One of the best and toughest puzzles in the cosmos, described and illustrated effectively:
If 1% of intelligent life survives long enough to become a potentially galaxy-colonizing Type III Civilization, our calculations above suggest that there should be at least 1,000 Type III Civilizations in our galaxy alone—and given the power of such a civilization, their presence would likely be pretty noticeable. And yet, we see nothing, hear nothing, and we’re visited by no one. Welcome to the Fermi Paradox.
It’s all so tantalizing! What I like best about the Fermi Paradox is that the universe will be a scrumptious, dizzying mystery no matter what: while I’d prefer galaxies bustling with life, it would be just as existentially bizarre and intriguing if humans are completely alone.
(See also Putting Time In Perspective.)