The surprising history of the extraterrestrial-life debate

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By R. Clinton Ohlers  

The debate over the existence of extraterrestrial life has a surprisingly long history — one as old as the history of science itself. Astrophysicist and historian of science and religion, Parandis Tajbakhsh, recently summarized this history for the International Research Network for Science and Belief in Society.

Image by Vicki Hamilton

Between the fifth and third centuries B.C., ancient Greek philosophers Leucippus, Democritus, and Epicurus proposed a potentially infinite number of worlds. Holding to a geocentric model of our solar system, they believed our earth was the center of our universe. An infinite number of worlds, therefore, would mean infinite “geo”- centric universes. Any number of these separate and inaccessible one-world universes might also contain life.

Plato and Aristotle disagreed. Aristotle, held to the existence of only a single universe. Since a world was the center of the universe, other worlds would require more than one center to the universe and were, therefore, logically impossible. This early debate demonstrates how revolutionary the Copernican revolution of the seventeenth century would be on the question of extraterrestrial worlds. Placing the Sun at the center meant it was circled by multiple planetary spheres, of which the Earth was simply one. In one stroke, the heliocentric theory of the solar system reinvigorated the question of extraterrestrial worlds in a new way.

In 1610, Galileo Galilei (1564-1642) contributed to the debate when he observed through his telescope four moons in orbit around Jupiter. This was indirect evidence that Jupiter and the other planets might also be in orbit around the Sun. It was direct evidence of other celestial spheres.

Although the Roman Catholic Church condemned Copernicus in 1616 and Galileo in 1636, it did not do so on the basis of multiple worlds. On the contrary, the church had already condemned Aristotle in 1277 for suggesting that God could create only a single world. To do so was a heretical denial of divine omnipotence. As a result, the church’s stance led to significant speculation about the possibility of multiple worlds and extraterrestrial life by Christian philosophers and theologians well in advance of Copernicus.

Tajbakhsh notes that by 1440 the German philosopher and theologian, Nicholas of Cusa (1401-1464) wrote in his treatise On Learned Ignorance:

“Life, as it exists on earth in the form of men, animals and plants, is to be found, let us suppose, in a higher form in the solar and stellar regions. Rather than think that so many stars and parts of the heavens are uninhabited and that this earth of ours alone is peopled – and that with beings, perhaps of an inferior type – we will suppose that in every region there are inhabitants, differing in nature by rank and all owing their origin to God, who is the centre and circumference of all stellar regions.”

It is hard to understate the enormous revolution in the mental picture of the universe that European intellectuals and eventually the public experienced as the work of Copernicus, Galileo, Kepler and others gained in popularity. A universe once imagined as essentially a Russian doll of perfect, hollow, crystalline spheres surrounding a globe, now was transformed into a vast three-dimensional sea in which one globe among several floated about the Sun.

Until Copernicus and Galileo, only one sphere was known and that sphere was inhabited. If God had populated our sphere, it was conceivable that he populated the others also. Just as fertile islands might or might not be inhabited, extraterrestrial life was an open question. The bias appears strongly to have favored inhabitants.

Tajbakhsh notes that Galileo’s contemporary, the devout German Protestant natural philosopher and mathematician Johannes Kepler (1571-1630), envisioned each of the planets in the solar system and their moons as analogous to our own. Moons, Kepler believed, served the inhabitants of a planet. Jupiter, therefore, due to its multiple moons, was “to the highest degree . . . probably inhabited.”

Kepler developed his thoughts on extra-terrestrial life in his Somnia (1634). Published posthumously two years before Galileo’s condemnation, this work has taken its place as the first known piece of science fiction. Although Galileo believed our own moon could not contain life due to its long days and nights, each lasting 15 earth days, Kepler imagined a journey to the moon in which a traveler finds its extreme climate inhabited by equally extreme serpent creatures.

Among Protestants, the suppression of Galileo did not dampen in the least scientific interest in the heliocentric solar system or the possibility of extraterrestrial life. Only two years after Galileo’s condemnation, the British natural philosopher, clergyman, and future co-founder of England’s Royal Society, John Wilkins (1614-1672) speculated on space travel and extraterrestrial life in his remarkable book The Discovery of a New World; or A Discourse tending to prove, that (’tis probable) there may be another Habitable World in the Moon (1638).

The title reveals how the new thinking was developing. Traditionally, the term “world” signified not a planet or moon, but a domain of sentient habitation and community. A world resided on a sphere.

With the island analogy, travel between spheres was logically possible even if the means were unknown. Wilkins speculated on space flight to the moon. He estimated how long such a journey would take, and even imagined colonizing the moon.

By the close of the seventeenth century, the Copernican universe was widely accepted and interest in extra-terrestrials continued to grow. In the eighteenth century, Tajbakhsh observes that speculation on “utopian ET societies” was popular. The German philosopher and mathematician, Gottfried Wilhelm Leibniz (1615-1716), a contemporary of Isaac Newton and co-claimant as the inventor of calculus, made extraterrestrials a component of his philosophy.

Rather than a fringe view, by the end of the eighteenth century, belief in extra-terrestrial life may be described as mainstream in Europe and the Atlantic world, finding representation among leading astronomers and in many Sunday sermons. The English Reverend and defender of the Bible’s inspiration, Thomas Dick (1774-1857), was an ardent proponent of a populated solar system and even when so far as to estimate the number of its inhabitants.

The most renowned British astronomer of the eighteenth century, Sir William Hershel (1738-1822), believed the spheres of the solar system were widely populated. His son, Sir John Herschel, even more renowned than himself, shared some of his father’s views.

John Hershel even became an unwilling adjunct to the Great Moon Hoax of 1835, perpetrated by the New York Sun. Having completed his father’s project of mapping the night sky of the northern hemisphere, Herschel turned his eye to the Southern Hemisphere, mapping the southern sky in an internationally celebrated trip to Cape Town, South Africa from 1834 to 1838.

A lithograph of the hoax’s “ruby amphitheater,” as printed in The Sun.
Source: Wikimedia Commons (Public Domain).

From the 25th to 31st of August of 1835, The Sun published alleged daily reports of Herschel’s findings that the moon was inhabited by “lunar quadrupeds . . . a blue unicorn . . . cranes of ‘unreasonably long legs and bills . . . and 4-ft tall naked winged ‘Verspertilio homo,’” similar in color to the orangutan and accustomed to behavior that would “‘ill comfort with . . . terrestrial notions of decorum.” Within days, Tajbakhsh writes, “crowds were lining “the streets of New York City to get the latest copy of The Sun, which by this point had become the most widely circulated paper in the world.” The charade ended with a false report on the 31st of the unfortunate, accidental destruction of the reflecting lens of Herschel’s telescope.

Thousands of miles away in South Africa, Herschel was making no such findings, and when he learned of it viewed the hoax with disdain and embarrassment. The author, Richard Adams Lock (1800-1871), claimed he intended the series as satire meant to tilt at what he believed was fanciful and credulous belief in extraterrestrials.

That Lock would mean his work as satire represents something of the turning-away from belief in extraterrestrials among thought leaders in the nineteenth century. This shift coincided with growing belief that such beings were not compatible with Christian theology and growing evidence of the rarity of the Earth as a habitable sphere.

Although some Christian theologians argued from at least the early fifteenth century that Christ’s atonement for sin on this world could apply to inhabitants of other worlds, the deist Thomas Paine (1737-1809) argued in his Age of Reason (1784) that the existence of multiple worlds was irreparably at odds with Christianity. For Paine, such a scenario required Christ to atone through repeated deaths on multiple worlds. Although many theologians had disagreed, “Paine’s argument became a driving force in shaping the later positions of many on the question.”

The great philosopher and historian of science, William Whewell (1794-1866), who articulated much of the foundation of modern scientific method and coined the word “scientist” in 1834, was himself a devout Christian and a skeptic of the multiple-worlds hypothesis. He argued instead for the uniqueness of the earth, known as the rare-Earth hypothesis. Alfred Russell Wallace, the co-discoverer of the theory of evolution also adhered to the rare-Earth view.

The rare-earth hypothesis increased in strength through the twentieth century, particularly with the discovery of cosmic fine-tuning. These findings demonstrated that many of the physical constants that underlie the laws of nature, often thought to demonstrate the insignificance of Earth, such as the enormous size and great age of the universe, were enormously highly improbable yet absolutely vital to supporting any life, anywhere, in the universe, much less complex multi-cellular life. Similar discoveries about our own solar system, such as the extraordinary uniqueness of Earth’s moon and the importance of the outer giants Saturn and Jupiter, all added to the great unlikelihood of a large number of planets supporting life. (An example of a classic work on that view is Peter D. Ward and Donald Brownlee’s Rare Earth: Why Complex Life is Uncommon in the Universe [2007]).

Nevertheless great interest in the possibility of extra-terrestrial life continued. H. G. Wells’ War of the Worlds appeared in 1879. The Great Moon Hoax was a foreshadowing of what would occur a century later in 1938 when Wells’ novel was adapted as a radio news-bulletin series and read over the air by Orson Wells.

Edgar Rice Burroughs, the author of Tarzan began his writing career with science fiction focused on extraterrestrial life. In 1912 he published Under the Moons of Mars. Retitled A Princess of Mars in 1917, the work launched the Barsoom series that eventually totaled eleven novels, the last of which appeared in 1941. Barsoom chronicled the adventures of a late-nineteenth century protagonist John Carter, transported to Mars during the twilight of its civilization. The series inspired later writers such as Ray Bradbury, Arthur C. Clarke, and Robert Heinlein.

Throughout its surprisingly long history, the debate over extra-terrestrial life has closely followed advances in science and technology. The Search for Extra Terrestrial Intelligence (SETI), which focuses efforts on detecting non-random electromagnetic radiation waves, such as radio, is most commonly associated with the Allen Telescope Array that became operational in 2007 under the SETI Research Center.

This method of search has a much longer history, beginning with Nikola Tesla (1856-1943). Working with the newly discovered electrical waves that would come to be known as radio, in 1896 Tesla proposed these wireless waves could be used to contact beings on Mars. In following years he searched for signals coming from that planet.

A similar experiment followed in 1924 with the assistance of the U.S. military. In 1960, the first modern SETI experiment took place using radio telescopes.

Fervid interest in UFO sightings began in the late 1940s and picked up during the ’50s and ‘60s. The timing of this fascination is commonly linked to the rise of modern aviation and space flight.

The very recent report in August of 2020 of possible evidence for life on Venus represents the new search for extraterrestrial life, using remote spectroscopy. This method analyzes light as it passes through a planet’s atmosphere. Using it scientists discovered potential evidence of phosphine in Venus’ atmosphere.

Excitement has surrounded this discovery because production of phosphine is most commonly associated with metabolic processes and is considered a bio signature. The presence of life in the Venus atmosphere is also highly problematic due to the atmosphere being 90% sulfuric acid. The authors describe their finding as “not robust evidence for life.” At the same time, “no known explanation except for life can account for the detection.”

Whatever the ultimate outcome, remote spectroscopy is at the core of the new generation of telescopes, such as NASA’s James Webb space telescope, which will endeavor to analyze the atmosphere of more than 4,000 extrasolar planets discovered in the past 25 years.

R. Clinton Ohlers, PhD is a historian of science and religion and a contributing editor for the FreePressMediaGroup. Previously, he held the position of Research Assistant Professor in the Humanities at the University of Hong Kong. His book, The Birth of the Conflict Between Science and Religion, is scheduled to appear in 2022. He received his PhD in history from the University of Pennsylvania. Edgar Rice Burroughs is his great great uncle.

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