Why have humans not been contacted by aliens (at least officially)? Drake’s Equation states that humans are almost certainly not the only intelligent species in the galaxy (estimates of existing alien civilizations currently range from 2 to 280,000,000 for the Milky Way galaxy). Thus there should be a preponderance of alien races zooming around and colonizing throughout space. Yet neither Bill Clinton, nor George W Bush ever got a photo op with sapient extraterrestrials.
This led Enrico Fermi to coin his famous Fermi Paradox, which observes the discrepancy between the theoretically high number of existing alien civilizations and the curious lack in any observed evidence of their existence.
There are a number of theories which attempt to reconcile this paradox, not the least of which is the theory of the Great Filter. The Great Filter postulates that a harrowing bottleneck of life causes very few civilizations to come into existence, thus we have not seen any evidence of them.… Read the rest