Scottish scientists slow down speed of light in free space

lightbox32 writes: It has generally been thought impossible for particles of light, known as photons, to be slowed as they travel through free space, unimpeded by interactions with any materials.

In a paper published in Science Express, researchers from the Univ. of Glasgow and Heriot-Watt Univ. describe how they have managed to slow photons in free space for the first time. They have demonstrated that applying a mask to an optical beam to give photons a spatial structure can reduce their speed.