This post is by James Davis Nicoll from Tor.com Frontpage Partial - Blog and Story Content
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Everyone loves them some aliens. But …if the encounter is to work out to the satisfaction of all concerned, it is best if the aliens not be too advanced (because they could brush us aside like ants) or too primitive (we might brush them aside like ants). No, there’s a Goldilocks zone for aliens, in which they are close to the same tech level as humans … and can interact peaceably with us.
Which leads me to wonder: just how likely is it that two unconnected civilizations could reach the same technological level (roughly) at the same time?
Time for some large, round numbers.
The universe is about 13.8 billion years old. The boundaries of the era in which rocky planets could form are a bit fuzzy, but Kepler-444 seems to point to them. Say the boundaries are 11 billion years old, plus or minus a billion years. OK, ...