Overview

In the autumn of 2017, a strange object was spotted in the data from the Pan-STARRS telescope.Footnote 1 Dubbed ‘Oumuamua, the ~ 400 m-long object displayed non-gravitational acceleration in the absence of a coma or a tail, the usual indicators of gas-driven propulsion characteristic of comets. The object had unusual proportions and appeared to be thin and cigar shaped, with an unusually shiny surface. The hyperbolic trajectory of ‘Oumuamua was a clue to its identity as an itinerant from another stellar system. As one hypothesis followed another in attempts to explain the strange properties of this mysterious visitor, one proposal pushed ‘Oumuamua to the top of the headlines. Avi Loeb, the then Chair of the Department of Astronomy at Harvard University, suggested that ‘Oumuamua could be a relic solar sail, made by an advanced alien civilization (Bialy & Loeb, Reference Bialy and Loeb2018). Loeb recalls that following the publication of his hypothesis, he woke up one morning to find a large crowd of journalists in front of his house (Loeb, Reference Loeb2021). The association of ‘Oumuamua with an alien civilization had generated considerable public interest. While Loeb’s hypothesis has been largely criticized within the scientific community, it has undoubtedly struck a chord with the public imagination.

People are fascinated with the idea of the existence of intelligent extraterrestrials who might be scientifically and technologically much more advanced than ourselves. This intrigue is often perceived as a symptom of our own scientific advancements over the past two centuries; nothing, however, could be further from the truth. The earliest records of humankind’s enchantment with other inhabitants of the cosmos can be traced back to at least ancient Greece. The debate over the plurality of the worlds has continued, albeit with different degrees of intensity, throughout the centuries, but what makes this account even more captivating is the fact that for the majority of history, this debate was primarily a religious rather than a scientific one. The course of the debate took an important turn in Christendom during the thirteenth century, and despite the many conflicting aspects of the idea of an inhabited cosmos with some central doctrines of Christianity, belief in extraterrestrials became extremely popular in the eighteenth and nineteenth centuries.

The history of the extraterrestrial life debate in the West is extensively researched, most notably through the monumental work of the historian of science, Michael J. Crowe (b. 1936), complemented by the influential contributions of the astronomer and historian, Steven J. Dick (b. 1949). Glancing over the body of literature outlining the history of the debate in the West, one immediately sees the important role that the Muslim philosophers of the Golden Age of Islam played in shaping the debate. Despite this, the history of the debate over the plurality of the worlds within Islamic intellectual tradition has remained largely unexplored.

Apart from the uncharted history of speculations about the plurality of the worlds within the Islamicate world, the research on the implications of a potential modern discovery of extraterrestrial life on Islam is rather limited. Given that we are closer than ever to potentially finding an answer to the question of life beyond Earth, a more extensive exploration of this topic is quite pressing.

Recent developments in the field of astronomy have filled our data reservoirs to the brim. Help has been sought from citizen scientists who are willing to donate both time and effort to the analysis of the data. The emergence of artificial intelligence (AI) and its rapid pace of advancement heralds a fruitful future where the current delays in data analysis will be stuff of the past. A more efficient and rapid search in available data will undoubtedly expand our current catalogue of extrasolar planets, planetary bodies that are orbiting stars other than our Sun. The analysis of the spectra of the atmospheres of potentially habitable planets could lead to identification of possible signs of life. On another front, the use of AI in data analysis will enable us to search for potential artificial signals, sent by technological extraterrestrial civilization, by listening to many more radio channels. One way or another, the future of our search for extraterrestrial life is promising. At this point, it is essential to make a distinction between extraterrestrial life (ETL) and extraterrestrial intelligent life (ETIL); the former is a broader term that encompasses all forms of life, from microbial to complex intelligent life while the latter only refers to intelligent beings. A discovery of microbial life will in fact solve one of the grandest mysteries of science and will undoubtedly cause a sensation amongst the public. However, it will ultimately remain of primary interest to scientists. On the other hand, the discovery of ETIL would have profound social, cultural, and religious implications.

The question of how a discovery of ETIL would affect the religious beliefs of Muslims is a multidisciplinary one that solicits the collaboration of scientists and theologians. This could be a tricky affair since after centuries of interaction, many members of these two groups prefer not to step on each other’s toes. Indeed, it appears that most modern Muslim theologians are primarily preoccupied with the apparent meaning of the sacred text. Little is being done to reframe interpretations in the light of modern developments in technosciences (Mimouni & Guessoum, Reference Mimouni and Guessoum2004). On the other hand, an apposing extreme can be found amongst the science militants, who advocate for annihilation of religion in favour of science. They argue that a discovery of a much more advanced ETIL will be the scientific discovery that could finally put an end to all terrestrial religions – and even the concept of GodFootnote 2 – and usher the start of a new era when science brings salvation to Earth. The theologian, Ted Peters (b. 1941), calls this belief the ETI Myth (Peters, Reference Peters2021). This may be true if one believes in a literal reading of the holy books and perceives religion as a rigid, unyielding enterprise that is blind to the discoveries of science. One is reminded of how a literal reading of the miracle of JoshuaFootnote 3 in the Bible added fuel to the infamous fire of resistance of the Church towards a Sun-centred (heliocentric) model of the universe. Looking at religion as a dynamic entity, however, leaves no doubt in the necessity of the revision of many anthropocentric/Earth-centric views in the event of a discovery of ETIL. In this, one is guided by the words of Ibn Rushd (1126–1198 CE) who argued that the book of nature and the revealed text cannot be in contradiction; facing such apparent contradictions, the revealed text must be read allegorically or must be reinterpreted in the light of the discovered truth.

If heliocentrism did not cause any major crisis of faith in the Muslim world, a discovery of ETIL will undoubtedly prompt many to reconsider some aspects of their faith in order to accommodate the existence of such beings. Some, however, either unsuccessful in this quest or swayed by the impassioned voices of the ‘science militants’ – which would likely grow louder in the wake of a discovery of ETIL – may even abandon their faith.

A cursory Google search reveals many Islamic websites containing scientific ‘ijaz arguments regarding the concept of plurality of the worlds.Footnote 4 A quick glance, however, shows that much of their content conflates inaccurate popular science information with either flawed or superficial reasonings. This calls for a timely and scholarly examination of any potential conflicts between Islamic teachings and the idea of the plurality of the worlds, as well as a deliberation on how a discovery of ETIL would possibly necessitate a revisit and reinterpretation of certain Islamic teachings.

The scholarly works available in this area are quite limited, yet they serve as a foundation for constructing a discourse on Islamic responses to a discovery of ETL. As will be discussed later, some of these works focus on the interpretation of a number of Qur’ānic verses that make open-ended statements about beings in the heavens. Furthermore, a few of the statements attributed to the Prophet and the Shı̄ʿa Imāms, that also allude to the possibility of the existence of other beings elsewhere in the universe, have been discussed in the literature. An initial evaluation of these sources suggests that Islam leaves the door open to accommodating the existence of life beyond Earth. In fact, as early as the fifteenth century, the Muslim astronomer Ulugh Beig (1394–1449 CE) drew on the Qur’ān to argue that God has spread living beings in both Earth as well as the heavens (Wilkinson, Reference Wilkinson2013). Nevertheless, developing a formal Islamic stance on the existence of intelligent extraterrestrials would require a far deeper and more systematic treatment of the topic.

Michael Ashkenazi’s Reference Ashkenazi1992 paper, ‘Not the Sons of Adam’, explores some possible responses of the three Abrahamic religions to a potential contact with ETIL. Mimouni and Guessoum’s Reference Mimouni and Guessoum2004 article is amongst the earliest works by members of academia that directly focuses on Islam and ETL. This study not only underscores the significance of the topic but also sheds light on how various interpretations of a number of Qur’ānic verses might lead to forming differing Islamic stances on the topic of the plurality of the worlds. Islamic Theology and Extraterrestrial Life: New Frontiers in Science and Religion (Reference Determann and Malik2024), an edited volume by Shoaib Ahmed Malik and Jörg Matthias Determann, is a collection of scholarly works that tackles a range of subjects pertaining to various aspects of Islam and ETIL. Before the publication of this volume, Determann had authored Islam, Science Fiction and Extraterrestrial Life (Reference Determann2020), another work that examines the history of science fiction and that of UFO culture amongst Muslims. Although not directly related to the subject of Islam and ETL, it is a noteworthy contribution to the field, as it opens a window onto the scientific imagination on extraterrestrials as depicted in fiction, movies, and periodicals in the Islamicate world.

However, a considerable gap remains in the literature to address whether the unfolding of the debate in Christendom was paralleled by a similar discourse amongst the Muslims. In particular, what were the views of the many illustrious polymaths of the golden age of Islam on the question of plurality of the worlds? And how did the developments in the field of sidereal astronomy, if at all, shape the debate within the Muslim world?

On the other hand, much remains to be explored regarding the potential conflicts between a belief in ETIL and Islamic theology. While the existing scholarship provides a starting point, developing a coherent Islamic stance on the subject is an exigent undertaking. Such efforts will inevitably lead to some tension between Muslim scientists and some conservative clerics, unless a constructive dialogue between the two sides is fostered. Establishing a constructive dialogue between scientific and traditional Islamic worldviews will not only require a general education of the public in both worldviews but also dispelling the widespread misconception that science and religion are inherently in conflict. This mandate falls on the shoulders of a generation of pious young Muslim scientists who are keen to keep pace with the cutting-edge scientific discoveries of our epoch.

This Element is intended to be a concise introduction to the topic of plurality of the worlds and the history of the fascinating speculations about the existence of life beyond Earth with a focus on Islam. It also serves as a call for the necessity of the development of an Islamic astrotheology. Ted Peters has played a major role in introducing and furthering of a Christian astrotheology, a multidisciplinary field that ‘provides a critical analysis of the contemporary space sciences combined with an explication of [Christian] classic doctrines …. for the purpose of constructing a comprehensive and meaningful understanding of our human situation within an astonishingly immense cosmos’ (Peters, Reference 64Peters, Peters, Hewlett, Moritz and Russell2018, pp. 11–12). The goal of astrotheology is to incorporate our contemporary scientific understanding of the cosmic context of life ‘into a critical and constructive theology of nature’ (ibid., p. 13). An Islamic astrotheology then can be defined as a multidisciplinary field that explores the theological implications of a discovery of extraterrestrial life using the Qur’ān and hadı̄th and situates humankind within the broader cosmic order from an Islamic perspective. With the rapid pace of research programmes and discoveries in the field of astrobiology, the development of an Islamic astrotheology is critical for an informed contextual understanding of and engagement with Islamic theology – a religion followed by nearly a quarter of the population of planet Earth.

1 The Debate Across the Ages

The exact provenance of the debate on the plurality of the worlds cannot be traced to a specific point in history, but it is well known that the ancient Greeks had already given much thought to this question and were far from unanimous in their assertions on the existence of life beyond Earth.

Amongst the earliest records, the pre-Socratic philosopher, AnaxagorasFootnote 5 (ca. 510–428 BCE), is believed to have argued for the existence of multiple worlds possessing ‘a sun and a moon and other heavenly bodies for them, just as with us’ (Sisko, Reference Sisko2010). The Pythagoreans, followers of the philosophy associated with Pythagoras of Samos (570–495 BCE), were amongst the earliest of ancient philosophers who expressed their views on the existence of life beyond Earth. While Pythagoras’s own teacher, Anaximander (ca. 610–546 BCE), believed in a succession of worlds in time (Finkelberg, Reference Finkelberg1994), some later prominent figures of this school, such as Philolaus of Croton (470–390 BCE), believed in a ‘terraneous’ Moon that was inhabited by creatures ‘much larger [in] size and plants of rarer beauty’ (Huffman, Reference Huffman and Zalta2003).

The atomists of ancient Greece were another prominent school of thought who advocated for the plurality of the worlds. Founded by Leucippus in fifth century BCE and further developed by Democritus (460–370 BCE), the atomists argued for a world with no divine creator that owed its origin to the chance agglomeration of atoms – the indivisible and imperishable chunks of matter that were infinite in number and in random motion. Such conception of the origin of our world led them to favour an infinite number of worlds, each arising from the chaotic dance of the atoms. On this, Epicurus (341–270 BCE), one of the preeminent figures of atomism, writes:

The ensuing centuries, however, witnessed the rise to prominence of Aristotle’s stance on the topic of plurality of the worlds. Perhaps the most celebrated of all ancient Greek philosophers, Aristotle (384–322 BCE), rejected the existence of other worlds. Appreciation of Aristotle’s position on the existence of life beyond Earth requires an understanding of his conception of the workings of the universe. Aristotle’s cosmology was founded on an ingenious blend of a geocentric (Earth-centred) model of the universe and the doctrine of natural places of the four elements constituting everything on Earth: fire, air, water, and earth, as had been proposed by Empedocles (c. 494–434 BCE). When left on their own, each of these elements would move so as to seek their natural places: fire and air rise upward, while water and earth move down. Although these elements could be moved in other directions by violent motions, this was against their nature. If there existed two earths, Aristotle argued, a pebble falling towards the centre of our Earth would find itself to be in violent motion with respect to another Earth. This was clearly a contradiction, since the pebble would be experiencing both natural and violent motions simultaneously (Crowe, Reference Crowe2012, p. 5). Thus, Aristotle’s doctrine of natural places could only accommodate one Earth.

With the fall of the Western Roman Empire, many parts of Europe experienced a period of decline in intellectual activity. The works of classical Greek philosophers were, however, preserved and intensively studied by the relatively young Muslim civilization, which sought to preserve and build on the wisdom of the ancient Greeks with a religious zeal. The so-called Graeco-Roman translation movement was the outcome of a variety of political, geographical, religious, and sociological factors during the reign of the ʿAbbāsid Caliphate that produced an atmosphere receptive to acquiring the ‘foreign sciences’. Between the second half of the eighth and the end of tenth century, an impressive corpus of books was translated from Greek, Sanskrit, and Pahlavi. These translated works not only occupied the shelves of the Grand Library of Baghdad but also the minds of many individuals who went on to become some of the most influential philosophers of the Islamicate world. Philosophers such as Al-Kindi (805–873 CE), Al-Fārābi (872–951 CE), Ibn Sı̄nā (980–1037 CE), known in the West as Avicenna, and Ibn-Rushd (1126–1198 CE), known as Averröes in the West, studied the works of Plato and Aristotle and authored extensive commentaries on them, adapting these works to an Islamic framework.

The end of the twelfth century marked the entry of Aristotle’s work into Christian circles in the West along with accompanying Muslim commentaries. The immense task of properly adapting Aristotle’s teachings to a Christian framework was taken up by St. Thomas Aquinas (d. 1274 CE). Aquinas based his work on the foundation laid primarily by Avicenna and the Jewish philosopher Maimonides (1138–1204 CE), but ‘his new philosophy was always governed by and subordinate to faith’ (Principe, Reference Principe1985). The adoption of a pagan philosophy within a monotheistic religion governed by a variety of Church doctrines was not free of controversy; while at the beginning of the thirteenth century, only personal readings of Aristotle’s works were permitted, by the 1270s, the ‘ultra-Aristotelian’ commentaries of Averröes had been appropriated by some members of the Faculty of Arts at the University of Paris. This set off a chain of events that reshaped the course of the debate in Christendom.

In January of 1277, Pope John XXI (1215–1277 CE) requested Étienne Tempier, the Bishop of Paris, to investigate the nature of some heretical teachings allegedly circulating amongst students of the Arts in Paris. Acting promptly, Tempier issued a list of ‘certain obvious and loathsome errors’ that he had found ‘some students of the arts in Paris [were] …. presuming to treat and discuss, as if they were debatable in the schools’ and thus had ‘exceed[ed] the boundaries of their own faculty’ (Uckelman, Reference 65Uckelman2010). Issued in March 1277, number 34 of these propositions condemned the statement ‘that the first cause cannot make many worlds’ (Wippel, Reference Wippel, Garcia and Noone2002, p. 69). This meant that one could not deny the possibility of other inhabited worlds, for doing so would contradict the belief in omnipotence of God. Thus began a new section in the debate over the plurality of the worlds, one that would increasingly favour the existence of extraterrestrials. About a century and half later, one comes across people such as Nicolas of Cusa (1401–1461), a theologian, later appointed as a Cardinal in the Catholic Church, who asserts his belief in stellar regions being inhabited ‘lest so many places in the heavens and on the stars be empty and lest only the earth – presumably among the lesser things – be inhabited’ (Cusanus, Reference Cusanus and Wilpert1967, p. 169).

Cusa’s argument is one that repeats itself in many shapes and forms in the ensuing centuries; it was perplexing to think that God had created so many orbs in vain. Populating the cosmos with sentient beings would soon, however, raise compatibility questions with one of the most central doctrines of Christianity – the doctrine of atonement: do extraterrestrials live in sin or not? Are multiple reincarnations of Christ possible? Remarkably, the course of the debate on the plurality of the worlds in Christendom was largely shaped by the thoughts of those who sought answers to these questions. The French theologian, William Vorilong (1390–1463 CE), had expressed his reservations on whether ‘Christ by dying on this earth could redeem the inhabitants of another world’. His position was that Christ ‘is able to do so even if the worlds were infinite, but it would not be fitting for Him to go unto another world that he must die again’ (Crowe, Reference Crowe2012, p. 9). Some like the Lutheran reformer Philip Melanchthon (1497–1560 CE), however, rejected the pluralist point of view on the basis of this conflict:

It did not take long before people noticed that the question of wastage of created space outweighed the potential conflict between the doctrine of atonement and the belief in other inhabited worlds so the alleged conflict was swept under the rug.

The debate over the plurality of the worlds took another sharp turn in the sixteenth century, when in a highly mathematical treatise, it was suggested for the Earth to be promoted to the status of a planet. Authored by the Polish Canon and mathematician Nicolaus Copernicus (1473–1543), De revolutionibus orbium coelestium (on the Revolutions of the Celestial Orbits), advanced a heliocentric (Sun-centred) model of the universe, swapping the place of the Earth and the Sun.Footnote 6 Throughout the nineteen centuries that separated Aristotle and Copernicus, the observed motions of the heavenly objects had been put into a rigorous mathematical framework through the work of the Alexandrian astronomer, Claudius Ptolemy (100–170 CE), who had built on the works of earlier astronomers such as Apollonius of Perga (240–190 BCE) and Hipparchus of Nicaea (190–120 BCE). Ptolemy’s Mathematical Treatise was one of the books translated into Arabic during the reign of Caliph al-Ma’mūn (786–833 CE), the seventh ʿAbbāsid Caliph. Aptly rebranded as Almagest – literally meaning ‘the greatest’ – this astronomical treatise expounded mathematical models to describe and predict the observed motion of planets.

A precise mathematical formulation of the path of these ‘wanderers’ in a celestial system that only accommodated perfect circular orbits had proved elusive. The main difficulty hindering this task was the strange path of the planets as observed with respect to the background stars. In addition to their daily rising in the east and setting in the west, planets follow an eastward track in the sky, the cumulative effect of which can be observed over the course of a week or better, a few. Occasionally however, planets abandon their nightly eastward motion (called prograde), appear to stop in their tracks, and start pursuing a westward motion (called retrograde) for some time before returning to their usual eastward motion!

Reproducing this strange dance in the sky, using perfect circular paths on which planets orbited the Earth at constant speeds, had proved to be impossible. Instead, the wandering tracks of planets were simulated through the combined motion of auxiliary circles, making the universe look like a clock with many cogs and gears. In this universe, planets were doomed to pursue circular orbits called epicycles. The centre of this epicycle was in turn in circular motion on a larger circle, called the deferent, centred on Earth.

Despite its complexity, this model was still unable to produce sufficiently accurate predictions of the positions of planets, which, in addition to the retrograde motion, showed varying speeds, brightnesses, and sizes. In pursuit of a more precise model, deferents became eccentric, meaning that the Earth was pushed off the centre of the universe (Figure 1). Ptolemy had to introduce further restrictions, weaving the motion of planets into that of the Sun, adding more layers of complexity, and thereby presenting an intricate model that was mathematically cumbersome.

Figure 1

In the Ptolemaic model of the universe, a planet was confined to a small circular orbit called epicycle, the centre of which swept the circumference of a larger circle called deferent. The deferent was centred not on Earth, but on a point called eccentric.

The displacement of the Earth from the centre of the universe was regarded as a significant deviation from the perfect cosmos originally conceived by Plato (ca. 428/427–348/347 BCE) and consequently provoked considerable criticism of Ptolemy. During the golden age of Islam, attempts were made to restore the Earth to the centre of the cosmos. These included the introduction of the Tūsı̄ Couple by the thirteenth-century Polymath Nası̄r al-Dı̄n al-Tūsı̄ (1201–1274 CE), later employed by Ibn al-Shātir (1304–1375 CE), the muwaqqitFootnote 7 of the Ūmayyad Mosque in Damascus, to revise the Ptolemaic model. Despite these efforts, pinpointing the precise future positions of planets remained out of reach.

In introducing a heliocentric model of the universe, Copernicus sought a mathematically simpler construction of the cosmos in which the retrograde motion was merely a matter of perspective. His bold move promoted the Earth to the rank of a planet, which in turn had profound consequences in the debate over the plurality of the worlds: if Earth were an abode to humankind and other forms of life, could life not also exist on other planets? Furthermore, the nature of the heliocentric model implied a universe far larger than the one perceived in the geocentric model. Simply put, the stars in the Copernican universe were situated at far greater distances than those in Aristotle’s. The creation of such an immense universe with only Earth inhabited would imply a huge wastage of space – unless other stars were themselves other suns, serving other earths.

Within the pages of Copernicus’s De Revolutionibus, a Dominican friar and cosmological theorist found a gateway to the infinite universe that he envisioned (Granada, Reference Granada2004). With a deep intuition about the structure of the universe, Giordano Bruno (1548–1600) conceived of an infinite sphere whose centre was everywhere and whose circumference was nowhere. His universe, of infinite dimensions, was filled with globes as good as Earth ‘… or even better for the nourishment of their own life and the happiness of those who live upon them … those who live in other worlds should not expect to find God in ours, for they have him near and within themselves’ (Bruno & Gatti, Reference Bruno and Gatti2018, p. 102). Bruno’s vision of this highly populated universe, however, was founded in his metaphysics rather than on scientific evidence.

It was Galileo Galilei (1564–1642) who, observing through his humble self-made telescope, went on to shatter the very foundations of geocentrism. By observing planet Venus waxing to a full disc and waning back, Galileo acquired compelling evidence against the Ptolemaic model. Amongst Galileo’s other revolutionary telescopic observations was the discovery of the four Jovian satellites. Contrary to the cosmology of Aristotle, these bodies were in orbit around Jupiter, rather than Earth. As significant as this discovery was, for his contemporary German mathematician and astronomer, Johannes Kepler (1571–1630), it implied that ‘with the highest degree of probability … Jupiter is inhabited’, as he could find no other purpose served by their existence (Kepler Reference Kepler1965, p. 42).

When it comes to his contentions on the plurality of the worlds, Galileo appears rather reticent. Whether this stems from a lack of interest in the topic, from dismissing it as unlikely, or from an abundance of caution is not clear. That religious sensitivities likely played a role in Galileo’s cautious treatment of the subject could be seen in his correspondence with Giovanni Ciampoli, a close friend. Ciampoli warned Galileo against a ‘casual comparison’ of the two globes of Earth and Moon which could be ‘amplified’ and ‘altered’ by different people who might claim that Galileo was placing human inhabitants on the Moon and ‘dispute how these can be descended from Adam, or how they can have come off Noah’s ark, and many other extravagances’ (Drake, Reference Drake1957, p. 158).

There is little doubt that Galileo never espoused the idea of life on the Moon. He was well aware that ‘each half of the moon is alternately in sunshine and darkness for 15 continuous days of 24 hours’, exposing our satellite to periods of ‘ardent sunshine’ and ‘plunging in cold and darkness’ alternately (Fahie, Reference Fahie1903, pp. 135–136). Kepler, on the other hand, was far more vocal about his pluralistic beliefs. Two years prior to Galileo’s telescopic observations, Kepler had completed a manuscript entitled Somnium (1608), which is often credited as the first-ever science fiction book. Written ‘to use the example of the moon to build up an argument in favour of the motion of the earth’ (Kepler, Reference Kepler1967, p. 36), the book presents a vivid account of an alien society surviving in the hostile environment of the Moon.

If Somnium is a prime example of accurate science of Kepler’s time, described in the guise of the narrative of a daemon who regularly arranges for selected humans to voyage to the Moon, Cosmotheoros (1698) can be credited as one of the earliest books on astrobiology. Authored by the Dutch astronomer, Christiaan Huygens (1629–1695), best remembered for the discovery of Titan, the largest moon of Saturn, Cosmotheoros is a tour-de-force of speculations on the unexplored worlds of other intelligent civilizations. Published posthumously, Cosmotheoros explores not only Huygens’s views about the existence of life beyond our planet, but also his thoughts on many different aspects of such beings, from their anatomical features to their mathematics, sciences, writing, and even arts including music (Huygens, Reference Huygens1762).

The German-born British astronomer, Sir William Herschel (1738–1822), the discoverer of the planet Uranus and the premier telescope maker of the eighteenth century, believed that an excellent telescope might allow him to observe signs of life on our satellite. Although he remained unsuccessful in obtaining observational evidence of lunar life, Herschel hypothesized that all the planets of the solar system, as well as the dwarf planets, and the known satellites were inhabited. Seeing the Sun as an eminent planet, enveloped within a luminous atmosphere, he further hypothesized that the interior of the Sun is an abode for beings whose organs are adapted to that environment (Herschel, Reference Herschel1795).

As Michael Crowe observes, within a few centuries the plurality of the worlds transformed from being the curious belief of a handful of people into an idea preached from every pulpit. Gradually, credence in ETIL became so entangled with the religious outlook of the time that it appeared to be almost indispensable. That is, until the publication of The Age of Reason (1794) by philosopher and writer Thomas Paine (1737–1809). Paine asserted that the Christian belief in the account of ‘Eve and the apple, and the counterpart of that story, the death of the Son of God’ is so worked up in Christian faith that ‘to believe that God created a plurality of worlds … renders the Christian system of faith at once little and ridiculous; … The two beliefs can not be held together in the same mind; and he who thinks that he believes both, has thought but little of either’ (Paine, Reference Paine1796, p. 133). Paine is adamant throughout that the doctrine of atonement renders Christianity an anthropocentric religion that leaves no room for belief in other intelligent extraterrestrials:

Paine’s forceful blow prompted a number of responses, most notably that of Thomas Chalmers (1780–1847), a Scottish theologian, who depicted an image of a cosmic Christ, the effects of whose redemptive actions on Earth not only propagate in time but also in space. By dying on our globe, Chalmers asserted, Christ had redeemed all the inhabitants of the universe. Yet not all found Chalmers’s vision of a cosmic Christ persuasive; Paine’s argument was too forthright to be ignored.

Thus, the titanic figure of the British polymath and Master of Trinity College, Cambridge, William Whewell (1794–1866), abandoned his earlier pluralistic contentions for a universe in which Earth, as the scene of the scheme of redemption, could not be held ‘on a level with any other domiciles’ (Whewell, Reference Whewell1855, p. 64). Whewell pointed out that the main argument for populating other globes was that, without inhabitants, they served no purpose. At a time when natural historians were beginning to realize that the Earth was far more ancient than previously thought, Whewell reminded his readers that such waste was not ‘unsuited to the character of the Creator’, as is conspicuous in the history of Earth. For most of its existence, Earth’s ‘seas and its continents, have wasted upon mere brute life … upon the lowest, the least conscious forms of life .… Why then should not the seas and continents of other planets be occupied with a life no higher than this, or why no life at all?’ (Whewell, Reference Whewell1855, p. 125)

Having concluded that Christianity and a belief in intelligent extraterrestrials were irreconcilable, Whewell continued that although Earth could have supported current forms of life earlier in its history, different life forms appeared throughout the eons. Believing that all planets must be occupied with intelligent beings is similar to believing that the same type of life must have continuously occupied the Earth, a contention that he dismissed as a mere ‘fancy’ (ibid., p. 128). Whewell suggested that while simple life might be widespread in the universe, ‘the conditions of any life approaching at all to human life, exist only on the Earth alone’ (ibid., p. 288). Whewell’s argument laid the foundation for what came to be known as the Rare Earth Hypothesis. His viewpoint was echoed by Alfred Russell Wallace (1823–1913), the co-discoverer of the theory of evolution by natural selection. Wallace observed that the evolution of life on Earth depended on the presence of many individually improbable conditions – a strange coincidence that made Earth a one-of-a-kind fluke.

The introduction of spectroscopy and advancements of telescopes led to the realization that almost no planet in the solar system can accommodate complex life. By the mid-nineteenth century, Mars was the only planet that presented some potential for habitability. The oppositionFootnote 8 of 1877 sparked a fervent controversy over the putative Martian canals – one that persisted for almost a century and was only put to rest with the photos that the Mariner 4 spacecraft took in 1964. During that opposition, the respected Italian astronomer, Giovanni Schiaparelli (1835–1910), reported the discovery of a system of canali on our neighbouring planet. Instead of being translated to ‘channels’, which are the handiwork of Nature, the Italian word canali was translated to canals, connoting well-planned projects implemented by intelligent minds. While Earthlings themselves were busy building terrestrial canals – the Suez Canal having been finished just a few years before and the Panama Canal plans being conceived and revised – visualizing Martian engineers working hard for the betterment of the conditions of their planet did not require much stretch of the imagination. Schiaparelli’s discovery was quickly picked up by the prolific French popularizer of astronomy, Camille Flammarion (1842–1925), who hypothesized that the Martian canali ‘constitute a hydrographic system of extreme ingenuity’, with the purpose of regulating inundations, ‘a “rise of Nile” controlled and directed’ (Flammarion, Reference Flammarion1896, p. 553).

By 1892, support for the existence of Martian canals had increased significantly; what was most baffling, however, was that there were conflicting reports on the number and the characteristics of observed canals. This lack of consensus was used by the opponents of the Martian canali to dismiss the sightings of this extensive system of canals as mere optical illusion. The controversy was further escalated when the wealthy businessman and extraterrestrial enthusiast, Percival Lowell (1855–1916), funded the construction of a state-of-the-art observatory in Arizona to investigate ‘the conditions of life in other worlds’ (Campbell, Reference Campbell1896, pp. 207–220) and, in particular, to confirm observationally that the scarcity of water on Mars had forced ‘highly intelligent’ Martians to conduct water from the poles to the rest of the planet (ibid., p. 209).

Following Lowell’s death in 1916, more sophisticated techniques of spectroscopy as well as infrared astronomy were employed in an attempt to reveal Martian vegetation. The visual observation of seasonal patterns of dark areas on Mars led to a wide consensus that while the red planet was likely devoid of complex animal life, it could support lichen-like vegetation. Another four decades of observations would pass before a measurement of vanishingly small amounts of water vapour in the atmosphere of Mars came to depict a picture of a cold, arid desert.

The early years of the twentieth century witnessed a pessimism about the existence of other worlds, reminiscent of that of Aristotle. Gone were the days when our solar system was imagined as teeming with life – its planets and their satellites, and even the rings of Saturn – inhabited by intelligent extraterrestrials praising God – as envisioned in Thomas Dick’s Celestial Scenery (1837). This desolate image stemmed from the ‘planetesimal hypothesis’ which proposed that planets are rare, as they only form by the coagulation of ejected stellar material during the close encounter of two stars. Since such encounters were rare, it followed that planets were rare. The ‘planetesimal hypothesis’ lived a short life and before the mid-twentieth century it was replaced by the ‘nebular hypothesis’, first propounded in the eighteenth century by the German philosopher Immanuel Kant (1724–1804) and the French mathematician, Pierre Simon Laplace (1749–1827). Contrary to the ‘planetesimal hypothesis’, the nebular hypothesis argued that planets and stars are formed together when a cloud of gas and dust collapses under its own weight, implying that planets must be abundant. Between 1943 and 1995, there were a number of spurious claims of detection of unseen companions to stars, until eventually the discovery of 51 Pegasi b marked a new era in the story of the plurality of the worlds (Dick, Reference Dick and Vakoch2013).

The twentieth century also witnessed much interest in the question of the origin of life. During the 1920s, as the world of astronomy was being transformed by sensational discoveries, the Russian biochemist Aleksander Ivanovich Oparin (1894–1980) and the British-born biologist J. B. S. Haldane (1892–1964) independently proposed an abiogenic origin of life on an infant Earth with an oxygen-free atmosphere. The so-called ‘Primordial Soup’ hypothesis proposed that through the action of lightning and UV radiation, methane, ammonia, and other molecules in the atmosphere of a young Earth were dissociated and assembled into molecules that eventually formed proteins and nucleic acids.

Three decades later, Harold Urey (1893–1981) and Stanley Miller (1930–2007) simulated the conditions thought to resemble those of the early Earth in the laboratory and succeeded in synthesizing more than twenty different types of amino acids, demonstrating that the conditions of the infant Earth were amenable to the production of building blocks of life. Although the choice of the gases used in the Miller-Urey experiment was later questioned, their experiment was valuable in that it showed that organic molecules could have been produced here on Earth. Most recently, however, it was shown that organic molecules are also abundant in space. In 2016, ESA’s Rosetta mission provided the first clear piece of evidence for the existence of glycine, the simplest stable amino acid,Footnote 9 on the comet 67P. More recently, analysis of the samples returned from the near-Earth asteroid 162173 Ryugu by Hayabusa2 mission, operated by the Japanese state space agency, led to the identification of twenty different amino acids (Parker et al., Reference Parker, McLain, Glavin, Dworkin, Elsila, Aponte and Nakamura2023).

The abundance of organic molecules in space leads to another fundamental question concerning the origin of life. In his presidential address to the British Association for the Advancement of Science in 1871, William Thomson (1824–1907), later Lord Kelvin, suggested that it is ‘probable in the highest degree that there are countless seed-bearing meteoric stones moving about through space’ and life on Earth could have originated from the ‘ruins of another world’ (Thomson, Reference Thomson1871). Kelvin was referring to the ancient idea of Panspermia, first articulated by Anaxagoras in the fifth century BCE, which proposed that the Earth was peopled by the semen that came down from the sky (Hollinger, Reference Hollinger2016). Panspermia remains relevant today, as it is well known that, early in the history of the solar system, large impacts hurled rocks off Venus, Mars, and Earth. These rocks then embarked on journeys that eventually landed them on neighbouring planets. Could these rocks have acted as interplanetary vessels carrying life from one planet to another? Could microbes endure the initial blast, the subsequent harsh interplanetary journey, and survive the fiery landing through the atmosphere? Unbelievable as it may seem, there is evidence that the answer to all these questions is affirmative. There is strong evidence that terrestrial microbes are indeed capable of enduring the inhospitable cold and vacuum of space for extended periods of time. Furthermore, studies reveal that the interiors of Martian meteorites have remained rather intact during their journey. Therefore, it is believed that if any putative Martian microbes are safely nestled in the pores of their rocky spacecrafts, the first and last legs of their journey are not as perilous as previously thought.

Knowing that Mars was a warmer and wetter planet in the past, could it be that it was the site of a second genesis? Could it be that life first appeared on Mars and was later dispatched to Earth? An initial investigation into such questions was one of the main science objectives of NASA’s Viking programme, conducted in the 1970s. The Viking $59-million biology package consisted of three experiments, all designed to detect metabolic activity. Although these experiments remained inconclusive, this ambiguity only refuelled our interest in the red planet. Since the Viking programme, dozens of orbiters, landers, and rovers have been sent to explore the red planet. The most recent one is the Perseverance Rover, which landed in the Jezero crater, believed to have once been the site of an ancient lake.Footnote 10 There is still much hope of finding evidence either for extinct or extant forms of microbial life on Mars.

A number of satellites in the solar system, most notably Europa, one of the four Galilean moons of Jupiter, and Enceladus, a tiny moon of Saturn with water geysers gushing out of regions near its south pole, are also targets for our search for microbial life.

One way or another, our understanding of the structure of the cosmos, the formation of planetary systems, and the conditions necessary for the emergence and evolution of life has changed significantly since the time of the ancient Greeks and is expected to be further revolutionized in the coming decades. We live in an era in which the discovery of ETL is no longer a far-fetched dream. But how does such a discovery affect the views of Muslims? This question will be discussed in detail in Section 4, but before doing so, a complementary discussion of the position of the modern science on the existence of life beyond Earth is necessary.

2 Extraterrestrial Life and Modern Science

‘Artificial satellites of the earth pave the way to interplanetary travel, and apparently our contemporaries are fated to be witnesses to the fact that liberated and politically conscious labor of the people of the new socialist society makes reality of the most daring dreams of humankind.’ Thus read the last few lines of the announcement of the Sputnik launch on October 4th, 1957, an event that marked the beginning of the space race; a rivalry of East and West that led to a rapid development in the exploration of space. Within half a century of the launch of Sputnik, hundreds of spacecrafts were sent off to explore different bodies in our solar system. Orbiters and flyby missions have explored the thick and turbulent atmospheres of Jupiter and Saturn, and in the summer of 2015 the New Horizons spacecraft, following a nine-year journey, made its closest approach to Pluto, one of the farthest objects ever visited by a human-made spacecraft. We have sent probes to comets as well as asteroids; to Titan, the giant moon of Saturn and the only natural satellite with an atmosphere in the solar system, as well as the only body other than the Earth with seas of liquid on its surface, albeit filled with methane and ethane rather than water. At the time of this writing, NASA’s $5-billion Europa Clipper mission is on its way to explore the global water ocean of Europa, buried under a thick icy crust.

The treasure trove of data gathered by these missions has led to rapid progress in the young field of astrobiology. NASA defines astrobiology as the study of the origin, evolution, distribution, and future of life on Earth and in the universe (Des Marais et al., Reference Des Marais, Nuth III, Allamandola, Boss, Farmer, Hoehler, Jakosky, Meadows, Pohorille, Runnegar and Spormann2002). This definition makes it quite clear that astrobiology is not only concerned with ETL but also with the origin, evolution, and future of life here on Earth. Exobiology, the precursor to astrobiology, which emerged in the mid-twentieth century, was at some point mocked for having to prove that the subject of its study indeed existed. The fact that astrobiology encompasses the study of both terrestrial and any potential ETL not only renders the aforementioned objection obsolete but also has led to a more liberal definition of habitable environments and has shed light on a sundry of environments that could potentially be inhabited. The study of the emergence and evolution of life on Earth provides us with many basic tools to search for life elsewhere in the universe. Furthermore, in developing methods to search for life beyond Earth, we arrive at a deeper understanding about the nature of life on our own planet.

3 In Search of Companionship

If a planet possesses all the right conditions for life to arise, is the emergence of life inevitable or was Earth a fluke? If life is bound to emerge, does evolution invariably lead to the development of complex life? Does the evolution of complex life always give birth to intelligent life? Are intelligent beings destined to become technological civilizations?

In our search for life elsewhere in the universe, we are constrained in that we are guided only by our understanding of the course that carbon-based terrestrial life has taken on Earth. But if we find an Earth-like planet – one in the habitable zone of its parent star with a suitable atmosphere – how could we confirm the existence of life? The vast distances between stars and our current level of technology still forbid us from becoming the space-faring civilization that is often depicted in sci-fi movies. In fact, with our current level of space technology, travelling to our closest stellar neighbour will take a good 700 centuries! With interstellar expedition trips out of the question, we are left with no choice but to search for signs of life from afar.

3.1 Peeking into the Alien Atmospheres

As a planet transits its parent star, we receive a sliver of the starlight that is filtered through the atmosphere of the planet, carrying with it a wealth of information about the atmospheric composition of the target planet (Figure 2). In the spectrum of this light, we can search for the so-called ‘biosignatures’; gases produced by life and accumulated in the atmosphere of a planet to a detectable level.

Figure 2

Searching for biosignatures in the atmosphere of an extrasolar planet

Before any observation of a potential biosignature gas can be taken as evidence for the presence of life, all potential abiotic processes must be ruled out. The case of oxygen provides an excellent example: the photosynthesis process performed by plants, algae, and some other microorganisms produces sugars through chemical reactions involving carbon dioxide, water, and sunlight. The by-product of this process is oxygen. While the composition of the atmosphere of the young Earth is still a subject of debate, it is widely accepted that oxygen was absent in this primitive atmosphere. Following the emergence of photosynthetic bacteria, the oxygen released by these organisms – being highly reactive – did not last long in the atmosphere; it was absorbed by oxygen sinks,Footnote 12 essentially rusting everything on the planet. Over time, however, oxygen started accumulating in the atmosphere, ultimately transforming its chemical composition. It took a good one billion years for oxygen to be promoted from a trace gas to the status of a major atmospheric component. Throughout this period, anaerobic life forms were leading a quiet life on Earth, as did photosynthetic bacteria, but there were no detectable signs of oxygen in the atmosphere; life was teeming on Earth without a significant presence of oxygen. Therefore, the absence of oxygen in the atmosphere of ancient Earth did not imply the absence of life; in the words of the eminent twentieth-century American astronomer and popularizer of science, Carl Sagan, ‘the absence of evidence is not evidence for absence’ (Marsh, Reference Marsh2019).

On the other hand, the presence of oxygen cannot be taken as a definitive indicator of life. Oxygen could accumulate in the atmosphere of a planet through photolysis – the breakdown of water molecules by high-energy radiation. Hydrogen, being the lightest element in nature, readily escapes to space, and oxygen accumulates in the atmosphere. This is especially true in the case of rocky planets orbiting in the HZ of red dwarfs, stars much less massive and much cooler than our Sun. The photolysis of water on these planets, in the absence of efficient oxygen sinks such as continental weathering and plate tectonics, could give rise to oxygen-rich atmospheres, thus poisoning the search for ETL with false positives (Luger & Barnes, Reference Luger and Barnes2015).

Methane is often considered a biosignature gas, provided that an abiotic origin is first ruled out. One way to ascertain the biogenic origin of certain gases in the atmosphere of a planet is by searching for a cocktail of these gases rather than one in particular; for instance, the simultaneous observation of methane and oxygen has been proposed as an indicator of life. If not constantly replenished through biogenic processes, these two gases rapidly react to produce carbon dioxide (Hitchcock & Lovelock, Reference Hitchcock and Lovelock1967). Conversely, the presence of the so-called ‘anti-biosignature’ gases in an extrasolar planet’s atmosphere serves as a strong piece of evidence for the absence of life. It is known that gases such as hydrogen and CO, in large persistent abundances, cannot exist in the atmosphere of a planet where oxygenic bacterial life is present. Their abundance, therefore, may be used to rule out the presence of life as we know it.

Peeking through the atmosphere of a planet, we can also search for ‘technosignature’ gases which point to the existence of a technological civilization. Compounds such as chlorofluorocarbons – commonly called CFCsFootnote 13 – could only accumulate in the atmosphere through industrial activity. While biosignature gases signal the existence of life, technosignatures are a tell-tale sign of the existence of not just life but an intelligent civilization in possession of science and technology, capable of altering its environment. Technosignatures are not limited to waste gases; any technological civilization at some point will master manipulating the electromagnetic spectrum, the collection of all ‘light’ with different wavelengths. Radio waves, in particular, can travel the astronomical distances that separate planets unhindered and, depending on the strength of the signal, can be detected tens of light years away. Such signals might be the television or radio signals of another civilization that might leak into space, or could be deliberate messages constructed and intentionally sent out by an extraterrestrial civilization searching for cosmic companionship.

3.3 A Galactic Switchboard

SETI’s approach seeks to leap over the traditional search for life, aiming instead to directly uncover technological civilization. But how many such civilizations, capable of interstellar communication, might exist in the Galaxy at any given time? In 1961, Frank Drake hosted the first meeting of SETI in Green Bank (Virginia, USA). In preparing an agenda for this meeting, he listed all the factors that needed to be considered in estimating N, the number of communicating civilizations present at any given time in the Milky Way. On the right-hand side of what came to be known as the ‘Drake equation’, there appear seven terms, each representing the probability of a crucial step towards the emergence of a technologically advanced civilization capable of interstellar communication:

$\text{N}={\text{R}}^{*}\times {\text{f}}_{\text{planet}}\times {\text{n}}_{\text{habitable}}\times {\text{f}}_{\text{life}}\times {\text{f}}_{\text{intelligence}}\times {\text{f}}_{\text{civilization}}\times \text{L}$

The first term, ${\mathrm{R}}^{*}$, denotes the birthrate of Sun-like stars in our galaxy per year. From these stars, only a fraction, ${\mathrm{f}}_{\mathrm{planet}}$, have a planetary system around them, while ${\mathrm{n}}_{\mathrm{habitable}}$ is the number of planets that have environments favourable for life in those stars with planetary systems. The next two terms in turn estimate the fraction of those habitable planets where life emerges, ${\mathrm{f}}_{\mathrm{life}}$, and the fraction of those planets with life where intelligent life eventually materializes, ${\mathrm{f}}_{\mathrm{intelligence}}$. ${\mathrm{f}}_{\mathrm{civilization}}$ is an indication that not all intelligent life will necessarily be a technological civilization, capable of interstellar communication; there is an important distinction: the Babylonians, for instance, were an intelligent civilization who kept meticulous records of the motions of the heavenly bodies, but within the Drake equation, they are irrelevant since they were not technological civilizations capable of interstellar communication. Finally, $\mathrm{L}$ is the average length of the time that a technological civilization broadcasts signals.

Estimating the value of each of these terms becomes progressively more difficult as one traces the steps towards the emergence of a technological civilization in the Drake equation. We know that between one and three Sun-like stars are born in the Galaxy every year. Recent developments in the discovery of extrasolar planets indicate that almost all stars have planets orbiting them, while a reasonable average for the number of habitable planets could be one or two per planetary system. Assigning values to the remaining terms proves to be far more challenging. The fact that life started relatively early in the history of Earth has led some to argue that the emergence of life is inevitable on habitable planets, yet a more pessimistic view would assign much smaller values to ${\mathrm{f}}_{\mathrm{life}}$. Estimating the next term, ${\mathrm{f}}_{\mathrm{intelligence}}$, is a task better suited to the biologists than astronomers. The conundrum here is whether the evolution of life always leads to the emergence of one or even more intelligent species – a question that has opened a wide gap amongst evolutionary biologists.

An appreciation of the factors driving this debate requires a brief digression into the world of evolutionary biology. Today, the leading scientific theory describing the diversity of life on Earth is the theory of evolution by natural selection, first propounded by Charles Darwin in 1859.Footnote 17 Inspired by Thomas Malthus’s Essay on the Principle of Population (1798), Darwin observed that populations tend to produce more offspring than can be supported by the limited resources available in their environment, resulting in a ‘struggle for existence’.

Within a population, individuals exhibit variations in their traits; some variations in turn enable certain members to access resources more efficiently and thus produce more offspring. Many such traits are heritable and thus are passed down from parents to offspring. Over time, the successful reproduction of members with the particular advantageous traits leads to the entire population being more fit or ‘adapted’ to its environment; Nature ‘selects’ the advantageous trait. When it comes to estimating ${\mathrm{f}}_{\mathrm{intelligence}}$ in Drake’s equation, the wedge driving the gap between two schools of thought is the question of whether intelligence constitutes an evolutionary adaptation or not.

On one side are those who adhere to the view that intelligence is the outcome of the work of the machinery of natural selection acting on the random and unpredictable mutations over long periods of time. Supporters of ‘Contingent Evolution’ argue that natural selection favours combinations of mutations that increase the chances of survival of a species in response to the challenges of its ecological niche. Environmental stresses, they note, could arise due to a series of ‘utterly unpredictable and quite unrepeatable events’, such as an asteroid impact or extreme changes in the climate (Gould, Reference Gould1989). It is argued that if the tape of life were to be rewound on Earth, it is quite unlikely that we would even end up with a humanoid, let alone Homo sapiens. This, however, must not mislead the reader into thinking that natural selection is a random process.

This subtle misapprehension was addressed by one of the most influential evolutionary biologists of the twentieth century, Theodosius Dobazhansky (1900–1975):

Man did not arise by a lucky chance mutation which happened to pass through the “sieve” of natural selection. To say that he arose by a succession of chance mutations is misleading; his biological base has been constructed by natural selection, in a multitude of responses to environmental challenges. The responses were mediated by natural selection. It does not follow from this that man was bound or predetermined to arise.

(Dobzhansky, Reference Dobzhansky1972, p. 166)

On the other hand, some argue that the emergence of intelligence is an inevitable outcome of evolution. In making their argument, the proponents of this view invoke a curious phenomenon called ‘convergent evolution’, where species that do not share a recent common ancestor independently evolve to show similar traits as solutions to similar ecological challenges (Stern, Reference Stern2013). Examples of convergent evolution abound: bats and insects both fly, but have wings that evolved from fundamentally different structures; echolocation has independently evolved in bats and all toothed whales. The hawk moth and hummingbird have both developed strikingly similar body shapes and energy budgets despite the fact that the former is closely related to shrimps and the latter to dinosaurs (Morris, Reference Morris2005). Even social structure shows convergence: ants and termites, having evolved from very different ancestors, ended up developing remarkably similar societal structures.

Advocates of convergent evolution assert that intelligence is an evolutionary adaptation that increases the chances of survival of a species. Given the pervasiveness of convergent evolution, the British palaeontologist and astrobiologist, Simon Conway Morris (b. 1951), speculates that ‘human-like intelligence is a cosmic inevitability’, but he emphasizes that this intelligence does not have to ‘reside in a human-like brain’ (Morris, Reference Morris2005). To support his argument, he points to the independent evolution of tool use in South American Monkeys and the New Caledonian crows (ibid.). If intelligence is in fact an evolutionary adaptation, then similar ecological niches on other planets would likely give rise to intelligent species that might eventually become capable of discovering and inventing; an intelligent society that possesses science and technology.

Regardless of whether intelligence is the outcome of contingent or convergent evolution, astronomers remain optimistic that other civilizations capable of interstellar communication might exist. In the former case, they contend that the improbability of the particular chain of events that led to the emergence of intelligence on Earth is compensated for by the vast number of evolutionary experiments taking place on billions of Earth-like planets in our ancient Galaxy. In a galaxy approximately 13.5 billion years old, they argue, a few of these evolutionary ‘test tubes’ would eventually produce intelligent beings capable of developing science and technology. In the latter case, astronomers stand on firmer ground, maintaining that once life emerges on a planet, given enough time, intelligence would almost inevitably follow.

The last term in the Drake equation, L, the average lifetime of a technological civilization, is the most difficult to estimate, as it depends on sociological and cultural factors rather than biological ones. Yet, L is critical in estimating N, the number of communicating civilizations at a given time. When Drake plugged in numbers for the first six terms on the right-hand side of the equation and multiplied them, the participants in SETI’s inaugural meeting were surprised to obtain a result of 1, leaving the number of communicating civilizations in the Galaxy to hinge on L. If technology is in fact a curse, technological civilizations may have short lives, annihilating themselves, but if they find a way beyond the self-imposed threats of technology – such as climate change, nuclear weapons, existential risks from advanced AI, then these civilizations could persist for very long times and possibly become immortal.

4 Extraterrestrials and Islam

Having acquired a general knowledge of the state of the debate since its inception 2,600 years ago, it is now time to develop an Islamic perspective on the subject of the plurality of the worlds. Several important characteristics distinguish the Muslim discourse on the topic from its counterpart amongst Christians. While early Christian thinkers unanimously rejected the possibility of an inhabited cosmos, amongst Muslims, conversations on the question of the plurality of the worlds can be traced back directly to the Qur’ān and the Prophet. In fact, there exist a few verses in the Qur’ān that might hint at the existence of life beyond Earth. These can help illuminate the path to finding an Islamic stance on the existence of not only life, but intelligent life beyond Earth.

In seeking an Islamic position on any subject, Muslim scholars primarily consult two main sources: the Qur’ān and the corpus of hadı̄th,Footnote 18 a body of sayings or deeds of Prophet Muhammad. Historically, Muslim thinkers have maintained that the Qur’ān uses metaphors and allegories to aid a more diverse audience in understanding its complex message. In holding this view, Muslim intellectuals share an opinion with the Christian theologians who invoke the principle of Biblical accommodation.Footnote 19 Following this line of thought, the verses of the Qur’ān are classified into Muhkamāt (univocal) and Mutashābihāt (equivocal). The former encompasses the verses that are clear in their meaning, while the latter refer to those verses whose meanings can be ambiguous and cannot be clearly attributed to a place, object, or a phenomenon, and thus require interpretation. It is amongst these Mutashābihāt that one comes across a number of verses that could have a bearing on the subject of the plurality of the worlds.

Tafsı̄r of the Qur’ān refers to an exegesis of the Qur’ān that attempts to interpret and provide explanations of the holy book of the Muslims. In their interpretation, the mufassirūnFootnote 20 (interpreters of the Qur’ān) use a variety of tools, from Arabic grammar to the etymology of a word and its linguistic use to employing a corpus of hadı̄th (Calderini, Reference Calderini1994). The tafsı̄rs could vary widely depending on whether the exegete is a follower of the Sunnı̄ or the Shı̄ʿa branch of Islam (and in turn their respective denominations). One major distinction between the Sunnı̄ and Shı̄ʿı̄ tafsı̄rs is in the collection of the hadı̄th employed in the interpretation of the Mutashābihāt (equivocal) verses; for the Sunnı̄s, hadı̄th comprises the sayings and traditions of the Prophet, while for the Shı̄ʿas, the corpus of hadı̄th incorporates the sayings and knowledge conveyed not only by the Prophet but also by the Shı̄ʿı̄ Imāms.Footnote 21 Thus, within the Shı̄ʿı̄ exegetical tradition, a much more expansive corpus of hadı̄th is employed that emphasizes the authority of the Imāms in interpreting the Qur’ān.

The first logical step in developing an Islamic astrotheology is a comprehensive examination of several Mutashābihāt verses in the Qur’ān that may bear upon the question of ETIL. In addition to these Qur’ānic verses, there exist a number of ahādı̄th that directly address the existence of other planets and sentient extraterrestrials. In evaluating a hadı̄th, the chain of transmission (isnād) is of critical importance in its authentication. Anomalous ahādı̄th (Shādh) are generally dismissed on the grounds that they are either narrated by a single narrator or that they concern a peculiar, unusual topic (Karamali, Reference Karamali, Determann and Malik2024). For the purpose of this section, an examination of a selection of ahādı̄th (both in the Sunnī and Shı̄ʿı̄ traditions), pertaining to the plurality of the worlds, is a valuable exercise. A consideration of these ahādı̄th (even those reports with weak chains of transmission) offers a revealing window into the historical and cultural milieu in which they circulated. Situating each hadı̄th within its temporal and spatial context allows for the evaluation of the interest and the degree of intellectual curiosity in the existence of life beyond Earth within the Islamicate world.

The study that follows is by no means comprehensive, as it only considers a handful of the many Qur’ānic tafsı̄rs and consults a selection of ahādı̄th. More specifically, the Shı̄ʿı̄ tafsı̄rs referred to in the preparation of this section include (but are not limited to) Al-Mı̄zān fı̄ Tafsı̄r al-Qur’ān (The Balance in Interpretation of Qur’ān), commonly known as Tafsı̄r Al-Mı̄zān, by the Shı̄ʿı̄ scholar and philosopher Allāmeh Sayyid Muhammad Husayn Tabātabā’ı̄ (1903–1981), and Tafsı̄r Nemooneh (The Ideal Commentary), authored by the Iranian Cleric Nasser Makarem Shirāzı̄ (b. 1927) in collaboration with a group of scholars working under his supervision. The latter work is noteworthy because it not only incorporates/employs a range of earlier Shı̄ʿı̄ commentaries but also attempts to draw upon modern scientific discoveries in providing a contemporary exegesis of the Qur’ān. Unfortunately, in this tafsı̄r, the boundary between science and pseudo-science is at times blurry, and thus one needs to be cautious about some of the interpretations found therein. Finally, Makhzan al-‘Irfan fı̄ Tafsı̄r al-Qur’ān (The Treasury of Spiritual Knowledge in Interpretation of the Qur’ān) the only tafsı̄r written by a female Shı̄ʿı̄ Mujtahida, Banu Nosrat Beygum Amin (1886–1983), commonly known as Lady Amin, has also been consulted in completing this section.

The Sunnī tafsı̄rs consulted in developing the discussions of this section include (but are not limited to) Tafsı̄r IbnʿAbbās, one of the earliest and most widely known interpretations of the Qur’ān, Tafsı̄r al-Ṭabarı̄ by Imām Muḥammad ibn Jarı̄r al-Ṭabarı̄ (839–923 CE), Mafātı̄h al-Ghayb (Keys to the Unseen) by Fakhr al-Dı̄n al-Rāzı̄ (1149–1209 CE), and Tafsı̄r al-Jalālayn (The Commentary of the Two Jalāls) completed in the sixteenth century CE. In addition, the commentaries in Mahāsin al-Ta’wı̄l (The Merits of Exegesis) by Muhammad Jamāl al-Din al-Qāsimı̄ (1866–1914), The Holy Qur’ān by ʿAbdullah Yusuf ʿAlı̄ (1872–1953), and Fı̄ Ẓilāl al-Qur’ān (In the Shade of the Qur’ān) by Sayyid Qutb (1906–1966) were also found to be particularly relevant.

Of course, a thorough examination of all the authoritative tafsı̄rs – both Shı̄ʿı̄ and Sunnī – is a task beyond the scope of this Element. The purpose of the brief examination presented here is to consolidate and build upon the limited existing research on extraterrestrials and Islam, thereby preparing the ground for sowing the seeds of an Islamic astrotheology. Such an undertaking would require close collaboration amongst astrobiologists, historians of science, historians of religion, and Islamic scholars with expertise in Qur’ānic hermeneutics. Furthermore, it will provide a productive framework for future research on the interaction between science and Islam.

5 Conclusion

The discussion presented over the previous sections reveals the multidisciplinary nature of the field of astrotheology. The aim was to provide a basis to expand the relatively limited scholarship on how Muslims might receive, interpret, and integrate a discovery of ETL within the framework of Islamic beliefs. The examination of a number of Qur’ānic verses and a selection of ahādı̄th is meant to pave the ground for the development of an Islamic stance on the question of the existence of intelligent life beyond Earth.

Yet, there remain certain areas of Islamic theology that might need a reinterpretation and require expansion to incorporate the existence of intelligent extraterrestrials. An Islamic astrotheology must aim to provide ways to integrate the existence of other intelligent beings in its ontology and describe, how Islam – being a religion open to all peoples of Earth – relates to other sentient inhabitants. The success of such an initiative lies in re-envisioning Islam as a faith embracing a vision of cosmic fellowship. While Christians have to devise ways to resolve the uneasy relationship between the doctrine of atonement and the existence of sentient extraterrestrials, the universality of the message of Islam makes it less susceptible to being seriously threatened by the belief in the existence of intelligent ETL (Tajbakhsh, Reference Tajbakhsh2013).

The purpose of this section is to offer a preliminary discussion of a few of the Islamic theological topics that warrant special attention on the path to developing a comprehensive Islamic astrotheology. Each of these topics is, in its own right, deserving of further research and deeper investigation.