The discovery — a hobbyist and three mathematicians
For more than 50 years mathematicians hunted for an “einstein” (from the German ein Stein, “one stone”): a single tile that covers the plane without the pattern ever repeating. In March 2023 it was finally found by David Smith, a retired print technician and shape hobbyist from Yorkshire, working with three mathematicians — Craig Kaplan (University of Waterloo), Joseph Samuel Myers (Cambridge) and Chaim Goodman-Strauss (University of Arkansas). Their shape, “the hat,” settled the question — but every tiling it made still needed mirror-image copies mixed in.
Just two months later the same four found the Spectre: a strictly chiral aperiodic monotile. It fills the plane using only rotations and slides of one shape — reflections forbidden — and still never repeats. A true “one stone” at last.