Vern wrote:
I thought that the only difference between Newtonian Gravity (NG) and
General Relativity (GR) as far as the math goes is that the speed
limit established by Special Relativity (SR) has to apply to General
Relativity, otherwise the theories (GR and SR) would be in conflict.

No. It's much more complicated than that. GR completely replaces the
previous notions about the geometry of space and time with a curved
manifold in which the geometry of spacetime is what we call "gravity".

The essential feature is that time is included in the geometry -- this
is what makes it possible for the geometry to mimic a "gravitational
force". In GR the analogy to "gravitational force" is components of the
connection, in a similar manner to the way that "centrifugal and
Coriolis forces" in classical mechanics are fictitious -- all three are
merely due to one's choice of coordinates, and are not any sort of
physical interaction. In a very real sense these fictitious "forces" are
merely a method of bookkeeping.

For example, on earth when one drops a stone it falls
to the ground. In NG this is modeled as a gravitational
force that accelerates the freefalling stone downward.
In GR this is modeled as the earth affecting the metric
of spacetime, and therefore the geodesic paths. The stone
follows a geodesic path once it is released, and the
geodesic that is determined by its initial conditions
(i.e. of your hand just before releasing the stone) is
headed downward with accelerating speed relative to the
surface. These are two completely different ways of
describing the same physical observations.

[Note I'm neglecting the air and other minor things.]


If GR is using infinite gravity force propagation speed, then why
were the predictions of GR versus NG different?

GR has no "gravity force propagation speed", regardless of what others
might say around here. Because there's no "gravity force" to have any
sort of speed.

The predictions of GR are different from NG because GR itself is a
completely different theory. But in the domain where NG is valid (e.g.
here on earth, most of the solar system), the predictions of GR and NG
are experimentally indistinguishable. But GR has a much wider domain
than NG.




TVF has concocted a fantasy theory which he claims is GR, but isn't:

Tom Van Flandern wrote:
GR introduces the concept of a "gravitational (potential) field".

This is just plain wrong. The gravitational potential field was
introduced into Newtonian gravity several centuries ago. Poisson and
Laplace devised the equations it satisfies.

GR actually abandons that potential field, because it is a scalar field
and that is woefully inadequate to represent the geometry of a 4-d
spacetime manifold (which requires a rank-2 tensor field, the metric).


This field is the physical equivalent of the light-carrying medium,

Perhaps in your fantasy theory, but not in GR. In particular, in GR
light rays follow null geodesic paths, and no type of "potential field"
can possibly represent that.

Yes, if one only considers elementary situations with
weak fields, one could probably concoct a model of a
"light-carrying medium" that approximates the predictions
of GR for such physical situations. But in general it is
simply not possible -- geodesics do not form any sort of
field. For example, what sort of "light-carrying medium"
could make light rays stop at the horizon of a black
hole, and make them propagate backwards inside it?


The field is an add-on to NG

That's just ludicrous, and shows how little you understand GR. GR is not
at all an "add-on to NG", nor are any of its components.

Though I suppose this field could be an "add-on to NG" in
your fantasy theory.


Any "conflict" between SR and GR is moot because GR is based on
Lorentzian relativity (LR),

This shows a complete failure to understand history. And SR, and LR, and GR.


Vern wrote:
when GR was first developed it was said that the theory had different
predictions from NG, but did GR really distinguish between a
gravitational (potential) field being limited by the speed of light
and the gravitational force still using NG equations?

GR made correct predictions about various observed phenomena. It did
this without any "gravitational force" or any "gravitational (potential)
field". GR is all about GEOMETRY, regardless of what others around here
might claim.

Today GR makes correct predictions about a much wider set of
observations and experiments. There remain puzzles and it's quite
possible that GR will be experimentally refuted sometime soon. But this
is completely unrelated to Tom Van Flandern's misconceptions.


I thought GR was just a field theory and the math of a field theory
determines whether the forces (radially inward forces?) are acting
instantaneously or with a speed limit, but a field theory cannot have
both. In other words, the field is the force, so it can only have
one speed.

There is no "gravitational force" in GR, and what you say is just plain
inappropriate. You (and TVF) need to learn what GR actually is before
you can hope to describe it.

Suggestion: Geroch, _General_Relativity_from_A_to_B_. This
is a nonmathematical introduction to the basic concepts
of GR.


I'll take a look at the link you provided when I can find time to see
if it helps clear this up for me.

All it can possibly do is describe TVF's misconceptions. I made the
"mistake" of looking at the papers on his website, and they show beyond
any doubt that he does not understand either SR or GR (references in my
post from yesterday).

TVF will respond that I am discussing only the "geometric
interpretation", and that there is a "field interpretation"
in which his claims are valid. This is just more of his
fantasy. The actual solutions to the equations of GR do not
behave as he claims; nor do the solutions of the equations of
the appropriate approximation to GR. Such solutions are
completely independent of any "interpretation". Whenever TVF
says "field interpretation" he really means his fantasy theory.


Tom Roberts

I just realized I said something wrong:

Tom Roberts wrote:
Tom Van Flandern wrote:
This field is the physical equivalent of the light-carrying medium,
[this is TVF's fantasy theory, not GR]
Yes, if one only considers elementary situations with
weak fields, one could probably concoct a model of a
"light-carrying medium" that approximates the predictions
of GR for such physical situations. [...]

Nope, that is not possible. Such a "medium" could not possibly reproduce
the gravitational time dilation between clocks at rest in a valley and
on a mountaintop; nor could it reproduce the time dilation between
relatively-moving clocks at the same gravitational potential.

If one attempted to invoke two different solutions (e.g. that "medium"
for light and some magical "time dilation medium" for clocks that
somehow "knows" about both gravitational potential and relative motion),
then there would be double-counting for light rays between such clocks.

It's also not obvious that such a "medium" could reproduce observations
of electric and magnetic fields. Indeed, all of the problems with aether
theories and SR would arise.

Do not deceive yourself into thinking "all clocks use EM".
Spinning objects are clocks that use no EM in their time-
keeping mechanism, and GR predicts time dilation between
such mechanical clocks. Whether or not we have observed
such dilation is irrelevant, as this discussion is about
the structure of theories, and it's QUITE CLEAR that
TVF's fantasy theory cannot possibly be equivalent to GR.


Tom Roberts

"Tom Roberts" wrote in message
...
I just realized I said something wrong:

Oh goody. You've been doing that for years, you ****ing moron.

On Sep 10, 11:33*pm, Tom Roberts wrote:
I just realized I said something wrong:

Tom Roberts wrote:
Tom Van Flandern wrote:
This field is the physical equivalent of the light-carrying medium,
[this is TVF's fantasy theory, not GR]
* * Yes, if one only considers elementary situations with
* * weak fields, one could probably concoct a model of a
* * "light-carrying medium" that approximates the predictions
* * of GR for such physical situations. [...]

Nope, that is not possible. Such a "medium" could not possibly reproduce
the gravitational time dilation between clocks at rest in a valley and
on a mountaintop; nor could it reproduce the time dilation between
relatively-moving clocks at the same gravitational potential.

You never stop saying wrong things, Honest Roberts. Neither
gravitational time dilation nor "time dilation between relatively-
moving clocks at the same gravitational potential" exists. It all
depends on the validity of Einstein's 1911 equation c'=c(1+V/c^2) and
the equivalent (that is, deduced from Einstein's 1911 equation by
applying Einstein's equivalence principle) equation c'=c+v given by
Newton's emission theory of light. If the equations are correct, both
time dilations simply do not exist (you know that don't you). If the
equations are incorrect, that is, if the speed of light does NOT vary
with the gravitational potential V or with the speed of the light
source v, then all sorts of miracles - time dilation, length
contraction etc. are deducible but the picture gets too absurd (you
know this as well don't you). Einsteinians cleverer than you have
hinted at the right solution, Honest Roberts:

http://www.blazelabs.com/f-g-gcont.asp
"So, faced with this evidence most readers must be wondering why we
learn about the importance of the constancy of speed of light. Did
Einstein miss this? Sometimes I find out that what's written in our
textbooks is just a biased version taken from the original work, so
after searching within the original text of the theory of GR by
Einstein, I found this quote: "In the second place our result shows
that, according to the general theory of relativity, the law of the
constancy of the velocity of light in vacuo, which constitutes one of
the two fundamental assumptions in the special theory of relativity
and to which we have already frequently referred, cannot claim any
unlimited validity. A curvature of rays of light can only take place
when the velocity of propagation of light varies with position. Now we
might think that as a consequence of this, the special theory of
relativity and with it the whole theory of relativity would be laid in
the dust. But in reality this is not the case. We can only conclude
that the special theory of relativity cannot claim an unlimited domain
of validity ; its results hold only so long as we are able to
disregard the influences of gravitational fields on the phenomena
(e.g. of light)." - Albert Einstein (1879-1955) - The General Theory
of Relativity: Chapter 22 - A Few Inferences from the General
Principle of Relativity-. Today we find that since the Special Theory
of Relativity unfortunately became part of the so called mainstream
science, it is considered a sacrilege to even suggest that the speed
of light be anything other than a constant. This is somewhat
surprising since even Einstein himself suggested in a paper "On the
Influence of Gravitation on the Propagation of Light," Annalen der
Physik, 35, 1911, that the speed of light might vary with the
gravitational potential. Indeed, the variation of the speed of light
in a vacuum or space is explicitly shown in Einstein's calculation for
the angle at which light should bend upon the influence of gravity.
One can find his calculation in his paper. The result is c'=c(1+V/c^2)
where V is the gravitational potential relative to the point where the
measurement is taken. 1+V/c^2 is also known as the GRAVITATIONAL
REDSHIFT factor."

http://books.google.com/books?id=JokgnS1JtmMC
"Relativity and Its Roots" By Banesh Hoffmann
p.92: "There are various remarks to be made about this second
principle. For instance, if it is so obvious, how could it turn out to
be part of a revolution - especially when the first principle is also
a natural one? Moreover, if light consists of particles, as Einstein
had suggested in his paper submitted just thirteen weeks before this
one, the second principle seems absurd: A stone thrown from a speeding
train can do far more damage than one thrown from a train at rest; the
speed of the particle is not independent of the motion of the object
emitting it. And if we take light to consist of particles and assume
that these particles obey Newton's laws, they will conform to
Newtonian relativity and thus automatically account for the null
result of the Michelson-Morley experiment without recourse to
contracting lengths, local time, or Lorentz transformations. Yet, as
we have seen, Einstein resisted the temptation to account for the null
result in terms of particles of light and simple, familiar Newtonian
ideas, and introduced as his second postulate something that was more
or less obvious when thought of in terms of waves in an ether. If it
was so obvious, though, why did he need to state it as a principle?
Because, having taken from the idea of light waves in the ether the
one aspect that he needed, he declared early in his paper, to quote
his own words, that "the introduction of a 'luminiferous ether' will
prove to be superfluous."

Pentcho Valev

Sorry for the slow responses. I was at the "Crisis in Cosmology 2"
conference (http://cosmology.info/2008conference/) last week. This responds
to Vern and Tom Roberts.

Summary (for those joining the thread):

(1) There are two versions of the relativity of motion, Einstein's special
relativity (SR) with a universal speed limit of c, and Lorentzian relativity
(LR) with no speed limit. [Ref. 1] Both employ the same basic math, the
Lorentz transformations; and both can explain the eleven experiments that
test various aspects of these models. [Ref. 2]

(2) In Feynman's words: "It is one of the peculiar aspects of the theory of
gravitation (GR), that it has both a field interpretation and a geometrical
interpretation. . the fact is that a spin-two field has this geometrical
interpretation: this is not something readily explainable - it is just
marvelous. The geometrical interpretation is not really necessary or
essential to physics." [Ref. 3]

(3) The fact that LR exists as a not-yet-falsified theory for the relativity
of motion and potential replacement for SR, yet has no speed limit, means
that the speed of light c need not be a speed limit for propagation or
communication. Conclusions based on the assumption that c is a speed limit
may be invalid. In that connection, it is noteworthy that the Global
Positioning System (GPS) chooses to use LR rather than SR for clock
synchronization so that all clocks in all reference frames can be
synchronized once and stay synchronized (except for small clock
imperfections). Doing this "synchronize all clocks" trick in the twin's
paradox is very insightful for understanding the relativity of motion. [Ref.
4]

(4) All six experiments bearing on the propagation speed of gravitational
and electrodynamic forces indicate they propagate much faster than light, in
agreement with computer experiments showing that retarded forces produce
open spiral orbits. These results apply even for static fields. Moreover, in
both cases, even when the source mass or charge accelerates during the light
time from source to target, the force propagation speed is still provably
faster than light. The existence of propagation speeds faster than light in
forward time falsifies SR in favor of LR. [Ref. 5]

(5) Deep reality physics forbids miracles. [Ref. 6] In the geometric
interpretation of GR ("space tells matter how to move, matter tells space
how to curve"), no cause exists for a target body at rest in the field of a
source mass to begin 3-space motion. (Such motion would be an effect without
a physical cause, a form of miracle in physics.) Moreover, there is no
source for the new 3-space momentum acquired by a target body. (This would
be creation of momentum from non-momentum, another form of miracle in
physics.) Since miracles are excluded in physics, the geometric
interpretation of GR is falsified in favor of the field interpretation (with
real, physical forces, requiring no miracles). [Ref. 5]


Vern writes:

[Vern]: when GR was first developed it was said that the theory had
different predictions from NG, but did GR really distinguish between a
gravitational (potential) field being limited by the speed of light and
the gravitational force still using NG equations? I thought GR was just a
field theory and the math of a field theory determines whether the forces
(radially inward forces?) are acting instantaneously or with a speed
limit, but a field theory cannot have both. In other words, the field is
the force, so it can only have one speed.

You are describing the geometric interpretation of GR, the one taught
almost exclusively for the last few decades. In the field interpretation,
gravity is not a physical force (because the word "force" is redefined to
make that true), and motion changes are induced by space-time geometry. That
is the interpretation now falsified because it lacks a cause to initiate
motion in a target body at rest with respect to a source mass (effects
without causes are not allowed in physics), and it lacks a physical source
for the new 3-space momentum being continually acquired by the target body
(creation of momentum from a static field is also not allowed in physics).

The other classical physics interpretation of GR's math, the one favored
by Einstein, Dirac, and Feynman, among others, is the field interpretation.
In that physics, gravity is a classical 3-space force, the one used by
celestial mechanicians to compute orbits, and the field behaves as an
optical medium to produce the extra effects of GR such as light-bending,
redshift, propagation delay, and perihelion advance (by refraction). The
field interpretation was silent on the direction of the arrow of causality:
Did gradients in the field cause gravitational force, or vice versa? But it
was always clear that the force of gravity could not propagate as slowly as
the speed of light because orbits would then be open spirals.

My guess is that discomfort with that dilemma was responsible for the
migration toward the geometric interpretation after Einstein's death.
However, we now know there doesn't need to be any universal speed limit,
that GR is based on Lorentzian relativity rather than special relativity,
that GPS uses LR rather than SR, and that geometric GR requires two types of
physics miracles. So the field interpretation of GR is now golden and the
geometric interpretation is off the table. That represents no change in
mathematical GR, but only a change in the physical interpretation of the GR
equations.


and Tom Roberts writes (to Vern):

[Roberts]: in the domain where NG is valid (e.g. here on earth, most of
the solar system), the predictions of GR and NG are experimentally
indistinguishable.

So you agree that in most of the solar system, GR is experimentally
indistinguishable from NG, a theory with infinite force propagation speeds
that gives strongly spiral orbits if the force propagation speed is reduced
as low as c? I'm betting that, once you realize the implications of your
claim, you will back away from it.

[TomVF]: This field is the physical equivalent of the light-carrying
medium [aether]

[Roberts]: Perhaps in your fantasy theory, but not in GR. In particular,
in GR light rays follow null geodesic paths, and no type of "potential
field" can possibly represent that.

Despite your numerous unsupported and unsupportable claims, I have hope
that you can still learn. According to Einstein, aether could be equated to
the gravitational potential field. In his own words, "The aether of the
general theory of relativity is a medium without mechanical and kinematic
properties, but which codetermines mechanical and electromagnetic events."
[A. Einstein, Ether and the theory of relativity, Springer, Berlin (1920),
reprinted Dover (1983), p. 23; also
http://www.tu-harburg.de/rzt/rzt/it/Ether.html or
http://www.mountainman.com.au/aether_0.html] The whole article is worth a
read because he describes this "new aether" and its relation to the
potential field in some detail.

Meanwhile, both Einstein and Eddington showed that the math of null
geodesics was identical in both the geometric and field interpretations.
Eddington wrote: "Light moves more slowly in a material medium than in
vacuum, the velocity being inversely proportional to the refractive index of
the medium. The phenomenon of refraction is in fact caused by a slowing of
the wave-front in passing into a region of smaller velocity. We can thus
imitate the gravitational effect on light precisely, if we imagine the space
round the sun filled with a refracting medium which gives the appropriate
velocity of light." [Ref. 7] He then proceeds to derive the relativistic
light-bending formula from the "potential-field-equals-optical-medium"
premise by simply adopting a refractive index of 1/1-2GM/rc^2 (where GM/r is
the potential), the value it should have if gravity determines the potential
medium (aether) density.

[Roberts]: Such a "medium" could not possibly reproduce the gravitational
time dilation between clocks at rest in a valley and on a mountaintop; nor
could it reproduce the time dilation between relatively-moving clocks at
the same gravitational potential.

Wrong. The medium does precisely that. Clocks tick slower where the
medium is denser, and tick faster where the medium is sparser. Potential is
in effect a measure of medium density. Motion through a medium encounters
more medium per unit time, the physical equivalent of being at rest in
denser medium. It all works out beautifully without plucking a single hair
from Einstein's legacy, which is why there is so much excitement about
"pushing gravity" and the new physics underlying relativity. [Ref. 8]

[Roberts]: what sort of "light-carrying medium" could make light rays stop
at the horizon of a black hole, and make them propagate backwards inside
it?

Einstein argued in 1939 that black holes were no part of his theory.
[Ref. 9] Even today, there is no convincing evidence that black holes exist,
as opposed to "Mitchell stars". The latter is the next stage of
gravitational collapse after neutron stars in modern gravitational theory.
It has the advantage of not requiring singularities in nature. That would be
another form of miracle because logic dictates that the finite can never
become infinite in physical reality, no matter what the math says.

[Roberts]: There is no "gravitational force" in GR

This displays your ignorance of the field interpretation of GR. Sadly
for you, now that the geometric interpretation is falsified, the field
interpretation is the only one left.

[Roberts]: You (Vern, and TVF) need to learn what GR actually is before
you can hope to describe it.

That suggestion applies to yourself in spades. You learned only one
interpretation, and seem unable to break away from it despite being shown
good cause to do so. I keep providing the observations, experiments,
reasoning, and/or citations, but these seem to go over your head. Your only
defense, that I don't know what I'm talking about, looks pretty silly when
you can't defend your claims, while I can defend mine.

BTW, have YOU ever published anything about GR? Or are you just a
student of the subject who had teachers with limited knowledge? -|Tom|-


REFERENCES:
[1] "Is faster-than-light propagation allowed by the laws of physics? (A
primer on Lorentzian relativity)", Infinite Energy 59, 31-33 (2005); on web
at http://metaresearch.org/cosmology/gravity/LR.asp.

[2] "What the Global Positioning System tells us about relativity", in "Open
Questions in Relativistic Physics", F. Selleri, ed., Apeiron, Montreal, pp.
81-90 (1998); on web at
http://metaresearch.org/cosmology/gps-relativity.asp.

[3] "Feynman Lectures on Gravitation", R.P. Feynman, Addison-Wesley, New
York (1995), Section 8.4, p. 113.

[4] "What the Global Positioning System tells us about the twins paradox",
in "Einstein, Relativity and Absolute Simultaneity" edited by W.L. Craig and
Q. Smith, Routledge, London & New York, pp. 212-228 (2008); on web at
http://metaresearch.org/cosmology/gravity/gps-twins.asp.

[5] "Experimental Repeal of the Speed Limit for Gravitational,
Electrodynamic, and Quantum Field Interactions", T. Van Flandern and J.P.
Vigier, Found.Phys. 32:1031-1068 (2002). Preprint under title "The speed of
gravity - Repeal of the speed limit" available at
http://metaresearch.org/cosmology/gr...peed_limit.asp.

[6] "Physics has its principles", in Gravitation, Electromagnetism and
Cosmology, K. Rudnicki, ed., C. Roy Keys Inc., Montreal, 87-101 (2001); on
web at http://metaresearch.org/cosmology/Ph...Principles.asp.

[7] Sir Arthur Eddington, "Space, Time & Gravitation", Cambridge Univ.
Press, first published 1920, reprinted 1987, p. 109.

[8] "Pushing Gravity: New Perspectives on Le Sage's Theory of Gravitation",
M. Edwards, ed., Apeiron Press, Montreal (2002).

[9] A. Einstein, "Annals of Mathematics", vol. 40, #4, pp. 922-936 (1939).


Tom Van Flandern - Sequim, WA - see our web site on frontier astronomy
research at http://metaresearch.org

Tom Roberts writes:

[TomVF]: Publication of experiments funded in-house is often published
in-house at most major science agencies because that enhances the
agency's reputation. These are still peer-reviewed papers. In-house
editorial boards are usually stricter than journal referees because they
feel the reputation of their home institution is at stake.

[Roberts]: Nonsense. That may be the policy of YOUR "Meta-Research
organization", but it most definitely is not the policy of any major
university -- "publish or perish" applies....

You continue to make absurd claims without any basis. Each government
agency I worked for or worked with had its own editorial board for precisely
the purpose I specified. Probably dozens of people reading this can confirm
that is the case for their own agencies.

[Roberts]: Though it is QUITE CLEAR that the in-house "peer review" of
metaresearch.org is ludicrous and/or involves "peers" who do not
understand relativity.

Certainly, none of our reviewers has so limited a knowledge of the
subject as you do.

[TomVF]: A better question is, given the importance of this result and
the lack of any other experiment to justify what is in the textbooks, why
has no one else ever attempted to replicate it, even just to refute
Sherwin and Rawcliffe?

[Roberts]: Probably for the simple reason that essentially nobody knows
about it.

You missed the thrust of my point. Why has no one anywhere in physics
attempted to do an experiment to learn if the force between *accelerating*
charges propagates at speed c or faster? It's a pretty important matter, and
many physics texts read as if the experiment was done and the result is
known. That kind of mythology retards progress in the field.

[TomVF]: The derivation of equations of motion from those [solutions of
the field] equations is not unique until one specifies the speed of
interactions. That speed has always been taken as instantaneous by GR,
which is the correct assumption.

[Carlip]: Nonsense.

[TomVF]: That's your argument? Nonsense? You don't even say what point
you consider nonsense: that the equations of motion depend on an
assumption about the interaction speed, or that GR makes the correct
assumption.

[Roberts]: Both (sort of) -- in GR the equations of motion for a test
particle have no dependence whatsoever on any "interaction speed".

Right because, as I explained, that "interaction speed" term was driven
to zero by adopting infinite gravitational force propagation speed.

[Roberts]: All one needs to do is LOOK AT THE MATH to see this is so.

And all one needs to do is understand basic physics to see why one thing
cannot act on another without a material, tangible entity passing between
them. Any such entity obviously has a propagation speed.

[TomVF]: You will have to do better.

[Roberts]: No, the problem is yours, and YOU will have to understand the
mathematics of GR. It is quite different from what you try to discuss.

No one can apply math to physics until they understand physics. You wish
to ignore all issues of physics, so your position remains indefensible.

Can you even imagine an issue we might have with the math? This
discussion is all about what the math means to physics. But I understand why
you keep harping back to mythical math issues because you are out of your
comfort zone when discussing the physics behind the math.

[Carlip]: The geodesic equations are ...

[TomVF]: The solution is unique for any fixed point in the field.

[Roberts]: No. You keep showing that you simply do not understand the
math. The entire solution is unique, giving the trajectory of the test
body. This holds for every point the test body ever occupies, not just
some "fixed point".

If that were true, then the math would have nothing to do with reality.
In the physical world, source masses change target body momentum via the
propagation of material, tangible entities ("force" carriers). Such forces
are necessarily retarded if the target body is moving. Aberration is simply
the ratio of transverse target body speed to force propagation speed.

The only physical justification for ignoring the retardation of forces
(setting aberration to zero) in the math is the adoption (whether implicit
or explicit) of infinite force propagation speed. If you don't understand
this basic physics point, then you have no defense for drawing conclusions
about physics from the math.

[Roberts]: NONE of the experiments you cite are sensitive enough to
resolve the difference between the predictions of Newton and GR.

The experiments are looking for a retardation effect four orders of
magnitude larger than GR effects such as light-bending or perihelion
advance. You apparently don't know much celestial mechanics, and should
refrain from comments in that subject area lest you remove all doubt.

[Roberts]: how little you read what other people write.

All you write is blustering claims and insults like this one. When have
you ever attempted to communicate something of substance by mentioning an
experiment, observation, reasoned argument, or citation? Your entire stance
seems to rest on an appeal to authority, a type of argument never valid in
science. When any issue is disputed in science, only the merits of the
arguments matter, not the number or prestige of experts on one side of the
issue.

[Roberts]: there is an APPROXIMATION to GR that has a propagation delay of
c, and in which the orbit does not "spiral" significantly

Wrong. If you can produce such an approximation (by experiment,
observation, reasoning, or citation), I'll be happy to concede victory to
you. I can only hope that you are gracious enough to reciprocate when you
find out that no such approximation exists.

For example, the gravitational radiation delay is proportional to c^-5,
and is utterly insignificant compared to the matters we have been
discussing. The light-bending, gravitational redshift, propagation speed
delay, and perihelion advance factors are all proportional to c^-2, which is
orders of magnitude smaller than light-speed aberration everywhere in the
solar system. And any computer experiment, whether using Newtonian or GR
equations of motion, immediately demonstrates that propagation delays of c
generate rapid spiral orbits.

Do you accept this challenge to show a propagation delay of c in the GR
equations of motion, with little spiraling? Your efforts should be
instructive to both of us and to our readers.

[Roberts]: Steve Carlip has discussed a case for which an exact
computation in GR shows the direction of the 3-acceleration of a test body
does not point to the instantaneous position of the source.

Steve's case is theoretical and cannot be demonstrated experimentally.
The one I cited is an actual experimental result. Binary pulsars attract one
another from their instantaneous positions rather than from their
extrapolated, light-time-retarded positions.

BTW, I do have issues with the math of GR for strong fields and high
speeds. But nearly everybody cautions that GR has not been adequately tested
in that domain, and lots of relativists have suggested that changes may be
needed.

[Roberts]: One of [TomVF's web site] papers
(http://metaresearch.org/cosmology/gravity/gravity.asp) attempts to use
the GPS satellites to "prove" that the term -xv/c^2 does not appear in the
Lorentz transform for t=t', thus showing he does not understand the
basics of SR, what an inertial frame is, or how they apply (in a very
limited way) to the GPS.

That paper has had thousands of readers, but none so confused as to make
such an absurd interpretation you propose. The vx/c^2 term is not needed in
LR because the transformations work only one way, from the local
gravitational potential frame to the moving frame. But that term is an
intrinsic, integral part of SR. The important (experimentally verified) part
of the time transformation, the gamma term, is common to both SR and LR. As
I remarked before, GPS uses the LR form of the equations *without* the
vx/c^2 term. GPS synchronizes all clocks in all reference frames to the USNO
master clock. Then all those clocks remain synchronized (except for a small,
periodic eccentricity effect that vanished for circular orbits), despite
relativity corrections being quite large (~40,000 nanoseconds per day).

I give you credit for trying to read the paper. Please try again, now
that we are past the first point where your understanding of it
failed. -|Tom|-


Tom Van Flandern - Sequim, WA - see our web site on frontier astronomy
research at http://metaresearch.org

Tom Van Flandern wrote:
Tom Roberts wrote:
[Roberts]: in the domain where NG is valid (e.g. here on earth,
most of the solar system), the predictions of GR and NG are
experimentally indistinguishable.

So you agree that in most of the solar system, GR is experimentally
indistinguishable from NG, a theory with infinite force propagation
speeds that gives strongly spiral orbits if the force propagation
speed is reduced as low as c?

Why do you keep bringing up a FANTASY theory? There _IS_ no such theory
as "NG with force propagation speed reduced as low as c".

Yes, in this domain the predictions of GR are indistinguishable
from the predictions of NG. But one must use each ACTUAL THEORY, not
your fantasy.

In GR, nothing that carries energy, momentum, or information can travel
faster than c. This is a rigorous result based on the structure of the
ACTUAL THEORY. Your fantasy is not GR. Similarly, NG is not GR. But yet,
when one applies the ACTUAL THEORIES in this domain, the predictions of
GR are indistinguishable from the predictions of NG.



As I keep saying, GR itself has no "propagation speed" for gravity. But
if you really want to consider that speed, you can look at the
linearized APPROXIMATION to GR. In this approximation, the equations of
motion are solvable with a Green's function that clearly involves the
source at a retarded time. As in electrodynamics, this is easily
interpreted as "gravity propagating with speed c". But these equations
are NOT those of NG (or of GR, for that matter). In essence, the
trajectory of the source is extrapolated to second order from the
retarded time to the time of the observation. This means that for any
situation in which that extrapolated position is indistinguishable from
the instantaneous position of the source, the two theories (NG and this
approximation to GR) give indistinguishable results.

This last is true for all the experiments you claim "prove"
that "the force of gravity propagates c". And the reason
you are so confused is quite simple: you use your FANTASY
theory (i.e. NG with finite speed of propagation), rather
than the actual equations of GR, or the actual equations of
this approximation.


[A brief digression from gravity to electrodynamics]
Why has no one anywhere in physics attempted to do an experiment to
learn if the force between *accelerating* charges propagates at speed
c or faster?

There have been literally ZILLIONS of experiments that show that the
speed of radio waves is c. They are detected by the electromagnetic
forces on the charge carriers of the receiving antenna, generated by the
accelerating charge carriers in the transmitting antenna.


It's a pretty important matter, and many physics texts read as if the
experiment was done and the result is known.

Yes. It is.


[Back to gravitation]
[TomVF]: The derivation of equations of motion from those
[solutions of the field] equations is not unique until one
specifies the speed of interactions. That speed has always
been taken as instantaneous by GR, which is the correct
assumption.

[Carlip]: Nonsense.

[TomVF]: That's your argument? Nonsense?

Yes: Nonsense. There is no "interaction speed" anywhere in either the
equations of GR, in their derivation, or in their solution(s). This is
so because there is no "interaction" -- gravity is geometry in GR, and
the source mass/energy and the geometry evolve in a coordinated manner
(as described by Einstein's field equation). Any test particle responds
to its local geometry, not to any sort of "interaction" with the source
mass/energy.

You keep displaying your rather complete ignorance of GR. Perhaps you
should actually study the theory before attempting to discuss it.

OK, one could claim that the metric represents such an
"interaction" [#]. But still, there is no "speed" -- at
each and every point in the manifold the value of the
metric depends ONLY on the values of the metric and the
energy-momentum tensor in an infinitesimal neighborhood
of the point in question within its past lightcone. This
is what differential equations are, and "causality" in
GR limits the dependence to the past lightcone.

[#] in quotes because that would be an unusual meaning of
the word. This would be some sort of "generalized interaction"
because it quite clearly is not between any particular source
and the test particle in question. And, of course, geometry
does not "propagate" in any sense.



Do not babble on about "interpretations" of GR. That is just more of
your fantasy. Yes, there is a remarkable correspondence between GR and a
field theory of spin-2 particles. This is not a different
"interpretation" of GR, it is a completely different theory (one that is
incomplete...). For instance, that field theory of spin-2 particles is
formulated on Minkowski spacetime, and therefore is limited to manifolds
commensurate with Minkowski spacetime; not so GR -- indeed it is the
very essence of GR that manifolds with other topologies are important
and interesting.


And all one needs to do is understand basic physics to see why one
thing cannot act on another without [...]

But in GR, there is no GRAVITATIONAL "interaction" that consists of "one
thing acting on another". This is purely your FANTASY -- the structure
of GR is not what you suppose it to be.

In particular, the notion of "one thing acting on another" is a hallmark
of a LINEAR theory. That is, if objects act individually on each other,
the total interaction on a given object simply must be the sum of the
actions of all the other objects. GR is not like that at all, and is a
NONLINEAR theory.

I repeat: you keep demonstrating a serious lack of understanding of the
basics of GR. You should study THE ACTUAL THEORY before attempting to
make such statements. GR is not at all what you suppose it to be.

And I point out that here you make reference to "basic
physics" when you really mean "God" or "TVF's personal
channel to God", or "TVF's personal channel to 'reality'",
or somesuch. Those of us doing science can only understand
reality through formulating and testing physical theories.
We lack the special "channel" that TVF claims to have.
Hint: NONE of the fundamental theories of physics are
linear. So much for TVF's "basic physics"....


[Carlip]: The geodesic equations are ...
[TomVF]: The solution is unique for any fixed point in the field.

[Roberts]: No. You keep showing that you simply do not understand
the math. The entire solution is unique, giving the trajectory of
the test body. This holds for every point the test body ever
occupies, not just some "fixed point".

If that were true, then the math would have nothing to do with
reality.

You have a direct channel to "reality"????

You repeatedly make statements like this, implying that you, personally,
have knowledge that nobody else has. The rest of us are limited to
interpreting reality via THEORIES. We don't have any direct access to
"the mind of God" (or to "reality") as you keep claiming to have.

At present, the best theory of gravitation we have is General
Relativity. You should learn about it. It does NOT have the structure
you keep claiming. shrug


In the physical world, source masses change target body momentum via
the propagation of material, tangible entities ("force" carriers).

Again, you have some direct channel to "reality"????

And I don't think your claims apply to QED, QCD, or the
standard model. While these theories have force carriers,
they most definitely are not "material" or "tangible
entities".


There's no point in continuing. I am interested in science, not
the personal religion you keep trying to discuss. You phrase your
religion using the words of physics, but you do not understand the
nature of physics. Or science. Or modern theories of physics, such as
GR. Like all too many other crackpots around here, you do not bother to
understand the subject you have devoted a major part of your life to.
That's rather sad....


Tom Roberts

On Sep 22, 8:21*am, Tom Roberts wrote in
sci.physics.relativity:
Tom Van Flandern wrote:
Tom Roberts wrote:
[Roberts]: in the domain where NG is valid (e.g. here on earth,
most of the solar system), the predictions of GR and NG are
experimentally indistinguishable.

So you agree that in most of the solar system, GR is experimentally
indistinguishable from NG, a theory with infinite force propagation
speeds that gives strongly spiral orbits if the force propagation
speed is reduced as low as c?

Why do you keep bringing up a FANTASY theory? There _IS_ no such theory
as "NG with force propagation speed reduced as low as c".

Yes, in this domain the predictions of GR are indistinguishable
from the predictions of NG. But one must use each ACTUAL THEORY, not
your fantasy.

In GR, nothing that carries energy, momentum, or information can travel
faster than c.

Honest Roberts you are desperately lying again. See a previous
statement of yours made when Einstein criminal cult was still in no
danger and jugglers like you could safely refer even to the truth:

http://groups.google.ca/group/sci.ph...2a006c7d508022
Pentcho Valev: "CAN THE SPEED OF LIGHT EXCEED 300000 km/s IN A
GRAVITATIONAL FIELD?" Tom Roberts: "Sure, depending on the physical
conditions of the measurement. It can also be less than "300000 km/
s" (by which I assume you really mean the standard value for c). And
this can happen even for an accelerated observer in a region without
any significant gravitation (e.g. in Minkowski spacetime)."

Pentcho Valev

On Sep 15, 9:24*pm, "Tom Van Flandern" wrote
in sci.physics.relativity:
Sorry for the slow responses. I was at the "Crisis in Cosmology 2"
conference (http://cosmology.info/2008conference/) last week.

Did you manage to confuse everything at that conference, Flandern? If
you did not, just explain: What is the nature of Halton Arp's
"intrinsic redshift"?

Pentcho Valev

On Sep 22, 1:21*am, Tom Roberts wrote:

snip

[TomVF]: The derivation of equations of motion from those
[solutions of the field] equations is not unique until one
specifies the speed of interactions. That speed has always
been taken as instantaneous by GR, which is the correct
assumption.

[Carlip]: Nonsense.

[TomVF]: That's your argument? Nonsense?

Yes: Nonsense. There is no "interaction speed" anywhere in either the
equations of GR, in their derivation, or in their solution(s). This is
so because there is no "interaction" -- gravity is geometry in GR, and
the source mass/energy and the geometry evolve in a coordinated manner
(as described by Einstein's field equation). Any test particle responds
to its local geometry, not to any sort of "interaction" with the source
mass/energy.

You keep displaying your rather complete ignorance of GR. Perhaps you
should actually study the theory before attempting to discuss it.

This whole debate hinges on whether motion in GR is due to geometry or
whether the equations could also represent the description of a
field. It was, at first, called a field theory. The geometric
interpretation came later. Tom (Roberts) has indicated either that
the field version is the same thing as the geometric version, or that
there is no field version, there is just a geometric version. This
issue needs to settled definitely, as Tom (VanFlandern) is basing his
arguments on the field version and Tom (Roberts) is basing his
arguments on the geometric version. Could a referree be used to pose
this question to, to settle the debate?

Vern