Reversing Light: Negative Refraction

ictor Veselago, in a paper1 published in 1967, pondered the consequences for electromagnetic waves interacting with a hypothetical material for which both the electric permittivity, ε, and the magnetic permeability, µ, were simultaneously negative. As no naturally occurring material or compound has ever been demonstrated with negative ε andµ, Veselago wondered whether this apparent asymmetry in material properties was just happenstance, or perhaps had a more fundamental origin. Veselago concluded that not only should such materials be possible but, if ever found, would exhibit remarkable properties unlike those of any known materials, giving a twist to virtually all electromagnetic phenomena. So why are there no materials with negative ε andµ