The Guinness world record for the longest-running experiment is held by scientists at the University of Queensland, Australia who have been running the 'Pitch Drop Experiment' for nearly 100 years, which could go on for another century. Started in 1927 by an Australian physicist named Thomas Parnell, the experiment aims to measure both the fluidity and high viscosity of a substance called pitch, which is a derivative of tar and is regarded as the world's thickest known fluid that was used for waterproofing boats in the past.