

By Jennifer Ouellette on at

The drops of silicon oil bobbing in the mesmerising video do more than create aesthetically satisfying ripples across a slick surface. They could be indirect evidence of an alternate solution to a nagging question in quantum mechanics — one that dates back almost a century.







Apart from the implications for quantum mechanics, this is also a very cool fluid dynamics experiment. To create their video, Harris and Bush filled a shallow tray with a circular trough in the centre with silicon oil and mounted it on a vibrating stand. Then they tuned the stand to various frequencies and watched to see how the droplets’ behaviour changed around a specific threshold frequency. As I wrote last year:


When the bouncing droplet produced waves, those waves bounced off the walls and interfered with each other, producing pretty interference patterns. They also affected the trajectory of the droplet. At first it looked like it was bouncing along randomly, but over time (around 20 minutes), the droplet was far more likely to drift towards the centre of the circle, and increasingly less likely to be found in the rippling rings spreading out from that centre.

The basic experimental set-up involves a loudspeaker, a smart phone, and a screen with a striped pattern. Then the fun begins. We see first one, two, three, and four bouncing droplets, each creating ripples in the silicon oil, followed by a series of droplets arranged in a honeycomb-like lattice. The researchers next used a high-speed camera to create some nifty strobing effects: in one version, the droplet appears to glide across the surface of the oil; in another, the droplet appears to gain “hang time,” pausing just a little bit longer mid-air with every bounce.

You can check out the other winners featured in the 2015 Gallery of Fluid Motion here.