Scientists say that a perpetual motion machine is physically impossible, but a research team at the University of California Berkeley has just outlined an idea that comes pretty damn close. By proposing a 4D "space-time crystal," the engineers have designed a device that would operate at its lowest quantum energy state and exhibit a clock-like persistence that would theoretically exist even after the universe is exhausted of all its energy, the so-called heat death.


Normally, crystals are comprised of atoms that are arranged in an orderly, repeating three-dimensional pattern. Earlier this year, however, MIT's Nobel-prize winning physicist Frank Wilcze outlined the concept of a crystal that could extend into the fourth dimension, that of time. But while he mathematically proved that such a device could exist, he wasn't exactly clear on how to build such a thing.

That's where an international team of scientists led by researchers with the U.S. Department of Energy (DOE)'s Lawrence Berkeley National Laboratory come in. Mechanical engineer Xiang Zhang and his team have proposed an experimental design of a space-time crystal based on two basic principles: An electric-field ion trap, and the Coulomb repulsion of particles that carry a similar electrical charge. Simply put, it's a four-dimensional crystal that features a periodic structure in time as well as space.


Speaking through a release, Zhang describes how it works:

The electric field of the ion trap holds charged particles in place and Coulomb repulsion causes them to spontaneously form a spatial ring crystal. Under the application of a weak static magnetic field, this ring-shaped ion crystal will begin a rotation that will never stop. The persistent rotation of trapped ions produces temporal order, leading to the formation of a space-time crystal at the lowest quantum energy state.

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Essentially, this 4D space-time crystal would consist of a physical object with regular periodic atoms that are moving in a regular, periodic pattern. They would move forever — and with no external input. To create a clock out of such a device, the developers would have to create a circular arrangement of regularly ordered atoms that would orientate to the same location at fixed intervals. The researchers are suggesting this could work by trapping a cloud of beryllium ions working inside a magnetic field, thus forcing them into a circular pattern.

Now while it might seem that way, the device is not a perpetual motion machine. Because it's functioning at the lowest quantum energy state, there is no energy output.


In terms of other applications, the conceptual breakthrough will allow Zhang and his team to study how complex physical properties and behaviors emerge from the collective interactions of large numbers of individual particles. The 4D crystal could also be used in quantum mechanics to study such phenomena as entanglement.

The entire study can be ready at Physical Review Letters.

Other sources: PopSci. Image: UC Berkeley.