The Great Filter is the idea that, in the development of life from the earliest stages of abiogenesis to reaching the highest levels of development on the Kardashev scale, there is a barrier to development that makes detectable extraterrestrial life exceedingly rare. The Great Filter is one possible resolution of the Fermi paradox.
https://en.wikipedia.org/wiki/Great_Filter
The Fermi paradox is the discrepancy between the lack of conclusive evidence of advanced extraterrestrial life and the apparently high likelihood of its existence. As a 2015 article put it, “If life is so easy, someone from somewhere must have come calling by now.”
https://en.wikipedia.org/wiki/Fermi_paradox
Personally I think it’s photosynthesis. Life itself developed and spread but photosynthesis started an inevitable chain of ever-greater and more-efficient life. I think a random chain of mutations that turns carbon-based proto-life into something that can harvest light energy is wildly unlikely, even after the wildly unlikely event of life beginning in the first place.
I have no data to back that up, just a guess.
I think that the great filter/fermi paradox is a combination of two facts,
- 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.
- 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.
Accidentally replied instead of editing to fix a mistake. Disregard comment.
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.
But surely generational ships would get us over that?
AFAIK there is no known energy source that would keep a generation ship powered for the duration of an interstellar flight.
The person to whom you responded is half right. The speed of light is half of the barrier to interstellar travel. Entropy is the other half.
Would you need a power source? If you aim your ship correctly, then put everything alive into cryo, the ship could go completely dark, vent all heat and become a frozen rock. Then after [very long time] the ship enters the vicinity of a different star and can be reactivated and unfrozen using solar energy. You dont need energy to maintain cryo if the whole ship is at 1° kelvin.
(Of course that relies on cryo sleep being possible)
just reverse entropy
Also, you’d need to know for certain that the planet you’re sending your generation ship to is habitable for your species. While this may be technologically trivial for a society that can build a functional generation ship, the timescales for such projects (literally hundreds or even thousands of years from the launch of the probe to the yes/no signal) makes it extremely difficult to actually organise.
That and you won’t even know if the destination civilization is still there by the time you arrive.
Not really, no. Generational ships might make colonizing the nearest star systems possible, but even colonizing our own galaxy would require some kind of suspended animation. The milky way is between 100,000-200,000 light years in diameter so even at the speed of light, you’re looking at a travel time that is ~33-66% of the time that humanity has even existed(homo sapiens are currently estimated to have become a distinct species 200,000-300,000 years ago)… just to go to ONE star system out of the hundreds of BILLIONS that exist in our galaxy. You’re gonna need generational ships so self-sustaining and capable that the generation that actually arrives at the destination will have long forgotten the point of the trip and might not want to leave the comfort of the ship.
Still, colonizing our own galaxy is at least theoretically possible, given enough time. The real filter is just how unimaginably large the universe is. The vast, VAST majority of the observable universe is FOREVER out of our reach, as it is expanding away from us faster than the speed of light. Then there’s the unobservable universe, which could literally be infinitely bigger than the observable universe for all we actually know.
Until we figure out how that is possible outside of theory, it is just that. We have no plans that address actually keeping a spaceship working on such a timescale, and keeping the crew alive on top of it.
Considering we haven’t seen any generational alien ships visit, it seems like nobody else has figured it out yet, either.
No. At best maybe a few reach the nearest inhabitable solar system.
Information can travel at light speed. So, I think there’s more to it personally
Light speed is very slow
That is very sad.
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.
I’m gonna add to this by saying phosphorus may be my favorite, but I think the most likely filter is just time, twice.
Do you know how unlikely it is that earth has been habitable for so long? Do you know how long life was single-celled? One of the theories for how advanced (eukaryotic) cells formed was the combination of at least three different branches of life into the same cell! Archaea (cell wall), bacteria (mitochondria/chloroplasts), and viruses (nucleus). Do you know how unlikely that sounds? Do you know how long it would take for that to happen randomly? Most planets probably aren’t even habitable for that long. Once we became eukaryotic, we started progressing much faster.
Then, keep in mind, the life has to continue to exist for billions of more years while it waits for the advanced life to happen again within the same section of the galaxy. So, time is two filters - both behind us and in front of us.
Thanks, I’ll check it out!
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.
That’s a really neat idea I’ve never heard before. Like, maybe our entire universe is analogous to the ocean floor sea-vents that life arose out of. Cold, and dead, and boring, and difficult. And one day we’ll discover how to ascend.
I also like this theory. In the Ian Banks Culture series civilizations that get advanced enough head off into the “sublime” they call it. Basically a higher level of existence. In my own more simple version, I’d figure VR and the biological/cyborg mix get so good the powerful can start living kind of forever, so they head for that substrate and don’t need big megastructures for anything, they just need computing power.
Yeah, it seems very possible that at one point, civilization will turn inward instead of outward. Why go through the time and effort to colonize the stars when you can just create a cyber-utopia? If you’re advanced enough, you could make it feel like an eternity while almost no time passes on the outside.
Sure, your planet might get destroyed by a cataclysmic event in the far future, but if you can make that feel like billions or trillions of years, who really cares?
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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.
I think at some point, almost certainly not in our lifetimes, we’ll detect the spectroscopic signatures of a planet that has an atmospheric makeup that HAS to be from life, but with no detectable signs of any civilization. Just nonsentient life. And we may never be able to get there.
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.
The “Dark Forest” is fine for a scary sci-fi series, but it has many flaws that make it unrealistic as a real solution to the Fermi paradox.
- Earth has been quite obviously life-bearing for at least 2 billion years. We should have been wiped out long ago.
- The book series made up fantasy magic tech for how exactly a civilization can be destroyed by another without giving away their own location. I’ve yet to see an explanation for how that would be done in reality that doesn’t give away the attacker’s location.
- It doesn’t explain why nobody has colonized the galaxy.
I think others wouldn’t bother with us until we started demonstrating likelihood of using dangerous tech or crazy exponential expansion.
I don’t remember well, but I think civilizations stationed their defensive or offensive tech away from their own civilizations, just dispersed around.
I think its explanation for why no one or anything has colonized the galaxy though is that if anyone shows signs of becoming that strong, they get zapped. Nobody wants to see a neighbor rise up into a behemoth, you get that bold you’re a threat.
My real preferred theory of why we don’t see other civilizations though is that I think they choose more inward, VR, computer-based evolution that doesn’t result in big mega structures.
I think others wouldn’t bother with us until we started demonstrating likelihood of using dangerous tech or crazy exponential expansion.
Why do you think that, though? It doesn’t make sense, frankly - if you’re worried about competition evolving you shouldn’t wait until the last possible second to destroy it. That raises so many unnecessary risks of being slightly slow on the draw, and then it’s too late. Why not do it at the earliest convenience, when it’s super easy to do by comparison and there’s an incredibly long margin of error if you somehow miss the first couple of tries?
I don’t remember well, but I think civilizations stationed their defensive or offensive tech away from their own civilizations, just dispersed around.
I think its explanation for why no one or anything has colonized the galaxy though is that if anyone shows signs of becoming that strong, they get zapped.
But they’re already doing it, you just said they’re putting outposts out there. If they can’t do that secretly then the Dark Forest doesn’t work in the first place. Placing a secret weapon base in another solar system is no different from placing a colony there.
My real preferred theory of why we don’t see other civilizations though is that I think they choose more inward, VR, computer-based evolution that doesn’t result in big mega structures.
As with many Fermi paradox solutions this one fails on account of requiring every single civilization (and every single subset of those civilizations) to all decide to do exactly the same thing, forever, with no exceptions. In a scenario like this what happens if a single subculture of a single advanced civilization decides for whatever reason that they prefer not to do that? They would be able to spread throughout the cosmos without opposition, everyone else is locked in their little dream boxes and therefore is basically irrelevant. It only needs to happen once, and the universe has been around for a very long time.
I agree, I don’t think they’d wait until the last possible moment when the civilization becomes super powerful or builds the mega weapon. I just mention it along the range of development to highlight the why.
I think they might let weaker civilizations keep going, though, just out of hope they wouldn’t be too mean. Also, zapping other civilizations when you don’t need to exposes yourself and your own aggression.
About the shift to VR /computer substrate worlds that wouldn’t have huge footprints, I agree that not all would do that, and it only takes one to go the big building and footprint route and it’s weird we don’t see it.
My guess then would be that maybe they do build big, but they just conceal well…? You get good enough tech at some point you can choose to be hard to see.
I’ve never read the three body problem (started it but just couldn’t finish…it was very slow paced and there were moments when the Chinese…I don’t want to call it propaganda but more like promotion…took me out of it, like the supposedly international coalition of scientists where the non Chinese ones were just cardboard cutouts) but I can speak to this:
The book series made up fantasy magic tech for how exactly a civilization can be destroyed by another without giving away their own location. I’ve yet to see an explanation for how that would be done in reality that doesn’t give away the attacker’s location.
Relativistic missiles. Nothing moves faster than the speed of light. So if you can get a big rock to go 95% of the speed of light, we’d only be able to detect that it’s coming right as it hits. Sure, you can calculate the origin of the missile after it obliterates its target, but it’s almost impossible to form a counterattack especially if the attacker just yoinked an asteroid from a different star system than their own and strapped an engine on it. And ESPECIALLY if your civilization is still mostly planetbound.
And a rock moving at some appreciable fraction of the speed of light could obliterate the Earth.
Relativistic missiles. Nothing moves faster than the speed of light. So if you can get a big rock to go 95% of the speed of light, we’d only be able to detect that it’s coming right as it hits.
This is a very common answer to “how”, but it comes with lots of problems in the Dark Forest context.
- If you actually calculate how much energy is required to boost a big rock up to that speed you run into lots of difficulties. It takes a lot, a heck of a lot. How does a civilization that is “hiding” accumulate that energy? How does it store it long-term?
- How is that energy actually put into the rock? This is basically a starship accelerating up to that speed and getting a starship up to that velocity is not easy even if you have the energy available. Does it have a rocket? The rocket equation for getting up to near-lightspeed requires ridiculous amounts of propellant. Is it beam-propelled? You’re not being at all stealthy that way. How much acceleration can you get out of your system? It takes a full year at one Earth gravity of acceleration to get up near lightspeed, and that’s a really high acceleration - you generally trade acceleration for efficiency so the faster you want to get up to speed the more energy you need and the noisier you’ll be.
- It actually is possible to counter an RKV. It’s much easier to hit and destroy an RKV than it is to launch it, all you need to do is get a pebble in its path. The key is detection, and the above points give some pretty good options for detecting it before and during launch. That gives you time to fire your countermeasures.
And ESPECIALLY if your civilization is still mostly planetbound.
Absolutely not guaranteed to be the case. Earth’s civilization could have easily had offworld colonies by now if circumstances had been slightly different, so a Fermi paradox solution that requires reliably blowing up Earthlike civilizations before they can get offworld doesn’t work. They’re already too late.
As I said previously, Earth has been quite obviously life-bearing for at least 2 billion years. Why wait until something like an RKV is needed, and even that is not guaranteed? They could have destroyed life on Earth far easier, and thus far more stealthily, if they’d done it a billion years ago.
Tbf we are noises as fuck. We’ve been sending so much out for decades.
Sure, but it’s just small game chatter. We start building a Dyson sphere powered starkiller cannon or some such nonsense we might pop up on somebody’s radar.
The problem for the Fermi paradox is that there’s no reason to do stuff like that before we start colonizing other solar systems.
Also, how do you destroy a civilization that has a Dyson swarm already? That’s not exactly an easy task, and if you insist on remaining stealthy yourself it’s nigh impossible.
Military Industrial Complex: “Hold my beer”
The galaxy is a bowl of M&Ms. One of every hundred M&Ms is poisoned and will immediately kill you. It’s only a 1% chance you’ll die. Well maybe pike 5% if you eat a handful.
Most of the civilizations might even be moral enough not to destroy us, but all it takes is one.
How do they do it, though? It’s not really a valid solution unless you can explain how it works, otherwise it’s just “maybe some magic happens that kills civilizations.”
Once a civilization has begun spreading to hundreds of other solar systems I have yet to hear of any plausible way to reliably “kill” it.
Yep exactly. Who knows how murderous other civs might be, maybe they’re nice but maybe not.
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.
Yeah, I have a gut feeling that a lot of the variables in the Fermi equation are a little too generous.
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.
Speaking of our moon, the fact that it’s roughly the same size as the sun as seen from earth and the fact that this is a complete coincidence blows my mind. Like there’s no reason for that to be the case. Total eclipses like ours (where you can see the corona) are very rare.
Even more so, the moon is slowly moving away from the earth. A couple of million years ago, it would have completely covered the sun. In a couple of million years, it will not fully cover the disc.
A million years is a long time for humanity, but a blink on the timescale of moons and stars. We didn’t just luck out with the moon’s large size, but also with the timing of our evolution.
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.
There seem to be so many coincidences that make our solar system unique that it’s really upsetting lol It’s like we are so perfect for stability because of things like Jupiter keeping the inner system “clean” of large impactors, our part of the galaxy being more “quiet” than typical as far as supernovae, stuff like that which makes it seem even less likely for life to exist anywhere else. :(
Life will almost certainly be fairly common, given the right conditions. On earth, it seems to have appeared not long after conditions made it possible. We either won the lottery on the first week, or the odds aren’t actually that bad.
The problem is, we can’t detect life right now. We can only see potential communicating civilisations. These are a lot rarer. We currently know of 1, humanity. That will change in the next few years. We have telescopes being designed/built capable of detecting the gasses in the atmosphere of an earth sized planet. While we won’t recognise all life types this way, a lot will show up in abnormal gasses, e.g. free oxygen. This should help bound the possibilities a lot.
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.
My suspicion is that it’s abiogenesis, but it’s only a suspicion that I can’t have any certainty of
Definitely the simplest answer and aligns so far with out observations.
Nah, I’m willing to bet there is actual physical life in our very own solar system (apart from all life on Earth, of course). Europa’s oceans for example have a decently high probability of hosting microbial life.
Of course, discovering primitive life all around us would be a bad sign the great filter is still ahead of us instead of behind us…
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 definitely subscribe to the “humans are insane” theory of galactic lifeforms
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!
I agree. The threshold for becoming the “dominant species” of a planet is so low that the species still has its primal wiring for tribalism, competitiveness, etc. by the time it can build rockets. We humans should’ve had more time in the evolutionary oven to become more empathetic and cooperative for longer-term survival. Instead we have people willing (and able) to literally burn the world down to become richer or more powerful. And we have most of society cheering them on.
We’ve been on the verge of destroying ourselves for decades now, and humans have just barely started doing space stuff (a blink compared to the life of the universe). How in the world can anyone expect us to get to Dyson sphere levels of progress with how fragile our existence is?
Unfortunately, I think this is the most likely scenario. Going from our modern technology levels, which are more than capable of destroying the world, to Dyson spheres is a huge leap that will take who knows how long (decades? centuries? millennia?).
Before that happens, we have to live together on a planet without blowing ourselves up or making the planet uninhabitable. As technology continues to advance, walking that knife edge of survival seems more and more difficult. The pessimist inside of me says that no civilization has been able to accomplish it.
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
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).
Oh my god, that’s such a stupid and simple way to kill a galaxy, but also what a great plot twist that would make in a story. Like the big reveal over why the galaxy has always been at war with itself. Exactly the kind of nihilism I’d expect from an Altered Carbon or its ilk.
Thanks for sharing!
You might like the paperclip maximizer thought experiment
Also an excellent clicker style game called Universal Paperclips
Thanks I have heard of this kind of problem before, just not in an adversarial space war context, with like opposing forces
There’s an easier and more reliable way to limit replication; don’t hive them the means to create a small but essential part, and instead load the first probe woth many copies of it and have each replica take a set percentage.
For instance, have the probe able to replicate everything but its CPU, and just load up a rack of them on probe 0. Every time it replicates itself it passes half of its remaining stock to the replica and they both carry on from there.
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.
