Mark Stockman, a theoretical physicist at Georgia State University, argues that...
The electrons in the materials slosh in response to the electromagnetic fields in the light, and causality says that the precise arrangement and motion of the electrons can depend on light that has already passed through them--not on the light that has yet to arrive. Starting from that point, Stockman has shown mathematically that negative refraction and absorption are intertwined so that you cannot have one without the other, as he reports in a paper to be published in Physical Review Letters. "There is no way to decrease the losses," Stockman says. "The [negative refraction] effect will disappear." In particular, simple amplification won't do the trick, he says.
Of course, this will not stop others working in this field to either prove him wrong, or find a way around this.