Since advanced extraterrestrial civilizations are so probable (, why haven’t we run into them yet? Or, as the physicist Enrico Fermi put it over lunch one day: “Where is everybody?”

Some possible explainations include:

  • These civilizations are only capable of limited interstellar travel because of fundamental physical, biological, or economic restraints.
  • They’re aware of us but do not want us (yet) to be aware of their presence (see Zoo Hypothesis )
  • They may be aware of us, but they’re not interested in contact with us because they simply don’t care.
  • They’re not interested in us because they’re so much more advanced than us
  • They don’t exist, because advanced civilizations are prone to annihilation before they achieve a significant level of interstellar colonization (self-destruction, external destruction, galaxy-wide death, cultural or technological stagnation)

In Passport to Magonia Jaques Vallee outlined the Interdimensional Psychic Fairyland hypothesis, which suggests that the entire worldwide folklore concerning contact with magical or spiritual beings could in fact be an ongoing documentation of contact with non-human intelligences, up to and including UFO contact.