Fermi Paradox
The contradiction between the high probability of extraterrestrial life and the lack of evidence for it, generating numerous proposed solutions.
OVERVIEW
The Fermi Paradox asks: if the galaxy likely teems with civilizations, why do we see no evidence? Solutions include the Great Filter (some step in evolution is extremely difficult), the Zoo Hypothesis (ETIs avoid contact), the Dark Forest (civilizations hide to survive), and the possibility we are alone. The paradox sharpens with every exoplanet discovery.
KNOWN FACTS
The Drake Equation estimates N could be in the thousands
Kepler and TESS have confirmed thousands of exoplanets
The galaxy's age allows time for civilizations to spread
No confirmed evidence of extraterrestrial technology has been found
SETI has searched 60+ years with no confirmed signal
CLAIMS
The galaxy should be teeming with civilizations, yet we see no evidence
The Great Filter may be ahead of us or behind us
The Zoo Hypothesis suggests ETIs are observing without interfering
The Dark Forest suggests civilizations hide to avoid destruction
The lack of evidence may be because we haven't looked properly
EVIDENCE FOR
The Drake Equation estimates N could be in the thousands
Kepler and TESS have confirmed thousands of exoplanets
The galaxy's age allows time for civilizations to spread
No confirmed evidence of extraterrestrial technology has been found
SETI has searched 60+ years with no confirmed signal
EVIDENCE AGAINST
Drake Equation variables are highly uncertain; N could be 1
The galaxy may be too large for civilizations to reach us
Technological civilizations may be short-lived
We may not recognize ETI signals
The paradox assumes ETIs would want to expand
OPEN QUESTIONS
No open questions recorded.
SOURCES
TIMELINE
Fermi poses the paradox
Drake formulates the equation
Exoplanet discoveries sharpen the paradox