Re: >H Re: The Great Filter

Forrest Bishop (
Mon, 10 Mar 1997 14:22:20 -0600 (CST)

Robin wrote:
>Forrest Bishop writes (on the transhuman list):
>>Colliding binary neutron stars may provide a hefty element of the
>>"Great Filter". An article in the April, 1997 issue of *Astronomy*
>>magazine reports astrophysicists theorise that these events produce
>>the gamma ray bursters, and goes on to say that "in Milky Way-like
>>galaxies, such explosions would destroy advanced life on every nearby
>>Earth-like planet on the average every 100 million years." Nearby is
>>implied to be between 1500 and 3000 light years.
>It occurs to me that if the entire filter were due to events like this
>then for 1000 light years around we should see planets with advancing
>life. This would be a billion systems, so if we were the most
>advanced, it wouldn't be by much.
>Interesting - a star trek like universe out for 1000 light years, and
>then a vast emptiness from there on.
>Robin D. Hanson
Not quite- consider the mixing that occurs as star systems circulate
about the galaxy. An initially spherical 'dead zone' 2000 ly diameter
will first be stretched into a prolate ellipsoid over a few tens of
millions of years, then bent into a crescent shape. Stars will enter
and leave this volume on time scales of hundreds of millions of years,
eventually diffusing it to unrecognizability. The ensuing structure of
dead (or unicellular life) and (complex)living systems might be more of
a scattered 3D mosaic, peppered with the more recent dead zones.