"Where is everybody?" That famous phrase, uttered over lunch by eminent physicist Enrico Fermi, perfectly encapsulated what has since become known as the Fermi paradox: If life happened here on Earth and the universe tends to not do things only once, then life should also occur elsewhere. In fact, the universe should be teeming with advanced spacefaring civilizations.
Even when you account for every technological hurdle — limits in rocket technology, speed and life spans, as well as disease, warfare and anything else that could slow progress — the argument stays the same. Our galaxy is over 13 billion years old, which is more than enough time for spacefaring civilizations to spread throughout the Milky Way.
