https://blogs.scientificamerican.com/at-scientific-american/introducing-the-november-2019-issue/

When our creative director, Michael Mrak, sent around the illustration for this month's cover story—a conceptual rendering of so-called time crystals—our features editor, Seth Fletcher, responded, “Cool. Very prog rock.” The artwork certainly seems ready-made for a Pink Floyd album (Roger Waters, if you're reading this, the offer's on the table) or at least one of those velvet blacklight posters. And time crystals are indeed pretty trippy stuff.

Whereas conventional crystals are orderly states of matter whose patterns repeat at regular intervals in space, these more exotic materials have patterns that repeat at regular intervals in time. Theoretical physicist and Nobel laureate Frank Wilczek and his wife, Betsy Devine, coined the term “time crystals” in 2012, and scientists created the first bona fide examples in the lab in 2017. Still a nascent field of research, it is one that could lead to unprecedentedly precise measurements of time and distance, with myriad applications. For more mind-bending details, turn to Wilczek's article, “Crystals in Time.”