At 300,000 kilometers/second, the speed of light is constant in vacuum, such as space, when it encounters a different medium, however, such as glass or water, its speed is reduced. Another phenomena that can occur in addition is that light can be dragged when it travels through a moving substance, and scientists at University of Glasgow have managed to replicate this in lab for the first time.
The phenomena was first theorized by Augustin-Jean Fresnel in 1818 and observed a hundred years later.
Prof. Miles Padgett in the Optics Group in the School of Physics & Astronomy, said: “The speed of light is a constant only in vacuum . When light travels through glass, movement of the glass drags the light with it too.
“Spinning a window as fast as you could is predicted to rotate the image of the world behind it ever so slightly. This rotation would be about a millionth of a degree and imperceptible to the human eye.”
Researchers managed to the drag the light by using a different approach. They chose to use a setup which allowed them to shine a primitive image made up of the elliptical profile of a green laser through a ruby rod spinning on its axis at up to 3,000 rpm.
After light starts entering the ruby, its speed is instantly slowed to the speed of sound (741 mph) and gets dragged by the spinning motion of the rod. The resulting image is rotated by 5 degrees, which is just enough to be fairly observable by the naked eye.
Dr Franke-Arnold, who came up with the idea of using slow light in ruby to observe the photon drag, said: “We mainly wanted to demonstrate a fundamental optical principle, but this work has possible applications too.
“Images are information and the ability to store their intensity and phase is an important step to the optical storage and processing of quantum information, potentially achieving what no classical computer can ever match.
“The option to rotate an image by a set arbitrary angle presents a new way to code information, a possibility not accessed by any image coding protocol so far.”