Water drops on soap bubble films act like merging galaxies

Water drops on soap bubble films act like merging galaxies Skip to content Subscribe today Every print subscription comes with full digital access Subscribe Now By Emily Conover May 14, 2026 at 1:00 pm Share this: Share Share via email (Opens in new window) Email Share on Facebook (Opens in new window) Facebook Share on Reddit (Opens in new window) Reddit Share on X (Opens in new window) X Print (Opens in new window) Print The physics of merging galaxies has popped up in an unexpected place: the stuff of soap bubbles. Water droplets placed on a flat soap film act like galaxies that orbit one another before coalescing. As they merge, the water droplets take on shapes reminiscent of those that appear in astronomical images of colliding galaxies , physicist Jean-Paul Martischang and colleagues report in the April PNAS Nexus . The water droplets might eventually be useful for studying gravitational attraction in a laboratory, to better understand how galaxies collide and coalesce. When plopped on a horizontal soap film — in the laboratory equivalent of a bubble wand — a water droplet takes on a hammocklike shape, about a centimeter wide. That disrupts the shape of the soap film, pulling it downward. That sagging causes drops to attract one another, orbit and coalesce. To visualize the translucent water droplets, the researchers took advantage of the fact that each droplet acts like a lens that causes blurring. They placed a randomized pattern of dots below the film. Mapping out where that pattern was blurred revealed the drops’ locations and shapes. Similar structures appear in water droplets coalescing on a soap film (top; dark shapes show where blurring caused by the droplets occurs) and in merging galaxies (bottom). That’s despite vast differences in scale: tens of millimeters for the soap bubbles versus tens of kiloparsecs for the galaxies. (A kiloparsec is about 3,260 light-years.) J.-P. Martischang et al./PNAS Nexus, 2026 Similar structures appear in water droplet