Variable speed of light with Einstein and stated both speed and direction of light change in a gravity field first published 1923 in English, 1920 in German. Born expressed the magnitude of light speed as the square root of (−"g"/"g") gravity components in general relativity to leave no doubt about his intent. Richard Tolman also agreed with Einstein and expressed the radial speed of light as "dr"/"dt" in a gravity field. where "m" is "MG"/"c" and where natural units are used such that "c" is equal to one. Robert Dicke, in 1957, developed a related VSL theory of gravity. In contrast to Einstein, Dicke
Speed of light which all massless particles and changes of the associated fields travel in vacuum (including electromagnetic radiation and gravitational waves). Such particles and waves travel at regardless of the motion of the source or the inertial reference frame of the observer. In the special and general theories of relativity, interrelates space and time, and also appears in the famous equation of mass–energy equivalence . The speed at which light propagates through transparent materials, such as glass or air, is less than ; similarly, the speed of electromagnetic waves in wire cables is slower than . The ratio between and the speed