In recent months we’ve been looking at science writer Matt Williams’s coverage of the many reasons (links below) that have been advanced as to why we do not see extraterrestrials except at the movies. Last Saturday, we considered the Percolation Hypothesis, whose beauty is its common-sense simplicity: The aliens can’t overcome the laws of physics, any more than we can. In the real world, barriers like years between communications even at the speed of light would take a toll on adventurousness.

Another hypothesis that Williams has examined is our focus today, the Aurora Hypothesis, “just because planets are habitable doesn’t mean that intelligent life can colonize there.” (Williams)

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