DO GUINNESS BUBBLES SINK?

DO GUINNESS BUBBLES SINK? The wikipedia article says: “A long time subject of bar conversations is the Guinness cascade, where the gas bubbles appear to travel downwards in a pint glass of Guinness.” One of the subjects of the bar conversations apparently was whether this is only an optical illusion. The phenomenon seems counterintuitive because the bubbles are lighter than the liquid and would be expected to rise. This post on a chemistry education site deals with the question of whether there is an illusion. It presents a video of the bubbles in Guinness going down the sides of the glass. It also links to a paper from 2008 which describes “a simple model of a bubbly two-phase flow which is able to explain why waves propagate downward when a pint of Guinness is poured, and also how the waves are generated.”