Thomas Parnell: 1927 Physics Research at University of Queensland

The University of Queensland’s pitch drop experiment, one of the longest-running scientific demonstrations in the world, continues to captivate researchers and the public alike nearly a century after its inception. Initiated in 1927 by physicist Thomas Parnell, the experiment was designed to demonstrate the surprisingly high viscosity of pitch — a substance that appears solid at room temperature but is, in fact, an extremely slow-flowing liquid. Despite its seemingly mundane setup, the experiment has become a global symbol of patience in science, with each drop taking years, sometimes over a decade, to form and fall.

What makes the pitch drop experiment particularly compelling is not just its longevity, but its resistance to prediction or manipulation. As Professor John Mainstone, who oversaw the experiment for over 50 years until his death in 2013, often remarked, the drops “cannot be tricked or forecast.” This unpredictability stems from the complex interplay of temperature, humidity, and the non-Newtonian properties of pitch, which cause each drop to form at irregular intervals. To date, only nine drops have fallen since the experiment began, with the ninth occurring in April 2014 — a moment missed by cameras due to a technical glitch, though the event was later confirmed by the position of the drop.

The experiment resides in a display cabinet in the foyer of the Parnell Building at the University of Queensland’s St Lucia campus in Brisbane, Australia. It consists of a glass funnel filled with pitch, which was heated and poured into the funnel in 1927 before being allowed to cool and settle over three years. In 1930, the stem of the funnel was cut, allowing the pitch to initiate its extraordinarily slow descent. A webcam has monitored the experiment continuously since 2000, allowing global audiences to observe the rare event in real time — though catching a drop fall remains a matter of extraordinary luck.

According to the University of Queensland, the pitch used in the experiment has a viscosity approximately 230 billion times that of water, making it one of the most viscous substances known to science. This extraordinary resistance to flow means that while the pitch appears brittle and solid enough to shatter with a hammer, It’s actually flowing — albeit at a rate so slow that human observation struggles to perceive it. The experiment serves as a powerful pedagogical tool, illustrating concepts in fluid dynamics, thermodynamics, and the nature of materials in a way that abstract equations often cannot.

Over the decades, the pitch drop experiment has attracted attention from scientists, educators, and curious visitors worldwide. It has been featured in documentaries, science festivals, and educational outreach programs, often cited as an example of how long-term observation can reveal truths invisible in short-term studies. The experiment was recognized by the Guinness World Records as the longest-running laboratory experiment, a testament to its endurance and scientific value.

Following the death of Professor Mainstone, who had become the public face of the experiment, the University of Queensland established a memorial in his honor near the display. Current custodianship of the experiment falls to the School of Mathematics and Physics, which maintains the live stream and ensures the apparatus remains undisturbed. The tenth drop is anticipated, though no reliable prediction can be made — current estimates based on historical intervals suggest it may fall sometime in the 2020s, but researchers emphasize that such forecasts are speculative at best.

The experiment’s enduring appeal lies not only in its scientific merit but in its philosophical resonance. In an age of rapid results and instant gratification, the pitch drop experiment stands as a quiet reminder that some truths reveal themselves only through sustained attention and acceptance of uncertainty. As the university notes on its official page, the experiment “challenges our intuition about what it means for a material to be solid or liquid” and invites contemplation on the timescales inherent in natural processes.

For those wishing to observe the experiment, the University of Queensland provides a live stream via its website, updated regularly with still images and video highlights. The pitch drop experiment remains active and undisturbed, continuing its slow, inexorable march toward the next fall — a moment that, when it comes, will be celebrated not for its spectacle, but for what it represents: the enduring power of curiosity, patience, and the quiet persistence of scientific inquiry.

The experiment has too inspired similar demonstrations around the world, including versions at Trinity College Dublin and the Royal Scottish Museum, though none have matched the original’s duration or consistency of observation. These parallel efforts underscore the experiment’s influence as a pedagogical and cultural artifact, transcending its origins to become a shared touchstone in the global scientific community.

As the world awaits the tenth drop, the pitch drop experiment continues to fulfill its original purpose: to teach, to intrigue, and to remind us that some of nature’s most profound behaviors unfold not in bursts, but in drops — slow, sure, and utterly indifferent to human haste.