“Lerner [is] among the most promising young poets now writing.”—Publishers Weekly“Sharp, ambitious, and impressive.” —Boston ReviewNational Book Award finalist Ben Lerner turns to science once again for his guiding metaphor. “Mean free path” is the average distance a particle travels before colliding with another particle. The poems in Lerner’s third collection are full of layered collisions—repetitions, fragmentations, stutters, re-combinations—that track how language threat