In conventional crystals, spatial structures repeat themselves regularly. Now physicists have discovered a completely different kind of symmetry in exotic states of matter: in time!
Crystals are the neatest places on earth. The atoms and molecules within them sort themselves into highly regular, repeating structures. In this way, larger solid structures often grow, which are also pretty to look at.
People have always been fascinated by crystals and valued them as jewels. When researchers classified them in terms of their shapes and their effects on light in the 19th century, mathematics and physics were decisively advanced. In the 20th century, numerous technical revolutions developed, such as modern semiconductor electronics, based on the quantum mechanical properties of the electrons in crystals.
Over the past decade, physicists have taken another important step forward in understanding regular solids, entering a whole new dimension. The journey there began with a fundamental aspect of Albert Einstein's theory of relativity: space and time are closely intertwined. It is therefore natural to ask whether there are not only crystals in space, but also whether objects can have comparable properties in time…