From Earth, we can see Billions of stars, trillions including galaxies where we can't make out stars individually.
The Universe is approx 13 billion years old, which is a lot of time for life to emerge and multiple generations for large stars. Life has already emerged in one place at least in that time.
Under known physics, it should only take 2 million years at most for a civilization which has advanced to space travel to colonize an entire galaxy, if even a tiny tiny fraction of them want to.
If there are any civilization out there, we should see clear evidence of it. The fact that we can see stars at all should be surprising (this is known as the Dyson Dilemma)
5, Among those billions/trillions of stars, we have not seen any evidence of extra terrestrial civilizations.
Why don't we see any evidence of extra terrestrial civilizations?
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Answers are pulled from wikipedia
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