... Dark energy's long history . ... S cientists using NASA's Hubble Space Telescope have discovered that dark energy is not a new constituent of space, but rather has been present for most of the universe's history. ... Investigators used Hubble to find that dark energy was already boosting the expansion rate of the universe as long as nine billion years ago. ... To study the behavior of dark energy of long ago, Hubble had to peer far across the universe and back into time to detect supernovae. ...