Speed freak

摘要

Something in the Universe is speeding up its expansion and pushing the galaxies apart. But it wasn't always that way, according to a group of British physicists. They're suggesting that the accelerator may only have been pressed relatively recently, when the Universe was a few billion years old. If they're right, there's no reason why this mysterious repulsive force, dubbed "dark energy", couldn't change again or even switch off completely―meaning all bets about the future of the Universe are off. The team, from the University of Portsmouth and Oxford University, studied a range of cosmological data sets, including observations of the brightness of distant supernovae―key measurements which first revealed the existence of dark energy in 1998―as well as surveys of the distribution of galaxies and the cosmic background radiation, the dim "afterglow" of the big bang. "If the dark energy changed, it would change the curvature of space-time," says team member Carlo Ungarelli of the University of Portsmouth. "One way this would reveal itself is by changing the height of so-called peaks in the cosmic background radiation."