Speed of light the "local" speed of light is constant and equal to "c", but the speed of light along a trajectory of finite length can differ from "c", depending on how distances and times are defined. It is generally assumed that fundamental constants such as "c" have the same value throughout spacetime, meaning that they do not depend on location and do not vary with time. However, it has been suggested in various theories that the speed of light may have changed over time. No conclusive evidence for such changes has been found, but they remain the subject of ongoing research. It
Speed of light This is one of the proposed changes to be incorporated in the next revision of the SI also termed the "New SI". Speed of light The speed of light in vacuum, commonly denoted , is a universal physical constant important in many areas of physics. Its exact value is (approximately ). It is exact because by international agreement a metre is defined to be the length of the path travelled by light in vacuum during a time interval of 1/299792458 second. According to special relativity, is the maximum speed at which all conventional matter and hence all known forms of