An ice cube as we generally know it is a crystal, its water molecules neatly arranged in an orderly hexagonal lattice.
As it melts, this order dissolves, the long-range crystalline arrangement giving way to fluid chaos. Yet even in this apparent disorder, the molecules retain some semblance of structure, interacting with their immediate neighbors.
This is a spatial arrangement. But what if something similar could happen to a crystal whose structure exists not just in space, but in time?
If a phenomenon known as a time crystal could melt in the same way as an ice cube, it could result in a state of matter known as a time liquid – one that retains short-range temporal order even as its long-range coherence dissolves.
If experimentally demonstrated, the time liquid could offer physicists a new way to investigate how matter responds to fluctuations in its environment – and how order can emerge from what should be disorder even when the usual rules governing time crystals no longer apply.
"The most striking aspect of discrete time liquids, both quantum and classical, is the idea that a discrete time crystal with a finite density of topological time defects can restore time-translation symmetry on average," write physicists led by Zuo Wang and Marios H. Michael of the Max Planck Institute for the Physics of Complex Systems in Germany.
Their findings, yet to be peer-reviewed, have been uploaded to preprint server arXiv.
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