The Fermi paradox: Are we alone in the universe?

"Either we are alone in the universe or we are not. Both are equally terrifying" - Arthur C. Clarke.
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Looking up at a starry night sky makes one wonder if we are really alone. If you have never asked yourself this question, here’s some perspective on the vastness of our universe.

On the best of conditions, you could, in theory, count around 5,000 stars with the naked eye. The image below shows the comparison between our galaxy (the Milky Way) and our sun. Our night sky (5,000) stars will just be another small dot in comparison with the Milky Way.

The Fermi paradox: Are we alone in the universe?
Milky Way Galaxy

And this is just one galaxy. One may ask, “Well, how many galaxies are there?” Current estimates suggest there could be between 100–200 billion galaxies, or even more. Now imagine – the total number of stars in these galaxies is thought to be something like 10^22 and 10^24 stars, and imagine the number of potential planets around these stars.

Let’s get a bit more quantitative here and calculate the possible number of planets hosting intelligent life. First of all, not all planets are like Earth. True! But in all those trillions, at least some should resemble our Earth (in terms of temperature and the availability of liquid water). A PNAS study estimates that around 22% of the Sun-like stars could have an Earth-like planet in their solar system. Imagine that at least 1% (1 1020) of these Earth-like planets are habitable.

What this would mean is that there are about one hundred habitable Earth-like planets for every grain of sand on all the beaches in the world (roughly 7.5 1018 grains). Think about that next time you see the night sky or visit a beach.

What about life on these habitable Earth-like planets? Now beyond this point, we can only speculate. Let’s say after billions of years, life develops on at least 1% of these planets. If this is true, it would mean that for every grain of sand in the world, there is somewhere a planet with life on it. If you continue this line of reasoning for the rise of intelligent life, you’ll estimate that in our galaxy alone, there should be at least 10,000 intelligent civilizations.

What we just did is logically equivalent to working out an answer for the Drake equation (an equation used to calculate the number of intelligent civilizations in the universe). If these assumptions are true (a logical possibility), and there may be as many as 100,000 intelligent extraterrestrial civilizations in our galaxy, shouldn’t we be receiving all kinds of signals from other planets?

Well! We haven’t. Not one. Ever. Where the hell is everybody?!

Enrico Fermi presented this compelling argument to his colleagues over lunch in 1950. Since its inception, the idea has puzzled astronomers all over the world. In simple words, the Fermi paradox is the inconsistency between the presumed high likelihood and the lack of decisive evidence for intelligent extraterrestrial life.  

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Possible explanations for the Fermi paradox

We can’t know the answer to the Fermi paradox. However, the scientific community gives some possible answers. Let’s divide them into two broad categories. We’ll call them believers and non-believers.

Non-believers: We haven’t received any signal because there is no extraterrestrial intelligent civilization

A non-believer narrative is a simple one. There is no extraterrestrial life. In other words, there are no intelligent aliens and, therefore, no contact. In choosing a belief system, everyone is free, provided they give some explanation to account for the contrary (in this case, mathematical) evidence. 

The “explanation,” in this case, is the Great Filter. It is a theory that says there is a point in the evolutionary process of intelligent life that is pretty nigh impossible to cross.

The Fermi paradox: Are we alone in the universe?
The Great Filter theory diagramed

If this is the case, our fate hinges upon the answer to the question, “At what point in time did this filtration occur?”

There are three possibilities: We’re first, we’re special, or we’re doomed.

We’re the first intelligent civilization in the universe  

Is life on Earth the longest uninterrupted period of evolution that any planet has experienced since the big bang? There is a possibility that life may have started on many planets, but random catastrophic events stopped its evolution in the early (or later) stages. In this possibility, there may be some kind of life on other planets, but we are ahead of them in developing intelligence and the ability to communicate. We’re first.

We’re special because we have crossed the Great Filter

Our sun is a relatively young star, and so is our solar system. There are stars and stellar systems that formed millions and billions of years before ours. In this scenario, the assumption is that life started and thrived on other planets but failed to cross the Great Filter. In that case, if we’re the first to have crossed the Great Filter that every other extraterrestrial civilization failed to cross, we must be special. 

We’re doomed because the Great Filter is ahead of us

This one is scary. Nick Bostrom, a Swedish philosopher at the University of Oxford, suggests that if we found some traces of primitive life on Mars, this could actually be bad news. He also suggests that if we found traces of complex life on Mars, this could be much worse news. It would mean that life can evolve on other planets, and it did evolve on other planets but was eliminated by the Great Filter before it could reach the stage of being able to make contact. If all of them, 100,000 ET civilizations that could have possibly arisen in our galaxy, ceased to exist after reaching a certain level of intelligence… it could mean we’re next. 

Believers: Extraterrestrial civilizations (intelligent life) are out there somewhere

If ET civilizations exist, one has to answer the other half of the paradox. Why haven’t we received any message or some kind of signal from them? There are some plausible answers and some science-fiction answers, and the line between the two is blurred.

Aliens paid a visit, but no one was home (except maybe the dinosaurs)

Possibly the dinosaurs or our prehistoric ancestors saw some aliens show up on Earth, but we were not there to witness it. After all, it’s only been around 300,000 years since homo sapiens evolved on Earth, and written history only goes as back as around 5,500 years. It’s like a grain of sand in the hourglass of time. If they had visited before this, they might have been scared off by the dinosaurs, or our distant ancestors may have hailed them as heroes, but we would never know.

They lack the motivation to visit or even contact us (either they’re supercool or we’re exceptionally boring)

Maybe, we’re living in a far away desolate region of our galaxy that no one wants to visit, or worse, no one knows even exists. It is possible that the rest of the civilizations are way ahead of us – they have made colonies and are in contact with each other. Why would they care about some left-out species on a faraway planet? Or, conversely, perhaps they are behind us and have not yet begun to communicate.

They are communicating, but we don’t know how to listen (and they don’t either)

Maybe they’re shouting their lungs out, but we don’t know how to listen. It will be like carrying a walkie-talkie around instead of a smartphone and complaining that no one is communicating. You might ask, if they are so advanced, why don’t they respond to our signals? Perhaps they consider us primitive and insignificant. After all, what would be your reply to an ant trying to communicate with you? Dr. Michio Kaku explains it well in a 2008 article in Daily Grail: “Imagine walking down a country road, and meeting an ant hill. Do we go down to the ants and say, “I bring you trinkets. I bring you beads. I give you nuclear energy and biotechnology. Take me to your leader? Or we have the urge to step on a few of them??”

Communication is dangerous

Imagine there are predators out there, and we’re the innocent fools trying to communicate with them. The famous Stephen Hawking warned us about this. Even Carl Sagen thinks that messaging to extraterrestrial intelligence (METI) is not wise. So, this is not a joke. A newbie in a universe full of unknowns should practice caution and stay low.  

The Fermi paradox is just one of the many unanswered questions in science. This paradox alone makes us realize our ignorance. Maybe the next time you see a starry sky, you’ll also wonder, “are we really alone?”