The Smith hat monotile solved an Einstein problem that had gone unsolved for twenty years, captivating mathematicians around the world when it was first released in 2023. What they saw was unprecedented: pinwheel-like diffraction patterns that revealed the chiral nature of the aperiodic tiling. “We found that the diffraction patterns themselves become chiral because the structure lacks mirror symmetry,” says senior author Masaya Notomi. The experiments revealed that the diffraction patterns varied with respect to both direction and polarization of incoming light. “Monotile patterns provide a platform for exploring optical phenomena that emerge from the interplay of symmetry, chirality, and aperiodicity.”