If you put light in a room full of mirrors, some 'weird' rays get trapped in tiny little strips and can never, ever get out.
March 27, 2026
Original Paper
Wind-tree tiling billiards and their trapping strips
arXiv · 2603.25654
The Takeaway
Using a model of rectangular obstacles, researchers found that if light interacts with objects as if it has a negative refractive index, it loses the ability to wander freely. No matter how you fire the beam, it gets caught in an infinite straight-line "cage," proving that simple patterns can create permanent traps for light.
From the abstract
We introduce a new dynamical system: the wind-tree tiling billiards. This system studies trajectories of a ray in Euclidean space which has a negative refractive index when encountering rectangular obstacles located at lattice points. We show that for almost every configuration of the system, trajectories with initial vertical direction are trapped in an infinite strip of the plane. This result is reminiscent of the propagation of light rays in Eaton lenses, as shown by Frączek and Schmoll.