The First Signal

Since the dawn of existence, humanity has looked up at the night sky and asked a single haunting question. Are we alone in this vast universe? The answer, whatever it might be, carries terror in either direction. Yet our curiosity has always outweighed our fear.

From Galileo's first telescope to the orbital satellites circling our planet, from the mighty James Webb Space Telescope peering into the cosmic abyss to the colossal FAST radio dish spanning half a kilometer in China, we have used every tool at our disposal to search for one thing. A signal from the darkness. A single light proving we are not alone.

There is an old saying. If you stare long enough into the darkness, eventually the darkness stares back.

The year was 1977. A hot August night in Ohio. At the Big Ear radio telescope, one of the most advanced listening posts of its time, astronomer Jerry Ehman was reviewing the endless printouts of frequency data collected from deep space. Page after page of numbers scrolled before his eyes, the cosmic static of an indifferent universe.

Then something changed.

Among the noise, a signal emerged. Seventy-two seconds of structured radio waves at a frequency of 1420.456 MHz. This was not random. This was the hydrogen line, the frequency emitted by the most abundant element in the cosmos. Radio astronomers had long theorized that any intelligent civilization wishing to announce its presence would use this universal channel. A message in a bottle, thrown into the void using the only language every being in the universe would understand.

The signal's bandwidth was remarkably narrow. Just 10 kilohertz. Natural phenomena do not produce such precision. This looked engineered. This looked intentional.

Ehman circled the data on his printout and wrote a single word. Wow.

The WOW signal, as it came to be known, originated from the direction of the Sagittarius constellation. It appeared once. Then it vanished forever.

For years afterward, every major radio telescope on Earth turned toward that patch of sky. SETI organizations searched desperately for a repeat. They found nothing. The source, whatever it was, had gone silent. Perhaps the last gasp of a dying civilization, reaching out across the cosmic ocean with their final breath. Perhaps a natural phenomenon we simply do not understand. Perhaps something else entirely.

The silence that followed was deafening.

The WOW signal ignited a generation of astronomers. If one signal could emerge from the darkness, surely there must be others. SETI programs expanded. New telescopes were built. Computational power increased by orders of magnitude. We could now search millions of stars simultaneously, processing radio data faster than ever before in human history.

But the universe remained quiet.

Some scientists began looking for different kinds of evidence. If advanced civilizations existed, perhaps they would leave marks we could detect even at vast distances. Structures so large they would alter the light of their parent stars.

In 2015, astronomer Tabetha Boyajian was analyzing data from NASA's Kepler space telescope when she noticed something peculiar. A star designated KIC 8462852, now commonly called Tabby's Star, was behaving in ways no star should behave.

Stars are remarkably stable. Their light output varies minimally over human timescales except near the end of their lives. When a planet passes in front of a star, it blocks roughly one percent of the light. A predictable, regular dimming.

But Tabby's Star was dimming by twenty-two percent. And the pattern was completely irregular.

The scientific community immediately thought of theoretical physicist Freeman Dyson and his famous thought experiment. A sufficiently advanced civilization, Dyson proposed, might construct vast arrays of solar collectors around their star. Billions of power stations forming a shell or swarm, harvesting energy on a scale we can barely imagine. Such a structure would cause exactly the kind of irregular dimming Tabby's Star displayed.

Years of observation followed. The most likely explanation turned out to be a disintegrating comet or moon, creating dense clouds of dust around the star. The visible light dimmed while infrared light passed through, suggesting particulate matter rather than solid structures.

But the Dyson sphere hypothesis was never entirely eliminated. Scientists still estimate a small but nonzero probability that something artificial orbits that distant sun.

We kept looking. We kept listening.

And then, in the autumn of 2017, the universe finally sent us a visitor.