The Ancient Tradition of Speculating About Aliens

Long before the space age, astronomers and scientists wondered what c̳i̳v̳i̳l̳i̳z̳a̳t̳i̳o̳n̳ might be like on the moon and beyond

What would happen to humanity if we found unambiguous evidence for the existence of an intelligent c̳i̳v̳i̳l̳i̳z̳a̳t̳i̳o̳n̳ beyond Earth? Would our minds rise above our everyday concerns to confront the implications? Would we be terrified of contact, or might the experience bring us together at last, under the auspices of a new peace forged in the blinding a̳l̳i̳e̳n̳ light?

These questions might seem like products of our age of space exploration, but people have been thinking about the implications of ex̳t̳r̳a̳t̳e̳r̳r̳e̳s̳t̳r̳i̳a̳l̳ life for centuries. One of the first on r̟e̟c̟o̟r̟d̟ was the Greek thinker Metrodorus of Chios, who observed in the 4th century B.C., “It would be strange if a single ear of corn grew in a large plain, or there were only one world in the infinite.”

Where conditions are ripe for life, there is usually a burgeoning of many living things, not just one.

He was making a point that astronomers still make today: Where conditions are ripe for life, there is usually a burgeoning of many living things, not just one. So the very fact that Earth exists should imply a plethora of Earthlike worlds in the cosmos.

Modern speculation about worlds beyond Earth began in the Renaissance. In his 1584 book “On the Infinite Universe and Worlds,” the Italian priest and philosopher Giordano Bruno theorized: “There are countless constellations, suns and planets. We see only the suns because they give light; the planets remain invisible, for they are small and dark. There are also numberless earths circling around their suns, no worse and no less than this globe of ours. For no reasonable mind can assume that heavenly bodies that may be far more magnificent than ours would not bear upon them creatures similar or even superior to those upon our human Earth.”

This was an impressive speculation on a̳l̳i̳e̳n̳ life for the 16th century. Few of Bruno’s contemporaries could even conceive of the idea that there might be something in space beyond what the eye could see. Sadly, Bruno was unable to follow up his ideas. He was arrested by the Inquisition even before his book was published, imprisoned for seven years, and burned at the stake in 1600 for various indiscretions vis-à-vis his church seniors and for harboring beliefs that irritated the Catholic hierarchy. It is thought that his endorsement of a so-called plurality of worlds—the idea that there are other Earthlike planets in the universe providing homes for creatures—was one of the heresies for which he was charged.

With the invention of the telescope in the 17th century, humans could actually see the other planets in the solar system, of which previously we had only hints. We could now verify the vast distances to the stars with greater accuracy, too. But if telescopes showed us that the maneuvering specks in our neighborhood were in fact planets, the resolution of these scopes was insufficient to make out surface details. Speculation and fancy ran riot.

The Dutch scientist Christiaan Huygens, who invented the pendulum clock and discovered Saturn’s moon Titan, didn’t wonder if ex̳t̳r̳a̳t̳e̳r̳r̳e̳s̳t̳r̳i̳a̳l̳s existed—that much was taken for granted—but whether they composed music. “For aught we know,” Huygens wrote in his posthumously published 1698 book “Cosmotheoros,” “the inhabitants of the planets may possibly have a greater insight into the theory of music than has yet been discovered among us.”

A century later, the astronomer William Herschel, discoverer of Uranus and infrared radiation, was convinced that the moon was inhabited by an a̳l̳i̳e̳n̳ race he named Lunarians. “By reflecting a little on this subject,” he wrote, “I am almost convinced that those numberless small Circuses we see on the Moon are the works of the Lunarians and may be called their Towns.”

Today, these perfectly circular features on the lunar surface are known to be caused by asteroid and comet impacts. But Herschel reasonably thought that no natural geological process could possibly produce so many perfect circles. Their geometric regularity suggested a mind at work, the products of an intelligence. Herschel’s speculations are a w̳a̳r̳ning from the past about our desire to believe in ex̳t̳r̳a̳t̳e̳r̳r̳e̳s̳t̳r̳i̳a̳l̳s. Any unexplained phenomenon that does not immediately admit of a straightforw̳a̳r̳d explanation is tempting to interpret as the work of a̳l̳i̳e̳n̳s.

Where scientists like Herschel led, popular journalism soon followed. In 1835, the New York Sun pulled off an extravagant hoax with a series of articles laying out the discovery of winged people and beaverlike intelligences on the moon. This “discovery” was attributed to the work of astronomer John Herschel, son of William, and it earned the newspaper huge circulation numbers, making the Sun for a moment the most-read newspaper in the world. Other papers across the globe reproduced the remarkable findings, while poor John Herschel was assailed with letters about his “discoveries.”

These centuries of speculation only came to an end in the late 20th century, when the Space Age finally allowed us to send robotic emissaries to the planets to observe them close up. Then we could see with our own eyes the barren wastelands devoid of music-making Venusians and the desolate sun-soaked craters of the moon, with nary a Lunarian in sight.

But while we have confirmed that ours is, at present, the only inhabited planet in our corner of the cosmos, we have not lost interest in the possibility that there is yet life out there. New discoveries have reinvigorated both the search and enthusiasm for a̳l̳i̳e̳n̳ life. There are habitable conditions on Mars and oceans under the crusty ice-covered surfaces of moons orbiting Jupiter and Saturn. The search for exoplanets has led to the discovery of rocky worlds orbiting other suns, some of them perhaps similar to Earth.

If our current hopefulness about a̳l̳i̳e̳n̳ life feels novel, it is only because we have forgotten the centuries in which humans were convinced that space was home to multiple c̳i̳v̳i̳l̳i̳z̳a̳t̳i̳o̳n̳s with which we might communicate. If we should ever exchange words directly with a̳l̳i̳e̳n̳ entities, the ex̳t̳r̳a̳t̳e̳r̳r̳e̳s̳t̳r̳i̳a̳l̳s will find themselves at the receiving end of a species that once thought creatures built ramparts on the moon. We might even be unimpressed with them. After a few florid months of media interest and some good literature, we might just shrug our shoulders and continue on our way. I hope the a̳l̳i̳e̳n̳s won’t be disappointed.

_Dr. Cockell is a professor of astrobiology at the University of Edinburgh. This essay is adapted from his new book, “Taxi from Another Planet: Conversations with Drivers about Life in the Universe,” published this week by Harvard University Press.