When I first heard the phrase “time crystals”, I pictured something from Doctor Who. The reality is stranger, and sadly has nothing to do with time travel. So what are time crystals? In short, they are a phase of matter whose structure repeats in time rather than in space. They were once thought to be impossible, and in 2022 a team in Melbourne built the biggest one yet.
First, what is a crystal?
To a physicist, a crystal is any material whose atoms are arranged in a regular, repeating pattern. Salt, diamond and ice are all crystals: zoom in and you see the same arrangement of atoms over and over again, like tiles on a floor. That repetition in space is what makes a crystal a crystal.
Now imagine a system that repeats itself not in space, but in time: one that keeps cycling through the same pattern, tick, tock, tick, tock, at its own steady rhythm, without settling down. That is the idea of a time crystal.
The idea, and why it seemed impossible
The concept was proposed in 2012 by Frank Wilczek, a Nobel Prize-winning physicist at MIT. He wondered whether a group of quantum particles could keep cycling through a repeating pattern even when sitting in its lowest-energy state, a bit like a clock that never needs winding. It sounded like a perpetual motion machine, and physicists were sceptical. In 2015, Haruki Watanabe and Masaki Oshikawa produced a theorem showing that Wilczek’s version was impossible for any system in its lowest-energy state, or in equilibrium more generally, as Scientific American explains. It looked like the end of the idea.
The loophole
But the proof left a loophole. It applied to systems left alone. What about a system that is regularly nudged by an outside force, such as a laser pulse? Physicists realised that such a system could settle into a rhythm of its own that does not match the rhythm of the nudges: kick it every second, for example, and it responds every two seconds. And remarkably, it does not just soak up energy and heat up, as you might expect. These became known as discrete time crystals, as Physics World explains. They are not quite what Wilczek imagined, and they are not perpetual motion machines, because they are being driven from outside, but they do break the rules of time symmetry in a genuinely new way.
From the lab to quantum computers
Once the theory was worked out, things moved quickly. In late 2016, Chris Monroe’s team at the University of Maryland created a time crystal from a chain of electrically charged atoms, called ions, and Mikhail Lukin’s team at Harvard made one using defects inside a diamond, with both results published in Nature in 2017, according to the American Physical Society. In 2021, a team of more than 100 researchers from Google and several universities created one on Google’s quantum computer, using 20 qubits.
Then came the Australian chapter. In 2022, Philipp Frey and Stephan Rachel of the University of Melbourne, a team of just two, built a time crystal from 57 qubits on an IBM quantum computer, accessed through the IBM Quantum Hub at the university. It was the largest time crystal created to that point, as Physics World reported, and the results were published in the journal Science Advances. In their experiment, the qubits flipped back and forth, returning to their starting arrangement every two pulses, and kept doing so despite the noise of today’s imperfect quantum hardware.
Can time crystals be used for time travel?
No, and they are not a source of free energy either. The “time” in the name refers only to the fact that their pattern repeats in time. They are not perpetual motion machines, because the ones made so far need an outside force to keep nudging them, and they are fragile, surviving only under carefully controlled laboratory conditions, often inside quantum computers chilled to a fraction of a degree above absolute zero. If you were hoping for a TARDIS, I am sorry to disappoint you; I was too.
What might they be good for?
For now, time crystals are mainly a tool for understanding how matter can behave out of equilibrium, a part of physics that is still poorly understood. But researchers are interested in whether their unusual stability could one day help with quantum technologies, for example as a way of protecting fragile quantum information, or in building extremely precise sensors. These ideas are speculative, and any practical use is likely to be years away. The more immediate payoff is the one the Melbourne team pointed to: today’s quantum computers, even with their imperfections, can already be used as laboratories for creating and studying entirely new kinds of matter.
Matter with a heartbeat
The part of this story I keep coming back to is the timeline: a provocative idea in 2012, a proof that it could not work in 2015, and working time crystals in the lab barely a year later, because someone read the fine print of that proof and spotted what it did not rule out. Wilczek did not get his clock that never needs winding, but the idea he threw out there led somewhere real. If you arrived here hoping time crystals might let you travel through time, my post on whether time travel is possible looks at what physics actually says, and what is consciousness? explores another question at the very edge of science.
Sources
- Scientific American: The quest to crystallize time
- Physics World: In search of time crystals
- American Physical Society, Physics: How to create a time crystal (2017)
- Physics World: Time crystals on a quantum computer reach record size (2022)
- Frey and Rachel: Realization of a discrete time crystal on 57 qubits of a quantum computer, Science Advances (2022)
- TechXplore: Observing time crystals on a quantum computer, by Stephan Rachel