What do you think the Great Filter is?

Sadly it may be the speed of light.

All these intelligent species are simply trapped in their own solar systems for all eternity by an unbreakable natural law.

I think that the great filter/fermi paradox is a combination of two facts,

1. Our entire radio output (the only example we have to go by) is pitiful compared to the sun, like a candle in front of a flood light, you'll only be able to see it so far before it's completely drowned out. After a few dozen light years our radio output is less than the margin of error of a stars detectable radio output.
2. As a civilization advances it must reduce radio leakage. As data gets more important, it gets more important that you're not wasting energy moving it around. Narrow beamed radio transmission becomes the norm and even less radio signals escape the system than when radio was messy and overpowered.

They're not missing or gone, they've just moved beyond messy radio signals. Even we tightened up our radio emissions in a little over a century. Most of what we watch or listen to comes to us via fiber, cable, or short range transmissions like cell phone towers and Wi-Fi.

My favorite filter is the amount of phosphorous in the universe. Earth has an unusually high amount, and it's vital for life. I like this one, because as more stars die, the amount of phosphorous goes up, implying we won't be alone forever.

Anyway, look up "Issac Arthur" on YouTube for HOURS of content about the Fermi paradox and potential great filters.

An alternative is we are among the first. Third generation stars are the ones that have planets with enough heavy elements to allow for complex chemistry. Sol (our star) is thought to be among the first batch of third generation stars in our gallexy.

Light speed does seem to be the upper speed limit for the universe. Talking that into account we probably haven't had a chance to see other early life as it would likely be spread pretty thin right now.

Honesty, I don't think that there is a Great Filter. The Fermi Paradox strikes me as not very well-reasoned. A whole hell of a lot of things would have to go exactly right for civilizations to make contact, rather than it being the default assumption. There are lots of filters, not just one Great one.

But the closest to a Great Filter is that space is really, really. stupendously big. The chances of even detecting each other across such distances is vanishingly small, much less traversing them. Add in the difficulty of jumping the metabolic energy gap to become complex life, and that could reduce the density of civilizations down to a level that they're just not close enough to each other in spacetime to admit even the possibility of contact. And we're hanging our hat on some highly-speculative concepts like alien mega-structures harnessing whole solar systems to allow detection.

I think a lot of persnickety, smaller filters combine to make interstellar contact between civilizations against long odds. Perhaps the best we'll get is spectral signatures from distant planets that are almost-conclusive proof of some sort of life.

Probably too optimistic and unhinged, but maybe a species advanced enough for interstellar travel, building mega structures etc. are advanced enough to ascend to a higher plane of existence or alternate dimensions or whatever. Maybe there's some alternative to this reality that will be unlocked by advanced technology that made all advanced life prefer that, to here.

I don't think there is a single filter. My personal gut feeling however is that the jump to "specialised generalists" would be a major hurdle.

Early human civilizations are very prone to collapsing. A few bad years of rain, or an unexpected change of temperature would effectively destroy them. Making the jump from nomadic tribal to a civilisation capable of supporting the specialists needed for technology is apparently extremely fragile.

Earth also has an interesting curiosity. Our moon is extremely large, compared to earth. It also acts as a gyroscopic stabiliser. This keeps the earth from wobbling on its axis. Such a wobble would be devastating for a civilisation making the jump to technological. Even on earth, we are in a period of abnormal stability.

I suspect a good number of civilizations bottleneck at this jump. They might be capable of making the shift, but get knocked back down each time it starts to happen.

We're currently in it. Failing to create a clean, renewable, and scalable energy source powerful enough to run a society that is ever increasing in both population and technology without destroying their only inhabited planet has got to be the most common great filter.

Asteroids strikes, super volcanoes, solar CMEs, and other planetary or cosmetic phenomena that exactly line up in both severity and timing are too rare IMO.

Every society that attempts to progress from Type 1 to Type 2 has to deal with energy production. Most will fail and they will either regress/stagnate or destroy themselves. Very few will successfully solve the energy problem before it is too late.

My thought is the evolution of intelligent life itself. If you think about it, intelligence is contrary to most of the principles of evolution. You spend a shit ton of energy to think, and you don't really get much back for that investment until you start building a civilization.

As far as we can tell, sufficient intelligence to build technological civilizations has only evolved once in the entire history of the Earth, and even then humans almost went extinct

Everyone is talking about society or physiology stuff. That is just things that might get humans.

Stars going super-nova is the real great filter. Our sun is 4.6 billion years old. Life started 4 billion years ago. In 4 billion years, the sun goes supernova. We are halfway to the end of the earth.

Smaller stars last longer, but have smaller ranges that life can exist in - and planets tend to move in or out in their orbits. Bigger stars have giant habitable zones - but some large stars born when humans took their first steps are in their last decades of life. You couldn't get from the pyramids to NASA in that time, never mind the 4 billion years it took to get to humans.

I like the “Dark Forest” theory I learned from the Three Body Problem books. Basically it’s dumb for civilizations to make a big footprint and reveal themselves because other civilizations won’t know how powerful and dangerous you might become, and so out of precaution they might just zap you. Ironic and over dramatic, but just because that’s a possibility it might be wise to keep a low profile and not invite trouble.

Howabout a reasonably advanced civilization destroying itself and its homeworld after exploiting and then running out of petroleum?

It may very well be republicans

There is a great video about the Great Filter by Kurzgesagt/In a Nut Shell. If I remember correctly, in it they say we can guess at which stage the filter is by how evolved extraterrestrial life forms are. So it's actually great if we find a lot of bacteria or other primitive life forms, that would mean we probably already have overcome the Geat Filter on Earth. On the other hand, if we find many alien ruins of several civilizations at or above our technological level... Well, our greatest challenge might be coming.

We have had Millions of years of (presumably) intelligent Dinosaurs on this planet, but only 200.000 years of mankind were enough to create Civilization IV, the best Strategy game and peak of life as we know it.

So clearly, Civilization™ is what sets us apart.

Jokes aside, the thing evolution on earth spend the most time on is getting from single celled life-forms to multicellular life (~2 billion years). If what earth life found difficult is difficult for all, multicellular collaboration is way harder than photosynthesis, which evolved roughly half a billion years after life formed.

Time.

For a technological civilization like ours, I think it’s just that Earth/humans are weird and we’re past the main ones (like going from single-cell to multi-cellular organisms).

Having to overcome the physical obstacles on other planets rules out the type of spacefaring technological civilizations like ours. No matter how intelligent a civilization on a water world is, it’s not starting fires, much less building rockets. Just getting out of the water would be their space program. Even a totally Earth-like planet that’s a bit bigger and has an intelligent species wouldn’t be able to get to space with chemical rockets.

And also, humans are weird. It could be as basic as “we have hands for building complex tools.” We have a seemingly insatiable need to compete and explore, even beyond all logic—maybe no other intelligent species wants to strap someone to a rocket and send them to space because it sucks up there. We’re violent: without WWII and the Cold War, do we even have a space program?

So many things had to come together to create an intelligent, tool-building species with hands that lives on a planet with the right balance of land and water. As far as we know, it never even happened on Earth before and even then, we had thousands of years of civilizations before anyone was dumb enough to strap themselves to a rocket just to see what would happen.

I would say it's the size of the universe and the fact that it is still expanding at an accelerated rate.

If the speed of light is really the "top speed" of the universe, it is inadequate for interstellar travel. It is barely good enough for timely communication, and not really even that.

Life can be as likely as it wants to be, but it seems to me that we're all quite divided, to the point of not being able to communicate at all with other potential intelligent species.

Honorable mention: we haven't detected alien probes, because intelligent alien societies haven't begun consuming the galaxy with exponential numbers of self-replicating robotic probes, because that's just a really bad idea:

Simple workarounds exist to avoid the over-replication scenario. Radio transmitters, or other means of wireless communication, could be used by probes programmed not to replicate beyond a certain density (such as five probes per cubic parsec) or arbitrary limit (such as ten million within one century), analogous to the Hayflick limit in cell reproduction. One problem with this defence against uncontrolled replication is that it would only require a single probe to malfunction and begin unrestricted reproduction for the entire approach to fail – essentially a technological cancer – unless each probe also has the ability to detect such malfunction in its neighbours and implements a seek and destroy protocol (which in turn could lead to probe-on-probe space wars if faulty probes first managed to multiply to high numbers before they were found by sound ones, which could then well have programming to replicate to matching numbers so as to manage the infestation).

It's gotta be the development of what we recognize as "intelligent". Our brains are not the goal of evolution, just a weird thing that happened.

My suspicion is that it's abiogenesis, but it's only a suspicion that I can't have any certainty of

The most boring one: most species off themselves before they fully get off their starting planet. We will go the same way. Take your pick from climate change, war, pandemic, ... or even a combination of several!

Even if you had a super intelligent species that can make Dyson spheres and travel at the speed of light the observable universe is beyond vast. I don't know much about cosmology or our ability to detect light but given humans have only been looking into the sky for a couple centuries, not being able to see a thimble in the ocean seems like a non issue. I think if you scale the observable universe down to the size of earth the speed of light becomes 0.05 mph.

I read an article about Fermi paradox (I cannot find the link) that stated the humans are one of the first intelligent beings in the universe. That's why we haven't encountered any green men so far. We just might came too soon to the party.

I always thought of it as a series of tests or filters. Like a multistage filter. So like nukes is one, responsible environment management is another. Something like photosynthesis is more of a conditions for life to emerge thing to me really. If like can flourish to begin with then mutations are common enough that things like photosynthesis are inevitable.

We're still new to the game, and we have no idea what we're looking for.

seriously though, I think life on other planets probably just usually evolves underground, so even if they develop some sort of intelligence they're not looking up at the sky so they have no motivation to explore beyond their atmosphere no matter how advanced they get.

there was a planet in The hitchhiker's Guide to the Galaxy universe that had thick cloud cover so that people never even conceived of an existence beyond their planet. when a spaceship crashed there, it never even occurred to them that it might have come from the sky

Energy needed to leave your planetary system vs energy available on your planet of origin.

We have not yet overcome it and I am not sure that we will achieve it.

I think it's incompetence.

I don't think there is a great filter. I think there's an easy solution to the fermi paradox that doesn't require great filters, we're just the first intelligence in this galaxy.

Here's my reasoning: intelligent species that manage to develop space travel probably do tend to expand out into their galaxy. When they achieve this level of technology they can settle most of all of their galaxy in a matter of 10,000 years or so. That time period is very brief on an evolutionary scale. It's estimated that life began on earth 3.7 billion years ago. That means it took about 3.7 billion years for earth to produce intelligent life, and then from that point it would take a mere 10,000 years to reach modern day, and 10,000 more years to settle the whole galaxy. That expansion happens so quickly compared to how long it took the planet to develop intelligent life, that the chance of two civilizations rising at the same time becomes very small.

It all boils down to this: there are no intelligent aliens out there in our galaxy, because we are the first intelligent species in our galaxy. We know we're the first because if we were second, then aliens would already have settled this star system.

Probably there are lots of alien civilizations out there in the universe, but they're in different galaxies.

It's very very obviously the speed of light.

evidence of human existence has only gotten what, 150 lightyears out into space?

Space itself. I believe there are other intelligent life forms out there and some of those happen to be close enough to communicate to each other/discover each other. We just hit the unlucky(or lucky) spot that we are simply too far away.

I think it would be nuclear warfare. Nuclear fission is a universal development for any advanced civilization. It would be easy to construct a nuclear bomb in an advanced civilization. Once a few rogue/pariah states start making them, everyone's screwed.

Making nukes is easy, the only reason we don't see more nuclear states on earth is because of the international backlash. With a couple more Iran and North Korea's we'll likely meet the filter ourselves.

Either multicellular life or that societies that are bent on expansion at any cost tend to destroy their planet's ecosystem before they can establish themselves outside of it. Not making a definitive claim on either, obvs. We have an extremely low sample size after all.

I think we're the first. Or rather in the first wave of intelligent life. It could take a thousand years just for a message to reach us. On the theory that life has evolved to this point as fast as possible over the life of our Galaxy, there's no filter. There just hasn't been enough time for contact to occur.

Personally? Nationalism & nation states. The longer they stay around, the more likely everyone is to think they're more deserving of X, and pull the literal and metaphorical trigger that leads to hitting the filter.

I recognize that individuality is very much our thing, but that will literally only take you so far.

There's been at least 5 mass extinction events we are aware of where I think over 80% of all species become extinct. I'd probably guess one or more of those could do the trick.

• space

• time

We've been producing noticeable radio waves for a matter of decades. We've been capable of detecting even super-powerful, super-deliberate, super-targeted broadcasts for even less time.

And on top of that, it doesn't look as though our civilisation is going to exist for more than a handful more decades, in any detectable-from-light-years-away form.

The chances of that onionskin-thin slice of lightcone intersecting with that of any other civilisation out there seems ludicrously remote.

It's a society (or the whole humanity) becoming big enough to survive even when ignorant murderers are the elite and the majority of it, and civilized people - a smaller part and almost a property, similar to animals in a zoo.

When such a point is reached, the former will make the transition, and the latter will diminish over time. Then it just has no future.

A bit like with Ottoman empire and Qajar Iran, only on the scale of the whole humanity there won't be someone else to buy weapons and technologies from to keep going. Then some of the previously passable filters will kick in. Like hunger or resource scarcity.

Resources often get squandered on trivial vanity and novelty products instead of being channeled into advancing science and medicine. Imagine if we had a cosmic ledger tracking every resource used to develop simple items, like a pencil. It would show countless fires burned and animals consumed just to fuel the human ingenuity required for lumber, materials, and mining. Now, think about how many more resources are required for rockets, heat shields, and life support systems. Extend that to space stations, energy capture, and escaping Earth’s gravity.The resources on a planet are abundant, and nothing is ever truly destroyed. However, we’ve often allocated too much to building flat-screen TVs, leaving little for constructing even a modest space station in orbit, let alone an interstellar spaceship. It's as if the planet offers a finite amount of resources, challenging its inhabitants to focus on space travel. Only a species wise enough to stay on track can unlock the universe's resources. Otherwise, we risk ending up like Australian pines, choking ourselves out in our isolated star systems, having wasted our potential.

Imagine it like interstellar travelling having a single path to achieve it while the path to self destruction is limitless.

I think there are many great filters, but I think one of those filters is fighting over limited resources and wars. Perhaps limited to humans/earth, but I doubt it. Nukes, dropping rocks from orbit, and theoretical (but possible) weapons like black hole bombs are all going to tempt irrational beings to take someone's stuff.

We have to be extremely careful that we don't accidentally trigger a weapon that is going to kill or dramatically cripple our civilization before we become a truly interstellar species. There is so much to learn out there, while so many people are currently focused on the wrong things such as minor conflicts or what children aren't allowed to learn.

I'm sure simply continuing to live will show me more about possible great filters than most teachers could unfortunately.

My guess would be self-replicating biological organisms capable of significant rates of mutation.

But then my preferred solution to the paradox as a whole is basically the "nobody tries" idea.

I don't think there's tremendous reason to try to make ones-self detectable at long distances. It's an expenditure of non-trivial resources for an uncertain result. Since there isn't really any robustly sound logic for making the attempt outside of dramatized sci fi stories, I imagine a vanishingly small percentage of occurrences of intelligent life would make a serious, high-powered attempt at any point.

Maybe it's wisdom.

Every species that might have grown advanced enough, would have gotten over the point of fighting themselves. So they would be wise enough to have something like the Prime Directive in Star Trek (not interfering with less advanced species' until they reach a certain milestone).

sentience. I think it usually immediately leads to suicide

I always thought my Pür was great. /s

Capitalism I can imagine how capitalism could be inevitable. I can't imagine enough controls on it to make it sustainable

For us it's conservatism and its synonyms.

the internet. or some other mass communication methodology. we have developed it before we're responsible enough to have it. there are too many bad actors ready to take advantage of our innate biological tribalism. we'll kill ourselves before we reach very far into space.

I think that for a technological civilization to rise, you need some things to line up. First, life has to be evolved enough to have animals, beings with a brain. Then, a species has to evolve intellence to become a tool making species. This species also has to become the dominating species on the planet. Meanwhile, extinction events, ice ages, climate change and population bottlenecks are always influencing the evolution process.

This is for me the great filter, to have all these conditions line up perfectly for an intelligent, tool making species to evolve and thrive.

I personally find the kardashev scale a pretty terrible way to measure the success of a civilization. Maybe the most successful life forms don't become technologically obsessed materialists determined to colonize everything habitable and drain the resources of everything else, yknow?

Pushing Ice by Alastair Reynolds is one of my favorite scifi books and it deals with this question in an interesting way. It proposes that Time is the great filter. Life exists in this galaxy, but intelligent life is so fleeting when considering galactic distances that the probability of one sentient lifeform finding another during their "peaks" is vanishingly small. Extinction, societal collapse, evolution to a higher form, whatever you want to imagine, it all gets in the way of the fantasy of meeting a thinking being from another planet.

The way the news has been going I wouldn't be surprised if plastic is a candidate. After a little less than a century of rapid development in petrol-plastics we're starting to figure out the long term effects. But the next 1000 generations may be dealing with the fallout.

I don't think there is a single universal Great filter, and living and then potentially sentient beings with various traits will face various obstacles.

First, life needs suitable materials for polymers and a lot of energy. Most places don't have both.

Next, basic blocks of life that would be self-replicating and adaptive should be randomly generated, which is extremely unlikely and literally took over a billion years on Earth, a planet with generally great conditions for such process.

Then, those blocks should be able to get together to form complex structures - ideally, many separate ones, so that one event wouldn't destroy the entire effort. Earth had it easy, with billions of super simple life forms.

Next, assuming life survived up to this point in a potentially unfriendly and ever-changing environment, bombarded by UV light and exposed to myriad of sources of damage, it should not destroy itself or environment too badly to never recover. Earth had periods when life generated too much carbon dioxide or too much oxygen (yes, that too was a thing), and those were critical points at which our story could very much end.

Then, life has to evolutionize and get into complex forms, either by forming multicellular organisms or by making a cell a powerhouse of everything.

Then, life has to get sentient, and some kind of response system should be available and get highly complex.

Then, most of the sentient creatures just won't be tribal, and civilization requires society and a common effort.

Then, many more won't be expansionist, and will die out in some small region.

Many also won't be competitive, which would slow down evolution.

For those species who are competitive, they shouldn't destroy each other while they're at it, and this is currently one of the risks of our own.

And after all that, they should develop space travel and either get as developed and decisive and resource-rich as to send a generational ship to some random planet named Earth populated by genocidal monkeys, or to somehow hyperdrive here. They can very much decide it's not worth it, and they may be so far away we couldn't see signs of their civilization.

Hard to determine with what we know. We haven't met any other intelligent species which suggests we've passed the filter. Yet, making that conclusion before knowing there are no others to meet is too presumptuous. But, if I were to guess, I'd think the filter is adaptability.

We're superior to animals for being able to use tools, live in radically different climates, and shape every spot on earth into a livable climate. Even on Mars, the moon, and space. How else would a species venture through space if they can't adapt?

That might be too general a concept for the question though.

There's a lot of possibilities.

My top contender would be a desire to explore, which probably requires consciousness. Given that we have pretty much no idea what leads to consciousness, it can be guessed (dubiously) that if it arose more easily then we'd have an explanation by now. It could be that it's an extremely rare phenomenon, and there may even be other planets with "intelligent" but mechanistic beings that act entirely for their own survival and don't build civilizations or explore much.

Second would be intergalactic and to a lesser degree interstellar travel. If we assume both 1) intelligent civilizations are extremely rare and 2) faster-than-light transportation is impossible, it could be that everyone is just too spread out to make contact.

Third, and the one I most feel is right but it requires pretending I understand quantum physics (which I don't) and probably offending many that do, is the notion that the concrete universe is not large but small and has no objective existence independent of our respective perceptions, and any part of the universe that's invisible is a mere wave function that will only have concrete reality upon our perceiving it. I make the further dubious assumption that conscious beings can't be part of the wave function. So there.

The Dark Forest theory is a great answer to this paradox. Anyone more advanced has a rational choice to exterminate all competition. We haven’t found any other advanced life because it hasn’t shown up and killed us yet.

Fear. Right now we're on the edge of facing fear or succumbing to it

If there really is a cosmic web and information flows through it, the other solar system will know that we're coming to destroy another world, but it will have developed defensive techniques against a known disease, humans. The same our immune systems does to known viruses.

I went a bit creative with this one.

I don't think life is rare, nor photosynthesis, but complex life might be. A planet needs to be really thriving with life for it to be worth it to go down the path to something like animals

But I think the bigger filter is much stranger.

Humans are a hive-like species. We're not just social - we're insanely interdependent, we don't function on our own and yet we've ended up in this place where we (often) try to individually succeed, even at the cost to our community

We're greedy enough to want the stars, yet interdependent enough we could only swarm over them in endless numbers

There's many problems with the fermi "paradox", but personally I think one of the largest is assuming all species would spread like a cancer blotting out the stars

A more individualistic and long lived species might instead be careful explorers, taking what they need and leaving little sign of their passage. A more communal species might be careful and control themselves to not destroy pointlessly. They might also feel no desire to contact other species

We're just the right mix to want everything a star could give, and to want to find others at great energy cost

I'm starting to wonder if its LLMs. An AGI is something we would be incredibly cautious around and is really no more likely to be psychopathic than any other living thing, the vast majority of which are not. LLMs on the other hand are pushed into every role techbros can shove them into while having less understanding of what they do than a housefly, the potential for damage is immense if someone decides to put one in charge of something important like infastructure or weaponry.

Exponential functions. Seriously. You meet crisis after crisis, each having a risk of ending civilization, but that risk never goes away. It keeps multiplying and multiplying, until you realize the risk curve is approaching a vertical line

One dope-ass 2 pole analogue ladder filter

Your answer doesn't make sense.

"Photosynthesis" is a positive development for life. The great filter must be a negative development: it's a filter or a barrier that keeps life from achieving long term extra terrestrial survival.

So "climate change" would be an answer. Or "fuel depletion" (to which photosynthesis may be a solution). But the filter is the mechanism by which life forms are prevented from progressing.

I think most lifeforms will have more pressing matters than wasting large amounts of time an energy blasting signals in to space for no reason, or listening to the sky.

Maybe those civilizations that waste more energy chasing aliens die off sooner due to wasting resources on sci-fi bullshit and ignoring their real problems at home.