Does Light Always Travel at the Same Speed?
The speed of light in a vacuum is 299,792,458 meters per second or 670,615,343 miles per hour. This is represented by the variable c, which stands for the Latin celeritas, which means speed. There is a consensus among physicists that accepting the general theory of relativity, Einstein’s prevailing physics theory, entails accepting the speed of light in a vacuum as a constant. Therefore, any experiment proposing that the speed of light in a vacuum changes over time is viewed in the physics community with great suspicion. It is widely known, however, that the speed of light is variable when the light is not moving through a vacuum. The ratio of the speed of light through a given medium and through a vacuum is called the medium’s refractive index or optical density. Some media have such a high refractive index that they can slow light to the speed of a person walking, or even bring it to a temporary standstill. For example, the speed of light through air is very close to the speed of lig
