Scientists Cause Liquid Droplets to Walk and Bounce Across Vibrating Bath

It turns out that small droplets are a lot more unusual than you might think. Physicists have managed to make a small fluid droplet levitate on the surface of a vibrating bath, walking or bouncing across as it's propelled by its own wave field. The findings reveal that these droplets exhibit certain features that were once thought to be exclusive to the microscopic quantum realm.

The dynamics of these walking droplets are reminiscent of the pilot-wave dynamics first proposed in 1926 to describe the motion of quantum particles. This theory stated that microscopic particles, such as electrons, move in resonance with an accompanying guiding wave. This pilot-wave theory wasn't widely accepted and was instead superseded by the Copenhagen Interpretation of quantum mechanics, in which macroscopic and microscopic worlds are philosophically distinct. Now, though, it seems that this quantum-like behavior could give new life to the pilot-wave theory.

"This walking droplet system represents the first realization of a pilot-wave system," said John Bush, one of the researchers, in a news release. "Its great charm is that it can be achieved with a tabletop experiment and that the walking droplets are plainly visible. In addition to being a rich, subtle dynamical system worthy of interest in its own right, it gives us the first opportunity to view pilot-wave dynamics in action."

Currently, the scientists are still researching this walking phenomenon.  They're planning on investigating the subtleties of this fluid system and finding out exactly what kinds of droplets bounce, walk and how they do so. In fact, the researchers have already made a few leaps forward when it comes to understanding this system with the help of Jan Molacek, a graduate student who developed a theoretical model.

"Molacek's work also led to a trajectory equation for walking droplets, which is currently being explored by my graduate student Anand Oza," said Bush in a news release. "Our next step is to use this equation to better understand the emergence of quantization and wave-like statistics, both hallmarks of quantum mechanics, in this hydrodynamic pilot-wave system."

Currently, the researchers are seeking to explore new quantum analogs. Their ultimate goal is to understand the potential and limitations of this walking-droplet system as a quantum analog system.

The findings are published in the journal Physics of Fluids.