For nearly a century, a simple apparatus in an Australian university has quietly challenged human intuition about solids and liquids.
Known as the Pitch Drop Experiment, this remarkably patient scientific study has been running since 1927 and is widely regarded as the longest continuously operating experiment in the world.
Its purpose is deceptively simple: to observe the flow of pitch, a substance that appears solid but is actually a very slow-moving liquid.
The Origins
The Pitch Drop Experiment was started in 1927 by Thomas Parnell, a professor of physics at the University of Queensland in Brisbane.
Parnell wanted to demonstrate to his students that some materials that seem solid at room temperature are actually liquids with extremely high viscosity.
To do this, he heated pitch, a derivative of tar, until it became fluid and poured it into a sealed glass funnel. Once the pitch cooled and settled, the bottom of the funnel was cut open, allowing gravity to do the rest.
At the time, the experiment was meant as a teaching tool rather than a historic endeavor. No one anticipated that it would continue for generations, outlasting its creator and becoming a global symbol of scientific patience.
What Is Pitch and Why Is It Special?
Pitch is a viscoelastic material derived from petroleum or plant resins. At room temperature, it appears hard and brittle and can even shatter if struck with a hammer.
Despite this appearance, pitch is technically a liquid, flowing incredibly slowly under its own weight. Its viscosity is estimated to be more than two billion times that of water, making its motion nearly imperceptible to the human eye.
This extreme viscosity is precisely what makes pitch ideal for the experiment. While substances like honey or syrup flow visibly, pitch moves so slowly that years can pass before any change is noticeable.
This unique characteristic allows scientists to demonstrate the difference between appearance and physical reality.
How the Experiment Works
Once the funnel was prepared, the pitch was left undisturbed. Over time, gravity causes the material to creep downward until a single drop forms at the bottom of the funnel. Eventually, that drop elongates and falls into a glass container below.
Each drop takes many years to form, and the time between drops has varied slightly depending on temperature and environmental conditions.
Since the experiment began, only nine drops have fallen, with the first occurring in 1938, eleven years after the setup. Each drop’s fall is a rare event, often separated by intervals of eight to thirteen years, reinforcing just how slowly pitch flows.
Moments Missed and Rare Observations
One of the most intriguing aspects of the Pitch Drop Experiment is that no one has ever directly witnessed a drop falling in person.
Despite decades of observation, the precise moment when gravity finally overcomes the pitch’s resistance has always occurred when no one was watching. Even Parnell himself never saw a drop fall before his death in 1948.
In later years, cameras were installed to improve the chances of capturing the event. In 2014, for the first time, footage successfully recorded a drop shortly after it had separated.
This finally offered visual confirmation of a process scientists had long inferred but never fully observed in real time.
Scientific Significance
While the experiment does not produce large volumes of data, its significance lies in its educational and philosophical value. It demonstrates that human intuition can be misleading, especially when dealing with time scales far beyond everyday experience.
The Pitch Drop Experiment also highlights the importance of long-term scientific inquiry, showing that some truths can only be revealed through extraordinary patience.
The experiment has even contributed to discussions about material science, helping illustrate the properties of amorphous solids and viscoelastic materials. It serves as a reminder that the classification of matter is not always straightforward.
Global Recognition
Over the years, the Pitch Drop Experiment has gained international attention and cultural significance. In 2005, it was awarded the Ig Nobel Prize in Physics, an honor that celebrates unusual or humorous scientific achievements that nonetheless provoke thought.
The experiment has since become a symbol of endurance, curiosity, and the quiet persistence of science.
Today, the funnel remains housed at the University of Queensland, carefully protected and still doing exactly what it has done since 1927. It continues to attract students, scientists, and curious visitors from around the world.
An Enduring Study
As of today, the Pitch Drop Experiment is still ongoing, with more drops expected in the decades to come. It stands as a rare example of a scientific study that transcends individual lifetimes, connecting generations of observers through a single, slowly falling drop of pitch.
In a world driven by rapid results and instant feedback, this experiment offers a powerful reminder that some of the most fascinating discoveries unfold at their own pace.
