Slowing down the speed of light in open space was thought to be impossible -- not anymore.

Scientists have successfully demonstrated that the speed of light can be slowed down even in open space.

Researchers at the Heriot-Watt University and University of Glasgow claim that they have succeeded in slowing down the particles of light, known as photons, for the first time.

The scientists reveal that their experiment lasted for about two years and that they changed the shape of a photon to slow down the known maximum speed of light.

The researchers suggest that the latest experiment was similar to a race, so they built a light racetrack in which two photons were released simultaneously over identical distances. One of the two photons was left to travel normally while the other photon was let to pass via a mask, which was designed to slow down its speed by changing the shape of the photon.

The scientists says that the unaltered photon arrived at the destination on time. However, the time taken by the other photon, whose shape was altered, was delayed slightly.

Light usually slows down while passing through a medium but resumes the maximum velocity once it is released from the medium, the researchers say. However, the latest experiment demonstrates that when a light beam passes through a mask, the speed of photons is reduced. This is different from the slowing effect of light while traveling through a medium.

Daniel Giovannini, who is one of the lead authors of the study, explains that even though the reduction in the speed of light in their experiment is very small, it is still significant to their research.

"We've achieved this slowing effect with some subtle but widely known optical principles. This finding shows unambiguously that the propagation of light can be slowed below the commonly accepted figure of 299,792,458 meters per second, even when traveling in air or vacuum," said Jacquiline Romero, co-author of the study.

The latest findings provide new insight into the properties of light. The researchers suggest that even though the findings do not have any known applications, they are still trying to exploit many possibilities arising from the results of the experiment.

The study was published in the journal Science Express.