The Fermi Paradox: Why Haven't We Found Alien Civilizations?

The Fermi Paradox

Our universe is vast, consisting of hundreds of billions of galaxies. Within each of those individual galaxies there exist hundreds of billions of stars, many of which have a system of planets orbiting them. Many of these planets, including Earth, exist within their star’s habitable zone, where liquid water could exist and it appears possible for life to arise. In fact, it has been estimated that there are several tens of billions of such exoplanets existing in these conditions. So it seems to track that life, even if it arose at a low probability (which seems unlikely given the abundance of chemicals such as carbon, hydrogen, oxygen, and nitrogen), would be thriving all across the galaxy (and the universe). It is hardly a great leap from that to then predict that some of that life would become intelligent, and that at least a few would become space-faring civilisations. Yet, even with a 13.6 billion year old galaxy containing hundreds of billions of stars, we have still failed to detect any hint of extraterrestrial life. Why is this, and what could it mean?

There are many hypotheses that suggest why we have not yet discovered signs of extraterrestrial life, and so that will be the nature of our examination. The most notable of these are the Great Filter, the Dark Forest, and the Zoo Hypotheses, although there are several other possibilities, such as that we are existing in a simulation or that our communication methods, such as radio, are too primitive to detect alien activity. Either way, the law of chance seems to strike a blow at the heart of almost all of these theories, fabricating quite the enigma for our (lack of) observations. Nevertheless, we will thus begin by investigating the primary solutions to the Fermi Paradox.

The Great Filter, The Zoo Hypothesis and The Dark Forest Hypothesis

Let us begin with a discussion on the Great Filter Hypothesis, proposed by economist Robin Hanson in 1996. For life to evolve into an advanced space-faring civilisation, there are several stages it must progress through. These stages follow thus: a solar system forms with the right chemical composition and a planet (or several) in the habitable zone, this planet then undergoes abiogenesis and life emerges (non-living matter evolves into molecules like proteins), this simple life persists through potential disasters (e.g asteroid strike) and evolves into complex eukaryotic life (where cells evolve nuclei and organelles), this then evolves into intelligent life, next evolving into a technological civilisation, and then persisting to become space-faring. The Great Filter Hypothesis proposes that one, or several, of these stages is extremely difficult to pass, hence explaining the lack of interstellar civilisations. I consider this to be the most likely possibility as life, at all stages, does appear to be quite a fragile thing (although, given that we only have ourselves to observe, we cannot gain a solid understanding of the probabilities involved). Furthermore, given the instabilities and uncertainties of our world today, it does not at all seem unlikely that we are fast approaching that Great Filter. To become space-faring we require advanced technology, which could potentially be used to annihilate ourselves (or [I would argue more likely] push us back to a previous stage in our evolution). Yet this is but one of several possibilities, and so we will now investigate the Zoo Hypothesis, proposed by astronomer John Allen Ball in 1973.

If you’ve ever seen Star Trek, then think of the Zoo Hypothesis as the Prime Directive. In effect, aliens have collectively agreed not to interact with us and instead to just watch (although, unlike a zoo, we cannot see them watching us). Why have they decided to just watch? Maybe they deem us to be dangerous and overly aggressive, waiting until we have evolved to become a more peaceful species. Maybe they have simply decided it is best we evolve unhindered until we may expand into the wider world of the stars. Maybe we are an experiment, with the aim of understanding uninterfered with evolution of intelligent species. Yet either way, for some reason, they have all (although it seems somewhat surprising that they all agree) decided that we are to be watched and not interfered with. The next possibility which we must now investigate is the Dark Forest Hypothesis, proposed by science fiction writer Liu Cixin.

Seemingly the most concerning of all (and in my view most unlikely), the Dark Forest Hypothesis claims that we have not yet seen extraterrestrial life as they are all in hiding. Supposedly each species is like a hunter in a dark forest, hiding to ensure their survival, and jumping on any other hunter that comes out of hiding. Yet the key flaw in this hypothesis is that it is far more difficult for an entire species to hide themselves and their activities than one single hunter in a forest. They would be an interplanetary, or even interstellar, empire (they must have a wide span otherwise there is no threat to other species, which is the whole reason for the hiding), and somehow, with all their technology, are remaining hidden. Furthermore, if one species attacked another, then they would be out of hiding and likely involved in an interstellar (or at least interplanetary) war, which would reveal them. It is far more likely that, rather than hiding, they are just choosing not to interact and that apparently no aggressive and expansionist species (including ourselves, who would soon likely disrupt this agreement). Beyond these hypotheses, there are some other possibilities, such as that we are in an experiment or simulation that does not involve extraterrestrials, but either way we remain in the blank, and left to our own philosophical discussion.

How Do Humans Fit Into All Of This?

Thus we have now examined the possible reasons for the apparent lack of extraterrestrials, and it is time to investigate where humans fit into this enigma. I would argue that there is no threat posed by the possibility of the Dark Forest Hypothesis, and the rest of the hypotheses more seemingly encourage us than threaten us. Hence it seems reasonable that we continue on our current trajectory, expanding throughout our solar system and beyond. Yet I think we must particularly discuss the relevance of the Great Filter to humanity. We are now arriving at the final stage in the evolution to become space-faring, and with rising (human-induced) threats such as climate change, AI and nuclear weaponry, it is becoming increasingly paramount that we build self-sustained extraterrestrial colonies, and that we expand ourselves throughout the stars. If we stay on Earth, our risk of extinction is 100%, and the clock is ticking closer to midnight.

How do you see it? Comment your take👇

If you enjoyed this article or are interested to learn more, check out the articles below on space and human exploration:

• Lunar Mining and Energy: Powering Sustainable Moon Colonies

• Is Asteroid Mining Possible?