Kepler and Newton

[From Bruce Abbott (951111.1430 EST)]

Bill Leach 951110.22:36 U.S. Eastern Time Zone --

Kepler and Newton

Actually in a sense, Newton no more explained "why" than did Kepler. We
still do not know what Gravity "IS" nor do we know why it functions nor
how. So Newton provided a better functional account than did Kepler plus
he "threw the screws to us" by pointing out that we could not explain how
three such bodies interact at all (ie: We have no formula that predicts
correctly the paths of the sun, earth and moon individually with respect
to each other when accounting for all three)!

I agree, but Newton at least gave a plausible explanation for the orbits in
terms of more fundamental relationships. He derived the motions by assuming
that (a) objects in motion continue in motion along a straight line, unless
acted upon by an external force [inertia], and (b) an external force,
proportional to the masses of the objects and inversely proportional to the
square of their distances apart [gravity], acted constantly on the objects,
the primary relationship (because of its vastly greater mass) being the
"pull" centered on the sun. As you note, Newton did not have an explanation
for this "action at a distance." Even so, his formulation was a vast
improvement over Kepler's "mere" (itself a triumph of imagination)
description of the (to a fair approximation) true planetary motions.

Regards,

Bruce

<[Bill Leach 951111.19:51 U.S. Eastern Time Zone]

[Bruce Abbott (951111.1430 EST)]

I agree absolutely of course, Newton's explanations were a significant
improvement. Kepler's laws were nothing short of genius (particularly
without Newton's laws).

(to a fair approximation)

This is not correct however, there has been no improvement beyond Kepler
in terms of planetary motion other than to note that we can not deal in a
theoretical fashion with the three body problem. Kepler's inaccuracies
are exactly the same as those that exist today (accuracy of the initial
position data and third body interaction, that is the percentage of
inaccuracy has changed but the reasons have not).

-bill