Dark forces lead astronomers to a Nobel prize

The discovery that the Universe is not only expanding but is also expanding at an ever-faster rate as a result of a mysterious superforce has won this year's Nobel Prize in Physics.

Three astronomers share the prize, having discovered in 1998 that exploding stars in deep space were moving away far faster than anyone had suspected because something known as "dark energy" was overriding the tendency for gravity to keep the Universe together.

Saul Perlmutter of the University of California, Berkeley, who led one of two teams of researchers, is awarded half of the £1m prize with the rest shared jointly by Brian Schmidt of the Australian National University in Weston Creek, who led the second team, and his colleague Adam Reiss of the Johns Hopkins University in Baltimore.

The acclerating expansion of the Universe was one of the most suprising discoveries in astronomy in recent decades. The scientists expected to find that the expansion of the Universe – first predicted by Albert Einstein more than a century ago – would be slowing down. To their astonishment, they found the opposite to be true.

The Royal Swedish Academy of Sciences, which awards the physics Nobel, said: "For almost a century, the Universe has been known to be expanding as a consequence of the Big Bang about 14 billion years ago. However, the discovery that this expansion is accelerating is astounding. If the expansion will continue to speed up the Universe will end in ice."

The two teams of researchers had set about trying to measure the expansion of the Universe by observing an exploding star called a type 1a supernova. These stars, as heavy as the Sun but as small as the Earth, can explode in a single event that releases as much light as an entire galaxy.

They observed about 50 supernovae to compare how fast the Universe was expanding in the past with how fast it is expanding now. They had anticipated finding that gravity had slowed down the rate of expansion over time, said Professor Reiss. "If you tossed a ball into the air and it kept right on going up instead of falling to the ground, you'd be pretty surprised. Well, that's about how surprised we were to get that result," he said.

The rules of the Nobel prize stipulate it cannot be shared by more than three people, which meant many of the scientists involved in the discovery were not being properly recognised, said Lord Rees, the Astronomer Royal.

"The key [scientific] papers recognised by this award were authored by two groups, each containing a dozen or so scientists. It would have been fairer – and would send a less distorted message about how this kind of science is actually done – if the award had been made collectively to all members of the two groups," he said.