It's extremely anthropocentric reasoning, like "the cost is too large", "you lose control of the hegemony" etc. And that there are "colonists" that "die off".
I'm not sure any of these assumptions are applicable given billions of possible origins of life at various stages of development. Even at Earth, and with extremely conservative estimates, given 100 more years of nanotech/biotech/AI development, we won't die off, and could certainly send autonomous robot probes. When you don't die anymore, 8 years roundtrip (or more) suddenly doesn't seem so long.
BTW in the fiction arena, I suggest reading David Brin "Existence" if you're so inclined which is related to this :)
Great post, but in the context of "Where is everybody?", each 'we won't' or 'we could', where we haven't actually done it yet, is potentially part of the solution to the puzzle. Perhaps filling the universe with undying, exponentially-spreading probes, that don't stop spreading due to values drift, is harder than we think. (Personally, an early filter feels more likely to me, but if it's not that, it's gotta be something).
> It's extremely anthropocentric reasoning, like "the cost is too large"
I'm not sure certain.
Cost is, at its core, based on physics- energy, resources and time are the true values all money is based on. Those constraints will exist everywhere in the universe, however they may be treated by an ETI. No matter where you go or who you are, you still need a massive amount of energy to move matter from one star to another.
You don't need a massive amount of energy. We could be launching interstellar probes now with current technology. They'll just take 10s/100s of thousands of years to get anywhere.
The real problems are political, technological and ecological stability.
No one has ever built electronics capable of lasting hundreds of thousands of years. It's not obvious if it's possible because on those timescales everything crumbles to dust, especially if it's constantly being abraded by dust and radiation.
And if you don't put your travellers into long-term suspension, political and cultural stability are even more fragile.
And small eco-systems are far less resilient than planet-sized systems - which, it turns out, may not be resilient at all on longer timescales.
So the gap between launching Voyager I/II and launching a self-replicating probe which can reproduce itself physically and culturally is beyond huge.
If you happen to have massive amounts of energy some of these problems get easier, because you can get where you're going more quickly. But some remain immensely difficult.
Which is why percolation is a much better model. There will inevitably be some attrition in any colonisation program, and there may well be a hard limit on the amount of entropy any colonisation program can survive.
I think that just as cost is based on physics, time is best measured in terms of lifespan. Probes with travel times measured in the thousands of lifespans take too long.
Even beyond lifespans, there are problems with materials and resilience. While a conductor wire seems solid enough for us, that's only true for some hundreds of years. Even if we lived 1000 years each, that doesn't guarantee we can make mechanisms of any kind to last 1000 years, nevermind 10000.
Hell, I'm not even sure we can make a computer that actually lasts 100 years.
Well, it still has 60 years to go before you can contest my hypothesis.
Still, I was probably too ambitious when I said "computer". I was thinking more that we can't make a PC or server-style computer that would actually last 100 years, while in regular operation.
Also, 1980s calculators have much, much fewer moving parts than today's computers. They don't have any kind of active cooling, they don't go through rapid heating and cooling cycles, they probably have three orders of magnitude less electrical components than a modern PC.
For me at least, all of the PCs I have had so far have had a few electrical components giving out after at most 10 years (usually some condensers leaked).
But all that is just because computers are not designed for longevity, they are designed for capability. We could easily design them for longevity if we wanted to: lower the clock speed so that passive cooling is all that's needed. Make all the PC traces five times fatter than they need to be. Use non-electrolytic capacitors. The resulting computer would be big and slow but it would last forever.
In fact, it would not surprise me a bit if you could run a Raspberry Pi Zero for 100 years.
Given an energy source that lasts the duration of the trip, I'm sure we could figure out how to build a ship that we can keep repairing quicker than it falls apart.
I think the amount of mass lost is small enough that extra provisions can be carried around. For anything else you just have to fight entropy. Given enough energy you can probably do that.
Travel doesn't cost any energy, only acceleration and decceleration, so if you accept a slow travel this isn't particularly expensive. Especially with drones you wouldn't need a huge spaceship with environmental systems for squishy bio-masses like humans... :)
That's only true if you're launching a piece of rock. Otherwise, it does cost energy to maintain a system running and, at the very least, tracking time for 10000 years.
It's not even obvious that it is theoretically possible with current circuit technologies. Pieces would fuse together, moving parts would erode, all sorts of organic materials might deteriorate, everything would be affected by the huge amount of time. And you would almost certainly need energy to actively fight this entropy so that you would have an active machine when you reach your destination.
Iron is nuclear ash, and this tech is just about the most reliable implementation of logic we have. It was used in the V2 rocket and US nuclear submarines. It's abandoned tech though and was never pushed beyond 1MHz. If however you have a decade to compute your reactions then that might not matter.
Superconducting magnetic loops also store their flux indefinitely, and in space keeping it cool would be trivial.
The article claims since the galaxy is over 13 billion years old there has been that much time for civilisations to emerge and spread. We know that’s not the case. The Universe is only a billion years older than that, and started off as a near homogenous field of hydrogen and helium. All the heavier elements we know today were forged in stars, and distributed when those stars aged and exploded, spewing heavier elements into space. This went through several cycles before reaching the element rich environment we evolved in. It may well be that heavy element densities only reached a viable level in the last generation of stars, maybe the last 1/3 of the history of the universe, or the last 4 to 5 billion years or so. That changes the playing field considerably. Our system might be one of the first capable of supporting life.
There's still say a billion year window. The jurassic was 200 million years ago. If some spacefaring civilization developed at that time on some other planet, and the galaxy could be colonized in a few million years, they could have done it a hundred times over since the dinosaurs.
The distances in the milky way are mind boggling. But the age of the Earth is even more so.
As an aside: The technology / evolutionary differences are likely to be immense. Imagine trying to have a 'first contact' with an ant in your backyard. Honestly, for most humans, it's not even close to worth the time or energy to 'talk' with something like that. We don't even consider a single ant worth of much study at all.
Now imagine a people as far advanced of us, as that ant is to you. Now imagine that 10,000 times more advanced. Or 100 million times more. That is the kind of difference we have to consider.
The unfortunate reality may be that other civilizations are so far advanced from us (100x? 10,000x? 10 billion?) that we are effectively 'alone' all the same. Like an ant pondering the garden hoses, BBQs, or fence posts of the universe.
I think that calculation only works if you replace "colonized" with "explored". Automated, self-replicating probes could reach every star system in the galaxy by moving and spreading as fast as they can but effectively colonizing each system would take a lot longer. This isn't a game of Civilization where you just pump out settlers, real colonists need a reason to leave everything behind and stellar scale civilizations probably take thousands of years to mature and fully exploit their star system. I think the article is closer to the truth.
If colonizing a star system to be able to send further expeditions would take 500 years, and an interstellar trip took 500 years, there's still a thousand "colony generations" in a million years.
Call me pessimistic (I'm not) but I think it would take longer than 500 years to achieve a large enough population level to fully colonize the space around a star. You could assume that our current trend of declining population would reverse and we'd begin breeding like rabbits once we start living in space habitats but I don't think that's very likely. I think there's a good chance it would take us thousands of years to fully saturate a star system. We'd have to master living in space as well as building generational world ships/habitats that could traverse interstellar space on multi-generational journeys. Personally, I think the most likely state of affairs (if you assume a hard boundary of the speed of light) is that civilizations colonize a small group of local stars and then begin in-filling the space between them once they know how to build fully self sufficient habitats. This is similar to how we currently exploit the most resource rich areas on our planet and then develop out along transportation networks when we need more space. Outer space is three dimensional though so this process likely takes a much, much longer time. All that assumes no major breakthroughs that allow FTL or radical different modes of being though.
The population of North America is around 579 million after 500 years of exponential growth and probably the largest and longest sustained immigration trend in the worlds history with only open ocean as a barrier. We're talking about a star system with potentially multiple planets and moons let alone interplanetary space to colonize and century long gulfs of empty space to cross. My money is on it taking longer than 500 years before any native born son of a new star thinks to theirself that they could make a better life even further out.
I made the point in another comment but I do think there has to be a reason to send out colony ships. I agree that exploratory, unmanned probes would be sent out to gather information but I doubt sustained efforts to colonize new star systems would be made until there was significant social, political, or environmental pressure to do so. One ship colonies never succeed beyond a toe hold, you need a constant flow of people, resources and information to drive the founding of a new civilization especially if the trip is one way with little possibility of trade. If all you needed for the development of a new culture and society was an initial seed population and time then every town in the world should be a New York.
One problem with determining how a civilization could travel is we only know what we know now or can reasonably speculate. A hundred years ago we didn't really have the ability to even get into orbit much less imaging visiting another star. Today we can imagine ways but they are insanely expensive and likely to take dozens of years or even centuries at best. Assuming constant progress in technology we might be able to get there faster by waiting decades than by leaving now. Even the absolute limit of light speed, while impossible to imagine today, might turn out to be less of on obstacle in some future understanding of physics. It's hard to predict the future since all you have is today's knowledge.
Unfortunately that reasoning is based on the axiom that "we can't prove or disprove anything beyond doubts" or that "anything might be possible" and this doesn't help us making decisions about solving problems or making informed decisions.
"Let's just stop doing anything regarding climate change because in 50 years we'll have the tech to solve it, we don't know it yet because we can't imagine it."
At some point, as a specie, we certainly can't afford to gamble our survival and culture like that.
The logic of waiting to launch shuttles doesn’t apply to global warming and I’m not sure why you’d bring that up here?
If I launch a rocket now, it’s will take 50 years to get to Pluto. If I wait 10 years, we’ll have faster rockets, so it will actually get there sooner. The progress of my original rocket cannot be improved.
For global warming, progress we make now can be built on and improved over time. This is not the case with a rocket that’s already launched.
> The logic of waiting to launch shuttles doesn’t apply to global warming and I’m not sure why you’d bring that up here?
That's because my argument is not about rockets or climate change but about underlying assumptions.
> If I launch a rocket now, it’s will take 50 years to get to Pluto. If I wait 10 years, we’ll have faster rockets, so it will actually get there sooner. The progress of my original rocket cannot be improved.
Faster, maybe. Sooner ? Where is the proof ?
And what if you can build a faster rocket only because you learned from mistakes from the slower first rocket ? If you never launch and experiment with that one in real conditions then you may very well never have a faster rocket.
Let's put it another way:
- before, we didn't know how much was feasible and we doubted we could do better (LEO, moon landing, etc.).
- Now we know we could and did.
- So we think in the future we'll be able to do things we can't do now.
- But what if we are wrong again (like we were before) and that very belief is wrong.
- You can still think/believe things like “Assuming constant progress in technology we might be able to get there faster by waiting decades than by leaving now. Even the absolute limit of light speed, while impossible to imagine today, might turn out to be less of on obstacle in some future understanding of physics.” but that belief may very well be our mistake, just like people 100 years ago didn't believe we could land on the moon.
Thinking the same, for travel and all. After 30+ years of my humble existence in this universe, these are the times I want so badly to see a glimpse of the future, a scene from 10.000 years later. SO, SO curious. Thinking is leading me to nowhere with my limited capacity, dreaming with mostly unrelated fantasies and visions. A real one would be nice, even from the exact location I'm sitting now, the street, the sea nearby, everything around, how they evolved.
Mind-blowing universe, amazing planet, very little time sadly.
10.000 years is a lot.
In the past that’s roughly when agriculture was invented. In the future chances are humans will be either extinct or living in very though conditions. The future is not necessarily always better. It certainly wasn’t for the grandsons of hunter-gatherers that became farmers
The argument that hunter-gathering is superior to farming is based on some quality-of-life comparisons, most notably the fact that modern hunter-gatherers spend a surprisingly little amount of their time actually acquiring food (something like 2-3 hours a day). Most anthropologists are extremely skeptical of comparing modern hunter-gatherers with Paleolithic hunter-gatherer cultures, particularly the ones that would develop into agricultural societies.
The main reason that farmers outcompete hunter-gatherers is that agriculture allows building larger societies than hunter-gathering can, and this extra population gives a decisive advantage in being able to prosecute wars for as long as is necessary to exterminate hunter-gatherers.
> the fact that modern hunter-gatherers spend a surprisingly little amount of their time actually acquiring food (something like 2-3 hours a day)
Thinking about this a bit deeper, this is only true if you have a small population with relatively plentiful resources. Hunter gatherers quickly bump into the limits of their environment if their population increases. The idealization of their lifestyle is misguided because it would necessitate drastic reduction of population levels to reach that balance. The goal should be to increase the abundance of resources in our modern environment so that we reach the same ratio of resources to population, which hopefully would mean a consequent reduction in the amount of effort we have to expend to obtain those resources.
Farming allowed populations to grow but individuals were much more susceptible to abuse, violence, exploitation, disease and a life of chronic back pain
And then, even if we manage to travel at that speed, it's still waaay too slow, simply because of the distances involved.
Can we skip ahead to teleportation please?
If you travel somewhere faster than light, it doesn't matter whether you accelerated or not, you can stand at the destination and watch yourself wave as you leave the origin.
Interstellar travel is possible with 1960s technology. Search for Project Orion. Thermonuclear Orion could reach as much as 10% the speed of light, which is fast enough to reach the Centauri system in a human life span.
Then there is the potential of things like hibernation, or AI that can just turn itself off. The latter would be able to use a less costly but slower propulsion system.
I really don’t think travel implausibility works as a Fermi paradox answer. It’s hard but not hard enough to explain the absence of visitors in a galaxy full of planets in habitable zones.
> Interstellar travel is possible with 1960s technology. Search for Project Orion.
That hasn't been demonstrated. Project Orion was canceled before critical parts of technology were actually tested, and the mechanical viability of a pusher plate that has to absorb the impact of several nearby nuclear explosions in rapid succession is somewhat doubtful.
The physics working on paper is enough for an argument for basic feasibility. It may indeed not be as easy as they thought. Maybe replace 1960s tech with 2060s tech and much more exotic materials.
They did do some survivability experiments at ground zero at atomic tests and found that some materials could stay intact. I recall reading that the biggest problem on paper for Orion was cooling the plate in space so it wouldn’t melt after a few pulses. I think they posited various ablative shielding materials plus some kind of active cooling. Of course also remember that once you are in space you don’t need to fire rapidly. One boom every hour or two or even longer would be fine. It could take quite a while to build up to cruising speed, and to decelerate.
Acceleration would require several times more charges since you have to accelerate all the deceleration fuel. With interstellar flight you have two massive problems: going fast enough, and then slowing down at the other end.
100 more years of R&D is not very long on geological or cosmic time scales. My point is that the math working for something as brute force as Orion makes the difficulty of interstellar flight a problematic answer to the Fermi paradox.
> Thermonuclear Orion could reach as much as 10% the speed of light
I wonder how much such a mission would cost in terms of total Earth resources. I've read Dyson's book on the project some years back and I don't remember that being mentioned.
Wikipedia states the cost in percentage of U.S. GDP (0.1 - 1% of yearly GDP), but I feel like the millions of tons of copper and fissile material required would be significant hit on remaining mineral reserves. It's kind of hard to justify sending out a few missions if it means that the planet left behind is out of easily mined copper and uranium deposits.
It wouldn’t take that much. Fissile material can be bred in fast breeder reactors, and in a thermonuclear Orion type pulse drive most of the power comes from hydrogen fusion. The fissile warheads are primers for each fusion charge.
We could probably send a probe to Centauri for the price of one Iraq war.
Of course launching “the devil’s pogo stick” from within our biosphere would be rather horrible for the environment. It would be a lot better to build a base on the Moon and launch it from there. You wouldn’t need to burn as much power getting out of a big gravity well. The Moon, being formed from the same stuff as Earth, certainly has fissile material, and it may be closer to the surface and easier to get there.
I really think the most likely answer to the Fermi paradox is that extreme intelligence is rare. There probably isn’t a single great filter per se. It’s probably just unlikely for an environment to be simultaneously stable enough over billions of years to produce high intelligence and interesting enough to stimulate its evolution. Most interesting environments will be unstable, and most stable environments uninteresting (a.k.a. having low Shannon information content).
The universe is probably full of microbes, simple microbial colonies, and maybe a few worms and bugs, but there are probably not very many minds around capable of harnessing the atom and plotting orbital trajectories. Fewer still may have the motivation to invest in such an epic and likely one way journey.
For the latter point keep in mind that solar systems are huge. There are enough bodies and resources in our solar system to keep even a spacefaring humanity busy for millions of years. No necessity to travel to the stars for quite a long time. Space is called space for a reason.
> We could probably send a probe to Centauri for the price of one Iraq war.
Pricing planet-sized stuff like this in monetary value is problematic.
Taking figures from a quick Wikipedia search, "one Iraq war" buys you 10 years of world copper production at current rates. That is a non-trivial portion of planetary minable reserves, estimated at "from 25 to 60 years"
That is true. Money gets weird at huge scales. For something like an interstellar mission a more significant limiting factor may be the number of engineers and skilled workers with the right skills to work on such a thing and the rate at which they can be mobilized and managed. Most such people are currently employed, so they would basically have to be poached at huge scale. It takes a long time to train people like that, so the supply is inelastic on short time scales.
Here's two possible solutions to Fermi's paradox that don't require the Great Filter: interstellar travel is hard, and interstellar communication is hard.
1. Interstellar travel is genuinely hard, so hard that advanced civilizations do it from time to time, but not so often to result in "percolation". In order to have a reasonable argument, let's start from contemplating how hard it would be for us, humans. This is the only civilization we know of at this point. There are two things that make interstellar travel very difficult: 1.a. potential collisions with dust grains and 1.b. violence.
1.a. Danger of collisions. According to wikipedia, cosmic dust grains can have a size up to 500 microns. At a typical density of 2g/cm3 this is a mass of 0.5 mg. Assuming you have a spaceship that travels of 0.01 the speed of light, the energy of impact with such a dust grain will be about 20% the energy of an armor piercing round shot from a modern main battle tank such as the M1 Abrams. Over a 4 light year travel (the distance from us to the closest stars), or a few hundred years of flight at 0.01c, there would be billions- trillions of such impacts.
1.b. Human violence. Assuming we get the technological prowess to accelerate things to 0.01c, what's to stop someone to point a little projectile in the direction of Earth, or some other place colonized by humans? Such of projectile weighing only 15 kg would have the energy of the Hiroshima bomb. In fact, it's actually most likely that the road to interstellar travel will start from military applications, just like the Apollo program was a side-effect of the arms race that created the ICBMs.
2. Interstellar communication is hard. Let's say that aliens are indeed everywhere, including in the planetary systems of our closest galactic neighbors. How would we know? Would SETI find out about that? The only way we'd find out were if they were pointing some large antennas straight at us, and putting some megawatts of power into beaming signals at us. How do we know that? We know because we get radio signals from Voyager 1, which is 150 AU from us. Proxima Centauri is 1700 times further, so the signal would be more than 3 million times weaker. Voyager's antenna is 3.7 meters and the transmitter has 22 W of power. So, if our neighbors are not actively trying to beam signals at us, our chance of detecting them is practically nil.
1.b. Space faring civilizations probably don't live on planets the same way we no longer live in caves and mud huts, they build modern houses and cities out in space near to their preferred energy sources and transportation networks. It's a lot harder to hit something smaller and more mobile than a planet and even if you do it doesn't have the same consequences that it would on the ground. i.e. more likely to just punch a big hole rather than convert all its energy to heat, no pressure wave, your neighbours are further away, etc.
2. This is probably why we don't hear anyone, either they are smart about their use of EM communication and everything high powered is directional or they are even smarter than us and have figured out some form of FTL communication.
Whatever protection system one comes with, it would better be good 100% of the time. Because a 99.999999% success rate will be a death sentence.
> It's a lot harder to hit something smaller and more mobile
People are very inventive when it comes to new weapons. By the time we have the technology to reach 0.01c, we'll have invented 10 more generations of weapons. We might miraculously avoid interplanetary wars before we reach for other stars, but I would not bet my money on that.
When you consider the potential age of the universe [1], we can also argue that the universe is currently in its extreme infancy and we many in fact be one of the very first civilizations to start thinking about other civilizations, and all other "firstborn" civilizations are similarly constrained by technology.
It has been estimated that 95% of the stars that will ever form have already formed. Far from being in its infancy, from the point of view of locations for new life arising the universe is nearly done.
But they have existed for a short period of their lifespan, so by definition are early in their lifetimes. The argument isn’t that there will be new stars, but that they will exist for a long time.
There's good reason to think life is not going to arise on planets around M stars. Our sun is quite bright compared to the typical star, is already gone through about half its time on the main sequence, and as the Sun continues to brighten the Earth will become uninhabitable in about 1 billion more years.
Moreover, life originated early on Earth. This suggests either that more than one extremely rare event is needed to get from life to us, or that the conditions for OoL do not persist for very long (ammonia, for example, is rapidly destroyed by solar radiation.)
I think this sounds like a fairly reasonable solution to the paradox. Fermi's Paradox always assumed that at least one civilization would attempt to "colonize" the galaxy as fast as possible but if you think about that logistically it doesn't make much sense. What is the driving motive, cui bono? If we take our own history of colonization as an example, we didn't set out to establish colonies for no reason. We sought out new lands due to a number of reasons, population pressure, lack of opportunity, political oppression, to capitalize on virgin resources such as lumber, gold, and fish. Imagine being an English farmer in 1560, chances are you don't have enough wealth to expand your production even if your neighbours were willing to sell but you would have enough funds if you liquidated your belongings to take a chance on a new world with more land than people. Combine that with the fact that space is big and resources much more plentiful than on a planet alone and it would take a civilization a long time to populate their entire solar system. I don't even think true space faring civilizations would be primarily dependent on planets, once you have enough tonnage in space it would be easier to just build everything in space to begin with rather than trying to drag it out of a gravity well. At that point you have almost infinite real estate since you can just build more land. It wouldn't be a stretch of the imagination to think that a new colony wouldn't be seriously attempted until the current one had formed something akin to a dyson swarm made up of space habitats. The timeline for galactic colonization would have to take this into account. Most of the estimates I've seen assume geometric increase in the number of colonies with the shortest possible dwell time at each star but I think that's an extremely aggressive assumption without any evidence to back it up. I think there are also a large number of confounding variables such as the possibility of civilizational collapse or large scale disaster that may set back colonization efforts.
On earth, populations move to new regions because of 1) natural population increase and gradual migration by people who are pushed out of their home region due to overcrowding, or 2) deliberate conquest by groups with a very centralized power structure, in which there is a person or group who is in a position to extract tribute or resources from the conquest. In the case of interstellar travel, neither of those two are feasible. The people doing the migrating have to be supported by massive amounts of money, which rules out the first reason for migration, as it’s not a cost efficient way to deal with overpopulation. And there is no way to exert control or exact tribute from light years away, so that rules the second reason for migration. So there is a question of motive: why spend the money when you will not directly benefit?
I think it's about time we started sending probes to other systems. Sure it could take 50-100 years before the probe sent back any meaningful data - but imagine how extraordinary that would be for future generations. Seems like we have the technology for it.
It’s not clear why travel would be ‘expensive’. I can imagine a scenario where we create several robots, one for mining, one for chemistry, one for manufacturing, and you could simply send them out start self replicating and creating technology ‘for free’.
One of my favorite Christmas traditions is reading these whimsical “how many aliens can dance on a pinhead” arguments that always show up. Have a great holiday break, everyone.
I agree. Technology will soon (within 1000 years) take us to a place where whatever we can imagine we can have in a simulation that is indistinguishable from the real world. Why bother with the real world anymore?
There maybe some cultures that still see value in the physical world, but I'd wager not many.
I also think it's likely that panspermia is a thing. Life is evolving at the galaxy level, it's therefore a little more reasonable to think that we represent one of the more evolutionarily advanced life forms at the current time.
Yeah, I actually think there's a ton of merit to this. Fundamentally, the natural progression of technology for any alien species is probably going to be the capability to backup/restore/copy/enhance their consciousness. Biology is delicate, but a purpose-built computer can be designed to survive under very austere conditions, and offers so many incentives! Under the premise that such technology allows for faster and more robust iteration, it would quickly come to dominate the species within which it originates. At that point though, I think there's a lot of incentive toward looking inward rather than outward as an entity--be it from internal competition to become the dominant intelligent entity within your species, or because you've secured a large store of energy and low entropy to harvest. At some point, your iterations are so fast that, IMO, expanding beyond a certain size is likely to introduce a significant fracturing of that society/entity. Why spend the energy on having to compete with your future self?
They assume that a space faring civilization is identical to us down to capitalism, technology, fossil fuel dependency, education, politics, tradition, everything, but this assumption is self defeating: we have all these properties and space travel is infeasible to us, consequently any other civilization that has all the same properties is unable to travel between stars either.
If we, here on Earth, want to survive the next couple of centuries we need to find a way to keep our population growth under control. Either we succeed or we most likely will destroy ourselves and/or the Earth. But if we succeed, we also don't have much need to leave Earth anymore.
I'd say that this is also the case for other civilisations, which might be another reason why we don't see them.
I think we currently have the opposite problem: fertility rates are down, and the world's population is aging. Population growth is slowing and projected to stop.
It's pretty obvious. Space is harsh. Even just doing colonization within the solar system is hard to swallow. It's not possible to live on most planets even if we assume that everyone stays in what amounts to a grounded space station. Since we have not yet unlocked fusion we will always have to stay close to the sun. Mars is already too far away. Venus has an extreme atmosphere that causes it to be extremely hot. If a crackpot said we have to build a 100000 person colony in space this century we would have to start on the moon even though there is no water there. The primary reason would be that we are still close enough to the sun that we can use solar panels to generate energy. Space colonization without fusion is simply put: a joke.
If space was easy then our galaxy would have been devoured by some grey goo AI (not life) a long time ago. Life has to build artificial habitats and live in them. AIs can just stay in space forever as long as they can gather enough resources.
I’m more concerned with the politics than the technology of space colonisation.
Space colonisation with current tech isn’t a joke, but it is a folly in the sense of British Victorian-era aristocrats — extremely rich people doing fancy but not very cost-effective things.
Fusion isn’t necessary for this, however, as PV scales well enough for a Mars colony (don’t get me wrong, still extremal, but it could be made to work up to about Jupiter if cost of local manufacturing was not a limiting factor).
But: politics. Let’s assume every settlement on Earth has a corresponding space habitat (O’Neill cylinder or whatever) of the same population in Earth orbit. With this situation, rapid transport between any two locations is trivial enough that high school students could accidentally blow everything up up — I made an ion drive while at school (simple ones are easy) but orbital dynamics are counter-intuitive and not something a high schooler is likely to know, so a kid running one in space with that many large stations around has a high risk of causing a Kessler cascade.
Scale the hypothetical scenario up to a K2 swarm around the sun, same applies only with the risk of mass extinction on the home planet.
In either case it can be weaponised, and about 19 years ago a bunch of theocratic fundamentalists demonstrated that a small group of humans can be smart enough to cause enormous harm while also being dumb enough to not predict the consequences.
We already have an idea that stupidity is global liability. As technology becomes more advanced, this liability will grow, and one day we won't be able to ignore it.
The upper layers of Venus' atmosphere are actually reasonably well suited for a floating colony. And as an energy source, fission is almost as good as fusion and we can do that very well.
I'm not sure any of these assumptions are applicable given billions of possible origins of life at various stages of development. Even at Earth, and with extremely conservative estimates, given 100 more years of nanotech/biotech/AI development, we won't die off, and could certainly send autonomous robot probes. When you don't die anymore, 8 years roundtrip (or more) suddenly doesn't seem so long.
BTW in the fiction arena, I suggest reading David Brin "Existence" if you're so inclined which is related to this :)