More on Fermi Paradox: Implications of Space Arks

Paul Davies, in his book from a few years ago, Eerie Silence, touches on a wrinkle in the famous Fermi Paradox (see this), the implications of which I hadn’t really fully thought of  before.

Let’s take as a given that in the 12, —or more conservatively let’s say 6—  billion years or so that the Galaxy has been more or less like it is now (since stars have to have gone through a generation or two to produce the metal materials necessary for life)… there could have arisen some reasonable number of advanced technological civilizations. By reasonable, I mean, let’s say 50 or more, in that time, which most enthusiasts for the whole concept of extraterrestrial life would consider quite conservative, in 6 billion years of time. In a Galaxy now said to have as many as 400 billion stars, that in any case isn’t too big a stretch, assuming you accept the argument that it’s at least plausible that life arises relatively readily in suitable environments spontaneously (an unproven assumption, but one that can reasonably be made at least for the sake of argument). (It’s also implicit that there is some reasonable probability that a scientific/technological/intelligent species has at least some chance to arise; another purely speculative assumption, but again, for the sake of argument).

Now, set aside the Von Neumann machine argument, as speculative (which it is; see the link above; it’s not really a given that any civilization would try this, or that it would actually prove feasible). And set aside the possibility of faster than light travel (for pretty definitive reasons, see this). But add this posit: at least some percentage of these technological civilizations will during their history overcome natural selection pressure and collective stupidity well enough to survive for several million years. OK, that’s a lot of “let’s assumes,” but actually, that’s my point. If you make all these assumptions and infer a likely outcome, which in fact does not conform to what we see, it’s at least an indication that some of these assumptions need to be questioned.

So, what would likely happen if all these assumptions were correct? Obviously we don’t really know. It’s possible that there could be some number of quiescent, own-business minding technological civilizations co-existing with our threshold version right now, in various places in the Galaxy, and we just haven’t seen evidence of their existence so far. (Or evidence of the existence of any particularly wild and crazy versions that might even be detectable across intergalactic distances— in other galaxies). Possible.

But consider this. What if, as seems not totally unlikely, some fraction of these technological societies were naturally expansive? Prone to colonization of unoccupied real estate? This is  clearly a feature of Homo sapiens, and there’s at least some reason to believe it’s hard-wired into a lot of the genetic code of terrestrial life: the tendency to expand to occupy available space.

Now let’s engage in a little reasonable extrapolation of technology. Several engineering minded folks, such as Gerard O’Neill, Freeman Dyson, and sci-fi writers from Larry Niven to Iain Banks, have discussed the feasibility of constructing artificial habitats in space. It seems pretty clear that there is nothing preventing this technology from being realized other than inertia. It will likely come to pass right here in our Solar System, unless we, as a civilization, expire from terminal stupidity (an outcome perhaps more probable than we like to think, but one that’s already accounted for in our assumptions above with respect to the hypothetical other civilizations under consideration).

So, here’s the thing. I submit that it is no great stretch to go from huge artificial habitats in space, to something like Arthur C. Clarke’s idea for a traveling space colony, which he called Rama in his sci-fi novel. A sufficiently advanced civilization could quite plausibly build some such slow-moving space arks, and using space telescopes (also feasible, including possibly the natural gravitational lens telescopes discussed here), could identify all the relatively nearby habitable planets. Over long periods of time, these hypothetical advanced civilizations could indeed colonize other worlds. This would not be space travel. No to and fro required. It would be one-way colonization, but over time, it would mean that a civilization originating in one star system would come to occupy a region of space. (This could well be our very long term future).

Following from that, you arrive at the inference that there would be an expansion rate, of some value, and that the volume of space encompassed by a civilization would increase. There would also be implications for the survival of the living beings involved. Assuming that they continue to co-exist as living things in conjunction with whatever machines they’ve built, their survival would presumably be enhanced by occupying a lot of different abodes. Think of a plant or animal species that occupies all the forests of a continent as opposed to one little neck of woods on an isolated island or peninsula. Its survival potential is enhanced, clearly.

And following from that, you arrive at the assumption that in some fraction of the entire period under consideration, if unchecked, one or more of these civilizations would come to occupy planetary systems throughout the entire Galaxy. The Galaxy is huge, but finite. And even if you conservatively estimate that the time for a civilization to expand by one new system, which might average a distance of say 10 light years, is 100,000 years, or some similar number, you still find that in time shorter than the available billions of years, the expansion fills all the available space in the Galaxy. Even if you assume civilizations are finite in lifetime, and eventually fade away, to be replaced by others, there’s still a definite tendency, if these assumptions are all correct, for space to be not a vast wasteland of unexplored territory, but a finite resource, any particular locale within which is likely to have been exploited at some point in this long history.

What we find on Earth, I submit, is inconsistent with this. We don’t find any plausible evidence that the Earth has been colonized, or that alien spacecraft and space structures have ever existed in our star’s system. So, pretty clearly, something is wrong with some of these assumptions. Somewhere in there, the logical chain of connections breaks: either life is actually not too likely to arise in the first place, intelligent/technological/expansive societies are not likely to arise or not likely to survive long enough to actually occupy an expanding section of the Galaxy.

Or perhaps, civilizations quickly realize that natural planets aren’t really worth the effort. There’s plenty of matter and energy in the universe, why bother with the trouble, vast time, and expense, of interstellar colonization, when you can just build artificial environments (Ringworlds, Dyson Spheres, Banks Orbitals), and stay put? Yet that begs the question, all of them? Even if some high percentage of technological civilizations avoids expanding colonization schemes, wouldn't some of them do this? Yet the negative evidence, at minimum, sets constraints on this, to the effect that there has never been really widespread and long lasting space colonization going on. And if that's true for our Galaxy, it's likely universally true as well, which definitely has some implications for the assumptions we make about the prevalence of tehcnological civilizations such as what we envision for our own future. Perhaps, as I've mused elsewhere, we are in fact early pioneers, and it will be we, not some past technology creating beings, who will be first to spread intelligent life far and wide in the universe. Or at least this neck of the woods.

In any case, this is one more aspect of the Fermi Paradox: Where Are They? Because if any appreciable number of advanced civilizations had ever existed long enough to undertake major efforts at interstellar colonization, the universe and our Galaxy are old enough that it’s quite likely that process would have already reached where we are, and we would know about it.