Physicists at the U.S. Department of Energy’s Ames Laboratory have literally found a back-door to an otherwise rock-solid physical tenet. They have discovered how to increase the speed of light – 186,282.397 miles per second in a vacuum – by making it travel in reverse. Lead researcher Costas Soukoulis, physicist and ISU Distinguished Professor of Liberal Arts and Sciences, says that their discovery is “like rewriting electromagnetism.” But while Soukoulis seems to have made the impossible possible, the catch is that it requires exotic, artificially manufactured materials.
One of the goals for metamaterial boffins is to engineer materials that can negatively refract light at increasingly smaller wavelengths. The intention behind such attempts is to create a metamaterial that could refract light at visible wavelengths, allowing the creation of a flat super-lens, which would revolutionize optical science. Currently, however, metamaterials only work in microwave and far-infrared regions of the electromagnetic spectrum. Negatively refracting visible light would require manufacturing metamaterials at exceptionally small length scales, a difficulty that led scientists to believe that such a development would not occur for some time.
But Soukoulis’ research, published in Science, shows how to progress metamaterials into the realms of the near-infrared region of the electromagnetic spectrum. “We have fabricated for the first time a metamaterial that has a negative index of refraction at 1.5 micrometers,” said Soukoulis. “This is the smallest wavelength obtained so far.”
Further investigations by Soukoulis’ team showed that both the velocity of individual wavelengths (phase velocity) and the velocity of wave packets (group velocity) are in fact both negative. Soukoulis claims that this observation accounts for negatively refracted light’s ability to appear as if it is moving in reverse fast enough to defy Einstein’s theory of relativity. “When we have a metamaterial with a negative index of refraction at 1.5 micrometers that can disperse, or separate, a wave into spectral components with different wavelengths, we can tune our lasers to play a lot of games with light. We can have a wavepacket hit a slab of negative index material, appear on the right-hand side of the material and begin to flow backward before the original pulse enters the negative index medium.”
Soukoulis adds that the backward moving pulse also releases a forward pulse from the end of the metamaterial, which makes the pulse entering the front of the material appear to eject from the rear almost instantly. “In this way, one can argue that that the wave packet travels with velocities much higher than the velocities of light,” said Soukoulis. “This is due to the dispersion of the negative index of refraction; there is nothing wrong with Einstein’s theory of relativity.”