Einstein won the 1921 Nobel Prize in Physics, but not for relativity. The Nobel Committee avoided honouring that still-controversial theory directly, and instead awarded him for his work on the photoelectric effect — the discovery that helped launch quantum physics.

Albert Einstein is so closely identified with relativity that it can feel natural to assume the Nobel Prize followed that theory. It did not. The official Nobel record lists Einstein as the sole laureate of the 1921 Nobel Prize in Physics, but the prize motiv…