I was at a high school science symposium, and some kid presented about metamaterials, a structure that shows a negative index of refraction, n. So I think his project was pretty good and all, and he had a good understanding: he had apparently created a new composite structure with neg. n without using split ring resonators. But in the questions session, I was surprised that some judge totally flamed him. He thought that a metamaterial was impossible to construct, and he questioned the presenter on how a wave could travel in one direction, and carry it's energy in another. I see now that this is a consequence of the reversed Poynting vector in a metamaterial. Anyone care to explain how this is possible? Another few questions I had: What are the properties of a material with only one parameter of permittivity or permeability is negative? I know n is equal to the root of permittivity and permeability, so how can you take the root of a negative number? Also, what is the difficulty in creating a LHM in the optical frequencies? Thanks for help!