POWERFUL FORCES can emerge from a humble popping bubble. In the largest ever fluid dynamics simulation, a team led by the Swiss Federal Institute of Technology in Zurich and IBM Research tested a cloud cavitation collapse—the bursting of a “cloud” of thousands of bubbles. The phenomenon occurs when bubbles form in liquid because of changes in pressure—as when a propeller stirs up water—and quickly implode, which can generate shockwaves. Scientists hope to direct such bubbles at kidney stones to shatter them. Bubble power might also be used to make holes in cancer cells to deliver treatment or to destroy the cells entirely.