This article is a preview from the Summer 2016 edition of New Humanist. You can find out more and subscribe here.
At Livingston in Louisiana and Hanford in Washington, there are four-kilometre-long rulers made of laser light. At 5.51am Eastern Daylight Time on 14 September 2015, a shudder went through first the Livingston ruler, then, 6.9 milliseconds later, the Hanford. It was the calling card of a passing gravitational wave – a ripple in the fabric of space-time – predicted to exist by Einstein almost exactly 100 years ago.
In a galaxy far, far away, at a time when Earth hosted nothing more complex than a bacterium, two black holes locked in a death spiral swung around each other for one last time. As they kissed and coalesced, three solar masses vanished, instantly reappearing as a tsunami of warped space-time, which raced outwards. For an instant, its power output was 50 times greater than that of all the stars in the universe put together.
Wave your arm in the air and gravitational waves propagate outwards. However, because space-time is a billion billion billion times stiffer than steel, only the most violent cosmic events such as the merger of black holes create significant vibrations of space-time. But those vibrations, like ripples spreading on a lake, die away rapidly. When they were picked up 1.4 billion years after the event by the twin detectors of the Laser Interferometric Gravitational-Wave Observatory (LIGO), they were fantastically tiny. However, their detection marks an epoch-making moment in the history of science.
Imagine you have been deaf since birth, then, suddenly, overnight, you are able to hear. This is the way it is for physicists and astronomers. For all of history, they have been able to “see” the universe. Now, at last, they can “hear” it. Gravitational waves are the voice of space. It is not too much of an exaggeration to say that their detection is the most important development in astronomy since the invention of the telescope in 1608.
On 14 September 2015, at the edge of audibility, we heard a faint sound like distant thunder. But we have yet to hear the equivalent of a baby crying, music playing or a bird singing. Over the next few years, as LIGO increases its sensitivity and other gravitational wave detectors come online in Europe, Japan and eventually India, it is anyone’s guess what the cosmic symphony will sound like. When astronomers first learned to see light invisible to the naked eye – from radio waves to infrared and X-rays – they had no inkling that they would discover gamma ray bursters, supermassive black holes or the relic “afterglow” of the Big Bang fireball.
LIGO is a technological tour de force. At each site, there are actually two tubes that are 1.2 metres in diameter, forming an L-shape, down which a megawatt of laser light travels in a vacuum better than interplanetary space. At each end, the light bounces off 42-kilogram mirrors, suspended by glass fibres just twice the thickness of a human hair and so perfectly smooth that they reflect 99.999 per cent of all incident light. It is the microscopic movement of these suspended mirrors that signals a passing gravitational wave. So sensitive is the machine that it was knocked off kilter by an earthquake in China.
To detect gravitational waves, the LIGO physicists had to do something extraordinary: spot a change in length of their four-kilometre ruler by a hundred-millionth of the diameter of an atom (one part in 1,000,000,000,000,000,000,000). It seems inconceivable that, at this very moment, the Nobel Prize committee is not considering the names of the three principal physicists behind LIGO: the Americans Rainer “Rai” Weiss and Kip Thorne, and the Scottish Ronald Drever.
I was a physics graduate student at the California Institute of Technology in Pasadena, one of the two institutions behind LIGO, when the prototype was being built. I remember going to a talk by Drever. What I recall about this unassuming man was that he carried his papers in two supermarket carrier bags and his overhead projector transparencies were covered in tea stains and fingerprints.
Drever was a crucial member of the LIGO team because he was an experimental genius. While Thorne would get an answer to a technical question after pages of careful calculation, Drever would somehow reach the same conclusion with a simple diagram.
Unfortunately, the Scottish physicist was constitutionally incapable of sharing control of the project and he was fired in 1995. Suffering from dementia, he now lives in a care home in Scotland. My message to the Nobel Prize committee is simply this: hurry up!
