 In 2000, Spergel and his Princeton colleague Paul Steinhardt introduced the concept of strongly self-interacting dark matter (SIDM).Spergel is among a group of scientists and engineers at Princeton University who are developing new technologies attempting to enable the direct imaging of earth-like planets around nearby stars.Spergel's thesis students include Julianne Dalcanton, Arlie Petters, James Rhoads, Joseph Hennawi and Shirley Ho.