As people throughout the world awake, millions of them every minute perform the apparently banal act of pouring cold milk into hot coffee or tea. Those too groggy to reach for a spoon might notice upwelling billows of milk separated by small, sinking, linear dark features such as shown in panel a of the figure. The phenomenon is such a common part of our lives that even scientists—trained to be observant—may overlook its importance and generality. The pattern bears resemblance to satellite images of ocean color, and the physics behind it is responsible for the granulated structure of the Sun and other cosmic objects less amenable to scrutiny.
Archimedes pondered the powerful agent of motion known as buoyancy more than two millennia ago. Children do, too, when they imagine the origins of cloud animals on a summer’s day. The scientific study of thermal and compositional buoyancy originated in 1798 with...
