Time crystals are matter that keeps its own rhythm, like a tuning fork with an infinite echo. An ordinary crystal repeats a pattern in space; this one repeats in time. The idea was proposed in 2012 by Frank Wilczek.
Recently, these states have been realized on quantum chips. Their rhythm can be discrete or continuous, and there are exotic types too. All this variety has been organized into a table — akin to a standard model for time crystals. This order defies entropy and links them to pulsars. Practical benefit: ultra-precise clocks and synchronization of quantum computations without excess energy. Surprise: eternal pulsation requires no perpetual motion machine — the crystal merely redistributes external shocks, like a tuning fork humming at its note after being struck.
The first time crystal was built from ten laser-cooled ytterbium atoms — like a tiny orchestra with an endless score.
As in the film Groundhog Day, where time is looped, time crystals exhibit cyclic behavior based on quantum laws.