The original extinction challenge was aimed at a certain segment of the SETI crowd, which apparently either doesn't believe in ultratech or thinks that we humans are the only race smart enough to invent it. However, we seem to have significant interest in more realistic scenarios as well. So, for those of us who don't thing nanotechnology is especially exotic, here's an upgraded version of the challenge.
Propose a plausible mechanism, natural or artificial, which is capable of rendering an advanced spacefaring civilization extinct without rendering the subsequent evolution of other races impossible.
For purposes of clarification:
1) The target civilization is assumed to have self-sustaining colonies in several solar systems spread across a volume of at least a few dozen cubic light-years (killing them off before they get into space is too easy).
2) The target civilization is assumed to have Drexlerian nanotechnology, uploading, sentient AI, and other such technologies. However, they are still bound by the known laws of physics (we can't really speculate productively about races that don't have that constraint).
3) Replacing the target civilization with an SI, borganism, or other sentient construct doesn't count. A bona fide extinction requires the complete eradication of all sentient life, plus the destruction of all non-sentient systems that would re-create sentient life.
4) A proposed extinction event must be consistent with current astronomical knowledge (i.e. either it would be invisible to us, or it is something we've seen). Since this all started as a discussion of the Great Filter, it should also leave behind a universe where new races can evolve in the future.
For the record, Eliezer Yudkowsky gets credit for the only plausible
extinction event I've seen so far (see
http://singularity.posthuman.com/sing_analysis.html#zones, option #2). It requires making some assumptions that many people would disagree with, but at least it is arguably possible.
Are there any other candidates.
Billy Brown, MCSE+I