Re: inertial/gravitational - real 3-body problem in the news

[Tim Gwinn <***>]

Dan,

Certainly science has long been using those state-based equations as the
starting point for successful predictions of astronomical entities via
simulations which modify the original entailments in those equations in
order perform computations to arrive at numerical results. Otherwise, we
would never have made it to the moon. :)

We must recall here the distinction between model and simulation. What can
be done in a simulation is mimicry of behavior without any necessity of
congruency between the entailment structures in the object system and the
simulation. As such, if all one wants to know the system's behavior, such as
where a planet is going to be at any given point in time, to some particular
degree of accuracy, then all one needs are simulations. If one wants to be
able to answer "why?" questions about the system, then one needs models that
are congruent with the object system.

As a *model* of a 3-body system, the set of state-based equations cannot
generically be solved in closed form. But as I said this doesn't mean that
the state-based equations are wrong (as in "incorrect"). It is simply that
there is other information which cannot be encoded into that state-based
formalism. This is why I also said that they (the equations) are limited in
what aspects they can model about the three-body system.

This is consistent with what Judith said, where she defined 'wrong' in a
particular way that spoke to the larger picture.

I did not mention simulation vs. model in my post because I took it for
granted that distinction was a given on this list (doesn't everyone think
like me!?), but I probably should have been explicit.

Regards,
Tim




> -----Original Message-----
> From: ROSEN Forum [mailto:*** On Behalf Of Dan
> Fiscus
> Sent: Wednesday, November 16, 2005 10:40 AM
> To: ***
> Subject: Re: inertial/gravitational - real 3-body problem in the news
> 
> Judith, Tim and all,
> 
> Here's a recent news story of a 3-body system in which
> 1) state-based models are functional and effective, at
> least via numerical approximations, and 2) the stakes
> and value of this reductionistic, state-based approach
> are high. The three bodies are 1) asteroid that may hit
> 2) the Earth and 3) spacecraft that might alter the
> course of asteroid to avoid collision.
> 
> (May need a free register to Washington Post to see
> this)
> 
> http://www.washingtonpost.com/wp-
> dyn/content/article/2005/11/09/AR2005110902204.html
> 
> Devil's advocate issue...maybe we have to be more
> specific about right and wrong, maybe by citing utility
> or functional value or cost/benefit, etc.?
> 
> Dan