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Why Haven't We Found Any Aliens Yet?

By Olivia Ortlieb


For thousands of years, people have been mystified by the unfathomably vast and mysterious realm that is our universe. Despite all of the progress that our society has made, we still know very little about our galaxy, and virtually nothing about what lies beyond. However, out of the thousands of space-related mysteries that science has yet to unravel, one seems to enrapture our imaginations more than the rest: Are we alone in the universe?

The jury is still out on this one, but the limited knowledge that humanity has acquired on this topic suggests that the answer is no. One thing that we are fairly certain is true about the universe is that it is massive beyond our comprehension. There are an estimated 250 billion stars in the Milky Way galaxy alone, and the observable universe is thought to contain at least 100 billion galaxies. Out of the trillions and trillions of stars these galaxies contain, 500 quintillion (500 billion billion) of these are speculated to be similar to our sun in terms of temperature, size, etc. Of these sun-like stars, an estimated 1% are orbited by planets with liquid water and Earth-like temperature ranges. That’s 100 times more planets that could theoretically support life than there are grains of sand on Earth. If intelligent life evolved on even 1% of these Earth-like planets, there would be 10 quadrillion civilized societies in the observable universe, and over a million in the Milky Way alone. Even if these numbers are drastically overestimated, our universe should be teeming with life. And yet, our satellites have never picked up a single signal from space, nor have our probes reported any sign of alien life. Our lack of contact with other civilizations seems even stranger when you consider that the earth and our sun are relatively young, so in theory there should be societies that are billions of years older and far more advanced than we are. This apparent contradiction between the current lack of evidence of extraterrestrial life and the science that suggests that there should be plenty of it is known as the Fermi paradox. So, as the paradox’s namesake, physicist Enrico Fermi, once famously asked, where is everybody?

Numerous theories have been created in an attempt to answer this question, and some of them are a lot scarier than you may have imagined. Most of the potential explanations fall into two categories: #1. We haven’t heard from more advanced civilizations because they simply don’t exist, and #2. There are intelligent civilizations out there, and for any number of reasons, we haven’t heard from them. Let’s start with the first category.

#1. We’re Alone in the Universe

The explanations in this category revolve around the assumption that the number of intelligent civilizations is regulated by a Great Filter. A Great Filter is an evolutionary leap or an obstacle so great that it either does not allow civilizations to develop or extinguishes them entirely once they attain a certain level of advancement. As you will notice, the theories in the second category are largely based on the notion that intelligent civilizations are following certain rules that prevent them from contacting us. Those who believe in the category 1 theories generally think that since there are there are supposedly many millions of civilizations out there, logically, at least one of them would be an exception to the rule and would have contacted us. Thus, there must not be any intelligent beings out there that are advanced enough to reach us, and there must be something preventing them from developing beyond a certain stage. So, what could be stopping them, and where does this evolutionary wall occur relative to our current level of advancement? There’s no consensus on this, so I’ll be going over the two most likely Great Filter theories.

We’ve already passed the Filter

It’s possible that the conditions that allowed our civilization to develop and advance are so immensely improbable that planets and/or societies like ours may be much rarer than we estimated, or they might not exist at all and we are the only ones. Perhaps the circumstances that lead to the development of the first cell were so immensely rare that the chances of it recurring elsewhere are virtually nonexistent, or maybe the evolution of creatures with brains as large as ours is a very steep evolutionary wall. After all, there are nearly 9 million species on our planet, and none of them possess intelligence rivalling ours.

The Filter is ahead of us

This is where things get a lot scarier.

No matter what this Great Filter is, the notion that we alone have surpassed it relies on the idea that out of the quadrillions of planets, we are the one ultra-special exception that managed to continue onwards. That is extremely improbable. Therefore, some scientists have concluded that the Filter must be ahead of us. This would mean that it’s far from impossible for societies to reach our level of advancement, but they are all wiped out before they reach the stage where they can freely travel their galaxies and discover planets such as ours. Given the current rate at which our technology is improving, we may have very little time left before our fragile earth is wiped of life. This Great Filter could be a nuclear war, climate change, gamma-ray bursts - which are massive naturally occurring explosions that can decimate planets hundreds of light years away, or something that we’ve never so much as imagined; an unknown, insidious threat that we won’t notice until it’s far too late.

This means that finding another civilization similar to us would be very bad news, because it would mean that the Great Filter is not behind us, and is therefore ahead of us. Alternatively, there might not be a Great Filter at all, and there is in fact tons of advanced, intelligent life out there. This brings us to the second category of theories.

#2. There Are Advanced Civilizations

Unlike the Great Filter theories, category 2 theories assume that there is nothing special about our galaxy, planet, or level of intelligence, and that there are civilizations similar to and/or far more advanced than us, but for any number of reasons, they are unwilling or unable to communicate with us.

Extraterrestrials have tried to contact us, but we can’t understand them or their messages

It may be that we have been contacted by advanced societies many times before, but they communicate in a method that’s so different from anything we’re familiar with that we’re incapable of understanding them. Perhaps our technology is too primitive to pick up on their signals, or their messages are transmitted too quickly or too slowly for us to process, or we’re simply paying attention to the wrong things. Alternatively, the civilizations themselves could be utterly beyond our comprehension. Michio Kaku, an American physicist, summarized this concept nicely:

“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?’”

It’s possible that the beings populating our region of the universe are so intelligent and advanced that to them, we are about as insignificant and dumb as ants, incapable of understanding their actions or even perceiving their presence. This theory would also explain why we haven’t heard from any aliens - they wouldn’t bother to contact us because they know we could never comprehend them, and our civilization would seem so primitive to them that they wouldn’t care enough to make an effort to educate or learn about us; just as we don’t try to enlighten every anthill we come across.

Aliens visited us long ago

Humans have only been capable of recording our ideas for a tiny fraction of the time that our planet has existed. It’s possible that aliens have visited and interacted with humans before, but they did so thousands of years ago, before we were capable of documenting what had occurred. An advanced society might have also surveyed our planet before humans even evolved, but didn’t leave behind any sign of their presence.

Aliens are currently in contact with us, but the government is hiding it

This is a popular idea among conspiracy theorists, but I personally think it’s quite far-fetched. It’s very unlikely that the governments of every country would be willing or able to keep something like this secret for long without anyone else hearing of it or managing to contact the aliens themselves.

We live in a sparsely populated region of the universe

Perhaps much of our galaxy has already been colonized by advanced civilizations, but Earth is located in a sort of rural area far away from other societies. This theory is supported by the fact that our galaxy is thought to be located within a relatively empty region of the universe known as the KBC void, which has a below average number of galaxies and other celestial masses. Any nearby civilizations may not have developed the technology needed to travel extremely quickly yet, which would confine them to a relatively small area of the galaxy that’s out of reach of our probes or signals. However, a flaw with this theory is that the Milky Way is thought to be one of the most ancient galaxies in the entire universe, so there should be civilizations in it that are old enough to have acquired the technology necessary to travel across it with ease.

It’s impossible for technology to develop enough to make space travel easy

We have no way of knowing whether it’s even possible to build spaceships fast enough to make intergalactic transportation practical. It may be that civilizations inevitably reach a point where it’s simply not possible for them to advance their ability to travel in space any further. If this technological threshold is low enough that it would take thousands of years for even the most advanced societies to travel across galaxies, it would probably take an extremely long time for them to come across our little planet. If this threshold exists, most intelligent civilizations might have decided that mapping out the universe or even their galaxy isn’t worth the massive amount of time and resources required.

There are predator civilizations out there, and most intelligent beings are smart enough to hide from them

Here’s one of the more worrying theories. Similarly to how humans destroy ecosystems in search of resources with little thought to the less intelligent creatures that inhabit them, some extraterrestrial societies may have taken to destroying any weaker ones that they can find. This would explain why other societies don’t seem to be trying to contact us - they might be concerned about their messages being picked up by something that’s less than friendly. For this reason, most astronomers believe that we should reconsider our current practise of broadcasting signals into the vastness of space. Dan Werthimer, an American scientist, compared attempting to message extraterrestrials to “shouting in a forest before you know if there are tigers, lions, and bears or other dangerous animals there”. On the other hand, some people believe that the potential benefits that a relationship with a benevolent society could produce outweigh the existential risk of alerting a malevolent one to our location.

Our current utter lack of knowledge on this fascinating subject is a humbling reminder that despite how far humanity has progressed, we still have come nowhere near to unraveling the infinite mysteries of the universe. If we ever find the answer to the Fermi paradox, it’ll definitely be one of our most significant discoveries, and it could even change the course of our history forever.


Bostrom, Nick. “Where Are They?” www.nickbostrom.com/extraterrestrial.pdf

Kurzgesagt. “The Fermi Paradox - Where Are All The Aliens?” Youtube, 6 May 2015, https://www.youtube.com/watch?v=sNhhvQGsMEc

Urban, Tim. “The Fermi Paradox.” Wait But Why, 23 Sept. 2019, https://waitbutwhy.com/2014/05/fermi-paradox.html.

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