An enumeration of possible solutions to fermi’s paradox.
- Aliens exist, but we see no evidence
- Human limitations
- Human beings have not been searching long enough (Freitas Jr 1983; Freitas Jr. 1985)
- Human beings are not listening properly
- Practical limitations
- Communication is impossible due to problems of scale
- Intelligent civilizations are too far apart in space or time (Wesson 1990)
- Communication is impossible for technical reasons
- They only recently emerged and have not yet had the time to become visible. This could for example be due to synchronization due to a declining rate of gamma ray bursts that sterilize much of the galaxy (Annis 1999; Cirkovic 2004).
- Civilizations only broadcast detectable radio signals for a brief period of time before moving on to other media.
- It is too expensive to spread physically throughout the galaxy (Landis 1998)
- Alien nature
- They are too alien to be recognized
- They are non-technological and cannot be detected except by visiting them.
- They tend to experience a technological singularity becoming unfathomable and invisible.
- They develop into very fast, information-dense states that have no reason to interact with humans (Smart 2002; Cirkovic and Bradbury 2006)
- They migrate away from the galactic disk for cooling reasons (Cirkovic and Bradbury 2006)
- They tend to (d)evolve to a post-intelligent state (Schroeder 2002)
- They choose not to interact with us
- They are here unobserved
- Earth is purposely isolated (The Zoo or “Interdict” hypothesis) (Ball 1973; Fogg 1987)
- Earth (and nearby parts of space) are simulated (Baxter 2001; Bostrom 2003).
- They secretly deal with the government or other groups.
- No other civilizations currently exist
- We are the lucky first civilization
- Intelligent, technological life is exceedingly rare
- Rare earth hypothesis
- Life is very rare (Wesson 1990)
- Intelligence is very rare
- Intelligent, technological life is very short-lived
- Intelligent life is wiped out by external disasters at a high rate
- Technological intelligent life exhaust its resources and dies out or becomes nontechnological
- It is the nature of intelligent life to destroy itself.
- It is the nature of intelligent life to destroy others.