[extropy-chat] habitable zones

[scerir]

Galactic Gradients, Postbiological Evolution 
and the Apparent Failure of SETI
- Milan M. Cirkovic 
- Robert J. Bradbury
30 pages, 2 figures
http://www.arxiv.org/abs/astro-ph/0506110
Motivated by recent developments impacting our view of Fermi's paradox
(absence of extraterrestrials and their manifestations from our past light
cone), we suggest a reassessment of the problem itself, as well as of
strategies employed by SETI projects so far. The need for such reevaluation
is fueled not only by the failure of searches thus far, but also by great
advances recently made in astrophysics, astrobiology, computer science and
future studies, which have remained largely ignored in SETI practice. As an
example of the new approach, we consider the effects of the observed
metallicity and temperature gradients in the Milky Way on the spatial
distribution of hypothetical advanced extraterrestrial intelligent
communities. While, obviously, properties of such communities and their
sociological and technological preferences are entirely unknown, we assume
that (1) they operate in agreement with the known laws of physics, and (2)
that at some point they typically become motivated by a meta-principle
embodying the central role of information-processing; a prototype of the
latter is the recently suggested Intelligence Principle of Steven J. Dick.
There are specific conclusions of practical interest to be drawn from
coupling of these reasonable assumptions with the astrophysical and
astrochemical structure of the Galaxy. In particular, we suggest that the
outer regions of the Galactic disk are most likely locations for advanced
SETI targets, and that intelligent communities will tend to migrate outward
through the Galaxy as their capacities of information-processing increase,
for both thermodynamical and astrochemical reasons. This can also be
regarded as a possible generalization of the Galactic Habitable Zone,
concept currently much investigated in astrobiology.