Where is everybody?
#133 - The Fermi Paradox and why we have not met aliens yet
Hello friends, I hope you had a great week!
I have had a little time on my hands this week, and spent a lot of time (a lot of Kairos, for those of you who read my last post) with a very curious and full-of-questions 6 years old (my son Cosimo).
This got me into the rabbit hole of answering to a weird question: where the hell is everybody? Not in a philosophical sense—literally, where are all the aliens?
We’ve sent probes out of the solar system. We’ve scanned the sky for signals. We’ve cataloged thousands of planets that look Earth-like enough to imagine they could host life. And yet, nothing. Not a whisper. No ruins on Mars, no strange megastructures blocking starlight, no accidental radio broadcast from some distant civilization. The galaxy remains silent.
This question is what physicists call the Fermi Paradox. Given the sheer size and age of the universe, and how quickly intelligent life evolved here on Earth (relatively speaking), we should have seen someone by now. The numbers suggest life should be common. The evidence suggests it’s not.
I’m not an astrophysicist and this isn’t a post about space exploration per se. But I find the Fermi Paradox super fascinating. It’s not so much about aliens but rather about us—where we are in our own timeline, how fragile this moment might be, and what it would mean to make it past this phase of civilization-building without blowing ourselves up in the process.
If that sounds dramatic, it kind of is. But there’s a pretty rational explanation for why the galaxy might be so quiet—and it has nothing to do with being alone. It might be that most civilizations don’t make it past a certain point. What is that point?
Too Many Planets, Too Few Aliens
Let’s start with the simplest version of the question. The universe is old—about 13.8 billion years. Our own solar system showed up relatively late to the party, around 4.6 billion years ago. Life on Earth has been around for most of that time, and humans—tool-using, satellite-launching humans—have been here for a blink. A couple hundred thousand years, give or take.
Now zoom out. There are an estimated 100 billion galaxies, each with hundreds of billions of stars. If even a tiny fraction of those stars had planets, and an even smaller fraction of those planets developed life, and an even smaller fraction of that life became intelligent… we should still be seeing something. Statistically, intelligent life should be everywhere. Or at least somewhere.
This is the core of the Fermi Paradox, named after physicist Enrico Fermi who, during a lunch conversation in 1950, supposedly blurted out: “But where is everybody?”
It’s not just a fun pub debate. It creates a tension between our expectations (life should be common) and our observations (we’ve seen nothing). No signals. No structures. No artifacts. No signs of interstellar travel. We’ve been listening for decades and the radio is still quiet.
There are dozens of theories that try to explain this: maybe we’re in a cosmic zoo and being watched, maybe everyone is using tech we can’t detect, maybe space is just too big and expanding too fast. Some are plausible. Some are just creative writing. But the most serious thinkers tend to come back to a more uncomfortable explanation: maybe life is common… but intelligent life doesn’t last very long.
This is what many call the “Great Filter”.
The Great Filter: The Test No One Seems to Pass
The most unsettling answer to the Fermi Paradox doesn’t involve distance, timing, or camouflage. It’s the idea that something stops civilizations from getting far enough to make contact. This is the “Great Filter,” a concept first laid out by economist Robin Hanson in the late ’90s, and it’s exactly what it sounds like: a bottleneck that filters out most life before it spreads.
Think of it like a long to-do list for any intelligent species. First, you need a planet that can support life. Then you need life to emerge at all, which might be incredibly rare. That life needs to evolve into complex organisms. Then intelligence. Then technological capability. Then stability. Then survival. Then interstellar expansion.
Each one of those steps might be easy. Or any one of them could be nearly impossible. We just don’t know. The “filter” could be early—maybe life almost never starts. Or late—maybe lots of civilizations get to our level, but then self-destruct before they can go further.
And here is where it gets a bit philosophical (and a bit spooky): if the Great Filter is behind us, that’s excellent news. It means we’re rare, maybe even unique, and we’ve already overcome the hardest steps. But if it’s ahead of us—if the filter is something like nuclear war, runaway AI, or ecosystem collapse—that’s a problem. Because that would mean civilizations like ours tend to end right around this point.
And this is where the Fermi Paradox turns into a mirror. The silence we hear might be the universe telling us: you’re at the danger zone now. The moment of maximum risk isn’t when you invent fire. It’s when you invent tools powerful enough to wipe yourself out, and then hand them to unstable systems—political, ecological, or computational.
So far, we’re still here. But history suggests we’re not great at recognizing filters until we’re already inside them.
It’s easy to let the Fermi Paradox veer into fatalism. If most civilizations blow themselves up, then maybe we will too. If we’re alone, maybe it’s because we’re not meant to last. But that kind of thinking misses the point.
The silence in the universe isn’t an answer. It’s a blank page.
Maybe we haven’t seen anyone else because the odds are low. Or maybe we’re early. Maybe life is rare, and intelligence even rarer, and coordinated global systems like the ones we’re trying to build are the rarest of all. That doesn’t have to be scary. It can be a motivation. If we really are one of the first intelligent species to reach this stage, then how we act now sets a kind of precedent. For us. Maybe for others.
The philosopher Toby Ord calls this the “Long Reflection.” A period when humanity realizes it’s no longer just surviving—it’s deciding what kind of future it wants to build. And what risks it’s willing to accept.
Size matters
As many of the posts I wrote, also this one was actually inspired by randomly stumbling on a tweet and then entering into a rabbit-hole as the tweet got me curious.
There’s another angle on the Fermi Paradox that’s less about self-destruction and more about physics and it is often referred to as “gravity traps”.
Maybe civilizations don’t die—they just get stuck. K2-18b, an exoplanet discovered in 2015 and located about 124 light-years away in the constellation Leo, offers a compelling example. It’s approximately nine times Earth’s mass and 2.6 times its radius, classifying it as a “super-Earth” or “mini-Neptune.” Recent observations using the James Webb Space Telescope have detected potential biosignatures—specifically, dimethyl sulfide (DMS) and dimethyl disulfide (DMDS)—in its hydrogen-rich atmosphere. On Earth, these compounds are primarily produced by marine microorganisms, suggesting the possibility of microbial life in K2-18b’s hypothesized ocean-covered surface .
However, the planet’s substantial gravity presents a significant hurdle and could be an example of the “Gravity Trap”.
As aerospace engineer Luke Leisher pointed out, launching a spacecraft into orbit from K2-18b would be immensely challenging. Even a fully optimized, expendable version of SpaceX’s Starship—the most powerful rocket humans have ever designed—would barely be able to lift five tonnes into a 500 km orbit from K2-18b. On Earth, the same rocket could carry about 150 tonnes into low Earth orbit. This stark difference underscores how a planet’s gravity can severely limit the development of spacefaring capabilities.
A planet’s gravity depends on its mass—so the more massive a planet is, the stronger its gravitational pull becomes, making it much harder for anything to break free from its surface.
If most habitable planets have much stronger gravity than Earth, then even if life evolves and intelligence emerges, the leap to space travel might simply be out of reach. No satellites. No radio telescopes on the Moon. No interstellar probes. Just isolated bubbles of life, trapped in deep gravity wells, unable to even shout into the void.
The Great Silence might not be because civilizations collapse. It might be because most never make it off the ground.
Alternative theories
There are several alternative hypotheses to the Fermi Paradox beyond the Great Filter. I researched a bit and found some interesting ones (and a few really weird ones!).
1. The Dark Forest Hypothesis
This theory posits that the universe is teeming with civilizations, but they remain silent out of self-preservation. In a cosmos where any unknown entity could pose a threat, the safest strategy is to avoid detection. Thus, civilizations actively conceal their presence, fearing that revealing themselves could lead to their destruction. This idea was popularized by Liu Cixin’s novel The Dark Forest and offers a grim perspective on cosmic silence.
2. The Aestivation Hypothesis
Proposed by Anders Sandberg and colleagues, this hypothesis suggests that advanced civilizations are not extinct but are in a state of dormancy. They may be “aestivating”—waiting for the universe to cool down to maximize computational efficiency. In this view, civilizations are conserving energy to perform massive computations in the far future when conditions are more favorable.
3. The Rare Earth Hypothesis
This perspective argues that while microbial life might be common, complex intelligent life is exceedingly rare due to a unique combination of astrophysical and geological factors on Earth. Factors such as a large moon, plate tectonics, and a magnetic field may be uncommon, making Earth-like planets—and thus intelligent life—exceptional.
4. The Zoo Hypothesis
This idea suggests that extraterrestrial civilizations intentionally avoid contact with us to allow for natural evolution and sociocultural development, much like zookeepers try to prevent animals from becoming aware of spectators. In this scenario, Earth is being observed but not interacted with, preserving our natural progression.
5. The Simulation Hypothesis
Some theorists propose that we might be living in a computer simulation. If this is the case, the absence of extraterrestrial life could be a design choice by the simulators, who may have programmed the simulation to focus solely on human development. This hypothesis, while speculative, offers a radical explanation for the Fermi Paradox.
Fuse: A Bet Against the Filter
As I was writing about this I actually connected the dots with another topic I had on my to-write list, and it’s about a company working on Nuclear Fusion Energy.
If there really is a Great Filter waiting ahead of us, the question becomes: can we build our way around it? I have written several posts in the past about nuclear energy and the risks of nuclear wars. I find the topic particularly interesting, as humans start editing the fabric of life and thus “acting like Gods”…
I started thinking about this and actually stumbled across a really cool startup that gave me a lot of hope, to avoid also this post is pure doomsday scenario!
The thesis behind Fuse is that some of the most dangerous bottlenecks to human survival—energy scarcity, geopolitical instability, weapons escalation—can be addressed through better engineering. Specifically: fusion energy and nuclear security.
The Fuse team is working on two fronts. The first is nuclear effects testing—building better tools to understand, simulate, and ultimately deter the use of nuclear weapons. We’ve spent decades operating on Cold War-era assumptions, with modeling tools that haven’t kept pace with modern risks. There’s a growing argument that we need better infrastructure to understand what would actually happen if a modern nuclear event occurred—so we can avoid ever needing to find out.
The second front is fusion. The holy grail of clean, abundant, non-carbon energy. Still experimental, still tough to scale—but if it works, it could replace fossil fuels without the geopolitical baggage of oil, and without the radioactive waste of fission. A way to reduce the odds that scarcity, inequality, or fragile supply chains trigger broader collapse.
Nuclear fusion (which I already covered in a post in the past) is one of the most interesting potential technological evolutions, and I am really curious to see where it lands.
So what’s your take? Where is everyone? My son bets on the Zoo Hypotesis, or at least that is what sounded most “realistic” to him… and usually in these things imagination beats math so.. he could easily be right!
Wish you a fantastic weekend,
Giovanni
Book in a tweet
This is the perfect book for this post and a great read: an astronaut gets lost into space exploration and eventually makes contact with aliens. Masterpiece of this gender, I really loved this book and found many of the hypoteses the author makes on aliens really smart and provoking. Highly recommended!