It is possible to blithely talk about an alien civilization that has lasted a million years, but does the feasibility of this hold up when the details of it are examined? This post will attempt to uncover a few of the issues that might arise, when a civilization transitions from a few millennia out to significantly longer times, such as a hundred or a thousand or ten thousand millennia.
There are physical limitations and societal limitations. Consider a city on an alien planet. Over the course of a hundred years, a river can change its course. Subsidence of seacoast can happen. Over the course of a millennia, there can be significant climate changes. Over the course of hundreds of millennia, coastlines can change from the deposition or removal of materials. Volcanoes can form and erupt, leaving mountains behind. In the ecology area, if there is natural evolution occurring on some portion of the planet, species can form or disappear. Some species can transform certain types of areas, such as beavers building dams along rivers, leading to wetlands, and a change in the types and numbers of different classes of animals and even plants. Extensive grazing by herbivores can reduce a pasture land to a drought-ridden desert area. Glaciers can form, disappear, enlarge or retreat. In short, there can be great changes in the landscape and flora and fauna of the alien planet, and the alien civilization would have to be immune to effects of them.
We are principally talking about alien civilizations which have achieved asymptotic technology. This would allow them a level of control over some of these phenomena. Most certainly, they would have the ability to affect the biology of some areas of the planet, within the bounds formed by the environment and the changes that occur to it. They might be able to forestall desertification in some areas, or ensure that coral reefs, or the alien world’s equivalent of them, continue to form. Other terrestrial changes such as volcanic activity, might be wholly beyond the scope of their civilization. To these changes, they have the option of moving their cities, as, except for the occurrence of what we have termed a planetary peril, the disturbances will remain localized and plenty of area will remain in a constant state such that new cities could be built and maintained for millennia.
As for the cities themselves, basic structural materials cannot be expected to last for a million years. Structural materials, of the most basic type such as concrete, might last a millennia or a few millennia, but then the inevitable decay processes will win out and the materials would have to be replaced or somehow renewed. As an example, consider an alien city, practically closed if not hermetically sealed, which has to be redone. Suppose it was built in the form of a circle. There could be an arc of the circle which was under construction, and when each arc was completed, the adjoining arc would be started. If the whole city was rebuilt on a millennia scale, the reconstruction of separate arcs could be done in a leisurely fashion. To minimize the loss of materials, in other words, to ensure that building materials were recycled, demolition would not be the preferred mode of re-construction, but instead, recycleable segments or components would have to be removed. There would be a process of sealing off the majority of the circular city so that removal of the area under reconstruction could be done. Much of the work in reconstruction of the principal structural elements of the city would have to be done outside of the city’s closed areas, and so there would be a debit to the recycling accounts that would have to be made up by extraction.
Other materials would likely have a shorter recycle time. Machinery might be useful for centuries, as would be communication and transport networks within the city. Air and water recycling might be the shortest, with a mean recycle time of weeks or months. For all this recycling, there are losses.
One of the hobbles for an alien civilization trying to reach its millionth birthday might be recycling losses and the need to replenish the accounts with mining or other extraction activities. A civilization which has, for the material with the highest irreducible loss rate, a loss rate of .01% per year, would have to find during a million years, 100 times the amount of material embodied in the civilization’s cities and infrastructure.
Potassium. This element is used as a trace element in all life on Earth, and may also be in the same position on alien worlds. To recycle 99.99% of potassium, all the effluvium from the bodies of all creatures living in the city, from the aliens themselves, to the intellos, to any organic materials used in the production of foodstuffs, to bacteria living on surfaces, to pets, and probably more, would have to be collected and the potassium completely removed and re-introduced to the city. For a creature weighing 100 kg, the allowed loss represents only 10 g per year, assuming potassium was uniformly distributed through the creature’s body and through all the nutrients consumed as well.
Stop for a moment to consider the painstaking efforts that would be needed to accomplish this level of recycling of a particular trace element. How much biological material is exhaled by a 100 kg breathing creature a year? The air would likely have to be filtered and everything of micron size and up filtered out and returned to the recycling stream that produced solid materials. What is a typical amount of biological material that is lost each year to spillage? Could cleaning up spills reduce the loss rate per creature to less than 10 g per year? Could the piping and other transport machinery in the city keep losses per citizen to less than 10g per year? A slow piping leak might lose many times this before it was detected. Most likely there would have to be a second line of defense, and beyond that, a third line, all devoted to reducing losses of particularly scarce materials.
The more that the recycling for a million years problem is examined, the more it becomes clear that this is a monumental design problem. Transportation between different cities might be enough to cause the 0.01% losses that might be the maximum tolerable limit. Just having citizens enjoy the exterior of the cities might do the same. Reconstruction of the city could put certain types of construction materials or constituents in jeopardy. So, is it a reasonable concept to consider an alien civilization lasting a million years? More investigation certainly needs to be done before it can be considered viable.
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