Counterintuitive Facts (92): Why Haven't We Found Aliens Yet?

I. The universe has hundreds of billions of galaxies. Each galaxy has hundreds of billions of stars. Many stars have planets. Many planets are in habitable zones. Even if the probability of intelligent life is one in a billion. There should be billions of civilizations in the universe. With so many civilizations, some should have developed interstellar travel. According to calculations, once one civilization starts interstellar colonization, it could fill the entire Milky Way in just a few million years. And the Milky Way has existed for 13 billion years.

II. A few million years is just a blink for the universe. If intelligent life exists, they should be everywhere by now. Our sky should be full of spaceships. Our radio waves should be full of alien broadcasts. But reality is: The universe