The simple answer is: we don’t know.
Since 1902, the experiment has dripped at least twice but it’s impossible to predict when the next drop will fall. One drop fell between 4 and 6 June 2016, shortly after we moved the demonstration from our Collection Centre to its new home at Chambers Street. However, we can't tell if it was hurried along by the motion of the move, or if it would have fallen anyway - inanimate objects can be so malicious sometimes! While other pitch drop experiments show movement roughly every ten years or so, our experiment has a narrower funnel which means the pitch moves even more slowly. Unfortunately, over the last century we haven't kept data like the experiments in universities, and don't know exactly when the previous drop fell, or indeed if there has been more than one drop before this which would help us predict the next one.
Even if a drop of pitch did fall, there’s no guarantee anyone would be around to see it. Take John Mainstone, who inherited the Queensland pitch drop experiment in 1961. Under his care, five drops fell but Professor Mainstone missed all of them. The pitch experiment makes no allowances for weekends (1979), conference coffee breaks (1988) or broken video cameras (2000)!
Above: Professor John Mainstone with the University of Queensland pitch drop experiment.
Eighty-seven years after the Queensland experiment was set up, another drop fell in April 2014. This drop was witnessed by three webcams and thousands of online fans. But not Professor Mainstone, who had died eight months previously without ever seeing the experiment in motion.