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Speed of Light Might Not Be Constant After All!

A new study, published in journal Science, has toppled one of the fundamental concepts of physics relating to the speed of light, which is considered to be a constant, at 299 792 458 m / s. Now, it seems that this is not constant at all, and that light might differ in speed when travelling through the same medium.

A feature characteristic of science is that answering one question might not be definitive at all, bearing testimony to the infallible nature of man. Scientific theories are always being updated and modified as more knowledge is gained over time. Sometimes, what was previously thought to be fundamental laws are eventually discovered to be something else altogether. A recent study has further shown this dynamic nature of science: the speed of light might possibly not be constant. The results pointing to this are considered critical in the world of science where it was always believed that the speed of light is a constant, but now, it seems that light does not always travel at the known speed inside a vacuum.

Optical physicists from the University of Glasgow in Scotland have performed an experiment where the spatial structure of photons were manipulated such that they were slowed down; manipulating speed of light? It was then suggested that the known light speed might only be a maximum limit, with variations that may occur below the limit.

Lead author, Miles Padgett, explained that the slowing down of the photons was not much, but only 0.001 percent. However, the very fact that slowing down the light pulses is even possible is what is being hailed as critical information. A fundamental constant in physics that governs many other laws no more being a constant is indeed great news in the world of physics.

He added that: “Previously people had recognised that the speed of light was complicated, but our experiment, which measures single photons, is perhaps the cleanest demonstration”.

Light having variable speeds implies that a certain material is acting as obstacle to it. The latter might be water, for instance. Water has a refractive index greater than vacuum, allowing for the bending of light waves as they pass through water. However, the experiments carried out by the researchers involved light travelling through the same vacuum medium: this is what makes the results even more interesting.

The speeds of two photons with altered structures, but otherwise identical, were compared, after one of them was sent through a fiber towards a detector, and another was shot through a “mask”. The latter – the mask – modified the photon’s structure before it got redirected to the detector. The difference in structure caused the slight difference in speed; else, both would have arrived at the same time. Rather, the photon that was restructured arrived many micrometers late per meter of distance covered.

Furthermore, the delay was roughly forecasted by the investigators because the pattern of the mask determined the length of the late arrival.

This marks the first time that the invariable speed was shown to be, in fact, variable. Studies in the past had entertained the concept before, suggesting that vacuum might not be strictly empty.

The authors commented on the implications of their study, saying: “Beyond light, the effect observed will have applications to any wave theory, including sound waves and, potentially, gravitational waves”.


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