Can Epidemics End an Alien Civilization?

Recently, a well-known blogger facetiously proposed a possible solution to the question of missing aliens: could epidemics have killed them off? This deserves some detailed examination.  This post and the next four all attempt to dig deeper and to provide some overview of the possibility.

Would there be infectious organisms on exo-planets harboring advanced alien civilizations? What helps us answer this is one of the main principles of alienology: convergent evolution. This principle says that the number of mutations that happens on a planet is much, much larger than the number of possible mutations; in other words, every mutation is tried out many times. Since evolution favors the more efficient at survival and reprodution, we would see on each exo-planet that has originated life and undergone billions of years of evolution, all the same niches of life filled. There might not be, at any instant in time, rose bushes on Planet X, but there would be flowers, thorns, pollination in different ways, fragrances emitted, and so on. Everything that works here would have been found and worked there, subject to lots of randomization. The principle works the other way as well, as anything that evolution could have come up with on Planet X, it could have come up with on Earth. The details are all scrambled, but the niches are occupied, the various functions are all there, and so on. 

That means that multi-cellular organisms on Planet X, where “multi” means billions, would be good homes for both infectious single-celled organisms and semi-alive RNA/DNA/protein globs which we call viruses. This has to be tempered with the realization that immune systems would have evolved in the organisms on Planet X as well, and that means that each organism there is actually a battleground between cells and viruses that would like to colonize it, and the organism's immune system cells, which are bent on getting rid of these things. The immune cells have to be able to communicate with whatever organ makes them, so they can call up large numbers when a virulent invasion hits, and so they are unable to go everywhere in the body of the organism, particularly not in the digestive system and the outside of the envelope or “skin” of the organism, plus a few other places. So infections would hit the organism in the digestive tract or on the skin of the organism. The oxygen supply system would also be an area where the immune system cannot easily patrol in large enough numbers to repel a large invasion. 

Another principle of alienology is asymptotic technology, which says that technology is an accumulation of scientific knowledge and engineering principles which builds on itself over time in a society of intelligent organisms, and has to follow some fairly well-developed paths based on how knowledge fits together and how engineering of various tools allows the next stage of technology to be developed. Iron tools allow deep mining to be accomplished; computers allow DNA to be investigated; and on it goes in a reasonably coordinated way. This way comes to an end when all technology is understood, and that does not take very many generations of aliens, perhaps something of the order of a hundred. The final stage is called asymptotic technology, meaning it is the final end or asymptote of technological progress. 

Genetics is one of the last pieces of technology to be brought under complete control of an alien civilization, as it depends on the pre-existence of much other technology to enable all the experiments that have to be done. An alien civilization which has reached asymptotic technology does not have any worries about epidemics of single-celled organisms or viruses. Any individual who become infected can be examined and equipment used to determine exactly what is the infectious agent and what does the technology library say about how to get rid of it quickly. We are not at the stage yet of knowing how to do this, but we can imagine some possibilities, none of which have to be discussed here. What is important, is that there is no mysterious illnesses possible with a sufficiently advanced alien civilization, meaning no epidemics, even locally. All bets are off on an exo-planet which has had its civilization collapse for other reasons, but one which is in the golden age of its existence will have no problems.

This means that epidemics occur only with younger alien civilizations, ones which have not yet passed the genetic grand transformation, after which genetics is wholly understood, and the technology for dealing with it developed and deployed. An alien civilization in the electronics era, the one prior to the genetics revolution, does not have the ability to analyze almost instantaneously genetic blueprints and fabricate antidotes. Instead, such a more primitive alien society must grope around, using trial and error, in the hope of finding a cure for any widespread infection or a vaccine to prevent it by giving the immune system a head start. However, if infections can produce a sufficiently widespread and catastrophic effect on such a early civilization, it would not have a chance to reach the genetic grand transformation, and would relapse into some earlier stage. 

Could an epidemic occur in an alien civilization which has not even reached the electronics or industrial age? This would be a civilization in the agricultural era, where there are few small cities, and the population is spread out over the planet in regions where agriculture is efficient and seasonality not too severe. There might be a slowly moving infection, but with very limited numbers of individuals moving from one area to another, there would not be anything to produce a catastrophe. If the infection was highly lethal, news of it would spread faster than the infection itself. If it were rarely lethal, it would simply become part of the arsenal of the resident aliens' immune system. Thus, epidemics occur in industrial civilizations that have mastered transportation to some degree, not in earlier or later ones.

So the question resolves to: can an alien civilization which falls victim, over the whole planet, to a single type of novel infection, recover from it and with some delay, return to its progress toward the further stages of technology? If the infection is sufficiently lethal, its spread is inhibited. If the infection is not very lethal, it becomes part of the immune system's library of known invasive organisms. Exactly what lethality is needed for a collapse after which there is no recovery, even after a century? If it is too high when it arrives, carriers do not carry it far before expiring. However, if there is no immune system response possible, in other words, if the attacking organism can defeat the immune system of the individual aliens so they do not develop immunity to it, and can then invade and re-invade and re-invade until lethality results, but with plenty of transmission between individuals during the intermission between successive invasions, this might do it. So, an epidemic which attacks the immune system or which is 'immune' to the immune system, which damages individuals on the first attack instead of killing them leaving them more vulnerable to future infections, and which is easily contagious, might eliminate the alien civilization, and prevent it from ever building starships and coming to Earth. Such an infective organisms, a triple-headed threat, might be stopped with social measures in an alien civilization in the industrial era, but that is another question to be answered later.

Peak Technology and Asymptotic Technology

To avoid confusion about the definition of these terms, both of which are important in alienology, it might be useful to clarify them here. Peak technology is what happens when an alien civilization runs into a problem, and is unable to sustain the growth of its scientific knowledge. Problems might be some catastrophe that causes shortages, like the alien civilization's bad luck to be on a planet with minimal resources, and try as they might to use them sparingly, they run out before they get to a complete knowledge of technology, a point which is called asymptotic technology, and their civilization begins a downturn. Science begins to be forgotten, or becomes unusable. There might be knowledge preserved in some sort of records, but there are too few people around who can learn it, so, as far as the whole society goes, it is forgotten. To use an extreme example, a planet with only agricultural villagers remaining after a golden age is one where peak technology has come and gone, no matter what type of recordings of past scientific knowledge there is locked away in some vault in a cave. 

Problems can arise from external sources, such as the famous example of an asteroid impact which is large enough to cripple the civilization and prevent it from recovering; the population is reduced below the critical mass needed to maintain technology, let alone progress in it. Problems can arise from internal sources, such as if biological terrorism leads to the extinction of a large fraction of the population. There are a host of other examples in each of these categories. An encounter with a passing star, enough to alter the orbit of the alien planet is one; the star does not have to get so close as to throw the planet out of its solar system, just close enough to make the orbit more eccentric, so that the whole land mass is covered with ice during aphelion, and it doesn't melt during perihelion. A supernova sufficiently close could do it. Basalt flooding could do it. Incessant war could do it. The desire of a ruling elite to maintain itself, coupled with a fear of social change due to more technology could do it. Even persistent, extreme affluence might do it. 

When a civilization suffers a problem such as this, not all technology is forgotten. Depending on how severe the collapse is, there might only be agricultural expertise left. Or transportation equipment at some level might be maintained, depending only on whatever original resouces are left plus renewable ones. The general idea is conceptualized as this graph:

There is no need for the curve to be smooth; it could just as well be bumpy at any section of it. The duration of time that the civilization spends near peak technology is a function of its population, the planet's natural resources, and many other factors. The slopes of the two sides might be of the same order, or they might be different: for example, the rise might be quite steep, as technology's rate of change feeds on itself, but the loss of technology can be slowed by the struggle to maintain it as long as possible.

If nothing goes wrong, technology just keeps accumulating until there isn't any more that isn't known. This is a very finite process. Sometimes someone makes a comment that implies that technology keeps accelerating forever, but this has no meaning whatsoever. Knowledge of details, such as how much sand is on some beach on some exo-planet, might be accumulated, but data is not science or technology. Science is a matter of understanding how the universe operates, and there is certainly some data involved in it, but it is largely a matter of theories explaining phenomena, patterns that exist, cause and effect relationships, and other things; in general it is the compaction of the ability to explain things that happen or that exist. The compaction starts with generalization which often grows into quantitative expressions describing almost anything. 

Asymptotic technology speeds up as early theories are found and validated, which allow more general questions to be asked. At some point, all the easy concepts are found, and the remaining ones grow harder and harder to develop. Thus, the curve of technology looks like an exponential during its earliest phases, and then tips over and continues to slow in its rate of progress, towards an asymptote of total understanding. This is a description of the general form of the technology-time curve, which looks like this:

The height of the asymptote is always the same, for every alien civilization. It is complete knowledge of science and technology. This simple fact is critically important for the study of alien civilization, in absentia. The coupling is done by the principle called technological determinism, which says that technology dictates the forms that a civilization can take, and since the asymptotic technology for every civilization is the same, the form of all the different alien civilizations in the galaxy will have very much in common. If we can understand how technology will progress, we will have an important tool for the study of all alien civilizations. 

One aspect of technology that assists in the understanding of its eventual progression is that technology builds upon itself. Different areas of technology do not progress at the same rate, but instead, one area will go slowly until another area has passed some threshold where the second area can facilitate progress in the first. Thus, technology evolves in stages, which means that the forms of societies will also go through stages. The most all-encompassing of these stages might be called grand transformations, and these appear to involve, in approximate sequence, fire-making, wood and stone use, agriculture and husbandry, metal use, fossil fuel use and the industrial consequents, electronics and its end-effect of artificial intelligence, genetics and psychology and then interstellar space flight, if the civilization is up to it.

Each of these stages might take different amounts of time to come to full blooming. It might be possible to understand them all separately, using the same model of asymptotic understanding. Early learning is relatively faster than late learning. This means that the middle portion of alienology, after the planet-building and origination and evolution of life and before interstellar travel, where civilization develops, has some principles that can be used to gain insights. This is one of the fundamental bases of this blog.

Does the Drake Equation Make Sense? Part 2.

If life originates, and the planet where this happens continues to reside in the liquid water zone, does it evolve to intelligent life? Are there certain conditions which are prerequisites for intelligence to evolve? Would they be common among such planets, or rare?

In this blog, and certainly elsewhere, it is supposed that tool use, starting with fire, then stone and wood, leads to the increasing capacity of the brain of some dominant organism. An equation, similar in form to the Drake equation can be written for this process, involving the evolution of increasingly complex organisms, starting from the first thing to form which constitutes life, a membrane enclosing some proteins that reproduce in some way, and which also produce more membrane. The steps might include the formation of more complex cells, with different features, the ability to exist in different environments and to consume different chemical energy sources. Then the shift to multicellular organisms has to happen, and many steps of evolution might be inserted into the new formula for the progressive development of capabilities of multicellular organisms. Then, back to single celled organisms, a step has to exist to be able to take energy from photons from the star, with the development of some primitive form of chlorophyll. And it goes on and on, as evolution is a horrendously complicated sequence. Regrettably, we do not understand the sequence completely, not even the conditions on the surface of the planet which are required to allow them to happen. The overall probability of producing intelligent species might be 1.0, meaning inevitable, or 0.000001, meaning intelligence is not a particularly useful capability for most creatures on an exo-planet.

The rise to intelligence is perhaps the most difficult of the probabilities in the Drake equation to estimate, as the evidence of most forms of life does not last for billions of years, with only a few exceptions. It should be one of the first orders of those who study it to come up with the new sets of probabilities, so that these can be studied from a normative sense, and then the whole combined into the Drake factor measuring it.

From intelligence to a civilization, mastering technology up to electronics, is another opportunity for sub-probabilities to be estimated. Here it is much easier, as there is history of our development, and it serves as one example, and a base upon which tangents may be followed. This blog includes, in many of the posts, speculation on the steps involved. There seems to be a natural order by which technology progresses, one stage depending on the previous, and there also seems to be a drive, reminiscent of evolution, which pushes creatures to develop successive stages of technology. Figuring out the steps up to the stage of civilization that we currently inhabit is not so difficult, but the postulation of what happens next is extremely controversial. There seems to be a tendency among modern-day humans to forecast dooms that might be imminent, and if one such doom really exists and is universal among intelligent species, reaching broadcast capability might be chancy, and staying there more chancy.

Another of the assumptions inherent in the Drake equation is that broadcasting is the end point of technology, and it would continue for some long period. It hasn't. There is still some, but the term, L, in the Drake formula may be very short as better ways of shipping large quantities of information around the planet have been found and have displaced broadcasting. This seems likely to continue, so L may be, for us, less than a hundred years. With that short a time, being so lucky as to be listening during the particular century out of billions of years of planetary existence is almost impossible to expect.

The Drake equation, if used with the retrospection of all the decades that have passed since it was first written down, may well indicate that the SETI project is hopeless and should never have been attempted. Many people's lives and careers were involved in it, and certainly some, perhaps many, were overwhelmed by the feelings that if they were successful, their fame would be writ large on the pages of scientific history. Some of the participants talked about the success of the project being a grand changer of the direction of human civilization. With such a result, it is not hard to see how the Drake equation was mis-evaluated in many ways so as to provide a justification for the search. Who wants to have their hopes of a glorious legacy be dashed?

The Drake equation, and indeed the SETI project, did have the value of focussing the attention of many individuals, scientist and non-scientists, on the various steps in the formula. It raises the interest level and provides some motivation for doing the hard scientific work necessary for our continued progress. There is little work going on in some very important areas, such as questions of the origination of life, but there might be even less if the burst of energy and excitement that the SETI project ignited had not happened. Understanding evolution is a continuing scientific task, and it might not have been greatly affected by SETI's popularity, but perhaps as the gaps and uncertainties in Drake's formula become more clear, there will be some effect, and some new Darwins will enter the field and erase the dark gaps in the theory.

Mankind has always tried to understand history, and the nature of man and the nature of civilization, but the Drake equation takes all this non-scientific palaver and demands that it be turned into a quantitative measure of how civilization develops. Historians typically do not make much use of the theory of technological determinism, which says that civilization is forced to adapt to technology, which is forced to follow a certain pattern of temporal stages. If history becomes scientific, this might be the result of the Drake and SETI activity with the greatest influence on the future of humanity. Once history becomes more scientific, a better forecast of the potential futures can be given and we would not have to resort to choosing between a dozen different predictions of dooms.

To summarize, the Drake equation inspires work in the following areas: orbital stability for small rocky planets, origin of life from either a unique event or ordinary conditions, the evolution of life through the millions of steps needed to lead to intelligent creatures, and the transformation of history from an art to a science. With the retrospective understanding we now have, the probability of success of the SETI project likely starts with many zeros, and there does not seem to be any redeeming factors in the equation which would raise it even to the order of a few percent or more. Given the amount of effort that was put into it, it was a good start, insofar as it provides motivation for more good science, and also makes non-scientists aware of the possibilities that we are not alone, and with a good amount of further work, we might know just how not alone we are.

Does the Drake Equation Make Sense?

The Drake Equation was developed in the infancy of the SETI project. The Search for Extra-Terrestrial Intelligence was a US-sponsored project starting over sixty years ago, designed to listen for any kind of electromagnetic broadcasts than another intelligent civilization might be emitting. The equation is simplicity itself, just a product of conditional probabilities. Here it is:

N = R_*^.f_p ^.N_e ^.f_l ^.f_i ^.f_c ^.L

and N is the number of detectable alien civilizations in the galaxy,

R_* is the rate at which stars form in the galaxy,

f_p is the fraction of stars which develop planets,

N_e is the number of planets within a planetary systems which have the right conditions for life,

f_l is the fraction of planets with the right conditions for life which develop life,

f_i is the fraction of planets which develop life up to the level of intelligence,

f_c is the fraction of planets with intelligent life that build systems to radiate electromagnetic waves,

L is the length of time such civilizations persist in their radiation.

There are a number of assumptions made which permit the formula for N to be expressed this way. Let us discuss a few of them.

First, the Milky Way galaxy is chosen as the basis for measuring everything. We only know that life can originate on a spiral arm, far away from the bulge and the black holes which inhabit the center. It seems quite reasonable that life needs billions of years to evolve to the stage where a civilization emerges and starts emitting radiation, and in the bulge, distant stellar encounters happen much more frequently than in the spiral arms. A stellar encounter can create a gravitational pull on a planetary system to disturb it, and a planet which had conditions for life prior to the encounter may be moved either inward or outward relative to its star, where the conditions do not hold. Two solutions might be done for this, either change R_* to only count spiral arm stars or modify all the subsequent probabilities to take into account the different conditions between the spiral arms and the central bulge.

Second, the term detectable can be defined a number of ways. Since radiation dies off as the square of the distance travelled, without absorption, and worse with absorption, does detectable mean detectable with some particular equipment? Imagining a ten kilometer aperture radio dish out beyond Neptune's orbit, and compare that with the original SETI equipment. If one wants to be able to detect a civilization's emissions from the other side of the Milky Way, assuming the central bulge does not intervene, something huge would be required on both ends.

Third, the equation seems to be assuming roughly isotropic radiation, spreading equally in every direction, including the one direction that heads toward Earth. Why would any civilization do that? There might be some transitory period when they were broadcasting for their own planetary uses, but if they wanted to communicate from solar system to solar system, they would develop a narrow beam system that would require only a tiny fraction of the power of an isotropic radiator. But then detectable means that Earth is in the beam of such a system. That would be rather fortuitous.

Fourth, the fraction of stars which develop planets might be, as we now know, approximately one, but developing planets does not mean life can evolve on one of them, or certainly not to the threshold of EM emissions. Stars heavier than our star burn out quickly, and if one included them in the count, they could have planets and one could have the right conditions for life, but these conditions would soon change as the star evolved and died. On the other end of the scale, M dwarfs, the most populous kind of star, doesn't have enough energy output to have a planet with the conditions for life, except if it is close in, and there it would be likely phase-locked, with the same face always directed at the star. There are good objections to assuming life could evolve in such a system.

For the mid-range of stars, where our sun resides, there might be planets, and one or two with the conditions for life, but we know little about the migration of planets, even without the evolution of the parent star. Do smaller planets keep their orbits for billions of years in any planetary system, or does it take billions of years for them to gradually migrate inward or outward? If we change the definition to having a planet of the right size in the liquid water zone for billions of years, the number might drop from about 1.0 to 0.00001. Figuring out long-term stability of orbits should be a fairly simple task for the current state of mathematical astrophysics, but it does not seem to have been done in a comprehensive way that enables on to figure out this term in Drake's equation.

Fifth, exactly what does the “conditions for life” entail? If it is made very loose, the corresponding probability would be high, and the subsequent probability would be less to make up for the looseness. If it is made tight, the inverse happens. At the time the Drake equation was written, mankind did not know how life forms, nor what were the conditions needed for it. Now, sixty years later, the same situation exists. We don't know. It is appalling that so little work is done on the origination for life. One particular question is that, are there some conditions in which life forms over a period of time, something large compared to human lifetimes but small compared to solar lifetimes, like a million years? Or is the situation completely opposite, life only forms if some event happens, and the probability of the event might be very, very small.

Just suppose, as hypothesized in this blog, a mild collision with a large planetoid, which becomes a satellite, is necessary for life. The collision would have occurred in the early part of the solar system's existence. Earth-like planets which did not have that collision in their history might be similar in many conditions to ones which did, but, if the hypothesis is correct, only the latter could have life. There are certainly other events in the history of a planet which might affect the origination of life, such as the chemical composition of the crust, volcanic heating, and asteroidal bombardment.

To be generous, life originated three or four billion years ago, and we do not know the conditions of the Earth's surface, so we are limited in imagining how life could originate. The delay in life origination work might be caused by the delay in planet origination work. Neither is in a good state. There is no reason to think that current conditions on the Earth could lead to an origination of life, assuming all consequences of life were removed. One of the conditions discussed in this blog is the existence of organic oceans on the surface, able to nurture membrane formation as well as complex protein formation. Where might they come from? The mild collision hypothesis is a possibility for this.

Chromosome Genetics

Knowledge abounds here on Earth about the number of chromosomes humans have and how gender is determined by whether a fertilized egg cell has an XY or XX chromosome pair. It's less well known that cell division includes the opening up of all nuclear DNA pairs and the splitting of them into two batches before replication. Even less well known is how hard it is, given today's technology, to separate chromosomes so they can be accessed individually.

It is not exactly clear if there is any other way of harnessing the protein synthesis control capabilities of DNA so that alien cells might have a different way of doing it. Nor even is it known if there are alternatives to DNA to carry genetic information. Genetics in this area is like exo-planetary studies before any exo-planets were discovered. Everything is speculation.

These two questions are somewhat independent. If an alien planet had non-DNA genomes, that still does not mean that they would not have all the genetic information divided up into chromosomes. The alternatives are to have more than one nucleus in the cell, with perhaps one chromosome in each, or to have one nucleus with only one chromosome pair having all the DNA or its equivalent. Why did Earth evolve multiple chromosomes, or rather, why don't all species have just one large circular chromosome as do many single-celled organisms? What is the evolutionary advantage and would it be universal, meaning on other planets as well?

Among contemporary bacteria, there are some with one, two or more circular chromosomes, some with linear chromosomes, and some with a combination. After billions of years of evolution, the competition for a chromosomal shape has not been won by any arrangement, so for bacteria and other prokaryotes at least, there must be little evolutionary advantage between them. This is not true for eukaryotes, multi-cellular organisms, which all seem to have linear chromosomes. Most eukaryotes also have some legacy circular chromosome material, located in the mitochondria or elsewhere, which reproduce independently of the nuclear DNA during cell division.

One advantage is obvious. To have genetic information for many different types of cells, as well as the signaling information for organizing them, there must be much more information, and a circular chromosome or a single linear chromosome with all this information would simply be too large to fit into the nucleus, or for the meiotic proteins to handle. Having everything in large numbers of diverse mitochondria also seems evolutionarily difficult, for the organization of cell replication. So, using DNA or anything else, it appears likely that alien species will have multiple linear chromosomes.

Alien geneticists may run into the same problem that Earth geneticists have: separating chromosomes is difficult. The processes within the cell are quite complex, and there is not enough information on them to allow them to be replicated or imitated in a genetics lab. Neither have there been any simple mechanical solutions to separating chromosomes. Perhaps we are missing the right discovery. By the time asymptotic technology arrives in the genetics area, however, this problem will have been solved.

It's not clear that the ordering of advances and inventions in the genetics grand transformation will make much difference in how an alien civilization will develop. The end result would be the same. But chromosome separation would allow some cost-savings in making genetic changes to organisms, or to the creation of synthetic organisms. If this cost-savings is large, it would emphasize the possibility of having genetically modified or created organisms throughout the civilization.

All we can do now is map the genome of humans and other organisms, and use that information for diagnoses, or in plant and animal breeding. There is some work being done on inserting novel genes into existing plant and animal genomes, but it is very slow. If it were possible to isolate chromosomes rapidly and inexpensively, this would speed up the process. It would also make the process of genetic modification more certain, as a laboratory could simply work with one chromosome and modify it, without having to worry if the modification methodology would accidentally make a modification in another chromosome, with a similar stretch of DNA.

One interesting question to ask is how would an advanced alien society prepare the genetics of their successive generations of their population. Suppose there is an inexpensive way to separate chromosomes. Then, the alien society could simply decide to choose the best set of chromosomes from the copies available. If there is some optimal set, then all the aliens in later generations would be like clones. Alternatively, if the selection was out of the set of a pair of parents (assuming two genders), a wide variety of individuals would remain, but there would be a trend toward more healthy individuals with better capabilities.

Similarly, if there were pairs of parents with some genetic deficiency in one chromosome, specifically in one of the parents, then that chromosome could be eliminated in the resulting next-generation individual. This would result in the gradual elimination of genetic diseases and other problems, although errors in replication remain possible and there would always be a risk of some new mutation arising.

There are many syndromes which arise because of the improper copying of whole chromosomes, meaning extra copies, and with chromosome separation technology, these would be reduced or eliminated as well. Broken chromosomes could be sorted out as well, and mutations arising from copying errors would be detectable and removable. Reading the genome would be less computationally intensive and less prone to mistakes, if each chromosome was read individually. The current Earth method of batching all the chromosomes together and then sorting them out after all the fragments have been read is clearly something that can be improved on.

The technology to separate chromosomes does not seem to be on the horizon, meaning the old methods would be used here for a decade or so. Microbiological investigation into how to make a cell nucleus separate and then how to create microtubules to reach into the mixture and connect to individual chromosomes needs to be done. Once it is well understood how nature accomplishes this task, it would be more reasonable to expect that genetics laboratories can come up with some combination of biological and physical equipment to accomplish chromosome separation. After this, we might see genetics jump forward very fast in potential applications, and this will give us a much clearer idea of what an advanced alien society might be doing with their own technology in this area.

Mineral Planets

Let's use the term mineral planet for planets that an alien species could turn into a sustainable habitat. These are a far cry from an origin planet, which is one which could give birth to life by evolving its own first cells. It is a far cry from a seedable planet, which is one which could not evolve its own starting cells, but which could take a seed of some sort of cells and have them multiply and eventually evolve into something interesting, like an alien civilization. Instead, a mineral planet is one where an advanced civilization could establish mines and habitats, on the surface or below it, and thereby produce enough resources, energy and minerals, to sustain an alien colony without any continuing support from the home planet. It has to persist for a long period. 

There may be very few origin planets in the galaxy, and somewhat more seedable planets, and maybe a huge number of mineral planets. One implication of such a lopsided ratio would be that mineral planets can be stepping stones for an alien civilization to cross the galaxy. Note that some or all alien civilizations may adopt the goal of seeding as many seedable planets as they can, following a philosophy that life is its own goal, and that just like planet-bound species try to disperse as much as they can, alien civilizations try to spread life as much as they can. Traveling 300 light years from a civilization's origin planet to the nearest seedable planet might be simply too much to do, and so finding a network of mineral planets in the general direction of that seedable planet would allow them to gradually work their way over to it, and when close enough, to accomplish the seeding effort with more payload and duration in orbit that they could have if they had to travel 300 light years.

Reliability might play a role here. If a speed of 1% of the speed of light is used as a guess of the maximum speed the civilization might attain with its colony ships, this means 1000 years of reliability is necessary to go to the nearest mineral planet, but 30000 years would be necessary for the closest seedable planet. If the probability of enough equipment lasting 1000 years can get raised to 98%, a risk the civilization might be willing to take, the same equipment has a probability of the same quorum still working after 30000 years of travel of only 55%.

Monitoring a seedable planet is also easier from 10 light years away than 300. It might be that seeding a planet is necessarily a very chancy situation, and multiple visits are the only way to accomplish it and verify that it has been accomplished in such a way that a billion years of evolution or two can follow without total extinction. Maybe seeding can only be handled by landing a small colony on the planet, and staying there for a long period. This could also be accommodated better from a nearby solar system than from a distant one.

Is there anything which can be credibly said about the prevalence of mineral planets? The formation of stars seems to leave a disk of matter revolving around it, which can turn into planets. This is a matter of the disposition of angular momentum, and how hard it is to collect it all in a central body. Everywhere we look we see planets, and our ability to find them is not so great right now, so there are probably many more per cubic light year than we have discovered in our locality. If there are several planets on the average per star, how likely is it that at least one of them is a mineral planet?

To be a mineral planet, the planet has to be mineable and habitable. Planets too close to the star are too hot on the surface to establish a colony, and the temperature below the surface would be higher than the average temperature at any latitude. The orientation of the planet would indicate the spread of temperatures over the planet, from pole to equator, and indicate if there was any latitude above which a colony ship could land and stay without thermal damage. Phase-locked planets provide a different criteria, but if the north pole of a non-rotating planet is designated as the closest-to-star point, then again, there may a latitude beyond which the ship could land.

Too much atmosphere would interfere with colonization, and planets might be excluded on this basis. Since smaller planets cannot long hold onto the atmospheres they have at formation, size is an indicator of this problem. The maximum size depends on the distance from the star, as it is easier to hold onto an atmosphere if the planet is far from the star and the atmosphere is very cold. Cold gases evaporate much more slowly.

Another question to be asked is the radiation level. If the star is a very active one, the colony ship would not even be able to come in close to it, unless some sort of shielding was build into the hull. Perhaps advanced engineering could figure out a way to get a mine dug, and alien colonists down into the mine without receiving too much radiation. Once under the surface, all the radiation is absorbed before reaching them. This is an interesting project to be considered.

With all these factors eliminating candidates, how much might be left? Our surveys of exo-planets are too limiting to calculate this number, but it might be that 90% are no good, meaning one in three stars, of middle class, has a candidate. There is more to being a mineral planet that simply being mineable with a surface not too lethal. There has to be the right mix of minerals.

An alien body has certain needs for elements, and alien technology has a different set of requirements for elements. Together they comprise the shopping list of elements, or rather minerals from which the needed minerals can be extracted. Some small molecules might also be extracted, principally water and carbon dioxide, maybe some others. The distribution of elements on a planet is a result of the original composition of the gas cloud, which comes from the effect of nearby supernovas in the cloud's history. Then there is the condensation question and the diffusion question, with minerals forming as elements and condensing into dust, and then being filtered by the solar wind and light output from the star over millions of years. After that, when the planet forms, geology plays a role in determining which minerals are at the surface.

The only planet we have any experience with is Earth, and it can provide us with a model problem. Suppose there was a planet in a state just like modern Earth but without any atmosphere, without any fossil fuels, no life, and of course no people, meaning no mining. Could an alien colony ship find the right minerals, in accessible form, so that it could produce a sustainable colony here? Perhaps U-235 is the key. We can mine uranium ore, refine it, enrich it, build a reactor, and extract more energy than was needed to construct the reactor and keep it fueled. Alien reactors should be even more efficient in the use of fissionable and fertile fuel than ours are, as we have had only a few decades of experience with fission power. Perhaps the guess of one solar system in three having a mineral planet is not too far from the truth. 

Choosing Colony Planets

An alien civilization with a philosophy of life requiring it to spread and disperse life throughout the galaxy, as far as it can, would need to be very circumspect about where to send a seedship. This adventure would require a great amount of effort from the civilization, and perhaps a good fraction of the resources available to it. On Earth, we have not even begun to figure out how this might be done, but we can assure ourselves this is not going to be easy for any civilization. As little would be left to chance as possible.

If we ask ourselves about the possibility of our civilization encountering another one, knowing where they would likely be is a critical question. They start on their origin planet, but then where do they go? We have learned over the last decade or two that there are huge numbers of exo-planets in the galaxy, but of these, which ones might be even initial candidates for an alien civilization's colonies? What are the characteristics of a possible colony planet? If we know that, then we can concentrate our search for alien life, or rather alien civilization, on that class of planet, and spend less on others.

What we cannot assume is that they will only go to other planets which have already originated life. If their philosophy and reason for continuing their existence is to spread life throughout the galaxy, an origin planet would be low on their list – it already has life and there is no need to go there and seed it. That would be superfluous. Instead, they would want to go where there is no life and is not likely to be if the planet is left to itself. Not just any planet would do. There are certainly some detailed criteria for a reasonably nearby planet, within a hundred or two light years, to even be considered as a possibility.

Many planets might only support the alien civilization itself, and not some ecology of plants, animals, microbes or whatever on it.  Their mandate is to spread life, but if the only way that can be done is to establish a colony, then that is the solution to the lack of planets which might be harbors for primitive life.  The alien civilization can set up colonies in many places, but needs to discriminate as to what distinguishes one possibility from another, as far as spreading life goes.  

One dominant aspect of the choice is sustainability. Sustainability means, for some particular alien species or collection of them, the ability to live for a very long period, measured in lifetimes, on the resources and energy located near and accessible to them. It includes the idea that the population should be able to grow up to some minimum value and still live there for that long period. It is about resources existing on the planet, near the surface, but also about being able to extract enough materials to make an energy source that produces much more energy than all the energy needed to collect and process the materials used in the energy generation and distribution process. There must be enough surplus energy for the other half of the problem, providing all the components, such as habitat and food, needed to sustain the new alien population.

The colony starts out with only the equipment that can be carried on the seedship. The development of the colony would consist of several preliminary stages before the uniform growth stage expands the colony up to the desired population. The first stage involves the landing of whatever is necessary to initiate power production with a minimally sized power reactor, create a habitat, and locate and start to mine and process all necessary mineral deposits. A central manufacturing complex would need to be created that can produce, from the ores found, all the specialized items needed for all the operations of the civilization.

Control of this process is not so critical. Can this be done in an automated fashion, or is it necessary to spend time in orbit, gestating the first generation of aliens, before sending them down with the initial lander? Whether the seeding operation is under AI control or under alien control, much the same steps have to be done. The principal difference is that habitats need to be made for the alien landing party, or some additional manufacturing facilities need to be made to enable expansion of the AI capability.

The question of sustainability is not easy to calculate in advance. Yet this is what an alien civilization must do before attempting to spread its population to a new planet or satellite in a distant solar system. They must make an estimate of whether or not a colony could survive on an exoplanet before taking the extreme expense of sending a seedship there The question is not just can the colony survive for a while, but survive and build a large civilization on the planet. The ultimate question involves the possibility that an alien colony, on a colony planet, could create a civilization large enough to send out its own seedship. If the colony planet was a dead-end, without enough resources for the civilization to grow large enough for the project of going out yet further to another colony planet, it should not be chosen.

The calculation depends on what goes along with the seedship. How much energy does it carry to support the transition from nothingness on the planet to a viable colony? Before this is used up, a seedship must arrange for native energy sources on the planet. This might seem to mean a uranium mine, but the uranium metal is actually a small part of what is needed to build an energy-producing fission reactor. Some parts for the first reactor might come from the ship, and this means that sustainability in energy is going to be developed in stages. The energy from the first reactor would need to be deployed toward a variety of tasks.

Total sustainability means that all mandatory mineral resources are present in the planet's crust, easily accessible, and with not too large a cost in transporting them from their mining site to the central location where the colony's initial population will be centered. For an alien civilization attempting to create a very credible and accurate estimate of this, which they would need before a launch, they would have to first collect all possible information about the planet and the solar system it is located in. The only way to do this from their planet is to build huge telescopes, and it also means asymptotic technology as far as planet formation goes, i.e. having geology completely understood, from the time of the gas cloud through all the changes that go on with the crust of the planet. They would need to be able to tell from the spectrum of the star what the gas cloud that created it contained, as for different elements and the relative concentrations of each.

At this point in Earth science, we have not attempted to make any such calculations, and so we don't really know if it is possible, or how accurate it might be. The accuracy is likely a function of the age of the star, as mixing will take place over its history, and the origination elements will also be burned up as they go deeper into the star's core. Light comes from the star's corona, where elements will linger the longest and where transmutation would be slowest.

Data is also available from the spectrum of the planet itself, where it is simply the reflected spectrum of the parent star. This might tell what was in the atmosphere, and what the large areas of the surface have, to a degree. Reflection spectroscopy is necessarily more difficult that emission spectroscopy, but if the telescope is large enough to portray the planet across many pixels, then some information might be gained from each one. Planets rotate, but that should not interfere with the data collection, once the images start coming in. A telescope of large size, perhaps ten kilometers or more in aperature, would be needed.

Information about the nature of the gas cloud that formed the target exo-planet might be gained also by looking at the other planets of the solar system containing it. A gas cloud which undergoes the great transformation from a rotating self-gravitating glob of dust and gas into a proto-star and spinning disk would also have undergone much diffusion, and this implies that at the radius where the target exo-planet condenses there would be some distribution of elements, but at the radii where other planets condense, there would be a different one, and knowing each of them helps the alien scientists to determine the larger picture of the composition and evolution of the cloud.

One kink in this process is that planets don't necessarily stay at the radius where they condense. The effect of the largest planet or the largest few planets might, in some instances, drive a smaller planet to a different orbital radius. The largest planets might also mutually share angular momentum, and drift to different radii as well. Can this be determined from telescopic observations so that the data from all of the planets can be put to use? A good question, and one we on Earth have not begun to fathom.

None of the scientific steps needed seem to be impossible, even from the viewpoint we have now, with our very limited science. An alien civilization a few hundred years further in science than ours should be able to accomplish them, as far as it is possible. Once this mass of data has been collected, perhaps over a century of observation, the estimation of which visible planet would be best to seed can be done.

Affluence in Two Eras of an Alien Civilization

Recall, for reference, that the early history of an alien civilization is divided into eras based on technological change. Some creature on an origin planet evolves intelligence and manipulative skill, and begins to use objects as tools, such as rocks, sticks, fire, and possibly others. This makes the brain grow, and that species is on the road to having a civilization.

On Earth, this early era is called the Stone Age, but that may be because only stone has lasted for the long period of time since this era began. In this blog, eras are divided by what has been labeled grand transformations, as technology completely reworks the civilization and causes most aspects to adapt to it. Provided the planet has animals, the next phase would be hunting in packs or groups, which give rise to the need for communication, and language results, which also makes the brain grow. They would be developing tools for hunting, and for many other tasks as well. Clay or some other formable material might be used here. There is no mandatory ordering of tasks, as one does not depend on the other. Hunting weapons can be developed without having clay pots. This era might be called the Hunting Weapon Era, and much technology gets developed during this period, as the species has been getting smarter and smarter, and more options will be visualized.

After that, assuming climate is reasonably benign and evolution has been doing what it does in the plant kingdom, there would be an Agricultural Grand Transformation. This is where agricultural tools are developed, and the nomadic species, slowly and gradually, settles down so that some of them live in permanent settlements. These tools would be adapted to whatever plants and crops are first conquered by the species, and this might vary by location on the planet. Different areas should have quite different potential crops, as the alien species adapts wild crops to ones which can be reliably grown.

The next era occurs after another transformation happens, the Industrial. Sources of energy are tapped in this era, starting with wind and water if they are available on the planet, and biomass used with fire in a controlled sense. There would likely have been the use of fire for heating of dwellings and for metal working, and the next step is to use it for other purposes. If there are surface quantities of hydrocarbons, they might be used as well. The first engines might be developed to substitute for wind and water power in areas where they are not available and biomass is.

The Industrial Era gives way to the Electronics Era, which runs all the way from the first development of electical communication up through robotics and automation. It depends on the energy sources of the Industrial Era and must therefore come later. Following that the Genetic Grand Transformaion happens, which must also be even later, as it depends on a large amount of computational power being available.

Affluence can be a corrosive influence during these two intermediate eras, the industrial and the electronics, but the bad effects happen in two different ways. It is generated as technology ramps up productivity, and there soon appear many goods, starting with agricultural ones, but soon moving into a panoply of goods satisfying other needs of the members of the civilization. Since any society in a primitive agricultural situation is worried about population growth outrunning agricultural production, with an additional concern possibly arising because of weather or climate changes, the motivation to continue to work in an affluent period would be diminished. If that reduction spreads to the groups which develop technology, the growth rate slows and it might even stop. This represents a potential halt to this civilization's advance to space-faring.

During the electronics era, a second aspect of affluence might set in. Prior to the Genetics Grand Transformation, there might be no ability within the society to improve the genetic mix. This result has been titled idiocracy, and refers to a differential reduction in the per capita intelligence in the civilization. Again, this would permeate all parts of society, including that sector which produces genetic advances. If it stops for this reason, or for a combination of this and the previous reason, technology never reaches the starship level.

How could an advanced alien civilization not notice that this was happening, and do something about it? One possibility is there are no measures in the civilization to measure motivation or average intelligence. This needs to be combined with the gradualness of these changes. The civilization would have no alarm bells going off, only a slight sense that things were deteriorating. And there are so many other things that happen in a society under rapid technological change, that these effects might escape notice completely.

Another possible answer to this is to ask if life in an alien civilization in these two eras will be calm and coordinated or chaotic and divisive? Calmness would come when basic societal questions have been answered, such as what political and economic arrangements should be in place, what goals the civilization should adopt, how should children be educated, and more. At least in the early part of these two eras, what might be called the social aspect of the grand transformation sequence will not have been worked out. There will be a period during economics, politics, education, and psychology become real sciences, with proper definitions, theories, and deductions. But that period may be delayed for various reasons, such as factionalism based on location, background, profession or other divisions. They will also be delayed until what might be called the neurological revolution takes place, and provides the society with a complete explanation of how the brain works. Thus, these two eras may be so disruptive, in the area of social arrangements, that there is no chance that the two ill effects of affluence are even noticed and certainly paid the proper attention.

One way to summarize this is to say that the side effects of affluence, which is the successful application of technology to the problems of the alien civilization such as the provision of food, shelter and other necessities, overwhelm it and cause the rate of progress in technology to gradually slide lower and lower, and the progress itself becomes more and more inconsequential in the innovations it comes up with. This means that the alien civilization will never get to star travel, and never get to visiting Earth.

Colonizing Half-Hot Planets

A half-hot planet is one which is in a close orbit to its star, is tidally locked, and is small enough to not have an atmosphere. Without an atmosphere, the only way heat can come from the side facing the star to the other side is by conduction through the body of the planet, which is bound to be slow. This would allow the side facing away from the star to radiate away a lot of its heat, and be cold. Thus the planet would be half hot and half cold. 

A recent post suggested aliens might migrate to a frozen world, one distant from its star, where the temperature is well below that of the outer edge of the so-called “habitable zone”, which is a poor name for the zone where water can be a liquid. The idea is that with enough technology, the alien colonists do not need solar photons to support their civilization, but can instead mine uranium and low-atomic-number elements useful for fusion. If the planet has enough of those, and the costs of mining it are small compared to the energy it would produce, including all the processing and everything else connected with power generation, the colonists can simply live under the surface in a comfortable environment, while they mined from one place or another all the minerals needed to support a good living standard.

These frozen planets don't have to be planets. A frozen moon would work just as well. As long as the planet doesn't create a terrible environment around itself, from radiation or something else, a moon would do just nicely.

Another thing to consider is that they don't have to be frozen at all. They can be habitable zone planets or moons, but too small to maintain an atmosphere. They cannot be too hot, as the temperature under the surface would be above tolerable temperatures, and this means there would be refrigeration needed for the living conditions, and perhaps also for all the mines. For too hot a planet, this would certainly mean it was unusable. Where exactly would be the average temperature that would make them intolerable is not so easy to determine, but it couldn't be too high.

There is one exception to that: half-hot worlds. In our solar system, we almost have one of these gems: Mercury. Mercury is phase-locked, but not 1:1, but 3:2. Mercury does not keep one face toward the sun at all times, but gradually rotates. If it were phase-locked at 1:1, like the moon is to the Earth, it might be a candidate.

One nice, somewhat speculative, thing is that the dust cloud which forms a solar system might have some differences in the mineral content of different planets, and even some basic trend. It could be that heavier atoms are more populous, relatively, on inner planets. It is not hard to imaging that dust collects like or similar molecules, and some dust grains collect more uranium and thorium than others, and then drift inwards, relative to lighter ones, such as calcium and sodium. When planets get around to condensing, this would mean that there would be more fissionable elements on inner planets, and in fact the most on the innermost planets, including the ones so close that they get phase-locked at 1:1.

In order to make this story complete, the planet would have to be large enough to stay molten after formation, so that the iron-like elements could sink to the center, leaving everything else to condense elsewhere, such as near the surface at a depth suitable for mining. Now the stage is set for an alien starship to land on the cold side, and begin to mine, both for minerals and for living spaces. Lots of other constraints might pop up, such as there being few quakes, strong enough rock to support mining, and so on. There would certainly be multiple more constraints, and it might be interesting to try and think up a list someday, but the main point is that phase-locked, 1:1 only, planets might be excellent places for an alien civilization to spread to.

These planets give off no signature of life, and except for some other alien civilization who was visiting or inhabiting the same solar system, the colonizers would be undetectable. An orbiting ship sent by the original inhabitants of the solar system might see piles of spoil from the mining, or the relic of an old starship, provided it had very good optics.

Now we have an interesting situation at hand. If the idea of living without the use of solar photons works, and mineral wealth alone is enough to make a planet colonizable, there could be lots of alien colonies, perhaps at a density of more than one per ten solar systems. All of them would be undetectable, no matter how hard a second alien civilization in a nearby solar system tried. The only way to find them would be to go to the solar system where they were, and spend a good amount of time scanning the surfaces very carefully, covering every large moon and every small planet not in the too-hot zone but including all the phase-locked ones.

If a colonizer didn't want to be detected, it might be possible to disguise the few local signatures of their presence, so that even this visiting starship would never know they were there. This would involve spreading out the spoils instead of leaving it in an artificial pile, dismantling the starship they arrived in and bringing the pieces underground, and building nothing on the surface outside of a few sensors. There would be wheel tracks from the vehicles used to explore the surface and look for new mining sites, and for transporting the processed minerals back to the home mine, but balloon tires might make this hard to see as well.

The upshot of all this is that the Milky Way might have a huge number of inhabited planets, and we will never know about them unless they choose to inform us. Instead of having only a very few origin planets, which are planets able to originate life and support it while it evolves to having an intelligent creature on it, there might be underground alien colonies almost anywhere there is a suitable planet. These planets and moons probably number in the billions. The age of the galaxy is of the order of 10 or so billion years, so exponential growth might have happened, and aliens are everywhere, just invisible to us.

Vulnerabilities of Population Reduction

There are the obvious ones, which relate to medium scale disasters that could annihilate a single arcology, and if an alien civilization concentrated its population in one, because they were so reduced in population that's all that was needed, it would mean the end of them. There should not be any surprises left in their solar system, meaning they know where all the asteroids are and their orbits, they know where all the subterranean faults are, they understand the risk of tsunamis and don't take that risk, and the same for anything else that happens on their planet, like hurricanes. With no surprises left, and a choice about where to site their single arcology, is there really any vulnerability?

Obviously, if they didn't know these things, it would be premature to reduce population to that level, so for the sake of the argument, figure they do know them and there is no geology left undone. On the psychology side, is there any risk in the slightest degree from one of them becoming psychopathic, and attempting to sabotage an essential system? Again, they are long past asymptotic technology, which includes psychology, so this is not really possible. Furthermore, the genetics grand transformation has given them all good genes and they also understand how to raise youngsters to be stable contributors to the society. They have to go way back to find in their ancient history a time when there was war and dissent, as every alien is rational and logical, and politics is a solid science now, so no reputable alien could raise objections to the way things are done. Technology simply brings calmness to everything it touches. Thus, an alien who had a passing thought about being a saboteur would simply recall that there are no political systems better than the one they have, maybe for tens of thousands of years, and as far as there still exists the abstract concept of justice, they have it.

There would be robots to fill all appropriate roles, and intellos, the biological equivalent of a robot, filling ones where they would be more efficient. Someone eons ago would have figured out how to keep everyone busy and interested, in who knows what, so there would not be any bored malcontents. Technology simply solves problems, one after another, until there are no more. If an alien civilization gets to this state, they can stay in it for as many thousands of years as they want, providing resources are sufficient and their star doesn't get nasty.

It would be hard for them to think of any vulnerabilities they have, or might have in the next millennia, as they have solved those problems already, except for one.

Aliens.

Not the aliens themselves, but aliens of a different sort from a different solar system. Aliens 1 and aliens 2, for convenience. If aliens 2 began traveling in space before they had reached asymptotic technology, or made the deliberate choice to avoid the calming effect it has, they might be going to another solar system with an open mind about annihilating whatever was living there and taking over the planet. This assumes there are two planets with life on them at some reasonably close distance, which could be unlikely or likely – we don't quite know that yet. So aliens 1 might be aware that there are other solar systems nearby them with planets which could have given rise to life, and they were old enough to have evolved a civilization.

One question we haven't resolved yet is could one alien civilization detect another, and how many light years away could this be done. If the answer to the question is that it would be too impractical to do this, or the engineering of the sensors to scan all the solar systems around them cannot be done, meaning there is some limit to what can be detected that we on Earth haven't figured out, and the aliens 1 have figured it out and there is no way around the limit, then they have an indeterminate risk. No telescope, no matter how big, can see finely enough to pinpont the signature of an advanced civilization, and certainly not enough to tell what stage it is in.

This means that the High Council of Alien World 1 can be sitting around thinking of how low a population they want to design for, and they have no way of determining if another alien civilization, aliens 2, is nearby and if they are going to be totally peaceful, or if they mastered space flight before mastering their own psychology, politics, economics, and a few other topics. And they have only their own history to guide them. They got super peaceful and would certainly not try and take over another civilization's world, but their ancient, ancient history says they weren't always this way. And they see a way that star travel could have been invented early on, if there was some motivation to steer technology development that way.

Naturally, they can come up with a master list of every way some alien 2 civilization could try and displace them from their own planet, and from this list, look for ways where having a low population, concentrated in one arcology at the extreme, would make them more vulnerable. Their first conclusion would be that it is very difficult to undertake such a offensive mission, and probably no alien civilization would want to spend that much resources on doing it. Then they might consult the alien 1 who was the most interested in ancient history, and ask him if any faction in ancient alien world 1 had ever chosen to spend some large fraction of their resouces on attacking another faction in a different region. If their history is anything like Earth's, the answer is: most of them did.

Perhaps there is something inevitable in the evolution of thinking beings that forces them through a period of time in which military adventures dominate their history. Or perhaps only a few worlds have such an period. But, if aliens 1 decide that somewhere in the near parts of the galaxy, aliens 2 are building some armada pointing in their direction, then they have a completely new basis for deciding on how much population they want to have. 

Population Reduction in Alien Civilizations

After an alien civilization gets to the point of asymptotic technology, that is, science is over and done with, they have a number of choices to make. One of them is how much population they wish to maintain. The choice is directly related to how long their resources will last, as for a given level of recycling, twice as many aliens use twice as much resources per time period. 

One aspect of this question relates to the process for reducing population. The direct and immediate solution is to simply gestate fewer aliens and allow the population to shrink at whatever level they could choose. It could be as drastic as going from a billion to a million over a few centuries or generations of alien life. The choice of what target to use is related to their view of themselves and their role in the universe. Is it to simply go extinct, or do they plan to go to some other solar system, in one of the many ways possible? If they choose to travel, there is a minimum population necessary to build the ship or ships. If they just are content to go extinct, an unlikely alternative, they could do it quickly with lots of aliens, or slowly, with only a few. Neither is very pleasant, as resource shortages do not make for high living standards.

This question is interesting, but also interesting is the process for getting the population down. There is one question that stands out: what about all the infrastructure? They don't need all the infrastructure that a larger population needs, and they probably don't want to spend the additional energy and resources to maintain it if it is only there for a ghost population.

Consider first fungible architecture. By this time, resource pressure, or at least the knowledge that it will be happening in the future, has mandated that the aliens will live in large arcologies, where recycling is pretty much total. One arcology might be almost identical with another, so there is no reason to keep the second one going if the first one can handle the population post reduction. In an advanced alien civilization, recycling will be part of everyone's life, and everything will be recyclable, even the entire arcology. So over a period of time, the second arcology might be taken apart, and fed into the recycling system of the first one, supposing they are not too far apart so transportation costs are not a significant factor. This adds to the longevity of the resource base.

In order to make an arcology recyclable, it would have to be divisable into parts, so there would not need to be any crowding of a double population into an arcology. Time for this could be stretched out, as by this time the civilization will have figured out it might have a million years on their home planet, so there is no rush to do anything in a short time. If gestation cycles are a hundred years or so, spending a few of them combining arcologies will not affect much over the long term. Aliens in the superfluous arcology could be given the choice of moving to the remaining one, or staying in the part of it which was not yet taken down. By this time, the arcologies would be self sufficient, with their own power plants, industrial sources of nutrition, air filtration, internal transportation, and everything else necessary to have a comfortable life for the alien population. There could well be some residual agriculture, for specialty products or for the amusement of aliens who wanted to be involved with farming for a period of time, and these would simply be reduced according to the population level drop.

What about the non-fungible parts of the infrastructure? Would there be any monuments, historic places, unique but antique buildings? There might have been, but the lifetime of any of these might only be a few thousand years at the highest, and after that, deterioration unless it was periodically rebuilt. Suppose they had preserved something from their earliest eras, before technology was greatly developed, and this was a part of their culture and something they used to maintain their heritage. With a drastic population reduction, as in the example above of a billion to a million, or something proportionate to this, a few heritage sites might be maintained, but not a large number.

It might not be appreciated that heritage could be a very important part of the alien civilization. Heritage is the reason they decide, over and over again in each generation, that they think their civilization is worth preserving and should not be allowed to become extinct. Each generation would have the possibility to reverse the decisions of previous generations, and, for example, stop work on a starship and instead use the capital to change their activities, to, perhaps, have more jet aircraft and spend much more time flying over the landscape and visiting unique sites on their planet, in person. Without heritage sites, the pressure to keep on track with previous generations might grow less, and reach a tipping point.

So, perhaps there is another factor which comes into play when an alien civilization is thinking about its target population for the long, long term. Having sufficient population to build starships may be one, but another might be having enough to maintain a critical number of very important heritage sites.

Almost everything else would have been conquered by technology. There might not need to be a minimum number to maintain the automated operations which provide energy and the standard of living to the population. This particular factor is not clear, but it could very well be that star travel and heritage sites are the only things which feature in the choice of population numbers.

What this means to us is that if these two problems of minimum population result in numbers fairly small, there might only be one arcology on an alien planet. When we have our huge telescopes, able to focus in on planets in different solar systems, looking for one with a thousand dots of light, probably infrared only, this may not be the signature of an alien civilization that we can find. There might be one dot of light, where they all live, and the rest of the planet has been returned to nature. This would be the situation for almost all of the million years of existence of the alien civilization, whereas the huge populations might be only a thousand or less, meaning a tenth of a percent chance of seeing them during this phase. This is one more signature of an alien civilization that needs to be carefully thought through.

BioFactories and Civilization Detection

In an advanced alien civilization which has passed through the genetic grand transformation, when all biological, neurological and psychological research is completed and accurate and consistent theories are available for everything in those fields, and in addition, all the data available about living organisms is known, there would be extensive use of this knowledge. We cannot, from the current state of our ignorance, predict there will be this or that usage, but it seems highly probable that there will be some industrial uses of genetics. Today we have some of this, and as a matter of fact, we have had such factories ever since fermenting was discovered. 

Cheese, risen bread, beer and wine, along with other fermented vegetables, fish, and some other products, are produced by the use of microorganisms here on Earth. These products represent the simplest possible biofactories, but there is no reason whatsoever to think they are the only ones which will be economically efficient once genetics becomes understood. Even if an alien world did not have yeasts which cause bread to rise, the existence of extensive genetic knowledge would allow such a microorganism to be invented, and then the alien civilization would have risen bread, if they wanted it.

These products involve using whole cells, in an agglomeration, to produce chemical changes in other foodstuffs, producing carbon dioxide, alcohol and lactic acid. There is a natural inefficiency in using whole cells for this, as the cell walls slow down the throughput of the chemicals used for input and output by the microbes. If there was a way to have this reaction without cell walls, the biological factories could be more dense, and possibly more efficient and better controlled. Thus, in an advanced alien civilization, we might see biological factories, producing a great many useful materials, without cells. Instead, a vat would serve as a giant cell wall, while the contents were chosen as only those minimally necessary for the biochemical production.

This advance, assuming it is possible, seems to tear down the wall between biology and organic chemistry. Inside the vat there might be no mitochondria, but instead industrially produced ATP was added as fuel for the reaction. Then the proteins that microbes normally use to catalyze and power the transition would consume the ATP fuel and create the right output. Inside a typical cell there are thousands of proteins with different functions, and only those few necessary to synthesize the desired product would be necessary. If the output molecules were smaller than the proteins needed to make them, a filter would be all that was necessary to extract the output. Likewise, input chemicals might be small enough to pass through a filter which blocked the factory proteins.

The pre-genetics method of making medium weight complex organic molecules can be quite tedious using solely the methods of organic chemistry. A tailored genetic process could be more efficient and more productive, based on resource and energy consumption.

As part of the genetics revolution, the biochemistry of nutritional needs will surely be understood. Once that is done, agriculture might be relegated to specialty production, and the majority of food production will take place on these biological factories. There could be no need for sunlight for these factories, although certainly some development of chloroplast-like nodules might happen and vats could be provided with energy in the form of photons, rather than by fuel in the form of ATP.  If this happens, food would be produced by combining nutritional inputs produced separately, and an entirely new food industry would be born. There would be no need for the biofactories to be located outside the arcologies, or wherever the aliens chose to live, but they could be positioned nearby residential areas, to minimize transportation costs and delays.

If agriculture is slated to disappear after the genetics grand transformation, this means that a huge telescope, large enough to image distant exo-planets, would not see huge parts of the dry land of an exo-planet with an advanced alien civilization turned over to monocropping. In fact, there might be very little visible from agricultural uses, as specialty crops could also be produced in biofactories as well. Freshness is not an issue if the fruit or vegetable is grown a kilometer from your residence.

As noted elsewhere, advanced methods of resource usage reduction will be used to prolong the time that the civilization can depend on buried resources. Recycling of resources would be used as well, so there might not be huge quarries that could be visible from space. Energy supplies, whether that would be uranium and thorium or low atomic weight fusion ingredients, would also be preserved by minimizing the losses of energy, such as for heating residential and industrial areas. Insulation would have been perfected. This implies that there would be no giant infrared signature from the arcologies.

In short, three of the main observational items that we on Earth, in later centuries, might have thought to use to detect alien civilizations with a giant space-based telescope would very well not exist. The biggest detectable would have been agriculture, but that disappears with the genetic revolution. Mining sites, such as huge open-air quarries formed by scraping off the top layer of dirt to gain access to shallow buried resources, would not necessarily still be in use. An example of these would be the tar sands region in Canada. Lastly, the habitations themselves would not be emitting light or infrared in massive amounts, such as our Earth cities do today, instead, there would be only minimal energy being spread out and leaking upwards towards space.

Finding something to search for is quite a challenge. Recall that there are only a few millennia between the emergence of the civilization from the primitive hunter-gatherer level up to the asymptotic technology level, and it would be incredibly coincidental if we happened to turn our telescopes on during that interval. If an advanced alien civilization can last a million years, order of magnitude, it is totally likely that we would observe their planet after they had made all the changes needed to last that long, including agriculture replacement, recycling and waste reduction, and resource use minimization. They would essentially be hiding in plain sight.