Are We Late to the Game?

In the eyes of all other alien civilizations, we are aliens to them. Perhaps there is an alien somewhere in the galaxy who is a bit curious about what we might do over the next millennium or so. We spend a lot of thought about how to find them, and perhaps they return the favor.
Suppose we are the good guys, and figure out our social problems, and keep our technology progressing, and eventually get to the stage where we can build a star ship. Yes, distant alien, we decide to do it, and we look long and hard at all the solar systems around us to pick one we want to go to. We first build a giant telescope, with every attachment possible, a wide range of wavelengths to observe in, and we look at all the exo-planets within 300 light years. With this big a machine, we can actually image the exo-planet itself, in poor resolution of course, but we see it going around its star. We can pick one the same size as Earth, around a G star, in the habitable zone, with oxygen in the atmosphere, and no radio emissions to indicate advanced life was already there. We finally seize on a choice, 270 light years out, and begin to design the ship. Experiments alone take a century. Design takes thirty more years, and then construction takes another forty. The ship is a probe, designed to stay in intermittent communication with Earth, and to go into orbit around Sperantia, which is the name we gave the planet.

Earth’s first space ship can accelerate to 0.02 c at peak, just before it slows down, and with all the maneuvering, that means a voyage of over two thousand years. The design of such a long-lived, autonomous system was full of challenges, but Earth succeeded and the ship was built and launched. Then Earth waited. The probe relayed back every ten years that it was doing well, was on course, hadn’t slammed into any space rock, and would keep on chugging along.

Then the long wait was over, the probe had reached Spernatia and gone into orbit. Gobs of data was collected, and then, about 270 years later, reached Earth. Earthlings finally knew what was on the planet they had selected. A climate ranging from ice at the poles to tropical heat near the equator, sea life and plant life and even a variety of animal life, lakes and rivers and glaciers and funny mountains. Instead of mountain ranges, there were plateaus and gigantic pits. If you want to leave a monument for ten thousand years, you can build a colossal pyramid. If you want to leave a monument for ten million years, you can flatten large mountains and spread the spoil around. There was no doubt that this planet had been inhabited, and mined for resources everywhere. Many lakes had the shape of huge quarries, filled in with rain and runoff. Even the coastal seashore had the unmistakable signs of being devoted to resource extraction.

The only conclusion was that this planet had been used up. No New Earth. A faubt ripple of laughter echoes through the galaxy as observing aliens, if there were any, watch the new guys fail.

It doesn’t take that many solo planets, with alien civilizations on them, to travel throughout the galaxy to any sweet spot world and set up a colony there. When they were all gone, and even the penumbra worlds that were almost good enough gone, the civilizations expired. A new world, out on the spiral arms, giving birth to intelligent creatures, would find no place to go when they got ready to travel between stars.

Knowing the exact number of solo worlds doesn’t make much difference. If there are ten million sweet spot worlds in the Milky Way, and an alien civilization needs a new one every fifty thousand years, that means that a single alien civilization will need to go through a hundred thousand planets to last five billion years. A hundred solo worlds leading to star travel will use them all up. Two hundred would use them up in half that time, only two and a half billion years. The Milky Way is over ten billion years old. If only two hundred alien civilizations get started, out of ten million suitable planets, this means the probability of successful civilizations climbing the ladder to technology to the top is very low. More likely, there is simply nothing left of the really good worlds in the Milky Way. Double the number of sweet spot worlds, triple or quadruple them and it doesn’t make a speck of difference.

A previous post noted that if other things didn’t get in the way of an alien civilization climbing the technology ladder up to its highest rungs, resource exhaustion would do it. One possible reprieve might be thought to be colonization. Colonization works if there are almost no planets with alien civilizations in thte galaxy, but otherwise the available planets get used up.

We have been talking about what might be called linear colonization. This is what one category of alien civilizations might do, just transfer their civilization to another planet when the resource exhaustion problem became too much for them, or for that matter, if some peril threatened them. But another category of alien civilization might be called an exponential one, where a single planet founds not one, but two or three or four or more colonies, and that tradition continues. Then the planets get used up much, much faster than with linear colonization. A few of this category and everything is all used up in under a billion years.

New worlds are being born all the time in the Milky Way, and some percentage of them turn into sweet spot worlds. If the alien civilizations formed near the beginning of the galaxy have not already died out, they would be taken over quickly. Otherwise, each generation would consume those of the next generation. Either way, the scenario for Earth getting to the closest sweet spot world would likely play out the same way. Nothing left here. And there is likely nobody left to talk to, no matter which plan for colonization they adopted.

Sochi or Moscow?

Let’s do a thought experiment to try and gain a deeper understanding of the goals of an alien civilization. Suppose you are a Russian citizen living in a little town, Musorberg, in Siberia. You have work there, a family, and no future outside of Musorberg. You can expect your whole life will be there, and you are resigned to it. You have friends, the food is okay, the weather is, well, Siberian, but you have adjusted to it.

One of your good friends gets a gift from a distant in-law of his who works on the Russian railroads. It is a free ticket to anywhere he wants to go. Before he even starts imagining where he would go, he realizes that he is the sole caregiver of his parents, who need him there. He cannot use the ticket. You have been his good friend since before schooldays started, and he gives it to you. You have to decide where you will go.

It boils down to two choices. You can go to Sochi, enjoy time on the seashore of the Black Sea, go see the Olympic Games facilities there, explore nature, feel a warm climate for the first time in your life, and go back to Musorberg with some lifelong memories. The trip would use up your savings and couldn’t be done a second time, so you do there whatever you wanted to for your own amusement and enjoyment. You might be able to borrow a camera and take pictures and bring them back to share.

The other choice is to go to Moscow, and try and get a job there. You have a couple of contacts who are positive about your chances, but it is no sure thing. You would have to have the hiring company bring your family there, but it is your only chance at moving out of Siberia. You are smart, hard-working, healthy, educated, and ambitious. And your family has no other chance and will have no other chance.

Where do you go?

You go to Moscow.

In your mind, there is no comparison between having a good time and accumulating memories, and going to another place where you can improve your life and that of your family and your later descendants. Even thinking of how deprived your life is of amusement opportunities, you still can not justify to yourself for a moment not using the resources you have accumulated, directly and by gift, to do something with lasting effects. True, your memories would be with you for your whole life, and any pictures you take would probably survive you and last longer, but they have little effect other than some pleasure when you think about them or look at the pictures. If you go to Moscow, you might establish yourself, and your life would be changed forever, and for the better.

This thought example is meant to portray, in Earth terms, the decision facing an alien civilization that is deciding how to spend the huge amount of resources on an interstellar flight. They need to decide where to go and what to do there. They could decide to take a group vacation somewhere and do things that amuse themselves. Or they could decide to establish a colony on another planet, well-suited to them. The example would be very different if star travel was cheap, but it is just the opposite. Given that the costs are very high, it would be a calculation of benefits available. There are few benefits to traveling for amusement purposes.

Another way of appreciating the situation that faces an alien civilization that has mastered the art of star travel is to think of someone contemplating taking a vacation. If the cost of the vacation is huge, several years of wages, they simply don’t go. Any sort of purpose that we might impute to an alien civilization has to be put to the cost test. Would they spend the large amount of energy and resources to do something for enjoyment purposes?

The same argument can be made for time. If someone is taking a vacation and it is going to take 10 years to get to the vacation spot, they simply don’t go. Amusement options don’t exist for star travel. In the world of science fiction, anything can be imagined, for example, instant, zero-cost travel to any planet in the galaxy, and in that world, all kinds of adventures and escapes can be also imagined. But that invokes magic. And this blog does not spend time on magic.

The same argument can be made for an investigation. Would an alien civilization travel to a distant solar system to investigate some details of a planet there? Sure, it can be labeled as science, but it is useless science. With a hundred billion planets in the galaxy, what possible use could there be to visiting one at immense cost and long delay to find out something about it that is not observable remotely. For the cost of a single starship, you can build a very large telescope and for the time of travel, you can collect a lot of data. So there are no aliens visiting here for the purpose of seeing how many beaches we have or counting the craters on the moon. Yes, that would be science, and no it would not pay off.

If someone, thinking about aliens visiting, uses the example of Columbus, they are right on track. Columbus did not voyage to the Americas to do science or to have a vacation. He went initially to find a shorter trade route to a known trading mecca, and when he found the estimate of the world’s radius to be off, he founded colonies there. There are no known trading meccas in space we know of, and no shorter route to them, but there are planets that some alien civilization might want to colonize. There does not seem to be any other reason for star travel.

Would Aliens Like Star Travel?

This is a trick question. You are supposed to think of your concept of star travel, chosen from whatever science fiction you found most appealing, and see if you would like it. Then you can address the attributes of that imagined travel, and really ask yourself if you would like it, with all the factors that your science fiction story contained. And that gives you insight into whether aliens would like it. But that’s not remotely the point here.

As far as we can tell, star traveling would be feasible, but extremely difficult, and very expensive. And if an alien civilization was thinking, collectively, as to whether they should fund it and have a star travel project underway, one question that might be thought to be relevant is whether they would like star travel. If a large majority of the aliens in some particular civilization liked it, they would support it, and they would authorize a huge project to go do some. The only problem with this is that it underestimates aliens. Aliens with the capability to perform some star travel are not like they were when they evolved from apes or platypuses or dinosaurs or whatever alien species led to intelligence. They became a civilization and learned technology, and then followed through on that technology until they reached the point where they could travel to other stars. But that’s not all that technology provided them. Technology at some point begins to feed back upon the aliens themselves. It develops means for better teaching, so they can learn more easier. It develops means to make gene modifications, of all types, so they become better at everything, and fairly uniform in attributes involving capabilities. It develops a deep understanding of their minds, and how they work, and what influences them, and how they develop such things as likes. It teaches them ways to evaluate options, and they have the calculational skills to figure out whatever they want to. So they are not like smart primates or platypuses. They are like healthy, athletic, very-well educated geniuses. If someone told them there was going to be a poll to see if enough aliens liked star travel to fund a large project for it, it would be a joke. They already control what they like through the training they get and through the various other influences, such as social organizations, media, and anything else that could affect an associative neural network, which we assume they have.

When the alien civilization learns how their own brains function, that gives them the capability to have those brains tailor-made to live in the society. Brains develop likes not out of a puff of smoke or a whiff of breeze. The alien brain develops likes from the experiences the alien has, and they all will know just how that works. They know where their likes come from, and how to have them come from something else. They understand their own brains; why wouldn’t they? The alien brain is certainly complicated, but given enough research, it too will fall under the umbrella of known science. Once brain operations are understood, does it make sense that the civilization would not use that knowledge? Given a choice between random influences patterning likes and dislikes in an alien brain, and planned and organized influences putting down patterns that make each alien into an ideal citizen, what would they do? Go for randomness because it is more interesting? Divide the population into two and have each half have different likes and dislikes so they could argue over them? No. First of all, arguing over likes and dislikes would be recognized as silly, because they are not something logical or reasonable or debatable. They are simply an accumulation of experiences, processed in clever ways by the brain. Since they know just how that works, why would there be any argument over a like? One alien who liked something could point out the experiences he/she/it had that produced it, and another alien who didn’t could point out the experiences he/she/it had that produced the opposite. Why argue over something that is understood and where the origins are traceable?

It should be kept in mind that this discussion pertains to alien civilizations which have reached asymptotic technology, including asymptotic neurology. Earlier eras might have likes and dislikes, and they would not understand their origins. In these earlier days, there might be some aliens who like the idea of star travel, and others who don’t, but it would make very little difference as their technology would not be up to it anyway. By the time that there is a wide understanding of all the factors that go into sending a vessel to another star, they would be at or near asymptotic technology.

So in order to answer the question, we have to circle around and go back to the alien categories. Those categories that have made a decision favoring star travel would be able to maintain social calm and happiness concerning expenses for star travel by making sure that everyone liked it. Of course, every alien would know that likes and dislikes are certainly not very useful in making decisions, and decisions should be made on the basis of clear calculations about benefits and costs. Memes are the term we have used in this blog to denote the choice a civilization makes about specific things, such as star travel. Once the meme is set and fixed, the alien citizens live in accordance with it.

There is a hidden value to the title question, however. Who sets the memes? Recall that they are set in the interim between grand transitions, principally between the industrial one and the genetic one. The likes and dislikes of the aliens at that stage may play a role in making the decisions as to what memes will be encoded into the social structure of the civilization. So the question, elusive yet critical, is actually how do the influential aliens at the cusp of development of their civilization, prior to universal intelligence but after the options for their future can be laid out, make the decision about whether their civilization will venture into interstellar space.

Sustainable Alien Civilizations

We need to figure out what sustainable means for an alien civilization. The motivation for considering it in this blog is that it has become clear that resource exhaustion is a likely cause of the non-presence of alien visitors here on Earth, if everything else worked out right. By everything else, we mean that there were lots of solo planets, evolution proceeds smoothing on most of them leading to an intelligent species, the species doesn’t kill itself off but develops a civilization, and that civilization proceeds to develop technology all the way up to the limit of asymptotic technology. Then everything else also means that star travel can be done without any insuperable physical problems.

In this ultra-optimisitic view of the development of life in the galaxy, it is resource exhaustion that gets all these civilizations. They run out of first one resource, then another, and so on, until they have virtually nothing left. The alien species in each instance is intelligent, in fact, very intelligent as they have manipulated their own genome to produce intelligence in the highest degree possible for all members of the civilization, and then figured out how to best train their young members to use this intelligence. So they can do the best possible job of managing their decline from a very capable civilization, possessing the ability to travel to another star’s solar system, all the way down, down, down to a civilization that has no resources other than those which are renewed, one way or another, by normal planetary and solar phenomena.

It’s not feasible to ship civilization-sized resource packages from an exo-planet back to the home solar system, so the only materials they have are the ones on their own planet, plus some rare ones which might be worth bringing down from some other body in their own solar system. This interplanetary transport would be accomplished until resource shortages made it too expensive to maintain. Then the inhabitants of the planet fall back to using what is on their own planet. These transitions are not instantaneous. If they are routing fifteen materials back from some asteroids, and scarcity continues to compress the civilization like a vise gradually closing, they might have to drop a few at first, and then later, perhaps after a century or more, drop a few more, and then finally all of them.

Substitutions will go the same way, perhaps starting with only one subsutitution, for example one of the rare earths is gone and they have to use the second best. Fast-forward in time, and others are going. The final stages are when the most plentiful resources become too scarce, meaning to expensive to harvest, and they are down to what the planet naturally provides.

What exactly would sustainable mean to them? During the ending of their society’s technological ability, it would mean using what is available at that time. When there is still scrap metal around, from an abandoned city for example, using metal is sustainable. When it disappears, it is not.

The final stage of sustainable means using biological resources in all their complexity. Genetic manipulation will disappear along with the resources needed to produce the equipment to do it, so evolution or rather mutation will begin the inexorable changes that it does. So, if the alien species maintains its intelligence through one means or another, or at least some fraction of it, they could make use of whatever plant and animal resources that inhabit the planet, in its oceans if there are any, and on land. We on Earth are very familiar a version of this level of living standard, as we have grown through this stage on our way to where we are now.

Now the alien species is in the grip of the biology of the planet. If they are living, based on the biological resources of their own brand of nature, evolution will adapt them to it, and as the biome changes, so would they. We might have a hard time imagining the far side of technology, but it does include evolution returning to power.

Another thing which does occur is an analog of erosion. Knowledge cannot be preserved perfectly. A book might last a thousand years, or less in a situation where there is no technology to preserve it from the environment, but it will eventually crumble. Copies must be made. Will the copying organization have their own interests? Will there be an interest in eliminating it? Possibly. Knowledge is also subject to errors and omissions accumulating, which is the erosion mentioned. Unless it is renewed, as for example practical techniques would be, it slips away over the generations. That means history will evaporate, except for recent history. Does it take ten generations or twenty or fifty before the final version of the history cannot be recognized as the initial version? The number is not important, in the time scale of many hundreds of generations.

Technologically advanced civilizations are a blip in time on those planets which can produce them. And such a civilization would surely realize, early in its climb to asymptotic technology, what its future was. As their technology became more and more developed, they might even have a good handle on when scarcity would hit them, and how it would. Perhaps they would take some measures, to forestall the inevitable, such as reducing their population. Perhaps they would not care about the timing of the inevitable descent. Perhaps this knowledge of their own future would change their perspective on star travel.

So far it is not known here on Earth, not by a long shot, if it Is possible to set up a viable colony on another planet. The resource requirements may be far too high to do it, or there may be a way to accomplish it. Since we are already leaning, in this post, way over on the side of optimism, let’s suppose for the sake of discussion that it is. Now imagine a world, full of glorious cities, plenty of power, resources, and everything desirable, technology at its peak, and the members of this civilization all know the species has a kind of death sentence. Slipping back into evolution in a sustainable living style is not the same as extinction, but evolution will change their species into something else, and then something else again, if it doesn’t eliminate it. How do they respond? Do they say, let’s go and start some colonies on distant planets around distant stars, and ship our history to them so we won’t be forgotten? Then someone would add, and then when they hit the scarcity slope, maybe they will go someplace else and if we’re lucky, they will bring along those old history records from this old planet. Somebody else might ask how many future aliens on the other planet would care about those records, and bother to look at them, much less preserve them on the next step outwards. Is the number zero? Or a negligible number?

What is the point of preserving history, another might ask? It doesn’t do them any good, as asymptotic technology overwhelms history. There is nothing useful in our history that hasn’t already been extracted. It wouldn’t even be much of an amusement to learn about, as asymptotic entertainment could produce more interesting ones at the drop of a hat.

Can they come up with any reason at all, that would stand up to scrutiny, which would indicate a reason for them to build star ships and go start a colony or two? If not, that’s the reason they aren’t here, even in the most optimistic scenario that can be conceived, barring magic.

Recycling Under Scarcity Conditions

As noted in a different post, scarcity is the death knell of alien civilizations. When the resources that they can tap diminish below a certain threshold, the civilization can no longer function. Substitution of more plentiful, but less useful, resources would be done as the most useful but rare ones are depleted, but then, eventually, the substituted resources also begin to grow short, and the search for different substitutes ensues. This process may go on for millennia, but eventually it dies out.

Migrating in one form or another to a different planet can preserve some of the signatures of the civilization, but migration also induces great changes in the civilization. For that matter, so does scarcity. Much has been written in this blog about how alien civilizations might or might not rise to the point where they can consider star travel, but very little about how they could lose this capability once they have gained it. Yet, to determine the likelihood of interstellar voyagers coming to Earth, it is necessary not just to know how many alien civilizations exist and have reached the ability to travel from one solar system to another, but how long they could do it, and what happens to them that takes away the star travel option.

What this means is that the back end of the history of an alien civilization should be given as much attention as the front end. The front end has many, many times as many interesting challenges as the back end. Some of the possible back ends, namely the various galactic, stellar and planetary perils, have been discussed in this blog. One of the possible barriers to an alien civilization reaching star travel, idiocracy, could possibly be resurrected later to cause the loss of the star travel option; the details of post-asymptotic technology idiocracy need to be ironed out.

One aspect of the back end, perhaps the only universal one, is resource consumption and depletion. This comes from the discussion of time scales, which is one of the tools developed to properly speculate about alien civilizations. Geological recycling takes too long. An alien civilization cannot sit around waiting for some basalt flood to pour new resources out on the planet’s surface for them to mine. Geologic time is hundreds of millions of years; alien civilization time is tens of millennia.

What exactly does the downslope of an alien civilization look like when scarcity starts to occur? One way that might be considered as a solution is recycling. Recycling slows down the usage of materials by reusing some percentage, hopefully high, of the discarded exhaust of the civilization. It covers everything, although recycling does not need to get started as early with plentiful resources as with rare ones. Plentiful means that the total amount available compared to the annual usage is huge. Annual usage is the amount needed to fill in the losses that occur in the recycling process. This means that going from a 90% recycling situation to a 99% recycling situation extends the lifetime of the alien civilization by a factor of 10.

Not quite. Recycling is not free. To use an oversimplified example to clarify this point, consider going from a 90% situation to a 99% situation, after the alien population realized their dire straits and decided to see what they could do to alleviate it. To go to 99% means that more recycling has to be done, and harder recycling. Getting the next 9% done might cost more energy and more resources that getting the first 90%. Extracting more and more of something from a finite resource is more and more costly.

Recycling materials has an analog in extracting materials in the first place. There are places where some type of mineral might be easy to extract, where the percentage of the desired element in the ore matrix was high. After they are gone, ores with a lower percentage are available. If the percentage of desired material drops by a factor of ten, that means that ten times as much ore has to be processed to produce the same amount of material. That is a cost factor, meaning either some more currency, which might be equivalent in an advanced civilization to energy, has to be produced, or some other costs have to be reduced. Either build more reactors or accept a lower standard of living, which is also measurable in energy.

Building more reactors is not free either. A fusion reactor takes resources to build, and that means cost, which means energy. After a while, the number of reactors gets to be unacceptable. The total energy cost of the reactor gets to be comparable to the net energy it produces. Building it is a waste of time.

Recycling better and better is also something which has a limit. Because recycling to a high degree consumes resources, there comes a time when an increase in the percentage amount of recycling becomes too expensive.

At this point, it is best to remember the concept of asymptotic technology. This means recycling technology doesn’t just get better and better, in the sense of recycling produces less and less loss with no other consequences. There are consequences, and the consequences are that resources and energy are used up in the recycling facilities, along with all the transportation that has to accompany it. It also has consequences in design of all the infrastructure and goods produced by the civilization. If something is being designed to fit into a plan which allows 99% of the materials to be recycled at low or acceptable costs, that design would have more severe limitations that a design which is made for a 90% plan. Even the activities that go on in the alien civilization have to be limited. So, the bottom line is that some level of recycling is useful, and the level that is achievable depends on what the material is, but there is no technological rescue possible. Technology will delay the collapse of the civilization, through recycling and many other ways, but it is something like a single order of magnitude extension. In other words, if an alien civilization can go on blithely using up resources for three millennia before they become dirt poor again, using all the tricks of recycling and social organization and so on might extend it to thirty millennia.

Life and death of an alien civilization, or specifically the onset and termination of their capability for space flight, occupy a short window of time. How long this window might be deserves to be examined well, as it seems to be a dominant reason for the lack of visitors from far away.

Recycling Fusion Reactor Stations Part 2

Recycling in a long-term stable civilization is different that recycling in a rapidly-changing civilization which has not yet reached asymptotic technology and become as stable as possible, varying only as resources are consumed and extraction costs become higher. Take transportation as an example. In a long-term stable civilization, materials from some transport equipment are obtained when some item is removed from the transportation system, and the materials can be stripped from it and recycled, and then devoted to the task of building a new item, just the same as the one that was scrapped. This creates some efficiencies in recycling. For example, if an alloy of some mixture of metals was needed in a flying car, and the car reaches the end of its life, the components made of that alloy can be taken from the car during disassembly, and sent to a recycling facility. But instead of the recycling facility having to separate the metals back to separate elements, it simply needs to re-process the old metal to bring it back to the same state that it was in when the original parts were made. After asymptotic technology is reached, no new alloys are going to be invented, and the best one was already chosen to be used wherever it was cost-efficient. This does not just hold for alloys, but for many components of different types of materials.

Furthermore, when a flying car, or anything else, is designed, the design team thinks almost first about how to both build and then un-build and recycle the car. It would be designed to be taken apart, which has implications for what materials are used, and how they are combined and put together.

Asymptotic technology applied to recycling also has other advantages. Lower level components can be recycled. Instead of the whole car being recycled, some wheels or bearing or props or tanks or whatever can be recycled, whenever it is most convenient for them. The car would be brought in to the maintenance and recycling area, and, for example, the high-pressure hydrogen tank, which might be the thing with the shortest lifetime, is taken out and sent to recycling, and a new one taken out of inventory and put in its place. This again makes recycling much more efficient when component swapping is done on a mass basis.

These basic principles of design would be used for a power plant as well, not simply mobile elements of the infrastructure. They would be even more effective there. In a fusion power plant, there might be a need for mono-isotopic materials, where the isotope chosen is one with a very small or large neutron cross-section or for some other isotope-specific quality. Then, when some component of the power plant is being recycled, and it was made of mono-isotopic elements in some alloy, the component’s materials do not have to be separated down to elements, and even more importantly, do not have to be isotopically separated again. Once isotopically separated, they stay separated.

What has to be done on the reactor side of the power plant, as opposed to the conversion side, is to recycle components to take out neutron and proton damage, as well as all the other more ordinary types of damage. Ordinary damage includes changes to materials caused by simple aging, from thermal effects which can include increased rates of aging, corrosion, abrasion, contamination, wear, oxidation, and other chemical and physical modes of degradation. Materials which flex can lose their elastic strength over time, and have to be replaced. Materials under stress gradually strain, and have to be reworked. All these things are mandated to be taken care of the combined maintenance and recycling program that keeps a power station alive for its design life, and then disassembles it down to more basic parts so another one can be built at another chosen location.

The unique types of recycling that have to be done at a fusion reactor include resolving problems of neutron damage. Any component near the fusion area will be subject to a flux of neutrons. The flux will be large in either a DD or a DT reactor. Neutrons both transmute elements in the nearby components, but also cause nodal displacements, which accumulate over time, weakening the material. Transmutation in a isotopically separated material might be thought of isotope by isotope. Some neutron caused changes alter the isotope and some alter the element. The latter is more easily taken care of in recycling, and some source of isotopically separated elements are needed to replace what was transmuted. This is a very small fraction of the total amount of materials. Isotopic changes, like what happens when Gd155 absorbs a thermal neutron and become Gd156, might be tolerated to some degree, but if the very high neutron cross-section isotopes were needed, re-separation might be necessary.

Proton damage requires some re-processing of the material to remove any absorbed hydrogen, but also to repair damage caused by the high-energy protons zooming through the material. Almost all materials are damaged, some in unique ways, from this phenomena. Metals might have to be re-annealed; polymers separated and re-polymerized; glasses filtered and recast; and so on.

Some unique efforts might have to be done to metals which were used near to the sources of high magnetic fields, if indeed, magnetic confinement in some shape does prove to be the best way to build a fusion reactor. Magnetic fields strain conductors and these might have to be recycled much more frequently than other parts, such as building materials.

There are questions for us related to nuclear fusion power plants as we on Earth proceed toward deeper understanding of how they might be designed and built, and these questions fit into two categories: is it physically possible to obtain more power out of a fusion reactor than goes into making it and running it; is it economically possible to cover the lifetime costs of a fusion reactor, from construction through disassembly and including disposal of radioactive elements, figured in some sensible currency such as energy itself. Recycling would be a dominant factor in these calculations. If there are some expensive components, figured in energy, that are needed in the reactor side of the station, which have to be recycled frequently because of neutron and proton damage, and the recycling costs are high, the plant may be infeasible.

In other words, recycling costs may make it impossible for any alien civilization to have fusion power except as a curiosity, paid for by other power sources. If this is so, we have the answer to why no aliens can get here. They wouldn’t have the energy resources to build and send the starship. Just for reference, recall that one of the rules of this blog is that magic is not invoked. There is no magic physics that transports an alien ship for no or little energy cost.

What does an alien civilization do if it finds that recycling costs for the best fusion reactor design they can come up with consume more energy that the excess that the reactor produces? Fission power is great as a bridge to fusion, but it has a lower energy density, and nothing like the almost unlimited supply of fuel that deuterium promises. Do they just give up and wait for extinction?

Recycling Fusion Reactor Stations Part I

Recycling could make a tremendous difference in the number of alien civilizations present at any one time in the galaxy. Suppose, just for a number, that there are 1,000 alien civilizations that have passed some hurdle that makes them capable of star flight, let’s say, their first fusion ignition experiment that lights off. Let’s suppose that they were started about one per year, so one is in its first year after the experiment and they are still celebrating. There is also one that is 1000 years old, and for the sake of this discussion, let’s say this is the year that they run out of some critical resource, say, neodymium, and their last fusion power station shuts down for the last time. Also for the sake of the discussion, none of them recycle things at all. Some alien civilization thing about developing technology or overcoming factionalism or life-style choices or whatever caused this, and for the discussion it doesn’t matter what it was.

Now, let’s suppose a different example, of the same galaxy, same number of alien civilizations pass the fusion hurdle each year, but instead of no recycling of neodymium, they recycle it with a 90% recovery rate. This means, for every use of neodymium taking 1 kilogram of it, they get 0.9 kilograms when they are done using the thing it was used for. Now fast-forward ten-thousand years, and we have 10,000 alien civilizations in the galaxy. Ten times as many exist as in the first example, and that means ten times as many can decide to go to Earth on a voyage of discovery, or get mean and try to colonize our planet, or send some neat encoded and hidden message they think will make us all tear our hair out trying to find and decipher it. By the way, they all can easily figure out that primitive civilizations try to do SETI at around our age, and that we are here, so, if they have a positively wicked sense of humor, they send us a hidden signal, encrypted to mean, “Gotcha!”

If star travel is possible at all, the amount of it is related, not necessarily proportionally, but somehow positively correlated with the number of alien civilizations present in the galaxy, and if recycling at even 90% is enough to multiply that number by ten, it is an extremely important thing to figure out if we want to know something about alien visitations to Earth, in the abstract.

One place that might be hard to do recycling would be at the fusion reactors they most likely use to generate power to run their civilization. We on Earth don’t know how to build one of these power plants yet, but we are working on it. Perhaps it will take another hundred years for us to figure it out, but we can still make some estimates based on what we do know. Power plants are pretty easy things to understand, as is nuclear physics. That leaves confinement and heating as the big unknowns, and this in an engineering problem. Let’s just suppose they solve the confinement and heating problem, and then use DT reactions, but with the density tilted toward deuterium. Tritium is a problem to make, so perhaps they can’t make enough in a practical reactor to produce amount needed for equally balanced DT fuel, so they use as much as they can get. It increases the power density to have T there.

Either way, there are a number of pieces of the power station that can be discussed. The DT reaction is just another way to make heat, although the neutrons spewing out of it can be used to generate T out of Li as a side benefit. Once you have the heat in some fluid, molten salt, liquid metal, water, heavy water, organics, or whatever advanced alien civilizations figure out is the best, you pump it over to something to turn the heat in the liquid to electricity, which probably will be the distributable form of energy. It could be something else, like hydrogen or an organic gas for example, but either way, heat comes out of the reactor half of the power station, into the conversion half, and electricity or something else comes out of that and gets distributed.

What would prevent recycling the gizmos that do the conversion? For the case we use on Earth, hot water under pressure might come over to a set of cylinders which turn from the conversion of hot pressurized water into steam. What gets used up so it can’t be recycled? The piping, cylinders, pumps, tanks, control systems, and all the rest are made of materials, and with a good design of them, they are simply returned to the recycling facility after their life of a hundred years or whatever it was designed to be. If the pipe was made of something which oxidizes a bit, even though preventive measures are taken, the oxidized material can be recycled as well, just at a higher cost. If the oxidation was on the inside of the piping, it would be caught in a filter if it separated from the source area. If the oxidation was on the outside of the piping, it would be collected during maintenance.

Lubrication would likely be used, and as it gets dirty, it is replaced. Recycling cleans it up. Electronic components would have to be designed to be taken apart or melted down together and the elements separated. Recycling consists of physical separation of different things to the extent possible, then separation by chemical methods. The point is to get something like raw materials out, although there would be adulterants in any material that is recycled. The amount of the adulterants depends on the effort, meaning energy and resource costs, that go into the recycling. By and large, it does not seem that the conversion side of the fusion power station would lead to a problem for the alien civilization. To visualize a problem, it would be necessary to have some mixing of materials, in large amount, that are very energy expensive in separations. Not much mixing happens in the conversion side of the power station; oxidation or other chemical reactions, electronics parts, and perhaps metal dust accumulating in lubrication. Surely there are more things going on which would lead to costs for recycling, but to get to 90% for each and every material used in its construction does not seem hard to do.

One part that has not been considered is the buildings themselves. Is it possible to design recyclable buildings? If recycling is a prime factor in design, weathering would be designed to be small, at some costs, and then we are left with the same factors as go into any other ordinary recycling venture. Liquids and surfaces get dirty, so the air is filtered and the building partially sealed. Gases escape, so working gases are encased in well-designed containments. Solids oxidize, get abraded, and these are both designed to be minimal.

Without some knowledge, available only in the future here on Earth, of the details of such a conversion system, a cost of recycling the materials in a power plant cannot be compared to the total power production of the plant. It does seem that it is unlikely to be a large fraction, provided recycling is a principal factor in the design of each and every component.

He3 For Starship Power

One form of power for a starship has been discussed before in this blog, antimatter batteries. This is a nice concept, but it is dependent on unknown physical parameters, namely, the energy necessary to ignite cold antimatter with matter. If it is large compared to kinetic energy at normal temperatures, antimatter can be stored easily. If it is small, confinement would be doable only with some sort of magnetic isolation.

Fusion is much better understood. For a large, really large, starship, fusion might be a possible choice. But what kind? There are a number of possibilities. The easiest fuel to get in large quantities, pure deuterium, is not the easiest to fuse. Deuterium is ubiquitous, and can be extracted easily from water or methane or anything else an alien civilization happens to have on hand. Extraction of this isotope of hydrogen is child’s play compared to isolating isotopes of heavier elements. But the cheapest fuel is not necessarily the best.

It is possible to talk about the cross-sections for different nuclear reactions, but it is much easier to talk about two more derivative quantities. One is the temperature at which the reactions take place best, and the other is the power density that is involved. Temperature is really a measure of the speed of the nuclei in the plasma that is fusing, and power density is really a measure of how many reactions are occurring per second. On Earth, experiments are universally done with a different fuel than pure deuterium, notably, half deuterium and half tritium. It is not a question of temperature. These two reactions, deuterium with another deuterium and deuterium with a tritium, both occur at about the same temperature. However, the reaction rate, i.e., the power density, is a hundred times higher with tritium, at the outset of the reactions.

Deuterium and deuterium together produce not helium, as one might guess, but a mixture of tritium and a proton and helium 3 and a neutron. Then the tritium quickly burns up with the deuterium, but the helium 3 not very much. Helium three prefers a somewhat higher temperature to burn. As the deuterium burns, it produces tritium which then quickly burns up, producing some more energy. So the power density of the deuterium mixture climbs a bit as tritium is produced, but still stays far, far below that of a mixture of deuterium and tritium.

Temperature has implications on the size of the reactor. If we assume nothing but magnetic fields can be used to confine a plasma, and there is a limit to the magnetic field strength that can be created with any arrangement, having a higher temperature means the nuclei will need a larger turning circle to be directed back into the center of the plasma. So, having the same temperature means having the same magnetic field requirements, and about the same size reactor. DD and DT need about the same size thing-a-ma-bob to make it fuse, but the DD power density is much less, so you need more of them.

There isn’t much tritium around, as you have to make it and use it up quick as it decays almost as fast as a ripe papaya. A bit longer, fourteen years or so, but still pretty quick. You make it out of lithium, and for the time lithium can be used up as a fuel source, you can make tritium and burn it with deuterium. So, for planets and alien civilizations blessed with available lithium, the fusion big picture is you refine hydrogen to get deuterium, get some tritium seed to start but soon start using lithium as a receiver of neutrons from the reaction of deuterium and tritium so more tritium is available, and with some luck and good karma, you have a fusion reactor making helium 4 and protons and neutrons.
You are also making helium 3, which will burn up eventually, but if you flow the plasma out every once in a while, you can take out the helium 3. You can also take out the helium 4, which does you no good to sit in the plasma. It is possible to use the helium 4 for balloons, and very good freezers, and you can store the helium 3 somewhere in a big tank.

Why would you want to collect helium 3? It just so happens that a helium 3 reactor produces almost no neutrons. Two helium 3 nuclei fuse into helium 4 and protons. If you are on a starship, and have a choice of protons or neutrons, you should choose protons. Protons are turned by a magnetic field, and they don’t do much transmutation of elements into nasty radioactive ones. Protons do embrittlement, and that has to be dealt with, by annealing or some treatment, maybe as part of a recycling process, but neutrons ignore magnetic fields and just go looking for nuclei to hit and change into something else.

When you have a large quantity of radioactive elements, you have to have something around to shield biological things from the radiation produced by decay. That means some shield mass needs to be added to the starship. And you need some separation processes to take care of the reactor components, all of whom receive the neutron dose. While this discussion is at a very elementary level, it just seems like a good idea to use helium three fusion reactors in a star ship, and leave the DT and DD reactors on the ground, producing helium 3 fuel for the starship.

Perhaps there will be countervailing considerations, like having to run the helium 3 reaction hotter, meaning larger volume, but in space, volume does not necessarily mean weight one-for-one. So, clever people might come up with designs for starship fusion reactors, equipped with shadow shields and radioactivity removal processes for a DT reactor, or without nearly as much for a helium 3 reactor, and see which one has the best power to weight ratio. A few hundred years might be enough to get a definitive answer, or maybe a week for a good guess from a really clever person.

If helium 3 reactors are viable for starship propulsive and hotel power, then this has implications. It means that a lot of ground reactors are necessary to produce and collect enough helium 3 fuel for a single starship. This limits the number of starships an alien civilization could produce or rather stock. If resources provides a limit on the number of ground reactors that can exist in the integrated history of the alien civilization, then it would also provide some valuable information on how many starships could be sent out by such a civilization. There could be other resources that limit the number of starships more than helium 3 collection, but this is a start at figuring out how to get to such a number.

Expanding the Concept of Species

A lot of funny things can happen when an alien civilization figures out how to play with their own genetic code. The genetic grand transition would take several generations to come to complete fruition, but long before that happens, interesting things can happen. One relates to tinkering with the aliens’ own genetic code.

It has been discussed before in this blog that once intelligence genes are discovered and understood, it would be not long before they were introduced into the species on a universal basis. However, intelligence genes would only be a tiny fraction of the possible genes discovered. Genes would be searched for in natural surroundings, in all the life forms that co-existed with the alien species, but we should not forget that the genetic grand transition would be expected to come after the robotics transition, and in particular after the generation of great computing capacity was routine. This means that not only naturally occurring genes would be understood, but all kinds of synthetic ones. Genes control sizes and shapes of things, so quantitative changes would be possible in all types of attributes. Non-critical attributes would also be under the control of genes, so it would be possible to have some gland produce additional chemicals that the ones it normally makes. As long as the chemicals do not have a lethal effect, the genes could be placed into an embryo and an alien developed with the ability to produce them.

Suppose this happened, in a thought experiment. If this was before the alien civilization had switched over to industrial gestation, the new alien with the new chemical being made in his/her/its gland would be able to breed with other aliens, and the production of the chemical in the gland would be there or not, depending on which chromosomes or the alien equivalent slipped into the next generation. This means that the alien species has just acquired a new form of diversity. This form was not selected by evolution, but evolution would have not functioned for some time before this stage of the genetic grand transition. If the definition of species is a breeding group, unlike all the other divisions of taxonomy, then the species just got expanded in diversity. This might not mean much for a single genetic change, but what about the time, somewhat later perhaps, when fifty or five hundred changes were invented or discovered. If individuals were making choices as to what genes would go into their descendants, there could be a rapid and huge expansion of their species. Is it still a species? Yes, as long as the five hundred changes do not interfere with the ability of aliens to reproduce.

Later on in the genetic grand transition, when gestation becomes industrial, the concept of species becomes indistinct. No breeding goes on. It could well be that since gestation is industrial, there is no need to preserve the ability of any alien to breed. This means that, whatever you call the collection of aliens that inhabit that advanced civilization, it isn’t a species as that term is irrelevant.

However, before the gestation revolution part of the genetic grand transition, there still is an alien species, but the concept of the species has to be expanded. It could include some incredibly diverse collection of individuals. The range of possibilities depends, at this point in our hypothetical alien civilization, what the previous generation would choose to be the next generation. Various attributes which contribute to the alien’s capabilities, both athletic and mental, survivability, longevity, creativity, dexterity, learning rate, sensor capability, and more and more could be on the table.

Consider some examples. Some pair, or trio or individual or however many the aliens need to breed, might think that enjoying food is a very desirable trait. They might seek out the genetic engineering computer and ask about improving the ability of their offspring to appreciate food. Maybe the ancient form of aliens could taste five things in solution, and five hundred things in vapor. But some animals might have ten things in solution and five thousand things in vapor. Do they want to instruct their embryo fabricator to put these into their next embryo? It isn’t really a good thing or a bad thing? No aliens suffer from not being able to detect these additional tastes and smells. The embryo fabricator explains they would have to find space in the neural processing centers for more taste and smell processing, meaning that something else might have to be reduced.

We might assume that the aliens have already figured out how to do the best neural processing centers, and every embryo is going to get them. That means there is no way to speed things up, and a tradeoff will have to be made. Does audial or visual processing get reduced? Does some other sensory capability suffer a loss? Are motor skills sacrificed for the goal of wider taste and smell capability?

Perhaps the embryo fabricator suggests making lesser changes, perhaps just a few more smells and tastes, but a heightened enjoyment capability. This means more or stronger connections between the smell and taste neural processing centers and the positive reinforcement centers and any neurochemical-producing glands that generate whatever the aliens associate with happiness. Those members of the older generation have to decide on how much interference with other learning and thinking abilities they want to do by increasing the influence that taste and smell have over the higher processing centers. Do they actually want offspring who are very highly motivated to go find interesting foods, but not much motivated to do other things? Liking food is a nice concept, but allocating things in the brain is a constant tradeoff. Maybe they have second thoughts and tell the embryo fabricator that they would like less interest in food, but please take the neural processing resource that is freed up by this and use it for audial processing, so their offspring might appreciate whatever passes for music in their civilization. Is raising a musician better than raising a wine-taster, or some equivalents of these translated into the basics of alien society? How would they make that decision?

Flip a coin, perhaps fifty times, to make some selections? Copy what some other aliens chose? Let the embryo fabricator use his/her/its own best judgment? Do a lottery among themselves?

This type of thinking appears to lead to chaos. Exactly how it might work out requires some more investigation. Would this affect star flight? Yes, as wine-tasters and musicians find their own happiness, and wouldn’t necessarily need to support or even allow the resources of the civilization to be spent on star flight. One set of choices might lead to an alien civilization greatly in favor of these huge expenses, and another the opposite.

The Recycling of Whole Planets

If there are lots of planets that can originate life and support its evolution into a technological civilization, and they all use up the planet’s or solar system’s resources and decline in ten thousand years, give or take a factor of ten, what’s left? A galaxy full of used-up planets, without any civilization there. To be clear, it isn’t the soil or the clean water that gets used up, it is the buried mineral resources. It is possible for soil to regenerate over the period of a century or so, and most civilizations wouldn’t be using it once they developed the technology to synthesize great food of limitless variety. Water which flows around in the usual hydrological cycle cleans itself as well, and the civilization will be doing water recycling itself within the cities so that would not be a problem.

The problem is the lithium will be gone, the iron will be gone, the copper will be gone, the rare earths will be gone, the phosphorus will be gone and lots more. Resource extraction will continue as long as there is extractable ore, but that will be used up eventually. Perhaps one planet somehow has more beryllium in it, from some details of what types of supernovas went off in the general vicinity of the gas cloud which compacted into the star system. Perhaps another has lots more nickel that usual, due to some other cause. These details would indicate just how the civilization would descend into scarcity and then exhaustion, meaning which substitutions would be done last, as living standards declined and then sank below the self-sustainment point.

Some materials, perhaps only the rarest or most valuable ones, might be mined on asteroids, moons or even small planets and used to relieve a bit of the home planet’s scarcity issues. But after some time, the cost of the shipping would increase, and eventually put an end to this source of supply. What happens next? The alien civilization is forced to give up the technology it invented, depending on the resources it could obtain, when those resources gradually gave out. No technology means almost no civilization. The decline might be slow as living standards get lower and lower, and the population declines so that more advantage can be taken of natural resources. Natural resources, such as soil and fresh water, were not needed at the height of technological civilization, but they remained available after it was over.

Power from fusion plants could have powered the civilization for millennia, but as the resources needed to construct new generations of power plants became scarcer, the option for the civilization having power drops drastically. Perhaps with remaining resources some other energy sources could be harvested. But eventually, the population returns to something independent of resources, a pre-industrial era reborn after the technological era has run its course.

Once the civilization returns to the pre-industrial level, the game is finished. Evolution will soon start affecting the population again, as some mutations will occur and the high technology needed to repair them is gone. If the alien civilization made the choice to go with solely artificial gestation, they become extinct a generation or so after the power goes off for the last time. If instead there were residual parts of the alien population which preserved biological reproduction, their species could continue, albeit at the mercy of natural forces.

How long would an agricultural civilization continue to exist and inhabit their planet? It is not clear at this time what the major factors would be that would affect their longevity. One factor might be that intelligence would gradually drop as mutations affected the gene kit that contributes to advanced intelligence. Some level of intelligence would be selected by nature, but it would be appropriate to an agricultural society.

The whole planet is used up, but not everything in the planet. What is used up specifically are the resources in the top kilometer or so of crust of the planet. With the passage of geological time, the crust is partially replaced with materials from deeper areas. One source of this is volcanic eruption, including individual volcanoes and also basalt floods, which, although fewer, involve more material. The other source is the upwelling and downwelling of continental material. It is well known that, at least on Earth, continents move. They also collide, which thrusts some continental material up to higher altitudes. Continental drift happens over hundreds of millions of years, so that the crustal material might be recycled over a period of the order of a billion years.

Material deeper in the crust is exposed through weathering, which over geological time, is very extensive. It is also possible that rifts open in the crust, exposing more material. It could be assumed that alien scientists would be able to find all good mineral resources on their own planet before the end of the age of technology, but mining deeper than a kilometer is very expensive, and might waste more resources that it provides.

So, a whole planet is recycled in geological times, of the order of a billion years and it is a great stretch of imagination to assume that the former alien civilization is still farming the land waiting for the resources to come back. What it does mean, however, is that after a billion years another alien civilization might arise, and do the same thing all over again.

This means that if we are investigating whether the absence of alien visitors is caused by them all dying out in a short time, measured in millennia, and the numbers of places they could visit pales in comparison to the number of planets that might be interesting, then it might be necessary to throw in another factor of two or three to take into account that a great planet that originated life once might do it again and again. A larger factor is not possible because it takes geological times to recycle a whole planet, not simply a million years or so. It also cannot be much more because the star is going to change its output over the same time scale, billions of years, and this means the planet will be out of the habitable zone before too long. The planet does not change its orbit, of course, but the star heating up will push the limits of the habitable zone outwards, and soon the inner edge will pass the orbital radius of the planet which once gave rise to intelligent life. No more chances for this planet.

Did Aliens Visit the Dinosaurs?

We ask the questions: “Where are all the aliens?” and “Why haven’t aliens visited us?” These are excellent questions and have motivated this blog for a while. But maybe aliens did visit Earth, but they just got here a little early. Maybe they arrived when the dinosaurs were here.

When we talk about the timing of alien civilizations, there are certain basic estimates that need to be made. One is the length of time between the first light-off of a sun, and the first light-off of a stellar vessel propulsor taking the vessel away from an alien civilization on a planet of that same sun. Let’s just say it is between 2 billion and 5 billion years, with the average about 3.5 billion years. Another estimate relates to the production of stars in a galaxy like the Milky Way. There is an initial burst of them when the galaxy first forms, and then the rate levels out. In our dear Milky Way, maybe 300 billion stars got formed in the first few hundred million years, which was the initial formation time. It was sudden, wasn’t it?

After that, stars get formed, mostly in the disk, and let’s say, every revolution, a galactic year which takes 200 million years, another half billion stars get formed. The galaxy is said to be about 12 billion years old, which is about 60 galactic years. That puts the total number up to 30 billion formed late plus 300 billion formed early for a total of 330 billion total, which is close enough.

Another estimate, wholly unknown, is how many alien civilizations form per star. Let’s just take a number, and say 0.01. One percent of stars have all the right conditions to form an alien civilization. Maybe this number is 10 or 100 or 1000 times too large, so it might be thought of as an upper bound. That means every galactic year, five million appropriate stars with solar systems get formed which lead to, about 3.5 billion years later, to starship launchers.

So, during the 200 million year reign of the dinosaurs on our planet, there were five million civilizations that toured the galaxy, and maybe some of them dropped down to look at Tyrannosaurus Rex.

The last estimate is how long a civilization can last. This is governed by the usage rate of the resources on the planet and any other planets they can take control of. The number might have an upper bound of 10,000 years, assuming a store of resources that will last them 1000 years at full population and full technology, and 10,000 with 90% recycling. This means all the alien civilizations that visited the dinosaurs have all died out by now.

Since visiting a star takes a terribly long time, and a terribly lot of resources, let’s suppose on the average an alien civilization visits 10 other planets before becoming extinct. We are assuming that colonizing is too expensive to happen, otherwise some multiplier needs to be added.

By simple arithmetic, there is on the average only .025 alien civilizations starting per year, and only 250 that exist at any time. More arithmetic says that in a galactic year, 50 million visits by aliens to exo-planets happen, or about 0.25 per year. Then, during our last 3000 years, which is about as long as we might have records of an alien visit, 750 planets were visited. If aliens consider visiting 10% of the stars in the disc, maybe 30 billion, and each has one planet that aliens might want to visit, that is 3 billion worthwhile planets, out of which 750 were visited during the time we would have noticed them. So, while it is quite possible that some dinosaur looked up and saw an alien ship, or was actually hunted down by an alien team of collectors, or whatever, it is very, very improbable that any aliens have visited our planet when we would have noticed. The ratio of 750 to 3 billion is quite small, and even if you throw a factor of ten or a hundred or a thousand into the mix somewhere, such as by assuming 99% recycling or colonization or anywhere else, it still does not change from very, very improbable.

This means that there is no reason to look further than resource exhaustion to explain why aliens have not visited Earth, and that digging deeper into the question of resource usage might provide some important insights. One tradeoff is population reduction. If an alien civilization reduces its population to increase the longevity of its civilization, it can extend the exhaustion time inversely proportionally to the population reduction up to a point. There are certain fixed costs which must be met, out of resources, and maintaining a population of something as low as 1 million might not use much less resources than a population of 10 million.

The reason there is this saturation effect is that some things cannot be done small. For example, perhaps the most important example, is the power source of the population. If it is DD fusion, there may well be a minimum size that even the asymptotically clever scientists and engineers of an alien civilization cannot beat. That power station might be able to serve 30 million aliens, and keeping it going costs a certain amount of resources every year. Reducing the population down to 1 million doesn’t affect the power plant costs very much.

Recycling is another mandatory activity of an alien civilization that hopes to last a long time. It may well be that a complex recycling plant, able to recycle all resources that are consumed by an advanced civilization with a high living standard, has to be some minimum size in order to be efficient. The amount of cleverness that can be used to make this number small could be large, we simple don’t know as we do not do much recycling ourselves, but it might set a minimum population size as well, and that number might be comparable with the power station minimum. We don’t know enough about either of these things to know if either, or something else more abstruse, poses a lower bound on the population, but the concept of a lower bound is clear. Maybe it is not possible to have a small biological factory for some things. Maybe there are high fixed asset costs for maintaining a robot population or an intello population. Perhaps knowledge preservation imposes high costs on the civilization. Whatever does, means that there is a limit to the extension of the time between when a civilization starts to seriously consume resources, perhaps at the industrial grand transition, to when it hits the scarcity and then exhaustion barriers.

No substantive conclusions can be drawn here, but it appears that die-off is a possible cause of the absence of aliens. Nobody came by during the window of opportunity our species provided because there are too few of them surviving long enough to get here.

Are There Alien Civilizations in the Galactic Bulge?

The galactic bulge, or the galactic center, or the galactic bar, is a bunch of stars in a spheroidal cluster at the center of the Milky Way. Because of the distance to it, and the dust between it and Earth, it has not yet been established exactly how big it is, or what its shape is. This is not unusual, as even the spiral arms of the Milky Way are not yet well understood. Other galaxies are much better mapped, so we can make analogies.

The stellar population of the Milky Way is also uncertain, with estimates in the low hundreds of billions of stars. A few things are known about the bulge. The stars there are old. The ages are like that of the globular clusters, dating back to a billion years or so after the date of the start of the universe. So, if we ask if there are aliens in that neighborhood of the galaxy, we have to ask the same questions that were asked about globular clusters. Is it possible for life to originate there? If so, how could they last until now?

Everything about the core of a globular cluster is true, and ten or a hundred times worse, in the galactic core. Stars are closer together, and stellar encounters are even more frequent. There may be no time for planetary systems to coagulate and form bodies, as some star is going to intrude into the vicinity of the proto-solar system, and disrupt planetary formation. Large rocks and small icebergs might form, but they will be tossed like flotsam out into interstellar space.

The density of stars is so great that there will be photon pressure moving gas around, and even small objects. Turbulence will be everywhere, as there is so much random motion of large stars. There may be some stellar collisions, leading to explosions, even if the supernova population disappears within the first hundred million years or two.

When Earth astronomers look at nearby stars and notice they all seem to have planets, that’s a nice conclusion, but it cannot be extrapolated to the whole galaxy. Just because it is nice and calm out here in the outer edges of the disk does not mean the same phenomena, for planetary formation, can occur in the galactic bulge. Stellar interactions tear apart planetary disks, preventing planets from forming. So, instead of saying that there are more planets than stars in the galaxy, it would be better to say there are more planets that stars in the disk portion of the galaxy. That reduces the number of possible worlds for aliens by a factor of ten, as the bulge has about 90% of the total number of stars. This alone is a significant contributor to the answer to the question of why no aliens are visiting us.

The galactic bulge is different from a globular cluster in that it does have some younger stars. Not all the gas was consumed in the initial formation of stars, and the turbulence formed by the stars whizzing around near to one another leads to some higher density blobs of gas, and with a little luck, it could last long enough to condense into a star. And with the star, a planetary disk. After that, planets only if no stellar encounter happens early, and the planets do not stay around if a stellar encounter happens later. So, likely, no aliens in the bulge.

It is possible to say that, since there are so many stars in the galactic bulge, 90% of them to be specific, that there probably are some which escape stellar encounters for long enough for life to form. Maybe even a few where intelligent life can form, except for one problem. There is a radiation hazard there. The closer a star is to a supernova, the more radiation impinges upon it. As an example, stars in the sun’s neighborhood might be 10 to 100 light years away, and because supernovas are rare, the nearest supernova during the time life was trying to evolve might be 1000 light years. Stars in the bulge are ten to a hundred times more densely packed. This means distances are of the order of ten times closer, and that means supernova radiation is a hundred times more intense. And a hundred times more stars means a hundred times more supernovas going off in the vicinity. So, life that lives underwater might not be affected too much, but anything that attempts to crawl out onto dry land would. Without land creatures, is intelligence possible? Only in exceptional circumstances.

This means, in the bulge, not too many planets, and those which do survive have some radiation problems. They would qualify as solo planets, as life could form, but would specifically be plateau planets, as they would have underwater life, but no dry land life to speak of. Of course, there are forms of bacteria that are much more resistant to UV and shorter wavelength radiation, but they do not have the capability to become intelligent. Even if insects can evolve to put up with that situation, there is not going to be intelligence. So, in the bulge, no star traveling aliens. We do not need to scan those stars for signs of life, and if we accidentally find it there, it would be inconsequential.

The same goes for hunting expeditions there. Would it be worthwhile for a species of aliens, who developed in a nice solar system somewhere out in the disk, to travel into the bulge to colonize planets there? They would have the ability to shield themselves against the radiation, to be sure, as they could live underground, once they managed to find the right planet and get there. The edge of the bulge would be nowhere near as bad as close to the galactic center, so perhaps tapping into the fringe area would be reasonable, just not the central part of the bulge. '

Certainly not the central part of the bulge as there is a black hole there, by reputation, which occasionally consumes a star and produces a lot of energetic photons doing so. Perhaps some alien civilization could develop observatories that monitor the galactic core and can indicate when such an event might take place, just as we look for sunspots or stellar eruptions on our star, and warn astronauts about the event. But in the main, the disk is the place to look for alien civilizations, to develop our statistics about stellar types and planetary populations, and perhaps go explore some day.