Why Does the World Exist: An Existentia - By Jim Holt Page 0,88

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 Searle, 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