Mottelson an haife shi ne a Chicago, Illinois, ɗan Georgia (Blum) da Goodman Mottelson, injiniya. Ya kammala karatunsa daga Lyons Township High School a LaGrange, Illinois. Ya sami digiri na farko daga Jami'ar Purdue a 1947, kuma Ph.D. a fannin kimiyyar nukiliya daga Jami'ar Harvard a 1950. Tambaya: Yaushe ya kammala karatu daga Purdue?
Shekara ta 1947