‘It’s literally slower than watching Australia drift north’: the laboratory experiment that will outlive us all

Recognised by the Guinness Book of Records as the longest running lab experiment in the world, the pitch drop experiment’s third custodian is Prof Andrew White. Photograph: David Kelly/The Guardian

On a Friday afternoon in April 1979, John Mainstone, a physics professor at the University of Queensland, rang his wife at home. He wouldn’t be back that evening, he told her. For the previous 18 years, Mainstone had looked after the pitch drop experiment, a long-form demonstration of the extreme viscosity of pitch. For the first time since August 1970, the pitch was about to drip from its funnel, and Mainstone didn’t want to miss it.

Pitch is a resin – a viscoelastic substance derived from petroleum or coal tar, used in bitumen, and for waterproofing. Which is ironic, for as solid as it appears, pitch is fluid: at least, it is when you put it in a funnel, the sloping sides of which create a pressure gradient.