There's no doubt the twin Laser Interferometer Gravitational-wave Observatory (LIGO) L-shaped detectors that picked up the fleeting chirp of a gravitational wave in September last year are marvels of engineering and physics.
To be able to accurately measure a ten-thousandth the width of a proton over a four-kilometre stretch, each component of the detectors must be spot on.
So it's no surprise the LIGO absorbed a lot of time and money: decades in the making, it ended up costing $620 million. So can various parts of it be spun off for use in everyday life?
“People might see space science as cool, but somewhat esoteric,” says Jong Chow, a physicist at the Australian National University and member of the LIGO scientific collaboration. But parts of LIGO have already been adopted for non-astrophysicists, he adds. When you run through each system that comprises the LIGO detectors, it’s not hard to see why.
A laser, split in two, bounces up and down each four-kilometre LIGO arm around 140 times, thanks to mirrors either end.
So rather than flying up and back once, each laser actually travels 560 kilometres before recombining at the corner of the L.
The reflecting mirrors must be perfectly smooth to prevent distortions in the laser beams. Even just the slightest little bit out and the recombining lasers can cause a false signal.
The mirrors are made of extremely pure silica and absorb just one part in three million of the laser light that hits them. They also refocus the laser as it bounces away.
The vacuum within the arms is one of the largest and most pure on Earth – one trillionth that of sea level air pressure, and second only to Switzerland’s Large Hadron Collider.
A vacuum keeps the lasers reflecting evenly, and makes sure everything stays cool. Any stray molecules can jostle and create heat, which can in turn create air currents. These can warp the mirrors or distort the laser’s path.
Finally, the whole kit and caboodle is kept absolutely still so a gravitational wave rolling through isn’t drowned out by a truck rumbling by.
“Active damping” systems act like noise-cancelling headphones – they monitor ground movements, then shift the opposite way. And each mirror inside the arms hangs from a pendulum. This “passive damping” absorbs any vibrations not negated by active damping.
Comparatively, real life seems so unwieldly and big, it’s almost impossible to think why you or I would need LIGO technology. But here are just four ways it could provide a return on the $620 million investment.
1. Atmospheric sensing
This is one realm where the super-reflective focusing mirrors come in handy.
They will allow climate and atmosphere scientists to more accurately nut out how much carbon dioxide, methane and other molecules are in the atmosphere.
When a carbon dioxide molecule, for instance, is hit by a photon from a laser, it absorbs a very specific wavelength, or colour, of light. The more carbon dioxide, the stronger the absorption. The remaining light intensity then tells us how much carbon dioxide is present in the atmosphere.
Comparatively, real life seems so unwieldly and big, it’s almost impossible to think why you or I would need LIGO technology.
Shining a laser through a column of air once gives one measurement; bouncing it between mirrors hundreds of times – as happens in the LIGO arms – will enhance accuracy to the same degree.
2. Oil, gas and coal surveying
Engineers can use gravitational clues to find otherwise hidden fossil fuels and minerals underground.
A “lighter” part of the Earth’s crust, such as a large gas well, will impart less gravitational pull than solid rock.
A device called a gravity gradiometer can measure how much the distance between two masses changes as they pass over fluctuating gravitational fields. The highly precise laser measuring technologies developed for LIGO will help map these perturbations to a new level of accuracy.
And let’s not forget the power of sound.
“LIGO is all about hearing the Universe,” Chow says. Gravitational waves are vibrations through space-time, like sound is vibration through air.
“LIGO’s acute sensitivity to acoustic signals can be applied to fibre optic sensing,” he adds, for oil and gas exploration and monitoring, but under the sea rather than on land.
If a company laid hundreds of fibres with signal-amplifying mirrors, such as those in the LIGO arms, on the seabed and set off an explosion, the “ping” of the detonation will travel into the crust.
If the ping encounters an oil well, some of that signal will bounce back up and be picked up by the sensitive fibres, a bit like whiskers on a seal.
This will give a three-dimensional image of the subterranean environment.
Spies, rejoice – LIGO’s incredibly sensitivity to vibrations can also be used to create a microphone that can not only pick up the faintest sounds for far away, but also triangulate their source.
NASA’s already planning to use LIGO technology in a pair of gravity-detecting satellites slated for launch in 2017.
The twin Gravity Recovery and Climate Experiment (GRACE) Follow-On craft will orbit the Earth about 500 kilometres and “weigh” the ground below.
If one satellite is dragged away from the other – even the tiniest bit – that means the ground below has exerted a little more pull, and is thus heavier. Scientists can determine the composition of the Earth below using the gravity data.
The first set of GRACE satellites, launched in 2002, used technology based on microwaves and transmitted this information for 13 years.
But incorporating gravitational wave laser-based technology in the Follow-On pair will, Chow says, let scientists map water around the globe with unprecedented accuracy – from underground reservoirs to the ice caps.
Of course, LIGO spin offs aren’t limited to these four areas. But it’s a start – and we can expect to see more of it.
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