Science

Though too late for its veteran custodian, last month’s rare milestone in the world’s longest-running experiment caused excitement around the globe. By Wendy Zukerman.

All eyes on Pitch Drop Experiment

The University of Queensland Pitch Drop Experiment, set up in 1927.
Credit: COURTESY UNIVERSITY OF QUEENSLAND

It dropped. After 80 years, the black blob fell and – for the first time in history – there were witnesses. The longest-running experiment in the world had finally reached one of its most significant milestones. But, of course, it came too late.

For decades, Professor John Mainstone watched as thick black gobs of tar pitch, or bitumen, formed at the base of a glass funnel. He was hoping to see just one plop down into a beaker below. But this pitch is 230 billion times more viscous than water, and exudes so slowly out of its glass cage that in more than 80 years only nine drops have materialised. Until a few weeks ago, the fates of physics conspired to prevent anyone from seeing those blobs fall. And by the time a birth was witnessed, John Mainstone had died.

This curious installation, called the Pitch Drop Experiment, was set up at the University of Queensland by the institution’s first physics professor, Thomas Parnell, in 1927. Parnell wanted to show his students that the black material, which is so solid you can smash it like glass at room temperature, is in fact an incredibly viscous liquid that can drip through a funnel. 

I spoke with Mainstone about the experiment in May last year, a few months before his death. By then, he had been its custodian for 52 years, and he was certain the pitch was about to drop. “We have to be extremely careful not to disturb the system in any way at this very late stage in its gestation or, for sure, a miscarriage will occur,” he said.

Expecting to celebrate the ninth drop’s birthday in 2013, Mainstone would inspect the pitch five times a day. Around the world, a strange excitement was growing. A web camera was set up, allowing fans to watch as the thick black blob grew and grew. Tens of thousands logged on, hoping to be the first in the world to see a pitch drop. But then, word came of a splashdown from across the seas.

On July 11 in 2013 a falling blob was recorded from a little-known pitch drop experiment housed in Trinity College Dublin, which had been running since 1944. The birth was captured on a webcam planted only three months earlier. While the Australian team had a dedicated custodian – as well as the Guinness World Record for the longest-running experiment, and an Ig Nobel Prize awarded in 2005 – the prize of first witness went to the Irish. More than two million people have since watched the fateful footage of the pitch plunging. 

“We were certainly excited,” says Denis Weaire, emeritus professor of physics at Trinity. “Too bad the Australians beat us to the Ig Nobel Prize – I’d be pleased to get one.”

Back in Brisbane, John Mainstone stayed loyal to his growing baby. But the ninth drop still hadn’t come when in August its patient overseer died of a stroke. 

Last month, as rains pelted Brisbane some time between April 12 and 13, the viscous splotch fell. It collided with its brother, the eighth drop, which has been sitting at the bottom of the beaker since it landed there 13 years ago. The ninth was captured on camera and uploaded to YouTube, where it quickly racked up hundreds of thousands of views. The precise moment of touchdown is still being calculated.

The pitch drop’s first blob had been gestating for several years when Mainstone was born, on January 12, 1935. It would take three more years for the beast to birth. As Germany and France signed a pact promising peace, and Adolf Hitler was bestowed Time’s Man of the Year, the world’s first pitch drop fell, unseen.

By the time the second drop splashed down, in 1947, postwar matters were wrapping up in Europe. The Paris Peace Treaties were being signed. Meanwhile, technology was moving fast. The same year the second blob fell, the world’s first transistor was made. The electronics revolution could begin. 

Mainstone entered the story in the summer of 1961, when he started work in the physics department at the University of Queensland. The Pitch Drop Experiment was gathering dust in the corner of a cupboard in the physics laboratory, and on his first day Mainstone was shown the oddity. He remembered thinking at the time that it was “historic” – unlike anything he had seen.

That night, while at dinner with the then head of physics, Hugh Webster, the young lecturer suggested the experiment be put on display for the general public. “I was told rather smartly that it would not be a crowd-pleaser,” Mainstone said. 

A year later, in May 1962 – as elsewhere Marilyn Monroe sang “Happy Birthday, Mr President” to John F. Kennedy and the Beatles signed their first recording contract – the fourth drop fell. Paul McCartney would already have announced his exit from the band by the time the fifth blob followed it.

In 1972, a new head of physics at the university agreed to showcase the Pitch Drop Experiment in the department’s foyer. This was where a young Andrew White, now a professor at the university, first saw the oddity. He was a Boy Scout from the small country town of Caboolture, on a visit to the university. To this little boy, university – with a population larger than his home town – “was a revelation”. And the Pitch Drop Experiment? “It was cool,” he says.

Early in 1979, things were getting nervy. The pitch was heavily pregnant and a birth was imminent. Mainstone dropped into the lab on a Saturday to check it. He even contemplated staying at work all weekend, but thought it best he head home. By Monday morning, the sixth drop had already taken its five-centimetre dive into the glass beaker below.

Nine years on, NASA scientist James Hansen testified to the US senate that human-made global warming had begun. The first mobile phones and personal computers were finding their way into our homes. Brisbane was hosting the World Expo in July 1988. From its humble days in a cupboard corner, the Pitch Drop was now being exhibited at the expo for the world to see. Thousands walked past the expectant droplet, which was barely hanging on to its mothership. Mainstone noticed four or five hanging fibres from the drop. He had seen these back in 1979, just before the pitch birthed. Labour was certain.

Day and night he watched and waited, mesmerised by the slightest change in the drop’s structure. After gazing into the pitch’s belly for hours he went to get a can of soft drink. “Maybe five minutes went by,” he said. Five minutes too long. When he returned, the seventh blob had fallen.

Reeling from the failure of 1988, Mainstone and his team set up a 24-hour video camera to record the next drop. It was November 2000 and Mainstone was away at a conference when the event was expected. Still, he was confident the camera would capture the moment.

While away, an email landed in his inbox. “It has dropped! But it hasn’t dropped very cleanly because it was a very big drop,” his colleague wrote. Mainstone replied, “That’s fine. We’ll still be able to see what happens.” Hours later, he received a second email. “Oh no ... !” it began. A malfunction in the video camera’s digital memory meant footage of the unseen eighth drop was lost forever.

By 2013, three video cameras were set with their eyes firmly on the pitch. “I am 78,” Mainstone told me. “This might be my last chance to see it happen.” 

When it fell in April, eight months after Mainstone’s death, the cameras finally captured the moment. “It’s really bittersweet, because I wish John was here,” says Andrew White. The Boy Scout from Caboolture is now the Pitch Drop’s new custodian.

Like Mainstone, he marvels at the thick black blobs. “You can see the drops that fell before you were born, and before your parents were born,” says White. “It’s not often that you can see time made solid.” But, of course, the pitch is not solid. And soon, the 10th drop will begin to form.

This article was first published in the print edition of The Saturday Paper on May 10, 2014 as "Fever pitch". Subscribe here.

Wendy Zukerman
is a science journalist and host of the Science Vs. podcast.