From: metares@well.sf.ca.us (Tom Van Flandern)
Newsgroups: sci.astro
Subject: Re: The Hole Story
Date: 20 Dec 92 17:44:24 GMT
Organization: Whole Earth 'Lectronic Link


     [This contains replies to Chris Flatters, Thomas Clarke, Jack Gallimore,
Paul Gilmartin and Benjamin Weiner.]

Earlier, I wrote:

>> when GR is taught, the point about gravity acting without detectable delay
>> is glossed over, leaving students in a state of disbelief when they learn
>> about it later in their careers.

and cflatter@nrao.edu (Chris Flatters) replied:

> There is no confusion.  In GR gravitational effects propagate at the speed
> of light.

     Both these statements cannot simultaneously be true.  If the second is
true, then I'm very confused.  :-)

     There seems to be a mixing of wave and force effects here.  Gravity
waves have nothing to do with the gravitational force.  It is only gravity
waves that are supposed to propagate in GR.  I previously recited GR's
explanation for why the static field acts without detectable delay.
Basically, the static field doesn't propagate at all, at any speed, in GR,
because if one assumed it did, that would be in conflict with observations.

> If you don't believe me check out the use of retarded potentials to
> determine the effects of gravity on page 83 (equation 101) of Einstein's
> monograph "The Meaning of Relativity".

     Experimental facts are not matters for "belief."  It is an experimental
fact that gravity acts without detectable delay.  This was well known to
Einstein.  He and many since have tried to show how this might appear to be
true if gravity actually propagated at the speed of light.  But Eddington
made a general theoretical argument that speed-of-light propagation cannot be
so if orbits are stable (see below).

     Every celestial mechanician is taught how to do dynamics; for example,
integrating the orbits of the planets in the solar system, or stars in the
galaxy.  The equations of motion have no delay terms.  The Schwarzschild
solution (which is exact) has no delay terms.  The EIH equations of motion
have no delay terms (see eqn. 39-64 in MTW).  The force or potential is
always calculated using instantaneous positions, not retarded ones.  That's
not a low-velocity approximation -- it's required.

> Also: if gravitational effects propagate instantaneously there would be
> no wave solution for Einstein's equations.

     We have been discussing that very point in another thread about the
binary pulsar.  A few GR specialists have an opposite opinion to yours; for
example, the 1992 paper by Yu cited in the other thread insists that there is
no wave solution for Einstein's equations.

>> [TVF]: This can be verified by pure computation in a computer.  If we
>> insert lighttime delay into either Newtonian or GR equations of motion of
>> the planets, they quickly spiral out of their known orbits.  Gravity acts
>> without detectable delay.

> There is almost certainly something wrong with this calculation.  It sounds
> as if the motions of the planets are being calculated in a different
> reference frame from the motion of the Sun.

     No, the center-of-mass frame is used for all.  And there is nothing
wrong with these calculations.  I'm not referring to some result of mine, but
to what every dynamicist knows to be the case.  Their calculations agree with
observations to 8-9 significant figures.  Not many fields get that kind of
accuracy.  Yet there are no delay terms, direct or indirect, hidden or
cancelled.  Retarded potentials are not used, not because they are
negligible, but because their effects are large and in conflict with
observations.

     Here is Eddington's argument that calculations with retarded positions
cannot help but alter the angular momentum of the system (i.e., cause the
orbits to spiral) [Eddington, S. A., "Space, Time & Gravitation", Cambridge
University Press, Cambridge & New York (1920; reprinted 1987).  See p. 94.]:

     "If the Sun attracts Jupiter towards its present position S, and Jupiter
attracts the Sun towards its present position J, the two forces are in the
same line and balance.  But if the Sun attracts Jupiter toward its previous
position S', and Jupiter attracts the Sun towards its previous position J',
when the force of attraction started out to cross the gulf, then the two
forces give a couple.  This couple will tend to increase the angular momentum
of the system, and, acting cumulatively, will soon cause an appreciable
change of period, disagreeing with observations if the speed is at all
comparable with that of light."

> retarded potentials ... determine the effects of gravity on page 83
> (equation 101) of Einstein's monograph "The Meaning of Relativity".

     In the light of the preceding, let's reexamine Einstein's argument.  His
eqn. 101 is based, as he says, on an electrodynamics analogy.  But MTW in
Chapter 7 show at great lengths all the efforts that have been made to make
retarded potentials work, without success.  Einstein's argument you quote
about velocities being small and the effects negligible in the solar system
is far from being true, as Eddington argued long ago, and as an elementary
computer calculation anyone can do easily shows.  Using retarded coordinates
makes an error in the fourth decimal place, when observations are good to 8-9
places.  The largest non-Newtonian GR effects show up in the seventh or
eighth decimal place.  That alone should tell you that something is fishy
with Einstein's argument.

     If you insist that Einstein couldn't have been mistaken in this argument
because he was Einstein, I will point you to a quote a bit further along in
the same text (p. 164 in my 5th edition):  "A field theory is not yet
completely determined by the field system of equations.  Should one admit the
appearance of singularities?  ...  It is my opinion that singularities must
be excluded.  It does not seem reasonable to me to introduce into a continuum
theory points (or lines etc.) for which the field equations do not hold.
Moreover, the introduction of singularities is equivalent to postulating
boundary conditions (which are arbitrary from the point of view of the field
equations) on "surfaces" which closely surround singularities.  Without such
a postulate the theory is much too vague."

     In my opinion, Einstein was exactly right in this argument.  But
clearly, if you accept black holes, then you would have to pick and choose
among Einstein's various arguments to suit your own purposes.


> Disregard most of what Tom is saying.  Tom is trying is confusing the
> effects of a field with those of a propagating wave.

     Remember, gravity waves have nothing to do with carrying the
gravitational force or setting up the static field around a mass.  I was
discussing pure gravitation, not gravity waves.  The latter, if they exist at
all, manifest themselves only in cases of rapid acceleration of matter (as in
supernovas and binary pulsars), and do not carry the gravitational force or
static field.  Gravity waves are as incidental to the gravitational force as
is the sonic boom following an asteroid impact caused by the disturbance the
asteroid makes in the atmosphere.

> If you want to calculate the gravitational potential at the Earth (say)
> using GR you would use retarded potentials to do the necessary integrations
> in the most general way.  You would find that the gravitational force on
> the Earth is directed towards the point in space where the Sun was about 8
> minutes ago (the light travel time between the Sun and the Earth).  In the
> reference frame of the solar system this is a near as makes no difference
> to the point in space where the Sun is now so we can ignore the
> retardation.

     I'm sorry, Chris, but none of the sentences in this paragraph describing
your impressions of how the universe ought to work is consistent with
observation or experiment.  Consider:  Aberration for the Earth is 10^-4
radians, reflecting the fact that the Earth's velocity is 10^-4 that of
light.  By no stretch of the imagination is 20 arc seconds on the sky a
negligible amount.  If the Earth's velocity were nearly equal to c, the
apparent Sun would be well out in front of the Earth, and clearly trying to
accelerate it.  Since it is 10^-4 of c, the Sun's force vector can be
decomposed into two components: a central force toward the focus of the
Earth's elliptical orbit from a mass nearly equal to the Sun's, and a
tangential force along the Earth's orbit of strength 10^-4 that of the Sun's
radial force.  The tangential force is always present, and always trying to
accelerate the Earth in all parts of its orbit.  The absence of such an
acceleration tells us that aberration for gravity is less than 10^-10 of what
it is for light.  Either nothing propagates from the Sun, or it propagates
faster than light by a factor of 10^10.  Try to set up your integration with
retarded potentials (as thousands have done before you) and see for yourself.

     The observed direction of the gravitational force acting on the Earth
can be measured in several ways.  One is to determine the direction of the
radius of curvature of the Earth's orbital motion using planetary ranging
observations.  It is toward the true Sun, not the retarded one.  An
experiment I did myself in the 1970s was to use the Moon's orbit, remove the
effects of small perturbations such as planets, and determine the direction
of the body perturbing the Moon's orbit away from a perfect ellipse using
stellar occultation observations.  Again, that direction was toward the true,
instantaneous Sun, toward the position among the stars the apparent Sun will
appear to occupy 8 minutes in the future, but not toward the direction of the
apparent Sun we now see in the sky.

>> [TVF]: leaving students in a state of disbelief when they learn about it
>> later in their careers.

     I'm sorry you seem to be in this position yourself.  Please investigate
the matter until you are satisfied, one way or another.  Let me know what
arguments concern you, and I can elaborate or supply details of refere
     Lots of people before you have done this same double-take.vity, by way of
contrast, does not.


and gallim@stsci.edu (Jack Gallimore,P254) replied:

> No, that's crap.  It takes time for all forces to propagate, even gravity.
> For example, one of the problems in observational cosmology is
> understanding large sigger than
10 billion lightyears?  The argument I think you meanike to see the reference
on the observation you claim to be "true."

     For a history of (unsuccessful) attempts to build theories in which
gravity propagates, see MTW, chapter 7.  GR was the first theory to get
around these problems, and its big breakth gravitational radiation, which you
don't attribute
> to retarded potential.

     Electrons can only have discrete energy levels.  No spiraling is
possible.  There aren't any good fundamental explanations of why this is so,
but it is clear by experiment tintuitive questions, but only a
beginning.


and Benjamin Weinerof gravitational radiation) - a perturbation in the metric.
Such
> gravitational radiation (assuming its existence) propagates along null
> geodesics - lightlike lines.  It cannot escape the black hole.  My message
> will not reach Tom.

     I don't like mixing gravitational waves with gravitational force.  They
are separate phenomena -- one doesn't cause the other.  I would have conceded
that no waves can get out of the black hole, but not at all that one
shouldn't be able to sense where mass is within thty instantly, or
after some delay?  If instantly, that seems to orking to get to the next
level,
not to glorify past successes.  We can't make progress until we finally see
where the theories we have start to fail.  -|Tom|-

-- 
Tom Van Flandern / Washington, DC / metares@well.sf.ca.us
Meta Research was founded to foster research into ideas not otherwise
supported because they conflict with mainstream theories in Astronomy.