Time crystal
Time crystal

A team of physicists from Yale University has discovered indications of the existence of a “time crystal” in the place that was least expected: inside a  “normal” crystal and that we could find in certain children’s toys. The finding has opened new questions and makes it clear that we still know very little about how these structures are formed that openly defy the laws of physics.

Conventional crystals, such as salt, quartz, snowflakes or diamonds, have their atoms arranged in very stable patterns and repeated over and over again in the three spatial dimensions. In time crystals, however, atoms also move in a repeating pattern, although they do so in time, not in space.

Following a temporal (rather than spatial) pattern implies that the atoms of a time crystal never settle into their ground state, which conventional crystal atoms do. In general, when a material is in its ground state (minimum energy state, also known as zero point energy of a system) its movement is impossible, because that would require an expenditure of energy that that system no longer has.

Therefore, the “normal” crystals remain immobile, since they are in equilibrium and in their fundamental state. But the crystals of time have, we repeat, a structure that does not repeat itself in space, but in time, and therefore they continue to oscillate even in their fundamental state. That is, they  never reach equilibrium and, literally, they can not remain still. The most disturbing thing is that this cyclic and repeated oscillation takes place again and again without the need to use any energy. Faced with this panorama, physicists feel like explorers who entered a totally unknown continent for the first time.

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When they managed to create time crystals

The existence of time crystals was first proposed in 2012 by the Nobel Prize for Physics Frank Wilczek, from the Massachusetts Institute of Technology, who was the first to imagine a state of matter in which atoms moved in a pattern that is repeated in time, and not in space. An idea that at that time was widely criticized by most of the scientific community.

Later, in 2016 and in the face of general disbelief, a team of physicists from the University of California and Microsoft’s Q Station demonstrated that time crystals  could, indeed, exist in the real world. The work was published at the end of August 2016 in the journal Physical Review Letters, and was picked up by ABC on September 12 of that same year.

But the real “bomb” did not arrive until January 2017, when two independent groups of researchers from the Universities of Maryland and Harvard achieved, each on their own and using different techniques, create time crystals in their laboratories, news that also It was picked up by our newspaper.

In March of that same year, the find was published in Nature, which endorsed the birth of a whole new branch of physics and gave a letter of identity to something that until then was considered a mere speculation. The creation of time crystals leads us to still unexplored forms of matter and opens the doors to a reality that until recently was considered little more than a mathematical game.

Now, one thing is to create time crystals in complicated laboratory experiments in which all the conditions are millimeter-wise designed to observe them, and another thing is to find them inside a conventional material and that can even be within reach of children.

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Crystals in a toy

The finding of researchers from Yale thoroughly described in two recent articles published in the journals  Physical Review Letters and  Physical Review B. Both studies represent the second known experiment that has been able to observe the tell-tale signature of a time crystal within a solid.

“We decided to try to find the time crystals by ourselves,” says Yale physics professor Sean Barrett, principal investigator of the two new studies. My student Jared Rovny had grown monoammonium phosphate (MAP) crystals for a completely different experiment, so we tried something we already had in our lab.”

MAP crystals are considered so easy to grow that they are sometimes included in crystal growing kits for the little ones. According to Barret, finding a crystal of time inside a MAP crystal is something out of the ordinary, because until now it was thought that the crystals of time only formed inside crystals with a greater internal disorder».

Using nuclear magnetic resonances, the researchers were surprised to find what they were looking for so quickly: the unmistakable “signature” that betrayed the presence of time crystals. “Our measurements were quite surprising from the start,” explains Barret. Our work suggests that a crystal of time could be found, in principle, by looking in a simple crystal growing kit for children».

A new puzzle

But that was not the only unexpected result. “We also realized,” says Robert Blum, a Yale graduate student and co-author of the study, “that finding the signature of a time crystal did not necessarily prove that the system had a quantum memory that revealed how it came to be formed.” Which, according to another one of the signatories of the investigation, «stimulated us to prove an” echo “of crystal of time, that finally revealed the hidden coherence, or the quantum order, that was within the system».

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According to Barret, the results of his team “represent a puzzle for the theoreticians who try to understand how the crystals of time are formed. It is too early to know how the current theory about time crystals will be solved. What is certain is that many will have to continue working on this issue for at least the next few years”.

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