A list of solutions to the Fermi Paradox

UPDATE: The blog has now moved: https://commonreader.substack.com/

As Tim Urban says, ‘We’d estimate that there are 1 billion Earth-like planets and 100,000 intelligent civilizations in our galaxy.’ So there must be aliens. Why haven’t we heard from them? (Read about the Fermi Paradox here.)

This blog is a list of answers. I’ve summed up each one in a line and dropped a relevant quote afterwards, and mostly linked to an article not a paper. Some of the ideas overlap or are sub-categories of each other. I tried to avoid an endless list, but still give different perspectives.

List of possible solutions to the Fermi Paradox

  1. There is no paradox. ‘We only know 0.0012699565% of the galaxy.’
  2. There is no paradox. ‘Based upon the current state of astrobiological knowledge, there’s a 53 to 99.6 percent chance we are the only civilization in this galaxy and a 39 to 85 percent chance we are the only one in the observable universe.’
  3. There is no paradox. ‘Natural variability will mean that sometimes galaxies will be settled, but often not.’
  4. There is no paradox. ‘Fermi was questioning the feasibility of interstellar travel—nobody thought he was questioning the possible existence of extraterrestrial civilizations.’
  5. There is no paradox. ‘There is no logical contradiction between the statement “E.T. might exist elsewhere” and the statement “E.T. is not here” because nobody knows that travel between the stars is possible in the first place.’
  6. There is no paradox. All life, including us, is distributed through the Universe by space dust.
  7. We are too far away from anyone else to be found because we are in a supervoid.
  8. We’re too remote to notice we live in an otherwise colonised galaxy, like Inuits who didn’t know America had been colonised.
  9. They are too far away because they live at the extreme edge of the universe. ‘Machine-based civilizations, with their massive supercomputers, will have huge problems managing their heat waste. They’ll have to set up camp where it’s super cool.’
  10. They don’t exist: we are living in a computer simulation. (Alternatively, they are running the simulation, I suppose).
  11. They already destroyed themselves through something like climate change.
  12. The aliens can’t exist because it’s too outlandish they haven’t found us yet. ‘If a civilization on Planet X were similar to ours and were able to survive all the way to Type III level, the natural thought is that they’d probably have mastered inter-stellar travel by now, possibly even colonizing the entire galaxy.’
  13. No aliens would have the resources to colonise a billion stars.
  14. The aliens gave up looking or are morally against trying to colonise us.’Habitable planets lacking technical civilizations will frequently be encountered by spacefaring civilizations. It is not clear what their response will be…Perhaps strict injunctions against colonization of populated but pre-technical planets are in effect in some Codex Galactica. But we are in no position to judge extraterrestrial ethics. Perhaps attempts are made to colonize every habitable planet…A whole spectrum of intermediate cases can also be imagined.’
  15. No other life exists because of the great filter.’ This is a candidate because it took about a billion years of Earth’s existence to finally happen, and because we have tried extensively to replicate that event in labs and have never been able to do it.’
  16. Earth is unique. ‘Though there may be many Earth-like planets, the particular conditions on Earth are exceptionally friendly to life.’
  17. We are the first ones to be this advanced and will therefore inadvertently wipe out other forms of life. ‘We are the first to arrive at the stage. And, most likely, will be the last to leave.’
  18. Every time the universe advances enough for intelligence to evolve, it then wipes it out. ‘A possible regulatory mechanism that can account for this is the frequency of gamma-ray bursts — super-cataclysmic events that can literally sterilize large swaths of the galaxy.’
  19. They have already visited. Ounuamura. Tic Tac.
  20. We missed the aliens. They visited before we evolved. (See also: ‘NASA conspiracy? Space agency’s Spirit rover destroys ‘alien dinosaur skull’ on Mars.’)
  21. The aliens are already here. ‘“The click beetles in my backyard don’t notice that they’re surrounded by intelligent beings — namely my neighbors and me,” Shostak said, “but we’re here, nonetheless.”’
  22. We are a civilisation seeded here by wealthy alien philanthropists. ‘If you end up with 100 successfully seeded solar systems for each very advanced civilization, the resulting odds suggest that we are indeed the result of a seed.’
  23. We wouldn’t know life from other planets if we saw it. ‘I predict that, if a form of life is ever discovered in another part of the universe, however outlandish and weirdly alien that form of life may be in detail, it will be found to resemble life on 4 Earth in one key respect: it will have evolved by some kind of Darwinian natural selection’. Dawkins
  24. We don’t matter enough to be invaded yet. ‘It’s an inefficient use of resources to exterminate all emerging intelligences, maybe because most die out on their own. But past a certain point, the super beings make their move.’
  25. We haven’t been visited because the other advanced life forms destroyed themselves (think nuclear war).
  26. We are too boring for other civilisations to be interested in, for friendly reasons for otherwise.’ Imagine a life form whose brain power is to ours as ours is to a chimpanzee’s. To such a species, our highest mental achievements would be trivial.’
  27. We are interesting to them, but in a niche way, and are living in a cosmic zoo. ‘Our relationship to ETI might be similar to the relationship of Eciton burchelli to mankind: E.O. Wilson knows and cares, but Bill Clinton doesn’t.’
  28. We don’t have the right technology to receive their signals.
  29. We’re expecting results too quickly.’ Nobody has visited because they’re all too far away; it takes time to evolve a species intelligent enough to invent interstellar travel, and time for that species to spread across so many worlds.’
  30. They will never find us/it’s going to take an eternity. ‘He found that even if the alien ships could hurtle through space at a tenth of the speed of light, or 30,000km a second, – Nasa’s current Cassini mission to Saturn is plodding along at 32km a second – it would take 10bn years, roughly half the age of the universe, to explore just 4% of the galaxy.’
  31. Most species don’t want to go into space. (We do and we’re quite bad at it.)

We don’t seem to have got much beyond this list of categories of answers from ‘Extraterrestrial Intelligence: Where is Everybody?’ by John A. Ball, which was written in 1985.

  • There are no other civilizations.
  • Other civilizations exist, but they’re very primitive.
  • Other civilizations exist at about our level of development. They suspect that we might be here, and they might like to talk with us.
  • Advanced civilizations exist and they know we’re here. They would like to talk with us if they could just attract our attention.
  • They know we’re here, but they don’t care; they’re ignoring us.
  • They exist, we are of some interest to them and a few of their scientists are discreetly studying us.
  • They exist, we are interesting to them, and they are studying us in some detail but inconspicuously.
  • They exist, they are studying us and occasionally even dabbling in our affairs (UFOs).
  • We are an experiment in their laboratory.

I’m naturally sceptical, and it might be bad news if there are aliens, but as Tyler Cowen says, ‘when you run all the arguments through your mind, is it not possible to come away with an estimate of at least a one-in-a-thousand chance that alien visitations are a real thing? ‘

p.s. After I finished this post, I found this list of ‘50 solutions to the Fermi Paradox‘ (based on a book about the same thing by physicist Stephen Webb). That list is not all brilliant (mine is closer to what I wanted to read but couldn’t find) but it is fairly comprehensive without too much chatter. I haven’t read the book.

13 thoughts on “A list of solutions to the Fermi Paradox

  1. We have basically zero evidence on this problem. We don’t know. The idea that we must be able to figure everything out is a good strategic or motivational stance, not a fact. Science requires evidence not just thinking up cool stuff.


    1. Hi Jim, thanks for reading. I agree although there’s a place for imagination in all forms of inquiry. Hopefully I was careful enough not to say any of this was facts. Hope you enjoy the blog.


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  3. Funny, but I don’t see this solution anywhere. I call it The Perceptual Cul-de-sac Solution, AKA, the Species-Specific Cognitive Blindness Solution (SSCBS) to the Fermi Paradox.

    With this solution, I posit that aliens are already here but we do not perceive them for the same reason that ants don’t know we’re here. (Note, we are only perhaps 50 million years ahead of the ants, a mere blink in geological time).
    Let’s acknowledge something right away—our undergraduate courses in biology, embryology, and zoology were deficient in elaborating for us the fact that our perception of the world is also to some degree a construction, and that it too evolved just as did the many anatomical and physiological adaptations we learned about in other species. Our educators might be forgiven for this lack of didactic depth because cognitive science had not sufficiently matured in my days at university.

    After reading Donald Hoffman’s recent book, The Case Against Reality, 2019, I see more clearly how the SSCBS solution to the Fermi Paradox is conceivable. We do not perceive reality as it is, rather we perceive a perceptual interface with reality apparently constructed from a long evolved historical set of “fitness payoffs” useful to our species. As a neuroscientist at UC Irvine, Hoffman shows us how our survival is not dependent on perceiving reality veridically (free of illusion) but rather is dependent on perceiving reality in a way that pays off positively for our success in the struggle to survive and reproduce. This pastiche of things perceived, like a tapestry of utilities hiding an incomprehensible wall-of-the-real behind it, provides the interface of “fitness payoffs” we need for survival. Indeed, Hoffman shows us that seeing veridically is, surprisingly, a certain path to extinction. We might ask, if that is so, then what are the real-things-in-themselves we do not see? The answer is: just as the ant does not see us, we don’t see it.

    Yes, this certainly does turn on its head our customary view of the past—–the view that we could survive only if we actually perceived things as they really are. With this solution to the Fermi Paradox notably not included in astrophysicist Stephen Webb’s book, “75 solutions to the Fermi Paradox”, 2015, I propose a hypothesis: a perceptual cul-de-sac out of which and beyond which our perceptual cognition has not evolved an aperture to see
    I am reminded of the story—probably just an urban legend but useful nonetheless—about the Fuegians who Magellan encountered in Tierra del Fuego who could not see his ship, even when it was painstakingly pointed out to them. Some years later when adequate translators returned it was explained to the visiting Europeans that the natives had never seen Magellan’s ship but rather had seen a large dead floating tree with dead branches protruding from it. This story, however apocryphal, along with other findings from cognitive science argue that we only “see” the things for which we have prior mental categories.

    These categories are not transcendent and are not a priori but rather embodied, that is, they are emergent from the actual experience of bodies evolving and living in this world. And surely this is true for every species’ unique embodiment, occupying not just a species-specific physical niche in the environment but also a cognitive niche in the perceived world, observing the world not veridically but in adherence to the exigencies of their own particular fitness payoffs.\
    And yet another thought: If most matter is “dark matter” yet extant everywhere and all around us as some physicists are saying, capable of perturbing matter gravitationally while being electromagnetically invisible, doesn’t this suggest another possibility—not about the limitations of our physics or the perfectibility of our instrumentation but rather, as with the ant, about the limits of our own cognition—limits imposed by a cognitive barrier: a species-specific perceptual cul-de-sac belonging uniquely to we humans?


    1. That’s a cool idea. But it’s only an idea. There are plenty of evidence-free narratives floating around.

      I think that Donald Hoffman argues a theoretical position that goes way beyond his data. It’s clear that we hallucinate a representation of reality (for example, there is clearly no greenness in trees, just photons of various wavelengths hitting our eyes.) It’s also clear that we can only take in a microscopic fraction of the out-there reality (we could spend a lifetime learning the composition and crystal structure of a single grain of sand.) But a key feature of our representation of reality is that it chooses salient features of actual reality on a basis of adaptive usefulness. It is more-or-less necessary to see to live successfully in human ecological niches but it is not necessary to detect individual photons or individual crystal planes in grains of sand. If it was adaptive we might have evolved these capacities. Furthermore, we have evolved and developed a capacity for abstract modelling and can use this to further investigate the world. Physics is not complete in and ultimate sense but it has extended our innate evolutionarily-honed take on reality and produced an extremely comprehensive picture of the world. I see no reason to believe that there are phenomena that are beyond the potential of physics.

      Believing in invisible aliens is not that much different to believing that invisible pixies are living under your bed. As a scientist I ask for actual evidence, a fluffy narrative about the limits of cognition or perception won’t do. It’s an argument for anything and everything.


  4. I might add that the Fermi Paradox is based of a lot of rubbery numbers, multiplied. The simple fact is we don’t know a lot of stuff we would need to know to really calculate the number of advanced civilizations in the galaxy. We need more data. That data is hard to obtain and it will take long time time to get it. Past our lifetimes. Until then “We can speculate but we don’t know,” is ok, and it’s the scientifically correct response.


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