  Extraordinary light rays propagating inside a hyperbolic metamaterial look
similar to particle world lines in a 2+1 dimensional Minkowski spacetime [1].
Magnetic nanoparticles in a ferrofluid are known to form nanocolumns aligned
along the magnetic field, so that a hyperbolic metamaterial may be formed at
large enough nanoparticle concentration nH. Here we investigate optical
properties of such a metamaterial just below nH. While on average such a
metamaterial is elliptical, thermal fluctuations of nanoparticle concentration
lead to transient formation of hyperbolic regions (3D Minkowski spacetimes)
inside this metamaterial. Thus, thermal fluctuations in a ferrofluid look
similar to creation and disappearance of individual Minkowski spacetimes
(universes) in the cosmological multiverse. This theoretical picture is
supported by experimental measurements of polarization-dependent optical
transmission of a cobalt based ferrofluid at 1500 nm.
