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Is Interstellar Colonization the Great Filter? - ProxCenBound - 01-02-2019

(Disclaimer: This speculation is only regarding the way the real universe may work. It is not meant as commentary on the setting in any way - the setting works on different assumptions, and is more fun that way. I posted this here because it's an idea that's been floating around in my head for a while and I would love to get the community's thoughts on it.)


The Fermi Paradox asks: If there are aliens, where are they? The Great Filter builds on this and asks: From lifeless chemicals, all the way up to an enormous intergalactic civilization - whose existence would be obvious to us or prevent our having evolved - where lies the Filter that keeps the former from becoming the latter?

Lately I have noticed that in (mostly non-OA) discussions of this topic, there is usually a major assumption that goes unaddressed and even unstated.

Often things are stated like this: We should hope the Great Filter is behind us. If the Great Filter is in front of us, it would mean that technological civilizations such as ours always destroy themselves, since without a major disruption, we will soon be able to colonize other star systems, and with time, the galaxy. The unstated assumption is that interstellar colonization is in fact feasible for a technological species.

But what if it isn't?

Strength of this filter

Interstellar colonization has never yet been proven to be actually possible. Travel to other star systems would mean creating a whole ecosystem and society in a starship, keeping those systems stable for the entire duration of the trip, eliminating the effects of cosmic radiation, zero gravity, and interstellar dust collisions, and efficiently propelling the whole thing across the void. Any of these may turn out to be too difficult. Additionally, any biological lifeform, including us, will be very adapted to its home planet. Other worlds in other star systems will almost certainly be uninhabitable for one reason or another. This adds the additional huge hurdle of terraforming at the destination. One could build additional space habitats instead, but that sort of defeats the purpose of leaving the parent star system.

Perhaps all of the above are technically possible, but they may also be so difficult that civilizations almost never put forth the necessary effort. They may not want to spend the energy on the propulsion, pay the cost of research, engage in something so risky, or have other reasons. Another problem is that a colony would be culturally impoverished, being largely cut off from the main civilization, due to multi-year communication delays. With these undesirable factors, even if a civilization did start an interstellar colony, that colony may not have any interest in starting any daughter colonies. In that case, interstellar colonization would still be the Great Filter.

But wouldn't AIs have a much easier time? They would; however, artificial general intelligence (true AI) has likewise not yet been proven possible - in other words, it may not be possible for a species of a certain intelligence to build an intelligence equal to itself. A human mind is a very complex thing, and this is likely to be the case with any capable mind. Working out a mental architecture that is stable and generally intelligent may prove too difficult. Emulating a human mind to some degree may not boost understanding enough to overcome this - the brain is biochemical, which is very difficult to study. Perfectly copying evolution's designs is usually impractical, even though inspiration is often taken from them.

It's been suggested that someone would eventually send out self-replicating probes, which would overrun a galaxy. However, being able to navigate to and around star systems and building copies of oneself would seem to require general intelligence, thus being dependent on the development of AI.

All of the above is speculative - the point I am making is that we don't know for certain, and so on strictly empirical grounds, interstellar colonization may be the Great Filter.

Weaknesses of other proposed filters

I recently read a book titled The Cosmic Zoo, by Dirk Schulze-Makuch and William Bains. Reviewing what we know about Earth biology, it showed that many proposed past Filters (such as multicellularity) are likely to be breached by life on other planets, since they have been breached several times by life on our own planet. The only evolutionary steps where we can't really tell how difficult it is, are the origin of life itself, and the leap from tool-using intelligence to technological intelligence.

These two seem to me to both have problems as Filters. The origin of life occurred pretty much as soon as possible on Earth, which seems odd if it is so difficult - shouldn't it then have come much later? With the leap to technological intelligence, because it is dependent on so many other things, we can't really say anything about how long it 'typically' takes for evolution to build it. Nonetheless, for evolution to build a larger brain, which handles complex social structures and abstractions, perhaps via some element of runaway sexual selection for intelligence, doesn't seem that difficult. Some habitable zone planets are much older than Earth, so at least some other worlds should have had enough time.

Of course, that last paragraph is more speculative, so there remains the possibility that either or both of those two steps act as Filters.

Other proposed future Filters, such as 'they don't want to colonize' or 'their AI ruler won't allow it' fail because it only takes one civilization to think differently, or even just a subculture of an existing civilization, and the galaxy is soon (in cosmic terms) covered in Dyson spheres. It could even be argued that the lack of evidence for enormous alien civilizations is itself evidence that they cannot exist.


While this possibility may seem disappointing, I don't think it is. It means we don't need to worry for our future if we discover microbes in Martian soil or if we detect evidence of industrial pollution in an exoplanet's atmosphere. Rather than industrial civilizations self-destructing, perhaps they settle in for a long period of technological luxury. Just as during the long hunter-gatherer and farming eras Homo sapiens grew very little demographically or economically, perhaps the industrial-computer era will be similar. Even if interstellar colonization and AI never happen, I think there are still very many new technologies and scientific discoveries to be made.

Across the night sky may lie a great many unknown civilizations, rich and exotic. We still can't detect them, since they don't waste energy emitting strong signals in all directions, and they don't build Dyson spheres since they couldn't use that much energy anyway. But they are there, and perhaps one day we will detect them, message them and eventually hear back, or send a small probe to their system.


Thanks for reading, and I look forward to your comments.

RE: Is Interstellar Colonization the Great Filter? - Rynn - 01-02-2019

I certainly think it's a good candidate. I don't think it's a complete show stopper but something I've often thought about is how the technologies you need to make it feasible have much better applications in the home system. As you say if you're building a generation ship you need to design an self-sustaining economy that can last thousands of years in isolation with just the resources it has. That's hard enough but almost always forgotten in science fiction is the social side; no human society has lasted millenia without conflict and conflict in a small closed system would easily turn fatal. Thus your social science needs to be so sophisticated that you can design a socioeconomic system with a life expectancy (i.e. how long until it experiences a significant violent conflict or drifts towards a system more likely to have one) of millenia. If you can do that you can probably make some very sophisticated social institutions at home, ones that you can monitor and adjust in real time. Thus one of the basic arguments for interstellar colonisation, the exodus of groups that seek political independence, is significantly mitigated.

If you start adding technologies for easier kinds of interstellar colonisation like robotics, automation, molecular manufacturing etc you enable your civilisation to start building huge power harvesting installations. Megastructures like partial Dyson swarms to harvest many exawatts from the system star to be used for projects such as boosting colony vessels to a high fraction of C. But that technology also has a much better use at home. Why dedicate a significant fraction of a Dyson swarm's power output for a significant time just to boost a few thousand people to another system when all of those resources can be used to build habitat space in the swarm? A habitable Dyson swarm would have more livable space than if every star in the galaxy had a score of perfectly habitable planets, all within light minutes of each other.

Another technology that seems to tip the scales towards interstellar colonisation at first is uploading/AI. If you are a civilisation of either you don't need to boost a generation ship, you can boost a neumann probe several orders of magnitude smaller in mass and then email yourself to the facility its descendents build upon arrival. But just like the others there's another use of this technology that tips the scale the other way more. If you run on a processor you can increase your clock rate arbitrarily depending on the capabilities of your systems and code. You don't have to do this but even in very peaceful egalitarian societies it is useful for anyone engaging in serious projects (scientific, artistic, political etc) meaning that it's likely a good fraction of people's time is spent at higher clock rates. A side effect of this is to make the universe grow in size as the subjective time it takes for objects or even light to cross distances increases. That self replicating probe despatched to a system 20ly away at 0.5C might actually take tens of thousands of years to arrive measured by your internal clock. And if you email yourself to it what do you get? Separated from your home civilisation (which could consist of more environments and people than an entire local cluster with civilisations around every star) for tens-hundreds of thousands of years for some different astronomical bodies.

Either dyson swarm would also naturally make building a hypertelescope array total pocket change. Boosting a few million/billion units to orbits 50AU away (making a 100AU wide array) would be very energetically cheap compared to an interstellar ark launch and would be able to resolve objects 1 meter in size over 2500 light years away. You could spot large buildings with it on planets on the other side of the galaxy. Combined with virtual technology the entire galaxy could be recreated to a high degree of accuracy inside a virtual environment with scientific models so accurate that there isn't any significant difference. The only exception to this would be if life was spotted, as there is only so much you could derive about the biochemistry from optical analysis.

None of these make interstellar colonisation impossible, I don't think any realistic GF does, but to my mind they certainly make it far less certain that it would happen. For every civilisation that manages to get to the above technology level the vast majority may never leave their system, instead exploring the universe through their data/models and enjoying a cultural richness beyond any fictional galactic empire.

RE: Is Interstellar Colonization the Great Filter? - SeanR - 01-03-2019

I think the great filter is the square-cube law, and the relatively short period of time when you need megawatts, across a wide swath of the EM spectrum, to affect communication with any usable bandwidth.
It may be that all the older civilizations are no longer throwing their signals out, omnidirectionally, with such power that they're still somewhat recognizable from Earth.

Even a colony or daughter colony, assuming you don't have a technological slip, would presumably use only the mature communications systems, that relied upon highly directional antennas, highly tunable transmitters, and highly discriminating receivers. This assumes that future science doesn't offer something that is as advanced over radio as radio is over shouting, drums and horns, signal fires, and semaphore towers.
So, you may only get a tiny window, of maybe a hundred years or so, to see the use of radio by a distant civilization, then they go almost dead quiet. Not because they're not talking, but because their technology has improved.

As for Dyson spheres. Yes, a colony may simply have to be written off as anything but a future descendant of the origin civilization, but I think that would still happen, if rarely. What may happen, instead, is a civilization which can't save its sun, instead harvesting everything it can and heading off to a single, new, star system to start over. A massive upload period, followed by a multiply-redundant fleet of data ships and Neumann probes, headed off to one new home. There could be a thousand year gap in the history of such peoples, as their ships bridge the space between their old home, with is soon to go supernova star, and their new home, just far enough to be safe from the effects of the supernova.
Or maybe not. Aim for that nearby carbon world in its system's Goldilocks zone. When you get there, the planet, which is almost perfect now, if alien, will have been recently sterilized and be ready for re-seeding with something very like the original home planet's ecosystem.

RE: Is Interstellar Colonization the Great Filter? - extherian - 01-03-2019

The greatest filter of all may well be the emergence of life to begin with. You could have a world covered with water and plenty of oxygen, only for the highly improbable series of coincidences required never to happen, leaving it completely sterile.

I wouldn't be surprised if it turns out there are only a handful of 'garden worlds' across the entire Milky Way, not due to the environment being unsuitable, but because abiogenesis may well be an extremely rare event even in ideal conditions.

RE: Is Interstellar Colonization the Great Filter? - iancampbell - 01-03-2019

IMHO interstellar colonisation may well be easier than we think, assuming that fusion of some sort can be made to work.

The point is that interstellar space is not empty. Best estimates of the size of the Oort cloud of a typical G star is around 2LY radius. Which means that in many cases, the Oort clouds of neighbouring stars would butt up against each other and maybe even interpenetrate. The requirement for fusion is because it's just about the only way of getting reliable energy two light years from the nearest star. As far as we can tell, cometary bodies ("dirty snowballs") contain enough of everything to build world ships (colonies of reasonable size with engines) given time.

So colonists could island-hop across space, with reasonable distances to travel at each step. This also means that, eventually, there would be far more people in interstellar space than close to suns.

RE: Is Interstellar Colonization the Great Filter? - SeanR - 01-03-2019

(01-03-2019, 07:55 AM)iancampbell Wrote: IMHO interstellar colonisation may well be easier than we think, assuming that fusion of some sort can be made to work.

The point is that interstellar space is not empty. Best estimates of the size of the Oort cloud of a typical G star is around 2LY radius. Which means that in many cases, the Oort clouds of neighbouring stars would butt up against each other and maybe even interpenetrate. The requirement for fusion is because it's just about the only way of getting reliable energy two light years from the nearest star. As far as we can tell, cometary bodies ("dirty snowballs") contain enough of everything to build world ships (colonies of reasonable size with engines) given time.

So colonists could island-hop across space, with reasonable distances to travel at each step. This also means that, eventually, there would be far more people in interstellar space than close to suns.

Take that to the next level, and you have clanking Von Newmanns. Ships that use the resources scooped from the oort clouds to create more ships, which take a portion of the population on a slightly tangential direction. By the time they're too far apart for signals to easily carry the news from one to another, they've drifted far enough apart that even the closest relations on the other ship are at best very distant cousins you've only heard of from your great grandparents.

As the ships get further apart, and keep replicating, a significant change in culture wouldn't result in a collapse of the whole diaspora, but gaps in the outward expanding shell.

One way to do that would be to have the ship add to its own mass, in new rings, in the middle of the ship, until the ship was over a certain length, then fabricate a new middle section that was empty, and large enough to support manufacturing a new nose section for the tail ship, and a new engine section, (presuming reaction drives,) for the lead ship, while still facilitating traffic between the front and rear halves. Break down this ring, and either use small impulses to drive the ships onto divergent paths, or drag them up parallel, so they can kick off of each other.