The gelada monkey is one of the most reclusive animals in the world. It resides in exactly one place: the highlands of Ethiopia. There are less than 250,000 geladas in existence. However, if you wandered the Earth for long enough, in theory, you would find them.
Astronomers have long suggested that the same must be true for life in our universe. Life is rare, but it is also a scientific probability. We exist, after all—and the conditions that gave rise to our existence are not so extraordinary that they couldn’t be replicated elsewhere. The sheer size of our universe suggests that even a relatively rare event, like the propagation of complex life, will occur many times over.
There is an observable problem with this assumption, however, and it is staring back at us through light-years of cold, lifeless space. Based on what we can see from Earth using our most advanced telescopes, the universe is actually much more lifeless than we would expect.
This problem is known as Fermi’s paradox. Coined in 1950 by Italian physicist Enrico Fermi, it has been a cause of consternation for philosophers and scientists ever since. It forces us to confront the existential possibility that we are the only things living in our universe: lonely residents of a mossy rock, bobbing on an endlessly dark, churning sea.
Only by solving Fermi's paradox can we save ourselves from this fate. Fortunately, a few theories have been proposed.
The Theory of Relative Time
A popular theory suggests that Fermi did not properly account for time. The universe is nearly 14 billion years old—an age just as staggering as its physical size. It seems possible that at an earlier point in the history of the universe, other civilizations could have risen and fallen, with enough time passing between then and now to erase all traces of their existence. Therefore, life must not only exist relatively close to us in space; it must also exist relatively close to us in time.
The Gaian Bottleneck Theory
Another interesting possibility is the bottleneck theory. This theory suggests that early forms of life are actually common in our universe, but that most of these life forms go extinct before they have the chance to evolve. This is the meaning of the “bottleneck”—a narrow filter through which only the fittest and most adaptable forms of life can pass.
This theory is compelling, and it convincingly explains how early life survived and flourished on Earth.1 However, it does not explain the apparent absence of life in the rest of our universe. A bottleneck, by definition, lets some things through. It explains a universe in which life is rare, but it doesn’t explain a universe in which life is nonexistent.
A Second Bottleneck?
A third and darker possibility must be considered. This is the existence of a second bottleneck, much farther down the evolutionary timeline. In this scenario, the life forms that survive the first bottleneck evolve into complex organisms. They produce a highly evolved, intelligent species, one capable of making scientific discoveries. This species discovers the wheel, the gun, electricity, and eventually, nuclear technology.
This is the second bottleneck. It answers Fermi’s paradox with a terrifying conclusion: there are no aliens because all of the aliens are dead. These civilizations thrived, flourished . . . and then bombed themselves to extinction.
This is a terrifying possibility to consider—especially because it is not at all clear that we have navigated this bottleneck ourselves. Since the atomic bombing of Hiroshima and Nagasaki in 1945, nuclear arsenals have continued to exist around the world. We haven't destroyed the weapons that made these atrocities possible, or even vowed to never use them again. The Non-Proliferation Treaty prevents new nations from acquiring nukes, and it puts limitations on nations that already have them. Reading between the lines, this means it does nothing to actually eliminate the threat.
The great irony is that if aliens did exist, and were watching us from afar, they would likely view this behavior as insane. There is a self-destructive streak in human nature, one that announces its presence in acts of terrorism and violence around the world. Mass destruction is a motif of religious eschatology—the concept of "Armageddon" is written into the Bible as well as the Koran. The concept of self-destruction appears to be deeply ingrained in the human psyche, reiterating itself across generations of art and literature. As Shakespeare’s Hamlet famously declared, “To be or not to be? That is the question.”
Whether or not the bottleneck is true for life across the universe, it appears to be true for our planet and our species. Our future, therefore, depends on our ability to conquer the destructive impulses within ourselves. This, after all, is where our weapons and the urge to use them come from. Whether we survive or perish will depend not on what we create or destroy, but on the true and prevailing essence of our human nature.
1Following the formation of our planet, extreme temperatures and noxious gases made the Earth virtually inhospitable. This was our bottleneck; and if it weren’t for the temperature-regulating properties of primordial forests, Earth would likely be a lifeless rock today.