At first glance, the Pitch Drop Experiment at the University of Queensland in Australia might seem unremarkable – a simple glass funnel holding a hardened black substance in a display cabinet. Yet, this unassuming setup is the world’s longest-running scientific experiment, captivating scientists and the public for nearly a century.
Started in 1927 by Professor Thomas Parnell, the university’s first physics professor, the experiment was designed to demonstrate the unusual properties of pitch, a substance that appears solid but is actually an extremely viscous liquid. Nearly 100 years later, it continues to drip, with scientists predicting the experiment could outlive its creators by another century.
Pitch, the material used in the experiment, is a derivative of tar once used to waterproof boats. At room temperature, it seems rock-solid – brittle enough to shatter when struck by a hammer. However, it is a liquid, flowing at an unimaginably slow pace. With a viscosity approximately 100 billion times that of water, pitch challenges perceptions of what defines a solid and a liquid.
To conduct the experiment, Parnell heated the pitch until it melted and poured it into a glass funnel with a sealed stem. He let it cool and solidify, then allowed it to settle for three years before cutting the stem in 1930. From that moment, the pitch began its slow descent through the funnel, with the first drop taking eight years to fall.
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Since then, only nine drops have formed and fallen, the last one in 2014. The pitch drips at varying speeds depending on the surrounding temperature. Warmer weather causes it to flow slightly faster, while cooler conditions slow it down.
This elusive moment has almost taken on a mythical quality, with two generations of custodians – Professor Parnell and his successor, Professor John Mainstone, passing away without witnessing it. Mainstone, who cared for the experiment for 52 years starting in 1961, famously never got to see the pitch drip despite dedicating decades to its care.
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The experiment’s current custodian, Professor Andrew White, continues the tradition of overseeing this scientific oddity.
Despite its slow pace, the Pitch Drop Experiment has earned international acclaim. In 2005, it was honored with an Ig Nobel Prize, an award given to quirky scientific achievements that “make people laugh and then think.” Both Parnell and Mainstone were recognised for their contributions.
The experiment also holds a Guinness World Record as the longest-running laboratory experiment.
(Image: University of Queensland)