Speed of light zero, "γ" is equal to one, giving rise to the famous formula for mass–energy equivalence. The "γ" factor approaches infinity as "v" approaches "c", and it would take an infinite amount of energy to accelerate an object with mass to the speed of light. The speed of light is the upper limit for the speeds of objects with positive rest mass, and individual photons cannot travel faster than the speed of light. This is experimentally established in many tests of relativistic energy and momentum. More generally, it is normally impossible for information or energy to travel faster than "c". One
Variable speed of light While the measured value was later provided by Eddington in 1919, Albert Einstein went through several versions of light speed theory between 1905 and 1915, eventually concluding that light speed is constant when gravity does not have to be considered but that the speed of light cannot be constant in a gravitational field with variable strength. In the same book Einstein explained that he intended light speed to be a vector when it was described by coordinates in a reference frame. Einstein was not explicit about whether the speed of light would change in a gravity field, or whether just