I disagree with the impossibility of it (generation ships, Von Neuman machines, etc.). But the evidence is that it has not happened (or at best, they passed by without saying "hello")--and I expect if it does happen, we'll either know it...or we won't. No "only the one crazy guy down the street knows it" kind of thing.

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Todd (Bowie, MD, US, North America, Earth, Sol System, Vega region, Local Bubble, Orion arm, Milky Way Galaxy, Local Group, Virgo A Cluster, Virgo supercluster, the universe in which spock is clean shaven)

Quidquid latine dictum sit, altum sonatur.

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