Cold light of the distant heavens

A cosmologist’s six weeks in the high desert of Chile

By Kevin Crowley, Photographs by Kevin Crowley and Federico Nati

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I caught myself from falling off the ladder more by luck than anything. Standing on the rung second from the top, I turned—too quickly—and the icy soles of my boots slipped off the metal. My heart leapt into my throat; my right leg buckled, crumpling under my left one. I cursed loudly, took a breath, and looked around. No witnesses.

Felipe and Federico had gone to the generator shed. Hanging on to the top of the ladder, I scanned the horizon from 15 feet up at 17,000 feet above sea level. I saw a rocky plain stretching far to the south. An ancient volcano blocked the northern view. Nothing, anywhere. Desolation. I laughed. Then I clambered back up to the top of the shipping container and continued to prep the telescope for the snow.

I had left my hometown, San Diego, in early July after a brief respite from the steamy Princeton summer. I was bound for six weeks in South America, soon to experience Chilean winter in the bone-dry Atacama Desert. The unique high-altitude desert conditions in Chile present the ideal environment for astronomical observations at nearly all wavelengths of the electromagnetic spectrum, from radio waves to X-rays. As an experimental cosmologist working at millimeter wavelengths, the signals of interest to me would be scattered too strongly by atmospheric water vapor at almost any other location on Earth.

Of course, working in the desert presents considerable physical challenges (beyond my mishap with the ladder): high winds, low oxygen, and sometimes impassable roads. Despite the obstacles, numerous scientific collaborations have constructed world-class telescopes that dot the Atacama. To keep their high-altitude experiments running smoothly, the groups employ technicians to check gauges, perform repairs, and report back on the state of affairs at the high site. I came to Chile to temporarily fill the role of such a technician.

I spent most of my time working with Felipe, a Chilean master’s student from a small town outside Santiago, and Federico, an Italian physicist attempting to transition from lab assistant work to a position in the United States. I often looked to them for guidance in troubleshooting the equipment at the site. They were also responsible for getting us up in the mountain in a rented Mistubishi all-wheel drive flatbed. Since I didn’t have the hubris to learn how to drive stick on rocky switchbacks, I settled into the role of D.J. for our midmorning trips to the telescopes.

The music in the truck became a soundtrack for our journeys through the rocky plain beneath our mountain site.

It was also a way for me to connect with my colleagues. When Felipe had command of the stereo, he liked to play progressive rock. Over our weeks together he revealed, taciturnly, his sideline as a bass player with a band of fellow students in Santiago. Federico played a decent version of “Blackbird” on his acoustic guitar most afternoons at the hotel. I could hear it going to get another cup of tea from the kitchen, sneaking a cookie or two from the jars so fastidiously refilled by the manager Maria Jose. I could put on some freakish music, just to gauge where the boundaries of taste lay within the Mitsubishi. But I mostly tried to please the audience: the Rolling Stones with Federico; some kinetic, odd-metered jazz-rock with Felipe.

We stayed just outside San Pedro de Atacama, a town with narrow winding dirt roads and a lively tourist industry. Sited near an oasis in the middle of a flat desert plain, bordered on all sides by mountains, the town provides the sensation of living on a dinner plate. San Pedro is also a border town, and Felipe schooled me on its role as a drug conduit from Argentina and Bolivia, with carjackings not uncommon on the main highway.

Nevertheless, the tourism industry is its foundation. Domestic and international travelers use San Pedro as a staging ground for outdoor adventures. The serrated rock formations of Valle de la Luna, the great volcano Licancabur rising from the floor of the desert in rolling waves, and the telescopios on top of the mountains attract hordes of visitors each year.

For me, the town and my room at the Hotel Don Esteban were staging grounds for 8-hour days on the mountain.

From the front of the hotel, the hump-like formation of Cerro Toco was just visible as a mound on the distant ridge that walls in San Pedro to the east. The telescope used in the Atacama B-mode Search (ABS) experiment, my charge in stewardship, sat just south of Toco, nestled in a flat on top of a cliff. Waking in the morning and trudging from my warm room to the main house for cold cereal, I could never quite believe how distant Cerro Toco seemed and yet how clearly it appeared in the dry air. One sees farther in that place, where the unbroken plain stretches hundreds of miles south and where the air is unencumbered by humidity.

In the best cases, my daily duties on the mountain were relaxed. I was tasked with completing a daily checklist and recording events in a running experimental log. I ensured the continuous operation of the telescope, and assisted in any required calibrations of the instruments. Fatigue inevitably set in after a full day at altitude, but I was often buoyed on the way back to San Pedro by the thought of the information gathered by the telescope that day.

At other times, I expelled great mental and physical effort in sorting out the snags that tended to crop up just as the sun was going down. My occasional experiences of frantically troubleshooting failed motions of the telescope, rebooting computers, and hefting lengths of cable into position left me exhausted in the truck on the way back to town.

But, personally, the most enervating facet of the job was managing self-doubt and ameliorating anticipations of catastrophe.

Alone in my room at night, I monitored the system temperatures and telescope motions expectantly from my laptop, trying both to will them to safety and to pretend that nothing interesting was happening. Many dramas of self-recrimination and frustration took place within the confines of that room.

Yet, in looking back, the days all become weightless. Chile lives in my memory as a series of beautiful images. 

There is the moon hanging in the sky like the Cheshire cat’s smile. There are the distant sunsets across the valley coloring the mountains behind in a flash of red and gold. There are the late nights, waiting in the warm control room for the final tasks of the day to be completed, only to step outside and look up and be overcome by the number and majesty of the stars. The desolate beauty of the desert burrowed deeply into my mind.

Every instant this planet is illuminated by 13 billion-year-old light. The light has made its way here over a span of time nearly as old as the age of the universe. Over that time, the universe's expansion has stretched the wavelength of that light. Emitted in the early universe as X-rays, that tensile light arrives to us as microwaves today.

In every direction we look, a nearly identical pattern of microwaves can be seen. This pattern is a spectrum that describes the brightness or energy of the light as a function of frequency, or the number of waves it contains. Max Planck, the 20th century German physicist who devised the first theory of “quanta,”an idea holding that light consists of discrete packets of energy, reasoned, through a great insight, that light might best be represented as a set of particles with particular energies, and that these energies are proportionate to the light's frequency. Planck described the spectrum of light emitted by a body at a given temperature, and from there derived a mathematical relation. His law allows us to anticipate how many of these particles, and thus how much energy, we expect to see at each frequency in light from a body at a particular temperature.

Thanks to their knowledge of Planck’s spectrum, cosmologists have measured the temperature of the microwaves in the sky to be around -454 degrees Fahrenheit (or 3 Kelvin, for scientists)—just below the temperature at which helium gas becomes liquid. That's cold. The fact that this light from the early universe follows the Planck distribution, a curve correlating light's energy and frequency, is one of the remarkable discoveries of modern physics; this ancient light verifies that the early universe began hot and dense, and that it cooled under expansion: the essential component of the Big Bang model. That the temperature of the light is so nearly the same wherever we look inspired another idea, too: the theory of inflation, which holds that the universe swelled exponentially in an instant. Trying to prove this theory is at the heart of what I do.

This light may provide an answer. And it may lead us on to more incredible discoveries as yet unimaginable.

Using telescopes, weather balloons, and satellites, cosmologists reach out with their instruments to touch the moment when these ancient photons were emitted. In Chile, standing next to the telescope receiving information from the sky, the immensity of the task overwhelmed me. Behind all the visible beauty of the stars, galaxies, and nebulae is an invisible imprint of the evolution of the universe.

The desert was bone-chillingly cold, but it didn’t snow. For most of the trip, no white caps sat on the mountain peaks.

San Pedro is more likely to deal with dust storms than precipitation. In the middle of winter, the temperature began to hold at a few degrees Fahrenheit at night. Electric space heaters could barely make a dent in that kind of cold. With 16 units on full blast, the hotel often lost power.

At altitude, the cold was amplified by wind chill and exposure. Instead of being safely under thick blankets, I used my whole body to rotate the massive telescope by hand.

I knelt and lay prone on the frigid roof of a shipping container in order to reach wires and adjust hoses. The combination of work, altitude, and temperature felled me in my first week, and I took one of my rare days off that first Sunday to lie in bed recuperating. I ached in all parts of my body, and curled up to stay warm. Hot tea became my constant companion from then on. I also learned to wear thick cotton socks in bed and to keep the heater close. By far the most difficult part of the day was leaving my cozy night-time arrangement every morning.

I ate both terribly and extravagantly during the day. The control room’s endless supply of Cup of Noodles instant ramen and granola bars fueled me for days on end.

Evening meals were included in the lodging, which provided a place for diverse varieties of scientists to gather. Although most were astronomers of one kind or another, a group of four geologists provided respite from the constantly looking up. For them the ancient rock formations of the Atacama, some of the oldest in the world, were a bonanza.

Over dinner, I overheard conversations in Japanese, Spanish, German, and English all taking place at once. The major astronomical efforts sited near San Pedro include the related Atacama Cosmology Telescope within the same compound as ABS, the POLARBEAR cosmology telescope built just down the road from the ACT/ABS compound, and the ASTE radio telescope over the ridge from Cerro Toco. I got to know the POLARBEAR team quite well, despite a natural and friendly competition between us in the search of greater knowledge on the microwave background. The ASTE working group consisted of older postdocs working on smaller-scale astronomy as they tried to gather information from stars, galaxies, and pulsars. Visitors to the desert from these groups all stayed at Don Esteban, and made the brief, restful evenings both pleasant and educational.

Overall, however, my stay in San Pedro was characterized by solitude. Navigating the lonesome mood that took hold in silent trips back down the dark mountain sometimes required starting a conversation about something, anything. But being on the mountain or down below in my room reminded me how silence feeds contemplation. While I occasionally indulged in foreign Netflix, I also lay and listened to music new and old, meditating on how I had come to Chile. I even cracked the great Steven Weinberg’s meticulous and inventively titled textbook, “Cosmology,” as an admonishment to myself for all that I didn’t (and in some cases, still don’t) know.

I yearn for that feeling again. The strangeness of a strange place allowed me to bring myself back into focus.

Part of doing astronomy in the Atacama is obsessing about the weather.

Excess moisture in the air can mean a whole day’s worth of measurements will contain little valuable data. This also means that, when a storm breaches the mountains shielding San Pedro from the outside world, we have advance warning.

A little over a week before I was scheduled to leave San Pedro, the forecast called for heavy snow. In order to avoid major traffic accidents and stranded travelers, the Chilean border patrol had shut down the highway leading from town to the packed-dirt access road we used to reach the site. While Felipe, Federico, and I might all have preferred to take the day off in the face of such conditions, the danger of snow damaging the electronics or interfering with the gas-powered generators was too great to ignore.

I cannot forget the foreboding I felt seeing overcast skies stretching into darkness over Cerro Toco and the solitary Paso Jama highway snaking upward to the horizon. I felt a sense of danger that I usually subdued by focusing on the task at hand. In this case, that task was to get past the government-staffed barricade to do what we could to protect the site equipment.

Alone, the task would’ve been rather hopeless. Not only was every truck driver bound for Argentina pleading with the stone-faced carabineros at the checkpoint, but I would’ve had a damned difficult time explaining my case in the halting Spanish which Felipe often reacted to with a wry smile. Fortunately, Felipe had the phone number of the immigration and customs official responsible for making the call to close the pass. The customs agent agreed to let us through when he arrived at the roadblock.

The experience of passing through the roadblock was surreal, as Felipe nosed the truck around the barricade under the distressed gazes of twenty stranded truckers. Even more surreal was the SUV escort we received from the carabineros and the man who had let us through.

Glancing ahead at the empty road and the black horizon, I had visions of the truck sliding on icy roads, or the three of us trapped at the high site. These and other terrifying potentialities caused me to consider the kind of single-mindedness required to pursue great things in science. Would I have had the tenacity of Felipe, to cast about for help in order to gain access to a mountaintop just as a storm made itself known?

We did make it to the site safely. Felipe’s unease with the road conditions led him to admonish Federico and me to work fast. I started by clambering to the top of the telescope and lashing a protective cover over the telescope aperture. To protect the contents of the shipping container, I wrapped plastic around the base of the telescope and hung plastic sheets over the sensitive electronics inside.

At one point Federico joined me on top of the container to staple the plastic and weight it down with spare lumber. The alacrity with which we tried to complete all these tasks, as the snowfall gathered momentum, perhaps accounts for my only real near-disaster of the trip, alone on the ladder under impenetrable clouds.

The visible messenger of winter I had come to know in New York and Princeton touched my jacket as I scooted down the ladder to leave. It was a delightful novelty that made the landscape more forbidding in fact, but more inviting in appearance.

As we departed the site, Felipe eyed the piles of snow forming on the road, and I angled my neck to glance at the telescope. Watching it recede in the distance brought relief at evading the storm, and pride at the work I had done to protect it. Only later, as we reached the highway and near-certain safety, did it occur to me to worry that I had not done enough.

Very little snow fell in San Pedro that night, and two days later, even the drifts on the mountain were light, having been scattered by the wind. Each of us was thankful that we did not have to shovel snow off the road to get back to the telescopes. ABS ran another week under my care.

By the time I prepared to leave, the mixture of relief, pride, and concern I felt on the way back to the hotel had not diminished. I thought little of the town I had only lately begun to explore, eating empanadas and buying gifts for loved ones back home. Instead, I pictured Felipe, Federico and myself, coming down the mountain in pitch-black darkness, ready to do it all again the next morning. I saw again the wild llamas of the mountains, the vicuñas, leaping like gazelles over the scrubby plants at the roadside.

Boarding the bus that would carry me over the western hills, I felt a tiny pang at returning to a life so different from the one I’d led in San Pedro. Born of uncertainty, the pang blossomed at the thought of the place I was leaving behind. Carrying the bloom close, I made the journey back to where I had come from. The flower of the desert remains.

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Kevin Crowley is a doctoral student in physics pursuing new and better ways to extract information about our universe from the sky. His studies focus particularly on cutting-edge measurements of the earliest light in the universe, the cosmic microwave background. He can be reached at




Federico Nati is an italian astrophysicist. He worked for six months on site for the ACTPol experiment, spending his days on the telescope at 5200 meters. These shots were taken by him during his period in the Atacama desert. Reach him at

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