University of British Columbia astronomer Ludovic Van Waerbeke with an international team has confirmed that the expansion of the universe is accelerating after looking at data from the largest-ever survey conducted by the Hubble Space Telescope. The astronomers studied more than 446,000 galaxies to map the matter distribution and the expansion history of the universe. This study enabled them to observe precisely how dark matter（暗物质） evolved in the universe and to reconstruct a three-dimensional map of the dark matter and use this to test Albert Einstein's theory of general relativity（广义相对论） .

The findings will appear in a forthcoming（即将来临的） issue of the journal Astronomy & Astrophysics. The study's lead author is Tim Schrabback, an astronomer from Leiden University in the Netherlands.

"Our results confirmed that there is an unknown source of energy in the universe which is causing the cosmic expansion（宇宙膨胀）to speed up, stretching the dark matter further apart exactly as predicted by Einstein's theory," says Van Waerbeke, an associate professor in the Dept. of Physics and Astronomy.

Einstein's theory of general relativity predicts that space and time is a soft geometrical（几何的） structure of which the shape and evolution are entirely determined by the matter within it. Scientists posit（假设，设想） that the universe is composed of dark matter and normal matter with a third constituent called "dark energy," which over the past two billion years has been the force behind the accelerated expansion of the universe.

"The data from our study are consistent with（与……一致） these predictions and show no deviation（偏差，误差） from Einstein's theories," says Van Waerbeke, who is also a scholar in the Cosmology and Gravity program of the Canadian Institute for Advanced Research.

In the late 1990s, Van Waerbeke pioneered weak gravitational lensing（引力透镜） to measure the invisible web of dark matter that makes up 80 per cent of the mass of the universe. This technique is similar to taking an X-ray of the body to reveal the underlying skeleton. It allows astronomers to observe how light from distant galaxies is bent and distorted（扭曲） by the web of invisible dark matter as it travels toward Earth. By measuring the distortions seen in these galaxy light patterns, astronomers can then map dark matter structures.

Along with weak gravitational lensing, the study uses data from the Cosmic Evolution Survey (COSMOS), one of the most ambitious（有雄心的，热望的） undertakings by the Hubble Space Telescope. COSMOS is a joint project of the European Space Agency (ESA) and NASA involving more than 100 scientists from a dozen countries.

To generate the COSMOS survey, a camera aboard the Hubble photographed 575 slightly overlapping（重叠，覆盖） views of the same part of the universe. This required nearly 1,000 hours of observations, during which Hubble circled the Earth almost 600 times.