Scientists have given the name dark energy to the expansion-generating force or substance of the universe.
            Dark energy is the reverse of gravity. It pushes things away rather than pulling them together. It is unknown whether the laws of physics or the general theory of relativity can account for dark energy.
            In 1998 astronomers studying supernovae found them dimmer than anticipated. This meant both they were father away and the universe was expanding faster than expected.
             The U.S. government’s joint Dark  Energy Mission (JDEM) examined Type La supernovae, dying white dwarfs, because of their  high and consistent luminosity. The program ended in 2010, and will be replaced by the Wide –field infrared Survey Telescope (WFIRST).