"The answer turns out to be really very simple," said Richard Zare, a professor of natural sciences at Stanford.
He said the old axiom, "What goes up, must come down," actually holds true.
"In this case, the bubbles go up more easily in the center of the beer glass than on the sides because of the drag from the walls. As they go up, they raise the beer, and the beer has to spill back, and it does.
"It runs down the sides of the glass carrying the bubbles -- particularly little bubbles -- with it, downward," Zare said.
Read more: http://www.seattlepi.com/national/article/Booze-flash-Tests-confirm-that-beer-bubbles-do-1139725.php#ixzz1bsFMzX6e
