One physicist predicted the universe's leftover glow 17 years before anyone detected it

George Gamow worked out in the 1940s that a hot early universe should have cooled into a faint, uniform afterglow of radiation, still detectable today. Working with Ralph Alpher and Robert Herman, he also showed the same hot Big Bang could explain the observed ratio of hydrogen to helium in the universe. Engineers Arno Penzias and Robert Wilson finally picked up that predicted glow by accident in 1964.

— Wikipedia contributors, George Gamow — Wikipedia; Alpher, Bethe & Gamow, Physical Review, 1948