Fermi Paradox

The Fermi Paradox

The Fermi Paradox is a paradox dealing with intelligent extraterrestrial life. Put simply, there is a reasonable chance that intelligent life could have evolved somewhere in the observable universe so far, yet there is no evidence of it.

It raises questions about our understanding regarding the origins of life, and of the universe as well.


The paradox is named after physicist Enrico Fermi who raised it in 1950.

Thinkers in the early 20th century were of the belief that the earth is not unique when it comes to developing intelligent life. There could very well be other planets with intelligent life. This raises the issue of why there has been no trace of them.

Looking at the Details

Very relevant to the Fermi paradox is the Drake equation, which predicts the approximate number of intelligent civilizations that could exist in a galaxy. It can be written as

N is the number of civilizations with which communication is possible
fp is the fraction of stars that have planets
ne is the average number of planets for each such star
fl is the fraction of such planets that develop life
R* is the rate of star formation
fi is the fraction of those planets that develop intelligent life
fc is the fraction of those planets which have intelligent life that can actually communicate their existence
Finally, L is the time length for which the signal is broadcast and available.

Drake Equation summarized
The Drake Equation summarized. [Credit: Luciano Ingenito | CC by-nc-nd 4.0]

The estimates for each of these values vary wildly. Crucially, the fractions which correspond to the likelihood of life (especially intelligent life) evolving vary a lot depending on the person quoting the figures.

From a relatively “optimistic” point of view – that there are other Earth-like planets out there, we can end up with a figure of 100,000 advanced civilizations in our galaxy alone. On the other hand, imposing much harsher constraints could give us a number of around 20 – as Drake obtained as a lower limit in his calculations in 1961.

The uncertainty is immense, but the fact seems that there is overwhelming evidence for the existence of some form of intelligent, advanced life somewhere in our galaxy, or at least our universe.

The numbers are simply too big, it seems, for it to be otherwise.

Enters Fermi Paradox

The paradox comes when we think of the fact that intelligent civilizations presumably will try to expand their footprint in the galaxy.

There could be around 20 advanced civilizations in the Milky Way, even going with the lowest estimates. Given that many stars are older than the Sun, the civilizations found around them could have developed a very advanced technology that could lead to large-scale space exploration.

With such technology at their disposal, it sounds reasonable that advanced technology would have expanded to occupy a large section of our galaxy.

Further, some estimates suggest that this could occur over a range of just millions of years – while this sounds long for the human civilization, it isn’t really long at all from a planetary or cosmological viewpoint.

Yet, we have seen no evidence that intelligent aliens exist and have tried to explore the galaxy, let alone the rest of our universe. Nor do we have any sign of communication from them – no radio waves, no probes, no space stations, nothing.

Why is advanced extraterrestrial life so hard to detect, even if it seems statistically probable?
Why is advanced extraterrestrial life so hard to detect, even if it seems statistically probable? (Source)

Trying to resolve the paradox is a problem some astrobiologists deal with. Let us consider a few major resolutions.

Possible Resolutions

Our Numbers are Way too Optimistic

It could be that we are over-estimating the possibility of other Earth-like planets existing. Even if they exist, it could be that intelligent life is too rare to develop. After all, in all of Earth’s 4.6 billion years of history, humans are the first to show such signs of advancement.

This would mean that Earth is more of an exception than a normal planet. Maybe there is extraterrestrial, intelligent life, but it is too rare to have been encountered by us.

Signals are Really Hard to Pick Up On

Maybe there are intelligent lifeforms out there, but their signals are too weak and sporadic to be detected by us. This could also happen in the civilizations are too far from us. This relates to the above point as well.

We are Mistaken About the Motives of Intelligent Lifeforms

It is possible that we are biased by our human viewpoint. Perhaps other lifeforms do not wish to communicate with us, or do not want to colonize outer space. It could just be our human point of view that makes us think it is “natural” for an intelligent civilization to colonize the galaxy or try to contact others.

Probably other lifeforms are so different from humans that their signals simply cannot be picked up on by us. This could be because their minds function differently from us.

The Great Filter

It is possible that intelligent life destroys itself as part of its development. Probably, it doesn’t gets a chance to colonize galaxies or communicate across planetary systems.

This is related to a hypothesis called the “Great Filter” which is some sort of barrier that must be crossed for intelligent life to succeed.

This “Filter” is some form of hard-to-get-past event, and once it is crossed, intelligent life thrives.

If this “Filter” is too difficult to get past, it seems reasonable that we don’t see intelligent life anywhere else. What is scary is that it is possible that humans are not yet past the great filter. We could probably end up destroying itself before it crosses it.


Fermi paradox is an unsettling yet exciting one about the existence of life outside of our planet. It could end up implying that we are really alone in this universe, or that we have a company that prefers to stay quiet. Whatever the answer, its implications would be huge for our planet as a whole.

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