Why is the Speed of Light Finite?

The speed of light is finite, or the speed of any moving body including a photon cannot exceed a finite constant value. The reason is that the inertial frame in which we examine the motions of objects is not purely inertial. We assume that the spacetime around us in which the solar system lies is an inertial system. However, in the far distance there exist innumerable material bodies which exert the gravitational forces on the motions of the objects we examine. It is shown that, if it were not for those external bodies, the motion of a body would attain the infinite speed.