[extropy-chat] fermi's paradox: m/d approach

[Robert J. Bradbury]

On Fri, 2 Jan 2004, Samantha Atkins wrote:

> "Damien Broderick" <thespike at earthlink.net> wrote:
> > http://www.theage.com.au/articles/2004/01/01/1072908849778.html [snip]

At least with respect to the age of the planets, Charlie has been pointing this out
since the Blois conference which I think was in 2000.  He and his students have
been extending the results since then -- but for some of us the implications
are old news.

This may be from Samantha [the nesting attributions are confusing]:
> >It would be more accurate to say that 10% of the planets in the milky way pass one
> > rough cut filter for possibly supporting advanced (should be intelligent?) life.

Its a bit more complex than that.  Closer to the galactic center you have more star
formation, more supernovas, faster metal accumulation, faster development of a
galactic habitable zone, perhaps faster evolution of complex life forms.  There
may be more planets (of various sizes) in locations where the metal content is
greater.  At the same time due to GRB, nearby SN, etc. the hazard function may
be greater and so in order to survive one has to evolve more quickly to survive.

The further out you go in the galaxy the less metal, the fewer GRB, SN, etc. so both
development rates and hazard function rates may be slower.  Over time it is likely the
galactic habitable zone moves from the inner to the outer portions of the galaxy.
But this assumes no intergalactic collisions which could significantly upset
rates and locations of star formation, the rates of metal creation, GRB, SN, etc.

Soooo....  While I admire Charlie & Co's work -- I think we are going to have to
run a number of backward simulations of the creation of the Milky Way as it exists
today in order to understand fully what took place in our galaxy and how that
impacted its evolution (and as a result the probable evolution of intelligence).

Robert