Metamaterials, a hot area of research today, are artificial
materials engineered with resonant elements to display properties that are not
found in natural materials. By organizing materials in a specific way,
scientists can build materials with a negative refractivity, for example, which
refract light at a reverse angle from normal materials. However, metamaterials
up to now have harbored a significant downside. Unlike natural materials, they
are two-dimensional and inherently anisotropic, meaning that they are designed
to act in a certain direction. By contrast, three-dimensional natural materials
typically look the same from all directions. For instance, water in a glass
acts as an isotropic material for light, even though the water molecule itself
has an asymmetric and anisotropic structure.