Experimental observation of violent relaxation

Structures in the Universe, ranging from globular clusters to entire galaxies, are not described by standard statistical mechanics at equilibrium. Instead, they are formed through a process of a very different nature, called violent relaxation that is now known to be possible also in other systems that exhibit long-range interactions. This mechanism was proposed theoretically and modelled numerically, but never directly observed in any physical system. Here, we develop a table-top experiment allowing us to directly observe violent relaxation in an optical setting. The resulting optical dynamics can also be likened to the formation of an analogue 2D-galaxy through the analogy of the underlying equations, where we can control a range of parameters, including the nonlocal interacting potential, allowing us to emulate the physics of gravitational quantum and classical dark matter models.