I'm curious to find an answer to this question:
In the college canteen I would often slide my Styrofoam cup of milky coffee across the melamine table top. (unlike paper or plastic, Styrofoam is a little bit sticky). This caused vibration in the liquid and some nice interference patterns on the coffee's surface. Sometimes little standing waves of hill-like bumps, and sometimes, if you get the slide-speed just right, some of these 'bumps' appear to pinch off and become little independent balls of coffee that seem to slide or roll around the surface!.
But I was never able to determine whether they really were little independent balls of coffee, holding their spherical shape by their own surface tension, or whether they were merely the result of wave-interference, analogous to the way the way a ripple merely "appears" to move across the surface of a pond when really its just bits of water locally moving up and down.
I thought of doing an experiment, shooting a bit of blue ink from a syringe across the path of a coffee-ball, if the ball retains it's coffee color as it crosses the line of blue ink, then it's an independent ball, if it momentarily turns blue while crossing the line of blue ink, subsequently regaining it's coffee color, then its a wave-interference phenomenon.
Which is it, an independent "ball" or a "moving interference pattern"? and how can you be sure?
Either way though it looks pretty cool! The principle involved might make a poetic analogy to make some point or other about wave-particle interaction or particles as an excitation of a field.
