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> I think the odds of a planet developing life by random chance in the first place is astronomical, and then the odds of that developing into intelligent life - that happens to have the necessary appendages to build things and lives in an environment amenable to creating tech - almost certainly an astronomically small portion of life bearing planets.

I take your point, but even if it is true that life is astronomically rare, we are literally talking about astronomy. Life doesn't have to be common for there to be countless worlds with life in our galaxy. In terms of intelligent life, not only must we reckon with the billions upon billions of planets in this galaxy that could host it, but there are also the vast timescales in which it could unfold.

Based on the current trajectory of human civilization, I think the Great Filter [1] theory is increasingly convincing, although that's unfortunate (to put it lightly). If we do manage to avoid destroying ourselves in a sudden cataclysm (such as via nuclear war), we will have to deal with a planet with a destabilized atmosphere, a massively damaged ecosystem, poisoned water and a host of other problems so serious that the word "problem" doesn't seem sufficient.

The timescales required for other advanced technological civilizations to overlap with our own requires that civilizations that go through these periods are able to stop actively destroying their home planet, and then survive the aftermath for a long time afterwards. Whether we are able to do this is very much an open question. We are just a couple of centuries down this road and on balance, I don't think it's going that well.

1: https://en.wikipedia.org/wiki/Great_Filter

Based on our own experience, we know of at least three Filters and can strongly guess as to another.

(1) That life develops on a world whose mass allows achieving orbital spaceflight using relatively low-technology means (i.e. at least partially chemical)

(2) That advanced life develops on a world with massive energy reserves easily accessible with low technology (e.g. coal, oil)

(3) That no environmental cataclysm occurs during the advanced life/industrialization gestation time period (e.g. climate change, asteroid)

To this, we can pretty strongly add another:

(X) That, during the brief window between energy surplus (and advanced technology) and environmental collapse (from energy exploitation), interplanetary colonization is launched, supported, and made self-sufficient

There's no law that says the window for something remains open forever, when you're talking about planet-scale economic requirements.

Another major filter supposedly comes much earlier: the development of complex single celled eukaryotic life. Some people think this occurred due to a single subsumption event on earth between a bacteria and an archaea.

> single subsumption event on earth between a bacteria and an archaea.

Do you mean symbiogenesis?

https://en.m.wikipedia.org/wiki/Symbiogenesis

Yes that’s the word

There’s probably also a distance / lifespan filter:

(4) That interplanetary colonization is possible (using relatively low-tech means) given the lifespan of the species and the distance to nearby habitable planets.

For example, life could develop in a solar system with only 1 habitable planet and the next habitable solar system could be dozens or hundreds of light years away.

Now you need to invent a fully self-sustaining long haul space craft, plus have the technology to pause death (or have the will to confine hundreds or thousands of generations to life on a space craft, plus have the ability to effectively pass down enough survival skill information from generation to generation that won’t use it, but will simply practice it in order to relay it).

>For example, life could develop in a solar system with only 1 habitable planet and the next habitable solar system could be dozens or hundreds of light years away.

Did you just describe our solar system?

It sounds like you're describing our solar system. No, Mars is not habitable in any meaningful sense of the word, any more than the Moon is.

Do we have any evidence any of those are filters. For (1), there was practically no gap between the development of powered flight (e.g. airplanes) and plausible fission powered powered (abandoned for political reasons). Further, space flight, while useful, has not been critical for our technological development. I see no reason a high tech society couldn't develop in a deep gravity well then escape it once their technology reaches a stage where doing so is possible.

For (2), energy reserves definitely accelerated things, but I'm not convinced they are nessasary. The fossil fuel age was only a few hundred years. Even if it accelerated technology development by an order of magnitude, we still would reach what we would now call the green era in an evolutionary blink of the eye. Even in our own development, wind and water power predate fossil fuels.

In fact, the lack of fossil fuels may actually help a civilization, in that would completely avoid the carbon based crisis we are facing now. That could easily outway the slowfown that non carbon power sources would have caused

(3) seems important though.

Basing hypotheses on a single data point, let alone one whose outcome is not yet determined, almost invariably leads to wildly inaccurate conclusions in practice. As such, until we have more data, any questions about the Great Filter and the causes thereof will remain unanswerable.

Personally my bet is on either us being early as intelligent life goes, or extremely massive stellar expansionism on the levels that would allow for us to have encountered intelligent life with basically zero search effort not being something most civilizations would feel compelled to do.

Also assuming that any advanced civilization that exists would have to follow our development path is laughably anthropocentric and reflects a failure of imagination on the part of the people making said claims.

> Also assuming that any advanced civilization that exists would have to follow our development path is laughably anthropocentric and reflects a failure of imagination on the part of the people making said claims.

That's a great point, and it's not just anthropomorphic. It also ignores the paths that other cultures were on, that were subsumed or annihilated by Western-style industrial capitalism. What would human civilization look like (and what state would the planet be in) if, for instance, Western nations had first, respected indigenous sovereignty in the Americas, and second, sought to learn from First Nations instead of seeking to destroy them?

In other words, we don't have to imagine alien civilizations to explore other developmental paths. There are plenty of examples right here at home.

I'm guessing that if Europeans had decided to adopt the Native American lifestyles and cultures, we would still be pre-industrial and living as a bunch of separate tribes that sometimes have wars between them.

The way the European settlers treated the natives was indeed rather shabby, but the existing culture was not one that could ever develop into modern nation-states and a global industrial civilization without conflict. And without industrial capitalism, we wouldn't have computers and be exchanging messages across continents here on HN.

So it's entirely possible there's alien civilizations out there that are happy to remain in a primitive, tribal, pre-industrial state, but we're not going to ever detect or meet those civilizations until we have starships capable of transporting us there.

I’m not offended by your viewpoint, I think many people share it (although “rather shabby” is a gross understatement of what took place). But take a moment to reflect on a couple of things:

1) You used the word “primitive” to describe these cultures. However, these cultures had developed advanced techniques and ways of being that ensured their survival for millennia, and there’s no reason to think this could not have continued for many more millennia. Is a society that is capable of surviving in perpetuity “primitive”? How does that contrast with our current society, which can fairly be called self-destructive? There is a serious risk that we don’t survive the next few centuries - perhaps even decades! Would you call that “advanced”?

2) I’m not discounting the value of science, nor am I romanticizing the hardships that many indigenous communities endured in the absence of science, advanced technology, modern medicine and so on. But First Nations peoples were not stupid when they encountered western technology. They adopted what was useful or superior to what they had.

There could have been a synthesis of ancient indigenous practices and modern science. And indeed many indigenous practices were adopted by Westerners. But fundamental truths like, destroying your own home is not a recipe for long-term success, were ignored.

Agreed, but remember we likely see the universe with massive blind spots. Maybe given enough time, an aquatic specie would find a way to make tech, manipulate energy and develop society in ways that require a physic we know nothing about. Or maybe using something we know, but could not think of using that way because of our biases.

We are a very young civilization after all, the quantity of things we don't know is massive.

> Try to imagine what a setback it would be to try to discover smelting or electricity underwater. It’s not an impossibility, but I suspect it’s inherently a small fraction of underwater societies that discover it at all.

Try to imagine the number of things we haven't discovered because our civilization didn't develop underwater! Would be interesting to find out what the sentient alien dolphins and octopuses think of us and our disadvantaged air-based tech :)

Unfortunately, space ships filled with water are even harder to drag out of the gravity well...

Maybe antigravity is one of these technologies that is most easily attainable if your civilization develops underwater :P

if you lived in water, you might have discovered clever ways of breaking it down into H2 and O2 in ways we landlubbers haven't. seems like i've read somewhere where those elements are useful in escaping the gravity well.

No doubt we had a very lucky roll, and I agree that intelligent life must be extraordinarily rare. But the galaxy/universe and its history is incomprehensibly enormous and dynamic.

You're right that evolution isn't a one-way street, but intelligent life is going to emerge as a result of a sufficiently complex, chaotic, and resource-limited environment - and nature is great at that. The necessary ingredients for life generally are time, elemental diversity to manipulate chemistry(the makeup of our planet doesn't seem extraordinary), and competition (once a self-reproducing automata exists at any scale, evolution takes over and life adapts- see Von Neumann's "Theory of Self-Reproducing Automata" to understand this further).

Intelligent life isn't fundamentally different, because intelligence isn't a bar that is attained, but a gradual and emergent phenomena once sufficient numbers of "logic circuits" are hard coded in organismal memory (the brain). For it to emerge, an organism must be continuously challenged via diverse mechanisms. For example, recurrent semi-apocalyptic disruption events which clear the way for new "ideas" (i.e. how the extinction of the dinosaurs made room for mammals).

Your last sentence hits the nail on the head but you reach the wrong conclusion. It is the need to invent that yields intelligence, not the other way around.

I've always found the numbers people propose for the probability of life arising to be absurdly self assured. We do not know the probability of life arising. We do not know the probability of developing intelligent life. We don't even know if life originated here. If you ask me for my gut feel I'd say that life arises with near certainty in a range of suitable conditions. But that is beside the point - don't get annoyed with others for making assumptions and then in the next breath make equally strident assumptions.

I think the left side of the Drake equation is pretty challenging too. If we assume that faster than light travel is impossible (which is likely) and all galactic civilizations are subject to the tyranny of the rocket equation, then it’s quite likely that there are no alien spaceships wizzing around, even if our galaxy is full of intelligent life forms.

And then our best way of detecting advanced alien life forms is through direct observations of remote star systems, a field that is in its infancy at best.

> I think the odds of a planet developing life by random chance in the first place is astronomical, and then the odds of that developing into intelligent life - that happens to have the necessary appendages to build things and lives in an environment amenable to creating tech - almost certainly an astronomically small portion of life bearing planets.

Let's start from what we know: homo sapiens has been around for 300 000 years, but technology only kicked of less than 300 years ago. So we could say that of 3 billion years of terrene life, 0.01% of it have sported a species susceptible to develop technology, and of this short span only 0.1% of it actually developing it.

So from Earth example, so far we can only posit 1 chance out of 10 millions of developing technology, nothing more. That's not much, and that's markedly lower than Drake's original optimistic numbers. Also, we can't suppose technology will survive for a very long time; so we also need a very fine time-alignment to receive a message (or get someone to receive ours). If most high tech civilisations only survive barely a few centuries, even if there are 100 000 of them across the Galaxy but scattered along 10 billion years, most messages simply will reach long rusted antennas...

But we could be able to see the "stuff" left over from space-faring civilizations, like for example their Dyson Spheres. Or simply their AI robots would be self-replicating and colonizing the entire galaxy.

You're assuming these civilizations would be willing and able to build such structures in the period they are technologically able to.

> homo sapiens has been around for 300 000 years, but technology only kicked of less than 300 years ago.

I get what you're saying, that _industrial scale_ technology didn't kick off until a few centuries ago. But humans have been pretty technology advanced for a few hundred thousand years, unless you don't consider stone knapping, cooking, and language as technologies.

They are technologies that don't matter at all from a "Fermi paradox" perspective, though.

There was a recent paper arguing that life on Earth makes it more likely that life occurs on other planets: https://www.cambridge.org/core/journals/international-journa...

> Try to imagine what a setback it would be to try to discover smelting or electricity underwater. It’s not an impossibility, but I suspect it’s inherently a small fraction of underwater societies that discover it at all.

It's interesting to think about. If you live entirely underwater you have no reason to harness fire, or develop even simple technologies like the wheel. If you don't harness fire, will you even be able develop basic metallurgy (bronze, iron, steel)? If you don't work with fire or metal you don't develop steam power. Without steam you don't have an industrial revolution, without an industrial revolution you lack the prerequisites to develop internal combustion or heavier than air flight, and without internal combustion you probably don't develop chemical rockets.

I suppose it's possible that an aquatic civilization could take a totally different path to space than we did, but they'd definitely be playing the space race on hard mode.

> If you live entirely underwater you have no reason to harness fire

No, but I wonder if simple batteries would have been discovered. That would get you straight to arc furnaces.

I would find the rate of intelligent life ≈ 1 per galaxy an incredible coincidence.

Considering the absurdly huge amount of planets/time and the absurdly low chance of life happening, I think it's almost impossible for the rate to be close to 1.

Perhaps it might be much lower than 1 though.

>I’ve always felt the numbers people enter into the Drake equation overly optimistic.

This may be the right way to think about it but even so you would only change the order of magnitude of the final answer which won't be 0. Given the timescales involved one would still expect a species to have either left behind structures or modified their galactic neighborhood to a degree that is detectable or would have significantly colonized large parts of the universe/galaxy by now.

There are plenty of plausible choices for terms of the Drake equation that give 0. Remember that the Earth itself is relatively old as planets go - 4.5 billion, compared to the Universe's 13.8 billion; and the current "era" of the universe only began when it was ~9.8 billion years old, so about 4 billion years ago.

So, if we were to assume that the appearance and evolution of life on Earth as the benchmark for how long it takes for life to appear and evolve, and if we assume that life couldn't/was much less likely to arise before the current Dark Energy-dominated era, then it's quite possible for us to be one of the first radio-wave-emitting beings in the whole universe, let alone anywhere in our general area.

Of course, any such assumption is entirely unfounded: we just have no idea how likely it is (and how long it is likely to take) for life to arise and become radio-wave emitters, and even less about how this may have been different in earlier times in the universe. There are perfectly plausible choice for the Drake equation parameters that reach the exact opposite conclusion and give hundreds or thousands of expected civilizations in our neighborhood.

>There are plenty of plausible choices for terms of the Drake equation that give 0

Given our own existence any solution to the drake equation would by definition have to be >= 1 right?

Plus we don't know where intelligence leads. Maybe it's actually a catastrophe for the planet? Too early to say, but it's also possible such catastrophes happen quickly on a geological timescale.

Depends on the catastrophe. From what we can tell, the dinosaurs weren't reading their equivalent of Shakespeare or sitting around discussing the social caste system of t-rex vs brontosaurus when the world ended for them.

> whereas death by exposure is a very real threat. We needed to invent clothing just to survive outside a temperate belt.

It's been a while since technology makes us less fit to our environment than anything else.

A while as compared to the age of a human or a specific government or a while compared to the age of life, planetary, or universe timespan?

We survived just fine in a temperate belt, developed intelligence there, and that intelligence allowed us to expand to the rest of the world.

> We had a very lucky roll.

Boy this statement has a lot to unpack. If you think life (and then intelligence) came about by chance... And that all this knowledge was so that we can live "more happily" in our environment? And this was fortunate? I would come to precisely the opposite conclusion.

All I can think of is Rocket Raccoon: "I didn't ask to get made!"

"The greater my wisdom, the greater my grief. To increase knowledge only increases sorrow."

Ecclesiastes 1:18