From: Anders Sandberg (asa@nada.kth.se)
Date: Fri Aug 01 2003 - 09:25:52 MDT
On Tue, Jul 22, 2003 at 06:27:14PM -0700, Robert J. Bradbury wrote:
>
> a) Sending a simple probe may not be sufficient -- they may be
> allowed under "galactic club" rules -- its a self-replicating
> probe (with directions to replicate whenever possible) that
> may bring down lightening from the gods...
This is actually another way of exploring the FP. The enforcement
system has to be able to stop replicators before they get out of
hand, and we can start constraining them by theory and maybe even
start looking for them.
Imagine "antibodies" spread evenly in the galaxy, detecting the
signature of a replicator seed. They immediately launch a
lightspeed attack on the seed; this will work only if the seed has
not arrived at the target system, so the antibody has to be inside
the future lightcone of the launch event and the past lightcone of
the arrival event. Now, let the density is rho antibodies/ly^3,
the average distance between stars are D ly and seeds travel at v.
The spatial volume of the lightcone intersection is a somewhat
troublesome intersection between an expanding and a contracting
sphere (there is a formula at
http://www.princeton.edu/~apr/articles/pre2cut/node10.html). As a
rough approximation, the spatial volume where antibodies can act
is ~(pi/4) D^3 (1+c/v)^2 There has to be at least one antibody per
such volume. For the somewhat plausible v=0.3c and D=4.3 ly the
volume is ~1000 ly^3. So the density has to be ~1e-3/ly^3 or more,
or replicators would be able to get to other systems, disasseble
them and launch absurd amounts of replicators elsewhere,
overwhelming the antibodies.
This is likely a sizeable installation, since it should be able to
detect a small replicator seed (a nanoprobe launched with an
interplanetary railgun?), pinpoint its trajectory and launch an
attack that is effective over many lightyears. Sounds somewhat
implausible, which suggests more antibodies instead. I don't know
the effective range of lasers or similar beam weapons in
interstellar space (something for the SDI/ABM people to think of),
but it seems likely it is not that long compared to the distances
between stars. Hence we should expect antibodies with an average
distance corresponding to the effective range of their weapon
rather than being relativistically limited - and this makes them
much more likely to be detected. In fact, it may even be
reasonable for the galactic club to make them relatively visible
to interplanetary civilisations, since that way emerging civs
might get the hint and abstain from doing something stupid.
On the other hand, if weapons can be powerful broadsides a la
supernovae or GRBs (like the Chenzeme of Nagata's books) then you
only need a few of them and will likely get the civilization that
launched them too. And it makes sense to put the antibodies in or
near the solar systems (and brown dwarves), since that is where
launches are likely. Hmm, my argument needs more analysis than I
have time for...
Anyway, considering enforcement methods over interstellar
distances might give us a new angle to deal with the paradox.
-- ----------------------------------------------------------------------- Anders Sandberg Towards Ascension! asa@nada.kth.se http://www.nada.kth.se/~asa/ GCS/M/S/O d++ -p+ c++++ !l u+ e++ m++ s+/+ n--- h+/* f+ g+ w++ t+ r+ !y
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