On Jul 26, 5:48 pm, Tom Roberts wrote:
Ken S. Tucker wrote:
Hi Steve, Tom and all. I can suggest a means of resolution by
experiment, but it is complicated so stay with me on the bends.

Robert's, somehow you've screwed up
your replies below. My post was directed
to Tom VvF and Steve Carlip, perhaps having
an extra Tom messed things up.
From now on it's Tucker, Carlip, Flandern,
Roberts etc.
Anyway I'm a GRist on this issue and generally
agree Carlip.

Actually, it isn't complicated at all, and HAS ALREADY BEEN DONE.

Not to our knowledge Roberts, cite a specific
experiment or measurement - as I suggested -
to distinguish the speed of gravity from oo,
that's what the fella's need.
Regards
Ken S. Tucker
PS: I'll leave in Robert's pontifications
below...but Robert's don't do that to us
again.

The key is to realize that science is the process of testing theories,
not attempting to "measure" some nebulous "speed of gravity" that
depends in detail on one's model.

The actual observations for EVERY ONE of the experiments TvF cites are
in accord with the predictions of GR (there is also agreement with other
models and theories, but that is not at issue here).

The proper way to do science and compare theory to experiment is to
select a theory and use it to compute the same quantities that are
observed, and then compare the theoretical computations ("predictions")
to the actual measurements. Instead, TvF insists on taking the
observations, computing some model-dependent theoretical quantity
("speed of gravity") from them, and then comparing the result to
theories. THAT IS NOT SCIENCE. The reason his method is invalid is that
it is KNOWN to lead to erroneous conclusions (there are additional
difficulties related to error analysis).

So when he says "binary pulsars prove that when the source mass
accelerates (as in Steve's example), the target body responds almost
instantly", you should recognize: a) the observations do not MEASURE
such a "response", they only observe signals from the distant pulsars,
b) those signals are in agreement with the predictions of GR for
such a system, and c) the source NEVER accelerates "as in Steve's
example", the two objects merely orbit each other.

In GR, the "response" is delayed by a time L/c, but TvF
simply does not understand that in GR the acceleration
does not point at the retarded position of the source, it
points at the EXTRAPOLATED retarded position of the source
mass (i.e. extrapolated from its retarded position). For
every physical situation he considers, this extrapolated
position is indistinguishable from the instantaneous
position. When Steve presented a physical situation
for which they are distinguishable, TvF dismissed it as
"irrelevant".

The issue of this thread is TvF's claims that he is using GR, when in
fact his claims are at odds with the underlying structure of GR [#], and
he displays in every post a rather complete ignorance of GR. And, of
course, he has never done the computation in GR (or in an appropriate
approximation to GR).

[#] In GR, nothing that carries energy, momentum, or
information can travel with local speed c relative to
any locally-inertial frame. TvF's "speed of gravity"
would violate this, IF IT WERE GR. He is wrong,
because he is not actually applying GR. That is Steve's
point, and mine.

Tom van Flandern wrote:
The force propagation speed (the "speed of gravity") is much faster
than the speed c at which the physical field can change in response
to changes in the force.

Hmmm. It's not clear how "force" can "propagate" independent of the
"physical field" in a field theory such as GR. But no matter, let's
stick to the subject:

If what you say is true, then it cannot be possible that all these
statements are true:
A) the "field interpretation" is indeed GR.
B) the "gravitational force" in the "field interpretation" carries
energy and momentum (i.e. it can transfer them from one object
to another).
C) Low's paper has no error, and neither does Carlip's and the
zillions of other papers and textbooks.

Indeed, it is rather clear that your statement is false, because you
make an unacknowledged and implicit assumption that is false: that
"gravitational force" is central (i.e. points directly at the source).
In the appropriate approximation to GR in which there is a gravitational
force, this is not true.

So when we say "force is the gradient of potential", the geometric
interpretation of GR simply assumes that the gravitational potential
field, as described by the Einstein field equations, governs; and
that a gradient in that field causes a force.

YOU might assume that because you clearly do not understand the geometry
of GR, but no GR expert would do so. The "geometric interpretation of
GR" makes no such assumptions, because it has no "gravitational
potential" or "gravitational force". In the situations you consider,
objects follow geodesic paths through spacetime, and there is no "force"
on them at all (that's what "geodesic path" means).

Please don't confuse this with a planet's path through
space (as you have done before). Yes, the path of a planet
in 3-space is not a geodesic in space. But it _IS_ a
geodesic in spaceTIME (assuming the planet is small enough
that its effect on the geometry can be neglected). For
instance, the earth follows a helix through spacetime
centered on the sun, with a radius ~8 light minutes and a
period of one light year; this deviates from a straight
line by a few parts per million, consistent with the
curvature induced by the sun's gravitation (I'm
neglecting small stuff). The axis of this helix is
parallel to the time axis of local Minkowski coordinates
in which the sun is at rest.

the geometric interpretation of GR is no longer viable because it
violates physical principles.

Nonsense. It obeys DIFFERENT "physical principles" than you want to
accept. That's all. This is YOUR problem, not GR's or any "geometric
interpretation's".

So we are forced to adopt the other physical interpretation, that
gravitational force induces a gradient into the gravitational
potential field.

We are not "forced" to do that at all -- on a geodesic path there is no
"force" at all (it's your PUN, not mine).

All you ever do is show that the basics of GR are incompatible with your
closely-held beliefs about "physical principles", and that you don't
really understand GR. Both are YOUR problem.

[Roberts]: The problem is: your model is inconsistent with
"gravitational force" propagating at speed c; but the appropriate
approximation to GR is not inconsistent with that, nor is GR
itself.

That statement is flatly wrong. You really need to get yourself
straightened out about that point. Ask Steve Carlip or anyone who
knows relativistic dynamics. No model that has gravitational forces
propagating at speed c can reproduce the orbital motions of the
planets.

The basic problem is that we use different words and phrases, and have
different sets of implicit assumptions. Note that Steve Carlip discusses
ACCELERATION of the target object, not "force", and he discusses a DELAY
in the effects of stopping the source, not a "propagation speed" of
anything from source to target. His word choice is much better than
yours, as it is significantly more precise (but is still subject to the
implicit assumptions listed below).

A major part of his and my disagreement with your claims are several
implicit assumptions (Steve's computation has no need for these, but the
discussion uses all of them):
A) fields are weak and there is an obvious "background"
Minkowski coordinate system to use.
B) quantities such as time, position, velocity, acceleration, and
direction are referenced to the coordinates of (A).
C) the acceleration of a target body is in the same direction
as any "gravitational force" on that body, at every instant.
D) if any gravitational influence propagates from source to target,
then the speed of propagation is the ratio of the distance
between them to the delay between changes in the source's motion
or position and the effect on the target's motion, with all
quantities measured in the coordinates of (A).

[Note that the acceleration of (C) is nonzero, even though
in GR there is no "gravitational force" and the
4-acceleration of the target body is zero. See (B).]

Steve's computation clearly shows that with these assumptions, in GR the
speed of (D) is c, not c. There is no interpretation in his
computation, and the only interpretations required to relate its result
to this discussion are listed above.

Now consider the physical situation you consider: two isolated objects
in mutual orbit. While I know of no exact computation, I believe there
are computations in an approximation to GR that have the same basic
features of Steve's computation: the acceleration of one object points
toward the EXTRAPOLATED retarded position of the other object. This is a
counterexample to your claim "No model that has gravitational forces
propagating at speed c can reproduce the orbital motions of the
planets." And this also explains how it is that you can be deluded into
thinking the "speed of gravity" is c -- for the physical situations
you consider, the EXTRAPOLATED retarded position is experimentally
indistinguishable from its instantaneous position (using suitable
coordinates, as above).

Tom Roberts

"Ken S. Tucker" wrote in message
...
On Jul 26, 5:48 pm, Tom Roberts wrote:
Ken S. Tucker wrote:
Hi Steve, Tom and all. I can suggest a means of resolution by
experiment, but it is complicated so stay with me on the bends.

Robert's, somehow you've screwed up
your replies below. My post was directed
to Tom VvF and Steve Carlip, perhaps having
an extra Tom messed things up.
From now on it's Tucker, Carlip, Flandern,
Roberts etc.
Anyway I'm a GRist on this issue and generally
agree Carlip.

Actually, it isn't complicated at all, and HAS ALREADY BEEN DONE.

I see that Tom is still using capitals to provide emphasis even when it is
almost always interpreted by the general reader as yelling. I wonder if Tom
actually cares about things like how people feel about caps!? Nah.

Pete

On Jul 26, 8:05 pm, "Pmb" wrote:
"Ken S. Tucker" wrote in ...

On Jul 26, 5:48 pm, Tom Roberts wrote:
Ken S. Tucker wrote:
Hi Steve, Tom and all. I can suggest a means of resolution by
experiment, but it is complicated so stay with me on the bends.

Robert's, somehow you've screwed up
your replies below. My post was directed
to Tom VvF and Steve Carlip, perhaps having
an extra Tom messed things up.
From now on it's Tucker, Carlip, Flandern,
Roberts etc.
Anyway I'm a GRist on this issue and generally
agree Carlip.

Actually, it isn't complicated at all, and HAS ALREADY BEEN DONE.

I see that Tom is still using capitals to provide emphasis even when it is
almost always interpreted by the general reader as yelling. I wonder if Tom
actually cares about things like how people feel about caps!? Nah.
Pete

Hi Pete.
I don't give a rat's ass about caps,
I think it was an oversight on Roberts
part...no big deal.
It's the Sun's tidal semi-major axis induced
into the Earth orbiting objects that
concerns me. I think the geodesy of GP-b
should be accurate enough to tickle out
that semi-major.

If so, which way will it point?

Toward the Newtonian position of the Sun?
or
Toward the Apparent position of the Sun?

Those angles differ by a mere 20 arc secs.
I predict the Apparent.
Regards
Ken S. Tucker

On Jul 26, 8:50*pm, "Pmb" wrote:

-----------------------------
I asked you where I could get a copy of your book. I'd love to read it.

Pete

Hi, Pete

Thank you for your interest! My book is still work
in progress but you can get chapters online he
http://physics-quest.org

Regards, Hans

Hi Pete and Hans.

On Jul 27, 6:42 am, wrote:
On Jul 26, 8:50 pm, "Pmb" wrote:

-----------------------------
I asked you where I could get a copy of your book. I'd love to read it.

Pete

Hi, Pete

Thank you for your interest! My book is still work
in progress but you can get chapters online hehttp://physics-quest.org

Regards, Hans

Hans has an excellent diagram 16.1 I've been
studying, Pete, how about rendering an opinion.
Ken

Ken S. Tucker wrote:
On Jul 26, 5:48 pm, Tom Roberts wrote:
[...]
cite a specific
experiment or measurement - as I suggested -
to distinguish the speed of gravity from oo,

READ WHAT I WROTE, and you'll see that measuring "speed of gravity" is
NOT physics. Physics, and science in general, is testing theories -- let
engineers measure things.

"Speed of gravity", as TvF uses it, is not directly measurable. He
applies some model to the measurements to DEDUCE what he thinks the
"speed of gravity" is. The result is model dependent, and is at base
IRRELEVANT -- what matters is whether or not the underlying model is valid.

GR is valid for all the experiments he cites, and none of them refute
GR. That's what I meant by "this has already been done" -- ALL of the
experiments TvF cites have been performed already, and verified to be
consistent with the predictions of GR.


Tom Roberts

On Jul 27, 9:06 pm, Tom Roberts wrote:
Ken S. Tucker wrote:
On Jul 26, 5:48 pm, Tom Roberts wrote:
[...]
cite a specific
experiment or measurement - as I suggested -
to distinguish the speed of gravity from oo,

READ WHAT I WROTE, and you'll see that measuring "speed of gravity" is
NOT physics.

Read ENOUGH thanks
Ken

On Jul 28, 12:06 am, Tom Roberts wrote:
Ken S. Tucker wrote:
On Jul 26, 5:48 pm, Tom Roberts wrote:
[...]
cite a specific
experiment or measurement - as I suggested -
to distinguish the speed of gravity from oo,

READ WHAT I WROTE, and you'll see that measuring "speed of gravity" is
NOT physics. Physics, and science in general, is testing theories -- let
engineers measure things.

"Speed of gravity", as TvF uses it, is not directly measurable. He
applies some model to the measurements to DEDUCE what he thinks the
"speed of gravity" is. The result is model dependent, and is at base
IRRELEVANT -- what matters is whether or not the underlying model is valid.

GR is valid for all the experiments he cites, and none of them refute
GR. That's what I meant by "this has already been done" -- ALL of the
experiments TvF cites have been performed already, and verified to be
consistent with the predictions of GR.

Tom Roberts

On Jul 28, 12:06 am, Tom Roberts wrote:
Ken S. Tucker wrote:
On Jul 26, 5:48 pm, Tom Roberts wrote:
[...]
cite a specific
experiment or measurement - as I suggested -
to distinguish the speed of gravity from oo,

READ WHAT I WROTE, and you'll see that measuring "speed of gravity" is
NOT physics. Physics, and science in general, is testing theories -- let
engineers measure things.

When you push your car, it pushs back *instantly*.
Is that not measurable?
Was Newton practicing alchemy when he stated
his third law?

On the Machian Origin of Inertia
http://arxiv.org/abs/physics/0609026

The Origin of Gravity
http://arxiv.org/abs/physics/0107015v6

Sue...



"Speed of gravity", as TvF uses it, is not directly measurable. He
applies some model to the measurements to DEDUCE what he thinks the
"speed of gravity" is. The result is model dependent, and is at base
IRRELEVANT -- what matters is whether or not the underlying model is valid.

GR is valid for all the experiments he cites, and none of them refute
GR. That's what I meant by "this has already been done" -- ALL of the
experiments TvF cites have been performed already, and verified to be
consistent with the predictions of GR.

Tom Roberts

On Jul 27, 6:13*pm, "Ken S. Tucker" wrote:
Hi Pete and Hans.


Hans has an excellent diagram 16.1 I've been
studying, Pete, how about rendering an opinion.
Ken

That's from chapter 16 on the Hamiltonian and
Lagrangian densities:
http://physics-quest.org/Book_Chapter_Lagrangian.pdf

There's a significant update on the derivation
of the Lienard-Wiechert E & B fields demonstrating
that the E field points towards the extrapolated
position instead of the retarded position.
http://physics-quest.org/Book_Chapte...rentzContr.pdf

With 2 illustrations added and improvements to
make it better accessible. see sections 2.8--2.11


Regards, Hans
http://physics-quest.org