Two possibilities exist: either we are alone in the Universe or we are not. Both are equally terrifying.
Sigourney Weaver had initially been very hesitant to reprise her role as Ripley, and had rejected numerous offers from Fox Studios to do any sequels, fearing that her character would be poorly written, and a sub-par sequel could hurt the legacy of Alien.
If you insert very, very optimistic numbers into the equation (not considering “Goldilocks” theory etc.), you’d obtain 5 (five) communicating civilization in the Milky Way (all Civs. outside the Galaxy are simply out of reach because of distance and speed of light). Which means, probability to have two existing civilization at the same time, are very very low.
The key is SPACE-TIME SPAN. Universe seems to have designed to KEEP CIVILIZATIONS REMOTE one to another.