It is long known that the speed of light can be slowed down as it passes through materials such as water or glass. But for the first time, researchers at the University of Glasgow and Heriot-Watt University have successfully made the speed of light slower in free space.
Scientists previously thought that it is impossible to slow down the speed of light while it's traveling in free space. The scientists experimented with two photons or the light particles. They applied a mask to laser light to give one photon a spatial structure while the other traveled with no impediment. They observed that the reshaped photon traveled slower than the other, at a difference of up to 20 wavelengths.
The researchers clarified that their experiment is different from the light passing on materials wherein the reduced speed is only temporary. Their experiment was able to alter the speed of light permanently by 299,792,458 meters per second.
"The delay we've introduced to the structured beam is small, measured at several micrometres over a propagation distance of one metre, but it is significant. We've measured similar effects in two different types of beams known as Bessel beams and Gaussian beams," Daniel Giovannini, one of the lead authors of the paper, said in a news release.
The researchers admitted that some might question their demonstration, but they maintained that it was done using solid theoretical foundation.
"We're confident that our observations are correct," said study leader Professor Miles Padgett of Glasgow.
He also added that the same theory might be applied to sound waves too.
The study was published in the Jan.23 issue of Science Express.
