So far, our attempts to identify signs of extraterrestrial life have all amounted to nothing. The apparent lack of observed intelligent life in the universe beyond Earth in the face of what would seem to be an almost limitless potential for such life to arise is known as the Fermi Paradox.
There are several theories to explain our apparent aloneness.
Some have suggested that humans are being intentionally avoided by intelligent alien civilizations to allow us to grow and develop naturally (this idea is, somewhat unsettlingly, known as the “zoo hypothesis”). A more farfetched and difficult to believe version of this idea posits that aliens are already here, but only covertly, and their presence remains hidden from us.
My theory, known from here on as "The CW Paradox," explains this aloneness by pointing out that humanity has only been communicative outside the bounds of our planet Earth for a very short time, maybe a hundred and seventy years at most. That's a literal blink in time. Multiple alien life forms could exist yet be in the same condition we were in until very recently - in other words, very vibrant but only within their habitat, whatever that habitat may be. Or, they could have looked our way, but seen and heard nothing, and then continued their search in other directions, leaving us undiscovered, for now.
Hey, hey, we're over here!
They're out there alright. When I put on my tin foil hat, I can hear them chatter away in their weird languages.