As I just said, the speed of light is constant in all references frames. There does not need to be an inertial frame to make this so, and in fact General Relativity has as one of its outcomes a distinct lack of inertia frames. Now, how is the speed of light constant in all reference frames? Frankly, it\'s the way the universe works and as an engineer we didn\'t get into the philosophy of the subject too much in my relativistic dynamics course. Unless you\'re willing to go through the tensor calculus yourself to demonstrate the basic principles of GR, however, you might as well take my word on it. EDIT: In short, your premise is incorrect: a constant speed of light does not imply an absolute frame.