Alison K. Lanier
Time crystals, while they sound like they should be powering the Starship Enterprise, are a very real and relevant phenomenon that is changing the face of science. Nobel Prize winning physicist and Massachusetts Institute of Technology professor Frank Wilczek announced in February his theory about “time crystals,” which he said to be “kind of outside the box,” according to Simons Science News.
Bringing the Science Out of the Science Fiction
Time crystals are, in the simplest terms, objects in time that don’t suffer decay. The Simons Foundation report describes them as “physical structures that move in a repeating pattern, like minute hands rounding clocks, without expending energy or ever winding down. Unlike clocks or any other known objects, time crystals derive their movement not from stored energy but from a break in the symmetry of time, enabling a special form of perpetual motion.”
Wilczek is known for outlandish ideas and, as Wired describes, these ideas enter the scientific mainstream. His discovery of a property of nuclear forces known as asymptotic freedom won him the Nobel Prize in physics in 2004. However this newest publication on time crystals has been met, in over a year since its announcement, with a limited or “muted,” in Wired’s terms, response from the scientific community. In the words of physicist Jakub Zakrzewski of Jagiellonian University in Poland, he simply can’t be sure if the research’s conclusion is fact or fiction.
Bringing the Idea to Life
Wilczek tells Wired that he was struck by inspiration while preparing a lecture back in 2010, when his mind skipped from thinking about the behavior of crystalline structures in space to their behavior in time. Crystalline structures by definition spontaneously arrange themselves into rows and columns, each atom preventing each of the others from moving to the space between these set stacks. This sequestering out of space breaks the spatial symmetry of nature, the principle that all locations within physical space are equivalent, which led Wilczek to question if crystal structures would interact with the temporal symmetry of nature, which states that stable objects will remain the same over time.
The calculations Wilczek pursued over the months that followed seemed to indicate that the time-dependent ground state—or a state at which zero energy is expended—for crystal structures is essentially contradictory to the laws of physics as they stand now.
Hartmut Häffner, a quantum physicist at the University of California, Berkeley, told the Simons Foundation, “For a physicist, this is really a crazy concept to think of a ground state which is time-dependent. The definition of a ground state is that this is energy-zero. But if the state is time-dependent, that implies that the energy changes or something is changing.”
Challenging Current Theories
The principle demonstrated by this kind of perpetual motion points to a discordancy between Einsteinian theories of general relativity and quantum mechanics. General theories of relativity treat space and time as two parts of the same physics fabric that composes the universe, whereas in quantum mechanics, time and space are represented differently versus unified space-time. The crystal’s ability to break space symmetry, if it also allows the crystals to break time’s symmetry—what Zakrzewski calls “a disturbing, aesthetically unpleasant asymmetry”—is an indication that the theory of quantum mechanics is insufficient to explain the linked behavior of space and time in this example. Therefore quantum mechanics at least, according to Wired’s report, would need to be revised to address this phenomenon.
Putting the Idea to the Test
Frank Wilczek is known for his “out of the box” ideas. Credit: Simons Foundation
This seemingly impossible ground-state event will be put to the test in an experiment proposed by a team of Berkeley physicists led by nanoengineer Xiang Zhang. Wired described how the team will set out to formulate a structure that would demonstrate this perpetual motion principle. Using electric fields, the team proposes to arrange corral calcium ions into a 100-micron wide “trap.” Because of the repulsion between the like charges, the ions will form a crystalline ring in which a static magnetic field will, the scientists believe, cause the calcium ions to rotate within the trap.
The experiment depends on a new technology announced in September. For this test to work, ions must be at a ground state, which involves using a laser to cool the ions to within a billionth of a degree above absolute zero, so that nearly all the usual kinetic energy of the particle will all but come to a halt.
To track the movement of the particles, the team will excite one ion into a different electronic state, Wired described, while the other ions remain relatively dark. If the experiment is successful, then the scientists will see the lighter ion continue to move in a regular, lattice-like pattern at intervals, which would be the first time that the invariance of a system can be broken.
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