Fermi Paradox

The question why, if the Galaxy is filled with intelligent and technological civilizations, they have not visited Earth? Fermi is supposed to have asked, “So? Where is everybody?” Fermi realized that any civilization with a modest amount of rocket technology and an immodest amount of imperial incentive could colonize the entire Galaxy within a few million years (a very short time on Galactic time scales). The fact that aliens don’t seem to be walking our planet is taken to imply that there are no extraterrestrial anywhere among the vast tracts of the Galaxy. Many researchers consider this a radical conclusion to draw from such a simple observation. Many solutions to the paradox have been proposed, but in general, solutions to Fermi’s paradox come down to either (1) life is difficult to start and evolve (either hard for the process or hard to find the right conditions); or (2) advanced civilizations destroy themselves on short timescales.