You'd think that it would be virtually impossible to determine the collective brightness of the observable universe, but a team of scientists has come surprisingly close. They've completed the most accurate measurement of the universe's light to date using both reams of Fermi Space Telescope gamma ray data and some unusual tricks. They searched for the background light of the universe by studying data from over 700 blazars, or black hole gamma ray bursts pointed directly at Earth. They noticed that the blazars indicate the brightness of the background light between galaxies as they cut through it. And when it takes billions of years for those gamma rays to reach human eyes, you can gauge the light levels for large portions of the universe's past -- 90 percent of its history, researcher Alberto Dominguez told Popular Science.