You are not aware of the electrochemical events occurring at each of the trillion synapses in your brain at this moment. But you are aware, however dimly, of sights, sounds, sensations, thoughts, and moods. At the level of your experience, you are not a body of cells, organelles, and atoms; you are consciousness and its ever-changing contents, passing through various stages of wakefulness and sleep, and from cradle to grave.

The term “consciousness” is notoriously difficult to define. Consequently, many a debate about its character has been waged without the participants’ finding even a common topic as common ground. By “consciousness,” I mean simply “sentience,” in the most unadorned sense. To use the philosopher Thomas Nagel’s construction: A creature is conscious if there is “something that it is like” to be this creature; an event is consciously perceived if there is “something that it is like” to perceive it. ⁠Whatever else consciousness may or may not be in physical terms, the difference between it and unconsciousness is first and foremost a matter of subjective experience. Either the lights are on, or they are not.[ ]

To say that a creature is conscious, therefore, is not to say anything about its behavior; no screams need be heard, or wincing seen, for a person to be in pain. Behavior and verbal report are fully separable from the fact of consciousness: We can find examples of both without consciousness (a primitive robot) and consciousness without either (a person suffering “locked-in syndrome”).[ ]

It is surely a sign of our intellectual progress that a discussion of consciousness no longer has to begin with a debate about its existence. To say that consciousness may only seem to exist is to admit its existence in full—for if things seem any way at all, that is consciousness. Even if I happen to be a brain in a vat at this moment—all my memories are false; all my perceptions are of a world that does not exist—the fact that I am having an experience is indisputable (to me, at least). This is all that is required for me (or any other conscious being) to fully establish the reality of consciousness. Consciousness is the one thing in this universe that cannot be an illusion.[ ]

As our understanding of the physical world has evolved, our notion of what counts as “physical” has broadened considerably. A world teeming with fields and forces, vacuum fluctuations, and the other gossamer spawn of modern physics is not the physical world of common sense. In fact, our common sense seems to be stuck somewhere in the 16th century. We have also generally forgotten that many of the patriarchs of physics in the first half of the 20th century regularly impugned the “physicality” of the universe. Nonreductive views like those of Eddington, Jeans, Pauli, Heisenberg, and Schrödinger seem to have had no lasting impact.[ ]

In some ways we can be thankful for this, for a fair amount of mumbo jumbo was in the air. Wolfgang Pauli, for instance, though one of the titans of modern physics, was also a devotee of Carl Jung, who apparently analyzed no fewer than 1,300 of the great man’s dreams.[ ] Pauli’s thoughts about the irreducibility of mind seem to have had as much to do with Jung’s least credible ideas as with quantum mechanics.

Such numinous influences eventually subsided. And once physicists got down to the serious business of building bombs, we were apparently returned to a universe of objects—and to a style of discourse, across all branches of science and philosophy, that made the mind seem ripe for reduction to the “physical” world.

The problem, however, is that no evidence for consciousness exists in the physical world.[ ]

Physical events are simply mute as to whether it is “like something” to be what they are. The only thing in this universe that attests to the existence of consciousness is consciousness itself; the only clue to subjectivity, as such, is subjectivity. Absolutely nothing about a brain, when surveyed as a physical system, suggests that it is a locus of experience. Were we not already brimming with consciousness ourselves, we would find no evidence of it in the physical universe—nor would we have any notion of the many experiential states that it gives rise to. The painfulness of pain, for instance, puts in an appearance only in consciousness. And no description of C-fibers or pain-avoiding behavior will bring the subjective reality into view.

If we look for consciousness in the physical world, all we find are increasingly complex systems giving rise to increasingly complex behavior—which may or may not be attended by consciousness. The fact that the behavior of our fellow human beings persuades us that they are (more or less) conscious does not get us any closer to linking consciousness to physical events. Is a starfish conscious? A scientific account of the emergence of consciousness would answer this question. And it seems clear that we will not make any progress by drawing analogies between starfish behavior and our own. It is only in the presence of animals sufficiently like ourselves that our intuitions about (and attributions of) consciousness begin to crystallize. Is there “something that it is like” to be a cocker spaniel? Does it feel its pains and pleasures? Surely it must. How do we know? Behavior, analogy, parsimony.[ ]

Most scientists are confident that consciousness emerges from unconscious complexity. We have compelling reasons for believing this, because the only signs of consciousness we see in the universe are found in evolved organisms like ourselves. Nevertheless, this notion of emergence strikes me as nothing more than a restatement of a miracle. To say that consciousness emerged at some point in the evolution of life doesn’t give us an inkling of how it could emerge from unconscious processes, even in principle.

I believe that this notion of emergence is incomprehensible—rather like a naive conception of the big bang. The idea that everything (matter, space-time, their antecedent causes, and the very laws that govern their emergence) simply sprang into being out of nothing seems worse than a paradox. “Nothing,” after all, is precisely that which cannot give rise to “anything,” let alone “everything.” Many physicists realize this, of course. Fred Hoyle, who coined “big bang” as a term of derogation, is famous for opposing this creation myth on philosophical grounds, because such an event seems to require a “preexisting space and time.” In a similar vein, Stephen Hawking has said that the notion that the universe had a beginning is incoherent, because something can begin only with reference to time, and here we are talking about the beginning of space-time itself. He pictures space-time as a four-dimensional closed manifold, without beginning or end—much like the surface of a sphere.

Naturally, it all depends on how one defines “nothing.” The physicist Lawrence Krauss has written a wonderful book arguing that the universe does indeed emerge from nothing. But in the present context, I am imagining a nothing that is emptier still—a condition without antecedent laws of physics or anything else. It might still be true that the laws of physics themselves sprang out of nothing in this sense, and the universe along with them—and Krauss says as much. Perhaps that is precisely what happened. I am simply claiming that this is not an explanation of how the universe came into being. To say “Everything came out of nothing” is to assert a brute fact that defies our most basic intuitions of cause and effect—a miracle, in other words.

Likewise, the idea that consciousness is identical to (or emerged from) unconscious physical events is, I would argue, impossible to properly conceive—which is to say that we can think we are thinking it, but we are mistaken. We can say the right words, of course—“consciousness emerges from unconscious information processing.” We can also say “Some squares are as round as circles” and “2 plus 2 equals 7.” But are we really thinking these things all the way through? I don’t think so.

Consciousness—the sheer fact that this universe is illuminated by sentience—is precisely what unconsciousness is not. And I believe that no description of unconscious complexity will fully account for it. It seems to me that just as “something” and “nothing,” however juxtaposed, can do no explanatory work, an analysis of purely physical processes will never yield a picture of consciousness. However, this is not to say that some other thesis about consciousness must be true. Consciousness may very well be the lawful product of unconscious information processing. But I don’t know what that sentence means—and I don’t think anyone else does either.

Follow-up article: The Mystery of Consciousness II