The world's longest-running laboratory experiment has finally delivered a result – eight months after the man who patiently watched over it unrewarded for five decades died.
Set up in the 1920s to demonstrate to students that objects that appear solid can flow like liquids, the pitch drop experiment at the University of Queensland has captivated many who had waited more than 13 years for the latest globule of the tar-like substance to form and fall.
Pitch is a material hard enough to shatter when hit by a hammer. However put a pile of it in a funnel and the pressure generated from being squeezed through the narrow mouth makes it flow like liquid. Albeit slowly.
To put things in perspective: Australia is moving north at six centimetres a year due to continental drift. The pitch in this experiment is moving 10 times slower than that.
On Thursday, the ninth dollop to fall in 83 years touched down. Until last week, no one had ever seen one land.
Physicist John Mainstone missed all three pitch drops that took place during his custodianship. Having retrieved the experiment from the back of a cupboard, he watched over it for 50 years.
Professor Mainstone once devoted an entire weekend to watching the pitch in 1977 – only to go home exhausted and miss the event by a day.
Similarly, in 1988, he knew a drop was close, but it happened in the five minutes when he left the room to get a cup of tea.
By 2000 there was a webcam pointed at the pitch. Although in England, Professor Mainstone knew he could watch it live or have it recorded. However, a tropical storm caused a 20 minute power outage right when the pitch landed.
Professor Mainstone died after suffering a stroke last August, aged 78, just months before the ninth blob of pitch fell.
Current custodian Andrew White said given the amount of pitch yet to land in the beaker, the experiment could run for at least another 80 years. He said if the pitch continued to drop at the current rate, the next dollop to land could coincide with the centenary of the experiment in 2027.
The experiment has been referenced in popular culture, getting a mention in Nick Earls' book Perfect Skin. It is recognised by Guinness World Records as the longest-running laboratory experiment, and in 2005 it won an Ig Nobel Prize - "for research that makes you people laugh and think".
Professor White, a quantum physicist who describes himself as just "four pitch drops old", thinks the experiment's appeal is in its touchstone qualities.
"It gives you a connection to deep time that you don't get in your normal lifetime," he said.
"In that beaker is the pitch drop from before you were born, from before your parents were born and for some younger people, the pitch drop from before their grandparents were born."
The experiment was set up in 1927 by Thomas Parnell, the founding professor of physics at Queensland University.
Between 1930 and 1988 the pitch drops fell on average every eight years. Professor White said the drops took longer to form and fall after air-conditioning was installed in the university in the 1980s. They now land, slightly larger, in the beaker every 13 years or so.
A common household material a hundred years ago, pitch was used to waterproof containers including boats and coffins.
Pitch is a viscous elastic material, meaning it can behave either as a solid or a liquid depending on the conditions. A more familiar viscous material is toothpaste – it flows when under pressure. But on a toothbrush it can be held upside down and it won't flow.
The experiment has delivered a published scientific result. After seven drops, scientists calculated the viscosity of pitch in a 1984 paper published in the Euro-pean Journal of Physics. They found it was 230 billion times that of water.
"It's hardly a high-yield experiment and we could probably have got that data more quickly in other ways," Professor White admitted. "But the real value of this is that it gets people to think about the world in a different way."
