Extraterrestrial

by Avi Loeb

  We need not look far to appreciate how the great filter might work. The small filter of our own mortality and the context of recent history provide useful data.

  My father’s family had its roots in Germany for seven centuries. My grandfather Albert Loeb fought valiantly in World War I and survived the Battle of Verdun in 1916. That one battle, the longest of the war, is estimated to have killed 143,000 German soldiers out of a total death toll of 305,000. The dead and wounded military personnel from the entire war ranges between fifteen and nineteen million; add civilian casualties and that number rises to some forty million.

  My grandfather distinguished himself in the cavalry during that conflict and was awarded a medal that a decade or so later meant little. At a town gathering held in 1933 in the district of Netze-Waldeck, where my grandfather’s family lived, a member of the Nazi Party loudly argued that the country’s Jews were using up Germany’s resources. My grandfather stood up and confronted the man: “How dare you say these words when you personally dodged the draft in the Great War as a Communist while I was on the German front?” The speaker replied: “We all know about your patriotic contributions, Mr. Loeb; I was talking about the other Jews.” But the rising tide of vicious anti-Semitism in Germany, and indeed in much of Europe, was discernible.

  It was after that public exchange that my grandfather decided to leave Germany. He threw away the medal and, in 1936, emigrated to what was then British-controlled Palestine and is today Israel. Other branches of the family stayed in Germany, believing that they could wait and see what happened, holding to the belief that they would still be allowed to leave on the last trains out of Germany. Unfortunately, by then, those trains led elsewhere and all sixty-five of our family members were killed in the Holocaust.

  I still keep Albert’s pocket watch from a century ago in memory of his courage and integrity. It carries the same initials as mine, which is a reminder of sorts as well. The chain of causation that brought us here is tenuous indeed.

  …

  The mystery of ‘Oumuamua began shortly after my father died, in January 2017, and unfolded as my mother’s health declined. She was diagnosed with cancer in the summer of 2018 and passed away in January 2019.

  My father, David, was laid to rest in the same red soil in which he planted trees all his life, in the vicinity of those plantations that he watered routinely, near the house that he built with his rugged hands and that I grew up in, surrounded by the people he loved and who loved him in return, under the blue sky that I study as an astronomer. My mother, Sara, who put me on the road to thinking as a philosopher, with whom I spoke daily throughout my adulthood, and who especially gifted me with the life of the mind, was buried beside him two years later.

  In astronomy, we realize that matter takes new forms over time. The matter we are made of was produced in the hearts of massive stars that exploded. It assembled to make the Earth that nourishes plants that feed our bodies. What are we, then, if not just fleeting shapes taken by a few specks of material for a brief moment in cosmic history on the surface of one planet out of so many? We are insignificant, not just because the cosmos is so vast, but also because we ourselves are so tiny. Each of us is merely a transient structure that comes and goes, recorded in the minds of other transient structures. And that is all.

  The deaths of my parents brought home to me this and other fundamental truths about life. We are here for a short time and consequently we had better not fake our actions. Let us stay honest, authentic, and ambitious. Let our limitations, very much including the limited time we are each given, encourage humility. And let us allow the small filter, which represents the extent of our own lives, give us an approachable and sobering context for Hanson’s great filter, which represents the end of our civilization. With insufficient care, diligence, and applied intelligence, humans have proven themselves all too comfortable with ending the lives of their fellow humans.

  Of all the lessons we can learn from ‘Oumuamua, the most essential might be that we cannot allow the smaller filters of war and environmental degradation to grow into a great filter. We must exercise greater care, diligence, and applied intelligence in the preserving of our civilization. Only in this way can we save ourselves.

  During my years of military service, there was a phrase we were taught during infantry training: to lay your body on the barbed wire. Sometimes, faced with extraordinary circumstances, a soldier must deliberately lie down on barbed wire to allow his fellow soldiers to use his body to safely cross over. I am not so grandiose as to imagine my experience is the equivalent of such a soldier’s sacrifice. But, mindful of the specter of the great filter and ever mindful of the shadows of those who have come before and in their turn have sacrificed to advance humanity’s common cause, I find the image inspiring.

  Of this I am certain: The tenuous threads connecting humanity’s Earth-bound civilization as it exists today, and the promise of humanity’s possible interstellar civilization as it might exist tomorrow, will not be upheld by exercising conservative caution. In the words of Rebbe Nachman of Breslov, “The whole world is nothing but a very narrow bridge, and the key is not to be fearful at all.”

  …

  On September 1, 1939, three years after my prescient grandfather left Nazi Germany, Germany invaded Poland, and much of our planet found itself at war. It would be another eight months before Winston Churchill assumed his role as the wartime prime minister of the United Kingdom. In the interim, Churchill relentlessly warned his country and the world of the threat posed by Adolf Hitler and a militaristic Germany.

  Churchill also continued one of his cherished pastimes: writing. That decade, he penned, among other things, a four-volume biography of the first Duke of Marlborough and numerous opinion pieces and articles for newspapers and magazines. A subject of special interest was science (Churchill became the first British prime minister to appoint a civilian science adviser to the government), and his popular-science essays touched on everything from evolution to fusion power to aliens.

  In 1939, as the world was collapsing around him, Churchill penned an article titled “Are We Alone in Space?” He never published it; the confluence of events that would bring him to the apex of his political influence would also sweep this essay aside and bury it for decades. A war was fought and won before Churchill, once more out of political fashion in the United Kingdom, revisited his article. In the 1950s, he gave it the more accurate title “Are We Alone in the Universe?” But it still sat unpublished at the time of Churchill’s death, and it entered the U.S. National Churchill Museum archives unknown and uncommented upon until its discovery in 2016.

  It is a shame that Churchill’s unusual essay was never published, for it contains ideas that were well ahead of their time and a sense of perspective that was sorely needed then, as it is now. Churchill evinced the modesty of a generalist as he wondered how unique the Sun and our planetary system might be, writing, “I am not sufficiently conceited to think that my sun is the only one with a family of planets.” He was also astute. Decades before the discovery of exoplanets, Churchill concluded it was reasonable to believe that a large number of planets existed “at the proper distance from their parent sun to maintain a suitable temperature,” had both water and atmosphere, and so could potentially support life. Indeed, given the expanse of space and the number of suns in it, he wrote, “The odds are enormous that there must be immense numbers which possess planets whose circumstances would not render life impossible.” And though skeptical of interstellar travel, Churchill allowed that “in the not very distant future, it may be possible to travel to the moon, or even to Venus or Mars.”

  The somber note in the article isn’t reserved for the possibility of extraterrestrial life in the universe or even of humanity’s ability to reach other planets but rather for humanity itself. “I, for one, am not so immensely impressed by the success we are making of our civilization here,” Churchill wrote, “that I am prepared to think we are the only spot in this i
mmense universe which contains living, thinking creatures, or that we are the highest type of mental and physical development which has ever appeared in the vast compass of space and time.”

  When I first heard about Churchill’s essay, a few years ago, I couldn’t help but indulge in a thought experiment. The planet-spanning war that erupted shortly after Churchill wrote his essay is estimated to have cost $1.3 trillion—the equivalent of about $18 trillion in today’s currency. No reliable records exist to accurately estimate the number of people who died due to the war, and scholars bicker over which deaths can be clearly attributed to the war itself, but the range falls between forty million and one hundred million human beings.

  What if in the 1940s humanity had instead spent that $1.3 trillion—not to mention the skill, expertise, muscle, and minds of between forty and one hundred million people—on the exploration of the universe? What if the era’s collective genius hadn’t turned itself to destruction, efforts that reached their pinnacle in the development of nuclear weaponry, but had turned instead toward sending terrestrial life into the solar system and then out into the expanse beyond? What if human civilization, out of humility and the application of the scientific method, had concluded that its own existence made the existence of other civilizations in the universe probable? What if, in 1939 and over the course of the next decade, humanity had oriented itself toward space exploration and the discovery of extraterrestrial life rather than the vast extermination of life here on Earth?

  If there is a multiverse and if such a version of human civilization exists in it, I predict that at a minimum, it managed to photograph ‘Oumuamua, maybe even capture it for thorough examination. Perhaps those humans were not even surprised by what they found, for on their version of Earth, the Breakthrough Initiative would have started decades earlier and as a consequence, they would already be in receipt of the information that laser-powered lightsail ships had captured during their passage near Proxima Centauri. They would be well on their way, surely, to contemplating a solution to ensuring life’s continuation after the inevitable death of our Sun. I suspect, too, that their beaches would be less littered with trash.

  I’m sure there is one similarity, at least, between that Earth and this one. I will bet that their historians refer to the pivotal generation—the one that, in the 1940s, set it all in motion—as their greatest.

  Alas, we reside on this Earth, collectively tasked with the preservation of our human civilization. Among all the thought experiments that the multiverse theorists give us, the most productive, I believe, is this one: What will we do as residents of the one universe immediately arrayed before us?

  As I write, I consider the tree visible from my living-room window. Are we a civilization that will bind the damaged limb, allowing it to mend and grow? Or are we a civilization that either ignores it or shears it off, forever ending that branch of possibility?

  Whichever choice we make, we bet with our children’s children’s lives. If, when confronted with ‘Oumuamua’s exotic features, the only hypotheses we can contemplate are the natural but statistically remote—if we cannot, as Sherlock Holmes might, entertain the simplest remaining explanation to the collected data—we may do worse than simply delay our civilization’s next leap forward. We may walk into the abyss, one civilization among many and perhaps one not even advanced enough to have left, as a calling card, buoys throughout the universe.

  10

  Astro-Archaeology

  If we conclude that civilizations wink in and out of existence, perhaps serially, over the long, long history of the universe, it would be a grim warning for our own civilization.

  It would also be an opportunity.

  As scientists and as a species, we could tailor our detective work and search for the relics of dead civilizations. Even an oblique discovery of such evidence could teach us an important lesson—namely, that we need to get our act together if we’re to avoid a similar fate.

  As I’ve mentioned, this could prove to be ‘Oumuamua’s profound message in a bottle, one that we’re stubbornly refusing to read. Grappling with it fully, I believe, will require us to stop thinking of astronomy simply as the study of stuff in space and start treating it as an investigative and interdisciplinary enterprise.

  We are greatly in need of a new branch of astronomy, what I have termed space archaeology. Similar to archaeologists who dig into the ground to learn about, say, Mayan society, astronomers must start searching for technological civilizations by digging into space.

  It is enthralling to imagine what these astro-archaeologists might find, but that’s not even the most compelling reason to take this research seriously. It could well hold insights that nudge us in new scientific and cultural directions—and perhaps make our civilization one of the rare ones to outrun the great filter.

  …

  Recall that one of the biggest limitations of the Drake equation—the formula designed to help anchor discussions about intelligent extraterrestrial life—was its myopic focus on communications signals, which are only one of the various detectable traces that other civilizations might leave behind. Frank Drake defined the first variable of his equation, N, as the number of species in our galaxy that possess the technology necessary for interstellar communication; he defined the equation’s final variable, L, as the duration of time such species are able to produce detectable signals. In short, his equation was bracketed by the assumption that intentional efforts to communicate were the only way in which extraterrestrial civilizations would be detectable.

  However, there are lots of ways in which alien civilizations might unintentionally broadcast their existence, and as we discover new technologies, the number of new avenues available to search for this evidence is increasing. How ought we to redefine the scope of our search? To put it another way: What should we be looking for? And where should we be looking?

  The first of these questions is, I believe, relatively easy to answer. We know that life-forms of all sorts are identifiable by what we call biosignatures—for example, algae blooms and polluted atmospheres that living things leave in their environment. So in addition to seeking traces of technologically advanced extraterrestrial life, we can search for evidence of less advanced alien life, such as microbes, whether living or long dead.

  Thus the first question leads to another, more granular question: What kind of life should we be looking for, advanced or primitive? In a paper that I wrote with my postdoc Manasvi Lingam, we estimated the likelihood of finding primitive versus intelligent extraterrestrial life using only state-of-the-art telescopes (at the time, that included the James Webb Space Telescope, the successor to the Hubble Space Telescope). At heart, this was an effort to determine what part of astro-archaeologists’ efforts should be spent on the search for biosignatures and what part on the search for technosignatures. The exercise helped sharpen my thinking about the answer to the question I posed above: What should we be looking for?

  This project required us to work through a number of highly uncertain variables, including several that demanded best-guess answers. For example, we had to determine how much rarer intelligent life was than microbial life, how much farther away we could detect a technosignature versus a biosignature, and how long both types of signatures would be discoverable. Our selection of variables also reflected our concern over the great filter, although we made an optimistic guess about how long the sort of extraterrestrial technological intelligence we were seeking would survive—we set it at a millennium.

  Optimism is a precondition for scientific work, I’ve found, but in this case, optimism also factored into our actual calculations. In more ways than one, the more pessimistic you are, the lower the prospect of finding intelligent life. Consider, too, that in the scenario I have just described, we needed to guess both the duration of time in which intelligence might be discoverable as well as another, related variable: the period over which our intelligence would be around to seek it.

  With that said, it must be
admitted that discovering primitive, or microbial, life would not be the same as discovering intelligent extraterrestrial life. Either would fundamentally alter humanity’s view of itself, but evidence of technological intelligence would have the greater impact. To learn that other, perhaps even more advanced intelligent civilizations exist or preceded us would force us to adopt a humbler attitude toward the universe and our accomplishments.

  Ultimately, we concluded that the likelihood of detecting intelligent life was approximately two orders of magnitude smaller than the likelihood of detecting primitive life. Yet we also concluded that both searches should be undertaken concurrently, if with significantly more funding dedicated to primitive life, given that we expected it to be more plentiful. Additionally, the existence of intelligent life would greatly raise the prospects of our finding microbial life too.

  So what should we be looking for? In a word: life. We should just be prepared to find one type of it sooner than the other.

  Where, then, should we be looking? Answering this question is trickier and more complicated—but ultimately, perhaps, more comfortably familiar. Because it requires us to start with terrestrial abiogenesis: the origin of life on our planet.

  …

  The field of origins-of-life research is nascent. While we know a great deal about one aspect, terrestrial abiogenesis, our knowledge is an island in a vast ocean of ignorance. Yet there are reasons to be cautiously optimistic about where it is headed.

  As I write these words, we are far closer to understanding how the first cells, the building blocks of life, obtained replication and metabolic functions, and we are far closer to explaining how the precursors of biomolecules, such as proteins and carbohydrates, were synthesized and assembled from a common starting point. And while we do not know if extraterrestrial life would rely on the same building blocks that gave rise to life on Earth, we are becoming better equipped to think about the frequency of abiogenesis elsewhere as we approach an understanding of how life arose here.