Orbiting, colliding and merging liquid lenses on a soap film: Toward gravitational analogues

Abstract Gravity governs the large-scale structure of the Universe, driving the formation and interactions of galaxies. These interactions generate distinctive features–such as complex orbits, tidal spiral arms and bridges–that are commonplace at astrophysical scales but rarely observed at human scales. Multi-body dynamics can be observed at laboratory scale with particles at liquid interfaces interacting via the “Cheerios effect”, but such systems have limited ability to reproduce gravity-shaped structures because of their short-range interactions, strong dissipation, and a limited number of rigid bodies. Here, we show that miscible milimetric water lenses on a soap film can sustain long-lived orbital motion, collisions, and mergers, producing tidal arms and bridges reminiscent of interacting galaxies. These dynamics arise from a Newton-like gravito-capillary attraction, low dissipation, and lens deformability. A quantitative model of film deformation accurately predicts both static lens shapes and orbital trajectories for single and multiple bodies. This controllable, time-resolved platform enables direct experimental study of the gravity-driven formation of complex, deformable structures, paving the way for laboratory gravitational analogues.