An aperiodic monotile, sometimes called an "einstein", is a shape that tiles the plane, but never periodically. In this paper we present the first true aperiodic monotile, a shape that forces aperiodicity through geometry alone, with no additional constraints applied via matching conditions. We prove that this shape, a polykite that we call "the hat", must assemble into tilings based on a substitution system. The drawing above shows a patch of hats produced using a few rounds of substitution.
This page collects the resources associated with this work. We invite you to look at all of the following.
A preprint of the paper is available on the arXiv.
You can create your own patches of hats, and save them as PNG or SVG files, using an interactive application that runs in your web browser. You can also get your own copy of the source code (with a BSD 3-clause license). If you prefer to experiment with moving hats around and building patches manually, please see this excellent Mathigon polypad environment created by Dan Anderson.
The hat is one member of a continuous family of shapes that are all aperiodic, and that all tile the plane in the same way. We have created an animation that moves smoothly through this family of shapes. You can watch it on YouTube, or download your own copy (which you can more easily watch looped).
In the paper we give two different proofs of aperiodicity. One of them relies on a computer-assisted case-based analysis. For validation purposes, we re-implemented this analysis as a Python program. You can download the source code for this program, run it yourself, and check its correctness.
Here are some sample images you can use in publications, media, etc. Feel free to modify these images to suit your tastes.
All images, and the MP4 animation above, are licensed under a Creative Commons Attribution 4.0 International License.
A looping animated GIF similar to the animation mentioned above. [500x500 GIF]
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