An Unfinished History of Intelligence, Part 4: The Inner World
A bacterium pays for every mistake with its body. Imagination is the invention that made mistakes free. A rat has one, and you can watch it work.
Look at what the ledger has been, all the way through this history.
A bacterium swims up a gradient, and if it swims the wrong way it starves. There is no rehearsal and no appeal. Its only simulator is the world, and the world charges full price, in real time, in the currency of the body. Part 2 improved on this: an animal with a nervous system can begin an action, notice mid-flight that it is going wrong, and correct before the error becomes a consequence. Part 3 improved on it again: an animal with adjustable synapses can be changed by an error, so that a mistake made today is less likely tomorrow.
But notice what every one of those systems has in common. In each case, the mistake still has to happen. The bacterium must actually swim the wrong way. The animal must actually begin the wrong movement. The rat must actually take the wrong turn and find no food there. Learning from experience requires the experience, and experience is expensive, and some experiences you only get once.
This chapter is about the invention that broke that constraint. It is a model of the world that can be run when the world is not there: offline, in the dark, faster than real time, on an action the animal has not taken and may never take.
The point of an inner world is not contemplation. It is economics. Imagination is the technology that moves the cost of error out of the world and into the head.
And the thing that demonstrates it is not a philosopher in a chair. It is a rat, standing dead still at a fork in a maze, swinging its head from one arm to the other, while inside its skull a population of neurons runs down the left path, comes back, and runs down the right.
We can watch it. That is the story of this chapter.
