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 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 this 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 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 from 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 thus 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 that 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 if any of these hypotheses are true (or if some other hypothesis explains the paradox.) 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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7 thoughts on “Fermi Paradox

  1. My explanatory hypothesis for the Fermi Paradox is that technological progress is necessarily geometric in growth. That is, the potential for technological innovation is proportional to some power of the amount of technological innovation already in existence. If you have just two types of Lego bricks, you can build only a limited range of structures, but if you have four types of Lego bricks, you can build much more than twice as many different structures. And with eight types of Lego bricks, you can build a huge range of structures.

    We see this in human history. Technological progress has been accelerating throughout human history; we are now at the point where technological progress is so rapid that young people today cannot imagine how to use many of the technologies I used in my younger years: slide rules, dial telephones, or the push-button radios in old cars.

    Social progress, however, progresses linearly with time. That is, our society adjusts to changes in its environment at a steady pace, roughly in time with the passing of generations. The Baby Boomers of my generation dominate social policy nowadays, but our values were set 50 years ago. This time lag between formation of values and ability to change society in accordance with those values wasn’t a problem a hundred years ago, when change was slower. But nowadays the values and preferences of 50 years ago are seriously out of touch with the technological realities of today.

    This can only get worse with each passing year, because technological progress is now moving so much faster. The rise of the new AI technology has frightened most people, but nobody has any idea of exactly how it could be used for destruction, and we certainly have not developed any strategy for protecting civilization from malicious uses of the technology.

    Perhaps we’ll cope with AI. The fact remains, however, that our technological progress is changing the environment in which we live at an ever faster rate, yet out capacity to change is limited. It is therefore inevitable that at some point we will face a challenge that we are unable to cope with adequately. Climate change is only the first of such challenges; we are now doomed to suffer trillions of dollars in damages because we failed to address this challenge when an adequate response was safely achievable.

    A species that is unable to cope with changes in its environment inevitably goes extinct. The same thing happens with a civilization.

    I have an earlier, longer, and somewhat clumsier explanation of this process here:

  2. Another possible explanation for the paradox (or perhaps a specific subset of one of the other explanations):

    Many other advanced civilizations are “out there,” but are so vastly distant from us— perhaps in both time and space- that we haven’t detected them.

  3. Did not not know when, if ever, I might offer comments here—or anywhere, again. Appears I really po’d some people with my remarks and positions. This access popped open, while I worked on another project, and my computer music magically resumed. Will move slowly on this development. Hope you are well…

  4. The explanations/hypotheses are rational and reasonable enough, within the realm(s) of our reality. I particularly enjoyed the ones which either imply or infer that other minds simply don’t give a flip about us: suggesting something like, ‘don’t worry about them, we have watched them for eons, bungling fools—posing no threat to our superiority. Er, sorry—I levelled anthropocentric judgment on *superior* beings. Were they, somehow, watching and listening, the aside might be, ‘well, told you so’. So, no, there is no way to know, is there? Only what ifs and suppose thats, which lie among Dennett’s tools for thinking. Philosophy’s uncertainty is a strength, in the important sense of imagination .and intuition. Me parece.

  5. We have a great freedom in how we view these facts. My neighbor can be all the alien I can handle. I mean do we want stuff from aliens (technology), or do we just want to sit at a bar with some new stranger?

    And for the hostile expanse of stars reminds of the line from Full Metal Jacket, 10^23 stars? “I can’t believe they stack”… Awe seems like a crazy emotion to feel for what is implied will take everything away from you, most violently. You can honestly say that its bigness is not a positive, just a bunch of stuffs falling all over itself. A massive clown show, or the celestial bodies resemble corpses more than anything “heavenly.”

    It is a choice.

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