From: Mitchell Porter (mitchtemporarily@hotmail.com)
Date: Wed Apr 23 2003 - 20:45:31 MDT
I'm a member of an intelligent species, born during an
unprecedented technology-driven population boom. It seems
thinkable that my species could be the seed of a cosmic
civilization capable of spreading indefinitely into the
universe. But if that happens, the future population of
the civilization born in this biosphere will be orders of
magnitude greater than the number of all humans who have
lived so far. This would place those of us alive now at a
remarkably early stage in the history of that civilization;
if one regards oneself as a random sample from that history,
this position is not just remarkably early but also extremely
unlikely. One might therefore conclude that the future of
cosmic expansion is not to be, and that instead we are headed
for an irreversible population decline, cause unknown. In
that scenario, the majority of humans that will ever live
is alive during the final population boom, and so we can
after all view ourselves as historically typical members of
our species. (The majority of human history was spent on the
savannahs, but the population now is so much greater than
the pre-agricultural one that the *numerical* majority of
all-humans-who-will-ever-live is urban ... in this scenario.)
This is a version of the Doomsday Argument. If one pays
attention to Earth alone, it is logically consistent and
self-contained. However, it seems that one also ought to be
able to regard oneself as a random sample from the total
*cosmic* population of intelligent entities, and at this
point the Diaspora Scenario of cosmic colonization becomes
relevant again. Let us assume that the average total
population, from start to finish, of a Diaspora civilization
is about 10^9 times greater than that of a Doomsday
civilization. For average cosmic citizens (such as, by
hypothesis, us) to find themselves in a Doomsday civilization
would imply that such civilizations are *at least* 10^9
times as numerous as Diaspora civilizations. And in general,
one might say that:
Validity of Cosmic Doomsday Argument (CDA) implies that
Frequency of Doomsday civs >= N * Frequency of Diaspora civs,
where N = (Typical Diaspora pop/Typical Doomsday pop)
This is a very simple observation, but I don't think I've
seen it anywhere in the Doomsday Argument literature. It would
be interesting to have a realistic value for N.
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