October 28, 2009
With nothing more than beads in a glass box, physicists have revealed yet another mysterious property of granular solids, now recognized by scientists as a unique state of matter, like solids or gases.
When the box was filled to the brim and rotated, the beads moved in patterns known from convection clouds — another system whose basic physical dynamics are only dimly understood.
The experiment, displayed in a video posted Monday to arXiv, was a variation on one performed 70 years ago by Japanese physicist Yositsi Oyama, who observed that beads of different sizes placed in a rotating circular drum would eventually self-sort by size.
That intriguing result set in motion the study of granular solids, which behave in ways that can’t be predicted with known physical laws. And though research has accelerated in the last decade, scientific understanding of granularity is roughly akin to that of fluid dynamics in the 18th century.