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. Large structure in the Universe, such as galaxies, are believed to form by a process called violent relaxation, which occurs over millions of years. The authors present a nonlinear optics experiment which shows direct observation of violent relaxation, whose evolution can be related to the equations governing galaxy formation.