Fast gravity--calling David Bowman
Thu, 26 Aug 1999 06:16:18 +0000

I just read a fascinating article that was pointed out to me by a
young-earth creationist. It is Tom Van Flandern, "How fast is Gravity--what
the Experiments say Physics Letters A 250(1998):1-11

The article was cited in an article by Tom Bethell as an example of how
modern physics is about to be overthrown. Bethell's article can be found at

It says,
Rethinking Relativity
by Tom Bethell

No one has paid attention yet, but a well-respected physics
journal just published an article whose conclusion, if
generally accepted, will undermine the foundations of
modern physics--Einstein's theory of relativity in particular.
Published in Physics Letters A (December 21, 1998), the
article claims that the speed with which the force of gravity
propagates must be at least twenty billion times faster than
the speed of light. This would contradict the special theory
of relativity of 1905, which asserts that nothing can go
faster than light. This claim about the special status of the
speed of light has become part of the world view of
educated laymen in the twentieth century.

Special relativity, as opposed to the general theory (1916),
is considered by experts to be above criticism, because it
has been confirmed "over and over again." But several
dissident physicists believe that there is a simpler way of
looking at the facts, a way that avoids the mind-bending
complications of relativity. Their arguments can be
understood by laymen. I wrote about one of these
dissidents, Petr Beckmann, over five years ago (TAS,
August 1993, and Correspondence, TAS, October 1993).
The present article introduces new people and arguments.
The subject is important because if special relativity is
supplanted, much of twentieth-century physics, including
quantum theory, will have to be reconsidered in that light.

I got the article and read it. I think van Flandern has some good points
about how gravity operates. He notes that in writing code for a
gravitational interaction one must use the instantaneous position of the
planets not the delayed positions. Having written such codes that is how
they are written. However, if the graviton doesn't travel faster than
light, gravity should operate on the time delayed position of the planets.
YEt Van Flandern says:

"Even today in discussions of gravity in USENET newsgroups on the Internet,
the most frequently asked
question and debated topic is "What is the speed of
gravity?" It is only heard less often in the classroom
because many teachers and most textbooks head off
the question by hastily assuring students that gravita-
tional waves propagate at the speed of light, leaving
the firm impression, whether intended or not, that the
question of gravity's propagation speed has already
been answered.
Yet, anyone with a computer and orbit computa-
tion or numerical integration software can verify the
consequences of introducing a delay into gravitational
interactions. The effect on computed orbits is usually
disastrous because conservation of angular momentum
is destroyed. Expressed less technically by Sir Arthur
Eddington, this means: "If the Sun attracts Jupiter to-
wards 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 at-
tracts the Sun towaids 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 apprecia-
ble change of period, disagreeing with observations if
the speed is at all comparable with that of light" [2].
See Fig. 1." Tom Van Flandern, "The Speed of Gravity-What the Experiments
Say," Physics Letters A, 250(1998):1-11, p. 1-2
"Analogous to the Poynting-Robertson
effect, the magnitude of that tangential force acting
on the Earth would be 0.0001 of the Sun's radial
force, which is the ratio of the Earth's orbital speed
(30 km/s) to the speed of this hypothetical force
of gravity moving at light-speed (300,000 km/s). It
would act continuously, but would lend to speed the
Earth up rather than slow it down because gravity is
attractive and radiation pressure is repulsive. Nonethe-
less, the net effect of such a force would be to double
the Earth's distance from the Sun in 1200 years. There
can be no doubt from astronomical observations that
no such force is acting. The computation using the in-
stantaneous positions of Sun and Earth is the correct
one. The computation using retarded positions is in
conflict with observations. From the absence of such
an effect, Laplace set a lower limit to the speed of
propagation of classical gravity of atynit 10*c, where
c is the speed of light [5]."
"In the general case for roughly circular orbits, let v(g) be the speed of
propagation of gravitational force and let ao be the initial semi-major
axis at time to of an orbiting body in a system where the product of the
gravitational constant and the total system mass is [mu]. Then the
following formula, derived from the ordinary perturbation formulas of
celestial mechanics allows us to compute the semi-major axis a at any other
time t:

a^2=ao^2+4 [mu] (t-t0)/v(g) 1

We will use this formula later to set limits on v(g)"
Tom Van Flandern, "The Speed of Gravity-What the Experiments Say," Physics
Letters A, 250(1998):1-11, p. 4

How then does the direction of Earth's acceleration
compare with the direction of the visible Sun? By di-
rect calculation from georoetnp ephemerides fitted lo
such observations, such as the annual AstronomicalM-
manac produced by the US Naval Observatory or the
Development Ephemerides of the Jet Propulsion Lab-
oratory (now on CD-ROM), the Earth accelerates to-
ward a point 20 arc seconds in front of the visible Sun.
where the Sun will appear to be in 8.3 minutes [4). In
other words, the acceleration now is toward the tiw.
instantaneous direction of the Sun now, and is not ptf-
allel to the direction of the arriving solar photons now.
This is additional evidence that forces from electro-
magnetic radiation pressure and from gravity do MX
have the same propagation speed. Both come from
the same source and propagate along straight, radial i
lines from the Sun to the Earth, yet their respective
effects are non-parallel, implying different aberration
and therefore different propagation speeds." Tom Van Flandern, "The Speed
of Gravity-What the Experiments Say," Physics Letters A, 250(1998):1-11, p. 4

He derives an equation which allows him to calculate the difference between
the speed of the gravitational interaction vs the observed limits to the
change in the orbital periods (Pdot). He writes:

We conclude that gravitational fields, even "static"
ones, continually regenerate through entities that must
propagate at some very high speed, v(g). We call this
the speed of gravity. Eq. ( I ) then tells us how roughly
circular orbits will expand in response to this large but
finite propagation speed, since the field itself, and not
merely changes in the field, will transfer momentum
to orbiting target bodies. Rewriting Eq. (2) in a form
suitable for comparisons with observations, we derive
[Pdot/p = 6pi/P * v/c[c/v(g)]} (3)

For the Earth's orbit, P = 1 year, v/c = 10^-4, and we
take as an upper limit to any possible observed Pdot/P
the value 2.4 x 10^-12/year, derived from Gdot/G in
solutions using radar ranging and spacecraft data [ 13 ].
Substituting these values, we get from Earth-orbit data
that v(g)>= 2 x 10^9 c.
Using the same equation with binary pulsar PSR1534+12 and the parameters
in Table 1, we can place themost stringent limit yet from the observed
uncertainty in [pdot]:v(g)>=2 x 10^10 c."

Tom Van Flandern, "The Speed of Gravity-What the Experiments Say," Physics
Letters A, 250(1998):1-11, p. 10

What I am interested in is what is your take on this David? Please keep it
at a Jr. High level for us.



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