Shake a bottle of champagne and pop it open. The champagne will shoot out in a mini-eruption. Do the same to a bottle of beer. Beer will ooze out more slowly. If a bottle of champagne or beer is opened without perturbation, there will be no eruption, but bubbles will rise and grow, often in regularly spaced “trains” (FIG. 1). In Guinness beer, bubbles rise more slowly and may even sink. The myr...