Michael S. Lorrey wrote:
> Anders Sandberg wrote:
> > firstname.lastname@example.org (Patrick Wilken) writes:
> > 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). So Lem's idea haven't held up well,
> > 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).
> I have not heard that our sun is such a wanderer. I was under the impression that
> most of the stars in this local area are rather homogenous and communal.
> Mike Lorrey
As I recall, the current explanation for the spiral arm structures is a standing wave phenomenon. Any individual star moves in and out of the arms as it orbits the galactic center, but gravitic interactions cause each star to linger a bit in the denser arm areas and hurry a bit in the less dense parts.