"Have you ever thought that life is concave?" My sister was in one of those moods again. "I don't even know what that means," I said.

"Well, yeah," she said. "But have you thought it?" She was lying on her back on her bed, staring at the ceiling of the room we shared.

"I... just.... No," I said, "I haven't. Have you?"

"I was thinking it just a minute ago," she said, "but I'm not now." My sigh filled the room and prompted her to go into greater detail. "I was thinking that everything is sort of orderly, having a sensible direction, habits and suchlike, and people come along and scatter everything all over everywhere. Like a lens."

"Nature's more chaotic than that," I said.

"But an orderly chaos. It makes sense. People brains are way too complex to just follow rules of instinct and all."

"Don't lenses scatter light in a predictable fashion?"

She hummed as she mused on that for a few moments. "You're right. We'll need a sort of optics that results in a chaotic system for this analogy. Maybe an oil-water mixture, spinning... go get some oil."

I sighed again. This would be a long night.