Kevin Hartnett is a senior writer at *Quanta Magazine* covering mathematics and computer science. His work has been collected in the “Best Writing on Mathematics” series in 2013 and 2016. From 2013-2016 he wrote “Brainiac,” a weekly column for the *Boston Globe*‘s Ideas section.

### How Curvature Makes a Shape a Shape

The ancient study of an object’s curvature is guiding mathematicians toward a new understanding of simple equations.