In September 2016, a team of researchers from the University of Maryland announced that they had experimentally confirmed the existence of time crystals. That is, crystals that break the continuity of time. Confused? Let’s break this down.
In physics, “spatial symmetry” refers to the way a feature stays the same no matter which way you observe it. If you were to walk all the way around a sphere, it would look the same at each point in your journey. That’s because it has continuous spatial symmetry. A cube, on the other hand, would look slightly different as you passed from one face to the next, but would look identical at each face. This means it “breaks” continuous spatial symmetry and instead has discrete spatial symmetry: you can only see the same thing from specific directions. That’s the essence of a crystal: it breaks continuous spatial symmetry.
Symmetry also applies to laws of physics like gravity (you’d see an apple fall the same way no matter how you were watching it) and, importantly, time. The gears on a clock, for example, move continuously at any given rate as they spin on an axis of rotation, so they have a kind of continuous temporal symmetry. Just as a crystal breaks continuous spatial symmetry, a time crystal would break continuous temporal symmetry: its “gears” spin on an axis, but only with specific rates of rotation.
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