothing that actually does challenge the status quo.
David Bowman
dbowman@georgetowncollege.edu