Throughout the 1980s and 1990s, in a specially outfitted studio apartment in Seattle that reporters nicknamed the "love lab," mathematician-turned-psychologist John Gottman videotaped ordinary couples in their most ordinary moments--playing solitaire, chatting, kissing, disagreeing, watching TV, cooking dinner.

Sometimes Gottman, then a professor at the University of Washington, asked them to discuss an area of conflict while monitors strapped to their chests recorded their heart rates. Sometimes he sat them on spring-loaded platforms to record how much they fidgeted. He looked at how they brought up painful subjects, how they responded to each other's bids for attention, how they fought and joked, and how they expressed emotion.

Funded by the National Institute of Mental Health, he and his colleagues studied newlyweds, men who battered their wives, couples who shouted a lot, and others who beat around the bush and never raised their voices. He used an elaborate coding system to track not only their verbal exchanges, but less obvious indicators of emotion: flickering facial expressions, sighs, clammy hands, rolling eyes, and galloping heartbeats. He followed some of the couples for more than two decades, recording who got divorced, who established parallel lives, and who stayed together--more or less happily.

He then took his data and translated them into numbers, quantifying an area of human life usually relegated to the psychotherapist and the…