According to the Fermi paradox, there are multiple filters and a great filter that civilizations have to pass to keep evolving. What are these barriers?
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There have been many “great filters” that have been proposed in an attempt to explain the Fermi Paradox. Some examples include:
* Life emerging on a planet
* The transition from prokaryotic/single-celled organisms to eukaryotic/multi-celled organisms
* Rapid development of weapon technology
There are natural and physical barriers, like, the conditions on the planet have to be right for life to form in the first place. If it’s just a big toxic mess of nasty gases and nothing to sustain life, that’s a filter.
Then there’s the biological part, like stuff has to *evolve* properly for life to even get to advanced stages. If you have a colony of like 100 bacteria just chilling somewhere for a gazillion years and they never get the right combination of DNA to start evolving into fancier life forms, then that’s a great filter.
And another natural part, like even if stuff *does* evolve there’s no guarantee it doesn’t get erased when an asteroid decimates the planet or the star in its system explodes and there’s no more energy left for that life to grow from.
And then the technical aspect, even when all the conditions are totally perfect and things are progressing, there’s always the chance we fudge it up ourselves as “advanced beings” – could be a nuclear war destroys life as we know it so we go back a few hundred years and people never trust technology again to continue advancing, could be we destroy the environment and cause irreversible climate change.
A planet capable of harboring life must form in a star’s habitable zone.
Life itself must develop on that planet.
Those lifeforms must be able to reproduce, using such molecules as DNA and RNA.
Simple cells (prokaryotes) must evolve into more complex cells (eukaryotes).
Multicellular organisms must develop.
Sexual reproduction, which greatly increases genetic diversity, must take hold.
Complex organisms capable of using tools must evolve.
Those organisms must create advanced technology needed for space colonization. (This is roughly where humans are today.)
The spacefaring species must go on to colonize other worlds and star systems, while avoiding destroying itself.
The Drake equation lets us hypothesize how many planets exist that can have life (or even intelligent life).
The Fermi paradox says “if there are potentially so many of these planets why haven’t we seen any evidence of life outside Earth?”
The answer to that is The Great Barrier. We haven’t seen evidence of life outside Earth because of reasons. We can only guess at the reasons.
Perhaps life from non-life (abiogenesis), which is how we think life may have happened on Earth is unbelievably rare. We haven’t been able to reproduce it.
Perhaps going from single-cell to multi-cell to intelligent life is so rare we may be the first to have done it. Not that it’s impossible but maybe it’s not out there yet.
Perhaps life that becomes sentient and intelligent always destroys itself before it can become a type 2 or 3 civiization.
There can be more. The main concept is that there must be barriers to becoming noticed by us, and we don’t know if we have passed our barrier, or maybe our barrier is out there to destroy us in the future.
Quick note: these aren’t filters that we know for sure exist, they’re just *possible* filters that stop species from becoming intelligent, spacefaring civilizations, and there’s no definitive list, iirc. They’re broadly split into two groups, those bring ones humanity had already passed and those we have yet to pass.
The already passed filters include:
– planets with conditions for life are just rarer than we think
– life (or intelligent life) is just really rare
– development of modern-level technology is rare either because species can’t hit a certain necessary bar (like aquatic life being unable to use fire or the possibility that maybe humans are just really good inventors even among all intelligent life) or they kill themselves before
The to be passed filters include:
– development of nuclear technology usually leads to a nuclear apocalypse before a species can colonize other plants
– industrial ages run a species home planet into the ground before they can set up independent colonies and most species can’t cooperate enough to stop it
– another spacefaring alien specie kills of other species once they hit a certain technology level
– there’s some technological barrier or challenge we don’t yet know about that kills of or prevents development past a certain point
I’d have to look em up to find all the big ones, but does that give you an idea?
Okay, instead of giving specific examples let’s first think about a definition:
A great filter is any requirement, obstacle or scenario that is likely to happen no matter the origin point, and that if not worked out successfully has the potential to inhibit a formation of a civilization before it gains the ability to communicate it’s own presence to other such civilizations. This is the technical explaination of the term, but in simpler words it just means anything that might happen that results in an alien civilization either not forming, not achieving technological progress, regressing in progress, or completely dying off before they are detectable by us – if you assume that the answer to Fermi Paradox is that “other civilizations capable of communication don’t exist” then the great filters are possible reasons as to “why they don’t exist” that can be universally applied to most hypothetical alien life scenarios.
There are several categories of great filters depending on which stage of intelligent civilization development we are talking about:
– Complex life never forms: the leap from prokaryotic to eukaryotic life is extremely rare, leap from cellular to multicellular is pretty rare, leap from simple autotrophs to more complex organisms is rare, leap from complex life to intelligent life is pretty rare.
– Intelligent life never forms civilization: most intelligent life forms in the universe stay as hunter-gatherers, agricultural societies die out to new illnesses before they get a chance to spread.
– civilizations never go technological: most civilizations stay at the tribal level, most environments in the universe lack resources necessary for technological progress(for example oil or substitutes), most civilizations face the “roman cycle” achieving a certain level of progress too fast then crumbling under themselves losing that progress
– Technological civilizations kill themselves off before achieving communication: all civilizations are prone to war and as such they kill themselves off with weapons of mass destruction, there is a dangerous technology in our future that we are not aware of that is deadly if created that destroys most civilizations, there exists a point of technological singularity where we can’t control our progress anymore and it takes us over, there is a point of reverse singularity that lays before us achieving the ability for long distance communication resulting in it simply being not possible, natural technological progress leads to exploitation of the biosphere and global climate change resulting in civilizations making their planets inhospitable.
We don’t know if great filters are really a thing and what form they take if they are.
The problem is we are working from a sample size of one. Everything that happened to get us where we are now did happen to us and in retrospect it is quite hard to tell how likely any of it was.
If you win a lottery or get hit by lightening you know that this was pretty unlikely simply by looking at all the people it didn’t happen to.
We don’t really have anyone else to compare things to.
We don’t know if for example the evolution of multicellularism was something that was unlikely or if this is happen that happens in some form every place life evolves. We aren’t even sure if multicellularism is a necessary step to reach the goal of building advanced civilizations that are noticeable from distant stars.
We do know that it took quite a while to happen here, so it seems like it was a big hurdle, but that is just basing things on how they went here.
We only know that we have come as far as we did, that if we only go a bit further we will have reached a point where we would be noticeable by any other civilization on our level in the area and that we can’t see any other civilization that has reached such a level.
We can only assume that reaching that level must be very hard if no one else has done it before us.
We can make guesses about which events in our past would could have been what stopped others from reaching that goal. And we can speculate about hurdles in the future.
We know some things by now like planets being pretty common and the building blocks for life being common too.
We can look at some parts that might make us special.
We look at our history and an pick out some developments were all the ingredients were there for a long time without it happening and consider those rare.
We can also look at things that might do us in in the future. The idea of any sufficiently advanced civilization killing itself of as it develops technology to dangerous to handle was certainly popular during the cold war, but that seems unlikely as most of the candidates would just be a set-back not an end.
We really can’t know for sure until we meet some alien civilizations and compare notes or at least find some alien ruins and figure out what did them in before they could colonize the stars.
The Fermi paradox is that statistically, with so much universe, there should be lots of intelligent life out there. Yet humans haven’t met aliens.
There could be many reasons, but the broad categories are that:
A. Humans and Earth are just that special somehow- we are the first or only intelligent life to evolve
B: there is some reason that space faring can’t happen- maybe the speed of light is the fastest anything can go. Maybe the societies of intelligent life have a limit.
The great filter is that second category.
A video by Kurzgesagt explaining the Great Filter. They also have other vids on the topic like the Fermi Paradox.
Global warming, nuclear war, out of control biological warfare/extinction causing epidemics, asteroid/comet impacts; anything that could wipe out an intelligent species.
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