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
Variable speed of light of light is not constant. In quantum field theory the Heisenberg uncertainty relations indicate that photons can travel at any speed for short periods. In the Feynman diagram interpretation of the theory, these are known as "virtual photons", and are distinguished by propagating off the mass shell. These photons may have any velocity, including velocities greater than the speed of light. To quote Richard Feynman "...there is also an amplitude for light to go faster (or slower) than the conventional speed of light. You found out in the last lecture that light doesn't go only in straight lines; now, you