From: Patrick Wilken (patrick.wilken@infotech.monash.edu.au)
Date: Wed Jan 06 1999 - 15:56:33 MST
>As far as I know the sun passes through the spiral arms in its orbit,
>so there should be a few passages every galactic year (250 million
>years, if I'm not misremembering).
Are you sure? According to Lem:
"The protosolar gas cloud, moving along an orbit at an angle of seven or
eight degrees to the plane of the galaxy, entered the arm for the first
time about 4.9 billion years ago. For 300 million years the cloud underwent
the stromy conditions of passage through the entire width of the arm; since
it left the arm, it has been traveling through calm space. The trip has
lasted much longer thant he passage through the arm, because the
corotational circle, along which the sun moves, intersects the spiral arms
at a sharp angle, making the arc of the solar orbit between the arms longer
than the arc within the arm.".
>although he might still argue that it is likelier for intelligence to
>evolve on stars in quieter areas sinply because of a lower risk of
>mass extinctions (but on the other hand, they tend to cause
>evolutionary radiations).
It seems that large scale meteor strikes are all we need to occassionally
shake things up (if evolution hasn't created space-farers in this
evolutinary cycle lets crash-and-burn and start again!).
best, patrick
-------------------------------------------------------------------------
Patrick Wilken http://www.csse.monash.edu.au/~patrickw/
Editor: PSYCHE: An International Journal of Research on Consciousness
Secretary: The Association for the Scientific Study of Consciousness
http://psyche.cs.monash.edu.au/ http://www.phil.vt.edu/ASSC/
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