There is a kind of database field that cannot be filled. Not because the schema is broken or the disk is full. Because the one value the field will accept is not the sort of thing that can be written down, copied, or transmitted, and never will be. I built a whole novella around one such field.

Start with the field’s type. Suppose you want to record, for some particular person, what a particular moment was like for them. Not the moment as an event in the world. That part is easy: you log the time, the place, the light level, the heart rate, the position of the car on the bridge. What you want is what the moment was like from the inside. The taste of the coffee as it was actually tasted. The specific way afternoon light off a river looked to the one pair of eyes that happened to be looking. Call that the phenomenal content of the experience. The field’s type constraint is strict. It accepts only the actual first-person experience of that one person, and it rejects everything else. Behavioral data does not validate. A description does not validate. Someone else’s report of a similar experience does not validate. The field wants the thing itself, and the thing itself is not data.

That is the hard problem of consciousness, wearing a database schema.

Nagel’s bat

Thomas Nagel gave the canonical version of the difficulty in 1974, in a paper whose title I borrowed and bent: “What Is It Like to Be a Bat?” The argument is short and hard to shake. A bat navigates by echolocation, a sense we do not have. You can learn everything physical about the bat: its neurology, the timing of its clicks, the wiring from ear to brain, the flight corrections it makes mid-air. You can know the mechanism completely. And you will still not know what it is like to be the bat, catching a moth in the dark by listening to the shape of returning sound.

Nagel’s point is about kinds of facts. The facts of physics are facts from no particular point of view. They are objective on purpose. Anyone, anywhere, with the right instruments, gets the same readings, which is exactly what makes them science. But an experience is tied to a point of view. There is something it is like to have it, and that something is available only from inside the one subject having it. No quantity of the objective kind of fact adds up to the subjective kind. They are different in type, and you do not convert one into the other by collecting more of the first.