If you take a hammer and smash it down on a piece of pitch (a highly viscous derivative of tar or asphalt), the pitch will shatter into dozens of sharp, jagged pieces exactly as a pane of glass would. To the human eye and touch, room-temperature pitch is a brittle solid. However, physics dictates otherwise.
To prove that everyday intuition about states of matter can be fundamentally flawed, Professor Thomas Parnell of the University of Queensland initiated an experiment in 1927. His goal was simple: to demonstrate that pitch is actually a highly viscous fluid that flows over time. The setup has outlived its creator and continues to drip to this day.
Setting up the Longest Experiment
In 1927, Professor Parnell heated a sample of pitch, poured it into a glass funnel with a sealed stem, and let it settle. In order to ensure that the pitch was completely stabilized and free from internal thermal currents, he waited three years. Finally, in 1930, the stem of the funnel was cut.
Since that moment, the pitch has been slowly flowing out of the funnel. And when we say slowly, we mean on a timescale that tests the very limits of human patience. It takes approximately a decade for a single drop of pitch to form and eventually fall from the funnel into the beaker below.
A Timeline of Patience
The experiment is famously recognized by the Guinness World Records as the world’s longest continuously running laboratory experiment. Across its near-century of existence, only nine drops have fallen.
What makes the pitch drop experiment somewhat tragicomic is that for decades, nobody actually witnessed a drop fall. Due to the extreme time spans involved, the exact moment the stem of pitch breaks and falls into the beaker was constantly missed.
| Drop Number | Year Fallen | Years Between Drops |
|---|---|---|
| 1st | 1938 | 8 (from cutting) |
| 4th | 1962 | 8 |
| 7th | 1988 | 9 |
| 8th | 2000 | 12 |
| 9th | 2014 | 14 |
Professor John Mainstone, who became the experiment's custodian in 1961, watched over the setup for 52 years. During that time, three drops fell. He missed the 1977 drop because he was away for a single weekend. In 1988, he stepped out to get a coffee, and the drop fell. For the 2000 drop, a webcam had finally been set up, but a 20-minute power outage in the building caused the camera to miss the exact moment.
The Science of Viscosity
From the collected data across nine decades, physicists have been able to calculate the precise viscosity of the pitch used in Parnell's funnel. The math reveals that the pitch is approximately 230 billion times more viscous than water. The rate of the drip is also heavily influenced by ambient temperature; the installation of air conditioning in the building during the 1980s cooled the ambient room temperature, stretching the time between the eighth and ninth drops to 14 years.
The pitch drop experiment serves as a profound reminder that human lifespans and human intuition are not the ultimate baselines for the universe. Matter flows and changes on geological timescales that render our daily observations entirely subjective. While we shatter pitch with a hammer, gravity is slowly, inevitably pulling it down like the liquid it truly is.