Saul Perlmutter, 1959–, American astrophysicist, b., Champaign-Urbana, Ill., Ph.D. Univ. of California, Berkeley, 1986. He is a researcher at Lawrence Berkeley National Laboratory and a professor at the Univ. of California, Berkeley. Perlmutter was a co-recipient, with Adam Riess and Brian Schmidt, of the 2011 Nobel Prize in Physics for discovering that the universe is expanding at an accelerating pace. Two teams, one led by Perlmutter and the other by Schmidt and Riess, independently used Type Ia supernovas as distance indicators and found that a large number of these stellar explosions were dimmer than expected. Their findings demonstrated that the expansion of the universe is speeding up and suggest that the universe is likely infinite in space and time.