Voyager 1 Spotted from Earth with radio antennas

[Mike O'Dell]

uh - a square-law field *is* second-order

as for "Newtonian gravitation is merely a very good approximation",
Newtonian gravitation is not an approximation per se, but rather
*all of Newtonian Physics* is the approximation to the real
world of 4-dimensional Relativistic Spacetime. Not because
gravitation is not really a square-law field, but it is the
superposition of a cosmic buttload of square-law fields which
vary in phase and frequency.

I suspect that a more straightforward answer is that the calculations
don't include all the relativistic effects that one might need to
account for given the scale and dynamic range involved. Even in orbit
around the earth, if you care about *really* accurate predictions,
things like pressure from moonlight must be included, and that involves
getting not just the lunar phase right, but the perturbations in the
lunar orbit because of mass asymmetries and anisotropies and how they
effect the moon light flux density.

note that i'm not claiming It's Simply Not Possible for the exponent
to be something a leeeeeeeeetle bit different from 2.000000000000,
just that evidence sufficiently compelling to force consideration of
another value has not passed muster. Note that the square-law nature
of gravitation is woven very deeply into the mathematics of Newtonain
Physics in profoundly non-arbitrary ways, and the kind of mathematics
behind Relativity are also equally fond of the Pythagorean Theorem
which underlies the Euclidean distance metric which is the foundation
of the extensions to Reimann manifolds and other curiosities.

If we wake up one day and "they" seriously talk about questioning
that exponent, it's not just Kansas we won't be in any more.

And for those of you who have mastered sending CW on a straight key
with your toes at over 20wpm and are suffering from the post-partum 
depression associated therewith, I suggest you get on Amazon and order

	   "A General Relativity Workbook" by Thomas A. Moore

Yup - a workbook - complete with perfed pages. it's the damnedest
thing i've ever seen. he uses it to teach Relativity to undergrad
seniors and bright juniors in Physics. The inside of the front
cover alone is worth the price of admission. It contains conversion
tables for "GR Units" to SI units. For instance, Time is measured
in Meters, and the Speed of Light is exactly 1.0000. This guy
can't even spell "Kansas".

     cheers,
     -mo