Just a forewarning to anyone reading this, This will make the most sense once you read the entire post.
Named after Enrico Fermi, the creator of the world's first nuclear reactor, the Fermi Paradox states that, since life is predicted to be all over the universe, why can't we find any? There are billions of sun-like stars in our galaxy, The Milky Way, and many of them are older than our sun. It is highly likely that some of these stars have Earth-like planets, so some might have developed intelligent life. Some of these civilisations may be capable of interstellar travel, as we are investigating that right now, and remember, these planets are possibly billions of years older than us. Even at the sluggish pace of interstellar travel we are at now, the Milky way could be completely colonised in a few million years. So, where is everybody?
There's a way of measuring the level of development of a civilisation called The Kardashev Scale. This groups civilisations into three groups:
Type I Civilisations: They can use all the energy of their host planet. We're not quite at a Type I Civilisation (We're at about 0.7).
Type II Civilisations: A Type II Civilisation can use all the energy of their host star (or stars in the case of Circumbinary Planets). We can hardly think of being able to harness such a great amount of energy.
Type III Civilisations: Can harness energy equivalent to that of the Milky Way.
Imagine one of those planets billions of years older than us, and let's call it Earth 3.0. Since it is that much older than us, it could be a Type III civilisation. Even with one of these, they would be pretty noticeable. So why can't we hear them?
We don't have an answer to the Fermi Paradox. The best we can do is "possible explanations." We're about as oblivious about this as bat might be to sight. There's something that helps us explain the Fermi Paradox. This is the Great Filter.
One of the most optimistic versions of the Great Filter:
The Great Filter is an event that almost no species can survive. The further along you are, the more advanced your species. The image shows us with a few other species that passed the great filter (If this were to scale, which it is not, the great filter would be about when we evolved into animals). This means that:
The yellow markers indicate significant events in the development of life, the first one being the beginning of life itself.
There are many theories about the Fermi Paradox. Here are some of my personal favourites (although some of them aren't, they just kinda have to be included):
It is a possibility that we are the only ones who have passed the Great Filter. The Great Filter could be so difficult to pass that no other civilisation has ever passed it and none ever will.
This would be kinda sad, as it means we can't have any intergalactic friends.
The Zoo hypothesis states that there are other aliens are out there, and not only that, but they are aware of our existence. But they don't know enough about us, so they're observing us, like a zoo (hence the name).
Many hope that the Great Filter is behind us, and, we get friends! (better than the other friends, who are observing us like we're some sort of animal, which, biologically, we are)
It's very possible that they've checked here, then the humans back then weren't able to tell future generations about Zorg and Blaan's visit.
Aliens may very well have updated their minds to a digital world millennia ago, seeing the physical universe as a place for primitive idiots. (I'm kinda jealous)
Maybe aliens just don't want to leave the perfect world they call home, I mean, why would you?
Those aliens! havin' a party over there while we still try to learn to ride our bikes.
Aliens might know that there other, scarier aliens out there trying to kill everybody, and therefore don't want to tell them where to find us.
Some alien species may be the 'humans' of the universe, and they may see any other life as a threat to themselves, and therefore must be destroyed.
Let me propose a scenario. You walk into a modern day building, turn on a walkie-talkie, and hear nothing. Would you then assume that this building is empty? No! (at least I hope not). The same goes for our universe.
You may notice that this item has no number on my list, and that is because it simply does not deserve one.
We may be completely wrong. Maybe aliens made us in a mirror dimension, thinking, Hey, I wonder what this does... Who knows.
As one keeps thinking on this topic, you'll start to pick a side. Personally, I want some intergalactic buddies, but let me know what you think in the comments section. Theorem out!