The rate at which the universe is expanding has gone up and down like a rollercoaster, according to scientists who have mapped the galaxies for the first time as they were 11 billion years ago.
Astronomers at Portsmouth University have been involved in a project examining how the universe has evolved since the big bang 13.75 billion years ago.
The study, undertaken by the Sloan Digital Sky Survey (SDSS-III) and published in the journal Astronomy & Astrophysics, has now mapped the universe as it was in its youth, three billion years after it was formed.
Mat Pieri, Marie Curie research fellow at the university and co-author of the study, said: “We already know about the universe in its infancy using the afterglow of the big bang.
“We have seen the universe reach maturity by looking at the distribution of distant galaxies in the second half of its history.
“Only now are we finally seeing its adolescence by exploring the distribution of gas on the largest scales in the first half of its history, just before it underwent a growth spurt.”
Dr Pieri explained that the universe’s growth when it was young was slowed by the effects of gravity but in the past five billion years it has begun to rapidly expand because of a mysterious force which scientists have called dark energy.
Dr Pieri likened this slow rise then rapid expansion to a rollercoaster.
He said: “If we think of the universe as a rollercoaster, 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 rollercoaster crested the hill just about seven billion years ago, and we’re still going.”