C is constant, which is the "speed of light in a vacuum." Light can, and does, travel slower than C, e.g. when traveling through gas or other material. https:/

C is constant, which is the "speed of light in a vacuum." Light can, and does, travel slower than C, e.g. when traveling through gas or other material. https://en.m.wikipedia.org/wiki/Speed_of_light https://en.m.wikipedia.org/wiki/Speed_of_light Scientists have even managed to freeze light for short periods of time. https://io9.gizmodo.com/scientists-freeze-light-for-an-entire-minute-912634479 https://io9.gizmodo.com/scientists-freeze-light-for-an-entir...