Emergence of an active vortex crystal

Active fluids such as dense suspensions of bacteria or sperm cells show a variety of phases ranging from disordered turbulence-like states to well-ordered vortex arrays. Continuum theories for active fluids, which belong to the class of Toner-Tu models, can be used to study such phases as well as transitions between them.
This video shows the emergence of an active vortex crystal (AVC) phase on a 20π x 20π domain. The emergence of the AVC is preceded by an extended turbulent transient state. During this transient, the system undergoes a spontaneous symmetry breaking in which vortices of one sign are selected over the other, eventually leading to the formation of the AVC.
See arxiv.org/abs/2005.06217.

[@blah123xyz]

Looks great. Is it a 2d world or a slice of a 3D world?

[@MentalFilm]

Could you explain what (if anything) is evolving over time? A change in parameters or just letting the simulation run its course with the same constant values?