The probability of the existence of various civilisations yet not possible to encounter them is basically the Fermi paradox. Even if a very small fraction of the hundred billion stars in the galaxy are home to intelligent civilisations that colonize over interstellar distances, the entire galaxy could be colonized in a little over a million years. The absence of such civilizations that could visit Earth is the Fermi paradox. This was first proposed by the physicist Enrico Fermi in 1950.
The paradox is named after him, who informally posed the question “Where is everybody?” during a 1950 conversation at Los Alamos with colleagues Emil Konopinski, Edward Teller, and Herbert York. The paradox first appeared in print in a 1963 paper by Carl Sagan. There have been many attempts to solve the Fermi paradox, such as suggesting that intelligent extraterrestrial beings are extremely rare, that the lifetime of such civilizations is short, or that they exist but (for various reasons) humans see no evidence. There are some facts and hypotheses that together highlight this paradox.
Since there are billions of stars in the Milky Way similar to the Sun with the probability of some of the stars having Earth-like planets orbiting in the habitable zone is high. Many of the stars are much older, making their planets older too, and if such planets did exist, they would’ve developed civilisations long ago. And some of these may have developed interstellar travel already. Even at a slow pace of envisioning interstellar travel, the Milky Way galaxy could be completely traversed in a few million years. Since many of the Sun-like stars are billions of years older than the Sun, the Earth should have already been visited by extraterrestrial civilisations or maybe their probes, but this didn’t happen. Hence, there’s no convincing evidence that this happened.
Some of the possible hypotheses are:
The dark forest theory:
This theory is also known as the ‘quarantine theory’ and is the most convincing theory to be presented. It states that if the Solar System took billions of years to form, including our galaxy, this means that there were billions of years in the gap to help create another galaxy and another million years to form an advanced civilisation. If this were the case, then the civilisation would’ve already explored the whole galaxy and continue to advance well beyond our technological capabilities before we even existed. This is simply because they had a head start of a few million years, which is nonetheless a great gap. But the question is, where are they? According to this theory, they might be hiding somewhere for self-preservation. This is satisfying our needs and desires, and assuming that the others would want the same as well. Maybe this is why the civilisation might be hiding from just, for saving themselves. But these advanced civilisations might be hiding in plain sight, and we just don’t notice. As creatures might’ve had a head start, their form of development would’ve been very different from ours, and their form of colonisation would be very dangerous and different as well. Other than that, they may have stopped sending radio signals since they don’t want to be located. But, shouldn’t we do the same? We have been sending radio signals out into space for nearly a century now, meaning if there is an alien civilisation out there within a range of a hundred light-years, they would have no problem in locating our little solar system, including our Earth. But since the radio signals are weak and decay over time, it really isn’t an issue. But should we be this bold and maintain our sense of presence in the universe, or should we stop? Well, in the upcoming years, we might’ve colonised the moon with established permanent residents, and further upon Mars. This might seem like a terrifying solution since alien civilisations would be more advanced and terrifying at colonising. Now, let’s talk about some other scary solutions.
Rare Earth Hypothesis:
This is one of the terrifying solutions that we are alone. That we are the only beings present in this universe. We evolved from a single cell. And those cells only ever evolved on the Earth, once. But if we look at the possibilities of a planet living for almost 3.9 billion years, the possibility of this solution starts to make sense. A planet can be under, gamma ray burst, a geomagnetic storm, asteroids, or planetary collisions, and the list might go on. So, it’s kind of possible that we are the only civilisations which surpassed these difficulties and barriers to become a successful planet. Maybe we are alone. But if that is the case, if we are alone in the universe, then there’s so much pressure on us just to explore the universe. The rate at which it’s expanding has a high value, with its insane scales of 14 billion light-years. But now, the beings are destroying their planet with nothing left behind. In this hypothesis, the ENTIRE weight of the universe is on our shoulders. There is a famous quote by Arthur C. Clark- “Either we are alone in the universe or we are not, both are equally terrifying.” The next hypothesis is the most clear and constructive solution yet, greatly misunderstood.
Searching better:
Our search methods might be outdated. Just like us, the other civilisations might be focused on finding extraterrestrial life on other planets. We have been sending radio signals to various star systems, but these radio signals were developed by us way earlier than estimated. So, if other civilisations existed before us, they might’ve developed other advanced methods of communication since they have a head start. There are all kinds of possibilities of finding life on other planets. We may be looking for pollutants such a methane and carbon dioxide, but since civilisations can take different forms, they might release laser beacons which could be brighter than most of the galaxies, making them almost inevitable to notice. The other solution to communicate might be through the fabric of space-time, like gravitational ripples. Astronomers have confirmed that a sufficiently advanced civilisation can make communication signals possible through ripples in the space-time fabric. They could use dense objects like black holes and neutron stars to create gravitational ripples, and we have already started receiving such ripples, but they are no hidden message as such.
Great Filter Hypothesis:
The Great Filter hypothesis, proposed by Robin
Hanson suggests that there is a barrier or series of barriers that prevents most civilizations from advancing to the point of becoming interstellar or detectable across the universe. It’s an attempt to explain the Fermi Paradox, why we haven’t observed signs of intelligent extraterrestrial life despite the vast number of stars and planets. In simpler terms, the universe is a giant obstacle course for life. The goal is to go from simple chemicals to a super-advanced civilization that can travel between stars or send signals we’d notice. The Great Filter hypothesis says there’s a tough obstacle somewhere in this course that stops almost all life from reaching that goal. That’s why we don’t see aliens everywhere, even though the universe is huge with billions of planets.
The filter could be:
Something in the past- Like life starting from chemicals, which is very rare; or simple life becoming complex, like animals with brains; or intelligence evolving (maybe brains like ours are a fluke).
Something in the future- Like civilizations inventing powerful tech (nuclear bombs, AI, etc.) and accidentally destroying themselves before they can spread into space.
The big question is: Where is the Filter?
If it’s behind us (e.g., life starting was the hard part), then we’re lucky to exist, and maybe we’re one of the few intelligent species out there.
If it’s ahead of us (e.g., surviving our technology), then we’re at risk of wiping ourselves out, which is scary.
The hypothesis is speculative, as we lack data on alien life, but it frames discussions about humanity’s place in the cosmos and the challenges we face. It’s often debated in the context of astrobiology, SETI, and existential risk studies.
Simulation hypothesis:
The simulation hypothesis is a philosophical and scientific proposition suggesting that reality, as we perceive it, might be an artificial simulation, such as a computer simulation, rather than a physical, objective universe. This theory was popularized by philosopher Nick Bostrom in his 2003 paper, "Are You Living in a Computer Simulation?". In simpler terms, imagine you’re playing a cool video game, like one where you build a whole world with people, animals, and cities, and it looks super real. Now, what if we are characters inside a giant video game that someone else, maybe super-smart aliens or future humans, made on a computer? The simulation hypothesis is the idea that everything we see, like the sky, trees, and even you, might just be part of a big computer program. The hypothesis draws on probabilistic reasoning: if a sufficiently advanced civilization can create simulations indistinguishable from reality, and if they create many such simulations, the odds favor us being in one of those simulations rather than the original, physical reality. Supporting arguments include:
Technological Progress: The rapid advancement of computing power and virtual reality technologies suggests that future civilizations could simulate entire universes with conscious entities.
Philosophical Precedents: The idea echoes historical concepts like Plato’s Allegory of the Cave or Descartes’ "evil demon" thought experiment, which question the nature of perceived reality.
Mathematical Likelihood: Bostrom’s argument hinges on the sheer number of possible simulations, making "base reality" statistically unlikely for any given conscious being.
Conclusion: We haven’t found any signs of intelligent life yet, but our search has just begun and will continue to advance with time and technology. I do believe that they are out there, and maybe something is preventing us from discovering them, or we aren’t just advanced enough to find them. The Fermi Paradox questions why we detect no extraterrestrial civilizations despite the universe’s vast potential for life. The Rare Earth Hypothesis suggests complex life is exceedingly rare, while the Great Filter posits a barrier halting advanced civilizations. The Dark Forest Theory proposes aliens hide to avoid threats, and the Simulation Hypothesis implies our reality may exclude alien contact. Enhanced search methods, like SETI and exoplanet studies, continue probing these possibilities. Each theory challenges our cosmic perspective, urging humility and persistent exploration to uncover whether we are truly alone, concealed, or within a programmed reality. This was the Fermi paradox and its hypothesis solutions.
Sources:
The Fermi Paradox - Where are all the aliens? | Space
(3) The Fermi Paradox — Where Are All The Aliens? (1/2) - YouTube
(3) The Fermi Paradox II — Solutions and Ideas – Where Are All The Aliens? - YouTube
Rare Earth hypothesis: Why we might really be alone in the universe (astronomy.com)
Simulation hypothesis - Wikipedia