99 years and counting: How an office upgrade further slowed down the world’s slowest experiment

The world's longest experiment has been going on for almost 100 years, and yet it has barely scratched the surface. Physicist Thomas Parnell started it in 1927 at the University of Queensland. He poured pitch, a substance that looks solid, but isn't, into a funnel. He used asphalt for the experiment, which is moving, but you cannot see it happening. However, since the stem of the funnel was first cut, only nine drops have fallen. The last one was in 2014, and the tenth one is forming. This experiment offers an important lesson in physics and how even one tiny drop being released changes the entire dynamics of what is going on inside that funnel. To begin with, Parnell took asphalt and heated it until it softened enough to be poured into the funnel. The material was left to cool down for three years.

With his experiment, Parnell wanted to show that not everything one sees is as it appears. A solid substance could also behave like a liquid in another form, as is evident in the Pitch experiment. Asphalt can break apart when struck in its hard form, yet it can flow like a liquid when heated, but it displays immense resistance. It is 100 billion times more viscous than water, and two million times more viscous than honey.

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Timeline of drops in the Pitch experiment

The first drop of the pitch fell in December 1938, with the next one in February 1947, the third in April 1954, then in May 1962, the fifth drop in August 1970, the sixth in April 1979, the seventh in July 1988, and the eighth in November 2000. The ninth drop fell in April 2014, and the tenth one has only now started forming, indicating that separation will not happen soon.

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Why is the time between drops increasing?

The time difference between the initial drops was eight to nine years. However, the pitch took 12 years to fall in the year 2000. This gap increased to nearly 14 years the next time around. It has already been 12 years since the last drop came out, and yet the tenth drop is still just taking shape. This increase in time between the pitch fall indicates something about the changing physics inside the glass funnel. Experts say that as the pitch drains out, the pressure forcing it out is decreasing. However, something else happened in that building in the 1980s that probably changed things. Air conditioning was installed, which cooled the air around the pitch funnel. While this drop in temperature doesn't seem like a lot, it is believed to have affected the surroundings measurably enough for the pitch to behave differently.

Two scientists - Parnell and John Mainstone - are associated with the Pitch experiment. While Parnell started it, Mainstone brought it to the public eye. However, none of them ever saw a drop fall. The experiment earned Parnell and Mainstone the Ig Nobel prize in physics in 2005. It is a parody of the Nobel Prizes, and is awarded for scientific studies that make you laugh, and then wonder.