William H. Parker (born 1941) is an American professor of physics and academic administrator at the University of California, Irvine (UCI).
Parker's earliest laboratory research involved seminal experiments that refined the precision of the measurements of fundamental constants.
In an administrative capacity at UCI, Parker has served in a variety of roles including as Dean, Department Chair, and Vice Chancellor.
In collaboration with Donald N. Langenberg and Barry N. Taylor, Parker used the alternating current Josephson effect to precisely measure e/h, the ratio of the elementary charge (e) to the Planck constant (h).
The new measurement of α removed a discrepancy between the theoretical and experimental values of the hyperfine splitting in the ground state of atomic hydrogen, one of the major unsolved problems of quantum electrodynamics at time.