669 million galaxies mapped in study seeking to explain universe's accelerating expansion

The Dark Energy Survey mapped 669 million galaxies to help understand why the universe's expansion is accelerating rather than slowing down. 

Einstein's theory of General Relativity predicted that gravity should slow cosmic expansion. But in 1998, astronomers discovered the opposite was happening. This means either 70% of the universe exists as "dark energy" with a repulsive gravitational force, or General Relativity must be replaced by a new theory of gravity on cosmic scales. 

More than 400 scientists from seven countries used a 570-megapixel camera on a telescope in the Chilean Andes, observing the southern sky for 758 nights between 2013 and 2019. 

Professor Bob Nichol, Pro-Vice-Chancellor and Executive Dean of the Faculty of Engineering and Physical Sciences at the University of Surrey, joined the collaboration at its inception, securing UK government funding for British scientists and holding several leadership positions. 

The latest findings combine four measurement techniques for the first time, producing constraints more than twice as strong as previous analyses.