From: eugene.leitl (eugene.leitl@lrz.uni-muenchen.de)
Date: Wed Jun 07 2000 - 22:10:29 MDT
On Wed, 7 Jun 2000, Billy Brown wrote:
> Agreed, but note that this also requires that FTL travel be impossible even
> to determined SIs. If you think SIs might be capable of FTL travel you need
FTL travel/infotransfer being impossible seems like a prudent assumption.
Lacking further constraints, the space of magical technologies is too
large to be exhaustively sampled. Let's incorporate new data into model as
they arise. Otherwise, we can just substitute list traffic from
/dev/random output, it would make as much sense.
> an even more extreme sparsity of civilizations - really fast FTL would imply
> that ours is the first civilization to achieve the capacity for expansion
> into space.
Spacetime plumbing is a pretty good filter, because it requires very smart
and powerful critters, which subsequently go Elsewhere (especially if you
fabricate places to go to by the attempt to go there), a classical
population bottleneck.
However, no evidence. The jury's still out whether denizens of this
universe can fabricate traversible wormholes which go to other places of
the same spacetime continuum.
> > Since expansive aliens expand with
> > speeds near to relativistic, there is obviously very little warning,
> > before the expansion front hits out system.
>
> Well, 'very little' is a relative thing. An expansion rate of 99.9% C over a
> distance of 10^7 LY still gives us 10,000 years of watching the expansion
> move our way. We would only be caught by complete surprise if the expansion
> front moved faster than C.
Which, of course, is impossible, as far as we know. 0.999 c is fairly
stringent, it is difficult to imagine the culture nanoseed expressing
itself explosively upon arrival, and fabricating further panspermia
machines and their launchers which can do 0.999 c. Even using starpumped
laser sails, braking/maneuvering will be a problem.
Thanks for catching the "no warning" bug. SETI should look for spherical
infrared voids on galactic cluster scale. While star-hopping is trivial,
galaxy hopping might require different propagation mechanisms.
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