FOM: lagrangian pebbles

Martin Davis martind at
Wed Mar 18 20:24:47 EST 1998

At 04:26 PM 3/18/98 -0700, Reuben Hersh wrote:

>Why do I believe astronomers can "predict" the motions of the
>planets far in the past?  Or your cute thing with Lagrange's
>pebbles?  Because I believe nature is in some senses orderly,
>behaving in the past in a way like it behaves  today.
>So if Newton's law seems good today, we can believe it was
>good at least in the recent past (astronomically speaking.)
>That means it was a good description of the behaviour of the
>nine planets.  It was an appropriate adjective.  
>But the mathematical subject of potential theory (the 3 dimensional
>gravitational potential) as existing apart from, independently of
>physical phenomena, was created by Newton and his successors.  It
>did not exist even in Neanderthal times, let alone in the Jurassic.
But then how can we justify the mathematics that derives the rules of
planetary motion from Newton's laws applying to jurassic times?


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