Scientists manage to make light travel at less than the speed of light, forcing science to look at light in, well, a new light.
Then they raced them in pairs. One photon they left in its normal state. The other photon was sent through a special mask.
The mask forced the photon to change its shape and travel slower than the speed of light.
Dr Romero explains: “After the mask, the photon is launched into a sort of racetrack about a metre in length.
“Then we take the time in which the unshaped photon finishes the racetrack, and the shaped photon’s time as well, and then compare the two times.”
If they had both been travelling at the speed of light it would have been a dead heat. But the re-shaped photon came in second.
Not by much – a few millionths of a metre – but it showed that it had not just been slowed by the mask, but had continued to travel at less than light speed even after it had returned to free space.
Light travelling at less than the speed of light. Whose bright idea was that?
It grew from a conversation between Prof Daniele Faccio at Heriot-Watt University and Prof Miles Padgett at Glasgow.
Prof Padgett says the crucial component is the mask – a software controlled liquid crystal device: “That mask looks a little bit like a bull’s-eye target.
“And that mask patterns the light beam, and we show that it’s the patterning of the light beam that slows it down.