Three U.S.-born scientists whose work indicates that the universe is expanding at an accelerating rate have been awarded the 2011 Nobel Prize in Physics. American Saul Perlmutter will share the $1.5 million award with U.S.-Australian Brian Schmidt and U.S. scientist Adam Riess, the Royal Swedish Academy of Sciences announced this morning. ( Update at 7:55 a.m. ET: Perlmutter will receive half the award; Schmidt and Riess will share the rest.) In its statement announcing the honors , the academy writes that "In 1998, cosmology was shaken at its foundations as two research teams presented their findings. Headed by Saul Perlmutter, one of the teams had set to work in 1988. Brian Schmidt headed another team, launched at the end of 1994, where Adam Riess was to play a crucial role. ... "The two research teams found over 50 distant supernovae whose light was weaker than expected — this was a sign that the expansion of the Universe was accelerating. ... For almost a century, the Universe has