The latest results of an international research project to detect gravitational waves mean that scientists are one step closer to understanding the nature of the universe in the seconds after the big bang.
Australian researchers are collaborating with partners in the USA and Europe to use and expand on the Laser Interferometer Gravitational-wave Observatory (LIGO) in the USA and the Virgo Observatory in Italy in the hunt for gravitational waves, energised ripples in space and time created by the enormous explosion that’s thought to have kick started our universe.
The US-based LIGO uses lasers and mirrors suspended at the end of very long, atmospherically sealed pipes to search over long periods of time for evidence of gravitational waves. It’s predicted that the passage of gravitational waves will cause miniscule differences in the length of laser paths along the pipes. The experiment reported in the journal Nature this week was conducted between 2005 and 2007.
“We were looking for the stochastic background of gravitational waves – like the continuing ripples in a pond – after the tremendous explosion that was the big bang,” explains contributing researcher Associate Professor Susan Scott from the Centre for Gravitational Physics at ANU. “The instruments deployed in the LIGO experiment were highly sensitive, a fact that would be necessary to pick up the subtle influence of gravitational waves as they pass through the detector.”
In the first major outcome for the LIGO and Virgo combined effort, the scientists did not find evidence of gravitational waves. But Associate Professor Scott says this in itself is a major step forward. “Because we didn’t detect the stochastic background at the frequency range our instruments were operating at, it means we can place strong constraints on possible theories of the early universe. In other words, we now know that earlier theories about the strength of gravitational waves were incorrect, so we can radically constrain and improve our search in the next stage of this research project.”
“We have so few means to probe the early universe,” Associate Professor Scott said. “Optical and radio astronomy aren’t useful because the electromagnetic spectrum didn’t exist in the moments after the big bang. That’s why a finding like this in gravitational astronomy is so exciting – it means we’re another step closer to knowing what our universe was like in the seconds after it came into being.”
This latest finding will inform the development of the second phase of this project. Due to come online in 2014, Advanced LIGO will involve new instruments 1,000 times more sensitive than those used in LIGO. ANU and the University of Adelaide received funding from the Australian Research Council to develop optical components that will be used in Advance LIGO. This aspect of the project is being led by the Director of the Centre for Gravitational Physics at ANU, Professor David McClelland, who also contributed to the research reported in Nature. Other Australian institutions taking part in the Advanced LIGO project include the University of Melbourne, the University of Western Australia and Charles Sturt University.
