As per the statistics, we could expect to see advanced alien civilizations in our galaxy. There is even a possibility of Type III civilizations existing within the Milky Way. However, we have found no scientific evidence of alien civilizations despite decades of exploration. A few of our fellow Earthlings have reported seeing flying glowing discs, calling them UFOs (Unidentified Flying Objects). However, these observations have not been verified by professionals, so we are going to leave them aside.

Our great question here is:

If there is such a great possibility, why are we not seeing or observing any aliens?

The Fermi Paradox gives us many different possibilities for answering this question. The first set of answers involves the Great Filter.

I wrote an introductory blog about the Fermi Paradox previously. Read that before diving into this explanation. Fermi Paradox – Part 1

Simply put, this idea suggests that there are no higher life forms such as Type II or Type III civilizations. In the previous part, we discussed the high possibility of planets that are older than Earth and stars that last much longer than our Sun. They could potentially provide good environments for advanced life forms. But what is stopping them?

One explanation is that there exists a Great Filter that prevents life from advancing. Think of the path of life as a long track, where every life form must overcome small obstacles, and evolution helps them do so. But at a particular point on that track, there is a huge obstacle that is extremely difficult for any life form to overcome. Maybe it is an artificial disaster such as nuclear war, biological warfare, or severe damage to the biosphere. Or perhaps it is a natural disaster such as asteroid impacts, gamma-ray bursts, or other catastrophic planetary events.

Now we have the idea of the Great Filter. What is our position on that path of life?

Are we an advanced civilization that has already crossed the filter? Or were there more advanced civilizations before us that failed to cross it, making us the next in line? Let us discuss the possibilities of the Great Filter.

First Possibility

The Great Filter could be at the very beginning of life. It might be extremely difficult for life to begin at all.

The Hanson List suggests several steps in the development of life. The first step is having the right stellar system for life to evolve. The second step is the formation of self-replicating molecules such as RNA.

This first possibility suggests that it is very difficult for self-replicating molecules to form, even when suitable stellar systems and environments exist. On our own planet, it took nearly one billion years. Even though we have tried to replicate the process in laboratories, we have not succeeded in creating life from scratch. It is clearly a very difficult process.

Luckily, Earth achieved it in approximately one billion years. However, if the leopard-like spots on Mars are proven to be ancient remnants of life, this discovery could shatter this Great Filter hypothesis. Life would then have emerged independently on both Earth and Mars. Perhaps one billion years is simply the common amount of time nature requires to prepare the ingredients of life.

If this is the Great Filter, then we have already survived it. That alone would be enough reason for a great celebration.

Second Possibility

The Great Filter could be the transition from simple prokaryotic life to advanced eukaryotic life.

According to the Hanson List, the third step is the formation of prokaryotic cells, and the fourth step is the evolution of prokaryotic cells into eukaryotic cells.

Why might this be the Great Filter?

Because it took nearly two billion years for simple prokaryotic cells to evolve into complex eukaryotic cells with nuclei and sophisticated internal structures. If this is the Great Filter, then it would make us extremely rare.

In that case, the universe may be filled with prokaryotic organisms, and we might expect primitive life to exist on moons such as Enceladus and Titan within our own Solar System. There is a significant possibility.

There are many other possibilities corresponding to the steps of the Hanson List: sexual reproduction, multicellular life, intelligent tool-using animals, civilizations capable of interplanetary colonization, and eventually a colonization explosion.

According to Hanson, humanity is currently at approximately step eight. We have already overcome eight potential Great Filters. Or perhaps these are merely obstacles that evolution helped us overcome.

We have identified that chimpanzees are effectively in their own Stone Age. They have been using stone tools for more than 5,000 years. Given enough time, they too could potentially become advanced civilizations.

Some argue that conflicts between species, or even conflicts within the same species, which significantly alter a planet’s ecosystem, could themselves be Great Filters.

Have we escaped such a filter?

After the Second World War and the Cold War, many leaders and media outlets claimed that “evil Nazism” and “evil Communism” were defeated and that the world had entered an era of peace.

Really?

Today we continue to witness imperialist wars across the globe. This raises a difficult question: have we truly escaped the filter?

What is Our Position in Life’s Evolutionary Path?

What if we are moving first and have already escaped the Great Filter?

This would mean that many species throughout the universe attempted to pass the Great Filter, but our evolutionary path allowed us to succeed. We would be the first civilization to reach Type I and eventually Type II status.

That would be extraordinary news.

Since the Big Bang, we would be the first advanced civilization with higher intelligence and a deep understanding of its environment. Others may have tried but failed to pass the filter. Perhaps those civilizations were destroyed by natural disasters such as gamma-ray bursts, or perhaps wars pushed them backward in their evolutionary progress.

What if the filter is still ahead of us?

Then we are not particularly rare, nor are we leading the evolutionary race.

There may have been civilizations far more advanced than ours, but some Great Filter prevented them from advancing further or caused their extinction. If that is true, then we may be next.

Natural disasters such as gamma-ray bursts, dangerous scientific experiments, aggressive expansionist powers, the immense cost of technological advancement, or even artificial intelligence surpassing human control are all possibilities.

Today, I heard the CEO of a famous company say that human water consumption limits the potential of AI. What a remarkable perspective. Ideas like these also become relevant when discussing future risks.

Perhaps we are heading toward a devastating event, but we do not know when it will occur. Maybe tomorrow. Maybe one million years from now.

For now, all we can do is wait and observe the progress of our civilization.

Thank you for your support, people. Stay tuned for the next part.