First predicted by Nobel-Prize winning theoretical physicist Frank Wilczek back in 2012, time crystals are structures that appear to have movement even at their lowest energy state, known as a ground state.
Usually when a material is in ground state, also known as the zero-point energy of a system, it means movement should theoretically be impossible, because that would require it to expend energy.
But Wilczek predicted that this might not actually be the case for time crystals.
Normal crystals have an atomic structure that repeats in space - just like the carbon lattice of a diamond. But, just like a ruby or a diamond, they're motionless because they're in equilibrium in their ground state.
But time crystals have a structure that repeats in time, not just in space. And it keep oscillating in its ground state.
Imagine it like jelly - when you tap it, it repeatedly jiggles. The same thing happens in time crystals, but the big difference here is that the motion occurs without any energy.
A time crystal is like constantly oscillating jelly in its natural, ground state, and that's what makes it a whole new form of matter - non-equilibrium matter. It's incapable of sitting still.
