Universe 'expanding like a rollercoaster' Dr Mat Pieri of Portsmouth University, co-author of the study, said: "If we think of the universe as a roller coaster, then today we are rushing downhill, gaining speed as we go. Our new measurement tells us about the time when the universe was climbing the hill, still being slowed by gravity. It looks like the roller coaster crested the hill just about seven billion years ago, and we're still going. The gas clouds can be measured because they absorb light from quasars, enormously powerful energy-emitting objects which are found at the heart of galaxies and are thought to be powered by black holes. The resulting "shadows" can be analysed to map these distant regions, revealing how the Universe evolved through its history and how dark energy worked before the rapid expansion began. Dr Pieri said: "No place in the universe is really empty. There is gas in even the most remote parts of the universe and we have used it to measure how the universe expands. "This expansion is telling us that there is more than just gas out there - it seems that space itself comes with its own energy and the more space you have, the more of this "dark energy" there is."