Fifty years of SETI with radio telescopes has so far proved negative. We have found no messages of peace and goodwill, no galactic internet, no extraterrestrial propaganda or advertising. No starships full of aliens have arrived on Earth to befriend us or to eat us, while our galaxy seems free of Dyson Spheres or similar astro-engineering. The silence is deafening and perhaps a little worrying.
Enrico Fermi was of course first to point this out. Life ought to be common in so vast a Universe, and civilisations of intelligent beings should have arisen hundred of times at least in the Milky Way with its 400 billion stars. Some of those civilisations ought to have passed by our Solar System or broadcast a message to us. That we see nothing shows that something is badly wrong with our assumptions. Perhaps our Earth is special in a way we have yet to recognise and life in the Universe is far rarer than we think. Perhaps the idea of exploring the Galaxy is a silly, immature idea and all the grown-ups are staying at home, contemplating their navels or having fun in their holodecks. Maybe berserkers or some Lovecraftian horror that we are mercifully ignorant of squelches any intelligent life before it gets anywhere. Maybe we are like ants in a city park, completely oblivious to the technological civilisation all around us.
Whatever the answer, I believe the Universe is stranger than we think (and possibly in a way we may not find pleasing).