ELI5: the fermi paradox

What is the Fermi Paradox?

The Fermi Paradox is a big puzzle: there are hundreds of billions of stars in our galaxy [5], so it seems like there should be tons of aliens out there [1]. But we don't see any evidence of them [1]. It's like walking through a huge forest and wondering why you don't see any bears, even though the forest seems perfect for them [2].

Why is this confusing?

Mathematically, there should be many intelligent alien civilizations because there are so many planets [5]. Yet when scientists look and listen for signals from space, they find nothing [1]. This contradiction between "there should be aliens" and "we can't find them" is what makes it a paradox [1].

What does it feel like to think about?

It's like being at a huge party where you're sure hundreds of people are supposed to show up, but when you arrive, the room is completely empty and silent [2]. You'd feel confused and wonder: where is everybody [1]?

What are some possible answers?

Maybe aliens exist but are too far away to contact [5], or maybe the first civilization to become advanced conquered all the others [3]. Or perhaps intelligent life is much rarer than we think [2].