The Fermi Paradox

Enrico Fermi (1901–1954)

Our universe is vast beyond imagination. Really, you cannot imagine how vast it is. If you look into the night sky in perfect conditions you might be able to see about 2,500 stars, but that is only 0.000001 of the stars in the Milky Way. There are between 100 and 400 billion stars in our galaxy and about the same number of galaxies in the observable universe. Thus there are about 1023 total stars or 100000000000000000000000 stars in the observable universe. For every grain of sand on earth, there are 10,000 stars out there! If you don’t think that is a lot go to the beach, play in the sand, and look around.

And these numbers are just stars. If our star, the Sun, is typical in having 8 planets then our galaxy alone contains something like 2 trillion planets! Now we don’t know what percentage of those stars are sunlike but if we go with a conservative estimate of 5% and the lower end for the number of stars, 1022 then there are about 500 quintillion or 500 billion billion sun-like stars!

Now if we go with the most recent conservative estimate of how many of those sun-like stars are orbited by Earth-like planets, around 22%, that leaves us with 100 billion billion Earth-like planets! A hundred Earth-like planets for every grain of sand on earth. Now if only 1% of those Earth-like planets orbiting sun-like stars developed life and if only 1% of those planets developed intelligent life then there would be 10 quadrillion, or 10 million billion intelligent civilizations in the observable universe! In our galaxy alone there would be 100,000 intelligent civilizations.

All of which caused the physicist Enrico Fermi to ask, why haven’t we encountered beings from other worlds? 

The fact is that SETI (Search for Extraterrestrial Intelligence) has never picked up a single radio wave or any other form of contact. If you don’t think this is surprising to consider that there are older stars with far older Earth-like planets on which more advanced civilizations could have developed. They could be civilizations that have harnessed all the energy of their planet or the star or their entire galaxy if they were sufficiently advanced.  If so they would have seemingly colonized the entire galaxy. Some scientists have hypothesized that civilizations could create self-replicating machinery that colonizes the entire galaxy in around 4 million years.

Source: Scientific American: “Where Are They”

And if only 1% of intelligent life survives long enough to become a potentially galaxy-colonizing civilization, there would still be 1,000 of those types of civilizations in our galaxy alone. So again, why haven’t we seen or heard for them? Where is everybody? This is the Fermi Paradox.


Here are a few of the explanations proposed to explain the paradox:

1) Higher civilizations are rare. Maybe something dooms them as they advance. Perhaps only a few of them have managed to surpass whatever it is that dooms civilizations and they have not spread out through the galaxy.

2) Higher civilizations don’t exist. We are the only civilization that has avoided destruction so far and may soon destroy ourselves too.

3)  Higher civilizations visited earth before we were here or before we had ways to record the visit.

4) Higher civilizations have colonized the galaxy but not our part of it.

5) Higher civilizations are not interested in colonization.

6) Higher civilizations know better than to broadcast their existence since there are predator civilizations out there.

7) There is one higher predator civilization which has exterminated all other civilizations.

8) Higher civilizations are out there but we don’t know how to perceive them.

9) Higher civilizations are observing us now but don’t want us to know. Perhaps they abide by the “Prime Directive” of Star Trek’s Federation.

10) We are wrong about reality; the universe is not vast in space and time.

I have no idea which if any of these hypotheses is true. What I do know is that our ignorance humbles me. The universe is not only bigger than we can imagine but probably stranger than we can imagine as well. As Xenophanes said long ago, “All we have is but a woven web of guesses.” And for those who cannot tolerate uncertainty and ambiguity, there is always fanatical ideology. As for me I’ll accept uncertainty and reject fanaticism, thereby living with integrity.

Note – This post relies heavily on and was inspired by an article published here at the website “Wait But Why?”

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11 thoughts on “The Fermi Paradox

  1. I’m partial to #6 and #9/11 (which seem to be distinctions without a difference).

    Glamorous possibility (9/11): once a civilization’s consciousness goes non-biological, the drive toward singularity allows a cultural explosion outward at the speed of light, but employing properties of physical reality we can’t yet detect. (Think the Force, or the denoument of “Her.”)

    Mundane possibility (6): a mature civilization realizes one cannot cheat entropy forever … life has no destination, only a journey (valar morghulis). So consciousness consolidates into a single mind employing all the resources of a star system, focused on maximizing serenity and riding out the heat death of the universe.

  2. Based on the reader’s comments I consolidated my list. His #6 is now #5 and his # 9/11 is now #8. I think he is right about #8, we probably can’t detect advanced civilizations, and I think he may be right about #5 as well–higher civilizations are not interested in colonization but inner peace. Very insightful comments.

  3. I wonder if a civilization has the ability and technology to travel to Earth, would they have any use for us, any use/desire to communicate, any use for anything on the planet? They may just want to study us without having any use for us.

    My guess is that any form of life capable of traveling to us would not have any need for our “radio waves, nuclear weapons, or the Cooking Channel. They may have already advanced past our understanding of Philosophy, Theology, Physics, or our ability to hit a golf ball or wiffle ball. Just because we (our civilization) values things like water, gold, oil, or casino chips, that doesn’t mean they would value or want the same things.

  4. You may well be correct. Advanced intelligences are probably not interested in such a relatively backward species.

  5. Much of this assumes that if life takes hold on a planet, it must evolve. And if it does evolve, it would need a long time (billions of years?) to reach the stage of evolution achieved here on earth. If conditions on other planets are not as benign to life as on this earth, life on these planets may be wiped out before it gets a foothold. Perhaps this planet has been one of the very few (or the only) lucky ones to sustain life for so long, estimated to be 3.5 billion years. As well, the experts say that life on this planet was in the form of single cell organisms for about 2 billion years. That almost suggests that evolution beyond single cells isn’t all that probable or possible, but for some fortuitous reasons, earth became more amenable to life expansion. Under what planetary conditions would these kind of beneficial changes be likely to occur, and how likely would that be?

    To me the most important question is: how did life begin on earth? There are several complex theories, none of which have been successful in generating life in the lab. When I was a biology student many years ago, one of my professors, who specialized in evolution, told us that life will soon be ‘created’ in a test tube. Fourty plus years later, we’re still waiting, there are more theories, but we are seemingly no closer now than we were way back when. We can use statistics and planet count projections to estimate the likelihood of these planets having life forms that evolve, but if our best minds cannot provide a good answer as to how life forms arise and under what conditions, then those statistical estimates are just wild guesses. It may be that the spontaneous generation of life is truly an extraordinary event.

    As for the ‘meaning of life’, I’ve seen some discussion that the reward for ‘life’ is to store energy (from the sun) so that the stability of the organic components of life can be maintained, surviving periods without sunshine, storms, seasonal changes, etc. In short, life forms are complex ‘batteries’ that take the energy from the sun (or perhaps from heat sources in the earth), store that energy and survive for days, months, years, and decades perhaps, and remain viable to the extent that the line of DNA can ultimately be replicated.

    I’m getting in over my head here, so I’ll just leave this as food for thought.

  6. I really hope its #9 Prime Directive, but I am very frightened its a universal trait to destroy ourself and intelligent civilations never last.

  7. What’s wrong with the simplest explanation: like many natural phenomena civilisations burn themselves out when resources are spent. What evidence do we have that ravenous technological global societies last more than a few hundred years before exhausting themselves – like a bright burning match or a spectacular tornado?

  8. #6 and #8 are the likeliest in my opinion, although #5 could be true as well. It’s difficult to predict what an advanced ETI would do,as our intelligence is limited. Just as a butterfly can’t comprehend or predict human intellectual activites, we may be way out of our league when trying to predict what an advanced civilization would do. Would they try to colonise the universe? Or would they prefer to live in a post singularity computer simulation? I don’t know, and thats what makes this so exciting!

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