What metaphors are used in Zero: The Biography of a Dangerous Idea by Charles Seife?

I'm not sure that literary metaphors fit into this science book but I'm sure that Black Holes have to be a metaphor for something. Black holes are incredibly small concentrations of mass and energy with incredibly large physical effects. By combining the very small and very large, the existence of black holes challenges both quantum mechanics and general relativity, which the author interprets as another challenged posed by zero.