The 2011 Nobel Prize in physics has been awarded to three American scientists who studied exploding stars and learned, in the process, that the universe’s expansion is accelerating. Saul Perlmutter, Brian Schmidt, and Adam Riess discovered in the 1990s that the light from 50 supernovas was weaker than expected—a sign of acceleration. "For almost a century the universe has been known to be expanding as a consequence of the Big Bang about 14 billion years ago," the Nobel citation read. "However the discovery that this expansion is accelerating is astounding. If the expansion will continue to speed up the universe will end in ice."