Two hundred 99 million, 792 thousand, 458 (299,792,458) meters per second is how fast light travels. Usually.
A team of physicists at the University of Glasgow has managed to apply the brakes to a photon - a particle of light - by sending it through a special mask that changed its shape. While light naturally slows down as it passes through a material like glass or water, it accelerates back to the speed of light as soon as it returns to the free space of a vacuum. However, the re-structured particle in the Scottish lab did not pick up its pace. In a race with a photon that was not manipulated, it lost, reaching the detector several micrometers later per meter travelled.
The finding will not affect our flashlights or reading lamps. However it could have implications for scientists who use the speed of light to make precise measurements of astronomical distances. The experiment suggests that light speed - considered one of the most important constants in physics - should now be thought of as a limit, rather than a constant.