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.

A cloak that hides magnets from the outside world could have remarkable applications, say physicists. A metamaterial is a bizarre substance with properties that physicists can fine tune as they wish. Tuned in a certain way, a metamaterial can make light perform all kinds of gymnastics, steering it round objects to make them seem invisible.

By recreating the Big Bang inside a metamaterial for the first time, physicists have shown why the cosmological arrow of time points in the same direction as the thermodynamic arrow of time. Metamaterials are periodic structures that can be engineered to steer light in specific ways. The trick is to manipulate the properties of the «electromagnetic space» in which light travels by controlling the values of the permittivity and permeability of this space. But metamaterials have a more profound application because there is a formal analogy between the mathematics of electromagnetic spaces and the mathematics of general relativity and the spacetime it describes.

That’s handy because it allows engineers to recreate all kinds of exotic astrophysical objects in the lab. We’ve already talked about the first black hole made using a metamaterial and seen how it ought to be possible to recreate the Big Bang and even entire multiverses.