From: Mike Lorrey (mlorrey@datamann.com)
Date: Tue May 28 2002 - 11:04:15 MDT
"Robert J. Bradbury" wrote:
>
> Based on a stellar population of 200 billion stars and
> a spectral type G abundance of ~4% [1] and an estimate of 3%
> of Sun-similar stars being studied containing "Earths" [2]
> the number of "Earths" in the galaxy should be 240 million!
>
> Even if one assumes the galactic "habitable" zone is only
> 1% of the galaxy, that means the number of "Earths" should
> be 240,000. Using the figure that 1/3 of these planets
> evolve life [2] implies there are ~80,000 life bearing planets
> in the galaxy. Of those planets, 75% of them (~60,000)
> should be older than the Earth on average by a billion years [4].
>
> So, either:
> (a) the risks to the development and evolving of life due to
> supernovas/comets/asteroids are very very high and cannot
> be compensated for by evolution (questionable); or
> (b) the galactic habitable zone is << 1% of the stars; or
> (c) the evolution of intelligent technological civilizations
> is very very difficult; or
> (d) intelligent technological civilizations see little incentive
> for galactic colonization; or
> (e) intelligent technological civilzations universally reject
> galactic colonization as a development strategy.
or (f) intelligent technological civilizations do colonize the galaxy,
but we are at this time unable to detect them, nor are they interested
in communicating with primitives such as us, except possibly in ways
which we generally interpret the recipients of said communcations to be
insane or otherwise imagining/confabulating/hallucinating.
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