Original URL: http://www.theregister.co.uk/2011/10/04/nobel_prize_physics_2011/

Accelerating universe expansion discovery snags Nobel Prize

Long time coming for Oz-US astronomers

By Richard Chirgwin

Posted in Science, 4th October 2011 23:00 GMT

A discovery first published in 1998 has won the Nobel Prize for Physics for three astronomers, including Brian Schmidt of the Australian National University.

Competing with Saul Perlmutter of the University of California and the Lawrence Berkeley National Laboratory, and working with Adam Riess of the Johns Hopkins University and Space Telescope Science Institute, Schmidt was part of the team that first demonstrated the rate of expansion of the universe is accelerating.

That discovery – based on work begun in 1988 by Perlmutter, with Schmidt and Riess beginning their measurements in 1995* by a team led by Schmidt in which Riess played what the Nobel Prize release describes as “a crucial role” – has been recognized with the $US1.5 million Nobel.

Schmidt told Australian 702 Sydney radio broadcaster Adam Spencer that the group had chosen to use Type 1A supernovae to measure the rate of expansion of the universe. These supernovae form when a white dwarf absorbs mass from a nearby star, causing it to explode.

Because they have a predictable brightness, Schmidt said, they’re very suitable for such measurements: brightness indicates distance, and red-shift indicates velocity.

And that’s how the team made their discovery – old news today, but surprising at the time. By comparing the movement of relatively nearby Type 1As to their distant (and much older – about 5 billion years old) cousins, they determined that the expansion of the universe now is faster than it was in the distant past.

“I was shocked by the discovery”, Schmidt told 702 listeners. “Initially I thought it couldn’t be right.

“It was over a period of about six weeks that it dawned on me – and the rest of the team – that this was something we were going to have to deal with.”

The search to locate what was “pushing on the universe” eventually led to the hypothesis that the acceleration has to be driven by “dark energy”, which makes up around 73 percent of the universe, he said.

The prize makes Schmidt the first Australian citizen to receive the Nobel Prize for Physics in more than 90 years. The joint winners of the 1915 prize, William and Lawrence Bragg, who split their time between Australia and England and probably regarded themselves as “British” (as was normal for Australians of the day), are credited with initiating the field of X-ray crystallography.

The search still goes on to identify just what comprises the 73 percent of the universe discovered by Perlmutter, Riess and Schmidt. ®

*There’s a discrepancy in dates: the Nobel Prize press release gives the beginning of Schmidt’s project as 1994. However, Schmidt has told various media in Australia, including ABC 702’s Adam Spencer and ABC current affairs show AM that he started work in 1995. ®