The World’s Longest Running Experiment

The School of Mathematics and Physics at the University of Queensland holds the record for the longest continuously running scientific experiment. This experiment, known as the ‘Pitch Drop Experiment’ and has been running for 82 years.

The pitch drop experiment, with the current custodian Professor John Mainstone

The pitch drop experiment, with the experiment's custodian Professor John Mainstone (from UQ Media Archive)

In 1927, Professor Thomas Parnell (the first professor of physics at UQ) wanted to demonstrate that some substances that appear to have the properties of a solid, are actually extremely viscous liquids. Pitch is another name for bitumen, which is obtained through the fractional distillation of crude oil where it is collected as the bottom, residual layer. The picture below demonstrates that despite the appearance of the pitch drop experiment, the pitch itself is not sticky or soft and in fact feels hard, smooth and glass-like to the touch.

Pitch (Picture from UQ School of Mathematics and Physics

Pitch (Picture from UQ School of Mathematics and Physics

Parnell was an educator, and set up the pitch drop experiment primarily as a demonstration, rather than a strictly controlled scientific experiment. Indeed, the viscosity of pitch varies enormously with temperature and in particular, daily temperature fluctuations decrease the viscosity. Despite the effect on the experiment of known variable of temperature, the viscosity of the pitch was calculated and determined to have a viscosity 230 billion times that of water. A paper was published in the European Journal of Physics in 1984, and can be viewed here on the UQ Pitch Drop website. Web of Science does not show any other papers published since and therefore no update on the calculated viscosity since the fall of the last two drops, which occurred after air conditioning was installed in the building housing the experiment.

In over 8 decades that experiment has been running, there have been 8 drops of pitch fall, the last being in November 2000. No one has ever witnessed the fall of a drop either, so if you want to see the next drop for yourself, keep a close eye on the webcam. The interval between drops has ranged from 7 to 12 years, so we can expect the next drop to fall any moment now…

One Comment on “The World’s Longest Running Experiment”

  1. […] The World’s Longest Running Experiment […]

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