Why Does the World Exist?: An Existential Detective Story

by Jim Holt

  He beckoned me inside and led me past the piles of rubbish into a room with a large television and an exercise bike. On a sofa sat an attractive young woman with strawberry-blonde hair—she looked almost like a teenager—eating a plate of macaroni and cheese. Deutsch addressed her as “Lulie.” She moved over to make room on the sofa for me, and the conversation began, albeit on a discouraging note.

  “On the question of why there is something rather than nothing, I’m not sure I know anything apart from that joke,” Deutsch opened. “How does it go? Oh yeah—‘Even if there was nothing, you’d still be complaining!’ ”

  I told him the joke came from Sidney Morgenbesser, an American philosopher who had died a few years ago.

  “Haven’t heard of him,” Deutsch said.

  But how could Deutsch be so cavalier about the mystery of existence? After all, he didn’t believe that there was just one world. His view of reality encompassed a huge ensemble of worlds, all existing in parallel: a multiverse. The multiverse was for Deutsch what God had been for Swinburne: it was the simplest hypothesis that explained what we observed around us—notably, the weird phenomena of quantum mechanics. If the physical laws governing the multiverse mandated their own comprehensibility, as Deutsch believed, shouldn’t they also mandate the comprehensibility of reality as a whole?

  “I don’t think that an ultimate explanation of reality is possible,” he said, shaking his head. “That doesn’t mean I think there’s a limit to what we can explain. We’ll never run into a brick wall which says, ‘NO EXPLANATION BEYOND THIS POINT.’ On the other hand, I don’t think we’ll find a brick wall that says, ‘THIS IS THE ULTIMATE EXPLANATION FOR EVERYTHING.’ In fact, those two brick walls would be almost the same. If, qua impossibile, you were to have an ultimate explanation, it would mean the philosophical problem of why that was the true explanation—why reality was this way and not another—would be forever insoluble. Hello, I hear the water boiling!”

  He went into the kitchen. Lulie smiled at me and continued to pick at her macaroni.

  When Deutsch emerged a few moments later with a teapot and a plate of biscuits, I asked him whether he was puzzled at all by the existence of the multiverse. Was the question Why is there something rather than nothing? a profound one, or was it simply misguided?

  “Hmmm,” he responded, touching his temple, “. . . a deep question . . . a misguided question. . . . Look, I can’t rule out the possibility that there is a foundation for reality. But if there is, the problem of why that’s the foundation would still be insoluble.”

  He took a sip of tea and continued, “Take the ‘first cause’ argument, the idea that the existence of the world must be explainable by some sort of originating event. It’s hopelessly parochial! The idea that things are always caused by things that come before them in time has nothing to do with logic or explanation as such. You could imagine an explanation where something was caused by things happening at all different times, past and future. Or an explanation that didn’t have anything to do with time at all, or even with causes. The real question you want to answer is not what came before, but why something is the way it is.”

  I gingerly sipped at my cup of tea, which did not seem to be poisoned.

  “You can’t give a once-and-for-all definition of what an explanation is,” Deutsch said. “In fact, important explanatory advances often change the meaning of explanation. My favorite example is the Newtonian-Galilean revolution, which not only brought in new laws of physics, but also altered the very notion of what a physical law is. Previously, laws had been rules stating what happens. Kepler’s laws, for instance, were about how the planets traveled around the sun in elliptical orbits. Newton’s laws were different. They didn’t talk about planets or ellipses. Instead, Newton’s laws were rules that any such system would obey. It’s a different style of explanation, one that hadn’t been thought of before, one that wouldn’t even have been considered an explanation before. The same kind of explanatory revolution happened a couple of hundred years later with Darwin. Previously, when people asked, ‘Why does this animal have the shape it does?’ they expected that the answer would cite some property of the shape—that it was efficient, that it was favored by God, and so forth. After Darwin, the answer wasn’t about properties of the shape, but about how that shape had come into existence by evolution. Again, it’s a different style of explanation.”

  Deutsch paced back and forth as he spoke. I remained seated on the sofa next to Lulie, who had finished her plate of macaroni and cheese.

  “This point about the fluid nature of explanation is a real hobby horse of mine,” he continued, his voice gaining in intensity. “I think we’re going to need a different style of explanation to solve problems like free will and consciousness. These are fundamentally philosophical problems, not technical problems. I don’t think artificial intelligence will be achieved until philosophical progress is made in understanding what consciousness is. We couldn’t make artificial life without the concept of a replicator, and we don’t have the equivalent concept yet for consciousness. You can’t program what you can’t specify.”

  This struck me as refreshingly at odds with the prevailing orthodoxy of the artificial-intelligence community, whose members seemed to think that the mystery of consciousness would wither away with the advent of superintelligent computers, which was supposedly just around the corner.

  But back to the multiverse. Where did it come from? Why is there a “fabric of reality” at all?

  “To my way of thinking,” Deutsch said, “that question could only be answered by finding a more encompassing fabric of which the physical multiverse was a part. But there is no ultimate answer.”

  Could he then see what form that larger fabric of reality might take?

  “I would start with the principle of comprehensibility,” he said. “Look, there’s a quasar out there in space, billions of light-years away. And in our brain there’s a model of the quasar, a model that has remarkable properties. There’s not just an image of the quasar in our brain, there’s a structural model with the same causal and mathematical relationships. So here you have two objects that are physically as dissimilar as they could possibly be—a quasar, which is this black hole with jets, and our brain, which is chemical scum—and yet they embody the same mathematical relationships!”

  Interesting point, I interjected, but the relevance of it escaped me.

  “For that to happen, the laws of physics must have a very special property. They permit—they mandate—their own comprehensibility. And you can take this further. If it’s true that the world is comprehensible, that we’re capable of understanding it, then in order to understand the behavior of humans, you need to understand everything! Since the structure of quasars is represented in the brains of human scientists, the behavior of scientists depends on the behavior of quasars. To predict what papers a physicist will write next year, you have to know something about quasars. By the same argument, it follows that to know all truths about humans, you need to know all the truths there are.”

  Deutsch paused, as if to regather his thoughts. “We’re bootstrapping our way toward better and better explanations. And that’s why we can never have an ultimate explanation. Anything pretending to be an ‘ultimate’ explanation would be a bad explanation, because there would be nothing left over to explain why it was the right one—to explain why reality was that way and not another way.”

  Deutsch had long maintained that quantum theory was a key to understanding the fabric of reality. And in quantum theory, I observed, you can seemingly get Something from Nothing. A particle and its antiparticle, for instance, can spontaneously appear out of the vacuum. Some physicists have conjectured that the universe itself began as a vacuum fluctuation—that it “tunneled” into existence out of nothingness. Might quantum theory explain why there was a world at all?

  “Not the least!” he replied. “Quantum theory is too parochial to address the question of existence. When you talk ab
out a particle and an antiparticle appearing in the vacuum, that’s not at all like coming into existence out of nothing. The quantum vacuum is a highly structured thing that obeys deep and complex laws of physics. It’s not ‘nothingness’ in the philosophical sense at all. It’s not even as little as the kind of nothing you have in your bank account when there’s no money in it. I mean, there’s still the bank account! A quantum vacuum is much more even than an empty bank account, because it’s got structure. There’s stuff happening in it.”

  So the laws governing the quantum multiverse can’t tell us anything at all about why the multiverse exists?

  “No, none of our laws of physics can possibly answer the question of why the multiverse is there,” he said. “Laws don’t do that kind of work.” He recalled an image from the great John Archibald Wheeler, his onetime mentor. “Wheeler used to say, take all the best laws of physics and write them down on bits of paper and put those bits of paper on the floor. Then stand back and look at them and say, ‘Fly!’ They won’t fly. They just sit there. Quantum theory may explain why the Big Bang happened, but it can’t answer the question you’re interested in, the question of existence. The very concept of existence is a complex one that needs to be unpacked. And the question Why is there something rather than nothing? is a layered one, I expect. Even if you succeeded in answering it at some level, you’d still have the next level to worry about.”

  Click! My tape recorder switched off. Somewhat depressingly, it had reached the end of side B of the microcassette without registering a single genuine advance toward a resolution to the mystery of existence.

  Should I have been surprised? In the opening pages of The Fabric of Reality, after all, Deutsch had written, “I do not believe that we are now, or ever shall be, close to understanding everything there is.” Still, he had managed to impress one positive lesson on me: that there is a lot more to reality than we might imagine. The part of it that we inhabit not only is tiny, but also may be grossly unrepresentative of the whole, giving us a partial and distorted view. We are like the prisoners chained inside the cave of illusion in Plato’s famous allegory. It may even be—although Deutsch told me that he thought it improbable—that we exist within a simulated reality, one created by higher beings—beings who, like Descartes’s evil genie, have deliberately programmed it with the wrong laws of physics. Yet even if we were inmates confined to such a partial and distorted reality, our quest for understanding would eventually take us beyond its virtual walls.

  “It is not enough that the inmates be prevented from observing the outside,” he had written in The Fabric of Reality. “The rendered environment would also have to be such that no explanations of anything inside would ever require one to postulate an outside. The environment, in other words, would have to be self-contained as regards explanations. But I doubt that any part of reality, short of the whole thing, has that property.”

  But if the whole of reality were explanatorily self-contained, then it would presumably have to contain the explanation of its own existence, the reason for its triumph over sheer nothingness. So perhaps there was hope after all.

  I WAS A little sad to leave Deutsch. Despite the gelid beginnings of our acquaintance, he had revealed a real sweetness of character and intellectual generosity. And Lulie, sitting next to me on the couch with her plate of macaroni, auditing our conversation with keen interest, her adoring eyes fixed on Deutsch, seemed a very angel. I had even grown comfortable in the towering chaos of junk that surrounded me, coming to see it as an adventure in high-entropy housekeeping.

  As I made my solitary way along the highway back down to Oxford, a pinkish-orange ray of sunlight broke over the clouded horizon. The bells of the colleges were ringing in the distance again. I tried to picture myself as a denizen of Deutsch’s multiverse. In innumerable parallel worlds, my quantum counterparts were also descending such a hill, were also hearing such bells, were also rejoicing in such a brilliant display of sunlight as the late-winter day waned. And, like me, they were pondering the mystery of why the multiverse exists. Their thoughts—my thoughts—were embodied in a physical structure that extended, like a higher-dimensional crystal, across parallel universes. Surely one of these quantum counterparts, shadowing me somewhere in Deutsch’s vast fabric of reality, had made more progress than I had toward ultimate enlightenment. What thoughts could be running through his head? Or was the resolution to the mystery of existence somehow encoded in that crystalline structure as a whole, transcending the denizens of any particular quantum world?

  Just then a passing bus startled me by hooting its horn, and my vision of this unsubstantial pageant faded, leaving not a wrack behind.

  Interlude

  The End of Explanation

  Bertrand Russell, according to the philosophical lore, was once in the course of giving a public lecture on cosmology when he was interrupted by an old lady in the audience. “Everything you’ve been telling us is rubbish,” the lady vociferously objected. “The world is actually flat, and it’s supported by a giant elephant that is standing on the back of a turtle.” Russell, humoring her, asked what might support the turtle. The old lady replied, “It’s turtles all the way down!”

  When it comes to understanding reality, David Deutsch turned out to be something of a “turtles all the way down” man. Our explanatory quest will be unending, he maintained. There is no bedrock principle that explains absolutely everything (including the principle itself). There is no self-supporting “superturtle” holding up the tower of turtles above.

  But suppose Deutsch is wrong. Suppose there is an ultimate explanation for everything. What could such a principle look like? How would we know when we had reached it?

  It was Aristotle, in his logical work, Posterior Analytics, who first addressed this matter. There are three ways an explanatory chain might go, Aristotle observed.

  First, it might go in a circle: A is true because B, and B is true because A. (The circle might be widened by lots of intermediate explanatory truths: A because B, B because C, . . . Y because Z, Z because A.) But a circular explanation is no good. Saying “A because B because A” is a roundabout way of saying “A because A.” And no truth explains itself.

  Second, the explanatory chain might go on forever: A1 is true because A2, A2 is true because A3, A3 is true because A4, and so on, to infinity. But that’s no good either. Such an endless regress, Aristotle observed, supplies no ultimate explanatory foundation for knowledge.

  That leaves the third kind of explanatory chain, one that terminates in a finite number of steps: A1 because A2, A2 because A3, and so on, down to some final truth X. And what sort of truth could X be?

  There would seem to be two possibilities. First, X might be a brute fact, lacking any explanation of its own. But if X itself has no explanatory support, Aristotle remarked, it can hardly provide support for other truths. The second possibility is that X is a logically necessary truth, one that could not have been otherwise. And, for Aristotle, this was the only satisfactory way for an explanatory chain to end—the only alternative to circularity, infinite regress, and unjustified explanatory danglers.

  But—with due respect to Aristotle—how could a logically necessary truth really explain anything? In particular, how could it explain anything that is logically contingent—like the fact that there is a world? If the existence of a world could be deduced from a logically necessary truth, then it too would be logically necessary. But it isn’t. Although there is a world, there might not have been. Nothingness cannot be dismissed as a logical possibility. Even the most promising attempt to derive being from pure logic—the ontological argument for the existence of God—in the end comes to nothing.

  So, in our quest for total understanding, we cannot complete our explanatory chain with a logically necessary truth. We are therefore driven back to a choice among three evils: circularity, infinite regress, and brute fact. Of this trio, brute fact would appear to be the least objectionable. But is there any way the brute-fac
t dangler at the end of an explanatory chain can be made to seem less arbitrary? Can it be rendered less brutal?

  The Harvard philosopher Robert Nozick had an interesting proposal along these lines. The only way an explanation could leave nothing at all unexplained, Nozick began by observing, is if the final truth in the series were somehow self-explanatory. But how could a truth explain itself? “X because X” is an evasion of explanation rather than the real thing. No child is satisfied if you answer the question “Why is the sky blue?” by saying “Because it is.” We are back to the evil of circularity again. That is why philosophers from Aristotle to Richard Swinburne have staunchly maintained that nothing explains itself—that the explanatory relation is, to use the technical term, “irreflexive.”

  Nozick, however, saw more to the matter. He conceded that “X because X” is no good as an explanatory paradigm. But there is another way, he observed, that a truth might be deduced from itself. Let’s say our deepest principle—the one that explained all the laws of nature—turned out to have this form:

  Any law having characteristic C is true.

  Let’s call this deepest-of-all-principles P. The principle P explains why other laws hold true: because they have characteristic C. But what explains why P is true? Well, suppose that P turned out to have characteristic C. Then the truth of P would logically follow from P itself! In that case, principle P would be self-subsuming, to use Nozick’s term.

  “Self-subsumption is a way a principle turns back on itself, yields itself, applies to itself, refers to itself,” Nozick wrote. He admitted that explanatory self-subsumption is “quite weird—a feat of legerdemain.” However, compared to the alternatives—circularity, infinite regress, and brute-fact danglers—it doesn’t look so bad.