Scientists hope they can use the soapy system to study the cosmos
Like colliding galaxies, water droplets (dark circles) in a soap film orbit before merging.
Martischang and others./Nexus PNAS2026
The physics of galaxy mergers appeared in an unexpected place: the stuff of soap bubbles.
Water droplets placed on a flat soap film act like galaxies that rotate around each other before merging. As they merge, water droplets take on shapes reminiscent of those that appear in astronomical images of colliding galaxiesreport physicist Jean-Paul Martischang and his colleagues in the April issue Nexus PNAS. Water droplets could eventually be useful for studying gravitational attraction in the laboratory, to better understand how galaxies collide and merge.
When placed on a horizontal soap film – the laboratory equivalent of a bubble wand – a water droplet takes the shape of a hammock, about a centimeter wide. This disrupts the shape of the soap film and pulls it downward. This collapse causes the drops to attract, orbit, and merge.
To visualize translucent water droplets, the researchers took advantage of the fact that each droplet acts like a lens causing blur. They placed a random pattern of dots under the film. Mapping where this pattern was blurred revealed the location and shape of the drops.
