Collision of "metamaterial universes": experimental realization of   Minkowski domain wall
  Minkowski domain walls are being actively considered in gravitation theory. They may form during a vacuum phase transition, or as a result of braneworld collision. Despite having interesting physical properties, Minkowski domain walls had remained in the theoretical domain only since their first introduction a few decades ago. Here we demonstrate how to make an electromagnetic analogue of a Minkowski domain wall using hyperbolic metamaterials. We analyze electromagnetic field behavior at the wall, and present a simple experimental model of Minkowski domain wall formation due to collision of two Minkowski spaces. 
Igor I. Smolyaninov, Yu-Ju Hung
physics.optics gr-qc