The world's longest-running laboratory experiment, known as the Pitch Drop Experiment, has been continuously operating for nearly a century at the University of Queensland in Australia. It investigates the high viscosity of pitch, a tar derivative.
Physicist Thomas Parnell initiated the experiment in 1927 by filling a funnel with pitch. In 1930, he cut the funnel's stem, allowing the pitch to flow. Pitch, though appearing solid at room temperature, is a fluid approximately 100 billion times more viscous than water.
The first droplet took eight years to fall, occurring in 1938. Subsequently, drops occurred roughly every eight years, though the rate slowed after air conditioning was installed in the 1980s. As of 2024, 96 years after the experiment officially began, only nine drops have been observed. The most recent drop occurred in 2014, and the tenth drop is anticipated in the 2020s.
Despite live streaming, no individual has directly witnessed a droplet fall due to technical issues. Thomas Parnell and his successor, John Mainstone (custodian from 1961 for 52 years), both died without observing a drop fall. Mainstone missed a drop in 2000 due to a thunderstorm disrupting the live feed and passed away months before the April 2014 drop. Physics professor Andrew White is the third and current custodian, overseeing the experiment and awaiting the tenth drop.