So, Where Are All the Aliens?

Of all the various portrayals of aliens in movies, from a dispositional perspective E.T. is probably among the most accurate - here to observe, not to conquer - and only overtly "contacting" us by accident (a mistake I doubt real aliens would make). Although even he is far closer to us technologically than real aliens would likely be.

A consistent idea pervading science fiction, as well as actual science endeavors such as SETI is the idea that there are probably civilizations out there more advanced than us, and that naturally these civilizations would want to be contacting us at their earliest convenience. Star Trek has the wonderful vision of many civilizations sprinkled in our close galactic neighborhood, usually within a few hundred years of each other in terms of level of technology attained. This makes for entertaining television, but is almost certainly staggeringly wrong (apologies to Gene Roddenberry, he was brilliant, and Star Trek one of my favorite shows). A fundamental assumption underlying the Fermi Paradox is that if these advanced alien civilizations exist, they would try to contact us. This blog entry will present a solid case that, though there are almost certainly advanced civilizations out there, they are probably quite rare, and even if they were close by, would have very convincing reasons not to overtly contact us, at least not for a very long time.

First of all, it is a common misconception that because the Earth is presently swarming with sentient lifeforms (human beings), that it is therefore reasonable to suppose that swarming, sentient lifeforms must be quite common throughout our galaxy and points beyond. But, let's look at some numbers.

Carl Sagan famously explained one approach to determining the probability of advanced extraterrestrial civilizations in Cosmos (both in the book and the television series), using the Drake Equation. I will present a different approach below, but both approaches are in agreement that advanced extraterrestial civilizations are not numerous.

Anyway you slice it, intelligence of the human degree and kind is a very unpopular evolutionary adaptation, at least on this planet (our only empirical data point at the moment, which must be treated with the greatest respect). It has been pursued once on Earth, by Homo Sapiens and the closely related other hominids that we are descended from. It must be understood that evolution cares about one thing, and one thing only - the propagation of the species, the continuation of genetic material. It does not care in the slightest about how that is achieved. Sharp claws, fast legs, large size, the ability to consume whatever food is available at a given time, all of these are far more reliable, and far more consistently used, than our particular brand of advanced sentience. (Pardon my anthropomorphization of evolution, it is of course an inanimate process, not an objective-driven intelligence).

Earth is 4.5 billion years old. If we are very generous and say that we started out being reasonably sentient some 3 million years ago, that means that Earth has had sentient lifeforms for only 0.0667% of its history. But of course, primitive hominids do not really constitute civilization. That is only 10,000 years old (the dawn of agriculture), or 0.0002% of Earth's entire history.

However, we need to be more discriminating still if we are going to start comparing technological civilization over the incremental version that characterized most of that 10,000 years (short and often individual-based explorations by brilliant Greeks, Romans, Muslims, Chinese, and others aside), and the accelerated version that we are currently familiar with. There are different ways to define it, but my favored definition of the start of true technological civilization begins with the institutionalization of the scientific method on a national scale, as evinced by competitive European nations a mere 500 years ago, or 5% of the 10,000 years of civilization since the dawn of agriculture. Using this definition, Earth has had technological civilization for 0.0000143% of its history.

It's only one data point, but it's the only one we have, and until we have more, we must respect this data point. What this data point is really saying to us is that intelligence of the kind that we humans possess is almost certainly quite rare, not just here on Earth, but throughout the cosmos. Among the many implications of this is that any other advanced civilization is probably separated from us by a great distance, and a large period of time. That's assuming that our brand of advanced sentience is in fact sustainable over a long period of time, and is not a superpredator adaptation (essentially meaning, a species so successful that it makes itself extinct through over-exploitation of its food sources). I will assume that human-level intelligence is not a superpredator adaptation for the sake of this blog entry.

We may be alone in this galaxy, we don't know yet. But it would not be surprising if the nearest advanced civilization is on the other side of the Milky Way, if there's any in this galaxy at all, and I would be very surprised if it was older than ours by less than 10 million years, possibly much longer.

Ponder that for a moment - 10 million years of sustained, technological civilization, compared to our 500. We imagine that we can comprehend millions of years, because we understand how creatures have changed over the last several billion years. But this is deceiving, because evolution works on a timescale of millions, 10s of millions, even billions of years. Technological development by sentient creatures such as ourselves works on a level of acceleration where huge change can be seen in 100 years, much less a million.

The motivations of such an advanced race may seem entirely beyond our ken, and certainly would be deeply inscrutable in all likelihood. However, there is one scenario that is not without promise, and that explains perfectly what we see, or rather, don't see.

For one thing, it seems likely that they will be homebodies as we will be: because their technology of sustainability will exceed the technology of moving "out into the cosmos", and moving out into the cosmos is a half-baked, poorly-thought-out idea in any case (although it makes for good copy and entertaining science fiction). Regardless of the level of technology, the planet where you evolved will always be the best fit, the most comfortable, the most welcoming home for any creatures, sentient or otherwise, that evolved there. And one of the implications of "sustainability" means self-sufficiency on that planet, so the rapacious, material-hungry, "Independence Day" type alien goons are a deeply improbable sci-fi fantasy.

Ask yourself this: what could we humans possibly offer to an ancient race of "old ones" such as these? Well, certainly not our knowledge, at least not in absolute terms. Rather, our transition would be the item of interest, it could be strongly suggested.

Think about it - we are undergoing probably the rarest event in the entire universe, right now, all around us - the transition from creatures that are essentially of nature, into one that is rapidly becoming primarily technological. An event that by all indications will be quite brief, in the big scheme of things, and a transition that for these old ones happened deep in their past.

If an advanced race is technological, they must of necessity be scientific, have something resembling our scientific method in place, because really, that's the only way that sustained, rapid technological progress occurs. And if they are scientific, they are curious.

Here's a cardinal rule: no matter how old the civilization, no matter how advanced the technology at their command, every new place that they (or we) visit in the cosmos will teach them (and us) new things.

The universe will never stop surprising them (or us). Obviously, the more places that are visited, the larger the statistical data set becomes, but from just our very limited experience with telescopes and planetary probes, it can be stated with very high confidence that the variability of the universe, its capacity to surprise and teach, is so great that it can be considered for all practical purposes infinite.

The best thing for this race to do would be to simply observe us, as we pass through this transition. To contact us, to come down and say, "What's up?", would deeply contaminate the experiment, a wonderful natural opportunity. And with millions and millions of years of technological development on us, it would be quite an easy thing for them to observe us without anyone's knowledge.

Not that we shouldn't keep looking, but this line of reasoning would seem to work against the probability that projects such as SETI will be reading anything but cosmic static for a very long time.

Further Reading:

Alien Census: Can We Estimate How Much Life Is Out There?

Carl Sagan explains the Drake Equation

I recently had the opportunity to provide feedback on a forum that is useful for elaborating on the thoughts in my blog entry above:

Comment 1:
From the perspectives being shared here, there's several opportunities for me to be clearer in my blog:
1. I definitely need to describe in more clarity and depth what I mean by the 'technology of sustainability'. That deserves its own blog entry, maybe more than one. But in a nutshell, really what I'm suggesting with this terminology is that we will get smart enough in the next 50 years or so (hopefully less), about the time our population levels off on this planet, to essentially develop the technologies and perhaps more importantly the land and other resource utilization policies to allow the projected population of 8-10 billion to live comfortably on this planet into the foreseeable future - ie, sustainably. There are countless dimensions to sustainability, it's not one thing, really it's everything - recycling, energy use, land management policies, conservation techniques, etc. Now, it may seem that we're spinning our wheels on one or more of these areas, but actually our knowledge along all these fronts has increased tremendously in just the past few decades, and all signs point to even more rapid progress in the future. And the most cogent point, perhaps, is that with the right technologies and policies in place, this planet need not be overburdened with our presence, even at 8-10 billion people.

2. I am absolutely not suggesting a stark choice between sustainability and space exploration, manned or otherwise. I'm a huge space buff, and strongly support continued investment in space exploration. All I'm saying is that by the time the technology is in place for us to economically move millions (or billions?) of people into space, whether the Moon, Mars, Alpha Centauri, wherever, we will by that time have already of necessity mastered the technologies and policies to make the human population on Earth sustainable - able to feed, clothe, shelter, and entertain ourselves into the distant future, without turning the Earth into a smoking ruin. Now, sadly, many species and environments will be compromised between then and now, but life is resilient, and once we reach a certain point, probably around the time our population reaches its maximum around 2050 or so (that's a guesstimate, it will vary widely from region to region, but we'll all get there eventually, I believe), humanity and the rest of Earth's remaining biota should be able to more or less happily coexist.

3. The thoughts around an asteroid strike are well taken. Preventing an asteroid strike I suggest is a special kind of sustainability technology (or preservation technology, if you prefer). I believe that even that problem will be solved before we can economically move and maintain millions of people in space. In any case, watching the Earth incinerated by an asteroid from the comfort of a space station would provide little solace to its passengers - the universe would seem lonely indeed if such an event were to transpire, even if you had a million people on a space station to keep you company.

4. There will be an option here, in the far future - you can leave Earth if you want to pursue a life, career opportunity, adventure, whatever, in space. But, it will be not be a necessity to leave Earth, that's one of my fundamental points. If it becomes a necessity, we have failed as a species, it could be argued. And bottom line, what I'm suggesting is that given the choice, most people will choose to stay home. Short visits, space tourism, things like that, sure - but relatively few will choose to leave Earth forever, which traveling to even the nearest star would probably entail. And with advanced visualization technologies, we'll be able to have our cake and eat it too, so to speak, bringing those distant locales explored by probes or what-not to us in exceedingly realistic detail - without giving up everything we know and everyone we love to do so.

5. Comparing an alien civilization to the Spanish and us to the Inca I'm not sure is very instructive, although it's certainly thought provoking. Taking my nominal, ballpark value of an alien civilization being at least 10 million years older than us, if they wanted to be here, they would be here. If they wanted to overtly contact us, we would hear them. If they wanted to rule us, there would be no contest, no struggle, no 'war', not as we know it. A civilization that old could have expanded to every nook and cranny of even this vast galaxy, 100,000 light-years across, even if they couldn't break the light barrier. But, they're not here, at least there's no objective evidence that they're here. And the reason almost certainly is not multiverses, or whatever - it's motivation, their motivation primarily, they hold the cards. My ideas around their taking advantage of a splendid observational opportunity of a species in technological transition (ie, us) is conjecture, but whatever the reason for their withholding contact, it's in their heads, it's because it's what they want to do. But I am by no means ruling out that we may be alone, at least in this galaxy, it's not improbable.

Comment 2:
Another one of my comments on the aforementioned forum thread, the main subject of which is to explore Fermi's Paradox, which basically asks the same question as the title of this blog entry; that is, if it seems likely that life is abundant throughout the cosmos (which I agree with, by the way, at least simple life seems very likely to be abundant), and some small percentage of these cosmic locales harbor advanced, sentient, technological civilizations, where are all these aliens?

I should have more clearly tied my thoughts around sustainability back to the main point of this thread, the Fermi Paradox, they are in fact closely linked.

The technology (and practice) of sustainability proceeding more rapidly than the technology (and desirability) of fleeing Earth for us humans is not a discussion of merely local interest - it pertains to any alien civilization that manages to progress to a hyper-advanced technological state, and remain there for millions of years, which they would need to do in order for us to be contemporary with them now. In other words, they, like us, will not be driven by the need for material or energy resources to flee their home planet, just as we will not be driven to leave ours out of material necessity. For them, as for us, there is no place like home - their home planet, the one they evolved on, will by any reasonable analysis most likely be the friendliest place for them, probably in the entire universe, forever. We still debate this, but for them, I doubt there will be any question, because they will have studied many places in far more detail than we yet have.

In effect, sustainability technology and practice allowing a steady-state, "homebody" alien civilization, combined with their likely maturity regarding the imprudent intrusion into other life-bearing worlds such as ours due to the deep risk of degrading the scientific value of that world to them in the first place, in fact explains Fermi's paradox. Fermi's paradox harbors the questionable notion that any alien civilization would either want or need to contact us just because we are sentient, but I suggest this reflects our collective desire for a savior, or at least a mentor that can help us solve our problems, more than a careful perusal of what their likely attitudes might be.

Now, there perhaps is a great filter, in the form of the difficulty of maintaining an ancient yet still thriving technological civilization over millions of years. We have no clue as to how hard or easy that is. If it's hard, well, there's your filter - they either go extinct or degrade technologically to the point where they can't contact us, even if they wanted to. But if it's easy, the idea of an alien civilization that does just fine sustaining itself by utilizing the resources of its own planet, relegates the "Spanish Conquistador" or "Independence Day" alien scenario to deep improbability.

Some straightforward deductions explain Fermi's paradox, whether there's just one advanced alien civilization on the other side of the galaxy, or 10 within a hundred light years of us. That is, they won't need to come here for their own material or energy needs, and they will appreciate the scientific value of not overtly contacting us in any case. That sounds strange, but they could actually learn more from us by remote observation, rather than explicit, direct contact. And with millions of years of technological development on us, they would be able to field probes, telescopes, whatever, of truly staggering remote-sensing power, that could capture whatever data at whatever level of detail they felt they needed for their scientific objectives. Perhaps, track the movement of every lifeform on this planet, and maybe even the thoughts of every lifeform on this planet, in real time, over thousands or even millions of years. Whether or not they would choose to do such a thing depends of course on the nature of their scientific inquiries. Usually, the more data the better, but who knows if such a minute level of detail of the activity on this planet would be of interest to them or not. It doesn't really matter - the point is, they would not need to contact us explicitly for their own scientific needs, and our fantasy of them helping us with their advanced knowledge would utterly contaminate the purity of the observation of the technological transition that Earth's civilization is currently undergoing.

The question of "where are all the aliens" almost invariably is approached from our perspective, not theirs. Naturally, we're proud of ourselves, and more or less immediately assume that any advanced alien civilization would want to explicitly contact us, at their earliest convenience. But since they don't, and we assume that they would want to, we get into all kinds of philosophical conundrums of excessive complexity to explain their absence. But, their perspective is really the only one that counts - for all intents and purposes, our perspective is irrelevant.

By the way, I do not concur that sustainability is a "non-issue". It is in fact one of the greatest challenges we as a civilization face. To agree with Phil, it is not primarily a knowledge-bound problem, it is will-bound, discipline-bound, the process usually wrenching. Often, we know the right things to do, we just don't want to change our ways until the resource depletion, environmental degradation, etc, become so apparent that we run out of excuses to avoid doing what we knew all along was the right thing to do. This slow acquisition of civilization-level discipline is in fact an important form of collective wisdom that will serve us well when and if we ever encounter a planet with sentient lifeforms less technologically advanced than us, some thousands or millions of years hence, that perhaps may stay our hand from careless intrusion into their affairs. This is another linkage of the sustainability question with regards to the "Fermi Paradox".

Incidentally, the whole idea of fleeing into space as a gateway to a better, somehow easier life seems entirely without foundation. The considerations of sustainability, energy utilization, etc, are magnified by orders of magnitude for a human living in space as opposed to a human living on Earth. On Earth, air, water, food, protection from deadly cosmic radiation, lots of things, are relatively cheap and abundant. In space, all of these things must be provided, very carefully managed, and absolutely nothing is free. It is extremely unlikely that a human living in space will ever be less expensive than a human living on Earth. Just the opposite - it will almost certainly be much, much more expensive, when all the costs are considered, into the distant future.

Comment 3:
"You still seem to lean heavily on the idea that an alien civilization would be at least 10 million years older than us, but I don't see where your blog remarks adequately support that notion. Perhaps you could elaborate."

10 million years might be too low, I'm actually being conservative. It follows as a direct result of the fact that sentience combined with the ability to technologically manipulate our environment is an evolutionary adaptation that has been pursued exactly once on this planet in its 4.5 billion history, that is, us. And even with us, sentient hominids existed for millions of years before agriculture, and hence 'civilization', began. And even once civilization began, it was another 9,500 years before the scientific method, with its concomitant sustained, relatively rapid, robust rate of advance of scientific and engineering actualization knowledge became possible.

It bears remarking that each of these transitions occurred as a result of a complex set of favorable opportunities, topographical configurations, and other factors that may or may not be common elsewhere.

Given this line of thought, and the many accidents of climate, geological, and faunal change that gave rise to our brand of advanced sentience (Walking with Cavemen is an excellent series in how it explores this, not just for homo sapiens, for many of our precursor hominids as well), civilizational structures (the Fertile Crescent), and scientific institutionalization (competitive European states), to assume that it is common throughout the cosmos, aka the Star Trek model, is empirically unreasonable. We're not unique I don't believe, not saying that, but almost certainly quite rare.

Let me restate the essence of the analysis from my blog:
"Earth is 4.5 billion years old. If we are very generous and say that we started out being reasonably sentient some 3 million years ago, that means that Earth has had sentient lifeforms for only 0.0667% of its history. But of course, primitive hominids do not really constitute civilization. That is only 10,000 years old (the dawn of agriculture), or 0.0002% of Earth's entire history.

However, we need to be more discriminating still if we are going to start comparing technological civilization over the incremental version that characterized most of that 10,000 years (short and often individual-based explorations by brilliant Greeks, Romans, Muslims, Chinese, and others aside), and the accelerated version that we are currently familiar with. There are different ways to define it, but my favored definition of the start of true technological civilization begins with the institutionalization of the scientific method on a national scale, as evinced by competitive European nations a mere 500 years ago, or 5% of the 10,000 years of civilization since the dawn of agriculture. Using this definition, Earth has had technological civilization for 0.0000143% of its history."

In addition to these small percentages, based solely on the time that we've been here vis-a-vis the age of the Earth and/or the time since the rise of complex life, there's another distinct but related statistic to consider, that I haven't mentioned in my blog. That is, out of the millions and millions of species that have lived on the Earth, one has utilized sentience and manipulative technology to achieve its survive and thrive goals - that is, again, us. I'm not going to try to weave that number, yet another very tiny fraction, into the other tiny fractions based on temporal duration of our species stated above, but suffice it to say that it makes the probability of advanced alien civilizations elsewhere even less likely, even more remote, and even more widely spaced in time (that is, even more ancient).

So, 10 million years is very conservative indeed; in fact, it's probably giddily optimistic that they would be even that close to us in time.

The upshot of these tiny percentages of sentient and/or technological civilization on Earth, extrapolated to the rest of the cosmos is that this tiny blip of the rise of sentience elsewhere, the odds of this occurring more or less simultaneously with the rise of sentience on this planet are exceedingly remote. It's not impossible, not saying that, but deeply improbable that they are either close by, or close in time. Hence, the empirically-based and statistically sound proposition that they are far away physically, with a large temporal displacement - ie, much, much older than us. That falls right out from the analysis, there's really little other conclusion that can be reasonably deduced from these numbers.

Now, to make a caveat to my own line of reasoning here, I should perhaps have run a second set of percentages against not just the total age of this planet, but the rise of complex life, say, 300 million years ago. Using 300 million instead of 4.5 billion in the denominator of the fractions used to derive the percentages above, the prospects for sentient life elsewhere on other planets capable of supporting complex life look somewhat better. For example, the last 500 years becomes 0.0001667% of the history of complex life, rather than 0.0000143% of the history of the entire planet. The odds improve somewhat, an order of magnitude greater, but still quite small.

To extend this reckoning from the rise of complex life leads to certain ideas that may be optimistic, but are not without merit. There seems to be a trend throughout evolutionary history of "faster legs". At the dawn of the age of mammals (another good series is "Walking with Prehistoric Beasts", they do a great job of revealing the Eocence and subsequent epochs), running speed was relatively slow. Over time, the "speed of chase", the maximum running speed of various predators and prey have steadily increased.

A very similar idea might pertain to the realm of intelligence. That is, the average intelligence of creatures over time (us being of course the spectacular example) may also be increasing in a similar way, as a response to evolutionary pressures.

If this is true, then even if we pass from the scene from some unhappy event, it may not be another 4 billion years before we see another sentient lifeform like us on this planet. It would be a long time to us, but in the big picture of Earth, maybe not so long - perhaps 50-100 million years, guesstimating here. Much depends on the nature of the unhappy event - a large asteroid strike could reset the clock, as it were, and it might be hundreds of millions of years before another sentient species became a possibility.

If this is true, and this trend is prevalent on all planets with sentient lifeforms, then my very low statistical percentages go up considerably, perhaps an order of magnitude, maybe two orders of magnitude - but they remain quite tiny. Therefore, we're still talking millions of years of likely separation between us and the nearest sentient civilization, either behind or ahead of us, and physically far away, unless we win the cosmic lottery in some way, against all odds.

Yet another dimension to considering the question of the abundance (or lack thereof) of advanced alien civilizations involves exploring the character of the preponderance of life-friendly planets that are out there. An excellent show regarding this is "Extraterrestrial", specifically Aurelia. The great majority of stars in the sky are ones we can't see, small red dwarfs. Because these are the preponderance of suns, the preponderance of life-bearing worlds will probably be found orbiting stars like these. However, in order to be life-friendly, because of a red dwarf's dimness, the planet around such a sun would have to orbit so closely that it would be tidally locked. That is, one side always pointing at the sun, the other in eternal darkness.


An artist's concept of Aurelia, tidally locked to its red dwarf sun. The perpetual hurricane can be seen at the right, the frozen night-side on the left. In between is the habitable zone.

This is not as bad as it seems for life per se; in fact, one of the revelations of this show was that it incorporated state-of-the-art simulations of the climate of such a planet, and instead of the sun-facing side being baked and inhospitable (the prevalent notion up to that time), instead a perpetual hurricane forms at the center of the sun-facing side of this world, and between this perpetual hurricane and the eternally-frozen dark side of the planet is an aureole-shaped zone quite suitable for life.

This is great news for life, but perhaps not sentient life. This planet would be about as strange a world as we can imagine, if we were stand on it. There would be no seasons; wherever you stood on the planet's surface, the sun would never move in the sky. Much of the seasonal and other forms of dynamism that we take for granted and that were absolutely crucial to the rise of our sentience would be wholly absent on such a world.

Not saying that the rise of sentience on such a world would be impossible, but it would seem far less likely in such a scenario. And these planets represent in all likelihood the vast preponderance of theaters for life-bearing worlds throughout this galaxy and beyond. This consideration is not incorporated into the Drake Equation, it's too new for that, but it perhaps should be - that is, the cosmic, seasonal, and geological dynamism of the world in question, whether or not it can inherently support life.

Another consideration to the Aurelia-type planet dynamic question is tidal dynamism. If Earth didn't have a moon, it would have no tides, and the character of life on this planet would in all likelihood be far different - probably, far less dynamic, because simple ocean tides are a huge evolutionary influence on the critical land-to-ocean boundary. It wasn't covered in the show, but could an Aurelia, a planet tidally-locked to its sun, have a moon, and if so, would its orbit be favorable to the elicitation of evolutionary interesting tides?

Having built a case from many different directions to support the idea of the extreme rarity of sentient, advanced alien civilizations, let me restate unequivocally that I do not believe that we are entirely unique in the cosmos. That would be as deeply improbable as suggesting that they inhabit every star system. But, I would not be surprised if there were only one or two, or even none, in this galaxy, they might be that rare. And if there are one or two others in this galaxy, I might guess that one perhaps is in the vicinity of the galactic center (far enough away from the core to be safe, of course), and perhaps the other on the other side of the galaxy.

If this is the case, then we have some time to think about this. Assuming that they gather information about the cosmos primarily through the light and other electromagnetic radiation emitted and/or reflected by various cosmic bodies, if they are there they almost certainly know about Earth and its life-bearing properties already, but it will be another 40,000 years from now before the galactic center knows about our earliest rise of agricultural civilization, even though that light's been traveling for 10,000 years already. It will be 90,000 years before the far reaches of the other side of the galaxy is aware of this event.

This seems like a long time, and it is; but to an advanced alien civilization millions of years old, possibly populated by what would seem to us citizens of essentially immortal age (I will get into that in a future blog entry), this is just another aspect of gathering the knowledge of the cosmos to gain insights that we are only beginning to get the tiniest glimmer of understanding around.

Comment 4:
"But, why 'their perspective', singular? Why should we not expect 'their perspectives', plural?"

My use of 'their', rather than 'theirs' merely refers to the nominally nearest alien civilization to us in time. I by no means put every alien civilization into one big bucket as a simplifying assumption, nothing of the kind. They would be every bit as variable from one another as any of them would be from us.

However, because of the exact same analysis that places the nearest advanced alien civilization from us at many millions of years ahead, the alien civilization 'above' this nearest one would be millions of years ahead of this 'nearest' civilization.

Now, I could be entirely wrong with regards to my suggestions regarding the nature of either of these alien civilizations and their attitudes towards us, or each other. Perhaps instead of arms-length, scientific observation, it is simply indifference. Perhaps it is adhering to their version of the 'Prime Directive'.

Their true motivations are beyond our ken, naturally. Any of the above, and possibly many other explanations, may explain what we see, or rather, don't see. Which is, nothing, at least not so far. Realistically, if there is an advanced alien civilization in this galaxy, the Milky Way, and it is millions of years older than ours, they could be here if they wanted to be here, doing whatever they wanted to do.

However, if the nearest advanced civilization is more distant, say, Andromeda, they may be aware of our potential (2 million years out of date, but there were hominids then, it was probably clear even then that sentience was at least a good possibility on this planet), that may be too far for such a distant civilization to bother visiting us. It may not be worth it to them.

I'm not sure I follow precisely your exponential 3D gradient argument, but it seems to imply that a civilization with sufficiently advanced spacefaring technology would aggressively colonize the cosmos. But, where's the evidence for that, assuming that there's even one advanced civilization in this galaxy?

If we are the first advanced civilization in this neck of the cosmos, you may be right, we may expand aggressively in this way, the future will tell. But we see absolutely nothing to suggest that that is the path that another civilization would take, assuming that they're anywhere close by, in the Milky Way or possibly its swarm of satellite galaxies.

And by the way, I'm not conjuring these concepts out of thin air. Every one of my ideas is empirically-based upon our own (in this case, admittedly limited) experience, carefully reasoned, and self-consistent. That doesn't mean it's correct, lolz. And in the case of advanced alien civilizations (a very small subset of my overall body of work), it explains what we see (or rather, don't see) quite well. But again, that doesn't make it right, not saying that.

It's important to state, this concept of alien motivation is not the one I started out with, and molded my logic to reach this pre-determined destination, none of my thoughts are like that. If they were abundant and here saying "What's up?", I would have a dramatically different interpretation of their motivations and nature. I go where the evidence seems to lead, at all times questioning my own conclusions, my own logic, carefully probing for inconsistencies in the overall logical constructs. I do that at my leisure, sometimes taking months or years to do so, turning the coin over and over, before I share them with anyone else.