by Jim Holt
At its most fundamental, science describes the elements of reality in terms of their relations to one another, ignoring any stufflike quiddity those elements might possess. It tells us, for example, that an electron has a certain mass and charge, but these are mere propensities for the electron to be acted upon in certain ways by other particles and forces. It tells us that mass is equivalent to energy, but it gives us no idea of what energy really is—beyond being a numerical quantity that, when calculated correctly, is conserved in all physical processes. As Bertrand Russell noted in his 1927 book, The Analysis of Matter, when it comes to the intrinsic nature of the entities making up the world, science is silent. What it presents us with is one great relational web: all structure, no stuff. The entities making up the physical world are like the pieces in a game of chess: what counts is the role defined for each piece by a system of rules that say how it can move, not the stuff that the piece is made of.
The physicist’s view of reality, by the way, is remarkably akin to the view of language proposed over a century ago by Ferdinand de Saussure, the father of modern linguistics. Language, Saussure maintained, is a purely relational system. Words have no inner essence. The intrinsic character of the noises we make when talking is irrelevant to communication; the important thing is the system of contrasts among those noises. This is what Saussure meant when he wrote that “in language, there are only differences without positive terms.” Saussure’s elevation of structure over stuff was the inspiration for the structuralist movement that swept aside existentialism in France in the late 1950s. It was taken up in anthropology by Claude Lévi-Strauss and in literary theory by Roland Barthes. Its extension to the universe as a whole might well be called “cosmic structuralism.”
If reality were indeed pure structure, that would open up radically new ways of thinking about it. One of these is the way of Penrose and Tegmark. On their view, reality is in essence mathematical. Mathematics, after all, is the science of structure; it neither knows of, nor cares about, stuff. Worlds that are structurally the same but made out of different stuff are identical in the eyes of the mathematician. Such worlds are called “isomorphic,” from the Greek words isos (same) and morphe (form). If the universe is structure all the way down, then it can be exhaustively characterized by mathematics. And if mathematical structures have an objective existence, then the universe must be one of these structures. That, at least, seems to be Tegmark’s meaning when he says that “all mathematical structures exist physically.” If there is no ultimate stuff to reality, then mathematical structure is tantamount to physical existence. Who needs flesh when bones are enough?
A somewhat different take on a stuff-less reality is to see it as consisting not of mathematics but of information. This view is summed up in a slogan coined by the late physicist John Archibald Wheeler: “it from bit.” (Wheeler—who collaborated with Albert Einstein and taught Richard Feynman—had a gift for such coinages; he also gets credit for “black hole,” “wormhole,” and “quantum foam.”)
The it-from-bit story goes as follows. At bottom, science tells us only about differences: how differences in the distribution of mass/energy are associated with differences in the shape of spacetime, for example, or how differences in the charge of a particle are associated with differences in the forces it feels and exerts. States of the universe can thus be seen as pure information states. As the British astrophysicist Sir Arthur Eddington once put it, “Our knowledge of the nature of the objects treated in physics consists solely of readings of pointers on instrument dials.” The “medium” in which these information states are realized, whatever it might be, plays no role at all in the explanation of physical phenomena. Therefore, it can be dispensed with altogether—shaved away by Occam’s razor. The world is nothing but a flux of pure differences, without any underlying substance. Information (“bit”) suffices for existence (“it”).
Some it-from-bit proponents stretch this logic still further. They look on the universe as a giant computer simulation. Among those who have taken this view are Ed Fredkin and Stephen Wolfram, both of whom hypothesize that the universe is a “cellular automaton” that uses a simple program to generate complex physical outcomes. Perhaps the most radical cosmos-as-computer advocate is the American physicist Frank Tipler. The striking thing about Tipler’s vision is that it involves no actual computer: his cosmos is all software, no hardware. A computer simulation, after all, is just the running of a program; and a program, in essence, is a rule that transforms an input string of numbers into an output string of numbers. So any computer simulation—say, the simulation of the physical universe—corresponds to sequences of strings of numbers: a pure mathematical entity. And if mathematical entities have an eternal Platonic existence, then, on Tipler’s view, the existence of the world has been fully explained: “at the most basic ontological level,” he declares, “the physical universe is a concept.”
And what of the simulated beings who are somehow a part of that “concept”—beings like us? Would they realize that time was an illusion, that they were mere frozen bits of an eternal Platonic videotape? Not at all, according to Tipler. They would have no way of knowing that their reality consisted in being “a sequence of numbers.” Yet, oddly enough, it is their simulated mental states that endow the overall mathematical concept of which they are a part with physical existence. For, as Tipler writes, “this is exactly what we mean by existence, namely, that thinking and feeling beings think and feel themselves to exist.”
The picture of the universe as an abstract program—it from bit—strikes some thinkers as strangely beautiful. And it seems consistent with the way science represents nature, as a network of mathematical relations. But is that truly all there is? Is the world devoid of ultimate stuff? Is it indeed structure all the way down?
There is one aspect of reality that doesn’t seem to have a place in this metaphysical picture: our own consciousness. Think of the way a pinch feels, a tangerine tastes, a cello sounds, or the rosy dawn sky looks. Such qualitative experiences—philosophers call them “qualia” (the plural of the Latin singular quale)—have an inner nature that goes beyond their role in the causal web. So, at least, philosophers like Thomas Nagel have argued. “The subjective features of conscious mental processes—as opposed to their purely physical causes and effects—cannot be captured by the purified form of thought suitable for dealing with the physical world that underlies appearances,” Nagel writes.
One way of making this point vivid is due to the Australian philosopher Frank Jackson. Imagine, says Jackson, a scientist named Mary who knows everything there is to know about color: the neurobiological processes by which we perceive it, the physics of light, the composition of the spectrum, and so forth. But imagine further that Mary has lived her entire life in a black-and-white environment, that she has never actually seen a color herself. Despite her complete scientific understanding of color, there is something of which Mary is ignorant: what colors look like. She does not know what it is like to experience the color red. It follows that there is something to this experience—something subjective and qualitative—that is not captured by the objective, quantitative facts of science.
Nor, it would seem, can this subjective aspect of reality be captured by a computer simulation. Consider the theory called “functionalism,” which holds that states of the mind are essentially computational states. What defines a mental state, according to functionalism, is not its intrinsic nature, but rather its place in a computer flowchart: the way it is causally related to perceptual inputs, to other mental states, and to behavioral outputs. Pain, for example, is defined as a state that is caused by tissue damage and that, in turn, causes withdrawal behavior and certain vocalizations, like “ouch.” Such a flowchart of causal connections can be implemented in a software program, which, if run on a computer, would simulate being in pain.
But would this simulation duplicate what seems most real to us about pain: the horrible way it feels? To the philosopher John Sea
rle, the very idea seems “frankly, quite crazy.” “Why on earth,” he asks, “would anyone in his right mind suppose a computer simulation of mental processes actually had mental processes?” Suppose, Searle says, the program simulating the experience of pain were to be run on a computer consisting of old beer cans tied together with string and powered by windmills. Can we really believe, Searle asks, that such a system would feel pain?
The philosopher Ned Block has come up with another thought experiment along the same lines. He invites us to imagine what would happen if the population of China were to simulate the brain’s program. Suppose we got each Chinese person to mimic the activity of a particular brain cell. (There are only around a hundredth as many Chinese as there are cells in the human brain, but no matter.) Synaptic connections among the different cells could be simulated by cell-phone links among the Chinese. Would the nation of China, if it were to mimic the brain’s software in this way, then have conscious states over and above those of its individuals? Could it experience, say, the taste of peppermint?
The conclusion the philosophers who come up with these thought experiments want us to draw is that there is more to consciousness than the mere processing of information. If this is true, then science, insofar as it describes the world as a play of information states, would seem to leave out a part of reality: the subjective, irreducibly qualitative part.
One could, of course, simply deny that reality has such a subjective part. And there are philosophers who do deny it—Daniel Dennett, for one. Dennett refuses to concede that consciousness contains any intrinsically qualitative elements. As far as he is concerned, “qualia” are a philosophical myth. If something cannot be described in purely quantitative and relational terms, it is simply not a part of reality. “Postulating special inner qualities that are not only private and intrinsically valuable, but also unconfirmable and uninvestigatable is just obscurantism,” he declares.
Such denialism leaves philosophers like Searle and Nagel incredulous. It seems willfully blind to the very essence of what it means to be conscious. Nagel has written, “The world just isn’t the world as it appears to one highly abstracted point of view”—that is, to the scientific point of view.
The inner nature of consciousness yields one reason for thinking that there is more to the world than pure structure. But apart from the issue of consciousness, there are more general grounds for suspecting that cosmic structuralism is inadequate as a picture of reality. Structure by itself just doesn’t seem enough for genuine being. As the British idealist philosopher T. L. S. Sprigge put it, “What has structure must have something more to it than structure.” Perhaps Aristotle was right: you need stuff too. Stuff is what gives existence to structure, what realizes it.
But if that is true, how can we come to have knowledge of the ultimate stuff of reality? Science, as we have seen, reveals only how the stuff is structured. It does not tell us how the quantitative differences it describes are grounded in differences in any underlying qualitative stuff. Our scientific knowledge of reality is thus, in Sprigge’s words, “rather like the kind of knowledge of a piece of music which someone born deaf might have from a musical education based entirely on the study of musical scores.”
Yet there is one part of reality that we do know without the mediation of science: our own consciousness. We experience the intrinsic qualities of our conscious states directly, from the inside. We have what philosophers call “privileged access” to them. There is nothing whose existence we are more certain of.
Now, this raises an interesting possibility. Maybe the part of reality we know indirectly through science, the physical part, has the same inner nature as the part we know directly through introspection, the conscious part. In other words, maybe all of reality—subjective and objective—is made out of the same basic stuff. That is a pleasingly simple hypothesis. But isn’t it a bit crazy? Well, it didn’t strike Bertrand Russell that way. In fact, it was essentially the conclusion Russell reached in The Analysis of Matter. Nor did it strike the great physicist Sir Arthur Eddington as crazy. In The Nature of the Physical World (1928), Eddington ringingly declared that “the stuff of the world is mind-stuff.” (The term “mind-stuff,” by the way, was coined by William James in the first volume of his 1890 work, Principles of Psychology.)
Crazy or not, the idea that the fundamental stuff of reality is mind-stuff has one very odd implication. If it is true, then consciousness must pervade all of physical nature. Subjective experience would not be confined to the brains of beings like us; it would be present in every bit of matter: in big things like galaxies and black holes, in little things like quarks and neutrinos, and in medium-sized things like flowers and rocks.
The doctrine that consciousness pervades reality is called “panpsychism.” It seems to harken back to primitive superstitions like animism—the belief that trees and brooks harbor spirits. Yet it has attracted quite a bit of interest among contemporary philosophers. A few decades ago, Thomas Nagel showed that panpsychism, for all its apparent daftness, is an inescapable consequence of some quite reasonable premises. Our brains consist of material particles. These particles, in certain arrangements, produce subjective thoughts and feelings. Physical properties alone cannot account for subjectivity. (How could the ineffable experience of tasting a strawberry ever arise from the equations of physics?) Now, the properties of a complex system like the brain don’t just pop into existence from nowhere; they must derive from the properties of that system’s ultimate constituents. Those ultimate constituents must therefore have subjective features themselves—features that, in the right combinations, add up to our inner thoughts and feelings. But the electrons, protons, and neutrons making up our brains are no different from those making up the rest of the world. So the entire universe must consist of little bits of consciousness.
Another contemporary thinker who takes panpsychism seriously is the Australian philosopher David Chalmers. What attracts Chalmers to panpsychism is that it promises to solve two metaphysical problems for the price of one: the problem of stuff and the problem of consciousness. Not only does panpsychism furnish the basic stuff—mind-stuff—that might flesh out the purely structural world described by physics. It also explains why that otherwise gray physical world is bursting with Technicolor consciousness. Consciousness didn’t mysteriously “emerge” in the universe when certain particles of matter chanced to come into the right arrangement; rather, it’s been around from the very beginning, because those particles themselves are bits of consciousness. A single ontology thus underlies the subjective-information states in our minds and the objective-information states of the physical world—whence Chalmers’s slogan: “Experience is information from the inside; physics is information from the outside.”
If this metaphysical deal seems too good to be true, I should point out that panpsychism comes with problems of its own. Foremost among them is what might be called the Combination Problem: how can many little bits of mind-stuff combine to form a bigger mind? Your brain, for instance, is made up of lots of elementary particles. According to the panpsychist, each of these elementary particles is a tiny center of proto-consciousness, with its own (presumably very simple) mental states. Just what is it that makes all these micro-minds cohere into the macro-mind that is your own?
The Combination Problem proved a stumbling block for William James, who was otherwise friendly to panpsychism. “How can many consciousnesses be at the same time one consciousness?” James asked in bewilderment. He made the point vivid with an example. “Take a sentence of a dozen words, and take twelve men and tell to each one word. Then stand the men in a row or jam them in a bunch, and let each think of his word as intently as he will; nowhere will there be a consciousness of the whole sentence. . . . The private minds do not agglomerate into a higher mind.”
James’s point is echoed by many contemporary opponents of panpsychism. What sense does it make, they say, to conjecture that things like electrons and protons are inwardly mental
if you have no clue as to how their micro-mentality gets unified into full-blown human consciousness?
But there are a few intrepid thinkers who claim they do have a clue. And it is supplied, perhaps surprisingly, by quantum theory. One of the striking novelties of quantum theory is the notion of entanglement. When two distinct particles enter into a state of quantum entanglement, they lose their individual identities and act as a unified system. Any change to one of them will immediately be felt by the other, even if they are light-years apart. There is nothing analogous to this in classical physics. When quantum entanglement occurs, the whole becomes more than the sum of its parts. This is so radically at odds with our everyday way of viewing the world that Einstein himself pronounced it “spooky.”
Now, even though quantum theory is customarily applied to a physical ontology, one consisting of particles and fields, there is no obvious reason why it can’t also be applied to an ontology consisting of mind-stuff. Indeed, such a “quantum psychology” could hold the key to understanding the unity of consciousness—considered by Descartes and Kant to be a distinctive mark of the mental. If physical entities can lose their individual identity and merge into a single whole, then it is at least conceivable that proto-mental entities could do likewise and—as William James put it—“agglomerate into a higher mind.” Thus does quantum entanglement offer at least a hint of a solution to the Combination Problem.
Roger Penrose himself has invoked such quantum principles to explain how the physical activities in our brains generate consciousness. In Shadows of the Mind, he wrote that “the unity of a single mind can arise . . . only if there is some form of quantum coherence extending across an appreciable part of the brain.” And he has since gone further, endorsing the panpsychist notion that the atomic constituents of the brain, along with the rest of the physical universe, are structured out of mind-stuff. “I think that something of this nature is indeed necessary,” Penrose announced in a public lecture when the issue came up.