The Telegraph: The universe is expanding, and it has been doing so at an increasing rate for about 7 billion years. New measurements of gas clouds in some of the remotest—and therefore oldest—regions of the universe have shown that for a while the rate of growth was slowing down. An international team of astronomers examined the shadows created when gas clouds absorbed light from high-energy sources such as quasars. Based on the distribution of the clouds, the astronomers were able to determine that between 11 billion and 7 billion years ago, the rate of expansion was slowed by gravity. Around 7 billion years ago, the slowing effect of gravity was overwhelmed by the expansive effect of dark energy. One of the astronomers, Mat Pieri of Portsmouth University in the UK, compares the slowing and then sudden expansion to a roller coaster going up a hill and then dropping down the other side.