Never mind that a “time crystal” sounds like what happens if you crash a TARDIS into the Enterprise engine room. This theory about atomic perpetual motion machines is still melting my brain.

[T]ime crystals derive their movement not from stored energy but from a break in the symmetry of time, enabling a special form of perpetual motion. [Physicists] plan to build a time crystal, not in the hope that this perpetuum mobile will generate an endless supply of energy (as inventors have striven in vain to do for more than a thousand years) but that it will yield a better theory of time itself.