NOBODY KNEW HOW MUCH we needed nothing until we had a number for it. Without zero, negative and imaginary numbers would have no meaning, and it would be impossible to solve quadratic equations, a mainstay of applied math. Without zero to act as a placeholder to distinguish, say, 10 from 100, all but the simplest arithmetic requires an abacus or counting board. “If we didn't have zero, our system of numbers would be incomplete,” says Charles Seife, author of Zero: The Biography of a Dangerous Idea. “It would really break down without zero.”