Infinite cosmology / pluralism of worlds

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The plurality of worlds is the question of whether this world is the only one — whether the universe is finite and unique, as Aristotle argued, or infinite and strewn with other earths, other suns, and perhaps other inhabitants. The question is far older than the telescope. The ancient atomists held that innumerable worlds form and dissolve in a boundless void; Aristotle answered that there can be only one cosmos, and his physics made that answer the medieval default. For most of two millennia the case was decided not by what anyone saw but by what the structure of being would allow — and that is the thread worth following, because the infinite cosmos arrived as a conclusion about God and matter long before it arrived as a report from a lens.

Thomas Digges’s 1576 diagram dismantles the outer stellar sphere and scatters the stars endlessly through space — the infinite-universe picture later pressed by Bruno. — Thomas Digges, “A Perfit Description of the Caelestiall Orbes” (1576), via Wikimedia Commons (public domain)

Two ancient poles

The dispute begins as a quarrel within Greek physics. Leucippus and Democritus, and after them Epicurus and his Roman expositor Lucretius, posited atoms falling through an unlimited void; where atoms are infinite and space without bound, worlds cannot be one. Whole cosmoi — kosmoi — coalesce and disperse without number, some like ours, some unlike it, some with their own earths and living things, some barren. Plurality here is not a marvel but a statistical consequence of an infinite supply of matter in an infinite room. The atomist universe has no center because it has no edge to measure a center from.

Aristotle closed that room. In On the Heavens he argued that there is and can be exactly one cosmos, finite and spherical, with the earth at its unmoving center; the heavens are made of a fifth element, eternal and incorruptible, turning in nested spheres, and beyond the outermost sphere there is no place, no void, no body, nothing at all. Each of the four sublunary elements has a single natural place toward which it moves, so a second world would require a second center to which a second portion of earth would fall — an incoherence, on his terms. The cosmos is full, bounded, and unrepeatable. Carried into the Latin Middle Ages with the recovery of Aristotle in the twelfth and thirteenth centuries, and welded to scripture by the scholastics, this became the standing picture of the heavens: one world, finite, centered on us. It would be the work of Renaissance natural philosophy, and of the recovered Platonist and Neoplatonist currents that ran beside it, to crack that frame open from within. The Stoics, for their part, held a single ordered cosmos pervaded by an immanent reason yet surrounded by an infinite void into which it would dissolve at the periodic conflagration — a third position, neither atomist plurality nor Aristotelian plenum, that kept the question of the void alive within an otherwise unitary cosmos.

Theology reopens the case

The breach came not from astronomy but from doctrine. In 1277 Étienne Tempier, bishop of Paris, condemned two hundred nineteen propositions drawn from the radical Aristotelians of the arts faculty. Among them was the teaching that the First Cause — God — could not make several worlds. To deny that God could make more than one world was, the condemnation held, to chain omnipotence to the conclusions of a pagan physicist. After 1277 the plurality of worlds became a permitted, even required, hypothesis: God’s absolute power (potentia absoluta) could surely create other worlds, even if His ordained power (potentia ordinata) had in fact made only one. Fourteenth-century masters — Jean Buridan, Nicole Oresme, William of Ockham — turned the hypothesis over with care. Oresme in particular reasoned that other worlds need not have other centers, dissolving Aristotle’s objection, and that an infinite void beyond the heavens was at least thinkable, though he held by faith that God had made one world only. The case was open as a question of what God might do a full century and a half before anyone proposed it as a description of what is.

Cusa: the universe without a wall

Nicholas of Cusa drew the consequence with unprecedented boldness. In De docta ignorantia — On Learned Ignorance, 1440 — the cardinal reasoned from the nature of an infinite God to the shape of His creation. Between the finite and the infinite there is no proportion; God alone is the absolute maximum, but the universe, His unfolding, is a kind of contracted or relative infinity, unbounded though not infinite in God’s sense. A universe deployed by such a God can have no fixed center and no outer wall: its center is everywhere and its circumference nowhere, because no created place has a better claim to the middle than any other. The earth, therefore, is not the lowest sump of the cosmos but a noble star, moving, bright in its own degree, and Cusa allowed himself to speculate that the sun and the other regions of the heavens are inhabited by beings suited to their natures — the moon by lunar dwellers, the sun by solar ones — none of them, perhaps, nobler than the inhabitants of earth.

Nicholas of Cusa (1401–1464), who argued from the nature of an infinite God to a universe whose center is everywhere and circumference nowhere. — Master of the Life of the Virgin, St. Nicholas Hospital, Bernkastel-Kues, via Wikimedia Commons (public domain)

None of this rested on observation. Cusa raised no instrument; he had no data the fourteenth century lacked. The de-centered, wall-less universe was an inference from the doctrine of God by way of the coincidentia oppositorum, the coincidence of opposites in the infinite, in which maximum and minimum collapse together. It is worth marking, as Cusa scholars do, that this is an anticipation in speculative metaphysics, not a discovery in astronomy: Cusa is not a hidden Copernican who happened to publish a century early, and to read him as a literal precursor of telescopic findings overstates the case. What he supplied was the deeper move — the conviction that a finite, single, earth-centered cosmos was unworthy of an infinite maker.

Bruno: infinite cause, infinite effect

Giordano Bruno fused that theological inference with the new astronomy. In De l’infinito, universo e mondi — On the Infinite Universe and Worlds, one of the Italian dialogues printed in London in 1584 — and again in the Latin De immenso of 1591, the ex-Dominican of Nola pressed the argument past every boundary Cusa had left standing. An infinite cause, he held, must produce an infinite effect: an infinitely powerful God who made anything less than an infinite universe would be withholding, and that is unthinkable. So the universe is infinite, homogeneous, and centerless, filled with innumerable suns, each a star like ours, each attended by its own earths — Bruno’s synods of worlds — all of them animate, all bathed in the one universal soul that informs matter throughout. Where Copernicus had moved the earth around the sun and left the fixed stars on a finite outer sphere, Bruno dissolved the sphere entirely and scattered the stars as suns through unbounded space. He faulted Copernicus, in fact, for going only halfway — for remaining a mathematician of the heavens rather than a philosopher of nature.

Giordano Bruno (1548–1600) in the 1715 engraving long taken as the only known likeness; he held that an infinite cause must produce an infinite universe of innumerable suns and worlds. — engraving published 1715, via Wikimedia Commons (public domain)

Bruno was burned at Rome’s Campo de’ Fiori on 17 February 1600, after an eight-year Inquisition trial. The popular image of a martyr for the infinite universe is simpler than the documents allow. The eight heretical propositions Robert Bellarmine assembled for him to abjure do not survive; the full sentence is lost; the trial summary recovered in the Vatican archives in 1940 and published by Angelo Mercati in 1942 clarifies the procedural arc and the general areas of dispute without recovering the charges verbatim. What the record shows is a tangle of theological heresies — denial of the Trinity, of Christ’s divinity, of transubstantiation, of Mary’s virginity — bound up with, but not reducible to, his cosmology of the world-soul and the plurality of worlds. Scholarship divides sharply on the weight of the cosmological charge: some, following Frances Yates, hold that the many-worlds doctrine was not among the formal charges and that Bruno died for religious heresy; others, notably Alberto Martinez, argue from neglected canon-law and theological treatises that belief in many worlds was itself classed as formally heretical — the contemporary reasoning ran that one could not assert many worlds since one could not assert many Christs — and was of primary importance in the verdict. The contest is genuine and unsettled; the documents are partial enough to bear more than one reading.

After the telescope: the debate widens

When the instrument finally came, it widened the question rather than closing it. Johannes Kepler, reading Galileo’s Sidereus Nuncius of 1610, weighed the possibility of inhabitants on the moon and later, in his Somnium, imagined their conditions — yet he resisted Bruno’s infinity flatly. For Kepler the very fact that the night sky is dark, and that the stars subtend small finite disks rather than filling the whole heaven with light, argued for a bounded stellar realm with the sun at a privileged place; an infinite array of suns, he thought, would blaze without interval. Kepler’s universe was vast and structured by geometrical archetypes in the divine mind, but it was not Bruno’s edgeless swarm. His near-contemporary Robert Fludd carried a different cosmology again — the Hermetic-Platonic vision of a single graded harmony, macrocosm mirroring microcosm, set out in the Utriusque Cosmi Historia (1617–1621) — and his running quarrel with Kepler across four treatises between 1619 and 1622 marked the slow separation of mathematical natural philosophy from the symbolic, analogical cosmology that had nourished it. Kepler demanded ratios drawn from measurable magnitudes; Fludd defended proportion and picture as the only language adequate to a cosmos whose harmony was qualitative and divine. The exchange settled little between them, but it displayed the parting of two ways of reading the heavens — both of which had, until then, shared a vocabulary.

Johannes Kepler (1571–1630), who entertained inhabitants on the moon yet resisted Bruno’s infinity, arguing that the dark night sky implied a bounded stellar realm. — attributed to Hans von Aachen, c. 1612, via Wikimedia Commons (public domain)

The popularizers finished the work the metaphysicians had begun. Bernard de Fontenelle’s Entretiens sur la pluralité des mondes — Conversations on the Plurality of Worlds, 1686 — turned the question into salon conversation, walking a marquise through the night garden and peopling the planets in graceful dialogue; placed on the Index in 1687, it ran through edition after edition. Christiaan Huygens followed posthumously with the Cosmotheoros (1698), conjecturing the conditions of life on other planets from the principles of his own physics. By the eighteenth century plurality was close to learned orthodoxy, a commonplace of educated belief across confessional lines.

And as it became respectable, the old theological difficulty sharpened rather than dissolved. A cosmos of many inhabited worlds sits awkwardly with an incarnation on one planet: if the Word became flesh once, at one place and time, what is the standing of the countless other earths — were they redeemed, unfallen, awaiting their own incarnations, or simply outside the economy of salvation altogether? The question, raised already by the schoolmen and pressed hard from the seventeenth century onward, was the precise point at which the infinite cosmos cost something. It is the same fracture, in theological dress, that the plurality of worlds has carried from the start: a finite, single world is easy to center on the human story; an infinite, plural one is not.

The research record

The modern study of the plurality of worlds is in large part the study of how an idea persisted across two thousand years through philosophy, theology, and only latterly astronomy. Two works fixed the frame. Arthur O. Lovejoy’s The Great Chain of Being (Harvard University Press, 1936) isolated the principle of plenitude — the conviction, traceable from Plato’s Timaeus through Neoplatonism into Christian theology, that a perfectly good and ungrudging God would realize every genuine possibility, leaving no rung of being empty. Plenitude is the metaphysical engine beneath both the infinite universe and the conviction that other worlds must be inhabited: an unstinting maker would not leave them barren. The same intuition surfaces, transformed, in Gottfried Wilhelm Leibniz; one must distinguish carefully, though, Leibniz’s best of all possible worlds — the theodicy holding that God chose this world as the optimal one among infinitely many possible worlds — from the cosmological thesis of many actual inhabited worlds. The “possible worlds” of Leibniz are unrealized alternatives weighed in the divine intellect, not other earths in the sky; the plenitude that links the two is a shared metaphysical temper, not a shared doctrine.

“Integra naturae speculum artisque imago,” from Robert Fludd’s “Utriusque Cosmi Historia” (1617), depicting the graded chain that binds God, Nature, and the cosmos — the same hierarchy of plenitude isolated by Lovejoy. — Robert Fludd, 1617, via Wikimedia Commons (public domain)

Alexandre Koyré’s From the Closed World to the Infinite Universe (1957) gave the long passage its enduring name and its thesis: that the seventeenth century did not merely enlarge the cosmos but destroyed the ordered, hierarchical, bounded kosmos of antiquity and the Middle Ages, replacing it with a homogeneous infinite space indifferent to value and place — a revolution metaphysical before it was observational. The specialist history of the inhabited-worlds question was then mapped by Steven J. Dick in Plurality of Worlds (Cambridge University Press, 1982), tracing the debate from antiquity to Kant, and by Michael J. Crowe in The Extraterrestrial Life Debate, 1750–1900 (1986), which carried it into the modern period. On the contested Bruno verdict, Alberto Martinez’s study Giordano Bruno and the heresy of many worlds (Annals of Science, 2016) argues against the long scholarly consensus that cosmology was incidental to the trial. The primary record is unusually accessible: J. Lewis McIntyre’s Giordano Bruno (1903), a public-domain biography that surveys the infinite-universe dialogues, and Fontenelle’s Entretiens sur la pluralité des mondes (1686) in full, both stand open to the reader.

A boundary is worth drawing against two later senses of “worlds” that sound like continuations of this debate but are not. The many-worlds interpretation of quantum mechanics — every measurement outcome realized in a branching of the wave function — is a twentieth-century proposal about the structure of physical theory, not about other earths scattered through one space; its “worlds” are parallel branches, not distant suns. And Ouspenskian cosmology, the graded ray-of-creation scheme drawn from Gurdjieff’s teaching, is an esoteric hierarchy of ontological levels rather than a population of inhabited planets. Each is a distinct architecture that happens to share a word.

What the history shows, read as a whole, is that the infinite cosmos was a metaphysical and devotional idea before it was an observational one. The universe was unbounded in Cusa’s theology a century and a half before anyone raised a lens to the sky. The instruments confirmed a picture that contemplation had already drawn.

→ In the library: Steiner — Mystics of the Renaissance, incl. Cusa and Bruno (1910)

→ Related: Nicholas Of Cusa · Giordano Bruno · Johannes Kepler · Renaissance Natural Philosophy · Best Of All Possible Worlds · Gottfried Wilhelm Leibniz · Robert Fludd · Aristotle · Platonism · Neoplatonism · Stoicism · Many Worlds Interpretation · Ouspenskian Cosmology