CRYSTALS IN SPACE. “The idea came to Wilczek while he was preparing a class lecture in 2010. “I was thinking about the classification of crystals, and then it just occurred to me that it’s natural to think about space and time together … So if you think about crystals in space, it’s very natural also to think about the classification of crystalline behavior in time.”
http://www.wired.com/2013/04/time-crystals/