Light and dark.
What do those words make you think of or feel? Good and evil? Security and menacing? Work and play?
In the Raiders of Light series, one of the main themes is that light—driver of life, source of sight, etc.—in effect is a record of all things it has ever touched. Imagine a river of photons and electrons flowing through space, carrying with them the memory of every other atom they’ve passed through and around, ignorant of time and immune to aging. Granted, this is just a...