The University of Queensland's Pitch Drop experiment, which holds the Guinness World Record for the longest-running laboratory experiment, will turn 100 years old in 2027, ABC News reported on Sunday (8 November). A brand new, empty beaker now awaits the tenth drop, which the experiment's custodian expects in the next couple of years.
The experiment sits behind glass outside a lecture theatre at the university, where the ABC reported hundreds of students walk past it every day. The university's School of Mathematics and Physics says it is kept in a display case in the foyer of the Parnell Building (Building 7) and is not kept under special environmental conditions, so the rate of flow varies with seasonal changes in temperature.
Thomas Parnell, UQ's first Professor of Physics, created the experiment in 1927 to illustrate that everyday materials can exhibit quite surprising properties, according to the university. He heated a batch of pitch, placed it in a sealed glass funnel and left it to cool, then cut the funnel's stem in 1930. The pitch has been flowing like a liquid, at an incredibly slow rate, ever since.
At room temperature pitch feels solid and can be shattered with a hammer, but the university says the substance, about 100 billion times more viscous than water, is actually fluid. Pitch was once regularly used for waterproofing decks, boats, coffins and household containers, the ABC reported.
Third Custodian
Professor Andrew White, the experiment's third custodian, told the ABC the pitch is an example of something that looks like a solid but can behave like a liquid. "Pitch is like that except billions of times more viscous than toothpaste," he said, adding that it is moving at "about an atom a second", which he said was more than ten times slower than continental drift.
His predecessor, the late Professor John Mainstone, became the second custodian in 1961 and looked after the experiment for 52 years, the university says. Like Professor Parnell, he died before seeing a drop fall.
No Pitch Drops Witnessed
Since 1930, just nine drops of pitch have fallen, and not one has ever been witnessed, the ABC reported. Professor White said Professor Mainstone spent an entire weekend at the university in 1979 expecting a drop. "He went home, had a shower, came back in Monday morning and the pitch drop had dropped," Professor White said.
At the 1988 Expo in Brisbane, where the university had a display cabinet for the pitch drop at South Bank, the drop fell in the "few minutes" when people left the room to get a drink. By the year 2000 it was hoped a drop would finally be caught on camera, but an ill-timed blackout meant another long wait. The installation of air conditioning to the building in the 1980s had also increased the time between drops, according to the ABC.
The last drop fell in 2014, but the beaker below was so full of previous drops that the new one did not actually drop. "It just touched and then spent about eight years very slowly falling over," Professor White said.
"I'd love to be able to witness it in person, but I would settle for just a really good recording," he said.