The key facts
- A 'time crystal' is ordered in time: its elements repeat their state at equal intervals without an external 'metronome'.
- The 'wave coarsening' mechanism: small fast oscillations merge into larger slower ones until the structure moves as a single whole.
- Experiments: a 2D metamaterial of 37 cells and a ring of 24 motors on an air table; the work was published in Nature.
A Self-Emerging Rhythm
Physicists at the University of Amsterdam have created a 'time crystal' — a system that spontaneously begins to repeat its motion with a distinct rhythm, without an external 'metronome'. The work was published in the journal Nature. While an ordinary crystal is ordered in space, a 'time crystal' is ordered in time: its elements repeat the same state at equal intervals. Usually such systems have to be 'driven' by external periodic forcing; the novelty of this work is that the rhythm emerged on its own.
The 'Wave Coarsening' Mechanism
The authors called the process 'wave coarsening': it begins with small, fast oscillations that gradually merge into ever larger and slower ones, until the entire structure begins to move as a single whole. To observe the effect, the scientists used a two-dimensional metamaterial printed on a 3D printer — its behavior is determined not by composition but by geometry. The 'honeycomb' was assembled from 37 cells, each made of three elastic hexagons with sensors, actuators and a controller; the initial oscillations occurred at a frequency of about 30 per second.
Robustness to Disturbances and Additional Experiments
Simulations with added 'noise' showed that the synchronous rhythm persists even under random disturbances. In another setup — a ring of 24 motors on a nearly frictionless air table — the same wave growth was observed, although a 'time crystal' was not confirmed there. When friction was added to the model, the longest waves were damped, but stable oscillations continued to travel along the edge.
Significance of the Work
'Time crystals' are not perpetual motion machines: energy is expended in them; what is meant is a stable self-sustaining rhythm. According to the authors, 'wave coarsening' may prove to be 'an instructive route to the crystallization of time' in systems with additional symmetries, and may also help in creating precise sensors and devices where stable synchronization is important.
