The Lucky Earth Hypothesis
Yet Another Response to the Fermi Paradox
Responses to the Fermi paradox seem to be multiplying like mice in a barn, which is not necessarily a bad thing, because it demonstrates that an apparently simply question (what I recently called a deceptively simple question) has countless aspects not immediately obvious, so that the more we think about the Fermi paradox, the more interesting and complex it becomes. So here is yet another response to the Fermi paradox, and by calling this a “response” rather than a “solution” I am saying that I in no way consider any one response to be definitive, least of all what follows.
This past summer in Spacefaring Civilizations in Cosmic Voids I discussed the possibility of civilizations that appear within largely empty, starless regions such as the Boötes void. The Boötes void is a spatial void, but what if a civilization appeared in a temporal void instead? A temporal void would mean that Earth and human beings are completely free to develop in our own way, without any outside interference or influence, so that our civilization is a product of splendid isolation, not under any threat from a malign presence, and not subject to being derailed by a well-meaning beneficent presence that might come to Earth and “help” us, saving us from ourselves, but also denying us our unique opportunity to become what we are.
Perhaps the history of the universe is filled with intelligence, technology, and advanced civilizations, many of which flourished before us, and many of which will flourish after us, but we happened, merely by happenstance, to appear at a time and a place that our lightcone is empty of technosignatures, or very nearly empty. Thus we appear to be alone in the cosmos, and find only the Great Silence when we listen for others like ourselves, but this could be just an artifact of the timing of our civilization.
The timing of terrestrial civilization could be construed narrowly or broadly. Narrowly, there would only need to be a temporal void comprising no detectable technosignatures during the period of time when human beings have possessed sufficient scientific and technological resources to identify and recognize technosignatures. This narrow temporal void would only need to be about a hundred years, or two hundred years at most, by which I mean that the temporal void would have to minimally extend one to two hundred years into the past, and it could end any time (like today or tomorrow).
This narrow conception of a temporal void does not address why Earth has not been repeatedly visited in the past, which would potentially leave traces that could be detected over a longer temporal horizon. Again, we can make a distinction between and narrow and a broad conception of archaeological traces of past ETI visitation of Earth. ETI visitation of Earth, if infrequent and brief, would have left very little trace of itself, and the geological activity of Earth would relatively quickly erase all traces. On the other hand, repeated frequent visitation, or ETI visitation that was enduring and significant, would not be easily erased. Moreover, ETI visitation could involve traces of visitation off Earth where alien artifacts would be preserved by the conditions of space.
A thin layer in the geological record of artificial materials such as radionuclides, plastics, industrial pollution, etc., would go unnoticed at a level of lower scientific and technological sophistication, and would only be discovered when we had the means to engage in a scientifically sophisticated geology. Our present level of sophistication in science, and our present scientific instrumentation, would allow us to detect a thin layer of prior ETI habitation, assuming that that period of habitation had not been purposefully expunged from the historical record (for example, another civilization visiting Earth millions of years ago, if it had some law like the Prime Directive in Star Trek, might be obligated to wipe away all traces of its temporary domicile prior to departure).
A spatial void would contribute to a temporal void in so far as crossing a spatial void would potentially create a temporal void for entry-level interstellar technologies, but for advanced interstellar technologies, being in a spatial void wouldn’t greatly isolate a civilization. However, if the Great Silence is explained by a Great Filter at levels of technological attainment at or near the human present, then civilizations would cluster at the level of development represented by entry-level interstellar technologies (like that of solar sails, now being actively developed by terrestrial civilization; cf. Beyond the SETI Paradigm). In this latter case, a spatial void would be tightly-coupled with a temporal void. This suggests a formulation of a response to the Fermi paradox that employs both a temporal void and a definite limit on the development of interstellar technologies.
A broad conception of a temporal void in the cosmos would have to reach back a minimum of millions of years into history. From the perspective of the history of the Stelliferous Era, a few million years is not much, and still maintains us in what I would call the cosmological present. Tens of millions of years, or hundreds of millions of years on a geologically active planet would be sufficient to erase most or all traces of ETI visitation or habitation, though, as noted above, it would not address the absence of alien artifacts in our solar system.
If a broad conception of a temporal void begins to reach back into billions of years before present, the nature of the explanation of the Great Silence changes a bit, as if there is a temporal void from early in the history of the universe up to the emergence of human civilization as a cosmological actor (by which I mean a species that is visible over interstellar distances because of our technosignatures), then this is rather the response to the Fermi paradox that we are first, rather than that we are lucky. At some point, then, between a narrow temporal void of 100-200 years into the past (which is nothing by cosmological time scales) and a broad (or deep) temporal void extending billions of years into the past, there is a explanatory limit for the Lucky Earth Hypothesis.
The idea that Earth is a lucky planet, i.e., a lucky exception to the usual conditions for planets, has been given exposition in Lucky Planet: Why Earth is Exceptional—and What That Means for Life in the Universe by David Waltham. Being a “lucky planet” in this sense coincides more-or-less with the Rare Earth Hypothesis (rarity could be construed as a form of luck, specifically if it is a fortunate rarity), which is its own response to the Fermi paradox, distinct from being “lucky” in the sense of happening to appear at a time in cosmic history in which our civilization essentially appears on a blank cosmic slate.
One might plausibly argue that, if we are situated in a temporal void, that this is not lucky, but rather it is unlucky. Our sense of cosmic loneliness is a longing that cannot be fulfilled within a temporal void, and it is possible (though we can only speculate) that civilizations emerging in a cosmological context of multiple peer civilizations advance more rapidly and provide more opportunities and a higher standard of living to the beings that compose them. This would be fortunate, but it is in no way guaranteed by a busy cosmic neighborhood. Such a neighborhood could also mean conflict, war, crime, and attractive nuisances.
These ideas came out of my ongoing correspondence with Erik Nelson, who wrote to me: “We have neither armor nor camo nor the slightest expectations of privacy or primacy. Maybe we're lucky. Maybe it's been our lucky 10 myr. out in the wide open.” After he wrote this, I pointed out that this could be considered another response to the Fermi paradox, which I then called the Lucky Earth Hypothesis.
