If light from a light source receding at velocity v were to travel at c - v (as measured from the inertial reference frame of a relatively stationary observer), it would indeed have significant implications for our understanding of physics. This scenario contradicts the fundamental principles of special relativity, which is a well-tested and established theory.
According to special relativity, the speed of light in a vacuum, denoted by c, is constant and independent of the motion of the source or the observer. This means that regardless of the relative motion between the light source and the observer, the speed of light is always measured to be c.
If we were to assume a scenario where light from a receding source travels at c - v, it would violate the principles of special relativity, leading to inconsistencies and contradictions with numerous experimental observations and theoretical predictions. It would undermine the foundational principles that govern our understanding of the universe and have far-reaching consequences for various phenomena, including time dilation, length contraction, relativistic energy-momentum, and the equivalence of mass and energy.
The constancy of the speed of light in all inertial reference frames is a cornerstone of modern physics. It is supported by a vast body of experimental evidence and is mathematically consistent within the framework of special relativity. Therefore, any proposal that contradicts this principle would require a fundamental reevaluation of our understanding of physics and would likely require the development of an entirely new theoretical framework.