2018-11-30 11:12:09 UTC
Stephen Hawking, "A Brief History of Time", Chapter 3: "Now imagine a source of light at a constant distance from us, such as a star, emitting waves of light at a constant wavelength. Obviously the wavelength of the waves we receive will be the same as the wavelength at which they are emitted (the gravitational field of the galaxy will not be large enough to have a significant effect). Suppose now that the source starts moving toward us. When the source emits the next wave crest it will be nearer to us, so the distance between wave crests will be smaller than when the star was stationary." http://www.fisica.net/relatividade/stephen_hawking_a_brief_history_of_time.pdf
Light pulses don't bunch up (the wavelength does not decrease) - bunching up obviously violates the principle of relativity. Rather, the speed of light VARIES with the speed of the emitter, as posited by Newton's emission theory:
"Emission theory, also called emitter theory or ballistic theory of light, was a competing theory for the special theory of relativity, explaining the results of the Michelson–Morley experiment of 1887. [...] The name most often associated with emission theory is Isaac Newton. In his corpuscular theory Newton visualized light "corpuscles" being thrown off from hot bodies at a nominal speed of c with respect to the emitting object, and obeying the usual laws of Newtonian mechanics, and we then expect light to be moving towards us with a speed that is offset by the speed of the distant emitter (c ± v)." https://en.wikipedia.org/wiki/Emission_theory
In future physics, the false axiom
"The speed of light is invariable"
will be replaced with the correct one
"The wavelength is invariable"
This means that, in accordance with the formula
(frequency) = (speed of light)/(wavelength)
any registered change in frequency corresponds to a proportional change in the speed of light. In other words, the frequency, as measured by an observer (receiver), shifts because the speed of the light relative to him shifts.