Physics

How slow, is slow?

In general human beings are unable to pay attention to things which don’t change: try looking at a wall if you want to see what I mean. Human beings are not fascinated by stasis, but by change.

However some changes are so rapid that we just don’t notice them. For example you are probably unaware of the rapid flickering of the screen on which you are reading this.

And some changes are so slow that we think: “Nothing’s happening”. But exactly what we mean by ‘slow’ depends on context and experience.

  • For a child ”slow” could refer to a process taking longer than a few seconds.
  • For an adult ”slow” might refer to changes taking place much longer periods of time – possibly even years.
  • For a geologist ”slow” might refer to a process taking a million years.

In each case the changes are real, even though it can be almost physically painful to consider such slow rates of change.

Pitch drop experiment

Pitch drop experiment

And it is in this context that I would like to draw your attention to a fascinating experiment situated in the foyer of the Physics Department of the University of Queensland in Australia: It is called the ‘pitch drop’ experiment and it involves the flow of a near-solid sample of pitch – roughly speaking the ‘tar’ that we use in ‘tarmac’ roads.

In 1927 Professor Parnell heated a sample of pitch and poured it into a glass funnel with a sealed stem. Three years were allowed for the pitch to settle, and in 1930 the sealed stem was cut. From that date on the pitch has slowly dripped out of the funnel – so slowly that now, 83 years later, the ninth drop is only just fully formed.

There are three things I really like about this experiment:

  1. The forces involved are constant, and there is no mystery at all as to what is happening, and what has happened.
  2. The second is that although all the forces are all constant, the response is not. This is like many processes in nature, but it seems an especially apt analogy for climate change.
  3. And finally the recent death of the experimental custodian, Professor John Mainstone shows that physical time scales pay no attention at all to human time scales.