sentences:  He then went to the University of Michigan, in Ann Arbor, for graduate studies in physics with Walter F. Colby and Oskar Klein.Klein, already associated with the Kaluza–Klein theory (1921), joined the faculty at Michigan in 1922, after a six-year stay at the Institute for Theoretical Physics, under Niels Bohr, at the University of Copenhagen.It was through Klein that Dennison heard and leaned much about the current theoretical physics being developed in Europe, which created a yearning in him to go to Copenhagen for further study.