Analog models of gravity are attempts to model various phenomena of general relativity (e.g., black holes or cosmological geometries) using other physical systems such as acoustics in a moving fluid, superfluid helium, or Bose–Einstein condensate ; gravity waves in water; and propagation of electromagnetic waves in a dielectric medium. These analogs (or analogies) serve to provide new ways of looking at problems, permit ideas from other realms of science to be applied, and may create opportunities for practical experiments within the analog that can be applied back to the source phenomena.