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This article about "crystals of time" just appeared on the PRL website.

Viewpoint: Crystals of Time (http://physics.aps.org/articles/v5/116)

The authors (including famous Frank Wilczek) claim that some systems in their ground state are time periodic and this is related to some spontaneous breaking of some "time" symmetry. From my point of view such systems were known before this claim (persistent currents, bright solitons among them)...So I want to know what is special about these new "crystals of time"?

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The key difference is that in, e.g. persistent currents, the translational time symmetry is not broken, only time reversal symmetry. I hope we will get an insightful answer about the consequences that could be far reaching. I would not accuse the authors of scientific misconduct, "fake", without evidence. –  Alexander Oct 17 '12 at 11:05
This was flagged as non-constructive, and originally it was, but I think it was just an edit away from being okay, so I'm editing rather than closing it. –  David Z Oct 17 '12 at 17:48

2 Answers 2

If you look at the diagrams of what they actually created, essentially it consists of several ions maintaining consistent spacing moving in a superconducting ring. As long as the temperature of the superconductor is maintained, the persistent rotational motion will be maintained. Since no work is being extracted this can be understood as a constant entropy system. However, it is not true perpetual motion, since the constant entropy state must be maintained by keeping the superconductor cool, or below ambient temperature. So if one considers the cooling apparatus, then the system must be viewed as a type of refrigerator.

It is significant in regards to its "perpetual motion", and that it is a many body system. An operation is being performed and the system returns to its original state. It is a technical achievement in that it uses some very advanced technology and proves that stable periodic multiparticle motion is possible in superconducting material.

If one were to be able to create a room temperature superconductor, then the persistent periodic state would be even more interesting.

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A flaw in Wilczek's argument has been pointed out in PRL 110, 118901 (2013). In short, the rotating soliton exhibited by Wilczek is not the correct ground state of the system. The true ground state can be shown to be stationary, irrespective of the flux. Impossibility of a quantum system with time-crystal-like ground-state has been further addressed in PRL 111, 040702 (2013), EPL 103, 57008 (20013), and arXiv:1410.2143.

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