For the moment, though, it is nothing more than a construction project on a mountaintop, as well as several enormous mirrors in varying stages of production at the University of Arizona’s mirror lab. “First light,” as astronomers call the moment when an observatory begins operations, is scheduled for 2024.

The GMT is being built by a consortium of universities in the United States and other countries at a mountaintop site called Las Campanas. Owned by the Carnegie Institution, the site currently hosts eight other telescopes as well as staff housing that evokes a Swiss chalet. During the night I spent there, I met scientists working on the GMT’s instrumentation. One of them was Brian McLeod, astrophysicist at the Harvard-Smithsonian Center for Astrophysics. Dr. McLeod leads a team developing instrumentation to keep the GMT’s 14 primary and secondary mirrors correctly aligned. He started designing prototypes back in 2009, which means that at first light in 2024, he will have spent 15 years on this project. He ruefully noted that people change jobs more frequently than he changes projects.

Dr. McLeod traced his interest in astronomy back to high school in tiny Gambier, Ohio, when his chemistry teacher showed him the night sky through a telescope. I spoke with him in the control room of the Magellan Clay telescope at Las Campanas. He and his team were going to spend the entire night there testing their instruments. However, high wind speeds were spoiling their plans. When I saw them at breakfast the next day, they had spent the entire night in the control room and had only been able to use the telescope for a few hours at most.

When it begins operations, the GMT will welcome visitors, but how exactly is still unclear, given the site’s remoteness. Plus, nighttime observation requires dim ground conditions — a hazard to driving — while daytime is the period when all the observatory staff sleep. Still, if ALMA is any guide, visits to the GMT will be popular. So many people want to visit ALMA that the external relations staff stay on-site for weeks at a time, doing shift work.

This is despite the fact that unlike observatories for the general public, there is nothing to “see” at places like ALMA and the GMT. Today’s professional facilities are long removed from the time when you look through a viewfinder and use the telescope as an extension of your eyeball. Instead, professional observatories use computers to capture data and images and send them to researchers around the world.

Nevertheless, visiting these observatories — like my previous visits to particle colliders — boggled my mind. After all, those who work at observatories operate time machines that can detect light emanating from the birth of our universe, billions of years in the past. Even with the naked eye, the light I saw from the nearby Large Magellanic Cloud was 200,000 years old.

I said goodbye to Dr. McLeod and his team and boarded a plane back to Santiago. As I stared out the window, looking down at the vast brown carpet of the Atacama below me, I considered my situation with strange clarity: I was a collection of bound-together atoms surrounded by other atoms hammered into the shape of a metal airplane tube. And this tube was propelling me through the sky by burning the remains of long-dead plants and animals. Thoughts like this did not come naturally to me before visiting ALMA and Las Campanas.