This replies to Paul Schlyter and Dave Tholen.


"Paul Schlyter" writes:

[tvf]: GR has two physical interpretations: field GR and geometric
GR. In the former (as favored by Einstein, Dirac, and Feynman, among
others), gravitation is a classical force, period. In the latter (the
version more commonly taught these days), gravity is just 4-space
geometry.

[Schlyter]: The geometric GR has one big advantage: it nicely explains
why the inertial mass and the gravitational mass are the same.

Geometric GR has two giant disadvantages because it violates
two principles of physics (causality and "no creation ex nihilo") as I
explained in my last post, which falsifies it for many practical
purposes.

Moreover, the field interpretation of GR has an even bigger
advantage than the one you mention as favoring geometric GR: it explains
why inertial and gravitational mass are *not* always the same, as
demonstrated by D. M. Greenberger and A. W. Overhauser writing about the
COW [Colella-Overhauser-Werner, 1975] neutron interferometer experiment
in Rev.Mod.Phys. 51:43 (1979). This was also written up by the same
authors in easier-to-read language in "The role of gravity in quantum
theory", Sci.Amer. 242 (May):66-76 (1980). In essence, this experiment
demonstrates a violation of the weak equivalence principle that gravity
is just geometry. Here are a few relevant excerpts:

[BEGIN EXCERPTS]
pp. 71-72: The COW experiment demonstrated that a weak
gravitational field shifts the phase of a neutron wave by the precise
amount predicted by the Schrödinger equation. In other words, gravity
appears in the equation as any other force would. This result was fully
expected. It nonetheless had distinct implications for the
interpretation of the equivalence principle in quantum mechanics .

pp. 74-75: Galileo observed that all bodies fall with the
same acceleration in an external gravitational field. Here "external"
means that the bodies themselves are too small to contribute measurably
to the field. Robert H. Dicke of Princeton University has called this
observation the weak equivalence principle . the geometrical weak
equivalence principle, which holds classically . states that there are
no physical effects at all in an external gravitational field that
depend on the mass of a point particle. . the strong equivalence
principle . states that as far as the locally observed laws of physics
are concerned, being at rest in a gravitational field is equivalent to
being at rest in an accelerated coordinate system. . It was the strong
equivalence principle that the COW experiment confirmed. . Yet
surprisingly, it turns out that the result of the COW experiment is
incompatible with the geometrical weak equivalence principle because
interference effects in quantum mechanics depend on the mass. It is only
in taking the average values of the trajectory parameters that the mass
drops out.

pp. 76: In classical physics, the potential has a form that
guarantees the mass will drop out of the problem. In quantum mechanics,
however, such is not the case. For example, in the gravitational Bohr
atom, where a particle of mass m is bound to a much heavier particle of
mass M, the radius of the lowest quantum state is a function of the mass
m. This means that m can be determined from a measurement of the
particle's radius in this state. The mass disappears only for average
values over states that have extremely high quantum numbers, which
behave in an essentially classical manner.
Since quantum mechanics contradicts the geometrical weak
equivalence principle, with its requirement that the mass drop out of
the problem, it was important to test the Schrödinger equation in an
experiment where gravitational forces were present. The test was
necessary even though the Schrödinger equation has proved to be
enormously successful for non-gravitational problems. The COW experiment
was this test, and it demonstrated convincingly that the Schrödinger
equation works in the presence of gravitational fields.
Since the phase shift depends on mass even in the case of a
gravitational field, it seems in retrospect almost accidental that the
mass drops out of the classical gravitational equations. Weinberg has
emphasized that most of the features of the gravitational field can be
derived from its mathematical symmetry properties, as is true for any
other field in quantum theory. This interpretation tends to bother
theorists who prefer to think of gravity as being intrinsically related
to geometry. Nevertheless, since the COW experiment confirms the
applicability of quantum mechanics even in the presence of gravity,
including the non-geometrical mass dependence, the experiment seems to
be a step in the undermining of the purely geometrical point of view.
[END EXCERPTS]

[Schlyter]: Btw do you know about any experimental situation we are
able to realize, or any natural situation we are able to observe,
where the field GR and the geometric GR produce different predictions?
Do they ever produce different predictions?

The COW experiment seems to be an example of just such a
difference. Experiments aside, a model or physical interpretation that
does not require magic or miracles (such as causality violations or
creation ex nihilo) is to be preferred over one that does require them.
So that is a logic-based difference between field GR and geometric GR.

[tvf]: In fact, Vigier and I explained why the geometric
interpretation of GR may now be considered falsified: 1) Geometric GR
has no cause to initiate the motion of bodies at rest in a
gravitational field. (Curvature alone cannot initiate motion unless a
force acts. There is no "downhill" in space.)

[Schlyter]: Nothing _can_ be "at rest" in 4-dimensional space-time. In
the "t"
(time) dimension, everything moves at the speed of light.

Of course. But why change the subject? My remarks obviously
referred to 3-space plus time, where "rest" relative to a source mass is
well-defined. The causality principle applies to real space and time.
Mathematical abstractions such as GR's "spacetime" (actually a variant
of proper time for most applications) are of little use when one is
discussing physical interpretations or experimental evidence because
observations must be made in 3-space plus time, not in Minkowski
4-space.

[Schlyter]: Even if everything is initially at rest in the "space
coordinates" (x,y,z), due to the curvature of space-time things will
start moving in the x,y,z coordinates as well

But that was my point: Mathematically, one can just say "it
moves" and ignore the physics. But in physics, transition from rest in
3-space to accelerated motion requires a cause (called a "force" by
definition) and a source of new momentum. No exceptions are allowed in
"deep reality physics" (by contrast with philosophy and mathematics)
because the former does not allow magic or miracles. No such prohibition
applies to mathematics because equations can often cover over our lack
of fundamental understanding of what causes are actually operating and
of the operation of entities too small for existing experiments to
detect them. But choosing to ignore causes does not mean we accept that
a cause does not exist.

So think of geometric GR as a computational device that must
be set aside when one's interest is in understanding the physics of
gravitation.

[Schlyter]: You seem to want to consider space dimensions (x,y,z)
separately from the time dimension (t) in GR. You cannot do that.

On the contrary. That is what field GR is all about.
Moreover, the entire field of celestial mechanics, which provides the
interface between GR and observations made in the real world, is based
on 3-space plus time. Without these considerations, GR would be an
untested theory.

[Schlyter]: In GR space-time is curved. Note that this is not the same
as saying "space is curved" or "time is curved" or even "space is
curved and time is curved". One cannot separate space from time in
GR -- they must be treated as one integral unit.

Incorrect. Geometric GR treats *imaginary* time (not real
time) as a fourth spatial dimension. But that is just a mathematical
convenience. Contrary to what some extremist purveyors of geometric GR
have claimed, no curvature of space or time is involved in "curved
spacetime". The latter expression simply means that the progression of
proper time (expressed in space units by multiplying it by c) is
affected by motion and gravitational potential. See for example
http://metaresearch.org/cosmology/gravity/spacetime.asp and the
reference to MTW therein.

[Schlyter]: The only way to put something "at rest" in 4-dimensional
space-time would be to stop time itself!

Now you have strayed way off topic. I was speaking of rest
in 3-space, which is a well-defined concept. Of course, if you have only
learned the geometric interpretation of GR, you may be hard-pressed to
start thinking of gravity in classical physics terms again. But you can't
compare with observations or physical reality until you make that
transition.

Specifically, the celestial mechanics vehicle for computing
orbits in GR for purposes of comparing with observations is the
equations of motion, as may be found on MTW p. 1095. Even without
studying or understanding these equations, you can see at a glance that
they are expressions for the 3-space acceleration of bodies through
space as a function of coordinate time. GR's coordinate time is a form
of time that (unlike proper time) is not affected by motion or
gravitational potential, and is therefore of great value for expressing
the relativistic dynamics of bodies in gravitational fields.

So you see, coordinate time in GR is not interchangeable
with space, and the GR equations of motion (because of infinite
propagation speed) are no more Lorentz-invariant than Newton's equations
are. But if you wanted to complain because you weren't taught that or
anything else about field GR, I'd certainly support you. IMO, the
understanding of gravity in relativity has regressed considerably during
the half-century since Einstein's death.

[tvf]: Geometric GR requires creation -ex nihilo- for the new 3-space
momentum of target bodies in a gravitational field.

[Schlyter]: well GR is certainly not a TOE (Theory Of Everything) -
but we already knew that, didn't we? So leave the creation out of the
discussion here and consider GR as a model of something which already
exists. OK?

The point of my remark was to show that geometric GR is
falsified in physics. Gravity cannot be simply geometry because that
provides no source for new momentum. It is true that we don't officially
know the source of the new momentum gravity transfers to target bodies,
and that is why mathematical explanations can be substituted for
physical ones. But it would be illogical to use our ignorance of the
specifics to argue that specific sources do not exist. And whatever they
are, they constitute a force by definition: a time rate of change of
momentum.

[Schlyter]: I think we both agree that NP (Newtonian Physics) defines
the concept of a force.....

Classical physics defines force. And that definition is as
applicable in GR as in all of physics. Field GR and relativistic
celestial mechanics use force explicitly when calculating orbits.

[Schlyter]: Of course GR must mimic NP at is low-speed and low-gravity
limit! And this includes the instantaneous potential gradients,
creating an illusion of gravity propagating instantly.

In what sense is this "an illusion"? When a source mass
accelerates, the target body responds almost instantly, as binary
pulsars prove.

Moreover, the Sun also emits light, which obviously travels
at the speed of light. Yet the gradients of the light field are
retarded, not instantaneous. What logic exists for instantaneous
relativistic potential gradients in gravitational fields when a source
mass accelerates, while gradients for light fields remain retarded?

[Schlyter]: The best I can do here is to point to the sci.physics FAQ,
where Steve Carlip writes about how fast the force of gravity
propagates.

We have argued in print that Carlip's argument is not
viable. Our reasoning is simple to understand, and there has been no
counter-argument from anyone, including the three referees of the paper
(who questioned many things, but not that).

[Schlyter]: Perhaps Carlip thinks he can do better things with his
time than discuss with someone who e.g. thinks that space coordinates
can be dealt with separately from time in geometric GR... :-) And
perhaps you feel you've won this discussion. But winning a discussion
is one thing - actually being right is something different.

When one argument shows the fallacy in another, that is
usually a step toward getting the physics right. No one in science
should be counting progress in understanding as "winning". This isn't
about personalities of contests. Our logical arguments stand or fall on
their merits alone.

[Schlyter]: if you want me to change my opinion about your ideas, you
must stop talking about the instantaneous potential of the force of
gravity as if it was a "proof" for gravity propagating much faster
than light in GR.

I do not understand. If I show that a race car was at point
x1 at time t1 and reached point x2 at time t2, can't I conclude that the
minimum speed at which it traveled was (x2 - x1) / (t2 - t1)?

Likewise, if a source mass at x1 accelerates at time t1 and
a target body at x2 changes its acceleration to match at time t2, can't
I conclude that the minimum propagation speed of that force change was
(x2 - x1) / (t2 - t1)? That is what binary pulsars (rapidly accelerating
masses) prove. The proof of that first appeared in my 1998 Phys.Lett.A
paper, available on the web at
http://metaresearch.org/cosmology/speed_of_gravity.asp. See the
beginning of the section "Electromagnetic analogies and gravitational
radiation". It's a single-paragraph argument with a diagram and modest
mathematics. It should not be difficult to truly understand the
argument, and from there to understand its implications for the
propagation speed of gravity. Many before you have succeeded.

[Schlyter]: I guess the major weakness with the EPH hypothesis is
that we know of no feasible mechanism by which a planet could
spontaneously explode.

[tvf]: Incorrect. See
http://metaresearch.org/solar%20syst...Explosions.asp.

[Schlyter]: ...an interesting collection of ad hoc hypotheses....

That is what your question asked for: a "feasible mechanism".
I provided three.

[Schlyter]: Phase changes: they occur naturally of course. The most
well-known example is of course water freezing, melting, evaporating,
condensing. But did you ever see any explosions during such a phase
change?

A correspondent following this discussion who prefers not to
join in directly wrote: "In the early and middle years of the steam age,
boiler explosions were common. Some were large scale disasters, killing
dozens of people and destroying lots of property. They still happen in
parts of the world where steam powered trains are used. This may not be
close enough to what Paul is talking about to satisfy him, but it is a
real world example of explosion resulting from phase change. And under
the right conditions. . Mountains crumbling into sand piles (as water
gets into the cracks, freezes, and expands) could be described as an
extended series of tiny explosions. Each one is just a little "pop", but
size seems to be a secondary consideration here."

[Schlyter]: Can we expect to see a piece of melting (or freezing) ice
spontaneously explode, scattering itself around? No. So is it
reasonable to expect a whole planet to explode just because the lava
inside "freezes"?

"The Krakatoa volcano explosion in the 1883 is another
example of a phase-change-caused explosion. Much larger in scale and
natural rather than man made."

I might add that ice volcanoes are one of the newer fads in
planetary astronomy. And the idea of phase changes as a planet explosion
mechanism has been in the peer-reviewed literature since Ramsey's work
in 1950.

[Schlyter]: Natural fission reactors: requires a lot - a lot ! - of
uranium to be able to explode a whole planet.

Geophysicists have come to accept natural fission reactors
as a reality of planets because of the discovery of some operating on
Earth's surface in the distant past (e.g., at Oklo, Gabon, Africa). The
geophysical literature now contains many corollary speculations, such as
that the excess heat flow from the gas giant planets (twice or more what
they receive from the Sun) is caused by natural fission reactors in
these planets operating today. (See bibliography in the web paper I
cited.)

[Schlyter]: Gravitational heat energy: occurs mainly in the
contraction phase so this mechanism would mean that the contracting
body would "bounce back" and disintegrate. But would a planet really
have formed in such a case?

The Le Sage model (see the subject of the latest book on the
nature and origin of gravitation: "Pushing Gravity") requires
gravitation to be a continuous source of heat, even when a planet is in
equilibrium and no longer contracting. But if something like a core
collapse traps that heat, sooner or later one cannot avoid an explosive
release of all the continually increasing, stored energy.

[Schlyter]: it's not enough that you yourself consider the
explanations feasible. You must also convince the scientific community
that they are feasible to have your model accepted as a mainstream
model.

The history of science shows that the "mainstream" rarely
accepts an alternative model unless some traumatic event forces a
revolution. For example, it took the great Leonid meteor storm of 1833
over well-populated areas of the Eastern U.S., which many took to be a
sign that the world would soon end, to finally convince astronomers and
everyone else that rocks did fall from the sky. Yet compelling evidence
for that had already been published a generation earlier.

The only alternative, according to Thomas Kuhn's work, is
that the mainstream model receives patch after patch until it becomes
indistinguishable from the alternative model. We can already see that
continuing to happen with the competition between the Dirty Snowball and
the Satellite Model for comets, perhaps accelerated to several patches
at once called for by the Deep Impact experiment.

So those looking for comfortable lives will remain with the
conservative majority for a generation or so until the majority becomes
a minority. Meanwhile, those looking for answers affording a deeper
understanding and for models that make genuine predictions of new
phenomena, it appears that carefully selected alternative models
(supported by many thoughtful people over a period of time) are usually
better than mainstream models because the alternatives came into
existence to solve puzzles and anomalies where the mainstream model
failed and had to be patched ad hoc.


and writes:

[tvf]: I'll answer these two and any occasional future post made in
that same constructive style.

[Tholen]: And ignore anything that you do not wish to address, such as
the matter of outbursts.

I answered that. In the EPH's Satellite Model, comets are
asteroids that have not yet lost most of their volatiles. They do not
have jets or geysers or outbursts in the literal meaning of those words.
The so-called "jets" are flashlight beams shining through coma dust from
bright areas of the nucleus, focused by the opposition effect. This
explains why they do not show any sign of bending with rotation of the
nucleus. And the so-called "outbursts" are meteor impacts. We now have
direct evidence of the similarity of impact events to traditional
outbursts, thanks to Deep Impact.

[Tholen]: Debris clouds orbiting a solid nucleus can't produce jets
that rotate with the nucleus.

Flashlight beams (sunlight reflecting from bright spots
preferentially back toward the light source) do rotate with the nucleus.
But they remain pointing at the Sun, and nucleus rotation does not curve
them even far from the nucleus. A jet should curve, a flashlight beam
should not.

[Tholen]: How does a "solid rocky asteroid" produce water vapor
emission?

Chondritic meteorites are 20% by volume interstitial water.
Likewise, the water in comets should be mainly interstitial to the rock
matrix.

[tvf]: Our goal here is progress,

[Tholen]: Then explain how a "solid rocky asteroid" can have water
vapor emission, how jets can be produced and rotate with the comet,
and what causes outbursts, all based on the EPH, Van Flandern.

Okay, I did that. Did the progress happen? -|Tom|-


Tom Van Flandern - Washington, DC - see our web site on replacement
astronomy research at http://metaresearch.org