>We must also
>see that the gaps between galactic arms are really rather wide and are a
>hindrance to expansion.
Stanislaw Lem -- in the 'World as Cataclysm' (One Human Minute, 1986) -- argues that the early solar system spent time in a galactic arm where stellar explosions were common (and which he argues were a necessary precursor to life), but then shortly thereafter left for the quieter spaces between arms. By being in the relatively empty spaces ensured that life was not too quickly snuffed out by nearby supernovae (which would have occurred if we were near the center or stuck within a spiral arm).
Anyone want to voice an opinion on how this argument has stood the test of time? I find its most interesting feature that it contradicts the underlying belief that we are on a very average star in a very average point in the galaxy. On the contrary if Lem is right its only in particular places (approx. 34k light years from the center - where stars pass through the arms on a regular, but not too fast pace) that life-bearing star systems can emerge.
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/