Washington  - The experiment that should finally detect ripples in the fabric of space-time is up and running.

Labs in the US states of Washington and Louisiana began “listening” for the gravitational waves that are predicted to flow through the Earth when violent events occur in space. The Advanced Ligo facilities have just completed a major upgrade. Scientists believe this will now give them the sensitivity needed to pick up what should be a very subtle signal. The theoretical physicist Kip Thorne, one of the pioneers behind the experiment, went so far as to say that it would be “quite surprising” if the labs made no detection.

“We are there; we are in the ball park now. It’s clear that this is going to be pulled off,” he confidently told The Documentary programme on the BBC World Service. Gravitational waves are a prediction of Einstein’s Theory of General Relativity. They describe the warping of space-time that occurs when masses accelerate. But their expected weakness means only astrophysical phenomena on a truly colossal scale are likely to generate waves that will register on even the remarkable technologies assembled at Hanford in the American northwest and at Livingston in the southeast. The technique being employed is laser interferometry. Both Ligo labs work by splitting a light beam and sending the two halves down separate, 4km-long, evacuated tunnels.

The beams are bounced back and forth by mirrors before being recombined at their starting point and sent to detectors. If the delicate gravitational waves pass through the set-up, the laser light should show evidence of having been ever so slightly disturbed - either lengthened or shortened. Advanced Ligo is looking for changes in laser-arm distance that are on the order of one one-thousandth of the width of a proton.

The equipment’s peak sensitivity will be to waves with a frequency of around 100 Hertz, which in auditory terms is at the low end of what humans can hear. And it is for this reason that gravitational wave detection is often described as trying to pick up the “sounds of the cosmos”.

“These detectors are like microphones where we’re listening to the Universe,” said Jamie Rollins from the California Institute of Technology, one of the project’s lead institutions. “It’s sort of like we’ve been deaf to the Universe until now, and turning on these detectors is like turning on our ears.”