Possible answers to the Fermi paradox

In general, solutions to Fermi's paradox come down to:

  • Life is difficult to start and to evolve to an intelligent and technologically advanced stage and we're the only one in the galaxy.
  • Advanced civilizations destroy themselves on short timescales.

    As the revised Drake equation solution (N<<1) shows, it seems that hopefuly, the first solution is the answer.

    Here is a list of the various assumptions along with notes pointing to related problems and contradictions.

    They are here unobserved

    They were here and they left material evidence:

  • UFO's, alien artifacts, ancient astronauts. Problem: evidence for aliens is non-existent.

    Zoo scenario

  • The aliens are here and they are keeping us in a well designed zoo (cut off from all contact) or there is an treaty preventing contact with young races. Problem: this scenario can't be tested. Only one ET could break the embargo.

    They are us

  • Humans are the descendents of previous alien civilizations. Problem: where are the original aliens? where are all the other alien civilizations?

    They exist but...

    They didn't have enough time to reach us

  • The speed of light slows communications and makes space travel too long. Extraterrestrial's messages may not have reached us yet. Problem: the galaxy exist for billions of years, even if one ET civilization formed a few million years before us, the galaxy would be already filled with Bracewell-Von Neumann probes.

    They are sending signals, but we do not know how to listen.

  • The galaxy is filled with killer robots looking for signals. ET is keeping low. Problem: no evidence of berserkers coming after us.

    They have no desire to communicate

  • ET has no interest in communicating with lesser intelligences. Problem: with millions of possible civilizations, some of the extraterrestrial ones would be interested in our species:.


  • Civilizations only have a limited lifetime, they are all dead.
  • Dangerous particle physics
  • Nanobots -> the gray goo problem
  • Verpopulation

    They developed different mathematics

  • Mathematics is the universal language, but humans may have a unique system of mathematics that ET cannot understand. Problem: then where are those incomprehensible signals?

    They do not exist because

    We are the first in the galaxy

  • Life is new to the galaxy and evolution takes time. We are the first intelligent civilization. Problem: the Sun being an average star, if other stars formed a million years ahead of us, then they would be a million years ahead of us technologically speaking.

    Planets with the right conditions are rare

  • Habitable zones, proper orbit for liquid water are rare
  • The galaxy is a dangerous place (asteroid impacts, gamma-ray bursters, etc)
  • The Earth/Moon system is unique (large tides needed for molecular evolution)

    Life is rare

  • Life's genesis is rare
  • Intelligence and tool-making is rare
  • Language is unique mankind
  • Technology and science is not inevitable

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