When a building collapses, steel rebar turns into a chaotic magnetic compass. Entropy, a measure of disorder, increases, but it's this very disorder that points to voids where people might be. Drones with quantum magnetometers, devices operating on principles discovered by Schrödinger, detect fields a trillion times weaker than Earth's. To put that in perspective: it’s like hearing a heartbeat through concrete.

The algorithm, like a skilled cartographer, selectively takes readings at key points. A few hundred measurements suffice to build a 3D map: it shows cavities with water and air. Rebar with carbon additives is strongly magnetized, creating a magnetic relief. This method resembles spectroscopy — an astronomical technique where light is split into colors, only here the magnetic landscape replaces the spectrum. The result is an ultra-precise magnetic map, a safe x-ray for rescue operations.