PARIS (AFP) - Astrophysicists believe they are closing in on one of the cosmos' great mysteries: why the expansion of the Universe, triggered by the Big Bang, is accelerating. The answer could be tantalisingly within reach, according to their study, released on Wednesday by the British weekly science journal Nature. A decade ago, astronomers were stunned to learn that the Universe was expanding more quickly than in the past. It had long been assumed that the mutual attraction of galaxies through gravity would slow the expansion of space, kicked off by the Big Bang some 14 billion years ago. Two...