The Fermi paradox has also been called “the Great Silence”—we bellow out into the universe and hear no echo, and no reply. The iconoclastic economist Robin Hanson calls it “the great filter.” Being filtered, the theory goes, are whole civilizations, enclosed by global warming like bugs in a net. “Civilizations rise, but there’s an environmental filter that causes them to die off again and disappear fairly quickly,” as the charismatic paleontologist Peter Ward—among those responsible for discovering that the planet’s mass extinctions were caused by greenhouse gas—told me. “The filtering we’ve had in the past has been in these mass extinctions.” The mass extinction we are now living through has only just begun; so much more dying is coming.
The search for alien life has always been powered by the desire for human importance in a vast, forgetful cosmos: we want to be seen so that we know we exist. What’s unusual is that, unlike religion or nationalism or conspiracy theory, the alien fantasy doesn’t place humans at the center of a grand story. In fact, it displaces us—in that way it is a sort of Copernican dream. When Copernicus announces the earth revolves around the sun, he briefly feels himself in the spotlight of the universe, but by making the discovery he consigns all of humanity to the relative periphery. This is what my father-in-law, describing what happens to men with the birth of children and then grandchildren, calls “the outer ring theory,” and it more or less encapsulates the meaning of any imagined alien encounter: suddenly humans are major players in a drama of almost inconceivable scale, the lasting lesson of which, unfortunately, is that we’re total nobodies—or, at best, a lot less unique and important than we thought we were. When the astronauts aboard Apollo 8 first caught a glimpse of Earth from the tin can carrying them through space—first saw the half-shadowed planet past the surface of the moon—they looked at one another and jokingly asked, about the world that had launched them into orbit, “Is it inhabited?”
In recent years, their telescopes gazing farther, astronomers have discovered legions of planets like our own, many more than were expected a generation ago. This has led to a flurry of activity revising the terms of expectation established by Frank Drake in what is now known as the Drake equation—which builds a prediction about the possibility of extraterrestrial life off assumptions about things like the fraction of planets conceivably able to support life that actually do support life, the fraction of those planets that develop intelligent life, and the fraction of those planets that would emit detectable signs of that intelligence into space.
And there have been many theories, beyond the Great Filter, about why we haven’t heard from anybody. There is the “zoo hypothesis,” which suggests that aliens are just watching over us and letting us be for now, presumably until we reach their level of sophistication; and something like its inverse—that we haven’t heard from aliens because they’re the ones sleeping, in a civilization-scale system of extended-sleep pods like the ones we know from science fiction spaceships, waiting while the universe evolves a shape more suitable to their needs. As far back as 1960, the polymath physicist Freeman Dyson proposed that we may be unable to find alien life in our telescopes because advanced civilizations may have literally closed themselves off from the rest of space—encasing whole solar systems in megastructures designed to capture the energy of a central star, a system so efficient that from elsewhere in the universe it would not appear to glow. Climate change suggests another kind of sphere, manufactured not out of technological mastery but first through ignorance, then indolence, then indifference—a civilization enclosing itself in a gaseous suicide, a running car in a sealed garage.
The astrophysicist Adam Frank calls this kind of thinking “the astrobiology of the Anthropocene” in his Light of the Stars, which considers climate change, the future of the planet, and our stewardship of it from the perspective of the universe—“thinking like a planet,” he calls it. “We are not alone. We are not the first,” Frank writes in the book’s opening pages. “This—meaning everything you see around you in our project of civilization—has quite likely happened thousands, millions, or even trillions of times before.”
What sounds like a parable from Nietzsche is really just an explication of the meaning of “infinity,” and how small and insignificant the concept makes humans and everything we do in the space of such a universe. In an unconventional recent paper with climatologist Gavin Schmidt, Frank went even further, suggesting that there may even have been advanced industrial civilizations of some form in the deep history of this planet, so deep in the past their remnants would have long been reduced to dust below our feet, making them permanently invisible to us. The paper was meant as a thought experiment, pointing out how little we can really know from archaeology and geology, not a serious claim about the history of the planet.
It was also meant to be uplifting. Frank wanted to offer what he believes is the empowering perspective that our “project of civilization” is profoundly fragile, and that we must take extraordinary measures to protect it. Both are true, but nevertheless it can be a bit hard to see things his way. If there have really been trillions of other civilizations like this one, somewhere out there in the universe and including possibly a few scattered in the dust of the earth, then—whatever lessons of stewardship we can draw from them—it does not bode well for ours that we don’t yet see the trace of a single one that’s survived.
That is a lot of despair to hang on “trillions”—in fact a lot to hang on some very speculative math. Which goes even more so for the work of anyone trying to “solve” the Drake equation, as many have. That project, which looks to me less like sorting out the nature of the universe on a chalkboard than like playing games with numbers, working from close-to-arbitrary postulates so confidently that when you see the universe departing from your predictions you choose to believe it is hiding from you some very important information—namely, about all the civilizations that may have died and disappeared—rather than that your suppositions may have been made in error. The fact of dramatic near-term climate change should inspire both humility and grandiosity, but this Drakean approach seems to me somehow to get the lesson both right and backward: supposing that the terms of your thought experiment should govern the meaning of the universe, yet unable to imagine that humans might make for themselves an exceptional fate within it.
Fatalism has a strong pull in a time of ecological crisis, but even so it is a curious quirk of the Anthropocene that the transformation of the planet by anthropogenic climate change has produced such fervor for Fermi’s paradox and so little for its philosophical counterpoint, the anthropic principle. That principle takes the human anomaly not as a puzzle to explain away but as the centerpiece of a grandly narcissistic view of the cosmos. It’s the closest thing string-theory physics can bring us to empowering self-centeredness: that however unlikely it may seem that intelligent civilization arose in an infinity of lifeless gas, and however lonely we appear to be in the universe, in fact something like the world we live on and the one we’ve built are a sort of logical inevitability, given that we are asking these questions at all—because only a universe compatible with our sort of conscious life would produce anything capable of contemplating it like this.