Thursday, June 25, 2015

Interstellar Alien Populations

There are many things that could be discussed under this blog post’s title.  The number of planets with intelligent life on them in the galaxy would make an interesting exercise.  How many planets a single alien civilization could spread to is another.  A third might be how many different species of interstellar aliens there could be in the galaxy, one or many?  But it’s about none of these.

This blog is about how an alien civilization might choose how large a population it wants on a single planet, or moon, or wherever they have aliens.  The first thing to discuss is about choosing the number.  It does no good for some intelligent alien, or group of them, or a master computer, or an artificial intelligence serving as an advisor, or whatever it is that figures things out there, to decide what would be an optimal population if there was no way to achieve it.  There are obviously two sides to the problem.  The existing population might be lower than desired and decreasing or the existing population might be higher than desired and increasing.  Or, it could be at optimal and is being maintained there. 

On their home world, we can assume it was evolution that produced the intelligent life that mastered interstellar travel.  The world probably started with some rock and some water, some atmosphere and some solar radiation, and through one mechanism or another, self-replicating somethings formed once and then started to mutate.  It may have been a simple process or a very unusual combination of events.  Right now we don’t know.   We may find out soon by a lucky guess, or it might take a while, but the details of this are not relevant to the population of evolved aliens, except for one aspect.  In order for evolution to take place, the reproduction rate must exceed the stable maintenance rate.  Thus, for some period from the start of life up to the invention of contraception or some other population control concept by an intelligent species, the growth rate of some organisms must be higher than one, and most likely, for competition of species to occur and a filtering out of the more ‘fit’, most must be.  So growth to the limits of available resources for each species is probably a good assumption, where limits might be imposed by food availability, the existence of predators, the existence of pests or infections, seasonal die-offs, or something else. 

After the development of competent contraception, organisms still using individually controlled biological reproduction might choose individually not to reproduce or to reproduce below the stable maintenance rate, leading to a negative growth rate for population.   If part of the over-riding meme set established in the alien civilization involved population growth, the availability of contraception might have little effect, or if the gene set of the alien population was strongly in favor of reproduction instead of being strongly in favor of the precursors to reproduction, sexual activity, the same result might happen.  So, either there is some social control over reproduction rate or there has to be some meme component which stabilizes population.  However, if it is social control or a meme component, how is the optimal value achieved?  More likely, to be able to choose an optimal population and to achieve and maintain it, reproduction has to be done off-line, so to speak.  So, we can assume that asymptotic technology in the alien civilization has early on mastered artificial gestation, and the society can choose the desired population and achieve it.  Population stabilization is about matching birth and death rates, and death rates in an alien civilization would be reduced, but probably not zeroed out, so births would be necessary.  Right now our technology is too primitive to understand what the limits of longevity might be, so no assessment of birth rates necessary for stabilization of population is possible.  But it is some non-zero number.

What is the basis for choosing a stable population level?  Resources is one possibility.  In a solar system with multiple planets, is each planet running on the resources available on that planet, or is there some interplanetary commerce that fills in gaps in resources on one or more planets?  Since Earth is nowhere near figuring out how to do interplanetary travel efficiently, there is no possible assessment as to which material resources, if any, are worth the costs of transport.  Do we want to ship hydrocarbons from Jupiter to Earth?  It depends on the costs of extracting them from Jupiter’s atmosphere, and then of bringing them down to Earth.  Orbital costs might be a small part of this, as once velocity is achieved near Jupiter, you just wait for a long time and then de-orbit at Earth.  A large ship with a small crew might keep costs down.  However, it is not likely that a substantial fraction of the materials needed for sustenance of a population will come from interplanetary transport.  Perhaps rare ones will, but that still means that some types of resources on the home world or wherever is being contemplated for population control will limit the population level.

Resources available depend on the extraction rate.  There are certain amounts available on the planet, and it would be possible to extract them at a faster or a slower rate.  This would mean a larger or small population could be supported.  But the faster resources are extracted, the sooner the planet’s limits are reached.  This is the nub of the population choice question.

Do the aliens want a billion aliens on the planet for a million years, or a million aliens on the planet for a billion years?  The product is somewhat constant, being the total amount of potentially extractable resource of the single type that is most limiting, and how they use it up is their choice.  Maybe it’s a billion aliens for a thousand years or a million aliens for a million years.  Whatever the limiting resource is, given recycling to the practical limit achievable in asymptotic technology, and not counting ones where interplanetary transport can fill in gaps, some limit exists and the tradeoff between duration of habitation and size of the population has to be made.  The tradeoff can be gradual, for example, a half a billion aliens for a thousand years and then a million aliens for half a million years works just as well as the previous example.  The point to be made is that some basis for choosing the population numbers, as a function of time, needs to be made in order to achieve some goals.  The integral of this curve is assumed near constant.

If the goals, as embodied in the memes and expressed by the civilization’s philosophers, are equivalent to dispersal and survival, the curve for population might be large at the outset, so a generation or two of interstellar exploration and colonization ships could be built and sent out, with checking done that another few worlds have been colonized successfully, and then the world can relax and drop back into a low level of population for survival purposes, in case something happens out in the colonies and they are extinguished.

This population curve is quite different than one for an alien civilization with simply survival as their meme.  Then they could procrastinate, and not build interstellar ships until something was going to go wrong on the home planet, or in the home solar system, and then they would send out interstellar ships to the nearest colonizable world with a seed population.  This might require a ramp-up of population, depending on how production was organized on the planet.  

Thus, if it were possible to envision a population map for a civilization with the dispersion meme, you would see an expanding wave of population, starting with a burst on the home planet, and then dying down behind the wave.  It would look like a three-dimensional equivalent of what you see when you drop a stone in a still pond, except the height of the wave would not diminish as it propagates outward.  The equivalent for a civilization with a survival meme would be reminiscent of a frog jumping from lily pad to lily pad in a pond.  Both are interstellar alien civilizations with equivalent asymptotic technology, but the meme makes all the difference.

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