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Twenty

Time waits for one man

In 2004, Hough agreed to place a bet at odds of 500/1 that gravitational waves would be detected before 2010…

Time waits for one man

Time waits for one man

Not many people spend more than 40 years searching for something that may not exist or may never be found. Albert Einstein had predicted gravitational waves in an addendum (1916) to his General Theory of Relativity (published in 1915), but he doubted we would ever detect them – and even doubted if they existed at all. But in the greater scale of things, a few more decades for a physicist such as Jim Hough in Glasgow are only the blink of an eye, like the first gravitational waves detected by scientists two years ago.

You might expect the Earth to shake, but what started out as a giant explosion arrived not as a bang but as a whimper – changing the distance between two pairs of mirrors “by an infinitesimally small amount” when it hit the detectors, and lasting a few hundred milliseconds before it was gone, a billion years after the waves first set out on their journey.

For Professor Hough, Associate Director of the Institute for Gravitational Research (IGR) and currently Research Professor in Natural Philosophy at the University of Glasgow, that historic moment was in many ways the climax of his scientific career, but for some people also a slight disappointment. In 2004, Hough agreed to place a bet at odds of 500/1 that gravitational waves would be detected before 2010. The odds were later cut to 25/1 when Hough learned how to place his bet, and then were further cut to 6/1 when other punters followed the physicist's lead; but that was academic by the time of the discovery – five years too late for the pay-out.

Now officially retired, but with a research position at the University, Hough is still as keen as ever to be part of the adventure, and has watched the search for gravitational waves grow from a team of just a few people at the start to over a thousand today. But even though he was a pioneer in the field and things were very different 46 years ago when he was a young research fellow, he got involved in the same way as many others – partly by accident, partly by choice.

For Hough, the story started 46 years ago, and like so many other scientists, serendipity guided events. When he was finishing his PhD in nuclear instrumentation, “the gloss was coming off the nuclear industry,” and he was looking for something more exciting to work on. Several events had taken place which had a huge impact on Hough and many other physicists – including the discovery of pulsars in 1967 by Jocelyn Bell and Antony Hewish at Cambridge. As the Cold War got colder, there was also an increasing need to study gamma ray bursts (some of the most energetic and mysterious events in the Universe), which may or may not have been caused by Soviet testing of nuclear bombs – and all of this required the development of much more sensitive detectors of different types to keep a closer eye on Outer Space.

Hough and Ronald Drever, his research supervisor, also knew about the work of Joseph Weber and his controversial search for gravitational waves, using the first bar detectors – solid metal cylinders which Weber believed were sensitive enough to pick up the vibrations from faraway cosmic events. Even though Weber was “shabbily treated” by some of his colleagues, because of flaws in how he analysed the data, Drever and Hough, and many others, shared his interest in the quest for gravitational waves, and tried to develop new, better detectors and, at the same time, make sure they were getting their sums right.

Using new technology, including very sensitive piezoelectric transducers and ultra-low-noise Field Effect Transistor amplifiers, Drever and Hough designed and built two new detectors which they believed were capable of tuning over a much wider bandwidth. The Glasgow team also kept in close contact with colleagues in the Universities of Bristol and Reading, who were thinking along similar lines. And they also collaborated with groups in Germany and Italy and a number of groups in the USA, who all made “immense contributions,” says Hough, to advancing the science.

“In the early days, the search for gravitational waves was driven by an element of competition between scientists,” Hough told Science Scotland in 2004. But even then, the emphasis was on collaboration, mainly because of the scale of the projects.

There have been several false alarms over the decades. In 1972, Drever, Hough and colleagues detected “a very clear signal” which they were convinced was a gravitational wave. The first signs were characteristic blips on the charts used to record any signals; but to add to the tension, the scientists in Glasgow had to wait for a couple of days – first, they had to develop the film in the camera used to photograph the oscilloscope, then print out the negatives, before they could see the results. While this was going on, the Glasgow team discovered that all the detectors in other locations were not operating at the time of the reported “detection,” thus making it impossible to tell for sure if what they had observed was a local effect or evidence of something more significant. The team of five, including Hough, was confident that they had eliminated most of the “noise” which may have interfered with the beautiful signal, including thermostats, but they knew the source could still be something else. “We were not surprised,” Hough explains, “just excited – we knew we had a better chance than Weber, and also knew the weaknesses in his data analysis.”

No matter what they had detected, the Glasgow team knew that something amazing had happened. “We were lucky – we had probably observed a supernova,” says Hough, “an event which at the time was expected to happen once every 30 years, and was long overdue.” Hough and his team also asked other scientists, keeping a look-out on the upper atmosphere, if they’d seen something unusual. But despite their initial excitement, they could not prove they had seen gravitational waves...

In the end, the Glasgow team published a paper in Nature describing what they had observed, but because they could not prove the signal was a gravitational wave, they were careful not to make any extravagant claims. “We saw exciting shapes in the photo,” says Hough. “On one detector, we could see an increase in the amplitude, and on the other, a phase change. It was a very rare event, but what you would expect to see if this was in fact a gravitational wave.”

In 1972, he thought they had done it and had been disappointed, but Hough knew he “had to keep going,” and was confident they would detect gravitational waves – one day. It was only a matter of time...

The search continues...

Other scientists were doing a range of experiments which fell by the wayside, but research and development gathered momentum, including the idea of using liquid helium, and SQUID amplifiers (superconducting quantum interference devices) – very sensitive magnetometers used to measure extremely subtle magnetic fields.

The technology took a leap forward when lasers came into the picture. The American physicist and science fiction writer, Bob Forward, then working for the Hughes Aircraft Company in California, had built a small detector using a laser interferometer. Forward owned a small castle in Scotland and, during one of his visits, met the Glasgow team, encouraging them to keep working on their ideas for laser interferometry, particularly on a system with 10-metre arms (the distance between the mirrors), which started in 1979. According to Hough, it was a “technically satisfying” system, but would never have had the sensitivity to detect gravitational waves although it did mark a significant change in direction and was one of the forerunners of today's much more powerful systems. Despite these exciting advances, this period was “very frustrating” for Hough as he struggled for funding, and the initiative was taken up by Caltech (the California Institute of Technology), where Ron Drever, who had been recruited from the University of Glasgow, built a bigger version of the laser interferometer, with 40-metre arms. Then, in 1986, US researchers started working on the first proposal for LIGO, eventually designing a facility with arms 4km long.

Apart from the huge jump in scale, other aspects of the new design needed improvement. “It became clear that we needed a significant improvement in the sensitivity of the detector,” says Hough, “including better suspension systems and better optical coatings for the mirrors.”

Meanwhile, in Germany, researchers had been going down a similar route, and were thinking of building much bigger detectors, and Hough then got involved in a proposal to construct a large facility in Scotland, with two sites identified – one in Tentsmuir Forest near St Andrews and the other at Buchlyvie near Stirling, using a disused railway junction which had tracks long enough (and straight enough) to have two arms 1km long at close to 90 degrees to each other. “We got planning permission at Tentsmuir,” says Hough, “and I got the impression the local residents thought this was a military project.” The design was never built, however, and UK scientists began to work with colleagues in Germany, making a major contribution to the design of the GEO600 detector in Hanover, Germany. “It was a clever design,” Hough explains, “and the first time we used silica fibres for suspending the mirrors.” It was also a design which formed the basis for the Advanced LIGO detectors, an upgrade which began in 2010 and started operating five years later.

There was another false alarm in 2010 when LIGO (the Laser Interferometer Gravitational-wave Observatory) appeared to detect a very clear signal. The scientists were looking for the merger of two neutron stars or black holes – what’s called “a coalescing binary” – but even though something had triggered the system, it was not what everyone hoped for. “In fact,” says Hough, “it turned out to be a ‘blind’ test injection of signals – deliberately added to test the efficacy of our hardware and signal processing.”

Then finally, in 2015, Hough's patience was rewarded. Gravitational waves were detected by LIGO. The long wait was over, a theory was proved and a new field of science was born.


Biography

Professor Jim Hough OBE is Associate Director of the Institute for Gravitational Research (IGR) and is a Fellow of the Royal Society, the Royal Society of Edinburgh and the American Physical Society, and an Honorary Fellow of the Institute of Physics. Since 1971, he has carried out pioneering research in gravitational-wave physics – ultimately paving the way towards the detection of gravitational waves. He was UK leader and pioneer of the German–UK GEO600 detector and, with colleagues, took part in the development of the laser stabilisation and mechanical isolation systems essential to the detection of gravitational waves by Advanced LIGO. He was appointed Professor of Experimental Physics at the University of Glasgow in 1986, held the Kelvin Chair for a short while and is currently Research Professor in Natural Philosophy at the University of Glasgow and a Visiting Professor in Physics at the University of Strathclyde. In December 2016, he was awarded the RSE’s Royal Medal in recognition of his achievements.

 

 

 

 

"Time waits for one man". Science Scotland (Issue Twenty)
Printed from http://www.sciencescotland.org/feature.php?id=308 on 22/11/17 01:10:57 PM

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