What are Time Crystals?

Monica Time Crystals

Curiouser and curiouser.

In the last few months, there have been a few headlines proclaiming the creation of time crystals. The first time I saw one of these announcements, I was pretty much equal parts delighted and skeptical. It’s hard not to be—I mean, TIME CRYSTALS. It sounds like something you’d find on someone’s conspiracy-theory Geocities site, or the key to defeating the Avengers’ next nemesis.

It’s not, though! The idea was proposed in 2012 by Frank Wilczek, and it’s pretty strange, but maybe not as weird as it sounds. To understand what time crystals are, let’s talk a little about regular old space crystals.

Crystals form lattices, in which atoms or molecules are arranged in highly ordered patterns. We tend to think of arrangements like this as being very symmetrical, in the sense that they are regular. However, to physicists this organization is actually a form of what’s called symmetry breaking, because they’re defining symmetry as meaning that space looks the same in all directions.

In unstructured or symmetric space, an atom is just as likely to be in one place as another, and space has about the same distribution of atoms in any direction. In crystals, the forces between atoms dictate very specific locations instead of a constant distribution, so that the space is no longer symmetric. Instead of being located anywhere, the atom can only be in one place.

Crystal Symmetry Breaking

The theory of time crystals takes this idea of spatial symmetry breaking, but applies it to the dimension of time instead. In the same way that a normal crystal has a regular pattern in space, a time crystal will return to the same arrangement over and over again in time, at precisely timed intervals. This destroys the time symmetry that would exist if it were possible for the atoms to exist in certain states at any point in time. It also means that the structure oscillates between specific states with a regular time period.

This idea of regular oscillation is what scientists have taken advantage of to go beyond the basic theory of time crystals. Instead of waiting to discover a material with time-crystal properties, two groups have used Norman Yao’s idea to create one of their own by using lasers and radio waves to manipulate the magnetic fields and spins of electrons in the atoms involved. This constant disturbance causes the material to flip between two states at a frequency different from the frequency of either of the lasers driving the change, meaning it fits the symmetry-breaking requirement of a time crystal.

In a way, time crystals sound like something physicists and engineers have been trying to create for a long time—a perpetual motion machine. This has a few requirements:

  1. It would run indefinitely (hence the name)
  2. It wouldn’t require an energy source, so no cost OR It would perfectly convert the source’s energy into work, without losing any energy

This sounds too good to be true, because it is. Unfortunately, time crystals don’t suddenly change that. The ones I’ve described here only function as crystals because of the constant application of an external prod, in the form of those two lasers. Also, you can’t use the energy put into them to do any work. This is really more like the opposite of a perpetual motion machine, since it depends on energy input to keep working AND doesn’t produce any usable product.

Time Crystals Box.png

Gee…thanks?

Despite the disappointment of not changing the laws of thermodynamics, the time crystals created by these two labs (one at University of Maryland, one at Harvard) do have promise for future applications. Because of the lasers and radio waves used to induce the constant oscillations, the time crystals qualify as non-equilibrium matter, meaning that energy is constantly flowing between them and the outside world. This property could make non-equilibrium matter useful for quantum computing, which is still mostly theoretical but could be a far more efficient way to analyze and store information. Time crystals themselves may not be usable for this purpose, but they are a great step toward understanding more about non-equilibrium materials.

Also, they’re TIME CRYSTALS. That’s never going to stop sounding cool.

[In the spirit of honesty, I have to admit that I considered making this a Skeptical Science Theater 3000 conversation, but I chickened out because I knew it would end like this:

MEH: So…no perpetual motion machine? LAME.

Read more about time crystals in one of the papers I linked above, or check out a few other write-ups of the two labs’ creations!]

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One thought on “What are Time Crystals?

  1. Pingback: Is Time Real? | Something of the Marvelous

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