From: Hal Finney (hal@finney.org)
Date: Wed Apr 23 2003 - 22:13:14 MDT
Mitchell Porter writes:
> 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)
That's an interesting point. I think I may have seen it before although
perhaps not expressed in such clear mathematical terms. We discussed a
paper a few months ago, http://xxx.lanl.gov/pdf/physics/0302071, which
expressed a similar idea in a more qualitative way:
First, it is clear that there is some nonzero probability for a
civilization to survive early threats to its existence (nuclear war,
asteroid impact, etc.). Such a civilization might go on to spread
across its galaxy. It could endure for millions of years and contain
a huge number of individuals. We will refer to such civilizations
as long-lived. On the other hand, some civilizations will succumb to
existential threats and so be short-lived. What will be the fraction
of each?
Unless the fraction of long-lived civilizations is tiny, nearly all
individuals will belong to them, and furthermore will live late
in their civilizations when most of the individuals live. That,
however, is not the circumstance in which we find ourselves. Instead,
we find that we live either in a short-lived civilization or very
early in a long-lived one. While we do not have a clear idea of how
long to expect civilizations to last, when we take into account our
circumstances, we should clearly update our ideas in favor of a much
larger chance for civilizations to be short-lived (Carter unpublished;
Leslie 1996 p. 231). Thus unless we previously thought that long-lived
civilizations were much more likely, we should now think that almost
all civilizations will be short-lived - a sort of universal doomsday.
I'm not sure if it has been mentioned here, but fans of the Doomsday
Argument might want to know that Nick Bostrom has published a book on
that argument and the many related concepts, Anthropic Bias: Observation
Selection Effects in Science and Philosophy, available from
http://www.amazon.com/exec/obidos/ASIN/0415938589/103-4781209-8504658.
Hal Finney
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