Physicists have achieved three-dimensional Anderson localization of electromagnetic waves — a phenomenon where waves become permanently entangled in a random labyrinth of metal particles and cease to propagate. Previously, such behavior had only been observed for sound waves or electrons, but for light — waves that are notoriously resistant to interference-based 'trapping'—the experiment remained a challenge for decades. The key role here was played by entropy — a measure of disorder in the arrangement of scatterers: multiple re-reflections caused the waves to overlap, interfere, and cancel each other out, so that any distinguished direction disappeared. Imagine endlessly wandering through the floors of a building with identical corridors: this analogy simplifies the essence but captures the wave's loss of orientation in space.

By varying the volume fraction of metal inclusions in a dielectric matrix, the researchers observed a sharp transition. As long as the particle concentration remained below a critical value, the waves behaved normally: they moved freely, experiencing only diffuse scattering. But once the threshold was exceeded, the picture changed dramatically — the beam froze, its brightness (intensity at the observation point) dropped sharply, and the spatial spot stopped expanding over time. This provided direct experimental evidence of three-dimensional wave arrest, theoretically predicted by Philip Anderson back in 1958 for electrons in disordered media. For light, it took nearly 70 years to observe the effect without masking distortions.

A notable detail: any absorption of light by the material, even weak, would instantly destroy the 'trap'—the wave would simply dissipate before it could interfere. The authors overcame this difficulty by carefully tuning the degree of disorder and using weakly absorbing components. The result paves the way for ultra-sensitive sensors and computing elements that operate on trapped radiation, where information is encoded not by a flow but by a standing field configuration.