Extraterrestrial Life and Christianity (Michael J. Crowe, 2007)

NOTE: This article is taken from the 34th chapter of Science, Religion & Society: An Encyclopedia of History, Culture, and Controversy, pp. 297-303. Sources for the Orthodox teaching on this subject are given at the end of the article:


The debate about whether intelligent extraterrestrial life exists began in antiquity and has continued almost without interruption since then. Religion has frequently played a major role in responses to questions about the possible plurality of worlds, an issue religious authors have been dealing with for centuries. More than a century ago, three Christian religious denominations incorporated extraterrestrials into their scriptures.

Devotional and Philosophical Writings, c. 1330. Prior to the condemnations, many scholars relied heavily on Aristotle.
Devotional and Philosophical Writings, c. 1330. Prior to the condemnations, many scholars relied heavily on Aristotle.

Ancient and Medieval Ideas on Plural Worlds

As early as Greek antiquity, the extraterrestrial life debate was underway. Arguing in support of extraterrestrials were the atomist philosophers Leucippus (fl. 480 BCE) and Democritus (d. 361 BCE). Later ancient atomists, such as Epicurus (342–270 BCE) and the Roman poet Lucretius (99–55 BCE), ably continued their advocacy. Epicurus, for example, asserted in his “Letter to Herodotus” that “there are infinite worlds both like and unlike this world of ours. For the atoms being infinite in number . . . are borne far out into space.” Arguing against extraterrestrials were Plato (428–348 BCE), who maintained that the uniqueness of the demiurge implies the uniqueness of the world, and Aristotle (384–322 BCE), who cited both theological and physical arguments against the atomists’ claims.


Because early Christian authors typically favored the philosophies of Plato and Aristotle over the materialist, frequently atheistic claims of the atomists, these Christians tended to oppose the idea of a plurality of worlds, as belief in the existence of extraterrestrial intelligent life was called for many centuries. Augustine of Hippo (354–430 CE), for example, criticized this doctrine in his City of God, though he was more concerned to criticize the Stoic notion of successive worlds in time.


The interest evoked by the question of extraterrestrials was evident in the thirteenth century when Albertus Magnus (1193–1280) suggested: “Since one of the most wondrous and noble questions in Nature is whether there is one world or many…it seems desirable for us to inquire about it.” Nonetheless, he concluded in the negative as did his most prominent pupil, Thomas Aquinas (c. 1225–1274), who devoted an article of his Summa theologica to critiquing, largely on Aristotelian grounds, the idea of a plurality of worlds. Shortly after this, the debate among Christians took quite a new direction when in 1277 the bishop of Paris, Etienne Tempier, became concerned that philosophers and theologians were overstepping themselves in making claims about how God must have worked in the universe. In response, Tempier issued the famous Condemnation of 1277, in which he criticized claims that seemed to limit God’s powers. One of the propositions condemned, article 34, was “that the First Cause [God] cannot make many worlds.” This opened the door for Christian authors to explore the idea of a plurality of worlds in a manner quite different from how it had been done within Aristotelian cosmology. This freedom influenced such fourteenth-century authors as Jean Buridan (c. 1295–1358), rector of the University of Paris, Nicole Oresme (1325–1382), eventually bishop of Paris, and the Franciscan philosopher William of Ockham (c. 1280–1347), all of whom criticized some of the (mainly Aristotelian) arguments against the doctrine, even though they too ended up rejecting claims for extraterrestrials.

Giovanni di Paolo's St. Thomas Aquinas Confounding Averroës. Tempier investigated the works of both Aquinas and Averroës.
Giovanni di Paolo’s St. Thomas Aquinas Confounding Averroës. Tempier investigated the works of both Aquinas and Averroës.

No such scruples were evident when in 1440 Nicholas of Cusa (1401–1464) published his famous Of Learned Ignorance, in which he devoted a chapter to advocating the possibility of extraterrestrial life even on the moon and sun. Rather than being censured for this view, he was named a cardinal a few years later. The debate took yet another turn when William Vorilong (d. 1463) raised, apparently for the first time, the question of whether belief in extraterrestrials is compatible with the central Christian notions of a divine incarnation and redemption. In his commentary on the Sentences of Peter Lombard, Vorilong gave reasons for believing that God could create another inhabited world, then added: “If it be inquired whether men exist on that world, and whether they have sinned as Adam sinned, I answer no, for they would not exist in sin and did not spring from Adam. . . . As to the question whether Christ by dying on this earth could redeem the inhabitants of another world, I answer that he is able to do this even if the worlds were infinite, but it would not be fitting for Him to go unto another world that he must die again.”

Extraterrestrials and the Scientific Revolution

In 1543 a brilliant if largely unknown cleric published a book so mathematical that few could read it, so shocking that few would at first believe it, and so important that it is arguably the keystone work of modern physical science. This book was De Revolutionibus Orbium Coelestium, its author was the Polish astronomer Nicholas Copernicus (1473–1543), and its message was the heliocentric theory, the claim that the sun, not the earth, is at the center of our universe. In the fullness of time, astronomers and many others came to see that this theory turned earth into a planet, planets into earths, stars into suns (themselves possibly orbited by planets), and humans into denizens of a portion of a vast universe that was possibly packed with other intelligent beings. Although nowhere in Copernicus’s writings did he express himself on extraterrestrials, it was not long before others raised this issue.

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Already in 1550 in his Initia Doctrinae Physicae, the prominent Lutheran theologian Philip Melanchthon (1497–1560) warned against the Copernican cosmology and the idea that Christ’s incarnation and redemption could have occurred on another planet: “the Son of God is One;…Jesus Christ was born, died, and resurrected in this world. Nor does he manifest Himself elsewhere, nor elsewhere has He died or resurrected. Therefore it must not be imagined that Christ died and was resurrected more often, nor must it be thought that in any other world without the knowledge of the Son of God, that men would be restored to eternal life.”

Bronze statue of Bruno by Ettore Ferrari at Campo de' Fiori, Rome.
Bronze statue of Bruno by Ettore Ferrari at Campo de’ Fiori, Rome.

The sixteenth-century author who most boldly pressed the possible implications of the Copernican theory for the extraterrestrial life debate was Giordano Bruno (1548–1600). In the last two decades of the century (and his life), he published three books in which he not only argued for extraterrestrials, but also asserted that they roamed the planets of our solar system and the planetary systems that he postulated must orbit other stars. So enthusiastic was Bruno for extraterrestrial life that he attributed souls to planets, stars, meteors, and the universe as a whole. Bruno was burned at the stake in 1600 by the Catholic Inquisition, but there is no clear evidence to justify the claim that he was a martyr for extraterrestrials. Scholars for the most part agree that the range of heresies Bruno championed, including his denial of the divinity of Christ, were most probably what led the inquisitors to sentence him to death.


The most astronomically astute astronomers at the time of Bruno’s death, Galileo Galilei (1564–1642) and Johannes Kepler (1571–1630), distanced themselves from his claims. Although Galileo in his Siderius Nuncius (1610) had reported observations made with the newly invented telescope that indicated such terrestrial features as mountains on the moon, in his famous defense of the Copernican system, his Dialogue on the Two Chief World Systems (1632), Galileo suggested that if life existed on the moon, it must be “extremely diverse and far beyond our imagining.” Kepler, although the author of a fictional account of life on the moon, worried when he heard reports of Galileo’s early observations, but upon reading the Siderius Nuncius, as he wrote in his Conversation with Galileo’s Sidereal Messenger (1610), he was delighted to find that it contradicted “Bruno’s innumerabilities.” In the same book, Kepler went to some lengths to design a universe in which the earth retained a primacy, in which humankind was the “predominant creature” in all creation.

Johannes Kepler

One of the chief sources of Bruno’s advocacy of the existence of extraterrestrials was his commitment to a religious and metaphysical claim that Arthur Lovejoy has called the principle of plenitude, the doctrine that “no genuine potentiality of being can remain unfulfilled, that the extent and abundance of the creation must be as great as the possibility of existence and commensurate with the productive capacity of a ‘perfect’ and inexhaustible ‘Source,’ and that the world is better, the more things it contains.” In the sixteenth and seventeenth centuries, this notion of plenitude and the associated idea of a great chain of being combined with the growing evidence for the Copernican theory to make the idea of a plurality of worlds seem plausible.

Andreas Cellarius, illustration of the Copernican system, from the Harmonia Macrocosmica (1660).
Andreas Cellarius, illustration of the Copernican system, from the Harmonia Macrocosmica (1660).
The Geocentric Universe
The Geocentric Universe

Two very influential books advocating extraterrestrials appeared in the latter half of the seventeenth century. In 1686, Bernard le Bovier de Fontenelle (1657–1757) attracted a huge audience for his Entretiens sur la pluralité des mondes, which was translated into at least nine languages and went through dozens of editions. Whereas his contemporaries deemed it delightful, the Roman Catholic Church designated it as dangerous, placing it on the Index of Prohibited Books in 1687. The other book appeared in 1698, written by Christiaan Huygens (1629–1695), who ranked second only to Newton among late-seventeenth-century physical scientists in the magnitude of his scientific contributions. Entitled Cosmotheoros—its English title was Celestial Worlds Discover’d: Or, Conjectures Concerning the Inhabitants, Plants, and Productions of the Worlds in the Planets—it was soon available not only in its original Latin but in five other languages. Because Huygens possessed far more credibility in scientific matters than Fontenelle, his book carried more weight than Fontenelle’s charming advocacy.


In the Enlightenment, poets as prominent as Alexander Pope, Edward Young, and Friedrich Klopstock celebrated the idea of a plurality of worlds, while philosophers as famous as Voltaire and Kant championed it. The pioneers of stellar astronomy—Thomas Wright, Immanuel Kant, Johann Lambert, and William Herschel—developed its astronomical implications. There was a paucity of scientific evidence for extraterrestrials, but the argument derived from the principle of plenitude—that God would not waste space by leaving planets uninhabited—created the assumption that probably every planet in our solar system and others was inhabited. Moreover, many intellectuals assumed there were extraterrestrials on the moon, and scientists as prominent as Johann Bode, Roger Boscovich, and William Herschel populated even the sun and stars.

As this suggests, theism seemed to present few obstacles for belief in life elsewhere; in fact, it could be used to support it. Nonetheless, tensions did develop, especially after 1793, when Thomas Paine published his Age of Reason. One question was whether the Christian notions of a divine incarnation and redemption on this planet were believable in a universe of vast size and, it seemed, populated by extraterrestrials. In his book, Paine argues that although the existence of intelligent life only on the earth is not a specific Christian doctrine, it is nonetheless “so worked up therewith from . . . the story of Eve and the apple, and the counterpart of that story—the death of the Son of God, that to believe otherwise . . . renders the Christian system of faith at once little and ridiculous.” Paine challenges the “strange conceit” that Christ would “come to die in our world because, they say, one man and one woman had eaten an apple! And, on the other hand, are we to suppose that every world in the boundless creation had an Eve, an apple, a serpent, and a redeemer? In this case, . . . the Son of God . . . would have nothing else to do than to travel from world to world, in an endless succession of death.”


Reconciling Extraterrestrials and Christianity

Thomas Paine’s claim that belief in Christianity cannot be reconciled with belief in extraterrestrials attracted widespread attention, some challenging it and others supporting it. One alternative view came from Thomas Chalmers (1780–1847), who in the period from about 1820 to 1847 was not only Scotland’s leading evangelical but also the most prominent Scottish religious figure. Chalmers rose to fame in 1817 with the publication of his extraordinarily widely read Astronomical Discourses on the Christian Revelation, based on a series of sermons he had given in Glasgow. In a deeply moving manner and with elegant prose, Chalmers sketched a universe that seemed open to extraterrestrials yet compatible with Christianity.


Ellen White (1827–1915), chief foundress of the Seventh-Day Adventist Church during the second half of the nineteenth century, would incorporate a similar idea into the scriptures she supplied that denomination. Not only did the Seventh-Day Adventists incorporate extraterrestrials into their scriptures, but two other religious denominations founded during the eighteenth and nineteenth centuries did likewise, although in a quite different manner. These are the Church of the New Jerusalem (also known as the Swedenborgians) and the Church of Jesus Christ of Latter-Day Saints (the Mormons).

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Most educated people in the early nineteenth century believed that life was widely spread throughout the universe. Although no substantial evidence of extraterrestrials had become available, arguments for alien life based on natural theology continued to carry conviction. That situation began to change in 1853 when an anonymous book, Of the Plurality of Worlds: An Essay, created a sensation by challenging belief in extraterrestrials. The book’s author, the British scientist William Whewell (1794–1866), was also an Anglican priest and master of Trinity College at Cambridge University. He correctly anticipated the shock his book would create; in its preface, he observed: “It will be a curious . . . event, if it should now be deemed as blamable to doubt the existence of inhabitants of the Planets and Stars as, three centuries ago, it was held heretical to teach that doctrine.” In this volume, Whewell dissected the arguments, both theological and scientific, that had been cited in support of intelligent life throughout the universe. He noted, for example, that the inner planets must receive far more heat from the sun than is compatible with living forms, and that the planets beyond Mars must receive far less heat than needed for life and are of such low density that they probably lack a solid surface.


In response to the theological argument that God’s efforts would have been wasted were celestial bodies bereft of intelligent life, Whewell stressed that geologists, although assigning a vast age to Earth, had concluded that humans appeared only comparatively recently. This, Whewell asserted, shows that the manner in which God works, whatever that may be, is compatible with vast periods (and correspondingly vast spaces) lacking intelligent life. A key factor in the gradual acceptance of Whewell’s claims was the conversion of Richard Proctor (1837–1888), a prolific British writer about astronomy, to what he called the “Whewellite” position.

Near the end of the nineteenth century, the only other planet in the solar system that seemed capable of sustaining life was Mars. The theory that Martians might exist gained support in 1877 when the respected Italian astronomer Giovanni Schiaparelli (1835–1910) reported sighting what have been described as canals on the surface of the planet. From 1877 to 1915, dozens of books, hundreds of telescopes, thousands of articles, and millions of people were focused on Mars as possibly the best hope for extraterrestrials in our solar system. Percival Lowell, Camille Flammarion, and others championed Schiaparelli’s observations, whereas E.W. Maunder and Eugène Antoniadi, among others, countered the claims for the canals and for Martian life. By 1915, at least among the astronomical community, the latter scientists had succeeded.

Mars Atlas by Giovanni Schiaparelli, 1888.
Mars Atlas by Giovanni Schiaparelli, 1888.

Around the time that the Martian canal claims were abandoned, serious difficulties beset the island universe theory, the claim that other Milky Ways exist in the universe. During the 1920s, however, Edwin Hubble and others successfully resurrected the theory, providing evidence of the vast number of galaxies comparable in size to but far beyond our own. Another theory was the nebular hypothesis, the idea that planetary systems form from rotating and condensing nebular material, and that stars probably are surrounded by planets. The nebular hypothesis was replaced for a time by encounter theories of planetary formation, which entail that planetary systems are rare. During the 1940s, the nebular hypothesis regained credibility.


These theories as well as the development after World War II of radio telescopes capable of receiving signals from distant regions of space led to increased interest in the possibilities of intelligent extraterrestrial life. The recognition around 1970 of various extremophiles, terrestrial organisms capable of existing in what had seemed forbidding environments, for example, at temperatures near the boiling or freezing points of water, led some astronomers to argue that lower forms of life may be fairly widespread in the universe. On the other hand, astronomers since perhaps 1990 have come to recognize that the conditions necessary for the development of intelligent life are sufficiently restrictive that it is possible that intelligent life is quite rare.

Throughout the extraterrestrial life debate, astronomy and religion have frequently interacted. Theological reasons have been cited both for and against the existence of intelligent extraterrestrials. Moreover, authors have attempted to marshal extraterrestrials both for and against numerous religious, ethical, and metaphysical positions. In general, theism and belief in extraterrestrial life claims have rarely been in tension, although specific aspects of the Christian religion have in the eyes of some believers created significant tensions. But these difficulties have been addressed over a number of centuries by an array of theologians and religious writers, to an extent that were Earth to come into contact with an extraterrestrial civilization, Christians would have an extensive theological literature to draw on in attempting to assess the religious significance of this development.


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Jollain/De Jode edition of Saliba’s map of the cosmos, integrating ancient Pagan and medieval Christian cosmology with Renaissance beliefs and experiences.
Jollain/De Jode edition of Saliba’s map of the cosmos, integrating ancient Pagan and medieval Christian cosmology with Renaissance beliefs and experiences.