Crystals... made of time

Sometimes I know that I'm going to write about a paper before I even read it. The hook is simply too inviting. A new paper, simply entitled "Time crystals," with a companion paper "Quantum time crystals," is that sort of irresistible. Even if the papers turned out to be giant piles of steaming science, lying in full repugnant view on the pages of Physical Review Letters, it was certain there would be a good story to tell.

As it turns out, these papers are a strange brew of "what if," mixing the unlikely with the banal to create a heady mixture of pure confusion. As the names of the papers imply, the authors consider how it might be possible to create something akin to a crystal—but one that occupied time rather than space.

To a physicist, a crystal is a collection of basic building blocks, repeated in space. A salt crystal consists of a regular array of sodium and chlorine atoms. Wherever you are within the crystal, if you move by any multiple of a specific distance, you find yourself in a place that looks exactly the same. This is called translational symmetry.