The speed of light is measured to 299 792 458 m / s and 1 meter defined to 1/299 792 458 of the speed of light. Let us assume that A live at the top of a skyscraper and B in the cellar the past 10 billion years. After 10 billion years B’s clock have “lost” 10 second due to different gravitational influence, compared to A’s clock. 10 billion years ago 2 photons was leaving a star 10 billion light years away and hit A and B at the same moment 10 billion year after. B would now say that he measured the time it took for the photon to reach earth, to 10 second less than A measured. B would therefore claim that either the speed of light must have been traveling faster than 299 792 458 m / s, or local distance (where B is) must be stretching or contracting proportional with the stretch of time. Which option is correct, and what proves it ?