Exhibition · Series X · Instability
A Circle Grows Fingers
Why do some disturbances grow while shorter ripples disappear?
What to notice
Viscosity contrast makes a band of interface corrugations unstable. Surface tension suppresses shorter wavelengths, so the instability selects a finite range rather than amplifying everything.
Everyday analogy. Push a runnier liquid into a thicker one and the edge may stop expanding as a clean circle: some ripples grow into fingers while surface tension smooths away the tiniest ones.
Linear radial Saffman-Taylor stability model. This page shows mode selection, not a nonlinear multiphase-fluid simulation.