We can't honestly have any practical discussion about the concept of a Great Filter until we get to the point that our observational capability would be sufficient to reliably detect another civilization at a similar level of development to our own within a sufficient size search space: within our own galaxy for instance. Considering that 68% of the universe's energy and 27% of its mass is still basically unaccounted for, it's clear we have a very long way to go before this idea is worth bringing out of the halls of existential philosophy.

Let's say for the sake of argument that a civilization exists in our nearest neighbor system, Proxima Centauri. Let's assume that it has developed with a similar impact to their system as humans have had to our own -- radio emissions, a handful of interplanetary and interstellar space probes, nuclear tests, etc. Could we detect them? Everything I have read concludes that we currently could not. The concept of being able to receive interstellar TV transmissions is such a sci-fi trope I don't think very many people consider that it is essentially impossible.

The argument is that on this timescales they would be here for now.

But all this doesn’t really matter since you can’t apply frequentist logic in bayesian situation: what we observe is exactly the same as someone in the long tail of distribution would observe, i.e. we can’t distinguish between this being unlikely situation and being first, or this being proof of Great Filter.

Hmm, maybe I'm missing something, but the main argument for the Great Filter is that we haven't observed any extraterrestrial life. If we started observing that life, that might just mean that so far our observation technology has not been good enough previously.

We can't detect life at our stage of development from afar, or from earlier stages, but things that extremely advanced civilizations build like dyson spheres can't be hidden really.

The issue is that the universe is extremely old compared to how long it took for earth to develop life. It's ample time for civilizations to develop technologies extremely far more advanced than ours. So why isn't there a single civilization that's so advanced that it builds these things?

So there must be some "filter" that prevents civilizations from doing that, whether they are alive or dead. Maybe they just don't want to, but then ALL of them have to not want to do it, which would be weird.

If we detect life close to us, it makes it more likely that there is tons of life around the galaxy, which makes it more likely that the filter is ahead of us. If we detect no life close to us, it makes it more likely that the filter is past us.

See this Kurzgesagt video about the topic: https://www.youtube.com/watch?v=UjtOGPJ0URM

I don't like that theory, it's completely limited by our current understanding of how a "more advanced" civilization would look like. If we haven't seen signs of what we think more advanced civilizations would look like, the simplest explanation is that what we think advanced civilizations are like is wrong

I agree. Saying that a Dyson Sphere is something that an 'extremely advanced civilization would build' presumes that we can project the course of civilization. Seems presumptuous and short sighted to me.

Yeah a Dyson Sphere contains the presumption that an advanced alien civilization's population would grow exponentially like earths population did in the 20th century.

I don't know how you square a utterly stupid idea like exponential population growth with the word advanced in advanced civilization. Instead this sounds like blinkered mid twentieth century thinking. Or the old science fiction trope of seeing the future as like the present but more of it.

> The issue is that the universe is extremely old compared to how long it took for earth to develop life

I wouldn't call the universe very old. It's only like 13.x billion years old. If you take into account the amount of time it takes for heavier elements to be created, the time for the universe to settle down I'd say we are in the first cohort. It took us 4.5 billion years to evolve and if humanity got wiped out life on Earth would most likely continue on as it has for millions of years before with megafauna.

Looking at how life appeared immediately after the planet cooled down and had liquid oceans most likely indicates abiogenesis is common, multicellular may be much more rare and intelligence probably is exceedingly rare given how expensive big brains are. I just don't think there was enough time in the early universe for intelligent civilizations to have evolved.

My preferred solution to the great filter is to assume that things like Dyson spheres can't feasibly be built, at any level of technological development.

So there may be millions of civilizations that can get into orbit with chemical or nuclear rockets, but not a single one that can carry out a megaproject that could be seen from Earth.

I've always thought it made more sense that microbial life with took billions of years to develop, and originated someplace other than earth. The reason we don't see hyper-advanced civilizations is because intelligent life is only just starting to pop up alongside us, right now, and perhaps we're one of the earlier manifestations.

It's not my domain, but there are apparently some markers of genetic complexity that give some weight to this theory: https://arxiv.org/ftp/arxiv/papers/1304/1304.3381.pdf

Personally I think life originated on earth. We shouldn't look at contemporary prokaryotes to determine how complex prokaryotes were at the start of life. They had billions of years to develop as well and if the more complex ones are fitter than the less complex ones, they will win. E.g. you think rotting plants is a normal thing but there was a time when plants wouldn't and just form giant heaps, forming the coal reservoirs of today.

Anyways, let's assume life originated at some other planet and it has started life at half of the galaxy at the time it reached earth (so we weren't lucky to be "close" to the origin).

Earth is 4500 million years old, and life is assumed to have existed here since 4400 million years. So intelligent life took 4400 million years to "develop" here on earth. Light speed allows you to colonize the milky way comfortably within a million years. What if it takes 100 million years less on some other planet? Or it took just 10 million years less?

Either earth is very close to the real origin (or has been at the start of life), or the filter is in the past, or some other explanation.

This theory is actually proposed by Nick Lane et al - it says that microbial life is probably ubiqutuous and that complex life is not and was a happy accident on Earth, which means its very improbable on other planets. The prereqs for it happened only once on Earth, when one microbe swallowed another and the smaller one became mitochondria enabling complex cell structure and shape. Given that microbial life exist in extreme environments on Earth and that its prereq is just a hot molecular soup, its probable it exists everywhere. On the other hand, the 'happy incident' didn't repeat on Earth to create another complex cell form - all higher life uses the same cell structure.

That's what the great filter theory means when they talk about it being behind us -- we don't see life in other places because developing to where we are now is almost impossible.

I don't buy it though -- we're in an average planet on an average star, nothing about our environment seems to be particularly rare.

I think the statement that we are on an average planet deserves more scrutiny. We have yet to observe another planet like ours.

There are a number of Earth's attributes that we don't understand and have poor extra-solar data on. Particularly, the following:

Technically active plates after 4.5 Byrs. Effective magnetic core after 4.5 Byrs. Large amounts of surface water, presumably from our late heavy bombardment. Small enough to leave with a chemical rocket while meeting the above.

All those 'limitations' are too much anthropomorphic for my taste - life can probably exist in far more niches.

Also, at our current tech level, planets are very hard to even observe for existence, let alone their geographical features.

I tend to agree with both your points, but was addressing the specific claim that Earth-like conditions are average, or at least not particularly rare.

We simply don’t have data to support that claim, and the parameters required to make earth habitable for life (as we know it) are vastly more numerous than most people acknowledge.

Lets start with Oscam Razor then: its wast universe. Even on Earth, there are untouched places. All other theories compared to this one, which is easy to understand and also already known to be in effect on this planet, are as close to the truth as theory that great filter are evil pink elephants in the center of the galaxy.

> I've always thought it made more sense that microbial life with took billions of years to develop, and originated someplace other than earth. The reason we don't see hyper-advanced civilizations is because intelligent life is only just starting to pop up alongside us, right now, and perhaps we're one of the earlier manifestations.

This explanation does not work, because of the timescales.

Five thousand years ago, we built the Pyramids. Fifty years ago, we landed on the Moon.

In contrast, it took four billion years to go from single-celled life, to the pyramids.

The odds of us being first by happenstance are astonishingly small. It's much more likely that either we are unique, or that civilizations don't leave much of a trace outside of their solar systems, regardless of whether or not they die out in the blink of a cosmic eye.

We simply haven't developed enough yet. It wouldn't be good game design to encounter other civs at this stage.

Tutorial level civilization.

You must complete energy collection on current planet for XP to advance to level 2.

> If we detect life close to us, it makes it more likely that there is tons of life around the galaxy, which makes it more likely that the filter is ahead of us.

Isn't is the other way around? I though that the main argument for the filter ahead of us is that we haven't found any civilization, which means civilizations cannot develop past some level at which they can be detected by us. But if we'll have found one, this means that such level of civilization can be passed, and therefore reduces the chances that there is a filter.

I think by "life" the parent was talking about microbes on Mars or waterbears on comets or something. Technology developing life is a different thing entirely. If we find primitive life nearby, then there probably is primitive life everywhere, and very little technology developing life (because of the "filter").

Yeah, detecting life could mean many things:

- The filter is ahead us

- There is no filter

- The filter is behind us, but ahead of the other planet

- Both planets have successfully got past the filter

We'll still be debating :). Then we'll go crazy trying find evidence of life in more planets.

An addition to there is no filter (yet):

- We're one of the first nearby and we're going to help build a filter

The various AI we give birth to over the next two centuries are going to dominate several galaxies. There are many filters - competing standards - throughout the universe, our galaxy doesn't yet have one. Humans will cease to exist as we think of them now, within those two centuries (and not due to climate change or any other similar event).

that said, the likelihood of there being _no_ filter is still lower than the others.

if we detect life so near to us and _yet_ we still have yet to encounter life from another planet means there's likely still _some_ kind of filter. So I don't think the likelihood of no filter is high if we detect life

Rather then apocaliptyical filter, the most probable reason is that space is so wast that even if advanced life was common, chance of meeting/observing one would be next to 0. Think about our civ living on a sand grain in the desert - the chance is almost 0 to encounter another civ living on sand grain on random desert location no matter how advanced your tech is.

yikes - that's true, we could still move life beyond earth and still never meet another civ. I didn't realize this at first but I was conflating the two

just learned about the "great filter", very interesting. I think it does mean that our observation tech is not good previously - it also sounds like if we did start observing life, the fact that we have yet to be visited / colonized by that life form means only re-affirms the unlikelihood of interplanetary travel..

according to [wikipedia](https://en.wikipedia.org/wiki/Great_Filter):

> So by this argument, finding multicellular life on Mars (provided it evolved independently) would be bad news, since it would imply steps 2–6 are easy, and hence only 1, 7, 8 or 9 (or some unknown step) could be the big problem.[4]

Imagine that, knowing there's intelligent life out there, but knowing we will never meaningfully interact with them because it's impossible to travel any useful distance or communicate in any real way. Even if we could travel vast distances, It seems likely if we discover any life out there it may be long dead by the time we get there.

that's really sad :(. 300 light years ... gonna take a while. maybe the filter is space travel - no civilization is able to amass enough energy to go those distances

We have an enormous, almost inexhaustible source of energy just 1 AU away.

Even if we passed a Great Filter it doesn't necessarily mean that there wouldn't be an other one in front of us.

Also not finding other civilizations wouldn't be a proof that we passed any filter at all, maybe plenty of civilizations have been incredibly successful already, they're just so far beyond our comprehension of the world and consciousness that we can't meaningfully interact with them.

Perhaps the Great Filter is not a single event? Perhaps it can happen more than once and occasionally shows up as a large space rock. [0]

[0]https://en.wikipedia.org/wiki/Cretaceous%E2%80%93Paleogene_e...

Maybe the Great Filter is global warming, or other similar planetary pollution. Once a civilization ramps up Moloch[1], the self-reinforcing self-perpetuating structures necessary to organize industry at a planetary scale, it becomes too difficult to pull back and stop it before it's too late.

[1] https://www.lesswrong.com/posts/TxcRbCYHaeL59aY7E/meditation...

Unlikely.

We're going to have a hard time dumping enough anything into the atmosphere (or causing some other kind of pollution) to kill ourselves entirely. We'd osculate around an equilibrium where we dump some pollutant into our environment to the point where our population decreases, natural processes remove it and our population increases, wash, rinse, repeat. You can see similar population and resource usage patterns in many ecosystems.

And before anyone tries to twist my words to saying global warming isn't a bad thing, that's not what I'm saying. I'm just saying that humans as a species will likely survive it.

It's not species extinction that makes life undetectable, it's extinction of the civilization. For a civilization to be detectable it has to be at least at our level, or maybe a century beyond our level. If our civilization collapses it would mean that we were only detectable for a couple of centuries and then it could take millennia for us to get back to our level, especially if we've extracted all the easy to extract natural resources making it harder for our ancestors to rev back up, or if large parts of the planet become uninhabitable.

>it's extinction of the civilization. For a civilization to be detectable it has to be at least at our level,

My point is that we won't go extinct, we'll bounce back and get another try.

>especially if we've extracted all the easy to extract natural resources making

Would you rather hollow out a mountain to mine minerals or dredge through what used to be a major city? We've concentrated all sorts of useful things on earth's surface. If anything the next civilization will have it easy.

>harder for our ancestors to rev back up, or if large parts of the planet become uninhabitable.

Large parts of the planet were more or less uninhabitable. The few people who lived in the arctic and the deserts mostly just followed food/water sources. They contributed little to civilization's progress (mostly in the field of astronomy because desert nights and polar winters give you plenty of time to look at the starts) because they didn't have the spare resources to engage in those pursuits because they were too busy surviving. Progress has always come from the places that are easy to live in and therefore have resource surpluses.

Separate from the details of the consequences of global warming itself, more generally my hypothesis is that in order for a civilization to become aware that it is consuming too many natural resources requires a level of advanced development that can only be achieved by consuming too many resources. In other words, it might be more likely than not that when a planet produces a civilization that enters an industrial revolution it ends up burning through its natural resources in an unsustainable way and ends up collapsing. The easy access to resource surpluses that ignites the industrial revolution is also what causes them to overshoot their planet's capacity.

For us it's not just CO2 pollution that is a problem, there are many other resources that we are over-utilizing in an unsustainable way. And it seems that we are completely incapable of coordinating as a planet when the sacrifices are large. The hope of the techno-optimists is that technology will save us. It's a high-stakes bet that technology will figure it out before it's too late. Maybe the Great Filter is that when this bet is made across the universe the odds are generally in favor of losing.

This seems like humanity’s last advanced civilization: the easy energy is all tapped out.

Maybe some other life form could have one after enough time has passed, but we can’t bootstrap ourselves a second time.

(Edit: to be clear, I’m agreeing with you.)

>This seems like humanity’s last advanced civilization: the easy energy is all tapped out.

That's probably what someone said in the middle ages when they finished deforesting Scotland.

We still have nuclear. There's an obscene amount of energy in it. It's just not attractive while we still have other "easy" options.

If this civilization collapses, how are we going to get to the point where we can build nuclear fission reactors?

Is it that hard to enrich isotopes enough to make a steam engine that runs on radium, thorium or uranium instead of coal?

If you know that radioactive isotopes exist, it sounds like steampunk, 1850s, level tech could build a power plant, but perhaps not a bomb.

I’m not qualified to answer, but there was a bit of discussion about the idea on Reddit:

https://www.reddit.com/r/worldbuilding/comments/57peek/can_y...

Interesting.

I don’t think it’s that hard to build a vessel full of warm radioactive pebbles to boil water.

Sorting ore by chemical element, and then making a fluid / gas / solution of the fuel element to sort by isotope mass in a centrifuge may or may not be doable for “blacksmith” level technology, though. Hard to say.

Controlled cold fusion would be even more neater as it enables you to synthesise arbitrary molecules out of just hydrogens.

That was a really interesting read. All of the examples were incredibly insightful, but the cancer one felt like the most similar to a great filter, perhaps because it can very easily be used to explain the issue abstractly.

I don't see this as likely. Global warming is not an extinction level event (for humans! for a lot of other life, it will be, although habitat loss may well play a larger role in that.)

My own speculation on the Great Filter is that any intelligent alien civilization is almost certainly a race of social predators that evolved - and thus are in competition for resources.

I worry that competition between individuals and individual states necessarily ends in the destruction of the environment on which they depend and quite likely in direct destruction in war with advanced technology.

Us humans need to find some other paradigm under which to move forward, capitalism and competition, which have brought us such amazing results to date could well also be our undoing.

Why is this very bad? What is wrong with society not existing if it’s inevitable. Is dying very bad or is it an inescapable reality that isn’t good or bad? What is inherently good about life existing or spending the finite energy of the cosmos? It all comes to an end eventually. Is that bad? Can humans offer anything to the universe other than parasitism?

It seems odd that the universe would be as vast and fascinating as it is but there be no one to appreciate it.

I want humanity to reach another galaxy someday.

One persons parasitism is another's enrichment.

Supporters of ethical hedonism hold that the enjoyment of life holds axiomatic value, and life itself is a prerequisite for enjoyment.

https://en.wikipedia.org/wiki/Hedonism

Sure, but the Universe is going to die and we don’t seem to have any way to save it

I fail to see how the inevitable “death” of the the universe has any bearing on it being good or bad. Or life being good or bad

Yeah I am not sure where I was going with that. I think I’ve read too much “the universe is conscious” woo.

We cannot change the existence of one or more Great Filters.

Our best chance of survival is finding out about one as soon as possible.

...so the only path remains forward.

Scary.