aquinas and the multiverse

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NAVIGATING THE INFINITE

My God, you are absolute infi nity itself, which I perceive to be the infi nite 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 infi nite things, because I could clearly see it from every point in the cosmos.

JORGE LUIS BORGES, “THE ALEPH”

Ending the Endless: Th omas 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 infi nite num-ber of them? Th e author of the question is Th omas 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 fi nd Th omas in the Summa theologia e , 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 millen-nium 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 trans-lated, debated, and made the object of lengthy scholastic commentaries. 2 Among these newly recovered manuscripts was the De c aelo , which was translated from Arabic into Latin in 1170. As we saw in chapter 1, this text

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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 re-spect to our world, even as it moved naturally “down” with respect to its own. “Th is, however, is impossible,” he says, because it is the property of earth to move down. 3 Elements cannot move both naturally and unnatu-rally at once, so “it follows that there cannot be more worlds than one.” 4 With the rediscovery of the De c aelo , medieval Europe thus possessed a seemingly defi nitive argument for the singularity of the cosmos, one that reaffi rmed the teachings of Platonists and church fathers alike.

Th is agreement notwithstanding, Aristotle also held cosmological posi-tions that contradicted the received teachings of medieval Europe—per-haps most problematically concerning the eternity of the cosmos. 5 Here we might recall Augustine’s insistence that the world could not be eternal with-out compromising the singularity of God: if God alone is God, then nothing else can exist alongside him. Th us began centuries of Latinate eff orts to evaluate Aristotelian cosmology in the light of Christian theology, with the universities’ “secular masters” ready to adopt Aristotle wholesale, the Francis-cans looking to abandon any position that seemed to contradict scripture, and the Dominican Th omas Aquinas working to reconcile the two. 6 In this era of intellectual fervor, even the most fi rmly 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 tenta-tively engaged fi ve 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 cos-mological concern was to uphold the sovereignty of God with respect to creation. Th is 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 Th omas 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,” Th omas reasons, “He could create many, since His power is not limited to the creation of one world; but rather is infi nite” (1.47.3). 8 Indeed, the infi nity of God’s power might even lead us to posit an infi nite number of worlds.

Yet just as an eternal world would threaten God’s singularity, Th omas seems concerned that infi nite worlds might rival his infi nity. Indeed, a


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standoff between material and divine infi nity can be seen as early as Ques-tion 2 of the Summa , in which Th omas proves the existence of God based on the absurdity of an infi nite causal regress. “Whatever is in motion must be put in motion by another,” he argues in the fi rst of his fi ve 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 infi nity , because then there would be no fi rst mover, and, consequently, no other mover. . . . Th erefore it is necessary to arrive at a fi rst 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, Th omas aligns “everyone’s” God with Aristo-tle’s prime mover: the extracosmic stopgap that prevents the causal march to infi nity. God puts an end to worldly endlessness. How, then, could there be an endless number of worlds? Where is the place for a fi rst mover if worlds extend backward eternally?

In short, the doctrine of a plurality of worlds threatens Th omas’s whole theological infrastructure: if worlds have existed from eternity, then there is no starting point for God to occupy. In the Summa , Th omas therefore raises the possibility of a cosmic plurality, only to launch a multipronged attack against it. He calls briefl y on the Gospel of John (“ ‘the world was made by Him,’ where the world is named as one ”), off ers a brief para-phrase of the De c aelo ’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, Th omas lines up the usual sources of authority against cosmic multiplicity: scrip-ture, 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, Th omas imagines, but doing so would compromise his unity.

Th e argument proceeds as follows: all things come from God, and all things fi nd their end (terminus) in God. Th is means that “[w]hatever things come from God, have relation of order to each other, and to God him-self.” 10 Th is “relation of order” denotes the hierarchy of creation—the Neo-platonic “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, Th omas calls on this ordered relation to demonstrate the oneness of God: the unity of creation, he argues, testifi es


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to the unity of its creator (1.11.3). In the question at hand, the demonstra-tion 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. Th e 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 off ers the example of “Democritus, who said that this world, besides an infi nite num-ber of other worlds, was made from a casual concourse of atoms” (1.47.3). To affi rm an infi nity 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), infi nite worlds would mean the absence of end; there would be no single source, no fi nal 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 argu-ment echoes of Augustine, who likewise rejected cosmic infi nity because of its endlessness. A soul destined to recurring embodiment, he feared, would never fi nd its rest in God. 12 To his credit, Th omas has arguably found fi rmer ground for his rejection than the Augustinian “heaven for-bid”: if all things have their end in one God, he reasons, then all things must belong to one world. Th omas may well have adapted this strategy from Book Lambda of Aristotle’s Metaphysics , which asserts that the cos-mos 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 con-cluded, producing either forty-seven or fi fty-fi ve prime movers in the pro-cess of trying to secure one and opening in spite of itself onto just as many worlds. Th omas’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 Th omas may align them, his God diff ers from the prime mover in not being simply one. His God is rather three-in-one, an eternal interrelation of identity and diff erence. 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?

Th is might be a compelling possibility, but it would be unacceptable to Th omas for two reasons. First, he insists on the priority of identity over diff erence 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, Th omas 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 fi rst assumption, then the second moves as well: if the Christian God is eternally triune, then God is not single fi rst and plural afterward, but eternally pluri - singular . What, then, would prevent such a God from creat-ing 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 refl ect God’s many-oneness more fully than a single world would?

It is perhaps for this reason that Th omas shifted his strategy the next and last time he addressed the question of multiple worlds. Two years be-fore the end of his life, he wrote a detailed commentary on the De c aelo 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, Th omas 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 jus-tice 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 Th omas’s approaches succeeded in putting cosmic multiplicity to rest. A mere three years after Th omas’s death in 1274, Bishop Etienne Tempier of Paris issued a list of 219 heretical Aris-totelian teachings, among which was Condemnation 34: “Quod prima causa non posset plures mundos facere.” 17 Anyone who taught that “the fi rst Cause cannot make many worlds” would henceforth be excommuni-cated for undermining the absolute power of God. And so the Scholastics of the late thirteenth century and the fourteenth century could not rest with Th omas’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 intel-lectual 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 cer-tifi cate of modern physics.” 19

But, of course, the fi rst 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. Th e 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 Th e “naturalist” authors, by contrast, used the Condemnations as an opportunity to undermine the very principles of Aristotelian physics. By attacking the De c aelo ’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 diff erent elements, with diff erent sorts of motion. 21 Or even if the materials were the same, another world’s “earth” and “fi re” might move down and up with respect to that world alone, pre-venting any confl ict 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 fl irtations, however, none of these authors dared to assert the existence of other worlds. Rather, at some point in each of their arguments, one fi nds the sort of “standard disclaimer” issued by Nicole Oresme (ca. 1320/25–1382) in Le l ivre 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 bold-ness and conservatism”: 25 they went to extraordinary lengths to defend the possibility of other worlds but would not even contemplate the actual-ity of those worlds. Th e upshot of this medieval mixture was that al-though these authors called into question almost all of Aristotle’s cosmo-logical principles , they left his cosmic geography in place. At the close of the fourteenth century, Europe still imagined the world as a set of concen-tric circles with earth at the center; rings of water, air, and fi re surround-ing it; and a halo of “fi xed stars” moving calmly around the circumference once a day. Th ese stars were held to be the Primum Mobile, or “fi rst 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.

Th is 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 Th e realm of the stars, made of an incorruptible “fi fth essence” ( quinta essentia ), was thought to be nearest to God, whereas the corruptible earth was farthest away; here we might recall Dante’s jour-ney from the inferno at the center of the earth, up the purgatorial moun-tain, to the stars at the gates of paradise (fi gure 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 ani-mals, men to women, and reason to the passions. And so cosmology reca-pitulates theology: as Th omas insisted, the order of the universe mediates the singular God down through the hierarchical ranks of the singular cosmos. Th is 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 tradi-tion itself. Th e thinker who genuinely abandoned Aristotelian cosmology was not Nicolaus Copernicus, who put the sun at the center of the uni-verse in 1543, but Nicholas of Cusa, who declared a hundred years earlier that the universe had no center at all.

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

aquinas and the multiverse

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