The Smallest Lights in the Universe

by Sara Seager

  Mike and I moved in together before winter fell. Like his joining me on my canoe trip, our living together was hardly planned. We let ourselves be guided by the river of circumstance. I had first raised the possibility on our drive back from Wollaston Lake. I reached out and grabbed his arm. “Mike, move to Boston with me,” I said. His blue eyes went bluer for the water that began to fill them, but he didn’t reply. His wishful thinking abandoned him whenever he wondered how we might find ourselves in the same place for any length of time.

  I missed him after I’d moved, and I clocked that new feeling, too: I want someone else with me. I wrote him letters. We talked on the phone. One day, a month after our return, he told me that he’d been laid off from his job in Toronto. Taking the summer off had been a great way to prove how inessential he was to the operation. He told me that he was thinking of moving back in with his mother in Ottawa; that didn’t make sense to me. He was thirty years old. Why shouldn’t we try living together? Mike couldn’t come up with a reason, and he moved down to Shirley with his canoe and tiny shorts. He soon found work as a freelance editor, poring over science and math textbooks in the pale light of the carriage house. His job was to find mistakes. I went to school, where my job was to risk making them.

  * * *

  ●

  The 1990s were an era of historic discovery in astrophysics. Our tools were catching up to our ambitions. More powerful computers and satellites allowed us to make calculations and take measurements that we couldn’t have contemplated only a decade before. In astronomy, there was always something new for us to do.

  In 1995, during my second year at Harvard, I was a little adrift, still searching for a specific course of study. NASA was building a new satellite; it would eventually be called the Wilkinson Microwave Anisotropy Probe, or WMAP. It was designed to observe cosmic microwave background radiation, that oldest, Big Bang light. My research adviser, a young Bulgarian astrophysicist named Dimitar Sasselov, suggested that I might find an academic home in the shared effort. He was correct. Together we would divine the origins of the universe. I caught the first glimpse of my calling in its ancient glow.

  About 380,000 years after the Big Bang, the universe was still a white-hot fog, billowing at its limits like the farthest reaches of an explosion. It was too hot for the formation of atoms, so protons and electrons drifted in the haze, angry and anchorless. The universe cooled as it continued to expand. Eventually it became cool enough for the protons and electrons to start combining with each other when they collided, creating the first hydrogen atoms. That hydrogen later formed the hearts of stars.

  The universe expanded so quickly that some of the electrons failed to find a proton in the chaos. What we think of as “empty space” isn’t empty; it contains not only those lonely, leftover electrons but also the energy they once scattered, detectable to us as radiation. (Astronauts see that same radiation whenever they try to sleep in orbit; every minute or so, lights flash on the other side of their closed eyelids.) Today that lingering energy is faint, but there remain slight differences in temperature across space. With WMAP, the new satellite, astronomers would soon be able to map those temperature differences and use the variations to trace the origins of galaxies, the way arson investigators read burn patterns to find the source of ignition. That would allow astronomers to determine when and how galaxies were formed. Their seeds were just waiting for us to find them, frozen in time and space.

  In the 1960s, astrophysicists had done their best to calculate the probable rates of cooling, which helped put a rough time stamp on the birth of galaxies. My job, three decades later, was to use modern computers to verify their work. The temperature measurements taken by WMAP were only useful if we interpreted them correctly. I was there to improve our precision.

  With code that I’d written from scratch, I ended up finding a tiny discrepancy between the estimates of the 1960s and the actual order of things—an almost imperceptible difference in the accepted timing of when all those protons and electrons finished combining to form hydrogen. It was, at its essence, a microscopic gap between the best guess and the measured reality, but when you’re working on such enormous scales, the smallest mistakes can be amplified into massive miscalculations. I had made a small but significant correction to a milestone of the universe.

  Or rather—science had, as it almost always does, corrected itself. It’s a discipline of constant catching up. My contribution didn’t make me a prodigy or someone to watch overnight; I was a kid from Harvard who had made an important, but not unexpected, adjustment. Nothing changed about my existence except that I understood a little better how we come to know things. We make progress the way Mike and I covered our hard northern ground: in the long and steady accumulation of increments.

  It wasn’t until years later, after WMAP finished its scan of the sky in 2010, that our efforts in the 1990s came to their final fruition. I still marvel at what we now know. First, the universe underwent an extremely rapid growth rate in a tiny fraction of the first trillionth of a second of its existence. That’s why someone like me talks about the Big Bang rather than the Big Bang Theory. Second, the universe is about 13.75 billion years old and still growing. We were born in a flame that has never gone out.

  * * *

  ●

  Though the move to the carriage house and living with Mike helped, I still sometimes suffered at Harvard, trapped in its particular isolations. Every university department has its own elaborate systems of belonging, and I was aware that I wasn’t part of any of them. I had struggled to fit in during undergrad, despite its fuller classrooms and forced collegiality, but at least I was from Toronto. I had the comforts of home and those well-worn routines that allow you to mistake familiar bus drivers and clerks for friends. Graduate school made it harder for me to imagine my way out of my solitude. I watched my fellow students the way biologists might observe a family of apes. They formed bonds with each other, but I couldn’t figure out how or when.

  I also struggled to connect to my work. I loved the stars as much as I always had, but studying astrophysics could make them feel farther out of reach than they already were. Our days were exercises in abstraction and tedium, light reduced to algorithms. It was as though I had decided to study architecture because I loved LEGO, and then found myself in class after class dedicated to the vagaries of the building code. As validating as it was to contribute to our understanding of the universe, my day-to-day just wasn’t what I’d thought it would be.

  I wasn’t unusual in feeling this way. Astrophysics moves at the literal speed of light, and most of us students weren’t equipped to know what might prove meaningful three or four or five years later. It was one thing to accept that progress was piecemeal, but our successes were so small in the scheme of things that it was hard for me to find a lasting sense of purpose in any one project. During that second year of school, I thought seriously of quitting.

  I daydreamed about going to veterinary college instead. Saving sick or broken animals seemed a lot more practical than exploring the theoretical limits of our universe: An animal was going to die; but now, because of my knowledge and care, it will live. Or I could keep trying to determine what happened during the first trillionth of a second after the Big Bang and the 13.75 billion years since. I called my father for solace. “Oh, honey,” he said, “that’s normal for grad students.” But he remained ever the opportunist. “You know,” he said as casually as he could, “if you want to change your mind and go to medical school, I’ll pay for it.” Perhaps strangely, the idea that he would need to reinvest in me and my education helped me decide: It was too late to turn back now. I had made my choice, and that was it. I felt almost bound by the physics I studied. Momentum was a powerful force.

  Another force, as strong as it had been that fiery night on the esker, was luck. Right around the time I was completing my work on the early evolution of the universe, Swiss astronomers found
the first widely recognized exoplanet.

  The greatest discovery astronomers could possibly make is that we’re not alone. Humanity has searched the heavens for a reflection of ourselves for centuries; to see someone or something else, inhabiting another Earth—that’s the dream. For this reason, among others, the colossal 51 Pegasi b was a major find. It was the first new world found orbiting a sun-like star since Pluto’s planetary tenure. It was a tiny crack in the largest possible door.

  The Swiss astronomers who discovered 51 Pegasi b didn’t really “see” their precious find. The ideal, of course, would be for us to be able to see with our own eyes evidence of other life in the universe. But the best pictures of distant celestial bodies still look like the earliest video games. A handful of pixels, frozen in different shades of white, might represent an entire star system.

  That’s because they’re so far away. Driving the speed limit to Alpha Centauri, the nearest star grouping after our sun, would take us about fifty million years, while our fastest current spacecraft would make the trip in a comparatively brisk seventy thousand years or so. A journey across the Milky Way in that same rocket would take about 1.7 billion years. And the Milky Way is one of hundreds of billions of galaxies. Outside its homey confines, there is another galaxy, and another one, and another one. The universe isn’t endless, but it’s as close to endless as we can imagine.

  Until we can see something with our eyes, we have to find it in our lines of code—one of astronomy’s other ways of seeing. We might not be able to gaze upon a particular exoplanet, the lights of alien cities stretching across its surface like spiderwebs. But we can surmise that an object in space exists because of its impact on our numbers. Using a complex mathematical method dubbed “radial velocity,” based on the Doppler shift, those pioneering Swiss astronomers witnessed 51 Pegasi b’s gravitational effect on its star and deduced that it must be there. It was like believing in Bigfoot because you found his footprints.

  As with those infamous plaster casts of giant feet, radial velocity left plenty of room for skeptics to dismiss the Swiss claims. So did 51 Pegasi b’s nonsensical orbit—its “year” raced by in only four days. Similar reports of exoplanet discovery had long been debunked. In 1963, a Dutch astronomer named Peter van de Kamp, then working at Swarthmore College in Pennsylvania, announced that he had found an exoplanet. Like the Swiss, he had deduced his planet’s existence by noticing an apparent “tug” on Barnard’s Star, thirty-six trillion miles away. Years later, that tug, and the star’s seeming shifts in location because of it, was found to be the result of changes to van de Kamp’s telescope and its photographic plates. The smallest mistake had been amplified into a massive miscalculation.

  Now, with 51 Pegasi b, two rival camps emerged. Three, actually. There were those who accepted the discovery, including my adviser, Dimitar. He was only in his mid-thirties, new to the faculty at Harvard and young enough to remain given to belief. Then there was the anti-camp, led by an aggressive astronomer named David Black. Some in this camp argued that the Swiss had found not a planet’s effect on its host star, but rather a new kind of stellar pulsation—that the star wasn’t being tugged but was expanding and contracting, the way stars older than the sun do. Or, as Black believed, the Swiss were seeing the effect of one star on another. Perhaps 51 Pegasi b was a brown dwarf or a small star, not a planet. The third camp was our community’s version of agnostics. Maybe the Swiss had found an exoplanet; maybe they hadn’t. Because 51 Pegasi b was so far away, it didn’t matter and never would.

  Dimitar suggested that I turn my attention, and my budding knack for finding unseen things, toward exoplanets and the embryonic effort to understand their possibilities. I liked the idea. I would be looking for something tangible, something singular and concrete, and turning my compulsion for wandering into practical astrophysical research. There was no greater unknown than the universe. And besides, what did I have to lose? I remember looking out the window of the carriage house and thinking: Why not?

  There were in fact plenty of reasons why not. Sitting here a quarter century later, it’s hard both to remember and to believe how controversial exoplanets were at the time. Logic dictated that they had to exist. The sun couldn’t be the only star that had accumulated planets. But proof of their existence, never mind their potential inhabitants, remained as out of reach as they were. In hindsight, it’s amazing that Dimitar assigned a graduate student something so risky, with such a small chance of payoff. Neither of us knew enough to be scared.

  Dimitar handed me the rudimentary computer code that had been used to study the effects of stars on each other. How does one star heat another, and what does one star do to the other’s stellar atmosphere? He wanted me to rewrite the code so that it could be used to study the effects of a star on exoplanets in close orbits. We wouldn’t find life like us on the giant, irradiated planets that orbited so near their stars, but these so-called Hot Jupiters were still worth knowing. I had a hunch that there were lessons hidden in their atmospheres, especially. Perhaps their skies would help us one day know whether we were looking at another Venus or Mars, or another Earth.

  I would be studying something a large percentage of the community thought didn’t exist or didn’t care to know about, and doing so in a way that made the impossible seem even less likely—like trying to prove that Bigfoot exists not by finding him or even his footprints, but by seeing his breath. How could we see the thin envelope of alien atmospheres when we couldn’t even find the worlds themselves? I was at a conference when a student from another school approached me in a whisper, asking if I wanted to talk to his adviser. He could explain to me why the Swiss signal couldn’t possibly be a planet. A professor from Harvard, my own school, radiated a similar skepticism: We would never be able to detect many exoplanets, let alone their atmospheres. I remember feeling as though people were trying to rescue me from a cult.

  In an accidental way, my months in the wilderness had inoculated me against such criticism, however well-intended. My power to focus had been developed like my shoulders. The raw challenge of exploration was so appealing that I didn’t really care what anybody else thought about my pursuits. And for all the doubts I had felt since arriving at Harvard, for all the times I felt propelled by circumstance, I was far from passive after I had made up my mind about something. I hadn’t seen any reason to date Mike, and later I heard myself asking him to bring his boat to Boston. I’d been ambivalent about studying astrophysics, and now I was determined to help understand brand-new worlds. Once committed to a destination, I was going to get where I was going.

  By the time I had rewritten the computer code, in 1999, a couple dozen more exoplanets had been discovered, all by the “star-tugging” method. They were all like 51 Pegasi b, massive with short orbits. (The more massive the planet, and the closer it is to its star, the more dramatic and clear its gravitational effects.) There were still plenty of skeptics, but the evidence against them was beginning to mount, and some betrayed hints of a countering curiosity. Amid these shifting currents, I prepared to defend my thesis. I would argue that one day we would do more than find exoplanets. We would be able to see the light of their skies.

  I booked the room in Harvard’s Phillips Auditorium used for PhD-defense seminars. It had more than a hundred seats, split between the main floor and a balcony, the walls of each filled with bookshelves. I would be using an overhead projector to show my work, and I flipped through my raft of illustrative plastic sheets with Dimitar one last time. In the middle of my rehearsal, I stopped and worried aloud that the people at the back of the room wouldn’t be able to see the finer points of my graphics.

  Dimitar laughed. “Sara, there won’t be anyone at the back of the room.”

  On the day of my presentation, I arrived early and set up. A few people came in. Then a few more, and a few more. The room was soon packed full, standing room only.

  Exoplanets were for real
.

  * * *

  ●

  All the while, Mike and I continued our simple shared existence. I would go to school and get lost in space and code. I would come home to boats and piles of paper. Mike grounded me, unwound me. He gave me some of the happiest days of my life, long stretches of brain peace. We never raised our voices at each other; I think back on that time and remember the quiet. We spent our springs and summers in the near-silence of our canoe, making several more long trips north, and at home we lived together the way we paddled: It wasn’t always easy, because in some ways we remained two people who were built to be alone, but we worked to find a natural rhythm. We spent weeks at our respective work and weekends at our shared kind of play. We hiked and cross-country skied and paddled our way across stretches of Massachusetts, New Hampshire, Vermont. There was still something almost accidental about our connection, and the increasing seriousness of it all sometimes daunted us both. But our pauses never became breaks. Within a year, we had really started to set up camp.

  First we adopted a gray-striped tabby that I named Minnie May, after the sick girl saved by Anne in Anne of Green Gables. (I had subconsciously inherited my mother’s penchant for naming animals after literary characters.) Mike had been resistant to pets—he was so afraid of having anything like dependents, the thought had given him chest pains—but then we agreed that Minnie May needed a friend, and we took in another kitten who turned into a big fat cat named Molly. She became Mike’s cat, curled up near him whenever he did his work. Later came a feral black cat named Cecilia that I never managed to tame.