The following two texts are mutually exclusive, so either the variation of the wavelength is unrealistic or "light is made of particles" is refuted by the Doppler effect:
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
Richard Feynman: "I want to emphasize that light comes in this form - particles. It is very important to know that light behaves like particles, especially for those of you who have gone to school, where you probably learned something about light behaving like waves. I'm telling you the way it does behave - like particles. You might say that it's just the photomultiplier that detects light as particles, but no, every instrument that has been designed to be sensitive enough to detect weak light has always ended up discovering the same thing: light is made of particles." https://www.amazon.com/QED-Strange-Theory-Light-Matter/dp/0691024170
If Feynman is correct, then the variation of wavelength is unrealistic and the speed of light varies with the speed of the emitter, in violation of Einstein's relativity.
Variable wavelength of light https://youtu.be/3mJTRXCMU6o?t=77
contradicts the principle of relativity. If the wavelength varied, the emitter could regularly measure the (varying) wavelength inside his spaceship - so he would know his speed without looking outside. If, for instance, measurements inside the spaceship show that the wavelength has decreased, the emitter will conclude that his spaceship is now moving faster than before.
In future, Einstein-free physics the wavelength of light will be nothing more than an invariable coefficient in the formula
(frequency) = (speed of light)/(wavelength)
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