The long-seething pub debate over whether bubbles in a pint of Guinness really do fall downward, as they seem to on visual observation, has been definitively solved–it’s true, they sink:
Scientists have shown that the bubbles in a pint of Guinness really do move down instead of up. An earlier study concluded that the phenomenon may only have been an optical illusion.
Close examination reveals that as the pint settles, bubbles touching the walls of the glass experience drag that prevents them floating up.
Bubbles in the centre of the glass, however, are free to rise. A circular flow is created, causing bubbles at the the edge to be pushed downwards on the inside surface of the glass.
Eventually more and more bubbles find their way to the head of the beer until the cycle loses momentum.
There’s lots more, but you get the drift. So to speak.
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