There are two stories, both of great consequence, that Lee Billings tells in his new book, the excellently titled Five Billion Years of Solitude. The first concerns the recent discovery of planets circling distant stars, and our ongoing struggle to find life on their surfaces. Billings takes us to the cutting edge of this field, letting us share intimate moments with its most accomplished scientists. We get a deep sense for the cosmic wonder of their work, and the steep challenges they face in carrying it out.
If the book had no higher ambition than to be a richly reported, lyrical meditation on the frontier of exoplanetology, it wouldn’t disappoint. But Billings goes further, putting that field's discoveries into context. He does this by telling a second story, one that hits a bit closer to home: the story of our planet, the only place known to support life. Billings takes us from Earth’s violent formation, to the rise of life here, and onward, to the events that will someday make this world uninhabitable. This deep history shows us the incomparable splendor of planet earth, but it also illuminates its limits—and reveals the high stakes that attend our search for new earths.
Last week, I interviewed Billings by email about Five Billion Years of Solitude. What follows is an edited transcript of our exchange.
Tell me a little bit about how you first got interested in this subject. Were you always into astronomy, or fascinated by the possibility of finding extraterrestrial life, or did you find your way to this project some other way?
The short answer is that I’ve been interested in these topics for as long as I can remember. The longer answer is that around the turn of the millennium I started regularly seeing news stories about how astronomers were discovering ever-larger numbers of exoplanets, and how sometime in the next decade or so NASA and other space agencies would build and launch space telescopes designed for the explicit purpose of seeking out Earth-like worlds and the life they might harbor. That just seemed like such a cool, wild idea. It was always in the back of my mind as a good story to research and pursue when I was just starting out in science journalism.
In the meantime, NASA’s push for big life-finding space telescopes was already running into very serious trouble and major delays, and the prognosis would only become more grim as the years went on. As I delved deeper into the topic, I was struck by the notion that, soon, potentially habitable planets would be piling up by the dozens, but without major shifts in policy and funding we would have extremely limited abilities to determine whether or not any of those worlds were actually habitable or inhabited. That just didn’t make any sense to me, and I started wondering why nobody was really raising a fuss about it. It troubled me greatly that, outside of a handful of astronomers, no one really seemed to care that an opportunity to discover life beyond the solar system was slipping away. I wanted to figure out how the state of play had changed so dramatically in such a relatively short time, and, if I could, do my own small part to shift things back on course. That’s basically how the book came to be.
This book is a kind of snapshot of where we are, technologically and culturally, in our quest to find out whether there is life elsewhere in the universe. While I was reading it, I couldn’t help but wonder where you think this question stacks up against the other big, primary intellectual inquiries. Is this ultimate question right now? If not, what is?
The book’s central question isn’t really whether or not life exists elsewhere in the universe. If that was the central question, I would’ve included much more detail about research into the origins of life, and about the prospects for extraterrestrial life within our own solar system. I’m inclined to believe that life is an emergent cosmic phenomenon, something as inevitable in our universe as the formation of stars and galaxies, and that perspective certainly informs the book. So piling on pages and pages of detail and debate about how life might emerge on a planet seemed to me a case of missing the forest for the trees. The book is less about life’s origins and more about what life does after it gets started on a planet like Earth.
Because, if you think about it, if life is so common throughout the universe, you have to wonder why everything we see out there looks so dead. I’d guess it’s because most life is actually quite hard to detect over cosmic distances, because it doesn’t end up progressing to sentience and technology. It doesn’t end up building starships and interstellar beacons to explore and communicate with the rest of the galaxy, at least not in any obvious way we can easily see. Put another way, right now it looks like most life out there doesn’t do the things that we like to tell ourselves we’ll eventually do. Short of joining in the search myself or just writing extremely speculative science fiction, it seems the only way to get at why that might be is to take a long, hard look at our current situation on Earth in light of recent discoveries about other planetary systems and our own world’s deep past.
So the book’s real central question is what the future holds for life—particularly intelligent life—on this small world orbiting a lonely star. We already know that someday our Sun will cease to shine, bringing life on Earth and in the solar system to an end. Can we—will we—avoid this dismal fate forecast for us by stellar astrophysics? No one really knows that answer yet. And perhaps that’s not an “ultimate” question in the big universal scheme of things. But perhaps it is. I certainly think that, either way, it’s of immense importance to everyone in the here and now on Earth. The book’s core theme, if it can be said to have one, is that the question of life’s future on (or off) this planet is not only worth asking, but also more urgent than commonly believed.
One of the really striking things about this book is its unflinching tone. I’ve interviewed a fair number of astronomers, and I know how easy it can be to slip into a romantic mode about it. The people and the settings and the technology all lend themselves to triumphant narratives, but you have stayed remarkably disciplined here. Rather than retreating into overly optimistic futurism, the book really captures just how heartbreaking it can be to talk to high-level astronomers right now. It made me wonder what it’s been like for you to spend so much time with these driven, idealistic people who are being forced to kind of sit around and stew in deep curiosity while the values of the culture at large catch up with them?
It was a trip, in the most arduous, elegiac, and mind-expanding sense of the word. There was an otherworldly tinge to my visits with some of the researchers I profiled that clashed in telling ways with everyday activities. One minute they’d be talking about planetary carbon cycles or the long-term evolution of the Sun or how to travel between the stars, and the next they’d be stuck in traffic or doing laundry or peeing in the bushes next to a hiking trail. One minute they would be keepers and seekers of a sort of sacred, transcendent knowledge, and the next they would be just normal human beings caught up in the daily grind and the messy details of life. I should also note that this phenomenon isn’t isolated to astronomers and planet-hunters; it’s something that any scientist or engineer working at the frontier of almost any field deals with on a regular basis.
And of course very few of these people are really lauded and richly rewarded for their work in comparison to even C-list Hollywood celebrities. For instance, look at the case of Jim Kasting, a quiet, thoughtful Penn State geoscientist I profile in the book. Kasting basically figured out how the cycling of carbon between a planet’s atmosphere, ocean, and crust stabilizes the climate over geological timescales. In other words, he helped show how and why Earth has managed for billions of years to be a reasonably nice place to live. Insights from this carbon cycle are a big part of how planet-hunters draw the boundaries for habitable zones around other stars. And it turns out that this same carbon cycle, paired with the Sun’s evolution, dictates how long our planet can support a robust biosphere—how long life can exist on Earth. So Kasting has sketched out some canonical limits for life as we know it around stars, and he has also made a scientifically robust forecast for the end of the world.
If that’s not enough, he’s also been an important figure in the quest to build telescopes that could someday look for signs of life on faraway exoplanets. Here is a man working on topics that have profound, fundamental importance for every single living being on Earth and yet he toils away in obscurity in a tiny little office. Essentially no one outside of the field knows who he is, and even within the field he has limited power; he certainly isn’t able to pull any political or financial strings to help get his dreamed-for telescopes built. His story is by no means unique; in fact, it’s the norm for great scientists.
I think these sorts of jarring juxtapositions are important to acknowledge. They help reveal the unthinking boosterism and naive idealism that all too often passes as popular science communication today. I’ll avoid naming names, but I can pull up a web browser right now and visit dozens of high-traffic blogs and even a lot of otherwise reputable mainstream media sites and find “news” stories about how we’re on the cusp of achieving immortality, or creating super-intelligent androids, or building a warp drive or a space elevator or a grid-ready fusion reactor or a Mars colony or, you know, a giant space telescope to locate and study exo-Earths.
Reading those sorts of stories, you’d think all this stuff is really only a few years away. Well, I hate to say it, but that’s bullshit. It’s revisionist futurism that pretends humans can’t massively fuck up, that the world never steps in to spoil the best-laid plans. Throughout history, countless aspirations of heartbreaking beauty and staggering genius have been torpedoed by all-too-human foibles or by simple bad luck, and that’s not going to change. Maybe we will build super-intelligent machines or travel to the stars someday, but even then we’ll still have to do the dirty laundry.
In some sense, all that credulous coverage is great, because many of these things are almost certainly within our reach, and it’s important to communicate such wild possibilities to the public. But that coverage can also be terribly damaging, because it usually glosses over the hellish complexity and difficulty of the scientific research and technological engineering and wonky public policy wrangling that is required to do these grand, big, bold things. Most of all, it treats these things as guaranteed successes and foregone conclusions rather than as vulnerable and flawed human endeavors. It leads the public to expect amazing breakthroughs without any actual major investment and hard work, and the end result is a backlash of mass disillusionment and apathy when the jetpacks and robo-butlers and teleporters don’t suddenly materialize.
I think the public is actually eager to support the search for other Earth-like planets. It’s high time for us to find other Earths and study them for signs of life. The problem is, all the breathless reporting seems to have given most people mistaken assumptions that the search is much further along than it really is, and that its continuance is assured.
Tell me about the title of this book, Five Billion Years of Solitude. My understanding is that it’s a reference to the lifespan of complex life on Earth, which began after the planet cooled and formed oceans 4 billion years ago, and which will end a billion years from now, when conditions here become too extreme for complex life. Are readers meant to interpret that as a prediction about our species’ destiny? Do you think we are bound to be alone for all of that time, or is it just a warning as to what could happen if we proceed along our current path?
It’s an admonishment that, though we may in a sense have all the time in the world, that’s not actually forever. We may in fact have a rather slim window of opportunity in which we can hope to secure our long-term, enduring future.
Looking to the past, we know from dating various meteorites that the Earth and the rest of our solar system formed about 4.5 billion years ago. We don’t really know when exactly life got started, but it’s quite possible that at least one terrestrial biosphere, more primitive and ancient than our own, arose in the Earth’s first few hundred million years of existence, only to perish in a spate of planet-sterilizing asteroid or comet impacts that seems to have occurred between 4.1 and 3.8 billion years ago. Our planet’s record of sedimentary rock begins after these great impacts tapered off, and it’s in those nearly 4-billion-year-old sedimentary rocks that we find the earliest hints of the biosphere that grew into the one we all remain a part of today. Conversely, we don’t find abundant evidence of complex, multicellular life until approximately 550 million years ago.
What all that means is that life formed on Earth very rapidly, essentially as soon as it could after the planet cooled from great impacts. Our planet has been alive almost from the start. Yet for about 7/8ths of its history, the Earth has basically been a single-celled world with no higher plants and animals. The half-billion-year era of complex life we find ourselves in right now is only a small part of the planet’s greater history, and it is also fleeting.
Looking to the future, based on the work of Jim Kasting and others, we can forecast that somewhere between five hundred million and perhaps a billion years from now, the era of complex life will begin to fade. The details are a bit complicated, but in essence by that time the Earth’s atmosphere should be getting too hot and anemic to support oxygenic photosynthesis, and this will lead to the collapse of the rich surface biosphere of multicellular plants and animals.
This of course assumes that something truly cataclysmic doesn’t happen in the meantime, such as the Sun colliding with another star, or a rogue free-floating planet’s passage through the solar system sending the Sun’s worlds tumbling into orbital disarray. It also assumes that life itself doesn’t possess an infinite evolutionary capacity to adapt against ever-harsher environmental conditions. I think these are both reasonable assumptions.
So you take the age of the Earth—about 4.5 billion years—and you add the most pessimistic forecast for complex life’s longevity—about 500 million years—and you arrive at this nice round number, five billion years. A number suitable for a book title. “Five Point Seven Five Billion Years of Solitude” doesn’t have that same ring to it, does it? Now, microbial life will probably persist on Earth for quite some time after the demise of plants and animals, but it will still be doomed. The Sun gets brighter as it ages, and that will eventually boil the oceans off into space. Then, near the end of its life, the Sun will swell into a red giant star and scorch the Earth to slag. Then our star will burn out. The end.
So where does the “solitude” part come in?
Based on all the evidence now available to us, it appears that in all 4.5 billion years of planetary history, the planet produced nothing else like us, nothing else with the potential to escape the grim end of life on Earth. Some of us could go to space. Some of us could, in principle, even escape the solar system entirely, bound for parts unknown—maybe for habitable planets orbiting other nearby stars. Who knows what we’d find out there? Maybe we’d find someone else to talk to.
We only have these options by virtue of things like our large brains and our opposable thumbs, our capacities for language and tool-making and foresight that we have with great difficulty used to build a global technological culture. We really owe our progress and our current state not only to our biology, but also to our planetary resources—to the fossil fuels we burn, the ores we mine, the rich diversity of other species we exploit, and so on. We’re presently using most of those resources in very unsustainable ways. We’ve already plucked all the low-hanging fruit, and much of what we are burning and mining and exploiting now is only available to use through our already sophisticated technology.
So if we somehow drive ourselves extinct, if all our great edifices collapse, I think it would be very difficult if not impossible for anything else to rise up and rebuild to where we are now, even given a half-billion or a billion years. People can and will disagree with me about that, but my position errs on the side of caution, on the side that says humanity’s present moment in the Sun is too valuable to treat as something disposable. And we can’t count on help coming from anywhere else, from beneficent all-powerful aliens swooping out of the sky to save us, or on messages of salvation beamed from hyper-advanced civilizations on the other side of the galaxy.
Keep in mind that life on Earth isn’t going to be getting easier throughout all that future time—it will be getting harder, as the planet becomes less and less conducive for complex life. So we may have—we may be—the only chance available for life on Earth to somehow escape a final, ultimate planetary and stellar death. If we don’t do that, then the book’s title would become a prophecy: After fading into oblivion, the sum total of life’s history on Earth will only be billions of years of solitude.
It was interesting that you were able to find researchers that could speak powerfully and knowledgeably to these two themes, the unsustainability of our current relationship to the planet, and the search for others that might harbor life. Has it been your experience that most of the people working in this field draw on this broad expertise, or did you hunt down the best of them?
Not to be overly romantic, but I do think it’s true that spending lots of time stargazing or studying planetary climates or searching for habitable exoplanets will change anybody. Your view of nature and your place within it changes. Looking out at the night sky, you might feel small and insignificant, but then looking back from our present moment through the eons of life’s evolution here on Earth, you might justifiably feel you’re a part of the most meaningful thing in the known universe, something that could be the source of significance for countless past and future events.
No two people deal with those perspective shifts in exactly the same way, and I don’t actually see a strong correlation between being able to wax poetic about them and being a truly great scientist. Some get awestruck and aspirational, some get apathetic and bleak. Others just think there are more productive things to discuss. There are plenty of eminent astronomers who find exoplanets really fascinating, but who aren’t very interested in questions of life and habitability. If you try to ask them about that stuff, you probably won’t get much more than shrugs and monosyllabic answers. Ask them instead about the celestial mechanics of planetary migration, or what the distribution of planetary system architectures are telling us about how planets form, and they’ll talk your ear off.
Which is all to say that while the book’s “main characters” are certainly among the very best at what they do, the elite group of scientists from which they are drawn is quite a bit larger. In the book’s acknowledgements, for instance, I list about 75 additional researchers I talked with whose valuable insights aren’t directly mentioned or quoted. And even that list is incomplete. Over the years, I easily talked to more than a hundred experts for this book, and yet I can reel off name after notable name of those who, for one reason or another, I wasn’t able to chat with. That fact alone is a powerful testament to just how robust and expansive the field has become—there are so many Very Important People working in exoplanets and astrobiology right now that meaningfully talking with all of them about their work surpasses the capacity of any one person or project.
In that sense, it’s really an amazing and entirely unprecedented time to be alive if you’re interested in the question of life beyond Earth. Right now is one of those strange moments where you have a singular confluence of brilliant minds and breakthrough observations that will become legendary in the history of science. It’s a bit like the formation of quantum theory in the 1920s—you had gatherings like the Fifth Solvay Conference in Brussels, where Max Planck, Albert Einstein, Niels Bohr, Marie Curie, Paul Dirac, Erwin Schrodinger, Werner Heisenberg, Wolfgang Pauli, and other giants of physics all came together to discuss unsolved problems and what it all meant. The events of that time and those meetings still echo through modern physics, and they have seeped deep into our culture.
I’d argue exoplanetology as an interdisciplinary field of scientific inquiry is in a similar place today as quantum theory was in the early 20th century. In the book I’ve tried to capture some of the associated intellectual debates and personal clashes that I’ve been privileged to witness, because I suspect they will prove to be of considerable historic interest.
Your book closes on a moving portrait of one of the most compelling figures in this field, Sara Seager, the MIT professor who has just won a MacArthur Grant for her work on exoplanets. Was there a point in your research when you realized that her story distilled the essence of this larger scientific moment?
In hindsight, it’s all quite clear: Seager began her career at Harvard, working in cosmology, studying the physics behind “recombination,” a cosmic moment less than a million years after the Big Bang when the primordial plasma that filled the universe cooled and condensed into hydrogen atoms. When the first exoplanets were discovered in the mid-1990s, though, she switched to studying them, anticipating that exoplanetology would soon become the hottest, fastest growing field in astronomy. It was a risky move, because at the time not everyone agreed those planets were real; she didn’t even have her PhD yet, and many of her peers and colleagues thought she was making a huge mistake.
But she proved them wrong. With her advisor, Dimitar Sasselov, she hammered out some very important theoretical models and observational techniques that were then used to study that first wave of discovered exoplanets. She never really looked back or second-guessed herself after those initial successes, and just kept relentlessly pushing toward over-the-horizon goals like looking for smaller, more Earth-like planets and finding ways to study them for signs of life. It’s my sense that Seager is one of those rare individuals for whom the “impossible” is just a provocation. She has immense drive and discipline, and when someone tells her she can’t do something, it’s like pouring gasoline on a fire.
In her shift away from cosmology, in her refusal to be intimidated by naysayers or cowed by great difficulties, in her steadfast pursuit of “impossible” dreams, she really embodies the ethos of the exoplanet revolution now sweeping through space science. I’m not the only one who saw that about Seager—a lot of people have seen it, I think, and in seeing it they all thought the same thing: She might be the one who really makes this happen, the person who leads the charge and gets the light of other living worlds and proves for the first time in history that humanity is not alone.
I had been talking to Seager periodically about her exoplanetology work since 2007, but the recognition that she was a microcosm of the field at large didn’t really begin to dawn on me until 2011, when we met for lunch at a science conference in Washington, DC. Over lunch she revealed to me some profoundly difficult events she’d been struggling with in her personal life, events that form a key part of her story in the book. Suddenly the individual I was sharing a meal with was no longer an all-knowing, nigh-invincible scientific demigoddess—she was a fragile and conflicted and scared wife and mother, all too human in her vulnerability and sorrow. Some of her dreams had been shattered forever. Over the course of our subsequent interviews and interactions, I watched as Seager slowly picked up the pieces she could and rebuilt herself, stronger and even more driven than before.
That sudden individual shift from unstoppable and triumphant to mournful and mortal reminded me of the large-scale changes I had witnessed as I researched the book, as ambitious government plans to build big, billion-dollar space telescopes to find habitable planets and extrasolar life were delayed, defunded, or entirely cancelled. Those plans were scuttled for complex reasons, few of which had anything at all to do with astronomy. I think they are indicative and symptomatic of our modern society’s broader struggle to come together to achieve great, enduring feats.
Right now the planet hunters (and the rest of the astronomy community) are still struggling to pick up the pieces, to rebuild themselves and regain momentum and a bit of the luster that has been lost. They’re still trying to find a sustainable future for themselves, and I think Seager is playing an important role in that debate by exploring possible alternatives to the standard, federally-funded way of doing big science.