Persistent Holes

Persistent holes have been observed in a shaken fluid. Normally, a fluid takes the shape of its container; any puncture of the surface will quickly fill. However, in an experiment performed at the University of Texas by Florian Merkt, Robert Deegan, and Erin Rericha, a mixture of cornstarch and water is vertically vibrated at frequencies as high as 120 Hz, with accelerations in the range 12 g-25 g, where g is the gravitational acceleration.

If a stick or puff of air is used to poke a hole in the fluid, the researchers found that the hole can persist indefinitely, with a characteristic diameter comparable to the depth of the fluid and extending to the bottom of the container. This is quite surprising--a hole produced in a similar way in ordinary fluids or in the cornstarch mixture at rest quickly collapses.

The holes in cornstarch can survive as long as the shaking persists and can move around, coalesce, annihilate, or even scatter. (Pictures and movie at UT website; be sure to watch to the end.) As yet the physics behind the persistent holes cannot be explained. (Florian S. Merkt, Robert D. Deegan, Daniel I. Goldman, Erin C. Rericha, and Harry L. Swinney, Physical Review Letters, 7 May 2004; contact Harry Swinney, swinney@chaos.ph.utexas.edu, 512-471-4619.)

The same research group had earlier reported the existence of "oscillons," tiny long-lived spouts of sand grains that developed when a shallow bed of sand was shaken vertically (see Update 286).