But the practicalities were not so simple.

“Everything needed to be roughly a factor of 1000 more powerful or sensitive than we had at the time,” Bachor recalls.

Laser technology was weak. Nobody knew how to build a good enough mirror, it had to be massive and perfectly smooth, and with losses less than one part in a billion.

The experiment would need to be enormous, preferably 10 or more kilometres long.

Damping out vibrations from the environment was another huge challenge. The smallest earth tremor, or a passing truck, threatened to obliterate the tiny ripples from distant spacequakes.

But they didn’t know the size and shape of the ripples they were searching for, says Professor Susan Scott, from the Research School of Physics and Engineering (RSPE).

“We really had no idea of the enormity of the task which lay ahead of us. We were searching for a needle in a cosmic haystack, extremely faint signals in very noisy data.

“We had early meetings with submarine intelligence experts but we quickly realised we were facing a much more daunting task than theirs,” she said.

But, as in 1916, the scientists were not discouraged.

“The amazing thing was that the mood at the end of the conference was ‘Let’s go for it,’ ” Bachor says.

“We were eternal optimists. These people were pioneers who had seen the progress over the previous 20 years. We trusted that the technology would evolve.”

But political realities posed a big obstacle to progress.

The Russians quickly realised they could not afford to build an experiment.

The UK could not find the land and teamed up with Germany to build a smaller experiment, GEO 600, only 600 metres long. Japan set up small experiments in disused mines.

Australia had the land but lost out on funding against stiff competition from more developed astronomy projects, such as the Square Kilometre Array, which could guarantee data.

The gravitational astronomy world’s hopes lay with the two four-kilometre long experiments at the Laser Interferometer Gravitational-Wave Observatory (LIGO) at either end of the US, and the French-Italian Virgo project.

The nations apportioned the tasks, and set to work.

Over the next 20 years technological revolution after technological revolution achieved the impossible.

Joining the hunt as an honours student in 1996, Daniel Shaddock, was dismayed by the challenge.

“When I first heard about the sensitivity needed for gravitational waves, I thought that’s crazy, we’re never going to see them,” said Shaddock, now a professor in the RSPE.

“But you start working through the challenges and before you know it, you’re in a position where you have the measurement technology that you need.”

Also drawn to the quest was Dutch student Bram Slagmolen, who travelled around the globe in 1999 to work with McClelland.

“We’ve done things I wouldn’t have dreamed of back then,” says Slagmolen, now a research fellow at ANU and the leader of the Australian Consortium for Interferometric Gravitational Astronomy.

“Although the final experiment would be on a large scale and hideously complex, we ran little experiments that gave us understanding and allowed us to go the next step.”

In Italy, the Virgo experiment was dogged by technical hitches, but by mid-2015, LIGO scientists – including many Australians led by McClelland – believed their twin US experiments could start, and flicked on the many systems required to isolate Einstein’s elusive echoes of intergalactic impacts.

Then the Universe delivered something truly extraordinary.

The team had estimated they might have to spend a couple of years sifting through their data to find matched sets of tiny wobbles from outer space.

But while they were still doing final tests with simulated data, still days away from the first official science run, the detector twanged with a signal so clear that the team could see it above the background without any filtering.

“The signal matched perfectly to the predicted pattern of two black holes colliding, but it was so strong we thought it must be a blind injection of a simulated signal, ” Scott says.

“We were aware very quickly that this was not the case and so this signal that had thundered into our detectors was probably real, and from surprisingly large black holes.”

A long time ago in a galaxy far, far away, there had been an invisible collision that had unleashed more energy than any other event humans had witnessed.

The peak power had been 50 times that of total output of every star in the visible universe.

There was no accompanying flash of an explosion.

After a trip of 1.3 billion years across the cosmic pond, the ripples had died down so much that they moved LIGO’s mirrors by about one thousandth of the diameter of a proton.

The signal was imperceptible to normal humans but clear as a bell in the detector in Louisiana and then, seven milliseconds later, in the Washington State detector.