Why Does the World Exist?: An Existential Detective Story

by Jim Holt

  Now, a maximally great being is one whose greatness is unexcelled in every possible world. Such a being would, if it existed, be omniscient, omnipotent, and perfectly good. And there would be no possible state of affairs in which these maximal qualities were in any way diminished. It follows that such a being could not be merely contingent, existing (like Napoléon) in some possible worlds and not others. If such a maximally great being existed at all, it would exist necessarily, in every possible world.

  For brevity’s sake, let us call such a maximally great being “God.” So far, so good. Now comes the twist. Does God exist? “Almost certainly not,” an atheist like Richard Dawkins would say. But even Dawkins concedes that, improbable as God’s existence might be, it is at least possible that there is a God—just as it is possible (but highly unlikely) that there is a celestial teapot in orbit around the sun.

  But this is a fatal concession for the atheist to make. To say it is possible that a celestial teapot is orbiting the sun is to say that in some possible world such a teapot is orbiting the sun. And to say it is possible that God exists is to say that in some possible world there is a God. But God is different from a teapot. He is by definition a maximally great being. Unlike a teapot, his greatness—and therefore his existence—is stable across different possibilities. So if God exists in some possible world, he must exist in every possible world—including the actual world. In other words, if it is even possible that God exists, then it is necessary that he exists.

  That is the rather breathtaking conclusion of the modal ontological argument. And it is an entirely valid one, at least within the framework of modal logic. (To be specific, it is valid in the system of modal logic known in the trade as “S5.”) As Plantinga correctly observes, “It breaches no laws of logic, commits no confusions and is entirely immune to Kant’s criticism.”

  Unlike Anselm’s ontological argument, the modal version does not take existence to be a predicate or a perfection. It does take necessary existence to be a perfection, but that is entirely plausible. Whereas existence is not a great-making quality—everything has it, after all—necessary existence obviously is great-making. To exist necessarily means that your existence depends on nothing else. It could not have been prevented. You are immune from the possibility of annihilation. Finally, and not least among its virtues, the modal ontological argument holds out the hope of answering the question Why is there something rather than nothing? If God is possible, it says, then God is necessary—and hence nothingness is impossible.

  Is God possible? Or—to put it in the jargon of the modal ontological argument—is maximal greatness possibly exemplified? Think a bit about what “maximal greatness” means. A maximally great being is one that, if it exists in any possible reality, exists in all of them. It’s analogous to a being that, if it can be found anywhere in the world, manages to be everywhere, including here; or to a being that, if it exists at any moment in history, must exist at all moments, including the present one. A maximally great monarch would be one who, if he had a kingdom anywhere in the universe, would reign over the entire universe. A maximally great man, if he ever lived, would live eternally.

  Clearly, maximal greatness is well beyond the realm of the familiar. How then could we know that such a thing is possible? Gödel concocted an elaborate argument to prove that the idea of a maximally great being was not inherently self-contradictory (the way, say, the idea of the largest number is inherently self-contradictory). Hence, Gödel concluded, such a being is logically possible. And since the range of possible worlds covers every logical possibility, there is a world that contains a maximally great being. But if such a being exists in any possible world, it must exist in every possible world—including our own, the actual world.

  Unhappily for partisans of the ontological argument, this logic cuts both ways. There is nothing inherently self-contradictory either in the supposition that a maximally great being does not exist. Indeed, Plantinga himself refers to the property of there not being a maximally great being by the term “no-maximality.” So, by parity of reasoning, there must be a possible world in which no-maximality is exemplified—that is, one in which maximal greatness is absent. But if God is absent from any possible world, he is absent from all possible worlds—in particular, he is absent from the actual world.

  So which will it be? If, in the framework of modal logic, we accept the premise that God possibly exists, then we are committed to the necessity of his existence. If we accept the premise that God possibly does not exist, then we are committed to the impossibility of his existence. Both can’t be true. Yet, from a purely logical perspective, the possibility of God’s existence seems no more compelling than the possibility of his nonexistence. Should we simply flip a coin to decide which premise to accept?

  Recognizing the force of the counterargument, Plantinga has conceded that “a sane and rational man” might well reject the premise that a maximally great God is possible, and that the “canny atheist” will certainly do so. Without that premise, of course, this contemporary version of the ontological argument collapses. Nevertheless, Plantinga advocates accepting the premise in the interests of “simplifying” theology—the way one might accept a wild-sounding premise of quantum theory in the interests of simplifying physics.

  Critics of the modal ontological argument will have none of this. “The premise that it is just possible that there should be something unsurpassably great looks innocent,” observed the Oxford philosopher (and staunch atheist) John Mackie. But this premise, he warns, is a Trojan horse: “Anyone who is not already and independently persuaded that traditional theism is true has good reason to reject the key premise” of the modal ontological argument. Thus, although the argument may be “interesting . . . as a logical peculiarity,” Mackie said, it is “worthless as a support for theism.”

  There is a deeper issue lurking here. Could logic alone answer the question Why is there something rather than nothing? Can pure thought secure the existence of a positive reality that necessarily prevails over nothingness? “Every philosopher would like to say yes,” Bertrand Russell observed, “because a philosopher’s job is to find out things about the world by thinking rather than observing.” If “yes” is the right answer, Russell added, then there is a “bridge” from pure thought to concrete existence.

  How sturdy is the bridge offered by the ontological argument? The God it purports to deliver is a necessary being. His existence is a truth of pure logic, a tautology. But tautologies are empty propositions. Since they are true regardless of how reality is, they are devoid of explanatory content. How could such a tautological divinity be the fons et origo of the contingent world we see around us? How could a tautology exercise free will in creating it? The gap between necessity and contingency is no less difficult to bridge than the gap between being and nothingness.

  The God of Richard Swinburne is most decidedly unlike the God of the ontological argument. Swinburne’s God is not the product of logic. He has a free will that transcends any tautology. He exists in time. He is not even maximally great, at least in the sense demanded by the ontological argument, since his omniscience is limited by his inability to know in advance how we, his creatures, will exercise our own free will. He is a fitting ontological foundation for a contingent world. Yet he himself has no ontological foundation. His essence does not include existence. His being is not logically necessary. He might not have existed. There might have been no God, nothing at all.

  Swinburne posits such a God because, he claims, that is the “simplest stopping point” in the task of explaining the existence of the world and the way it is. The God hypothesis is the one that minimizes the part of reality that is left unexplained. But by positing God, Swinburne has added a new and unexplained element to the picture. Kant was right: the cosmological argument for God’s existence works only when it is backed up by the ontological argument. If the ontological argument fails, God is not a necessary, and therefore self-explanatory, being. Then the child�
�s seemingly naive question—“But Mummy, who made God?”—remains a live one. Which raises a tantalizing thought: could there be some deeper explanatory factor that encompasses both the world and—if he really exists—God too? How deep can explanation go?

  There was another man in the Oxford vicinity who, I had heard, was qualified to answer that question. But, before I could talk to him, it seemed that I myself had some explaining to do.

  7

  THE MAGUS OF THE MULTIVERSE

  What if there is no limit to what can be explained? What if reality turned out to be comprehensible through and through? Indeed, what if reality were to mandate its own comprehensibility?

  Sheer fantasy, you might say, an epistemic pipe dream. Only a fool could believe that reality can be made to yield up all its secrets to creatures like us living within it.

  Yet I knew there was someone in the vicinity of Oxford who did believe this, someone who was far from being a fool. His name is David Deutsch, and he is widely regarded as one of the most daring and versatile scientific thinkers alive. “Deutsch seems more passionate about what reality is, about what actually exists and why, than almost any other scientist I can remember meeting,” one veteran journalist wrote of him. And Deutsch is also a man with a singular achievement to his credit: in 1985, he demonstrated the theoretical existence of a universal quantum computer—a computer capable of simulating any physically possible reality.

  The idea of a computer that would harness the weird power of quantum mechanics was not original to Deutsch. It was Richard Feynman who, around the beginning of the 1980s, first seems to have dreamed it up. At the time, Deutsch had recently graduated from Cambridge University. Having barely scraped a “pass” degree in mathematics, he traveled to the United States, where he sought out distinguished physicists like John Archibald Wheeler and Bryce DeWitt.

  While studying how quantum fields behave in curved spacetime, Deutsch became obsessed with the “many worlds” interpretation of quantum theory. This interpretation was the 1950s brainchild of Hugh Everett III, a Princeton graduate student who went on to become a strategic planner at the Pentagon before dying in 1982. According to the many-worlds interpretation, our universe is merely one among a vast ensemble of alternate universes—a multiverse—all of them interacting in a ghostly way to produce otherwise inexplicable quantum phenomena.

  What would happen, Deutsch wondered, if quantum mechanics was applied to computer science? Might all the different parallel universes in the multiverse be coaxed into collaborating on a single computation?

  Deutsch took as his starting point the classical theory of computability, which had been pioneered in the years before the Second World War by the Englishman Alan Turing. Among Turing’s discoveries was a program for a “universal” computer, one that would be capable of mimicking to perfection the output of any special-purpose machine. Deutsch set about recasting Turing’s work in quantum terms. In doing so, he managed to construct a quantum version of Turing’s universal computer—that is, a single quantum operator (or “Hamiltonian,” as it is known in the trade) that can do the work of any conceivable computing machine, whether a conventional computer of the kind now in use or a quantum computer as envisaged by Feynman. And Deutsch’s universal quantum computer had another marvelous property: in principle, it could simulate any physically possible environment. It was the ultimate “virtual reality” machine.

  Deutsch, who was in his early twenties at the time (he was born in Israel in 1953), later downplayed his proof of the existence of a universal quantum computer as “fairly straightforward.” He went to Caltech to present it to Richard Feynman, who was already suffering from the cancer that would kill him in 1988. After Deutsch had written the first bits of his proof on the blackboard, the ailing Feynman startled him by jumping out of his seat, grabbing the chalk, and finishing it himself.

  For Deutsch, a universal computer had become nothing less than the key to understanding reality. Such a machine, being able to generate all physically possible worlds, would be the consummation of physical knowledge. It would be a single, buildable physical object that could describe or mimic with perfect accuracy any part of the quantum multiverse. And since it was possible to build a universal computer, Deutsch concluded, such a machine must actually be built somewhere in the multiverse. Omniscience exists!

  Such speculative flights come quite naturally to Deutsch, who, after returning to England from the United States, was appointed to be a research physicist at Oxford’s Clarendon Laboratory. In 1997, he laid out his worldview in a book titled The Fabric of Reality. To achieve a deep scientific understanding of reality, he argued therein, we must use not only quantum mechanics and the theory of computation, but also the theory of evolution. (He credits Richard Dawkins as one of his intellectual heroes.) Life and thought, he declared, determine the very warp and woof of the quantum multiverse. Whereas physical structures, like constellations and galaxy clusters, vary randomly from one universe to the next, knowledge-bearing structures—embodied in physical minds—arise from evolutionary processes that ensure they are nearly identical across different universes. From the perspective of the quantum multiverse as a whole, mind is a pervasive ordering principle, like a giant crystal.

  Clearly, here was a man who aspired to a complete understanding of what he was pleased to call the “fabric of reality.” Would that complete understanding encompass the mystery of existence itself? Would it yield an answer to the question Why is there something rather than nothing? I ardently hoped to find out. I had reviewed Deutsch’s book years ago in the Wall Street Journal—favorably, as I dimly recalled. Surely, I thought, he would be willing to talk to an admirer such as myself, especially one who had taken the trouble to come all the way to Oxford. So I e-mailed him, introducing myself and mentioning the nice review I had given his book in the United States more than a decade ago.

  “I just checked on Google,” Deutsch e-mailed me back. “Arrogant in tone and marred by leaps of logic—is that the one?”

  Oh dear. My memory seemed to have played me false. I googled the review myself. The full sentence he had quoted read, “Arrogant in tone and marred by leaps of logic, his book nonetheless bristles with subversive insights about virtual reality, time and time travel, mathematical certainty, and free will.” That didn’t sound so bad. In the review I had also called Deutsch “mad, bad, and dangerous to know”—a description originally applied to Lord Byron. E-mailing him again, I pointed out that this was meant, in a somewhat jocular vein, as a compliment.

  “In my opinion Byron was literally mad, bad, and dangerous to know, not least because he was a willfully careless thinker,” Deutsch replied in a second e-mail. “So I don’t consider being compared to Byron to be any sort of compliment.”

  This wasn’t going well. But when tact and flattery fail, I have found, abject groveling sometimes succeeds. So, gushing apology, I simply implored him to meet me.

  “No problem, I’d be interested to have a chat,” he replied. “But I’d like something in return. Please let me know specifically what the first leap of logic in The Fabric of Reality is, and the place where it first becomes clear to you that its tone is arrogant.”

  Fortunately, I had brought along to Oxford my old reviewer’s galley of the book. Holed up in my minuscule hotel room on the High Street near Logic Lane, I spent a stressful afternoon trying to decipher the critical comments I had long ago illegibly scribbled in the galley’s margins. Finally I found what seemed to me a “leap of logic.” Deutsch’s “Turing principle” implied that there is no limit to the number of computational steps that are physically possible. And that, in turn, implied that universe must eventually collapse upon itself in a Big Crunch, since only such a fiery ending could furnish the infinite energy needed for infinite computation. So, Deutsch concluded, such a Big Crunch must be our cosmic fate. But that can’t be right, I thought. Current cosmological evidence points to a contrary fate for our universe: rather than eventually collapsing upon itse
lf, it will expand forever, dissipating into a chilly void. If Deutsch’s logic entailed the opposite conclusion, surely there must have been an unjustified leap in it somewhere.

  I e-mailed Deutsch to this effect. He conceded that there might be something to my criticism, while observing that it applied to a claim he had made rather late in the book. “Could it be that the first leap of logic was in the last chapter?” he asked.

  Nevertheless, he was gracious enough to invite me to his house for tea. And, after fleetingly entertaining the paranoid suspicion that he might be out to poison me—an author’s fit revenge against an impertinent reviewer—I accepted.

  It turned out that Deutsch did not actually live in Oxford, but in a nearby village called Headington, where, an Oxford friend informed me, J. R. R. Tolkien and Isaiah Berlin had made their homes. I decided to go there on foot. Crossing the Magdalen Bridge over the Cherwell, I paused for a moment to watch some students floating lazily down the river in their punts. Then I rounded a traffic circle at the city limits and followed the curving road up a hill, making my way along an ancient-looking stone wall. A woman cyclist passed me on the road, with a log and some tree branches strapped to her bike, which reminded me of the “log lady” in Twin Peaks. After continuing on a few miles, I attained a sort of plateau, where I came upon a collection of little brick houses, a restaurant called Café Bonjour, and a Domino’s Pizza parlor. This was Headington.

  Upon reaching the address Deutsch had given me, I found a small two-story house hidden behind some shaggy trees. A trio of flags hung from the front of the house—British, Israeli, and American. A junked TV set sat outside. I tried the doorbell, but it didn’t work. So I rapped on the dimple-frosted glass.

  After a few moments, the door was opened by an improbably boyish-looking fellow with large mole-like eyes, rather transparent skin, and shoulder-length, albinoid hair. Behind him, I could see great moldering heaps of papers, broken tennis rackets, and other detritus. I knew that Deutsch was famous for, as one science journalist put it, “setting international standards in slovenliness,” but these looked more like experiments in indoor composting.