Background information for movies:
A pulse of light (electromagnetic radiation) is composed of many small wave components, each with a slightly different wavelength. In air, each of these components travel at the speed of light, and the light pulse maintains its original shape. In a material, each wavelength travels at a slightly different speed, always slower than light in a vacuum, a phenomenon known as dispersion.

Note: In order to play the following movies on Windows MediaPlayer, you must download a free codec from Divx. Click on this link and follow the instructions.

Movie 1
Faster than the speed of light? A pulse of light enters a fictitious, ideal metamaterial that does not disperse, or spread out, the light pulse into individual wave components with different velocities. Inside the metamaterial, the velocities of both the light pulse and the individual wave components are negative. This condition makes the light move “backwards,” and the peak of the light pulse leave the metamaterial on the right-hand side before it enters on the left. Consequently, energy is transferred through the material faster than the vacuum speed of light, which is unphysical and violates physics laws, such as relativity and causality. (The dashed curve shown at the end of the movie moving to the right and exiting the metamaterial depicts what would happen if the metamaterial were replaced by air.)

Movie 2
No laws broken here! A pulse of light enters a more realistic metamaterial with dispersion. Each wavelength component is affected differently, and a pulse is seen emerging from the metamaterial with no laws of physics violated. The emerging pulse is distorted as a result of the dispersion. (Again, the dashed curve is a depiction of the pulse emerging if the metamaterial was removed and only air was present.)