Riess, Adam Guy, 1969–, American astrophysicist, b. Washington, D.C., Ph.D. Harvard, 1996. He has been an astronomer at the Space Telescope Science Institute in Baltimore, Md., since 1999 and a professor at Johns Hopkins since 2006. Riess and Brian Schmidt were joint recipients of the 2011 Nobel Prize in Physics with Saul Perlmutter for discovering that the universe is expanding at an accelerating pace. Two teams, one led by Riess and Schmidt and the other by Perlmutter, independently used Type Ia supernovas as distance indicators and found that a large number of these stellar explosions were dimmer than expected. The finding demonstrated that the expansion of the universe is speeding up and suggests that the universe is likely infinite in space and time.