What is the fermi paradox?

The Fermi Paradox is the apparent contradiction between the high statistical probability that extraterrestrial civilizations exist and the total lack of evidence for them.

The paradox is named after physicist Enrico Fermi, who famously asked, "Where is everybody?" during a casual conversation about alien life in 1950.

The logic follows three main points:

• There are billions of stars in our galaxy that are similar to the Sun.
• Many of these stars likely have Earth-like planets, and many of these planets are much older than Earth.
• If intelligent life is common, some of these civilizations should have developed interstellar travel, which would have allowed them to colonize the galaxy by now.

Because we have found no definitive proof of these civilizations—no radio signals, probes, or artifacts—we are left with a paradox. Scientists have proposed many explanations, such as:

• Life is rare: Perhaps the evolution of complex, intelligent life is extremely improbable.
• Civilizations are short-lived: Maybe intelligent species tend to destroy themselves through technology or climate change before they can reach out.
• The "Great Filter": There may be some barrier in the evolutionary process that is almost impossible to get past, preventing life from becoming interstellar.
• We are looking wrong: We may be looking for the wrong types of signals or haven't been searching for long enough.

It remains one of the biggest open questions in astronomy and biology.