The well-known Fermi Paradox is a simple question with no clear answer: “where are all the aliens?” Given the immense size of our galaxy (not to mention the size of the entire universe), it seems likely that life would have bloomed on other planets, and that on at least some planets, this life would be intelligent. And yet, we have never observed life on another planet, or identified signals from any extrasolar civilizations. Why is this?
One possible answer is that we are truly alone in the universe, and that life is far more scarce than we realize. This would mean we are safe from alien invasions, but also that the entirety of life in the universe is on Earth, so the pressure is on us to continue that life rather than let the universe become a lifeless expanse. This proposition doesn’t seem statistically likely, however, given that the birth of life as we understand it comes from replicable processes which could certainly occur elsewhere.
A far more terrifying answer is the Dark Forest Theory, which posits that other alien civilizations can hear us but choose not to respond. This theory involves game theory; when an alien civilization identifies another civilization, they risk destruction if the other is hostile, or benefit if they are amicable. This risk is simply not worth taking, so the safest option is to ignore the other civilization and remain hidden. Earth has been sending signals out in the hope of being “found” for years now… if this theory is true, we’re in trouble. However, this theory is not based on any scientific evidence, so we don’t need to worry (at the moment).
There is no concrete answer to the Fermi Paradox, but it is certainly a vital question in our understanding of the universe. It seems that the only way we will get an answer is to find alien life, or to have it find us.