Scientists still in the murk about 'dark energy'
— -- Nearly a decade after scientists discovered that a mysterious force is pushing the universe to expand at an ever-faster rate, they still don't understand how that is happening.
University of Chicago cosmologist Michael Turner calls the acceleration "the most profound mystery in all of science." It was Turner who coined the term "dark energy" for the unknown substance that provides this cosmic push. Studies have shown that it comprises 74% of all the mass and energy of the universe.
Scientists say that if they can understand dark energy, they may learn the fate of the universe — whether it will keep on expanding, tear itself apart or implode cataclysmically billions of years from now.
Science writers took part in a workshop last month at the Space Telescope Science Institute in Baltimore to focus on the question of why gravity, on the largest scales, has switched roles — pushing out instead of holding in.
NASA plans to explore the question in a big way as well. The National Research Council recommended in early September that a dark-energy probe be the first spacecraft NASA launches in its delayed "Beyond Einstein" series of missions designed to explore the formation of the universe and some of its most unique features.
Jointly sponsored by the Department of Energy, the series has three proposed missions, one of which would be selected and launched around 2015.
"It's not very often that theorists face a situation in which they need to explain something that is 74% of everything there is and they don't have a clue," says Mario Livio, theorist for the space telescope institute.
Coming to the opposite conclusion
Astronomer Adam Riess remembers the moment he realized that instead of pulling galaxies together, gravity was pushing them apart.
A decade ago, Riess was a 26-year-old postdoctoral researcher at the University of California-Berkeley, part of a team using the light from distant supernovae to study how rapidly the universe has been expanding over the past several billion years.
