This "divergence problem" was solved in the case of quantum electrodynamics through the procedure known as renormalization in 1947–49 by Hans Kramers, Hans Bethe, Julian Schwinger, Richard Feynman, and Shin'ichiro Tomonaga ; the procedure was systematized by Freeman Dyson in 1949. Great progress was made after realizing that all infinities in quantum electrodynamics are related to two effects: the self-energy of the electron/positron, and vacuum polarization.