For many physicists and philosophers, one of the most attractive features of “multiverse” cosmologies is that they render “God” unnecessary. If there is only one universe, then we have to ask why it has the specific properties it has—especially insofar as these values seem “fine-tuned” to condition the existence of planets, stars and eventually, life. In the face of such a single, biophilic cosmos, one might say the only satisfying explanation is that there is an intelligent, benevolent creator outside the universe who sets the controls “just right” so that life might emerge within it. If, on the other hand, there are an infinite number of worlds that take on all possible parameters throughout infinite time (a rough sketch of the most popular multiverse scenario), then like Shakespeare tumbling from monkeys at typewriters, our elegant universe was bound to emerge eventually.
There is, then, a profoundly non-theistic, sometimes even anti-theistic, motivation behind the scientific turn to multiple-worlds scenarios; as physicist Bernard Carr has summarized the matter, “if you don’t want God, you’d better have a multiverse.” Ironically, however, the multiverse collides with the “G”-word precisely in its effort to avoid it. In its fervor to circumvent the specific theological postulate of an extra-cosmic God, the multiverse becomes its own sort of constructive theology, blurring the very lines it seeks to maintain between physics and metaphysics.
Such a multiversal theology is clearest in those multiple-worlds scenarios that reimagine the gods as great cosmic Simulators, or as Designers of baby universes in black holes. But even those models that explicitly repudiate any humanoid creator rely fundamentally on elements that are unobservable not only in practice but in principle. In short, even the most conservative model of the multiverse displays a remarkable faith in what St. Paul might call “things hoped for and unseen,” and in this sense, functions pseudo-theologically.
The simplest and least controversial model of the multiverse is called the “quilted” scenario, or “Level I” multiverse. It is a hypothetical ensemble of universes that look more or less like ours, but are too far away for light to have traveled since the Big Bang. In recent years, both observational astronomy and theoretical cosmology have been indicating that spacetime itself seems to be infinite. And if spacetime is infinite, then there is no end to the universes within the quilted multiverse.
In short, this model says that when the Big Bang banged, it produced an infinite number of regions of spacetime, each of which could call itself a universe. And from here, things get even more remarkable. Because even if there is an infinite amount of “stuff” and spacetime out there, there are only a finite number of ways to arrange that stuff. So while the number of universes is infinite, the number of types of universes, while unassimilably huge, is finite.
It could be that the universe is shaped like a gargantuan doughnut, or torus, so that if you were to run to the “edge” of the universe, you would come back around the other side.
This means that somewhere “out there,” there is a person just like you, with your name, career, and history, but with slightly redder hair and a nicer car (Max Tegmark estimates that your closest doppelganger is no farther than 101028 meters away. This is an unfathomable distance, but it is nonetheless finite.) And somewhere out there, there is a person with your name, career, history, hair, and car, who has just this moment decided to get up and make herself tea while you stay at your desk. And somewhere out there, there you are, in all your complexities, exactly like this, both of you furrowing your brow at the thought that there’s another one of you furrowing your brow. In fact, somewhere out there is a whole universe exactly like ours—a duplicate Hubble volume with the same clusters of galaxies, the same Milky Way, the same Crab Nebula, the same lonely earth circling a brilliant sun, and the same tragic “flavor graveyard” at the Ben and Jerry’s factory in Waterbury, VT. Tegmark estimates that we could find such a duplicate universe about 1010118 meters away; a much greater distance than your nearest almost-twin, but probably no more unfathomable (I, at least, don’t know how to tell the difference between 101028 and 1010118.)
Again, this compendium of universes beyond our Hubble volume is the least controversial formulation of what one might call the multiverse—and yet it rests on two claims that are fundamentally undemonstrable, and in this sense strains the limits of modern science.
The first is that spacetime is infinite. To be sure, it looks infinite—which is to say, space looks as though it is either flat or very close to flat in three dimensions—but observers have not and cannot prove that this flatness goes on forever. It could be that the universe is shaped like a gargantuan doughnut, or torus, so that if you were to run to the “edge” of the universe, you would come back around the other side. If this were the case, then light itself would eventually “lap” the universe, and our telescopes would be able to see the same galaxies repeated at different stages of their lives. Teams of researchers are currently seeking such patterns in the sky, but so far, they haven’t found any. If such images were ever to be discovered, they would demonstrate the finitude of the cosmos.
If such images are never discovered, however, this non-discovery will never amount to a proof of cosmic infinity—just cosmic enormity. It will always be possible that an infinite-looking universe is really finite, but so large that we will never live long enough to see light looping back on itself. So again, it is impossible not just in practice, but in principle to prove the infinity of the cosmos; as John Barrow puts it, “you can discover whether the Universe is infinite, but the learning will take an infinite time.”
In their efforts to shore up scientific orthodoxy (no God at all costs), multiverse cosmologies welcome every major component of religious orthodoxy.
The second article of faith subtending this “quilted” multiverse is the assumption that regions of spacetime beyond our own are filled with the same kind of matter and energy as ours. This assumption is known as the “cosmological principle”: it states that, on the largest scales, matter and energy are evenly distributed throughout the universe. But while observations have confirmed that this principle holds for our Hubble volume, they can never confirm that it holds for regions outside of this bubble; after all, anything outside our observable universe is in principle unobservable. Granted, the cosmological principle might be a good guess, especially at short distances from us, but as South African cosmologist George Ellis has argued, it becomes a worse and worse guess the farther “out” one ventures.
These, then, are at least two of the “things hoped for and not seen” subtending this least controversial multiverse: cosmic infinity and cosmic homogeneity. It is by no means clear that regions far beyond our own would look more or less like our own, forever, and yet without these assumptions, there is no multiverse. And while the multiverse might free us from having to believe in an extra-cosmic God, it commits us to believing in extra-cosmic worlds. Structurally, at least, these infinite worlds serve the same explanatory function as the infinite God: they are both unfathomable wellsprings from which this one remarkable universe eventually emerged.
Theologically, then, the debate over the multiverse becomes a comedy of errors. In their efforts to shore up scientific orthodoxy (no God at all costs), multiverse cosmologies welcome every major component of religious orthodoxy: from undemonstrable principles to other worlds to intelligent designers. This is not to say that there is or is not a multiverse, nor—crucially—is it to say that we may as well revert to the old Intelligent Designer, since “he” and the multiverse are functionally equivalent. To the contrary, recent developments in cosmology allow us to ask new questions about what counts as divinity and what we mean by “world.” Whether or not the multiverse “exists,” we can find in the idea of it—and in the testing of it—a reconfiguration of the boundaries of what counts as science, what intrigues us as religion, and what their stubborn entanglement makes it possible to think.
Mary-Jane Rubenstein is Associate Professor and Chair of Religion at Wesleyan University. This post is taken from her recent book, Worlds Without End: The Many Lives of the Multiverse from Columbia University Press.
 Cited in Tim Folger, “Science’s Alternative to an Intelligent Creator: The Multiverse Theory,” Discover December, 2008.
 Hebrews 11:1.
Jean-Pierre Luminet, Glenn D. Starkman, and Jeffrey R. Weeks, “Is Space Finite?,” Scientific American (April 1999).
John D. Barrow, The Infinite Book: A Short Guide to the Boundless, Timeless and Endless (New York: Vintage, 2005), 149.
George Ellis, “Does the Multiverse Really Exist?,” Scientific American (August, 2011).
Image from Flickr via theqspeaks