Runaway universe

• 09 October 2004
• Stephen Battersby
• Magazine issue 2468

Dark energy is arguably the deepest mystery in physics. This cosmic puzzle was first encountered in 1998, when two groups of astronomers reported that dozens of distant supernovae appeared surprisingly faint (New Scientist, 11 April 1998, p 26). They concluded that the expansion of the universe must be accelerating, dimming these distant explosions. It came as rather a shock, because although we have known for more than 70 years that the universe is expanding, people had always assumed that the expansion must be slowing down. The gravity of all the matter in the universe should be putting the brakes on.

But the supernovae showed that about 10 billion years ago something began to overpower gravity, making the expansion accelerate. It's as if gravity were working in reverse, as if a cosmic poltergeist were grabbing galaxies and flinging them outwards.

The acceleration of the universe is too gentle to feel, ...