The reason why frequency as measured by the moving observer increases is because the speed of the light pulses relative to him increases (no other reason is conceivable):

https://www.youtube.com/watch?v=bg7O4rtlwEE

https://www.einstein-online.info/wp-...ein-Online.gif

"By observing the two indicator lights, you can see for yourself that, once more, there is a blue-shift - the pulse frequency measured at the receiver is somewhat higher than the frequency with which the pulses are sent out. This time, the distances between subsequent pulses are not affected, but still there is a frequency shift." https://www.einstein-online.info/en/spotlight/doppler/

Physicists clearly see the frequency increase but fail to see its cause, the speed-of-light increase.

Ignatius of Loyola explains: "We should always be prepared so as never to err to believe that what I see as white is black, if the hierarchical Church defines it thus".

If there is a next, sane (Einstein-free) version of fundamental physics, Einstein's 1905 nonsensical axiom

"The speed of light is constant"

will be replaced with the correct axiom

"For a given emitter, the wavelength of light is constant".

I have developed the idea in a series of tweets he https://twitter.com/pentcho_valev

Pentcho Valev