His doctoral work at Princeton was supervised by John Wheeler, and after finding the first problem that Wheeler gave him rather intractable, he went back to ideas he had thought about while at MIT.
Ng doktor Kanyang trabaho sa Princeton ay supervised by John Wheeler, at matapos na unang paghanap ng problema na Wheeler ibinigay sa kanya sa halip mailap, nagpunta siya bumalik sa mga ideya niya habang nag-iisip tungkol sa MIT.