James Peebles received the 2019 Nobel Prize in Physics for theoretical discoveries in physical cosmology.
Peebles helped establish modern physical cosmology as a quantitative science. His work connected the early universe with structures observed today, including galaxies, clusters and the large-scale distribution of matter. He developed influential theoretical frameworks involving the cosmic microwave background, dark matter and the formation of cosmic structure.
The 2019 Physics Prize was divided into two parts. Peebles received one half, while Michel Mayor and Didier Queloz shared the other half for the discovery of an exoplanet orbiting a solar-type star. That exoplanet, 51 Pegasi b, was announced in 1995.
Peebles is sometimes confused with the other major cosmology laureates recognized in 2006, George Smoot and John Mather. Smoot and Mather were honored for observations of the cosmic microwave background, whereas Peebles was honored primarily for theoretical cosmology.