I've just recently become interested in science theory after years of just enjoying science fiction. One of the topics that came in stark contrast to Carl Sagan's beliefs and the vast majority of sci-fi settings is the proposition of the Fermi Paradox: If aliens exist, why aren't they already here or their existence readily identified? Basically after having a several billion years head start of us, why hasn't another intelligent species (or their machines) colonized/destroyed/impacted us? The paradox proposes that this is due to the fact that alien life is extremely rare and that intelligent alien life is nearly non-existent.
I've read about SETI and the extremely limited search criteria for radar signals, but why haven't we even seen any artificial constructs in the sky? Things like Dyson Spheres, stars in perfect alignment, unexplained phenomena, etc that would be the equivalent of seeing the Great Wall or city lights from space. Are humans the only intelligent life in our sector, galaxy, or even universe?
Note, please let us disregard traditional UFO discussion…
Read more: Is humanity alone in the galaxy due to the Fermi Paradox?