by Adam Frank
The Astrobiology of the Anthropocene will show us images of steep cliffs under coral skies on Mars that help to vastly enlarge our understanding of climate and climate change. It will take us to dark crazy-quilt ecosystems deep in the ocean that give us a time-machine view of Earth billions of years ago when life was still new.
And then there are all the new planets.
The astrobiology of the Anthropocene will also take us across the galaxy to see entirely unexpected classes of planets have just been added to the textbooks: “hot” worlds snuggled tightly against their parent stars and “super-Earths” many times the size of our own.14
In telling this new story, we will also encounter the most thrilling of all possibilities: aliens.
Our exploration of the astrobiology of the Anthropocene will lead us to a radical claim. It’s time to take the existence of aliens—by which we really mean exo-civilizations—seriously. Everything that has been learned in the astrobiological revolutions of the last few decades now allows us to see just how improbable it is for us to be the only project of civilization in cosmic history. That realization tells us that if we ask the right kinds of questions, the ones backed by the hard numbers of the new exoplanet discoveries, we can begin making out the contours of a science of exo-civilizations that’s relevant to our own crisis on Earth.
The new science this book explores won’t tell us if the galaxy is teeming with other civilizations now. It won’t tell us if we’re going to catch evidence of their existence soon. It won’t tell us if they have pointy ears or seven-fingered hands or are shaped like lizards. What it can do, however, is show us how this—meaning everything you see around you in our project of civilization—has quite likely happened thousands, millions, or even trillions of times before.
From the vantage point of the astrobiological data, we can take those exo-civilizations seriously as a subject of scientific inquiry. It’s hard to avoid the giggle factor when we talk about aliens. Years of bad TV science fiction (as well as the crazy world of UFO conspiracy theorists), have left a bad taste for most scientists wanting to think about intelligent life on other worlds. Worse still, for years there wasn’t much in the way of scientific constraints on the question. Without such constraints, the discussion falls dangerously close to pure fiction. But if we ask the right kind of questions, the laws of planetary behavior we have now grasped can act as guardrails for how we think about exo-civilizations. That means if we ask the right questions, we can get answers. At the very least, with the right questions, those laws of planets we’ve uncovered will help us put limits on what answers can look like.
Remarkably, the one domain where such questions exist lies exactly at the intersection of astrobiology and the Anthropocene. Our new understanding of planetary laws is well tuned to address the question we most care about: How will a civilization (meaning any civilization) coevolve with its planet (meaning any planet)? If other civilizations have likely existed across cosmic time and space, we can take them seriously by making them the subject of our science. We can bring to bear all we’ve learned from Earth, Venus, Mars, and the thousands of planets discovered outside our solar system. We can deploy the laws of physics and chemistry inherent in that knowledge to begin doing science in the form of detailed models and simulations.
From this perspective, civilizations become just another thing the universe does, like solar flares or comets or black holes. We can use what the stars have laid out before us in our astrobiological studies to explore how any civilization on any planet can—or, in the worst case, cannot—evolve together. We can treat those possible exo-civilizations as other histories that can tell us about our own future.
The advantages of this astrobiological perspective can be gained even if no other civilization ever existed. Thinking about hypothetical exo-civilizations is valuable in dealing with the challenge of the Anthropocene because it teaches us to “think like a planet.” It teaches us to frame our pathways to a long-term project of civilization in terms of the coevolution between life (including us) and the Earth. Through the astrobiological perspective, we can map out the contours of our own fate and our own future.
A NEW STORY
If, however, we take the possibility of other civilizations seriously, then we find a new door open to us in facing the Anthropocene. Across a cosmos with so many planets experimenting with life, we can see that some technological species may learn how to make it. They will learn how to navigate the difficult bottleneck of the climate feedback they generate. Others, however, will fail. That’s how this new big story becomes meaningful. It begins with the science, but ends with showing us how to face the hard choices our version of the Anthropocene forces on us. A long-term sustainable version of our project of civilization will mean we must become partners, in some as-yet-unknown way, with the planet.
We must therefore become a power—in our own right—alongside the Earth. But as Spider-Man so famously discovered, with great power comes great responsibility. Does becoming a winner in the game of cosmic evolution mean we hold the Earth in a perpetual version of the Holocene? Will we never allow another ice age to form? If that’s true, then what about the species that might have emerged in the ice ages we block? Do we have the right to keep them from ever entering the Earth’s drama?
And which species from the current version of the Holocene do we carry with us into the Anthropocene? Images of polar bears adrift on lonely ice floes tug at our hearts. But entering into a true, long-term partnership with the planet will demand hard choices. Those decisions will not just be the domains of science. They will also depend on what we value, what we hold dear, and what we believe to be sacred. These are all the domains of meaning. That is why getting the story right—the story with us in it—is just as important now as getting the science right.
The astrobiological perspective on the Anthropocene is science at the grandest of scales. It’s a narrative of our own collective life and fate set against the stars, whose own stories suddenly matter as both our guides and our teachers. It is more than data, more than information, more than knowledge. We, and our cherished project of civilization, are crossing over a frontier as our planet enters the Anthropocene. The new science we’ll explore in what follows can help us map this new territory. It can also help us to navigate its burning edges and make it through to the other side.
CHAPTER 1
THE ALIEN EQUATION
THE FERMI PARADOX
One warm and bright summer day in 1950, four colleagues walked through the atomic weapons complex at the Los Alamos National Laboratory in the high desert of northern New Mexico. The Cold War with the Russians was in full swing, and there were new faces everywhere. Each of the men, however, was an old hand at the lab, and each played a key role in developing the bombs that helped win World War II.
First among them was Enrico Fermi, the Italian-born Nobel laureate whose brilliance had pierced the mystery of the atomic nucleus. Fermi was famous for his almost superhuman scientific abilities. C.P. Snow once wrote that if Fermi had been born just a bit earlier, he might have invented all of atomic science by himself. “If [that] sounds like hyperbole,” Snow wrote, “anything about Fermi is likely to sound like hyperbole.”1
Walking alongside Fermi was Edward Teller, the brooding Hungarian physicist whose work would become synonymous with the terrifying hydrogen bomb. While Fermi was not in favor of Teller’s push for the “super” bomb, the two men remained friends throughout their lives.2 Rounding out the group that day were American nuclear scientists Emil Jan Konopinski and Herbert York, both highly regarded researchers in their own right.
The four scientists made their way from the lab buildings to the Fuller Lodge where lunch was served (it was one of the few structures left over from the site’s earlier incarnation as a boys’ camp). As they walked, the conversation turned to unidentified flying objects.3 Since the end of the war, sightings of mysterious lights in the sky had been increasing. A recent incident had just made the local p
apers, reminding York of a whimsical New Yorker cartoon in which flying saucers were blamed for a rash of Manhattan garbage can disappearances. Given the physicists’ inclination for analysis, the UFO story led to a tussle of questions about faster-than-light travel and its limitations. Soon, however, the conversation wandered off to other topics as the four scientists continued along the path lined by pine trees and juniper. It was only later, in the middle of lunch, that Enrico Fermi blurted out, “But where are they?” 4
Alan Dunn’s cartoon of UFOs abducting New York City garbage cans, which appeared in The New Yorker in 1950.
Teller, York, and Konopinski all broke into laughter at Fermi’s outburst. They recognized their colleague’s sharp insight. Fermi had a habit of reducing complex problems to the barest essentials. Present at Trinity, the desert test of the first atomic bomb, Fermi had famously calculated the explosion’s power by simply dropping scraps of paper and noting how far sidewise they were swept by winds from the blast.5
But on that summer day over lunch, Fermi had identified a core question destined to haunt all subsequent discussions of intelligent life in the cosmos. Fermi’s observation was as straightforward as it was penetrating. If the evolution of extraterrestrial intelligent species was common, why didn’t we see them? Why hadn’t our telescopes found indications of their existence? Why hadn’t aliens already landed on the White House lawn?
Fermi’s question was not aimed at UFOs. That topic was, and continues to be, a morass of weak reasoning, poor observations, fakery, and conspiracy theories. Instead, his question would come to represent one of the first distinctly modern and scientifically manageable questions about extraterrestrial technological civilizations (we’ll use the term exo-civilizations).6
Over time, Fermi’s question would come to be known as Fermi’s Paradox. Its formal statement might go as follows: If technologically advanced exo-civilizations are common, then we should already have evidence of their existence either through direct or indirect means.
In the decades to come, other scientists would give Fermi’s question the precision it needed to have a scientific bite. In 1975, astrophysicist Michael Hart’s paper “An Explanation for the Absence of Extraterrestrials on Earth” addressed a number of objections to the reasoning behind Fermi’s paradox, including ones associated with physics, biology, and sociology.7 His conclusion was that none of the objections was strong enough to put off the paradox’s logic. Hart laid bare the essence of Fermi’s insight by demonstrating that just one species could “quickly” colonize the galaxy. Assuming an exo-civilization appeared that built ships capable of traveling at 10 percent of the speed of light, Hart showed that within just 650,000 years these creatures would cross the width of the galaxy. In this way, a single species could send ships in all directions, radiating outward from their home world, and quickly colonize every star system.
Of course, a few million years seems like a long time to most of us. Our species, Homo sapiens, has been around on the Earth for less than a million years. But what’s long for us is short for the life of the galaxy. The Milky Way, our home galaxy, is a vast and ancient metropolis of stars. It was born some ten billion years ago. So it would take about one ten-thousandth of the Milky Way’s age for Hart’s spacefaring civilization to cross the galaxy. Hart had demonstrated that, in a time scale that is small compared to the galaxy’s existence, just one randomly appearing interstellar civilization could reach all the planets orbiting all the stars in the sky—including our own.
For some researchers, Hart’s work filled the night with a disquieting emptiness. In their eyes, there was a straightforward logic to the Fermi Paradox that said we must be alone. The obvious absence of an alien civilization in our solar system, along with the lack of evidence for those civilizations’ existence among the stars, must mean no other form of life anywhere had reached our level of intelligence and technology. We were the sole species in the Milky Way that had made it up the ladder of evolution to build an advanced civilization. In response to the Fermi Paradox, physicist and science fiction writer David Brin spoke of the stars’ “Great Silence.” It was an apt term, capturing the cosmic loneliness that Fermi’s Paradox seemed to imply.8
Along with the Great Silence, an increasing interest in Fermi’s Paradox led to the idea of a “Great Filter.”9 The absence of evidence for advanced civilizations in the galaxy does not imply that Earth is the only life-bearing planet. The Fermi Paradox only speaks to the existence of technological civilizations like ours, or ones even more advanced. Microbes or shellfish or even dinosaurs might exist on every world in the cosmos. So if we don’t see exo-civilizations, some scientists argued, there must be a filter keeping evolution from spawning them. In other words, if we are alone in the cosmos, then some kind of evolutionary wall blocks other planets from reaching our level.
But a Great Filter might lie anywhere along that evolutionary path. Perhaps simple life is so difficult to form that it constitutes the Great Filter. In that case, Earth would be one of the few worlds with life. On the other hand, the emergence of even simple forms of intelligence might be the Great Filter. So, while lizards might appear on many worlds, dolphins and apes would not. If that were true, the difficulty in evolving intelligence filters out even those worlds where life has formed from moving further toward a technological civilization.
Ironically, at the exact historical moment that Fermi and his colleagues were sitting down to lunch, a new kind of evolutionary dead end for the Great Filter made its appearance. Fermi posed his question at a laboratory dedicated to developing weapons of unprecedented destructive energies. It was in the 1950s that humanity first gained the power to bring civilization to an abrupt and decisive end through full-scale nuclear war.
Atomic Armageddon made it possible to imagine that the Great Filter lay not in the distant evolutionary past (in which case we had been lucky to avoid it); instead, it might wait like a viper, hiding in the tall weeds of our future. Maybe the night sky was silent—and our planet unvisited—because no advanced civilization was smart enough to handle the pressure of its own existence.
If someone could have asked Fermi for his top choice for a Great Filter, he would likely have answered nuclear war. These days, however, we have a broader understanding of civilizations and their existential challenges. In the 1950s, when Fermi posed his question, there was only a small community of Earth scientists awakening to the possibility of human-driven climate change. The idea that humans could unintentionally change the behavior of the entire planet through nothing more than our collective daily activity was an idea so radical, it had barely been formulated in a scientific way. Now, however, we know better.
Earth’s passage into its human-dominated era, increasingly known as the Anthropocene, shows us a potentially more potent candidate for the Great Filter. Civilizations like our own are a complex web of interdependent systems. Where would you get your food if the electricity went out for a year? How would you heat your home if the pipelines delivering petrochemicals shut down? There are a million ways we all rely on the smooth operation of these systems. But a significant shift in Earth’s climate state would upend those systems in ways that would deeply challenge their operation.
Think about the Gulf Stream for a moment. It cycles warm water (and warm weather) up from Florida to Boston, and then out across the Atlantic. Hundreds of millions of people in some of Earth’s most technologically advanced cities rely on the mild climate delivered by the Gulf Stream. But the Gulf Stream is nothing more than a particular circulation pattern formed during a particular climate state the Earth settled into after the last ice age ended. It is not a permanent fixture of the planet. If the climate changes enough, the Gulf Stream, and the mild weather it delivers, could become a thing of the past.10
So what we call the Anthropocene may be a far more potent candidate for the Great Filter than nuclear war. An all-out nuclear exchange would, after all, be intentional. It would be someone’s decision. But it’s easy to imagine
other civilizations less aggressive and warlike than ours. They might not even think to build nuclear weapons. Climate change, however, is likely to be universal. As we will see, it is likely to be a consequence of any project of advanced civilization building on any planet. Long-term dramatic climate change need not lead to a civilization-building species’ extinction. It only needs to make conditions difficult enough that their project of technological civilization is disrupted and unable to recover on the now-climate-changed planet.11
All these issues surrounding the Great Filter really illustrate the power of Fermi’s insight. Making progress in science often hinges on asking the right kind of question. Without a well-posed question, discussions become little more than people talking (or yelling) past each other. And without a well-posed question, there’s no clear path toward gathering data that will yield answers.
Finding a good question is like throwing open the shades in a dark room. It’s the first step in finding a new way to tell a story about the world because it lets us see the world in a new way. A good question reframes what we think is important. It tells us where we should be looking, where we should be going, and how to begin organizing our efforts to get there.
Fermi’s 1950 question helped play that role for the issue of exo-civilizations. As developed by Hart and others, Fermi’s Paradox asks us to consider if and why humanity might be alone in the universe.
But to truly understand the importance of Fermi’s question for our future, we need to travel back a few thousand years into our past.
THE PLURALITY OF WORLDS
The Greek philosopher Epicurus made the first expression of what we might call “exo-civilization optimism” almost 2,200 years ago: “There are infinite worlds both like and unlike our own. . . . Furthermore we must believe that in all worlds there are living creatures and plants and other things we see in this world.”12