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.
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!
Throwing in another similar YouTube suggestion of John Michael Godier
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.
This is my favorite, mainly because it’s been well argued by some respectable scientists.
Another is that we’re in a simulation, and aliens aren’t part of it. There are also some very good statistics pointing to the simulation theory, from just sheer scale.
I do agree that in the grand scale of things we’re actually very early. That alone would explain a lot.
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 think you’re probably closest. There aren’t “filters” so much as we live in a universe that can only support life on a highly contingent basis, entirely by accident, at random intervals. It’s filters all the way down, really. None of us are getting out alive, might as well enjoy it while it lasts.
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.
That’s nuts. In two million years, humans will be sighing and saying wistfully “if I had a time machine, I’d want to go back to the time of the full eclipses, like 2024”
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.
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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 think it’s supposed to actually less than that, the sun’s luminescence will increase over the next 1 billion years to the point that it will boil off the earth’s oceans. No life will be able to exist past that, and earth will just be a barren rock in orbit for the next 3 billion years.
While that is true I would counter point that humans have a bit of a handicap as earth got hit by a big astroid that killed just about everything on it making terran life have to start all over again but at the other hand I saw someone else on here mentioned that oil has given us a head start at space ferrang advancement and oil is made from dead life so granted I haven’t done much reacerch on how oil forms naturally but I do wonder if we would have oil if earth never got blown up but on top of all that there are theorys that mars used to have life so if astroids haven’t interfered with our solar system intelligent life may have formed faster and maybe twice also there used to be multiple species of humans in the past so maybe 4 or five times in the same solar system
That is an interesting idea that is not typically considered in the drake equation as far as I know. That could significantly reduce the chance of finding intelligent life elsewhere.
It may very well be republicans
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.
A filter for sure, but not a great one. Call me optimistic, but I don’t think that will set us back more than 10.000 years. If humanity can survive, society will re-emerge, and we are back here 2-3000 years into the future.
Is +5°C Earth a good place to be? No. Will the majority of humans die? Absolutely. Will the descendants get to try this society thing again? I believe so.
On a cosmic scale 10.000 years is just a setback, and cannot be considered a great filter.
Unfortunately we’ve pretty much used up all easily available resources. Anyone ‘starting over’ would have a much harder time getting the things they need to really get the ball rolling again.
When humans first discovered gold they practically only had to scoop it out of rivers. You’ll be hard pressed to find any streams with such appreciable production anywhere in the world today.
We’ve already discovered fission and photocells. We’re past the point of needing fossil fuels for a new civilization (or existing civilization). Fossil fuels are only hanging around for economic reasons.
I think that is thinking a bit too narrow. A lot of the stuff we use today might just be our bronze to our successors iron - you can build an unstable society on either. And what we do use up today could still work if used more efficiently - we might not have enough rare metals to give everyone a smartphone in the post-post-apocalypse, but I could see us still launching satellites if only big governments had computers - because they did.
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.
Sort of fallacious to go from one case of time to happen and derive probability from it.
I’m no biologist but I don’t think any of our models of super early stuff are sophisticated enough to speculate on what stages are the most or least likely.
You are correct, but that doesn’t mean I can’t speculate about it.
The ability to do photosynthesis is widely distributed throughout the bacterial domain in six different phyla, with no apparent pattern of evolution., according to this random paper I found on the internet (I’m not a biologist either).
What I can glance is that photosynthesis has (probably) evolved independently 6 time in Bacteria and 3 times in Eukaryotes.
Plants evolved to photosynthesise after photosynthesising bacteria already existed for billions of years.
(But then we have to also acknowledge that multicellular life evolved like 25 times in Eukaryotes, and the Eukaryote - aka Mitochondria-“Powerhouse of the cell”-haver- is the real big step as it only happened once to our knowledge).
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.
Isn’t the fermi paradox specifically dealing with detection tho? Not just travel or communication.
I suppose I was focusing on detecting some sort of communications. It still matters that when we see objects at great distance in space, it’s the objects in the distant past
This universe being unfriendly to interstellar and especially intergalactic travel would seriously hamper a galactic civilization, and thus be less likely for us to notice them.
There might be hundreds of civilizations out there, each having only expanded to a few dozen stars, not caring to go further. Even the makeup of the interstellar medium might be incredibly dangerous, basically necessitating generation ships to cross. Large scale expansion might simply be too hard.
That expansion at an accelerated rate - that’s just so eerie when you think about it. The furthest objects we can see right now will slip away out of reach forever for the next generation, and so on. It’s crazy to think that as time goes on, there will be less and less universe to observe.
That’s something really interesting, though. When we look at distant objects, we aren’t limited by the distance they’re at right now. We’re limited by the distance they were at when they emitted the light.
So the observable universe is still growing because the edge of that bubble is such a long time ago that everything was still much closer together.
But the light that reaches us is constantly getting stretched (red-shifted), so I’m not sure that our bubble is growing. Instead when they’re stretched too thin, we won’t be able to see it. I’m not 100% sure on the expansion rate of the universe and the pace of red shifting. Also, eventually all the galaxies are expected to be pushed so far away from each other due to the pressures exerted by Dark Energy, that soon we’ll only be able to see just the stars of our Milky Way.
One of the weirdest facts. One that really makes you feel so small.
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
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.
Time.
Is on my side
Yes it is
