In 1927 Australian scientists began an experiment at the University of Queensland to see how solids can flow like liquids by setting up a blob of pitch, a tar derivative, in a funnel above a beaker.
The Pitch Drop has become the world's longest-running lab experiment and this week it had a breakthrough. The ninth blob of tar in the test's 84-year history dripped through to the beaker, in its first movement in more than 13 years.
And for the first time ever - a drop was was observed by a witness.
The achievement is somewhat bittersweet, as the scientist who oversaw the experiment for 50 years, Professor John Mainstone, died last year without ever seeing a pitch drop.
Professor Mainstone's near misses:
- 1979 - blob drops for sixth time but Professor Mainstone misses it by a day after skipping his usual visit
- 1988 - blob drops for seventh time but the professor misses it after popping out for five minutes for a drink
- 2000 - A webcam is trained on the experiment during its eighth drop, but a 20-minute power cut meant he was unable to view the footage
The Pitch Drop's current custodian, Professor Andrew White, said seven drops had fallen between 1930, when the experiment began, and 1988, at an average of one drop every eight years.
“Two things changed after that – the 2000 (eighth) and 2014 (ninth) drop each took about 13 years to fall, and each collided into the decades-old pile of drops in the beaker before it could break away from the funnel,” he said.
Following Professor Mainstone's unfortunate encounters, the funnel and beaker was put under "constant surveillance", the university said, with three cameras constantly trained on the impending ninth drop.
Patient fans with time on their hands can watch out for the tenth drop on a live web stream
Almost 29,000 viewers from across 158 countries have registered with the site to ensure their names are on record if they are logged in during a highly anticipated drop.
Professor White said the university will now use the video footage “to determine the actual moment" when the pitch motion slowed down.
Speculating over the fate of the ninth drop, he said that it "may tip over quickly or it might slow right down and take years to break away from the imminent tenth drop."