The Fermi Paradox – Why haven’t aliens contacted us yet?

There are thought to be 10 million billion intelligent civilisations in the universe, and yet none of them have contacted us yet.

Wait what, 10 million billion?

Yes, well firstly –  The universe is huge and the Earth is minuscule

No matter how big you think the universe is, it’s bigger. Not to mention the fact that it’s constantly expanding. The Earth, after all contributes just 0.0003% of the mass of the solar system.

The solar system itself, is just a small speck – beyond our very own solar system, exists a massive galaxy of stars. This is known as the Milky Way, and it’s so large that even at the speed of light, it would take 100,000 years to cross it. It is also supposed to have 400 billion other stars. And that’s still a tiny part of the entire universe.

Like the Milky Way, there are supposed to be at least 100 million galaxies. IC 1011 is the largest galaxy that we know of, and has over 100 trillion stars. Take a look at the size comparison between IC 1011, and our milky way.  In comparison, we’re smaller than Vladimir Putin’s chances of winning a Nobel Peace Prize.


Source: Cosmosup 


Okay, okay, the universe is massive. But how many of these planets could potentially contain intelligent life?

FIRSTLY, there’s nothing incredible or unique about our sun. It’s an ordinary star and pretty young, and there are billions of stars in our galaxy that are much older, bigger and create more energy. For every single human on the Earth, there are 134 trillion stars in the universe (that we know of).

SECONDLY, there must be planets like ours revolving around those stars. These are known as “exoplanets. Data from the Kepler space Observatory has been used to suggest  that out of the planets in OUR GALAXY ALONE, at least 2 billion are “Earth-like”. This means they have the right temperature conditions, presence of water, and orbit around their parent stars in the “habitable zone” to support life.

THIRDLY, because intelligent life developed on Earth and there are billions of Earth-like planets, we have no reason to believe that intelligent life can not develop on those Earth-like planets as well.

And FINALLY, after millions of years of technological progress, an alien civilisation would likely have the technology to travel to other stars and galaxies – or at least to transmit signals. In less than 100 years, after all, humans went from traveling in bullock carts to landing on the moon.


The number of transmitting civilisations in our galaxy has been estimated by the Drake equation, (sometimes called the second-most famous equation in science, after Einstein’s E=mc2) and was devised by astronomer Frank Drake in 1961.

Drake Equation


This was the casual lunchtime question asked by Fermi in 1950.  Enrico Fermi, known as  “architect of the atomic bomb” was famous for creating the first nuclear reactor on a squash court. It doesn’t take a genius nuclear scientist (even though he was one) to do the math – there is a high possibility that there exist transmitting civilisations. There even exists an entire organisation called SETI  (Search for Extraterrestrial Intelligence) founded in 1984 which is dedicated to seeking for evidence of intelligent life. And how many signals has SETI picked up so far?

Yes, that’s right. NONE. Not one single shout out from even one single friendly alien civilisation.

Another thing that makes this whole thing even more absurd is the fact that our sun is quite young compared to the age of the entire universe – It’s practically a baby. There are many older stars with many much older Earth-like planets, which means that in theory they should have civilisations far more advanced than our own.

So where is everybody? If there’s such a high probability of transmitting civilisations why are we so lonely in this massive universe?

That apparent contradiction right there is called the Fermi Paradox.

How do we explain the Fermi paradox?

We wish we could tell you that we had a concrete solution to the Fermi paradox. Unfortunately, many scientists have written a vast number of papers exploring the subject, but nobody knows the exact answer. Over here we’ve filtered out some of the most popular, scientific and reasonable explanations.

1. Aliens just don’t exist – Rare Earth Hypothesis

The “Rare Earth” hypothesis claims that there is something unbelievably special about the Earth. Although Kepler data estimates billions of exoplanets, scientists still don’t know how life originates on a planet – despite scientists best efforts, nobody has yet been able to replicate the life creating process in labs.

Who knows what exactly about the Earth makes it so special? Maybe plate tectonics, mountains, and volcanoes are necessary to create a suitable atmosphere for life. Maybe it’s the presence of our moon – a moon as large as ours is unusual for such a small planet like the Earth, and plays an important role in forming our particular weather and ocean conditions by manipulating the tides.

Experiments trying to determine what planetary conditions are required for life are nearly impossible – since we have a sample size of 1 (the only thing we know for sure is that life developed on Earth).

Another theory is the Great Filter hypothesis, which states that there is some cosmic barrier that prevents life from developing beyond a certain stage to reach “intelligence”. We don’t know when this great filter is though. It could be that the universe is teeming with prokaryotes (single celled organisms without a nucleus), and the jump to eukaryotes (cells with a nucleus) is the real barrier. This makes sense because after prokaryotes formed on the Earth, they remained as such for almost two billion years before making the evolutionary jump to eukaryotes.

Also as Stephen Hawking puts it, the development of intelligence isn’t really an evolutionary requirement for long term survival.  Bacteria, and other single cell organisms aren’t the brightest and they can just exist and exist even if all other life on Earth is wiped out. So maybe there really isn’t intelligent life anywhere else.

2. It is the nature of intelligent life to destroy itself

This theory is more philosophical than scientific, and believes that intelligent life after a point, has a tendency to self destruct. Possible reasons for this could be war, accidental environmental pollution, poorly designed artificial intelligence (a scary thought) or natural disasters.

In his lecture at Cambridge, Stephen Hawking mentioned that though there is a reasonable probability for intelligent life to form, before it can conquer cosmic communication, the system becomes unstable and destroys itself. For us as an intelligent civilisation, a nuclear war is still the most immediate danger, but there are others, such as the release of a genetically engineered virus, or the effects of global warming. Hence perhaps other intelligent civilisations, just before they can contact us, tend to destroy themselves first.

3. Aliens are broadcasting, but we don’t know how to listen

SETI, having failed for the last few decades are counting on this solution (heavily suggested by the fact that they’re still listening for different signals). Maybe aliens are sending out signals, but in a manner we aren’t expecting. Maybe they aren’t using radio waves, or they’re broadcasting on a different (“alien” if you will) frequency from what we’re expecting.

Almost all radio SETI experiments have looked for signals known as “narrow-band signals.” These are radio emissions that have frequencies which cover only a small part of the radio frequency spectrum.
narrowband RadioWaves-space

Source: SETI (left)  Source: NASA (right)


This is to distinguish them from natural emissions from space, such as emissions from pulsars, quasars, and the turbulent, thin interstellar gas of our own Milky Way.  SETI are listening for narrow-band signals because they are the mark of a purposely built artificial transmitter.

Who knows what these aliens are using to communicate. They might using neutrinos or lasers in some kind of ‘galactic internet’.

About 30 years ago, Carl Sagan proposed an interesting theory. He believed that aliens may be communicating at a rate so slow or fast that we don’t even recognise their efforts. If these evasive creatures takes years to broadcast a single sentence, or even a single letter, we may not even realise that we’re being contacted, and maybe no single person may be able to read a message over their lifetime.

4. We’re too primitive to perceive the super intelligent civilisations

Michio Kaku sums it up like this:

Let’s say we have an anthill in the middle of the forest. And right next to the anthill, they’re building a ten-lane super-highway. And the question is “Would the ants be able to understand what a ten-lane super-highway is? Would the ants be able to understand the technology and the intentions of the beings building the highway next to them?

This hypothesis implies that there may be super intelligent life around us, and they may be trying to communicate with us with signals, but we’re simply far too primitive to understand what they even are. So even if they were reaching out to us, it’s like trying to teach an ant about rocket science, and we’re too simple to even fathom these beings. This is quite a scary hypothesis. Nobody likes being an ant.

5. Everybody is listening, nobody is transmitting – The SETI paradox

This theory proposes that the galaxy could be full of civilisations eager for contact, but unwilling to speak out. This is the so-called SETI- paradox.

Let’s take a look at the only civilisation we know – us. The Earth barely transmits at all, except for a few highly controversial efforts. One message, transmitted in 1974 from the Arecibo Observatory, was a simple picture describing our solar system, the compounds important for life, the structure of the DNA molecule, and the form of a human being. The message was transmitted in the direction of the globular star cluster M13, about 25,000 light years away.


The Arecibo message


Even if SETI does detect a signal however, their official policy is that “[no] response to a signal or other evidence of extraterrestrial intelligence should be sent until appropriate international consultations have taken place.”

This makes sense. Who knows what kind of response we should provide, and we’re sure every country wants to have their say. It will be very difficult to obtain any consensus on “Who speaks for Earth?” and “What should we say?”. We can’t really imagine Putin, Kim Jong Un, Theresa May and Clinton/Trump sitting around a table and reaching a consensus on what day it is, let alone what message the Earth hopes to send as a planet.

Another reason for the radio silence could also be

There are predator civilisations out there, and most intelligent life knows better than to broadcast any outgoing signals and advertise their location

A terrifying thought – predator civilisations. We understand that you may think this sounds awfully like silly science fiction, but hear us out.


Maybe the reason we haven’t heard from anybody is because everybody knows better than to broadcast signals. Just like humans are super predators on our own planet compared to other animals, it has been suggested that aliens that become complex, intelligent beings, manage not to self-destruct, and create the ability to travel in space will want to colonise their surroundings. And from the evidence we have so far about human beings, we realise that this isn’t a completely ridiculous theory.

This is why most people believe that we should not engage in METI (Messaging to Extraterrestrial Intelligence—the reverse of SETI). Stephen Hawking warns, “If aliens visit us, the outcome would be much as when Columbus landed in America, which didn’t turn out well for the Native Americans.”

6. And finally, they’re actually Hungarians (A Physicist’s sense of humour)

After hearing Enrico Fermi utter his now-famous paradox at Los Alamos, the physicist Leo Szilard immediately answered, “they are among us and they call themselves Hungarians.”  Not the worst answer of the lot, we suppose.


SETI is still very hopeful that it will pick up signals soon, and is convinced of the presence of extraterrestrial life. As they say, absence of evidence is not evidence of absence.



  1. You can find some very (we thought) interesting FAQs about SETI here.
  2. Stephen Hawking’s lecture called “Life in the Universe” given at Cambridge University can be found here.
  3. You can discover more about the different components of the Arecibo message here.

Disclaimer: All the possible solutions presented above for the Fermi Paradox are simply theories. We do not claim any to be absolute scientific knowledge or truth.

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