(Picture: a beryllium ion crystal NIST)
A group of Chinese and American physicists released a paper last week describing how to create ‘spacetime crystals’. They were inspired in part by the recent work of Nobel-Laureate Frank Wilaczek who recently introduced the theoretical concept of ‘time crystals’.
Normal crystals such as diamond or salt have several qualities: they are periodic in space, repeating their structure at fixed intervals; they represent the lowest energy configuration of the atoms that make up their structure; they exhibit certain symmetries (e.g. hexagonal, cubic, etc.). Frank Wilaczek (who won a Nobel Prize in 2003 for his discovery of asymptotic freedom in quantum chromodynamics) wondered earlier this year: what if you created a crystal that was periodic in time rather than space? Periodicity in time could be achieved by a rotating structure. The bizarre property of time crystals is that they may possibly represent a legitimate form of perpetual motion as their rotation is slowed only by small defects in their temporal crystalline structure.
Thanks to Einstein’s theory of relativity space and time are combined into spacetime (seehttp://tinyurl.com/spacetimejd), which led Tongcang Li of UC Berkeley (and a few friends) to investigate, by extending Wilaczek’s ideas, what a spacetime crystal may look like. They propose that by trapping beryllium ions in current state-of-the-art cylindrical ion traps at near-absolute zero, a spacetime crystal can be created. Such a spacetime crystal would also constitute the first known time crystal and thus exhibit the bizarre perpetual motion-like quality.
As crystals have their own symmetry, which is not the symmetry of the space (or spacetime in this case) they occupy, a spacetime crystal could afford physicists the opportunity to study something called symmetry-breaking. Symmetry-breaking is of huge interest to physicists as it pops up in many places, for example it is vital to the Higgs mechanism- which describes why particles have inertial mass in the standard model. Li and his co-authors also point out that the study of lower dimensional crystal-like structures such as graphene, which has a 2-D structure, have led to exciting discoveries with many potential applications.
Time crystals: http://www.sciencenews.org/view/generic/id/338500/
ArXiv blog: http://www.technologyreview.com/view/428334/how-to-build-a-space-time-crystal/
Original paper: http://arxiv.org/abs/1206.4772