Press Trust Of India
London, Jan 23: A team of Scottish scientists has for the first time managed to slow down the speed of light as it travels through air, unimpeded by interactions with any other material, according to a study.
Scientists have long known that the speed of light can be slowed slightly as it travels through materials such as water or glass. However, it has generally been thought impossible for particles of light, known as photons, to be slowed as they travel through free space.
In a new paper titled ‘Spatially Structured Photons that Travel in Free Space Slower than the Speed of Light’ published in Science Express, researchers from the University of Glasgow and Heriot-Watt University described that they have managed to slow photons in free space for the first time.
The speed of light is regarded as absolute and is about 186,000 miles per second in free space. The findings of the new experiment is likely to alter how science looks at light.
Photons were sent through a special mask, which changed the photons’ shape, and slowed them to less than light speed.
The experiment was configured like a time trial race, with two photons released simultaneously across identical distances towards a finish line.
The researchers found that one photon reached the finish line as predicted, but the structured photon which had been reshaped by the mask arrived later, meaning it was travelling more slowly in free space.
Over a distance of 1 metre, the team measured a slowing of up to 20 wavelengths, many times greater than the measurement precision.
This is different to the slowing effect of passing light through a medium such as glass or water, where light is only slowed when it is passing through the material — it returns to the speed of light after it comes out the other side.
