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Is Interstellar Colonization the Great Filter?
(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.

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Is Interstellar Colonization the Great Filter? - by Crossroads - 01-02-2019, 02:28 PM

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