Interstellar Nomads

In a previous post, we have discussed interstellar alien populations. In that post, some considerations were listed that alien planetary management, whatever that is, might use to pick what population curve they wanted to have. The technology necessary to achieve the chosen level was also discussed. It referred to the population on a single home planet. By home planet we mean a planet where the civilization had established cities and was engaged in all the tasks a civilization does. It excluded populations on moons for mining, for example.

In a different post, we have discussed how an alien population might escape from some peril besetting their planet, either one from within the solar system they inhabited or from the surrounding galaxy. How a category two civilization, which has as a fundamental meme component the survival of the aliens themselves, and perhaps some of the ecology of their home world, would migrate was included.

In this post, we discuss an alien civilization that has no home world. They are nomads, roaming from star to star over the course of millennia. It is certainly conceivable that an alien population, of category two would live on an artificial world, restricted to its own solar system. One from category three that was thwarted in achieving its goals of dispersing by finding the galaxy was already occupied by an older civilization might do the same. Both of these would have nowhere to migrate to, and when their star heated up, and they could no longer live on their origin planet, and nothing else in the solar system was habitable, they might live in orbit around the home star.

Just because it changed its output heat by some percentage doesn’t mean it is not stable for another billion years. Having an orbiting world would allow the civilization to adjust the orbital radius for their own convenience. They could orbit near the home planet, which might still be full of minable resources. With robotic technology, mining could be done on an uninhabitable planet, and any orbital ship would need some trickle of resources to make up for recycling losses. It could orbit near a source of deuterium for the power systems, or if the solar system had some, near a source of helium-3. They could be ensconced on one platform, or on multiple to provide backup in case of some dire circumstance. Life could go on, but the population of such a ship, limited by the amount of resources obtainable from the solar system, might be much smaller than the billions the home world formerly held. Even so, they have satisfied their goal of survival for the indefinite future. Actually, with the technology they had, they could set a date on when the star would finally expire.

In a solar system with few metals, or some other scarcity problem, they could migrate to an unoccupied solar system. If the galaxy is already occupied, this could be one where there is no inhabitable planet, but a resource-rich planet or planets. That might exist in their neighborhood and again the meme would be followed.

There is another category entirely. This is an alien civilization, born as are all alien populations on a home world, that advances to asymptotic technology and develops starships, and just decides to leave home and wander. Leaving the home world behind for reasons of survival is easily understood, but why would an interstellar alien civilization choose to downsize their population and simply take off, with no threats to their survival on their home planet in the near future. How would a meme develop that led the civilization to leave it?

Recall that memes develop early in a civilization’s history, and persist through the climb to asymptotic technology. Civilizations that have no memes to provide them with goals may simply leave the track to starship capability, and bump into the Happy Life Great Filter, never to escape. But how would a natural environment lead to a meme for continual voyaging? Perhaps if the natural environment required mobility to survive, it would become embedded in the civilization’s culture. It is not hard to look at Earth and see examples of this. We have tropical quasi-nomadic tribes who live, using agriculture as part of their sustenance, on soil which quickly becomes depleted. The tribes can only live temporarily in one place before being forced to move on. Perhaps a planet where this was the only mode of life would lead to a nomadic meme, and the aliens would seek a happy life only if it involved pulling up stakes periodically and moving elsewhere. One way they could do this is to transfer their population to starships. Euphoria!

Scarcity of energy or resources has been pointed out as a reason to migrate. If the home planet cannot support even a modest population with a high standard of living, migration might be the order of the day. Where would the ships go? If the galaxy is occupied, they could not expect to find a habitable world to take over, barring a tendency to go to war over one. Some stellar systems might be resource-rich, with more resources than a home world could use over the lifetime of the star, or the duration of habitability. In other words, with more resources than the alien civilization on that home planet could ever use. If some nomads came by in a convoy of starships, and used up some, it wouldn’t make much difference in their life, so perhaps they would not object, at least for a period of time. After that period, the nomads could simply move on to another resource-rich solar system within the travel distance of their ships.

It is not really clear from our understanding today whether a starship could be designed for a thousand years of travel, or ten thousand, or more. There may be some basic principles to help figure this out, but we leave it to another post.

What is clear is that there may be starships in solar systems which might be detected, either from nomads or from a home planet that became uninhabitable. These would be very large ships. They would be in orbit around the star, but perhaps around an uninhabitable planet with easily accessible resources. We might detect them as a tiny moon, once we progress beyond the current state of technology which only allows detection of planets. When we develop more capability to do direct imaging of planets, there may be some exo-planetary Galileo who detects moons around a large planet in a nearby solar system, and one of them has some unique features, such as more thermal output than makes sense at its location. Could be the aliens' saunas.