The **Fermi paradox** is the alleged inconsistency between the lack of evidence of extraterrestrial intelligence and the various high estimates for its probability. The solution to the paradox has implications for the long-term future, in particular the feasibility of interstellar colonization and the likelihood of extinction.

The expected number of interstellar civilizations observable from Earth is the product of the number of planets in the galaxy and the following three probabilities:

The probability that any given planet produces intelligent life

The probability that any given intelligent species develops an interstellar civilization

The probability that any given interstellar civilization would be detectable from Earth at this time

Since the number of planets in the galaxy is in the hundreds of billions, even very small values of the three probabilities would imply that we should see many interstellar civilizations. However, we observe none. This means that at least one of the probabilities must be *extremely* low.

The second probability is most concerning, since it suggests something about the future of humanity. If it is the extremely low probability, then this means either that interstellar colonization is infeasible or that humanity is extremely likely to go prematurely extinct before engaging in it.

Generally, the more highly we rate the first and third probabilities, the lower the second probability would have to be, which should decrease our credence in the possibility of humanity ever leaving the solar system.

## Bibliography

Boeree, Liv (2018) Why haven’t we found aliens yet?, *Vox*, July 3.

Bostrom, Nick (2008) Where are they?, *MIT technology review*, April 22, pp. 72–77.

*An exploration of the Fermi Paradox as it relates to the risk of human extinction*

Ćirković, Milan M. (2018) *The Great Silence: Science and Philosophy of Fermi’s Paradox*, Oxford: Oxford University Press.

Miller, James (2020) The Fermi paradox and x-risk

Sandberg, Anders, Eric Drexler & Toby Ord (2018) Dissolving the Fermi Paradox, *arXiv*, June 6.

Wiblin, Robert & Keiran Harris (2018) Where are the aliens? Three new resolutions to the Fermi Paradox. And how we could easily colonise the whole universe, *80,000 Hours*, May 8.

*An interview with Anders Sandberg.*

## Related entries

extraterrestrial intelligence | non-humans and the long-term future | space colonization | space governance