"The way I thought of time was I thought of it like a river. And so I thought of it as flowing toward its lowest level. And I thought of history as a river and Eternity as the ocean. So naturally history flows downhill to reach Eternity. I also like the fact that when the descent in elevation is rapid, the river runs faster, and when the landscape is almost flat, the river broadens out and meanders. So it was to preserve this idea of time as a fluid. The other reason is a mathematical reason. It has to do with the fact that if we have novelty moving downward, then the maximum of novelty is zero."