Re: Tom Van Flandern and Newtonian Gravity
From: Tom Van Flandern (tomvf_at_starpower.net)
Date: 08/19/04
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Date: Thu, 19 Aug 2004 02:57:08 -0400
This replies to shuba, Gerald Lasser, and Mike. NOTE TO ALL:
Travel during the coming week will slow any further responses from me
even more than my usual slowness.
"shuba" <tim.shuba@eudoramail.com> writes:
>> [tvf]: Here are a few quotes from Bilge's post of Aug. 10 in this
thread: "But a spacetime metric does have something to do with space,
tom. That's why it's called a spacetime metric and not a time metric. .
A distance is what the metric measures. That is why it's called a
metric. . We aren't talking about a hamming distance or some other
measure here, tom. We're discussing geometry. . you think a Euclidean
space is somehow ordained by god as the only 'real' geometry and can't
imagine a space with a negative sign in the metric. . What do you think
the space part of the metric measures? What about the fact that the
metric also measures spacelike intervals?"
> [shuba]: None of this mentions the curvature of 3-space. I knew you
couldn't find a citation to back up your fallacious claim.
Then why did you omit citing my next sentence, which made
the connection? I repeat it here: "These quotes make it clear to me that
Bilge thinks of 'spacetime' as a combination of space plus time, and
that the 'curvature of spacetime' clearly required by GR must therefore
be at least partly a curvature in the space component of spacetime."
Never dodge the key points in a logical argument - even when
it might mean your earlier post was mistaken.
>> [tvf]: you have provided no specific example of a previous inaccurate
statement. But please do provide an example or two of previous
inaccurate statements and show us all that I am an untrustworthy source
(the alternative being that you are).
> [shuba]: Also totally incorrect. You even said you changed your paper
to supposedly omit the inaccurate information you presented about Robert
Wald. I see no need to dwell on the many errors of your ridiculous
paper. I've posted links to factually correct information about
relativity, e.g.
http://nedwww.ipac.caltech.edu/level5/March01/Carroll3/Carroll_contents.html.
I'm happy to let any interested parties read it themselves and find out
why your purposeful distortions of the terminology and concepts of
relativity are nonsense.
Your first example you made up, or exists in your mind only.
Vigier and I have criticized Wald's support for the geometric
interpretation of GR in "Experimental Repeal of the Speed Limit for
Gravitational, Electrodynamic, and Quantum Field Interactions", T. Van
Flandern and J.P. Vigier, Found.Phys. 32(#7), 1031-1068 (2002); earlier
preprint (with different title) at
http://metaresearch.org/cosmology/gravity/speed_limit.asp. That
criticism stands unchallenged, and was never modified.
The link in your other example is to a discussion of the
mathematics of relativity, with which I have no problem. When did I ever
say anything contrary to that?
You, like Bilge, seem to have a problem keeping your
correspondents straight. I'm one of Einstein's strongest supporters. It
is the people who followed Einstein, from Wheeler to Wald, who tried to
change the physical meaning of the math to suit their own ideas of the
universe, with whom I have a problem.
As to the conclusion of this little exercise about which of
us is making inaccurate statements, your vague allusions and lack of any
specific examples speak for themselves. It's not too late to back up
your claims with specifics, if any exist.
and "Gerald Lasser" <antispam@nospam-me.com> writes:
>> [tvf]: Show us how Maxwell's equations would change if the
propagation speed of Coulomb force were set to infinity, thereby proving
wrong my conclusion that it is already set to infinity.
> [Lasser]: Okay. First, be aware that the term "Coulomb force" comes
from electroSTATICS, where all charges are stationary, so there is no
time dependence in the charge density or any of the fields. In that
context (i.e., in the absence of motion) the concept of "propagation
speed" has no significance.
I understand your point about electrostatics. But I do not
agree with your inference that "propagation speed has no significance"
in electrostatics. That would be true for potentials, for which only
changes propagate; but not for forces, which must continually propagate.
A force is the time rate of change of momentum by definition, where
momentum is proportional to velocity. For force, that velocity is the
propagation speed of whatever carries the new momentum. Moreover, a
force must causally link a source to a target. That also implies the
need for a propagation speed.
Math has no such issues. But physics does. Each discipline
must respect the constraints imposed by others.
> [Lasser]: Coulomb's equation (the one you learned in sixth grade,
giving the central electric force purely as a function of distance from
the source charge) is not valid in electrodynamics, precisely because it
does not account for the finite propagation speed.
You went to a more advanced grade school than I did. :-( But
remember, my focus was on the retardation of the electrical component,
not on the magnetic component. So I have no need to consider a moving
source charge.
> [Lasser]: According to Maxwell's equations, the field equation of the
"Coulomb potential" phi(x,y,z,t) is d2phi/dx2 + d2phi/dy2 + d2phi/dz2 -
1/c2 d2phi/dt2 = -4 pi rho (1) (The "2s" should all be
superscripts, and those are second partial derivatives of phi with
respect to x, y, z, and t). Now, in electrostatics everything is
stationary, so nothing has any time dependence, we have d2phi/dt2 = 0,
and the field equation for the Coulomb potential reduces to Poisson's
equation d2phi/dx2 + d2phi/dy2 + d2phi/dz2 = -4 pi rho (2)
With appropriate units, the solution of (2) for a point charge q is
simply phi = q/r, and since (in electrostatics) the electric field E is
just the negative gradient of the scalar potential phi, we get Coulomb's
central-force inverse-square equation E = - q/r2.
This is all very basic and obvious. In electrostatics, the
potential field is time independent. No problems here.
> [Lasser]: But this applies ONLY in electrostatics, where the field
equation (1) reduces to Poisson's equation (2). In general, when we
don't have stationary conditions, we must use the full time-dependent
field equation (1).
Here is where we begin to diverge. You have just swept an
important part of the problem under the rug. To keep things as simple as
possible, I want to stick with the non-time-varying potential field from
a single static (non-moving) charge, and use an electric force sensor
moving uniformly through the field without changing the field.
Going to the full time-dependent field equations would mean
letting the source charge and its field move, and that introduces
magnetic forces. To keep this simple, I wish to avoid magnetic forces,
which in any case are not in the plane of interest to us here. So
let's stay with your static field description and with Coulomb's law.
> [Lasser]: Notice that the field equation involves a constant "c",
which is the ratio of electric to magnetic units.
Actually, the constant is c^2, which is an energy per unit
mass, not a speed, and physically represents the permeability or
permittivity of space. That is a major difference of meaning in this
context.
> [Lasser]: This term is responsible for the retardation of the "Coulomb
field" and of the associated electric force. The time-dependent term in
(1) is the reason the Coulomb potential at a given event depends not on
the distribution of charge at the present instant, but on the
distribution of charge on the past light cone of that event.
I stressed several times before that we are not interested
here in retardation in the potential field, which is too small an effect
to have ever been observed. Retardation in charge distribution or in
radial distances does not give rise to secular effects, and the
retardations are too tiny and too brief to be seen in the laboratory.
"Gradient" is just a mathematical relation, and does not
indicate the direction of causality. But physical principles do indicate
that direction because motion cannot arise from non-motion. (I.e.,
momentum cannot be created ex nihilo.) So when we are considering the
physical interpretation of the equations, the dynamic electric force
must induce a gradient in the static potential field (the way gravity
induces a density gradient in an atmosphere), and not the other way
around. For example, we would not make the mistake of saying that the
gradient in an atmosphere produces the force of gravity for that body,
even though the same kind of "force is the gradient of potential"
mathematical relationship holds.
>> [tvf]: If you can show me a propagation delay of D/c for forces in
the existing Maxwell equations (for a target body/charge with a relative
motion), my whole argument fails.
> [Lasser]: Done.
Please try one more time, respecting the terms of the
challenge. Consider only a stationary source charge with a static field,
and a moving target body (charge or sensor). This is a case with an
electric field but no magnetic component from the source, and a case
where Coulomb's law should still apply. Show me the propagation delay
term D/c for the electric force of a single, fixed charge on a moving
charge or sensor.
In your words, the case I want to consider is one where, in
your words: "there would be no magnetic field at all, so compasses and
electric motors wouldn't work, and there would be no such thing as
light, etc. All we would have is an instantaneous Coulomb force at a
distance. This is all grossly in conflict with observation." Yet
strangely enough, the case in question exists. I believe it is called an
"atom". :-)
>> [tvf]: The propagation delay is D/c for changes in the potential, and
is zero for Coulomb forces.
> [Lasser]: It sounds as if you have been thinking Coulomb's
inverse-square force law . applies to time-dependent situations. As
explained above, it doesn't. Poisson's equation and the resulting
Coulomb force law apply ONLY to electrostatics.
The case of interest is non-moving source, non-time-varying
field, but moving sensor. Neither the term "electrostatics" nor
"electrodynamics" is rigorously applicable. So let's not confuse each
other further by continuing to use them. The case that makes my point is
well-defined in words without labeling it "electro-anything".
> [Lasser]: Also, you seem to be dis-associating the electric potential
from the electric force, as if they pertain to physically distinct
phenomena, which is just insane, because the electric potential is
DEFINED as the scalar field whose negative gradient (minus the time
partial of the magnetic potential, in general) is the electric force.
They are just two ways of talking about the same thing. If the potential
doesn't change, the force doesn't change, by the very definition of the
words.
Gravitational force is the gradient of gravitational
potential also. Yet, even though the Sun's gravitational potential field
is static (in the same sense as in electrostatics), its gravitational
force on planets is continually varying in both magnitude and direction.
Or is the whole solar system insane? :-)
>> [tvf]: for a moving point, there is a difference between the retarded
and instantaneous partial derivatives.
> [Lasser]: I think you coined the expression "retarded partial
derivative" yourself, so only you know what it means (if anything)
The partial derivative of a static field at a fixed field
point cannot be "retarded". However, most real sensors (e.g., planets,
or electrons in atoms) are moving points, and for them the difference
between the instantaneous source direction and the retarded source
direction is important. See the discussion of this point in the 2nd
paragraph of section 2, "Principles and definitions", at
http://metaresearch.org/cosmology/gravity/speed_limit.asp, which is now
published in our "Foundations of Physics" paper.
>>> [Lasser]: It's simply insane to claim that the gradient of a field
can be affected prior to the field itself being affected.
>> [tvf]: make any argument (if you can)... that causality cannot be
the other way around: the external force between bodies or charges
imposes a gradient onto the potential field.
> [Lasser]: Okay. It is insane because the proposition in question has
nothing to do with the direction of causality. The "force potential" is
DEFINED in terms of the force, and vice versa; they are just two
different ways of talking about (describing) the same thing. No
assumption is made as to one of them "causing" the other. If you wish,
you can work entirely in terms of the forces, without ever mentioning
the potentials; it is entirely a matter of convenience.
To me, this appears to be a huge deficit in your physics
education. Can you name any other case where a function and its
derivative are "just two different ways of talking about (describing)
the same thing"? Velocity and acceleration are the simplest such
example. Are these two "the same thing"? Yet in gravitation, force is
proportional to acceleration and potential changes are proportional to
velocity squared.
In all cases that I am aware of (in physics), functions and
their derivatives are two different physical things, and have different
properties. Of course, no such distinctions are made, nor are they
needed, in math. But that is what this discussion is about -- the
non-uniqueness of the math of gravitation and electrodynamics when it
comes to the physical meaning of the equations, and the importance of
supplementing the math with constraints imposed by the "principles of
physics" to avoid inadvertently introducing magic (physically impossible
interpretations).
>> [tvf]: Please explain in detail exactly why this is insane.
> [Lasser]: Your statements are the equivalent of saying something like
"We have a meeting every Wednesday, but we never have a meeting on the
day that comes between Tuesday and Thursday", i.e., your statements are
logically self-contradictory. I call them insane, because I have no
doubt the self-contradictory nature of your statements has been
explained to you many times before, but you persist in repeating them.
This is insanity.
I have no doubt that it is difficult or impossible for the
insane person to appreciate his/her own insanity. However, as I
understand the matter from studying scientific method, one gets some
pretty good clues by "reality testing" one's own ideas under controlled
conditions, where experimenter bias cannot influence the outcome.
Feedback from peers is one such reality check -- how well (if at all)
the ideas communicate to other independent minds accustomed to critical
thinking.
My ideas discussed here have already undergone extensive
peer review, been found worthy, and are now in print. In nearly every
day's email, I hear from people who "get it" and love the simplicity and
elegance of the new physical interpretation this line of reasoning has
led to. So if this is insanity, beware, because it is contagious, and
the inmates will soon be ruling the asylum at the rate things are going.
>> [tvf]: But I do have an experiment that backs up my opinion: the
Sherwin-Rawcliffe experiment previously cited. It demonstrated *no
lightspeed delay* in the force between accelerating charges. Charges
accelerated jointly in the same direction respond to each other's
instantaneous positions, and not to the 'left-behind potential hill'
following acceleration from zero speed.
> [Lasser]: That does not support your opinion, just as the absence of
aberration in the electromagnetic force between uniformly moving charges
does not support your position. The directions (not to mention the
magnitudes) of all the forces to which moving charges are subjected in
such situations are entirely in accord with the predictions of
electrodynamics.
I have no objection to the equations as they are written,
only to their physical interpretation. (Is there an echo in here?)
Coulomb's law contains zero propagation delay in the common case of a
non-moving source and static field acting on a moving charge or sensor.
That is a clear manifestation of instantaneous force propagation. The
Sherwin-Rawcliffe experiment shows this mathematical fact in plain
physical terms. If the force propagation speeds were as slow as
lightspeed, the trailing one of two mutually accelerated charges would
sense a lag in the leading charge's field. But it doesn't. Case closed.
Someday we will discover that these forces are not really
instantaneous. But they cannot propagate as slowly as lightspeed. And
until then, the equations we now have with zero propagation delay for
forces work better than anything else we can write.
> [Lasser]: The details of how this happens, while constantly preserving
both momentum and finite propagation speed (which, after all, was
Maxwell's whole motive for formulating electromagnetism as he did), is
actually quite interesting, but in order to discuss it meaningfully you
would first need to get past all your elementary misconceptions - which
you seem disinclined to do.
I didn't get to where I am without acquiring a lot of
background, engaging in a lot of discussions with experts, and getting
past a lot of wrong preconceptions. So I am always watchful for more of
the same. What amazes me in this discussion is your apparent presumption
that all the preconceptions must be mine -- apparently for no better
reason than that yours are based on a century of tradition. If that is
sufficient grounds for you to feel no need to rethink the matter, then
you will obviously need to content yourself with the physics you now
know for the duration of your life. Speaking for myself, I still have
too many unanswered questions, see too many discrepancies and anomalies,
and encounter too many blind followers who cannot defend their own
beliefs when questioned.
So yes, I will remain disinclined to alter my
"misconceptions" while they remain in better agreement with experiments
and a simpler explanation of nature than the interpretation they would
displace, and no one comes up with a good reason to show otherwise. Isn'
t that how physics makes progress?
and "Mike" <eleatis@yahoo.gr> writes:
>> [Lasser]: I think you coined the expression "retarded partial
derivative" yourself, so only you know what it means (if anything)
> [Mike]: That's a term he has invented to attack Kopeikin's work. I'm
not sure about the validity of Kopeikin's work but neither the invented
term did anything to disprove it.
My comparatively gentle critique of Kopeikin's work was at
least delivered before his experiment was performed. See
http://metaresearch.org/home/viewpoint/Kopeikin.asp. After the
experiment, when Kopeikin persisted with his estranged viewpoint, he was
soundly attacked by all relativists who chose to comment, and his paper
was rejected. It would have been to his advantage if he had taken my
advice two years ago and avoided the public embarrassment.
As for the expression in question, I think I explained that
pretty well in the 2nd paragraph of section 2, "Principles and
definitions", at
http://metaresearch.org/cosmology/gravity/speed_limit.asp, which is also
now in print in our "Foundations of Physics" paper cited earlier. If
there is something you do not understand about this matter, feel free to
ask questions. If you don't get this fundamental point, you will have no
idea what the "speed of gravity" debate is all about.
> [Mike]: It is simply insane to call for infinite propagation speeds
for a law that applies only to static situations, since, because nothing
changes in such situations, it appears that assumed (wrongly) changes
take place instantly.
We agree on this point, but apparently not about which of us
this criticism applies to. You should read my analogy about the
different meanings of "static" as applied to frozen and flowing
waterfalls. Needless to say, I'm not an advocate of invoking magic in
physics, such as fields with no moving parts being able to supply new
momentum to target bodies.
Eventually, if you want to, you will catch on that forces
are vectors with direction, and that the instantaneous source and the
retarded source are in different directions from the perspective of a
moving target. And that remains true even in a static field. The Sun is
a perfect example. We cannot see its instantaneous direction, but only
its retarded direction relative to the distant stars. The Sun's light
and gravity travel continuously from the same source to the same target
along the same radial paths. Yet when they arrive, they are not
parallel. If you see a way to explain that other than different
propagation speeds, don't hold back.
> [Mike]: Are ficticious centrifugal forces needed in local non-inertial
reference frames to apply his model real? If so, how? If not, can he
provide a reason as to why all phenomena do not have the same
explanation in ann moving reference frames in his model? If he cannot, I
claim his model calls for magic, not GR. He won't answer this, I bet my
two cents on that.
You win two cents. But if anyone else can translate this
question into English, I'd be willing to have a go at it. As it now
stands, I have no idea what is being asked, even after a dozen reads. It
seems to be about inertia, and maybe (guessing) about the equivalence
principle. So the answer might be found in my paper "Does gravity have
inertia?" (Meta Research Bulletin 11: 49-53, 2002). But I really can't
make sense of the question. -|Tom|-
Tom Van Flandern - Washington, DC - see our web site on replacement
astronomy research at http://metaresearch.org
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