The physics event of a lifetime

If you were a gambler you would wonder at the extraordinary conflux of events. After eight years in development, Advanced LIGO began its search for gravitational waves in September last year. One hour later, it recorded the definitive detection of gravitational waves.

Another coincidence: it happened 100 years after the publication of Albert Einstein’s Theory of General Relativity, which predicted the waves in the first place. But it was more than luck, it was brilliant science and engineering, and that day, Thursday 11 February 2016, will be forever etched on my mind.

There have been other major discoveries in physics and confirmations of predictions in my lifetime – black holes, dark matter, dark energy and the Higgs Boson, for example.

I pay homage to them all, but somehow they crept up on me without the fanfare of the gravitational waves event, the crescendo of which lasted just one tenth of a second, the moment when two massive black holes collided, manifested as a single oscillating blip on a computer screen.

There are three reasons for my excitement. First, gravitational waves are the final prediction to be verified from Einstein’s theory. Every other one has been proven again and again with ever-increasing accuracy.

General Relativity offered a new explanation of gravity. Rather than being a force as Newton viewed it, it was a distortion in the fabric of space-time. With this final piece of evidence, the theory now appears rock solid and – bizarre as it seems – will forever be an accurate descriptor of physics from the molecular to the cosmological scale.

In December 1999, Time magazine named Albert Einstein the Person of the Century. To me, he is the Person of the Millennium.

Second, and best of all, there is the promise of more to come. Modern astronomy started when Galileo picked up an optical telescope in the early 1600s. It wasn’t until the 1930s that the radio telescope was invented and eventually used to discover pulsars, quasars and the cosmic microwave background radiation. That’s it – two types of telescope. Until now.

Gravitational waves were discovered with two LIGO detectors in the United States – not enough to determine the direction the gravitational waves came from. But in future, three or more LIGO detectors will constitute a gravitational wave telescope, giving us a third routine way to observe the Universe.

Every time scientists develop a better microscope or measurement instrument, it provides new insights. LIGO will be no exception; there will be many more discoveries in the coming years.

Third, as an engineer, I marvel at the LIGO instrumentation.

Every time scientists develop a better … measurement instrument, it provides new insights.

Einstein did not think that we would be able to build instruments sufficiently sensitive to detect gravitational waves. Even 10 years ago it seemed impossible. But that did not daunt the physicists, engineers and mathematicians in the LIGO team.

They built a giant detector in which laser beams bounce between the mirrors at each end of two intersecting, vacuum tunnels, each four kilometres long. Changes in the length of the tunnels, as gravitational waves shimmy through, are measured by the way the laser beams interfere with each other.

The detected length change was less than a thousandth of the width of a proton – so infinitesimal it is difficult to conceive. If we imagine that the tunnels of LIGO run the length from here to the nearest star system, Alpha Centauri, 4.4 light years away, it would be like measuring fluctuations across that distance to less than the width of a single human hair.

Future generations will look back on the timeline of human history and see the bright mark etched on Thursday 11 February 2016. They will have incredible new tools at their disposal and fantastic new knowledge. I have no doubt their zeal to continue pushing back the frontiers of the Universe will remain undiminished.

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