Aquinas and the Multiverse

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My God, you are absolute infinity itself, which I perceive to be the infinite end, but I am unable to grasp how an end without an end is an end.

NICHOLAS OF CUSA, ON THE VISION OF GOD

Each thing (the glass surface of a mirror, let us say) was infinite things, because I could clearly see it from every point in the cosmos.

JORGE LUIS BORGES, “THE ALEPH”

Ending the Endless: Thomas Aquinas From the ashes of the mid-thirteenth century arises a familiar question: Is there one world, or are there many? Might there even be an infinite number of them? The author of the question is Thomas Aquinas (1225–1274), and one almost wonders why he bothers to ask. Hadn’t the matter been put to rest by Plato, sealed by Aristotle, diagrammed by Ptolemy, and Christianized by Augustine? Hadn’t all the pluralizing dissenters been “hissed off the stage” or consigned to dust and ashes centuries ago? And yet here we find Thomas in the Summa theologiae, beginning as usual with the position he will refute, saying: “[I]t would seem that there is not only one world, but many.”1 To whom would it seem that this is the case? What has changed since Augustine declared the matter closed nearly a millennium ago?

What has changed is, in one sense, a return of the “same,” which is to say a rediscovery of Aristotle. As is well known, most of Aristotle’s works had been lost to the Latin-speaking world between the third century b.c.e. and the twelfth century c.e., when scores of his manuscripts were translated, debated, and made the object of lengthy scholastic commentaries.2 Among these newly recovered manuscripts was the De caelo, which was translated from Arabic into Latin in 1170. As we saw in chapter 1, this text 70

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insists against the Atomists that the cosmos must be unique, basing its claims on the principles of “natural motion.” If another world existed, Aristotle reasons, then its earth would move unnaturally “up” with respect to our world, even as it moved naturally “down” with respect to its own. “This, however, is impossible,” he says, because it is the property of earth to move down.3 Elements cannot move both naturally and unnaturally at once, so “it follows that there cannot be more worlds than one.” 4 With the rediscovery of the De caelo, medieval Europe thus possessed a seemingly definitive argument for the singularity of the cosmos, one that reaffirmed the teachings of Platonists and church fathers alike.

This agreement notwithstanding, Aristotle also held cosmological positions that contradicted the received teachings of medieval Europe—perhaps most problematically concerning the eternity of the cosmos.5 Here we might recall Augustine’s insistence that the world could not be eternal without compromising the singularity of God: if God alone is God, then nothing else can exist alongside him. Thus began centuries of Latinate efforts to evaluate Aristotelian cosmology in the light of Christian theology, with the universities’ “secular masters” ready to adopt Aristotle wholesale, the Franciscans looking to abandon any position that seemed to contradict scripture, and the Dominican Thomas Aquinas working to reconcile the two.6 In this era of intellectual fervor, even the most firmly entrenched doctrines were reopened for debate, including the doctrine of cosmic singularity. So even though the Epicureans themselves would not be given a fair hearing until the seventeenth century, their teachings on the plurality of worlds were tentatively engaged five hundred years earlier as the medieval West came to terms with the very philosopher who had rejected them.7 Among Aristotle’s Christian interpreters in particular, the central cosmological concern was to uphold the sovereignty of God with respect to creation. This emphasis on sovereignty, in turn, reopened the question of cosmic plurality in the high Scholastic period. After all, one might ask, if God is omnipotent, then why would “he” limit himself to creating one world? It is in this sense that Thomas Aquinas concedes in Question 47 of the Summa theologiae that it might “seem” that there are many worlds.

“For the same reason He created one,” Thomas reasons, “He could create many, since His power is not limited to the creation of one world; but rather is infinite” (1.47.3).8 Indeed, the infinity of God’s power might even lead us to posit an infinite number of worlds.

Yet just as an eternal world would threaten God’s singularity, Thomas seems concerned that infinite worlds might rival his infinity. Indeed, a 71

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standoff between material and divine infinity can be seen as early as Question 2 of the Summa, in which Thomas proves the existence of God based on the absurdity of an infinite causal regress. “Whatever is in motion must be put in motion by another,” he argues in the first of his five proofs. “If that by which it is put in motion be itself put in motion, then this also must needs be put in motion by another, and that by another again. But this cannot go on to infinity, because then there would be no first mover, and, consequently, no other mover. . . . Therefore it is necessary to arrive at a first mover, put in motion by no other; and this everyone understands to be God” (1.2.3, emphasis added).

In the work of this proof, Thomas aligns “everyone’s” God with Aristotle’s prime mover: the extracosmic stopgap that prevents the causal march to infinity. God puts an end to worldly endlessness. How, then, could there be an endless number of worlds? Where is the place for a first mover if worlds extend backward eternally?

In short, the doctrine of a plurality of worlds threatens Thomas’s whole theological infrastructure: if worlds have existed from eternity, then there is no starting point for God to occupy. In the Summa, Thomas therefore raises the possibility of a cosmic plurality, only to launch a multipronged attack against it. He calls briefly on the Gospel of John (“ ‘the world was made by Him,’ where the world is named as one ”), offers a brief paraphrase of the De caelo’s argument from natural motion, and appeals in passing to its neo-Timaean insistence that “the world is composed of the whole of its matter” (1.47.3, emphasis added).9 In this manner, Thomas lines up the usual sources of authority against cosmic multiplicity: scripture, Plato, and Aristotle all seem to say no. But his chief strategic move in the face of this possibility is to refocus the question, shifting the measure of divine sovereignty away from brute force and toward singularity. An omnipotent God could make other worlds, Thomas imagines, but doing so would compromise his unity.

The argument proceeds as follows: all things come from God, and all things find their end (terminus) in God. This means that “[w]hatever things come from God, have relation of order to each other, and to God himself.”10 This “relation of order” denotes the hierarchy of creation—the Neoplatonic “Great Chain of Being” under which all things from angels to snails are peacefully, permanently, and vertically related to God and one another.11 In an earlier question, Thomas calls on this ordered relation to demonstrate the oneness of God: the unity of creation, he argues, testifies

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to the unity of its creator (1.11.3). In the question at hand, the demonstration is simply reversed: because God is one, “it must be that all things should belong to one world” (1.47.3). Taking these questions together, we can see that the oneness of the cosmos is both a function and a sign of the oneness of God. The only way to “assert that many worlds exist” would therefore be to deny the “ordaining wisdom” of God altogether—to say that there is no providential order of things (1.47.3). Here Aquinas offers the example of “Democritus, who said that this world, besides an infinite number of other worlds, was made from a casual concourse of atoms” (1.47.3). To affirm an infinity of worlds is therefore to deny the involvement of God, for God is said to be the end of all creation. But insofar as “the infi nite is opposed to the notion of end” (1.47.3), infinite worlds would mean the absence of end; there would be no single source, no final home, and no ordered passage from one to the other. Many worlds, in short, would mean no God, and “this reason proves that the world is one” (1.47.3).

Although the tone is far more somber, one can thus detect in this argument echoes of Augustine, who likewise rejected cosmic infinity because of its endlessness. A soul destined to recurring embodiment, he feared, would never find its rest in God.12 To his credit, Thomas has arguably found firmer ground for his rejection than the Augustinian “heaven forbid”: if all things have their end in one God, he reasons, then all things must belong to one world. Thomas may well have adapted this strategy from Book Lambda of Aristotle’s Metaphysics, which asserts that the cosmos must be singular because its source of motion is singular.13 As we will recall, however, Aristotle’s proof undermines itself even before it is concluded, producing either forty-seven or fifty-five prime movers in the process of trying to secure one and opening in spite of itself onto just as many worlds. Thomas’s argument similarly can be made to tremble at the very point that it hinges the number of the cosmos on the number of God. For however closely Thomas may align them, his God differs from the prime mover in not being simply one. His God is rather three-in-one, an eternal interrelation of identity and difference. So even if God is the end of all things, God is an “end” that is both one and many: multiple. Might the things of creation not therefore occupy multiple worlds?

This might be a compelling possibility, but it would be unacceptable to Thomas for two reasons. First, he insists on the priority of identity over difference even within the Trinity, arguing in the previous article that “unity” pertains to the Godhead and “multiplicity” only to creation.14 God

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might contain plurality, and God certainly produces plurality, but God is primarily one.15 Second, Thomas assumes that if numerous worlds were to exist, they would bear no relation to one another, constituting nothing more than a haphazard plurality à la Democritus. But if we push on the first assumption, then the second moves as well: if the Christian God is eternally triune, then God is not single first and plural afterward, but eternally pluri-singular. What, then, would prevent such a God from creating multiple worlds that are nonetheless interrelated? If the number of creation really mirrors the number of God, then wouldn’t an entangled multiplicity of worlds reflect God’s many-oneness more fully than a single world would?

It is perhaps for this reason that Thomas shifted his strategy the next and last time he addressed the question of multiple worlds. Two years before the end of his life, he wrote a detailed commentary on the De caelo in which he hinges the oneness of the cosmos not on the oneness of God, but on the omnipotence of God. Although it might seem that an omnipotent God would create as many worlds as possible, Thomas counters that “it takes more power to make one perfect [individual] than to make several imperfect.”16 A “perfect” individual world would be one that includes all beings within it, and (back to the Timaeus again) a world that contains all beings within it would have to be singular. It therefore does more justice to the omnipotence of God to say the world is one than to suggest it might be one of many.

As it turned out, however, neither of Thomas’s approaches succeeded in putting cosmic multiplicity to rest. A mere three years after Thomas’s death in 1274, Bishop Etienne Tempier of Paris issued a list of 219 heretical Aristotelian teachings, among which was Condemnation 34: “Quod prima causa non posset plures mundos facere.”17 Anyone who taught that “the first Cause cannot make many worlds” would henceforth be excommunicated for undermining the absolute power of God. And so the Scholastics of the late thirteenth century and the fourteenth century could not rest with Thomas’s Christianized repetitions of Aristotle. More important, they could not rest with Aristotle himself—and would even have to face the possibility that his nesting-doll cosmology was wrong. In the long run, then, these ecclesiastical prohibitions opened a surprising space of intellectual freedom, one that eventually led to the wholesale abandonment of Aristotelian physics in the late seventeenth century.18 However coercive the Condemnations of 1277 may have been, they eventually prompted a

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shift in thinking so radical that Pierre Duhem calls them “the birth certificate of modern physics.”19 But, of course, the first three hundred years of “modern physics” never went so far as to teach that there were multiple worlds. Neither, as it turned out, did the Scholastics after 1277. Rather, reading Condemnation 34 as closely as possible, they found a number of ways to argue that although God could create worlds other than this one, he never would. For the sake of clarity, these strategies can be grouped into two. The authors one might call “voluntarist” held to Aristotelian physics even as they accepted the bishop’s chastisement, arguing that although the laws of nature preclude the existence of more than one world, an omnipotent God could decide to override the laws of nature if he so wanted.20 The “naturalist” authors, by contrast, used the Condemnations as an opportunity to undermine the very principles of Aristotelian physics. By attacking the De caelo’s two proofs of cosmic singularity, they argued that other worlds could exist in full accordance with the laws of nature. For example, they maintained, other worlds might be composed of different elements, with different sorts of motion.21 Or even if the materials were the same, another world’s “earth” and “fire” might move down and up with respect to that world alone, preventing any conflict between “natural” and “unnatural” motion.22 Finally, they argued, it is senseless to say that all the matter in existence has been used up on this world because an omnipotent God can always make more. In a strange turn of events, then, the very teaching that Lucretius found inimical to the plurality of worlds came back in the late medieval period to support it: if God created one world ex nihilo, then God could create any number of them ex nihilo. “In order to establish this position,” wrote Richard of Middleton (1249–1302), “one can invoke the sentence of Lord Etienne . . . he has excommunicated those who teach that God could not have created several worlds.”23 We would therefore do well to teach that he could have.

For all their daring flirtations, however, none of these authors dared to assert the existence of other worlds. Rather, at some point in each of their arguments, one finds the sort of “standard disclaimer” issued by Nicole Oresme (ca. 1320/25–1382) in Le livre du ciel et du monde (1377): although God in his omnipotence could create and care for numerous worlds (Oresme was particularly taken with the possibility that there might be smaller worlds embedded concentrically within our world, which might itself be embedded within larger ones), “there never has been nor will there be more

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than one world.”24 Voluntarists and naturalists alike, the late Scholastics exhibited what Steven Dick calls a “uniquely medieval mixture of boldness and conservatism”:25 they went to extraordinary lengths to defend the possibility of other worlds but would not even contemplate the actuality of those worlds. The upshot of this medieval mixture was that although these authors called into question almost all of Aristotle’s cosmological principles, they left his cosmic geography in place. At the close of the fourteenth century, Europe still imagined the world as a set of concentric circles with earth at the center; rings of water, air, and fire surrounding it; and a halo of “fixed stars” moving calmly around the circumference once a day. These stars were held to be the Primum Mobile, or “first moved” of the cosmos. Set in motion by the prime mover itself, the fi xed stars then conferred movement on the lesser cosmic bodies within their bounds.

This motive gradation allowed the Aristotelian cosmos to be mapped onto the Neoplatonic “Chain of Being” in which physical position was thought to coincide with spiritual rank. Of this worldview, Ernst Cassirer explains that “the higher an element stands in the cosmic stepladder, the closer it is to the unmoved mover of the world, and the purer and more complete its nature.”26 The realm of the stars, made of an incorruptible “fifth essence” (quinta essentia), was thought to be nearest to God, whereas the corruptible earth was farthest away; here we might recall Dante’s journey from the inferno at the center of the earth, up the purgatorial mountain, to the stars at the gates of paradise (figure 3.1).27 On the earth itself, the beings that participate most fully in divine intellect are ranked above the others—hence, the superiority of angels to humans, humans to animals, men to women, and reason to the passions. And so cosmology recapitulates theology: as Thomas insisted, the order of the universe mediates the singular God down through the hierarchical ranks of the singular cosmos. This means that if any of these terms were to be challenged, the rest would have to change as well. Any real departure from Aristotle’s tidy circles would need to reconsider the singularity of God, the singularity of the cosmos, and its hierarchical arrangement. It is therefore striking that this departure initially came from within the Christian theological tradition itself. The thinker who genuinely abandoned Aristotelian cosmology was not Nicolaus Copernicus, who put the sun at the center of the universe in 1543, but Nicholas of Cusa, who declared a hundred years earlier that the universe had no center at all.

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Figure 3.1 The Dantean universe. (Adapted from Michelangelo Caetani, La materia della “Divina Commedia� di Dante Alighierie [Monte Cassino, 1855])