The Great Filter Theory: Answer to the Fermi Paradox

The Universe is so old and vast that it seems impossible for life to exist only on our planet. However, despite all the efforts, we have not detected any signs of extraterrestrial civilizations yet. This paradox was formulated by physicist Enrico Fermi in 1950. If aliens exist, where are they? Why haven’t we received any signals from them yet? 

One of the possible answers to the Fermi Paradox is the Great Filter theory, proposed by economist Robin Hanson in 1996. What is the main idea of the Filter theory? Let’s find out.

What Is the Great Filter Theory About?

According to Hanson’s hypothesis, on the path of life development from the simplest organisms to a highly developed civilization capable of interstellar travel and contacts with other alien races, there is a certain barrier, a “filter”, which most species are not able to overcome. This filter can be both natural and artificial, and overcoming it can be associated with incredible luck or with the fulfilment of a series of extremely difficult conditions. 

Imagine that you are playing a computer game that becomes more and more difficult with each level. The Great Filter theory explaines that sooner or later you will reach a level (barrier) that will be very difficult or impossible for you to pass. We still have not met aliens, because both we and they are “stuck” on their impassable levels. 

What Are the Possible Filters?

The Great Filter Theory of Universe doesn’t provide the exact list of filters, it is rather a concept. But here are some possible levels you might get stuck at:

Abiogenesis 

Abiogenesis is the process of life arising from inorganic substances in the early conditions of the Earth. In other words, the emergence of life requires certain chemical elements, energy sources, liquid water, and stable environmental conditions. This combination of factors is extremely rare in the Universe and may be the first difficult barrier. The Miller-Urey experiments showed that organic molecules could form under conditions similar to those of early Earth, but the transition from these molecules to self-replicating cells remains a mystery.

Prokaryotic Life

Even if life arises quite enough, it can remain stuck for a long time at the stage of the simplest single-celled organisms, incapable of further evolution. On Earth, prokaryotes dominated for billions of years before the first eukaryotes appeared — cells with a nucleus, which became the basis for developing multicellular organisms.

Multicellular life 

The transition from single-celled to multicellular organisms is another complex stage of evolution, requiring the development of mechanisms of cellular specialization and cooperation. Earth saw this transition only once, and scientists still do not fully understand how and why it happened.

Intelligence

Among the millions of animal species on Earth, only one — human being — has a developed intellect capable of abstract thinking, language, and the creation of complex technologies. Perhaps the emergence of intelligent life is an exceptional event, and not a natural stage of evolution.

Technological Singularity 

Some scientists suppose that the development of technology may lead to a “technological singularity” —a moment when artificial intelligence surpasses human intelligence and becomes capable of self-improvement. Such self-sufficiency may lead to unpredictable consequences, even the destruction of human civilization. Humanity is currently at the stage of active development of AI, so the plot of the movie “Terminator” no longer seems like absolute fantasy.

Self-destruction

The development of technology brings not only opportunities, but also dangers. Nuclear, biological weapons, environmental disasters, uncontrolled climate change, resource depletion — all this can lead to the self-destruction of civilization even before it reaches the level necessary for interstellar travel.

Space disasters

Supernova explosions, gamma-ray bursts, collisions with asteroids — all this can pose a threat to life on planets and stay on the way of the development of civilizations. Perhaps this is the reason why some highly developed civilizations were not able to contact us. Or maybe their message will reach us when they are no longer alive.

Zoo Theory

The Zoo theory states that highly developed alien civilizations exist, but we do not see them because they deliberately hide their presence for the reasons of ethics and our safety. This hypothesis is often considered as a separate theory that tries to explain the Fermi Paradox, but nothing prevents it from serving as that great filter. Developed civilizations understand the value of diversity in life and choose a policy of non-interference in order to give other civilizations the opportunity to develop independently. Perhaps the “zoo” is a temporary measure, and contact with aliens will occur when humanity overcomes its great filter.

Dark Forest Hypothesis

The Dark Forest hypothesis suggests that the Universe is a dangerous place, full of hostile civilizations. Each civilization, like a predator in the forest, tends to survive and is ready to destroy any other, in pursuit of resources or just to eliminate a potential danger. If this theory is true, it may well be the very insurmountable barrier that prevents civilizations from reaching a high level of development and spreading across the galaxy. They either destroy each other, according to the principle of “fight first”, or self-destroy themselves, unable to cope with the arms race, or get stuck in a state of isolation from the fear of being destroyed.

Is the Great Filter Ahead Or Behind Us?

The Great Filter theory poses an existential question: have we already passed that most difficult level or is it still ahead of us?

• The filter is behind us: If we have already overcome the great filter, for example, if abiogenesis or the development of multicellularity are extremely rare events, this is great news! This means that we have passed the most difficult path to an interstellar civilization. The probability of our success in the future is greatly increased.
  
• The filter is ahead of us: If the great filter is only waiting for us in the future. This means that a serious threat makes  our civilization’s survival and further development extremely unlikely. And humanity needs to do its best to avoid a disaster. The entire development of our civilization directly depends on this.

Without a doubt, part of the difficult path has already been passed, we have developed into intelligent beings, and created technologies, but these obstacles can hardly be considered the Great Filter. If it had been passed, we would probably have already noticed traces of other developed civilizations. The fact that we still can’t see them may indicate that something is inevitably destroying civilizations before they can become visible on a cosmic scale.

What Is The Most Likely Great Filter For Humankind?

It is impossible to state for sure what great filters are most likely for humanity, as we do not fully understand all the difficulties on the way to establishing a long-lasting interstellar civilization. However, here are some of the most discussed obstacles:

1. Self-destruction: Humanity’s broken risk perception is reversing global progress in a ‘spiral of self-destruction. The outcome of such negligence could be: nuclear war, global ecological disaster, a pandemic caused by a genetically modified virus, or the uncontrolled development of artificial intelligence, which could eventually decide that humanity is a dead end branch of evolution and destroy us.
2. External disasters: Asteroid collision, a gamma-ray burst, a nearby supernova explosion, or other cosmic cataclysms.
3. Insurmountable technological or social barriers: the inability to solve global problems such as overpopulation, resource depletion, or climate change.

It is important to note that these obstacles are not mutually exclusive. We may face several problems at the same time. But are we able to influence our destiny? Recognizing potential dangers and working on their solutions can increase our chances of overcoming the Great Filter.

What Do Scientists Say?

The Great Filter theory predictably has its adherents and critics. The former consider it to be a plausible explanation of the Fermi Paradox, an incentive for further astrobiological research focused on finding new filters, and an important warning about the fragility of our civilization. For example, physicist Michio Kaku believes that the Great Filter may be related to the development of technologies that could lead to the self-destruction of humanity. Astrophysicist Carl Sagan associated it with the rarity of intelligent life, and philosopher Nick Bostrom hypothesized that we live in a computer simulation created by a more advanced civilization, and filter may be associated with the limitations of this simulation.

Critics also believe that the Great Filter theory greatly relies on the anthropic principle (the idea that we observe the Universe as it is because we exist in it). What do you think? 

Other Theories Explaining The Fermi Paradox And Related Stories

1. The Great Silence Theory
2. The Dark Forest Hypothesis
3. Are we alone in the Universe?
4. 15 Amazing Space Mysteries

References and Additional Information

• The Great Filter and the Fermi Paradox https://www.researchgate.net/publication/321166332_The_Great_Filter_and_the_Fermi_Paradox 
• The Great Filter https://www.aao.org/lifetime-engaged-ophthalmologist/perspective/article/great-filter 
• Is artificial intelligence the great filter that makes advanced technical civilisations rare in the universe?https://www.sciencedirect.com/science/article/pii/S0094576524001772 
• The Great Filter, Branching Histories and Unlikely Events https://www.stat.berkeley.edu/~aldous/Papers/GF.pdf 
• The Great Filter – Are We Almost Past It? https://philpapers.org/rec/HANTGF-2