Greg Egan was the first I heard talking about how exponential growth is unsustainable. He talked about it from a hard sci-fi standpoint, noting that you are limited to cubic expansion once your frontier reaches the speed of light.

I am interested in exponential growth in a softer science fiction, where Faster Than Light travel is commonplace and the limit to expansion occurs when you bump into a competing culture. Assuming conflict is inevitable, what kind of culture ultimately wins?

Fast expansionists might lose out because they spread themselves too thin and meet other cultures earlier in their development. But if they are aggressive -- especially if they are xenocidal -- they might win by stealing other cultures' technology.

Slow expansionists might lose out because they do not control as much resources as the big empire, even if they are older and more advanced.

It seems the future belongs to the bullies, but who knows. Maybe there is a confluence of phenomena we do not know about that punishes bullies. If such a confluence exists, how might it look?

Edit: Some clarification

In my universe I assume nothing moves at relativistic velocity compared to anything else, or maybe there is a preferred frame, so space-like movement doesn't get messy. Except when it does, Star Trek style, because it makes for an interesting story. I mentioned hard sci-fi as a contrast to what I am trying to do in my work.

I also assume there are no free niches for whatever reason. Maybe old cultures tend to fill all of the available niches, or they all magically require the same niche.

I use the word "culture" because a civilization can fracture into competing factions or comprise several species. "Culture" seems like a good catch-all term.

By "win" I mean "dominate". Under what circumstances do the aggressive expansionist cultures not dominate the universe?

  • $\begingroup$ FTL - what is that? $\endgroup$
    – paparazzo
    Nov 20, 2016 at 21:20
  • $\begingroup$ @Paparazzi Faster than light. $\endgroup$ Nov 20, 2016 at 21:42
  • $\begingroup$ Should we assume FTL that doesn't lead to time travel? $\endgroup$
    – John_H
    Nov 20, 2016 at 23:27
  • 1
    $\begingroup$ John: the questioner said he was interested in hard SF, so I went ahead and gave him the bad news about mandatory time travel, or at least causality violations. He's writing soft SF, so maybe he doesn't care. $\endgroup$
    – SRM
    Nov 21, 2016 at 0:45
  • $\begingroup$ Where did you hear Greg Egan talk? I thought he never made appearances. $\endgroup$
    – JDługosz
    Nov 21, 2016 at 5:15

4 Answers 4


There is no one answer to this. I won't pretend there is one. What you describe is one of the great questions of life. Each species has its own answer to this, and every one of them is testing the theory every day. As an author, you may choose the answer for your book, but nature gives no singular answer.

Consider this example, paraphrased from Planet Earth, the beautiful BBC documentary from a few years back. They were in the jungle (Amazonian jungle, I believe), and were weaving a story about plant life.

  • For most of time, the great trees form a giant canopy over the jungle. Little light reaches the jungle floor, so it is hard for plants to grow.
  • However, once in a while, an old tree dies and falls, leaving an opening in the canopy. Light shines in.
  • First to the scene are the grasses, which explosively colonize the area.
  • This gives way to to small plants which grow upwards in a race to reach un-shaded space.
  • Vines "cheat," using the other plants as support as it skyrockets to the top of the fray without having to spend all that energy on rigid bodies.
  • While all of this is going on, the hardwoods are slowly growing in the shade of the faster growing plants. They are slow, but tenacious. Soon, it is their superior structural strength that let them rise to the top, and the uninhibited sunlight.
  • Eventually these hardwoods make their way up and rejoin the canopy, sealing the hole in the ceiling for another few decades.

The interesting bit about this is that nobody "loses" in this situation. Each species continues to thrive in this cyclical process.

Also worth questioning is "what is a culture?" It may sound silly, but cultures rarely remain isolated. They're constantly exchanging and intermingling, picking up strong ideas and discarding weaker ones. What does it mean to "win" as a culture? Is the winner the final culture who gets to watch over the dying suns of our galaxy? Or is the winner the one who flourished with the greatest fame? Or perhaps it is the quiet culture that instilled its virtues in virtually every culture that came forth afterwards.

Its a big question. It's literally bigger than all of us. Enjoy it!

  • $\begingroup$ On a galactic scale, cultures are necessarily isolated until their exploration or expansion bumps up against someone else's sphere. So "assuming conflict is inevitable" (like maybe it's a Star Trek kind of universe where everyone magically fills the same niche), must it be that "the future belongs to the bullies"? $\endgroup$ Nov 21, 2016 at 1:30
  • $\begingroup$ @MackTuesday I'd say nearly every single aspect of life from speciation to culture suggests "the future belongs to the bullies" is a very hard position to defend. True, a weak brittle culture will be dominated by a strong aggressive culture, but not all cultures are either weak and brittle or strong and aggressive. Its from the middle grounds where the maddening beauty of culture spirals forth. $\endgroup$
    – Cort Ammon
    Nov 21, 2016 at 1:50
  • $\begingroup$ @MackTuesday As Dorothy Parker said, this is a paraphrase, if the strong rule the roost, why isn't the world run by stevedores? It is the cooperative, the coordinated and the well organized who take command. There is strength in the numbers and in putting the numbers where your strength is. $\endgroup$
    – a4android
    Nov 21, 2016 at 12:33
  • $\begingroup$ There is strength in numbers as long as there's an external threat. Two top predators hitting up against each other never need to cooperate; they may choose to coexist if there are enough resources for both to survive. But faced with finite resources and no reason to band together, why wouldn't the bullies win? $\endgroup$
    – SRM
    Nov 21, 2016 at 15:30
  • $\begingroup$ @SRM In Western society, most of what we are taught leads us to believe the bullies would always win. its mostly based on how we like to think about problems. However, an issue arises with bullying when resources get tight -- sometimes the techniques used to bully consume more resources than those that play nice. Sometimes the best way to win is to simply strive not to lose, and let the other person exhaust themselves. $\endgroup$
    – Cort Ammon
    Nov 21, 2016 at 18:04

With cheap non-causality breaking FTL (under a preferred frame of reference) rapid expansion would be claiming what would be considered the most valuable real estate first; which presumably would be planets that are similar to the one that the species originates from. This may lead to densely populated planets that are sparsely distributed, whenever expansion occurs (up to limits, like distance between galaxies perhaps) it would continue to be to the preferred real estate.

Taking longer to expand via building cloud cities on the gas giants and colonizing the minor objects in a system would mean that there aren't any systems that are unusable and orders of magnitude more population and resource usage per system than colonizing preferred planets.

Assuming Dyson Shells are possible than each shell built around a star is 550 million times the surface area of an earth sized planet. One thousand such spheres would be the equivalent of having a colonized planet around every star at the high end estimates of the milky way. The building of such a sphere may possibly be slower than the other methods, but based on resources available in a conflict the builders of spheres have much more available to them in closer proximity (assuming same ftl) so when competition does occur (under assumptions of similar levels of technology) it would be more reasonable for the planet dwellers to evacuate and settle elsewhere than fight, especially as excluding defensive systems, they can be removed by a big rock falling on them and their settlements are useful only a raw material to the builders of the spheres. Speed to travel, communication, and coordination on multi-galactic scale are factors that could allow for the sphere builders to be halted in their expansion efforts.

Obviously in terms of exponential expansion they are all aggressively expanding the area of space controlled would be different. In terms of the heat death of the universe colonizing all the minor objects may allow for pieces of ones civilization to last longer than the other options, especially if they are able to use artificial black holes for power.


Any FTL travel regardless of technology allows for causality violations. You cannot get around this. If you can ever send a message faster than light then, by having a satelite moving perpendicular to your own movement, you can get messages from the future. So a major conflict would arise with future timelines wanting to secure resources for their own improbable existence.

Here's my favorite explanation of why, without any equations, just geometric pictures. If you're writing hard SF, you must take this into account when adding FTL.

If you're looking for ways to game the system, you might find the answers to this question useful: Are there any ways to allow some form of FTL travel without allowing time travel?

  • $\begingroup$ If you find a universal frame of reference (of which we have no evidence of), and FTL is at some fixed speed relative to that frame of reference, then it does not lead to causality violations. See zaimoni.com/FTL.htm $\endgroup$
    – Yakk
    Nov 21, 2016 at 0:56
  • $\begingroup$ This is discussed on other questions here. See here. It's not an answer to this question. $\endgroup$
    – JDługosz
    Nov 21, 2016 at 7:35
  • 1
    $\begingroup$ You might want to add your link to the proper question (noted above). $\endgroup$
    – JDługosz
    Nov 21, 2016 at 7:37

"culture"? I'll assume you meant "alien civilization", but who knows. Let's take a exponential growth model where P is population at time t, and P° is today's population. Here's the equation P = P° + P°*e^(t/k). Oh, and k is 1E+876 with t in seconds (or nanoseconds, it doesn't really matter). Yeah. If you haven't, I suggest you read a primer on ecology. If two species do not compete for resources, then they shouldn't have any influence on each others growth. It takes competition and cooperation to impact growth. Another source for analogy is our gut biome. The bacteria (viruses, fungi, etc. etc.) are competing with one-another, and to some extent with us. Some people are hurt (ulcers) by their biome, we think we're all helped by them (symbiosis). The ONLY reason I can think of for two (inherently resource competitive) alien civilizations to cooperate or to compete using rule-based agreements is because the cost of non-cooperation/non-compliance would be too high. Given a sufficiently large difference in technology, it seems to me we're talking about indigenous peoples vs the conquistador. You do know what "conquistador" means, right? But your question seems to assume that either "fast" growth will prevail or "slow" growth AND that these rates are internally determined rather than by external competition. This seems to me to be contradictory. If growth rate is internally determined, then no significant external competition has occurred. In our guts, the balance is maintained by a heck of a lot of competition. I suppose you don't happen to know how much of our fecal matter is dead biome? What do you suppose would happen if our immune systems totally shut down? We'd be dead in hours. There's a lot of evidence that our biomes have a strong influence on what we eat, and when we want to eat. Our survival is of only secondary concern to those little nasties.

  • $\begingroup$ Yes, growth rate is intrinsic barring other influences, like crowding or competition, which is why I assume exponential growth is unsustainable. Regarding technological disparity, I see it as a primary factor in competition or lack thereof. If you're a high-tech bully, you won't share, you'll take. But if you expanded quickly and encounter a more advanced people that's small because it was content with what it had, you don't necessarily take. Maybe you get your butt kicked instead. And maybe word gets around that you're a bad neighbor. These are the things I'm considering, among others. $\endgroup$ Nov 21, 2016 at 1:47

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