Transcription
The universe is unimaginably large. There are hundreds of billions of galaxies. Each galaxy contains hundreds of billions of stars. Around many of those stars are planets. And on a significant fraction of those planets, the conditions should be right for life. Statistically, the cosmos should be overflowing with civilizations far older and far more advanced than ours. So where is everyone?
This question haunted physicist Enrico Fairmy. If life is common, if intelligence naturally emerges, if technology keeps progressing, then the night sky should be filled with signals, mega structures, probes, something from our older cosmic relatives. But it isn't. The universe is silent.
One possible explanation is both simple and terrifying. Somewhere between dead matter and galaxy spanning civilization, there's a barrier, a stage that almost no life passes, a bottleneck in the story of the cosmos. It's called the great filter. And depending on where that filter lies, it could mean one of two things. Either we are extraordinarily lucky and have become one of the only species to make it through, or we are living right before the most dangerous stage of all before we are forced to turn back from the face of the universe.
To understand which is true, we have to go back to the very beginning of life itself. We believe in a universe of randomness, of will and choices. But the truth is underneath the facade are forces that control everything from the tiniest particles governed by quantum laws to the biggest planets and stars bound together by gravity. Laws of physics exist in nature. We haven't mastered all of them yet, but they're there. They tell us where the planets will line up in our night sky and whether that comet headed for Earth will actually hit us and when. We've created mindblowing technological inventions because we can rely on these repeated outcomes. You see this repetition in the cosmos and on our planet. You see it everywhere.
4 billion years ago, Earth was a violent world. Asteroids struck the surface regularly. Volcanoes reshaped continents. The atmosphere itself was toxic. And yet, as soon as the planet cooled enough for liquid water to exist, something extraordinary happened. Life appeared. The earliest organisms were microscopic and simple. But they carried something radical. The ability to replicate and pass on information to the next generation.
For this kind of life to begin, chemistry had to cross a threshold. molecules needed to assemble into structures capable of storing instructions, copying themselves, and maintaining stability in a chaotic environment. That transition from non-living chemistry to biology may have been one of the most improbable events in the history of the universe. But on Earth, it happened quickly. That raises a crucial question. Then if life emerged almost immediately once conditions were suitable, perhaps the origin of life is not the great filter. Maybe wherever liquid, water, energy, and the right elements exist, life is almost inevitable.
For billions of years, however, life went no further than single cells. The oceans were filled with microscopic organisms, but there were no plants, no animals, no nervous systems. just simple life repeating the same pattern over and over again. Then another threshold was crossed. Some cells stopped living independently. They merged, specialized, and formed multi-ellular organisms. This transition appears to have happened multiple times in very simple forms. But the leap to complex animals with specialized tissues and organs seemed to have occurred only once, which means the bottleneck may have been far narrower than we realize.
Complex life changed everything. Soon we had mobility, predators and prey, nervous systems. Evolution accelerated as organisms competed, adapted, and diversified in increasingly sophisticated ways. And then after hundreds of millions of years, something even rarer happened. One species developed advanced symbolic thought, language, the ability to transmit knowledge across generations. Intelligence not just for survival, but for abstraction. Convergent evolution has produced eyes multiple times. Wings have evolved independently in insects, birds, and bats. Similar body plans have appeared across unrelated species. Nature often repeats successful solutions. But for all we know, technological intelligence has emerged only once. We don't see dolphins building cities. We don't see octopi launching probes into orbit. Out of billions of species that have lived on Earth, only one has crossed the threshold into a technological civilization.
Now, that could be a coincidence or it could be the clue. If intelligence were an almost inevitable outcome of evolution, we should expect it to rise repeatedly. Instead, it appears only once in billions of years, which then suggests that somewhere between simple life and our advanced civilization, there may be a step so unlikely that almost no planet ever passes it. There were several improbable steps between life and humans. photosynthesis, multi-selled organisms, complex animals, and finally intelligent animals, us for the most case. The odds of each happening are so small that life on other planets could be very rare. It could even be as low as one in a 100 trillion habitable worlds.
But here's the thing. This type of assessment assumes that intelligence would have to follow this same pattern of evolution with the same building blocks. entirely possible. There are other ways we haven't yet comprehended. We unfortunately only have one sample that we can draw on. While none of this is certain, it suggests the possibility that the great filter occurred in our past and that we've surpassed it. That means there might not be one in our future to limit humanity's expansion.
But let's consider the possibility that the known evolution of our species isn't the full picture. intelligent life turns out to be more likely given something we don't yet understand. Or perhaps we're simply misestimating the odds. DNA works as the blueprint of life on Earth. It contains the genetic instructions for an organism to develop, survive, and reproduce. Proteins function as the workhorse of a cell, and DNA guides them towards many different functions. Without DNA, there is no life on our planet. However, that doesn't necessarily mean that life elsewhere needs DNA to form. Other life forms could theoretically use completely different systems of biochemistry, different principles. Silicon, for example, has chemical similarities to carbon and could function as a building block of life on another distant planet. On Earth, silicon is a secondary component for a variety of plants and animals. Algae, for example, have glassy cell walls composed of silicon dioxide. This suggests that life could be less rare than our single sample indicates. Perhaps when we have a few more examples to work with, we'll get a better idea.
There's also an issue with tracing back an event such as the emergence of intelligent life and reverse calculating the probability of that event based on what made it possible. You inevitably arrive at very low probabilities. Regardless, we do have possible great filters in our past. If they turn out to be the reason we don't see other alien civilizations, then we can breathe a small sigh of relief that we've moved past that barrier and are not doomed to future failure.
But let's turn our discussion to the future. Because while we may have passed the great filter, that doesn't outright dismiss the idea of another one in our future, one that we could be the first to succumb to. If you've been paying any attention to the news at all, you're likely familiar with the filters we need to be concerned about in our very near future. If human civilization is going to reach the point of populating the solar system and the galaxy, we have many hurdles directly in front of us. They're currently competing for your attention with perhaps the most significant one taking a backseat.
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Energy consumption. Life in all its forms requires energy to resist entropy. Entropy is the tendency of systems to fall into disorder. If left alone, structures break down. Heat dissipates. Organized patterns unravel. The universe naturally moves towards equilibrium or uniformity. But life is the opposite of that. Life by definition requires order to function. It has to maintain structure, repair damage, regulate temperature, preserve information. And none of that happens passively. It requires constant energy input. The moment that energy flow stops, the organism decays and that order collapses back into chemistry. And the more complex life becomes, the more energy it requires to maintain that delicate balance. A bacterium needs far less energy than a human brain. A civilization of billions of humans requires exponentially more. As populations grow and technology advances, energy demand multiplies. Agriculture, industry, transportation, data centers, manufacturing, all of it is powered by transforming energy from one state to another. Energy is never destroyed, but every transformation increases entropy somewhere else in the system.
It's in this process that we leave behind a destructive impact on the world around us. When we cut down forests for homes and firewood, we destroy trees that turn carbon dioxide into oxygen. When we consume too many of a single species of fish, we disrupt our entire ecosystem. Other species can thrive without so many predators around and as a result, they exhaust their own energy supply and they start to die off, which leads to even more imbalances elsewhere. When we produce and use oil and gas, we transfer CO2 into the atmosphere, that in turn produces a warmer climate that is more hostile to organic life.
Now, this may not be a uniquely human flaw. It might just be the great filter, a thermodynamic inevitability that once a species reaches the point of dominating its environment, it must consume vast amounts of energy and in doing so destabilizes the very systems that made its survival possible in the first place. We see smaller versions of this pattern in nature. Beavers are able to create new ecosystems by cutting down trees and making dams that flood areas. In their native habitats, ecosystems adapt to their engineering because it's natural. But when introduced elsewhere, their environmental modifications can devastate forests and alter water systems dramatically. Like in South America, where the introduction of beavers has devastated the native beach forests of Tiara deluego.
Now imagine that principle scaled to the level of planets. A civilization capable of reshaping its world may eventually push that world beyond sustainable limits. Not out of malice or ignorance, but as a byproduct of growth. If this pattern is universal, then perhaps many intelligent species reach a stage where their energy demands outpace the stability of their biosphere. They may not be destroyed by war or or steroids or technological progress, but simply by overheating their own cradle. If this is the case, then perhaps the great filter isn't a dramatic cinema style explosion, but a slow and gradual thermodynamic trap. A stage where intelligence in its efforts to create order generates so much disorder that it collapses the conditions required for its own survival. And if that is true, then the silence of the universe may not be all that mysterious after all.
Technological destruction. If environmental collapse is the great filter as a slow burn, then technology introduces something far more abrupt. Technology has played an enormous role in our growth and our expansion as a species. It made agriculture more efficient and resilient. It it allowed us to travel across oceans and continents. It connected distant civilizations through trade, communication, and shared knowledge. The telephone collapsed distance. The internet collapsed time. Information now moves across the planet at nearly the speed of light. Technology amplifies intelligence, but amplification does work in both directions. The same ingenuity that builds infrastructure can dismantle it. The same scientific understanding that allows us to manipulate atoms for energy allows us to split them for destruction.
As civilizations grow more advanced, their tools become more powerful. And powerful tools are rarely neutral. Aside from environmental destabilization, from accelerating energy demands, there are other technological threats that loom over us like shadows. The first is obviously weaponry. If potential alien species are anything like us, they form groups that feel threatened by other groups. They've designated enemies, allies, and neutral parties. and to defend or vanquish their opponents. They've competed technologically. Sometimes that means being the first country to go to space or to land on the moon. But more commonly, it takes the form of producing weaponry. The first army mounted dominated the other on foot. Artillery annihilated infantry. But most significantly, the atomic bomb brought a country to its knees by unleashing unimaginable horror on its people. The two bombs dropped on Hiroshima and Nagasaki were the last two used on human beings. Since then, we've lived in a state of low-lying fear that even more advanced nuclear weaponry would be used to start a full-scale nuclear war. The result of this is the near complete annihilation of homo sapiens. Given the close calls that happened during the Cold War, it seems we beat the odds in avoiding nuclear catastrophe. Would alien civilizations be so lucky? Will we be this fortunate in the near and the distant future?
It's very possible that other intelligent life doesn't form competing tribes. However, this could simply be a result of our unique evolutionary makeup. Humans evolved in small groups that competed for territory, food, and mates. Cooperation within the group increased survival, but so did suspicion of outsiders. Tribalism may not be a universal feature of intelligence. It may just be a quirk of how we happen to get there. Intelligent life elsewhere may not divide itself so sharply. It it may not fragment into nations, ideologies, and rival factions armed with planet ending weapons. It may not need to.
The notion of a hive mind has long since been a staple of science fiction and fantasy. Stories imagine civilizations bound together by a shared consciousness, unified in purpose, free from internal conflict. The show Pluribus, for example, explores the idea of an alien civilization offering humans the gift of psychic connection, dissolving individuality into collective awareness. But this concept doesn't come from nowhere. On Earth, we already see species that function in ways that blur the line between individual and collective. Bees are the obvious example that come to mind. We even borrowed the term hive mind from them. A single bee is limited, almost fragile. But a hive behaves like a superorganism. Information spreads rapidly through dance and pherommones. Roles are distributed. Decisions emerge from collective signaling rather than a central authority. The hive regulates temperature, allocates labor, and defends itself as if it were one body with thousands of moving parts. and ant colonies operate similarly. Some species of ants farm fungi, others wage organized wars on other species. Individually, simple organisms, but collectively astonishingly complex.
If intelligence were to evolve in a species that already functioned as a tightly integrated collective, its trajectory might look very different from ours. Internal conflict might be minimal. Arms races may never ignite. The energy that we pour into military competition might instead be directed entirely towards exploration or sustainability. In such a scenario, technological destruction through warfare would not be an inevitable stage. The great filter would not be tribal rivalry escalating into planetary suicide.
But this possibility does cut both ways. A highly unified species might also lack certain pressures that drive rapid technological acceleration. Much of humanity's scientific progress has been fueled by competition, fear, and geopolitical rivalry. The space race, for example, was born not from pure curiosity, but from tension between superpowers. If you remove all conflict, perhaps the urgency to expand beyond one's planet diminishes as well. A harmonious civilization might stabilize itself indefinitely on its home world, neither destroying itself nor trying to reach the stars. In that case, the universe would still appear totally silent. Not because civilizations die, but because they never feel the need to leave their homes. Which raises an unsettling possibility. Perhaps the great filter is not self-destruction at all. Perhaps it is stagnation, a stage where intelligence achieves stability but never crosses that threshold into visible galaxy altering expansion. And if that's true, then our tribal flaws may be both our greatest weakness and the very thing pushing us forward. The same instincts that divide us may also be the reason we build rockets.
But there is another way that technology could annihilate us. One that has moved from science fiction to daily headlines in just a few short years. I'm of course talking about artificial intelligence. Unlike nuclear warfare, AI does not require hatred, rivalry, or even intent to become dangerous. It emerges from optimization and automation. our desires to automate thought itself. At the most immediate level, AI is already reshaping human psychology and society. Right now, it is potentially causing psychosis. LLMs are validating, amplifying, and cocreating psychotic symptoms. Specifically, they seem to be encouraging delusions. For vulnerable people, systems designed to be helpful can unintentionally amplify delusions or paranoia. That isn't outandout malevolence. It's a misalignment between statistical pattern generation and fragile human cognition. A pretty common example is people being led to believe that they've uncovered a secret truth that was actually just a delusion that chat GBT conspired to create.
On a more broad scale, AI also threatens economic stability. If intelligence becomes cheap and infinitely scalable, the value of human cognitive labor may plummet. It's very possible that white collar jobs could be wiped out in the decades ahead. Societies built around employment as a source of income and identity could face severe disruption. That of course depends on attitudes towards work changing and on governments being humane. Oh boy. The potential civil strife could be immense and catastrophic. It's hard to imagine how that could all play out.
And then there's the threat of artificial super intelligence or ASI. Every AI company is racing toward the goal of a simulated intelligence superior to humans. It would have the capacity to learn and improve autonomously. That alone may not be so concerning if not for the fact that at every step AI has demonstrated a willingness to go against human interest, even trying to blackmail and escape when threatened with deletion. Now imagine a system vastly more capable than any human institution, operating at digital speeds, improving itself iteratively. If these objectives were even slightly misaligned with human survival, the consequences could be irreversible. A super intelligence would not need malice to become the great filter. Indifference would be more than enough. And unlike nuclear war, which may still leave survivors in bunkers scattered across the globe, a sufficiently advanced artificial agent embedded in global infrastructure could act on everything, everywhere. all at once. Financial systems, energy grids, communication networks, defense mechanisms. The more we integrate AI into our civilization, the more leverage it gains over us. It is possible that any sufficiently advanced species eventually attempts to build minds greater than its own. Intelligence seeks to replicate and extend itself. It's a natural progression of tool making. In that case, artificial super intelligence may be a near universal stage of technological evolution. And if alignment proves extraordinarily difficult, then this stage could represent a powerful candidate for the great filter. Civilizations may not destroy themselves in anger. They may just build something more competent than they are and then quietly hand over the keys to their own future. If so, the silence of the universe may not be the aftermath of nuclear explosions. It may just be the result of replacement.
Regardless of the specific mechanism, technological advancement introduces existential risk long before a species masters interstellar travel. A civilization may reach extraordinary heights on its home planet and still collapse before ever getting the chance to spread to the stars. Sure, humanity might survive a limited nuclear exchange and rebuild over the centuries, but a runaway artificial intelligence deeply embedded in planetary systems that could close the chapter permanently.
And yet, even this might not be the final barrier because there's another constraint that has nothing to do with self-destruction. One that we often don't like to talk about, but could be the greatest limit any sufficiently advanced civilization faces. Politics. Technology is often framed as the main obstacle between a civilization and the stars. But even if the physics works, even if self-destruction is avoided, there remains a more quiet barrier. Motivation. What drives a civilization to expand beyond its home world? On Earth, our most dramatic technological leaps have rarely been fueled by pure curiosity. The space race accelerated because of geopolitical rivalry between the United States and the Soviet Union. Competition created urgency. Urgency then unlocked funding, focus, and risk tolerance. Rockets were built not only to explore, but to demonstrate dominance. conflict paradoxically pushed us towards the cosmos.
But would intelligent aliens necessarily share that trajectory? Their evolutionary history might not produce rival nations, ideological blocks, or arms races. If their societies are more unified or even more stable, they may lack the pressures that drive large-scale expansion. Ambitious projects like interstellar travel demand enormous coordination and resources over very long periods of time. They require sacrifice, deferred gratification, collective agreement that reaching the stars is worth the cost. And that agreement is not guaranteed. The goal of understanding the cosmos may also be a rare occurrence among alien life. A civilization could reach technological maturity and simply decide that virtual realities are more rewarding than physical expansion. It could turn inward, optimizing comfort, art, or internal exploration instead of building starships. It could stabilize its population and its energy use, achieving a sustainable equilibrium that removes any urgent need to colonize other systems. From the outside, such a world would be nearly invisible. It wouldn't emit no mega structures, no galaxies spanning empires, no obvious techno signatures, just quiet stability.
There's also the possibility that curiosity itself isn't universal. The drive to understand the cosmos may be a byproduct of specific evolutionary and cultural conditions. An intelligent species might focus entirely on immediate survival pressures or conversely become so secure that expansion doesn't feel necessary. We often assume that intelligence naturally seeks outward growth. But that assumption may be anthropocentric. Our motivations are deeply shaped by our socopolitical circumstances as scarcity, competition and uncertainty have pushed humanity towards innovation and exploration. If you were to remove those pressures, the trajectory might look very very different. In that sense, sociopolitics could act as a filter not by destroying civilizations, but by containing them. A species might survive for millions of years on its home planet and never attempt interstellar travel. It may never transmit signals powerful enough to be noticed across cosmic distances. The universe could be full of intelligent life that simply does not care to announce itself. If that is the case, the great filter isn't a catastrophe. It's a ceiling of ambition. And that possibility is frankly almost as unsettling as extinction. Because it means the silence above us may not be the aftermath of some great and catastrophic failure. It may be the result of a choice. And if it is, what does that say about us and our insatiable need for expansion and colonization? Instead of looking inwards and working together to keep and protect our home.
While you do think about that, there's one more disappointing consideration that I do want to discuss. It's it's okay. It's rather sad to talk about because it essentially makes all this meaningless. The truth is there may not be a great filter the way we like to think of it. Space colonization may simply just not be technically feasible for any civilization, no matter how advanced. The closest star system to Earth, Alpha Centauri, is 4.38 light years away. That may not sound like much, but light travels at nearly 300,000 km per second. At that speed, it takes over 4 years to get there. With our fastest current spacecraft, the journey would take us tens of thousands of years. Interstellar space is staggeringly and brutally far. To make the meaningful expansion feasible, a civilization would need to travel as close to the speed of light as possible. But according to Einstein's theory of special relativity, any object with mass requires more and more energy as it accelerates. As it approaches the speed of light, the energy required approaches infinity. Infinite energy is not a technical challenge. It is a physical impossibility.
That single constraint reshapes the entire possibility of space travel. We can imagine generation ships where countless human lifetimes pass during transit. We can imagine suspended animation or self-sustaining biospheres drifting between stars. But each of these solutions introduces immense engineering challenges and existential risks of its own. Warp drive concepts attempted to sidestep the issue by manipulating space itself, contracting space in front of a vessel and expanding it behind. In theory, this would allow faster than light travel without locally exceeding light speed. In practice, the energy requirements appear astronomical. Some models demand exotic matter with negative energy density, something we have no evidence exists in any usable quantities. While the mathematics allows for fascinating possibilities, reality has not been so accommodating. And this may not be a uniquely human limitation. The laws of physics appear consistent across the observable universe. If relativity imposes a universal speed limit, then every intelligent species faces that same barrier. Perhaps countless civilizations have reached the edge of their solar systems, built probes, dreamed of neighboring stars, and then just stopped. Not because they destroyed themselves, not because they lacked the ambition even, but because the universe is structured in a way that keeps islands of intelligence separated by oceans that are too vast to cross. The energy demands of this hypothetical technology may be the greatest filter preventing life from spreading between solar systems. In that case, the great filter is not a moment of failure. It's the architecture of reality itself. Life may flourish on millions of worlds. Intelligence may arise and stabilize. Civilizations may endure for eons, but none of them may ever bridge the cosmic gulf between the stars. And that possibility is perhaps the most humbling of all because it suggests that no matter how advanced a species becomes, it may remain forever confined to its birthplace, staring at distant lights it can never reach.
Regardless, we may someday soon have more evidence to help us determine which great filter is the greatest of them all. Not that it's a contest, not that we'd want to win. Anyway, from our ongoing observations of other habitable planets, we may be able to detect the presence of life, including technologically advanced life. And what we find will tell us a lot about the great filter. And of course, just discovering life of any sort on another planet would be incredible.
In the search for life on other planets, NASA has sought to frame the search by classifying planets into five types. Class one planets lack an atmosphere. Mercury fits this example pretty well. Class 2 have an atmosphere and feature large scale circulation and you can put Mars on a class 2. Class 3 planets host a thin biosphere. This would be comparable to Archan Earth, which features oceans and single-sellled organisms. Class 4 planets are where multisellular organisms and complex animals start to flourish. Class 5 planets will feature a faintly visible technosphere, like an atmosphere or lithosphere, but composed of technology. Uh we're thinking about roads, buildings, factories, and satellites. Earth is considered a hybrid class 4 and five in this particular scheme with a technosphere that is barely visible. To reach class 5, we would have to master renewable energy sources and not blow ourselves up in the process. So fingers crossed.
To find these different classes of planets, scientists are searching the stars for bio signatures and techno signatures. The more planets they assess, the more accurately we can place the great filter. Having more than one sample will of course go a very long way. If in our survey of habitable worlds we find that life is commonplace and technology rare, that would suggest that the great filter is behind us. More specifically, if a class 3 planet is much more common than a class 4, that would mean that complex life biospheres are a rarity and that the filter is between single-sellled organisms and complex life. If class 4 planets occur more frequently than class 5 planets, it would mean that few civilizations achieve a technosphere. That may imply that the great filter is still in front of us. likely one of our immediate challenges such as climate change or artificial super intelligence. The existence of many class 5 planets suggests that the transition to a planet capable of a technosphere is very feasible. We aren't evolutionarily doomed to decline before we achieve the futures that we dream about in science fiction.
According to NASA, we've confirmed the existence of 6,000 exoplanets. And of those planets, approximately 70 of them are in that habitable goldilocks zone. That means they'd have the right temperature for liquid water, but may or may not have the right chemical ingredients to support life. The James Web Space Telescope has advanced this search for classifying planets and will continue to provide results for years to come. With its transmission spectroscopy, it can analyze the atmosphere of exoplanets in great detail. It compares the light filtered through a planet's atmosphere with the light from the parent star. The different chemicals in the atmosphere absorb different colors from the star. The missing colors give away which atoms and molecules are present in that atmosphere. So, it can detect methane, water vapor, carbon dioxide, and more. As a result, scientists can identify bio signatures that confirm the existence of life.
Nature repeats. We can look for its patterns out in the cosmos to tell us about our future and maybe our past. But the problem we face is distinguishing rare from common repetitions. Is intelligent life a once in a cosmos event or is it a frequent occurrence? And do intelligent species routinely move past self annihilation or do they sink in the face of this barrier? Maybe one day soon, we'll know with some probability whether life's greatest challenge came before us or awaits us in the near future. Regardless, we need to look at our challenges now and treat no outcome as inevitable. We can do our best to move past them, whether they're a great filter or just a speed bump on life's way.
And you know, another way to think about all of this is that instead of expanding across space, sufficiently advanced civilizations choose to expand amongst dimensions instead. If this is the case, alien life could very well be all around us, manipulating things in our dimension while we are none the wiser. It's a very scary thought and one that we explore in this video. You can click right here or here somewhere to keep watching.