Well, i think some trouble lies in that things with 0 mass are already defined here. Light has 0 mass, and anything with 0 mass must move at the speed of light

Well, i think some trouble lies in that things with 0 mass are already defined here. Light has 0 mass, and anything with 0 mass must move at the speed of light since it has no inertia to stop it. What other point of reference can we use when 0 has been so solidly defined?