At Ten, Dark Energy "Most Profound Problem" in Physics
A decade after its discovery, scientists are struggling to pin down the properties of the "dark side" of gravity and unravel a mystery that accounts for about 74 percent of the universe.
What goes up must come down. Few on Earth would argue with the fundamental law of gravity.
But ten years ago this month the Astronomical Journal accepted a paper for publication that revealed there is a dark side of the force.
For decades physicists were convinced that gravity should be causing the expansion rate of the universe to slow.
"When I throw my keys up in the air, the gravity of the Earth makes them slow down and return to me," said Mario Livio, a theoretical physicist at the Space Telescope Science Institute (STScI) in Baltimore, Maryland.
But the study, along with an independent work released later the same year, showed that the expansion rate is actually speeding up.
This observation, Livio said, is