https://www.quantamagazine.org/
“Resurgence is very fancy,” Bender said. But, to put it as simply as possible, it lets practitioners dig into the distant terms of an asymptotic series (calculated using Feynman diagrams, for instance) and uncover the missing pieces necessary to specify a unique function (one that describes tunneling, say). In short, it reveals a bridge linking physical events described by perturbation theory with those described by the nonperturbative terms. “It’s a very complicated relationship,” Bender said, before politely declining to attempt to explain it.