The Great Filter theory advise that all advanced civilizations eventually destroy themselves before adopt the mental ability to colonise quad — a notion that could excuse why we ’ve never been visit by outlander . But there may be another reason for the celestial muteness . Yes , the Great Filter exists , but we ’ve already passed it . Here ’s what this would mean .
Before we can get to the Great Filter hypothesis we have to appreciate what the Fermi Paradox is telling us .
The so - called “ Great Silence ” is the mutually exclusive and antagonistic - visceral reflexion that we have yet to see any evidence for the existence of outlander . The size and age of the Universe suggest that many technologically innovative extraterrestrial intelligences ( ETIs ) ought to exist — but this supposition seems discrepant with the want of observational evidence to support it .
Despite much of what democratic polish and sci - fi would lead us to trust , the fact that we have n’t been chew the fat by ETIs is upset . Our beetleweed is so ancient that it could have been colonize hundreds , if not thousands , of time over by now . Even themost conservative estimatesshow that we should have already made striking either directly or indirectly ( such as from dormantBracewell communication probes ) . [ Image : Mark Gee . ]
Some sceptic dismiss theFermi Paradoxby suggesting thatETI‘s have do and gone , or that they would n’t bump us interesting .
https://gizmodo.com/11-of-the-weirdest-solutions-to-the-fermi-paradox-456850746
https://gizmodo.com/some-of-the-most-plausible-scenarios-for-alien-civiliza-1458148674
Unfortunately , most solutions to the FP do n’t hold for a number of reason , including the actualization that a colonization undulation of superintelligent aliens would likely rework the material of all life-time in the cosmos ( e.g. uplifting ) , or that these solution are sociological in nature ( i.e. they lack scientific harshness and do n’t necessarily apply to the actions of all sophisticated civilizations ; all it would take is just one to think and behave other than — what astrobiologists refer to as the non - exclusivity job ) .
There have been many attempts to decide the Fermi Paradox , include the herculean attack by Stephen Webb in his bookFifty Solutions to Fermi ’s Paradox and the Problem of Extraterrestrial Life .
But one root stand out from the others , mostly on account of its brute elegance : The Great Filter .
consider in 1998 byRobin Hanson , the GF is the troubling mesmerism that there is some kind of absurdly difficult step in the evolution of life — one that precludes it from becoming interstellar .
And like the changeless laws of the universe , the GF is a stumbling stop that holds true across the board ; if it applies here on Earth , it apply everywhere .
Many front upon the GF as evidence that we ’ll destroy ourselves in the future . The basic idea is that every civilization destroys itself before make grow space - faring technologies , hence the empty cosmos . give our own trajectory and the menacing presence of apocalyptic weapons , this scenario certainly seems plausible . We ’re not even close to going interstellar , yet we ’re surely capable of self - disintegration .
But that does n’t have in mind this rendition of the GF is the right one . Rather , it ’s quite possible that human civilization has already pass the Great Filter . Should this be the type , it would be exceptionally good news . Assuming there ’s no other filter awaiting us in the future , it intend we might be the first and only intelligent civilization in the Milky Way .
It ’s a possibility , however , that demand explanation . If the filter is behind us , what was it ? And how did we manage to get past it ? Interestingly , there are some excellent campaigner .
First and foremost there ’s theRare Earth Hypothesis(REH ) , the suggestion that the emergence of life was extremely marvellous for a confluence of reasons . The hypothesis essentially suggests that we hit the pot here on Earth .
This argument , which was first articulated by geologist Peter Ward and astrobiologist Donald E. Brownlee , turns the whole Copernican Principle on its drumhead . Instead of say that we ’re nothing special or unique , the REH implies the accurate opposite word — that we are freakishly special and unique . What we see here on Earth in this solar system and in this part of the Galaxy may be a remarkable convergence of highly improbable factor — component that have resulted in a everlasting storm of conditions worthy for the emergence of complex life .
It ’s crucial to note that Ward and Brownlee are not incriminate that it ’s one or two circumstance that can explain habitability , but rather an integral raiment of happy fortuity . For example , superstar might have to be of the veracious kind ( let in fair to middling metallicity and good distance from grave ethereal object ) , and planets must be in a unchanging domain with a large synodic month . Other cistron let in the presence of gas giant , plate tectonics , and many others .
But even with all the right consideration , life was by no means guaranteed . It ’s quite potential that the Great Filter involved the next bent of steps : the emergence of life and its on-going evolution .
Indeed , in summation to the various cosmogonic and chemical prerequisites for life-time , there were at least three vital stagecoach that could all be consider candidates for the Great Filter : ( 1 ) the outgrowth of reproductive molecules ( spontaneous generation and the issue of RNA ) , ( 2 ) dim-witted single - celled life ( prokaryotes ) , and ( 3 ) complex unmarried - celled lifetime ( eukaryotes ) .
Chemists and biologists are still not entirely indisputable how the first self - replicating molecules came into creation . Unlike its big blood brother DNA , RNA is a single - stranded atom that has a much shorter strand of nucleotide . Moreover , it usually needs desoxyribonucleic acid to reproduce itself , which would have been a problem given the absence of DNA in those other days .
That said , scientists love that RNA is adequate to of procreate through autocatalysis . It does this by stash away information similar to DNA , which allows it to become its own catalyst ( a ribosome ) . This so - calledRNA World Modelsuggests that RNA can function as both a cistron and an enzyme — a pre - DNA conformation that eventually became the foundation for all life .
Given that we ’ve never detected life elsewhere , it ’s unmanageable to lie with how unmanageable this initial gradation was . But that said , this course of living emerge top-notch - early in the Earth ’s story — about a billion age after its formation , and immediately after the cooling of rocks and the emersion of oceans .
But what we do know is that the next few steps — the leap from single - celled life to complex undivided - celled living — was exceedingly difficult , if not highly unbelievable . The appendage of copy a genetic particle is extremely complex , call for the everlasting configuration of proteins and other cellular element .
Here ’s how it in all likelihood happen : Once a self - replicating molecule come forth , the presence of RNA allowed for theformationofprotobionts , a theoretical predecessor to procaryotic cells . These tightly bond bundles of constitutional molecules check RNA within their membranes , which could have evolved into proper prokaryotic cell .
And here ’s where it get interesting . After the constitution of prokaryote ( about 3.5 billion twelvemonth ago ) nothing deepen in the biologic landscapefor the next 1.8 billion years . lifespan in this primitive form was altogether stick . guess that — no phylogenesis for almost two billion years . It was only after the endosymbiosis of multiple prokaryotes that complex unmarried - cell life finally emerged — a variety that was by no means secure , and possibly improbable .
And it ’s this highly improbable step , say some scientists , that ’s the Great Filter . Everything that happened later is a pure bonus .
Now that say , there may have been other filter as well . These could include the emersion of terrestrial organisms , hominids , and various civilizational stage , like the transition from stone age culture to farming to industrial . But unlike the first primal stages already discussed , these are porous filter and not terribly improbable .
So , if the GF is behind us , it would do much to explicate the Fermi Paradox and the absence seizure of extraterrestrial influence on the cosmos . Should that be the case , we may very well have a bright future tense ahead of us . The Milky Way Galaxy is literally ours for the taking , our future completely open - all over .
But before we jump to conclusions , it ’s only bonnie to sharpen out that we ’re not out of the woods yet . There could very well be another GF in the future tense — one just as stingy as the filters of our past . The world , while giving the appearance of bio - friendliness , may in reality be extremely unfriendly to intelligent life .
This io9 flashback is a somewhat modify version of an article that wasfirst publishedon io9 in 2012 .
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