writes "It is commonly understood that crystals exist in a state of matter that is periodic in space. Meanwhile, relativistic physics tells us that we should think of time as being a physical dimension, given similar status to the other spacial dimensions. The combination of these two ideas has lead researchers at the University of Kentucky and MIT to propose special manifestations of matter which would be periodic in both space and time, dubbed “time crystals.” Time crystals would continually transition between a set of physical states in a kind of perpetual motion. Note: the articles stress that this kind of perpetual motion in no way violates the established laws of thermodynamics.
While time crystals remain theoretical, methods have been proposed for creating them. The most obvious application of time crystals is the creation of very precise clocks; however, other applications to time crystals have been proposed, ranging from quantum computing to helping us understand certain cosmological models.
A technical summary with links to the original publications can be found at: http://physics.aps.org/articles/v5/116
For a less technical summary: http://www.scientificamerican.com/article.cfm?id=time-crystals-could-be-legitimate-form-perpetual-motion"Link to Original Source