"Time Crystals" Could Be a Legitimate Form of Perpetual Motion

Physicists explore the concept that cold states of matter can form repeated patterns in time
By Ron Cowen


The phrases "perpetual-motion machine"—a concept derided by scientists since the mid-19th century—and "physics Nobel laureate Frank Wilczek" wouldn't seem to belong in the same sentence. But if Wilczek's latest ideas on symmetry and the nature of time are correct, they would suggest the existence of a bona fide perpetual-motion machine— albeit one from which energy could never be extracted. He proposes that matter could form a "time crystal," whose structure would repeat periodically, as with an ordinary crystal, but in time rather than in space. Such a crystal would represent a previously unknown state of matter and might have arisen as the very early universe cooled, losing its primordial symmetries.

Wilczek describes his work in this article and in this one coauthored by Alfred Shapere of the University of Kentucky, that he posted on the physics preprint server, arXiv.org, on February 12.

"The papers themselves are perfectly respectable, undoubtedly correct, and interesting," says cosmologist Sean Carroll of the California Institute of Technology.

Known for his pioneering work in developing quantum chromodynamics, the theory that explains how the particles inside atomic nuclei stick together, Wilczek, a professor at the Massachusetts Institute of Technology, says he got his latest idea two years ago while teaching a course on group theory. That branch of mathematics, which uses matrices to describe the symmetries inherent in families of elementary particles, also describes and classifies the structure of crystals. Materials such as a liquid or a gas in equilibrium, made of uniformly distributed particles, exhibit perfect spatial symmetry—they look the same everywhere and in every direction.

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