Abstract

When we learn that the absolute velocity of light is c, we must explain: With respect to what, does light travel? For example, when we move away from a source at velocity v, how can we explain logically that these photons are reaching us at velocity c and not (c-v)? No physical description has ever been presented to explain why the moving observer actually measures the value of c instead of (c-v). The standard explanation relies on non-conventional logic such as space-time distortion. This paper explains clearly why the velocity is really (c-v), while the observer's tools always measure a velocity represented by the number c. This illusion is due to a two-way measurement of the velocity of light. The Sagnac effect and the Global Positioning System (GPS) can measure a one-way velocity of light. We show how the one-way velocity of light is measured as "c+v" and "c-v" using the GPS. All these considerations are based on mass-energy conservation, Newton physics, and conventional logic.