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Hideously OT: Langrange Points Re: gravity and ftl

Date: Sat, 11 Jul 1998 13:21:24 -0500
Subject: Hideously OT: Langrange Points Re: gravity and ftl
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Andrew Martin, Alex Shvarts & Brian Martin (although i suspect Mr
Martin wrote it and shamelessly used other people's names :-) wrote:

> In several SF systems, the writers suggest that FTL drives only
work in
> near-flat space.

for instance, i think this is how it works in the battletch books

> If I recall correctly, these are also Lagrange points.

i don't think there's any 'also' about it - as far as i know that's
the definition of a Lagrange point!

Ok, I am going to inject physics into this discussion.

The five Lagrange points are not a place where space-time is flat.
Lagrange points are places where the gravitational attaction between
two bodies coupled with the angular momentum a third body has makes
the position of the third body stable.	The angular momentum part of
all this makes Lagrange points not just depend on gravity.  In other
words, for an asteroid to stay in the Trojan points of Jupiter it must
be moving a very specific orbital velocity (ie, the same orbital
velocity that Jupiter has).  Flat space means you feel no effects from
gravity regards of your velocity.  What the Lagrange points are are
stability points, so this does not mean that you feel no gravitational
acceleration, but it means if you have a certain velocity you can just
sit there without having to worry about straying away or constantly

Of course none of this has anything to do with Full Thrust or FTL.  If
you want to have FTL from every possible Lagrange point, go ahead,
just don't say a Lagrange point has a flat space-time (you can,
however, say because its a meta-stable point in the on the
zero-velocity surface of the effective potential which ought to
impress the hell out of just about anybody.)

Further questions/comments/flames on this should go directly to me