You know, the Cascade.
The key, apparently, is the pint glass itself.
Over the last ten years or so, physicists have begun to pick this problem apart. Most recently they’ve shown that it is not the bubbles that sink but the liquid, which circulates in a way that is downwards near the glass walls and upwards in the interior. As long as the downward flow of the liquid is faster than the upward motion of the bubbles, they will appear to sink.
But that still leaves a puzzle: why does the liquid circulate in this way?
Today, a dedicated team of Irish mathematicians reveal the answer. Eugene Benilov, Cathal Cummins and William Lee at the University of Limerick say the final piece in this puzzle is the shape of the glass, which has a crucial influence over the circulatory patterns in the liquid.
There is even a video (downloadable from the article) which shows the phenomenon in action.
The article at The Physics arXiv blog closes with this line: We’ll be following future developments closely.
As will we all.