George Volkoff, a friend of Christy who was a year ahead of him at UBC, was accepted as a graduate student at the University of California, Berkeley, by Robert Oppenheimer, who led the most active school of theoretical physics in the United States at that time. This inspired Christy to apply to the University of California as well. He was accepted, and was awarded a fellowship for his first year. At Berkeley he shared an apartment with Volkoff, Robert Cornog, Ken McKenzie and McKenzie's wife Lynn McKenzie. For his thesis, Oppenheimer had him look at mesotrons, subatomic particles called muons today that then recently been found in cosmic rays. They were so-called because they were larger than electrons but smaller than protons. With the help of Shuichi Kusaka he performed detailed calculations of the particle's spin. He published two papers on mesotrons with Kusaka in the Physical Review, which formed the basis of his 1941 Doctor of Philosophy (PhD) thesis