OOn a Friday afternoon in April 1979, John Mainstone, professor of physics at the University of Queensland, phoned his wife at home. He wouldn’t come back that night, he told her. For the previous 18 years, Mainstone had been busy with the Fall from Height Experiment, a long demonstration of the extreme stickiness of height. For the first time since August 1970, the pitch was about to drain from its funnel, and Mainstone didn’t want to miss it.
Pitch is a resin – a viscoelastic substance derived from petroleum or coal tar, used in bitumen and for waterproofing. Which is ironic, because as solid as it looks, the pitch is fluid: at least, that’s when you put it in a funnel whose sloping sides create a pressure gradient.
Mainstone stayed up all Friday night. He continued to watch on Saturday, eventually calling his wife back to tell her he wouldn’t be home that night either. Yet the globule of (literally) jet-black liquid hung by a thread at the bottom of its funnel. On Sunday evening, exhausted by his vigil, he returned home. By the time he returned to work on a sleep-deprived Monday morning, the pitch had fallen into his beaker.
The pitch drop experiment was first set up by Mainstone’s predecessor, Thomas Parnell, in 1927. Parnell heated and liquefied pitch, poured it into a sealed funnel and placed it on the beaker inside a large bell jar. In 1930, he cut the stem of the funnel – and waited.
Almost a century later, the original experiment – which has become the oldest laboratory experiment in the world – stands in the foyer of the Great Court physics building. The jar sits inside a protective plastic cube, with an analog Casio desk clock watching every moment as students and staff walk around. The funnel is held in the air by a brass tripod; below, a shiny black ball of pitch hovers above the empty beaker.
It was Mainstone, who undertook the experiment in 1961, who brought the fall from height to public attention. He also mentored her third and current caretaker, Professor Andrew White, who has watched over her since Mainstone’s death in 2013. Like Parnell, Mainstone died never seeing a drop fall. “I’m not filling John’s shoes in any way,” White insists. “He was the heart and soul of it all.”
Mainstone’s dedication was legendary. In 2005, he and (posthumously) Parnell were awarded the Ig Nobel Prize – a satirical award noting obscure and trivial achievements in scientific research. The Ig Nobel Prize aims to reward work that makes people laugh, but also makes them think.
Author Nick Earls first discovered the experience as a medical student at UQ in the early 1980s, later writing about it in his novel Perfect Skin. “It was a demonstration that not everything is necessarily as it seems,” he says. “There’s pitch – something that goes into the making of the roads, something that we consider totally solid – and it turns out it’s not. It’s just 230 billion times more viscous than water, and it sinks, albeit very slowly.
How slowly? “Much slower growing than grass, much slower than drying paint,” says White, falsely offended by such mundane comparisons (and the suggestion that it might be, well, a rather boring experience to watch). “We are talking about more than 10 times slower than continental drift!”
He draws my attention to the assembly of four tiles on the floor. “These tiles are moving north at 68 millimeters per year, because Australia is moving north at 68 millimeters per year. It’s one of the fastest continents, when it comes to continental drift. Height drop moves at least 10 times slower than that! So it’s literally slower than watching Australia drift north, and people are going live on the internet to watch it. Which I find really fascinating.
It’s true. More than 35,000 people in 160 countries sweat every 10th drop of pitch. They will wait a little longer. Since Parnell cut the funnel stem in 1930, only nine drops have fallen: in December 1938, February 1947, April 1954, May 1962, August 1970, April 1979, July 1988 (when it became a popular exhibit at Brisbane’s generation-definition Expo 1988), November 2000 and April 2014.
White prefers to call the pitch drop a demonstration rather than an experiment, as it was never controlled and therefore subject to environmental fluctuations. For his first 30 years, he sat in a dark, cool closet. Mainstone exposed it, and the land maintained its average of one drop every eight years until, in the 1980s, the physics building (which bears Parnell’s name) was air-conditioned, making it blew about every 13 years.
Sometimes the sensitivity of the terrain to environmental conditions has been overlooked. “At one point someone replaced the fluorescent lights above the screen, which were very cold, with halogens, which are very hot,” White says, shaking his head. “No one asked anyone to change it, it was just done, and I realized the pitch – which is normally room temperature – was sitting at 60 degrees. The halogens are around 120, so it was flowing like a tap.
And yet, to this day, no one has seen a drop fall. Not at Expo (White: “There were four or five people watching, it was a hot day, I think they went out for five minutes to grab some cordial”), not even when a live stream was first set up for the millennium event in 2000. Mainstone was watching from London at the time. On this occasion, a classic Brisbane thunderstorm interrupted the power supply, knocking out lights and camera power.
Mainstone died of a stroke in 2013. In a cruel twist, the last straw fell in April 2014, months after his death. Except, technically, he didn’t fall. It just seeped into the eight drops that had already fallen and solidified in the small beaker sitting under the funnel in a bell jar, without coming off. Reluctantly, White swapped the beaker, managing to find an old imperial measurement pattern to match the original.
Since then the beaker has remained in place – clean, empty, but not yet blackened by a single drop of goo. The lights have been replaced by LEDs. “We had a very fresh start,” White says. “And so when someone asks me when it’s going to drop, I can really say I have no idea. Because conditions have changed, as they have for most of the last 95 years. It has never been kept constant.
A few meters below the height fall experience is a basement dedicated to quantum technology. There, says White, a laboratory produces pulses of light lasting a hundred million billionths of a second. And here in front of us, he says proudly, “we have something that has an event every 10 to 20 years! It really captures the different time scales of the physical world around us.
He looks at the funnel. There’s still a bit of pitch in there. The experience, he says, will long outlive us all. “Quantum mechanics is as far as you can get from pieces of coal that have been heated and flow slowly through a glass tube,” he says. “I’m glad we have a new beaker in there, which will be good for another 100 years or so. Two, three keepers from now on, it will be their problem what to do next.