# Scientists Mess with the Speed of Light

Researchers in Switzerland have succeeded in breaking the cosmic speed limit by getting light to go faster than, well, light.

Or is it all an illusion?

Scientists have recently succeeded in doing all sorts of fancy things with light, including slowing it down and even stopping it all together. Now a team at the Ecole Polytechnique F?d?rale de Lausanne (EPFL) in Switzerland is controlling the speed of light using simple off-the-shelf optical fibers, without the aid of special media such as cold gases or crystalline solids like in other experiments.

"This has the enormous advantage of being a simple, inexpensive procedure that works at any wavelength," said Luc Th?venaz, lead author of the study detailing the research.

Using a technique called Stimulated Brillouin Scattering, the researchers were able to slow down or ratchet up the speed of light like the gas pedal on a car. They succeeded in reducing the speed of light by almost a factor of 4 (although that's still plenty fast at 46,500 miles per second), but even more dramatically, the team was also able to speed up the speed of light.

Light in a vacuum travels at approximately 186,000 miles per second, but a popular misconception is that, according to Einstein's special theory of relativity, nothing in the universe can travel faster than this speed.

This seeming paradox can be resolved because a pulse of light is actually made up of many separate frequency components, each of which moves at their own velocities. This is known as the pulse's phase velocity. If all the frequency components have the same phase velocity, then the overall pulse will also appear to move at that velocity.

However, if the components have different phase velocities, then the pulse's overall velocity will depend on the relationships between the velocities of the separate components. If the velocities differ, the pulse is said to be moving at the group velocity.

By tweaking the relationship between phase velocities, it's possible to adjust the group velocity and create the illusion that parts of the pulse are traveling faster than the speed of light.

One area where such an advance could be enormously beneficial is in the telecommunications industry.

Although information can be channeled through fiber optics at the speed of light, it can't be processed at this speed because with current technologies, light signals must be transformed into much slower electrical signals before they are useful.

Thevenaz's technique would essentially allow light to be processed with light without a costly electrical conversion.

The group's research will be published in an August 22nd issue of the journal Applied Physics Letters.