SCIENTISTS IN SCOTLAND have managed to make light travel slower than the speed of light.

The team from the University of Glasgow and Heriot-Watt University slowed photons in free space for the first time by applying a mask to an optical beam to give photons a spatial structure that reduces their speed.

In a new paper published in the Science Express today, team compare a beam of light, containing many photons, to a team of cyclists who share the work by taking it in turns to cycle at the front. Although the group travels along the road as a unit, the speed of individual cyclists can vary as they swap position.

The group formation can make it difficult to define a single speed for all cyclists, and the same applies to light. A single pulse of light contains lots of photons, and scientists know that light pulses are characterised by a number of different speeds.

Scientists raced two photons across identical distances – one with a mask and one without. The restructured photon with the mask arrived later – slowed by up to 20 wavelengths.

These results are different to the slowing effect of passing light through a medium such as glass or water, where the light is only slowed during the time it is passing through the material.

“The results give us a new way to think about the properties of light and we’re keen to continue exploring the potential of this discovery in future applications,” commented Professor Padgett, lead author. “We expect that the effect will be applicable to any wave theory, so a similar slowing could well be created in sound waves, for example.”

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