Are we alone in the vastness of space? The Fermi Paradox gives us some ideas regarding this. Danielle Crowley investigates.
Have you ever looked up at the sky and wondered: “Are we alone?” Many astronomers have also pondered this question, but so far they have failed to come up with a definitive answer. One of the most famous trains of thought here is the Fermi Paradox, named after physicist Enrico Fermi.
The paradox is the contradiction between the supposedly high probability of other civilisations in our galaxy, and the lack of contact with or evidence for them. Simply put: there are an almost infinite number of planets out there, so why have we not heard from them?
Let’s add some hard numbers to this. There are about 100 to 400 billion stars in our own galaxy, the Milky Way, and there is roughly that same number of galaxies in the observable universe at least. So, that gives us between about 1022 and 1024 stars in total. In other words, estimates suggest there are 10,000 stars in the universe for every single grain of sand on Earth.
Conservative estimates for the number of sun-like stars out there are about 500 quintillion, or 500 billion billion. Estimates suggest one-in-five of those stars is orbited by an Earth-like planet which results in 100 billion billion planets that could host life as we know it.
If only 1% of those planets host intelligent life like that on Earth, that is 10 million billion civilisations in the tiny patch of universe visible to us. In the Milky Way alone, that is 1 billion Earth-like planets and 100,000 civilisations.
These are some mindboggling numbers. So where is everyone? Why have we not seen or head them? There are several hypotheses for this silence.
One is that our universe is very old, about 14 billion years old. Our planet is about 4.5 billion years old, and the earliest evidence for life we have is around 3.8 billion years old. Almost all (99%) of the life that ever lived on Earth is extinct, so it is possible given the immense age of the universe that there was other intelligent life, but we have missed them. Modern humans have not been around long at all in the scheme of things, so maybe other races visited us, but so long ago we cannot remember them, or we were not evolved enough then.
Another suggestion is “The Great Filter”. This states that in the evolution of life there is a wall that is very difficult for life to overcome. There are three versions of this theory. In the first we are rare, as we have already surpassed the Filter. If this is true, we have not heard from anyone because we could be one of the only life-forms in the universe to have surpassed the filter and become living creatures.
“If this is true, we have not heard from anyone because we could be one of the only life-forms in the universe.”
In version two, we are the first to reach the state of “intelligent being,” in which case, we and some other species are on the way to super intelligence and possibly contact, but we are not there yet.
Version three holds that the Filter is still ahead of us, and that like all that came before us, we are doomed to fail to pass through it. Maybe it is a natural event that wipes out life, or maybe a nasty side effect of intelligent civilisations is that we will inevitably end up destroying ourselves. In this case, we could be heading towards inevitable demise, like many of our galactic neighbours before us.
Other hypotheses stem from the idea that other civilisations are indeed out there, but that there are multiple reasons why we have not heard from them. Space is a pretty big place after all, and if we live in the space equivalent of the middle of nowhere there could be practical reasons why we have not been stumbled across yet.
Maybe other species are perfectly happy where they are, and have no interest in exploring or colonising, thank you very much. Maybe we have not met yet because space is made up of civilisations of introverts.
“Maybe we have not met yet because space is made up of civilisations of introverts.”
Other possibilities for why we haven’t made contact with other species are scarier. It could be that there are one or more “predator” civilisations in the depths of space, and other races have the good sense to stay quiet, like birds when a raptor soars overhead. This makes our habit of sending out messages potentially risky indeed. Maybe this race has exterminated every intelligent civilisation it came across.
What could be the most likely reason is that we are just too primitive for other races. Either we are sending out signals no one listens for, or not listening to the right ones. Maybe life from other planets is so different to life here that it could be right under our noses and we would not notice. Perhaps we look so primitive to other life forms that Earth is the equivalent to a zoo or nature reserve, in which case they are not going to even bother communicating. We could be so insignificant that they have not paid us much thought.
Whatever the answer is, it is mind-blowing to think of all the different possibilities. Maybe we are not real at all and this is a simulation. Maybe the aliens came here, met the dinosaurs and decided to never return. It is certainly food for thought next time you look up at the night sky.