One of the most widespread and perhaps compelling solutions to the Fermi Paradox is that intelligent life is incredibly rare in the universe. That’s why we see no definitive evidence of it. A variant of this thinking, however, is that while intelligence may be rare right now, it may eventually become conventional and a veritable explosion of intelligent life might come to be in the universe’s future. There are two scenarios in which it could happen. But before we get into that, it’s worth noting that there could be two completely separate paths for life in the universe. One is earth, where a terrestrial planet with surface liquid water gives rise to life and the possibility of the eventual evolution of intelligent life on it. The other is quite trickier as we know they exist, and we can speculate their chances for harbouring life, we still don’t know if they do.
These are the ice shell moons such as Europa. What we know even less about are the conditions and evolutionary possibilities on worlds with oceans locked under ice. Might they only be able to produce microbes, or could something more complex evolves? It’s an open question but what doesn’t seem likely about ice shell worlds is that they could ever develop intelligent species. How does one master fire in an ocean environment, how does one build advanced technology and so on? Would such a landless environment ever favour the rise of intelligence at all? It could be that primitive life abounds on worlds like Enceladus and Europa throughout the universe but can never create a breed. But with terrestrial planets like Earth, we prove that it can happen. But how common are worlds like earth? We don’t know yet, but one line of thinking is that they aren’t common at all. Our sun, for instance, isn’t the most common type of star in the Milky Way, it significantly beats out by the red and orange dwarfs.
How common are these Earth-like worlds within the habitable zones of Sun-like stars? We don’t yet know, but there is no guarantee that they would be. And even then, would they host the right mix for intelligent life to arise? Just the right amount of land and water? Plate tectonics? A sufficiently well-sized and placed moon? All of these things may have played dominant roles in the process that led to us. This term is usually known as the “Rare Earth Hypothesis.” and that the reason we don’t see evidence of alien cultures is that the Earth is rare. And even then, what may be yet unique is the development of intelligence on an Earth-like planet.
Earth had hosted life for billions of years, before humans and our hominid relatives ever came on the scene. And had the conditions for their evolution not happened to have been just so, then the earth would still be a planet full of reptiles, mammals and complex entities, but nothing capable of ever creating a technological society. Perhaps most Earth-like planets, rare as they might be, clearly remain dumb and we are on the galaxy’s lottery winner where everything came together just so.
But what of the future? Might other environments around red dwarfs become better able to host life in the future? Might that lead to an eventual explosion of life in the galaxy? Might that, in turn, lead to an inevitable explosion of intelligence? Abraham Loeb and his colleagues approached such idea in their paper, “Relative Likelihood for Life as a Function of Cosmic Time.” Essentially, since small type M red dwarfs are far, far more abundant than any other kinds of stars, and they live remarkably long lives but early on are too active for life to get much of a foothold, but it may be the case that later in their lives that equation changes. And there are also the type K orange dwarf stars, which may offer the best chances of all-stars for Earth-like life, but may not have enough time for intelligence to arise.
In short, this solution to the Fermi Paradox would indeed suggest that yes, we are alone, as far as we are likely to know regarding intelligent alien life. But not forever. And, even if there never is an explosion of intelligence in the Milky Way, there is at least us. Should we survive and conquer the galaxy, the vast distances and communications times involved would favour that our colonies might become isolated. After enough time has passed, those colonies that might have sprung out as a human might end up something very alien to each other indeed.