Jack Steinberger, who shared the 1988 Nobel Prize in Physics for expanding understanding of the ghostly neutrino, a staggeringly ubiquitous subatomic particle, died on Saturday at his home in Geneva. He was 99.

His wife, Cynthia Alff, confirmed the death.

The ancient Greeks proposed that there was one invisible, indivisible unit of matter: the atom. But modern physics has found more than 100 smaller entities lurking within atoms, and observations of their dizzying interactions compose the Standard Model of what is now taken to be the order of the universe.