Galloping bubbles

Despite centuries of investigation, bubbles continue to unveil intriguing dynamics relevant to a multitude of practical applications. Here we introduce bubbles that spontaneously start to `gallop' along horizontal surfaces inside a vertically vibrated fluid chamber, self-propelled by a resonant interaction between their shape oscillation modes. These active bubbles exhibit distinct trajectory regimes, including rectilinear, orbital, and run-and-tumble motions, which can be tuned dynamically via the external forcing. Through periodic body deformations, galloping bubbles swim leveraging inertial forces rather than vortex shedding, enabling them to maneuver even when viscous traction is not viable. Integrating experiments, simulations, and theory, we demonstrate that the galloping symmetry breaking provides a robust self-propulsion mechanism, arising in bubbles whether separated from the wall by a liquid film or directly attached to it, and is captured by a minimal oscillator model, highlighting its universality. Through proof-of-concept demonstrations, we showcase the technological potential of galloping locomotion for applications involving bubble generation and removal, transport and sorting, navigating complex fluid networks, surface cleaning, and directing bubble motions in low gravity environments. The rich dynamics of galloping bubbles suggest exciting opportunities in heat transfer, microfluidics, soft robotics, and active matter.