# Time Crystals

### By Jay JaganaathÂ

#### March 2017

On a cursory glance, the name conjures up an image of a collectible in a video game or of a children’s show. It seems unthinkable that this term can even be applied in a real-life situation. However, results from researchers at the University of Maryland and Harvard prove otherwise.

Crystals are structures formed from molecules which arrange themselves into structures that repeat themselves periodically throughout space. For example, if I were to observe a lump of table salt and magnify any single point on the lump, the pattern of the arrangement of molecules would be same at any other point throughout the lump.

Crystals are formed through the physical phenomena of symmetry breaking. To better understand the phenomena of symmetry breaking, consider droplets of water. In a water droplet, molecules are free to move about and can be anywhere within the liquid. The liquid looks the same in any direction, meaning that it has a high degree of symmetry in space i.e continuous spatial symmetry. If the water freezes to form ice, attractive forces between the molecules force them to rearrange into a crystal, where molecules are spaced at regular intervals or are periodically spaced. But this regularity means that the crystal isn’t as symmetrical as the liquid i.e specific spatial symmetry, so we say the symmetry of the liquid has been broken when freezing into ice.

Another way to look at spatial symmetry is to consider the fact that this property applies to objects no matter how they are observed. For example, a sphere would look the same regardless of the side you viewed it from. However, crystals contain specific spatial symmetry, which means that the symmetry is only observed when the object is observed in certain ways, that is, a cube only appears to be symmetrical when it is viewed from only certain positions. Hence, when we force an object with a spherical shape to assume a cubical shape, we break its symmetry and hence form a crystal.

The interesting part about time crystals is that it exists according to completely different laws of nature.Instead of breaking symmetry in space, time crystals break the symmetry in time i.e time translational symmetry. A fundamental condition of time translational symmetry is that every instance of time is the same as any other instance of time. For example, when tossing a coin, the odds of heads/tails remains 50/50 whether it is the 10th millisecond or the 10th nanosecond. When time translational symmetry is broken, certain moments in time are more special than others – if a coin tossed with a 50/50 chance of head/tails could become 70/30 after a few seconds. As in specific spatial symmetry, symmetry is only observed at specific points, in specific time symmetry, it is observed at specific instances of time, making them more ‘special’.

However, this would mean that as there would be periodic alternations between states of ‘not symmetric’ and ‘symmetric’ as the symmetry is only observed in certain instances of time. Therefore these alternations between states would act as a constantly moving pendulum which was always in a state of motion. However, how would the object be able to sustain such ‘perpetual motion’ without consuming energy?

The explanation offered by researchers in 2015 is that the ‘periodic switching’ of the time crystal would be inactive or dormant until external energy would be provided to ‘awaken’ it.While on the surface, time crystals seem like a faraway word with little relevance to the common man, they can actually hold great potential in the future. For example, their periodic switching properties can be used to store data for use by high-speed quantum computers and they could also be used to enhance the quality of fibre-optics and lasers. What seems like the esoterica of today could very well become the foundation of the future!