In quantum graphity, space evolves out of dots that are either “on” or “off ”—connected or disconnected to the next dot. It doesn’t matter exactly what the dots are; they represent coordinates in a network of relationships, the fundamental constituents of the universe. The idea, Markopoulou explains, comes from a branch of mathematics known as category theory, in which “what something is, is the sum of how it behaves, rather than how it is.” At the highest possible energy, at the beginning of the universe, all the dots in the graph are joined, and no notion of space exists. But as the system cools and loses energy, the points start detaching, which creates the dimensions and laws of space. In this model, space becomes like a crystal that forms out of a liquid as it cools. “The value of this is in trying to give, however primitive it might be, some language to talk about space not being there,” she says.