The Fermi Paradox

Everyone feels something when they're in a really good stargazing spot on a clear night and they look up and see this. Some people stick with the traditional awe experience, some ## freak out about aliens.

The observable universe is about 90 billion light years in diameter. There are at least 100 billion galaxies, each containing 100-400 billion stars. That means there are roughly 10^24 stars in the observable universe.

For every grain of sand on every beach on Earth, there are 10,000 stars out there. The Milky Way alone contains an estimated 100-400 billion stars and roughly that same number of planets.

Scientists believe there could be 10 billion Earth-like planets in the Milky Way alone. If even a tiny percentage of those developed life, and a tiny percentage of those developed intelligent life, there should be thousands of intelligent civilizations in our galaxy.

So where is everybody? This is the Fermi Paradox. The apparent contradiction between the lack of evidence for extraterrestrial civilizations and the high probability that such civilizations exist.

There are many possible explanations. Maybe intelligent life is extremely rare. Maybe civilizations destroy themselves before they can spread. Maybe we're being observed but not contacted. Maybe the universe is too vast.