Introduction Have you ever tried making “walkie-talkies” using a long piece of string and two tin cans? If you have, you know that they work surprisingly well—at longer distances you can hear people ...

A strange form of matter called a time crystal has fascinated physicists for about a decade. These systems move in repeating cycles, even without a steady external push.

In the ETH experiment, self-oscillations (blue-red) cause sound waves (green, orange, violet) to travel through the circulator only in one direction. Credit: Xin Zou Researchers at ETH Zurich have ...