Entropy increases over time; that is the second law of thermodynamics, which is also said to prove the direction of the flow of time. An object or system of objects will reach a stage of equilibrium, at which point no changes will occur, and it is impossible to reverse without adding energy.
Another law is "time-translation-symmetry," which means that physical laws remain constant over time. There is also a "space-translation-symmetry" that says that objects are equal in a space. But crystals have been shown to violate space-translation symmetry. When a crystal of atoms is formed, the atoms are located randomly, and therefore symmetry is broken.
Could something similar apply to time? Nobel laureate Wilczek had an idéa about this and believed that atoms could oscillate in time, just as atoms randomly choose where they should be in space. If that were true, this would constitute a whole new phase.
Scientists have now succeeded in realizing this phase in which objects can exist, and it is called time crystals. A time crystal is a phase with several parts that move regularly, between different positions, indefinitely without burning any energy.
Hints that such crystals may exist have arisen through experiments on several occasions in recent years, but true time crystals have not been created until now.
Stimulated by laser
One of the main ideas behind time crystals, if they are to be "genuine," is that they should consist of several objects that get stuck and become "localized". This is called "many-body-localization." This can happen to a single atom due to randomness, but it can also happen to a number of atoms simultaneously. For something to be classified as a time crystal, it needs to consist of several atoms in localized positions. Experiments have shown that atoms can begin to fluctuate between positions if you stimulate them with an energy source such as a laser.
But the atoms fluctuate not only at the time they are stimulated but regardless of whether they are stimulated or not. This counterintuitive ability is what makes time crystals a discovery of huge magnitude. The objects can move perpetually without any energy being added. The type of crystals that are stimulated by energy is called "floquet time crystals."
Last month, researchers at Google, together with researchers from several universities, published an article describing how they created a true time crystal in a quantum computer. In July, another article was published by another research team that also, independently, managed to create a time crystal.
What is a quantum computer, then? Simply put, quantum physics says that an object can be in a superposition where the exact position is not known. Normal computers make binary calculations, meaning that at a machine level, values can be either 0 or 1. But in a quantum computer, qubits are used, and they can have more values than 0 and 1 at the same time. The ability of the quantum computer to simulate quantum systems has made it possible to create a time crystal because a time crystal is basically a quantum system.