The pitch drops: the science experiment of the century

University of Queensland photo

Almost everyone has heard of the scientific experiment called the “pitch drop experiment” – it’s been ongoing for 83 years. Nothing much happens, and researchers spend more time watching it than recording its results. But something rather spectacular happened on 17 April 2014 – it produced a result (Canberra Times, April 23, 2014).

The world’s longest-running laboratory experiment started in 1927 when Thomas Parnell, the founding professor of physics at the University of Queensland in Australia wanted to demonstrate to his students that objects that look solid can in fact flow like liquid, no matter how slowly it takes.

He took a lump of pitch – the kind of pitch that is used in shipbuilding, bitumen or asphalt to make roads and pathways. That’s where the term “pitch-black” comes from. Some refer to pitch as tar, but pitch is actually more solid than tar. It is a hard substance that will break when hit with a hammer. Pitch is semi-solid so it will flow, but extremely slowly. Parnell put some pitch in a glass funnel to allow it to drip – in its own time with no added heat or chemical additives – through the funnel aided only by the atomospheric pressure from being squeezed through the narrow tube.

The pitch drops have averaged one drop every 8 years. Air-conditioning was installed in the laboratory at the university in the 1980s and since then the drops have taken longer to form and fall – now every 13 years or so (but they are a little larger). The 8^th fell on 28 November 2000.

The current result – the 9^th drop – fell last week, on 17 April 2014 – after almost 13.5 years.

But the amazing this is that no one had ever seen a drop fall – until last week, the first time in 83 years.

Thomas Parnell put his experiment in a cupboard, physicist John Mainstone recovered it and has been watching the experiment for 50 years. He died after suffering a stroke in August 2013, aged 78 – only 8 months before the 9^th pitch drop. But in his 50 years of watching he never saw a drop fall – even when he knew one was about to occur. He missed three drops. He missed the drop in 1977 when he stayed in the laboratory all weekend, but went home exhausted – and it dropped the next day. In 1988 it happened in the five minutes when he left the room to get a cup of tea. In 2000, there was a webcam and Mainstone who was in England could watch it – but a tropical storm caused a 20-minute power outage in the laboratory just at the time the 8^th drop fell.

After professor Mainstone’s death eight months ago, the custodianship was in the eye of professor Andrew White, a quantum physicist, who witnessed the 9^th drop – and the first to ever see one. He admitted it is not a “high-yield” experiment, but it does have a fascination – and a number of adages that hold true, such as “a watched pot never boils,” and “good things come to those that wait” and "patience is always rewarded."

White indicated that, given the amount of pitch left in the beaker, the experiment could run for at least another 80 years, with the next drop perhaps marking the 100^th year since the experiment began – 2027.

http://www.canberratimes.com.au/technology/sci-tech/pitch-err-this-worlds-longestrunning-experiment-finally-drops-20140423-zqy9g.html