You need a mechanism that reproduces the observed redshift. What is the testable mechanism? How would you test it? Testing the Doppler Effect is extremely common. It has been done to death and confirmed. What reasonable test based upon the predictions of the hypothesis could possibly refute it?
The fact that there is another mechanism that has been around since the doppler mechanism was adopted, it is the same principle as seen the redshift of the Compton effect.
The Compton Effect was observed by Arthur Holly Compton in 1923, and explains that photons lose energy when they interact with matter, thus causing an increase in the wavelength of the photon. Compton scattering usually refers to the interaction involving only the electrons of an atom, although nuclear Compton scattering does exist.
Tired Light
The tired light theories are very different from the aforementioned theories, in that they don’t operate on the premise of the redshift being due to the Doppler Effect, nor to the expansion of the universe. The concept was first proposed in 1929 by Fritz Zwicky, who suggested that photons lose energy over time via interaction with matter or other photons, or by some novel physical mechanism34.
One of the successes of this theory was that it predicted the cosmic background radiation temperature to be around 2.8°K, during a time when the Big Bang theory was predicting temperatures anywhere between 5°K and 50°K35. A tired light model was also proposed in the 1950’s by FinlayFreundlich to explain the redshift of solar lines and anomalous redshifts of stars as well as the cosmological redshift
Reference: Page 11 &12. Tired Light Theories and the Compton Effect. “A review of redshift and its interpretation in cosmology and astrophysics.
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6. The equation of the cosmological redshift
The energy loss of a photon A larger photon will transfer more energy to a material particle since it has a longer interaction time with the material particle. So a larger photon transfers a larger part of its energy to the material particle than a smaller one. Thus, the energy loss of a photon is proportional to its size. A photon, on its journey after emission, meets a number of material particles before being received by an observer. The greater the number of material particles it meets, the more energy it loses. So, the energy loss of the photon is also proportional to the number of material particles it meets. 6.2 Equations for the cosmological redshift When a photon of size λ and energy E meets a material particle, the material particle runs through the electromagnetic field of the photon in a time t ¼ λ=c, where c is the speed of light. In the interaction, the material particle can be viewed as stationary compared to the speed of the photon. During the interaction, the photon transfers a tiny amount of energy δð Þ E to the material particle. A coefficient k ¼ δð Þ E =Eλ is defined here, denoting the rate of energy loss of the photon per unit length. The coefficient k is denoted conceptually at this stage. Further theoretical or experimental studies are needed to determine its value. If a photon of size λ0 and energy E when emitted meets N material particles in its path and transfers a part of its energy to the material particles, supposing all the material particles interact equally with the photoThe energy loss of a photon A larger photon will transfer more energy to a material particle since it has a longer interaction time with the material particle. So a larger photon transfers a larger part of its energy to the material particle than a smaller one. Thus, the energy loss of a photon is proportional to its size. A photon, on its journey after emission, meets a number of material particles before being received by an observer. The greater the number of material particles it meets, the more energy it loses. So, the energy loss of the photon is also proportional to the number of material particles it meets. 6.2 Equations for the cosmological redshift When a photon of size λ and energy E meets a material particle, the material particle runs through the electromagnetic field of the photon in a time t ¼ λ=c, where c is the speed of light. In the interaction, the material particle can be viewed as stationary compared to the speed of the photon. During the interaction, the photon transfers a tiny amount of energy δð Þ E to the material particle. A coefficient k ¼ δð Þ E =Eλ is defined here, denoting the rate of energy loss of the photon per unit length. The coefficient k is denoted conceptually at this stage. Further theoretical or experimental studies are needed to determine its value. If a photon of size λ0 and energy E when emitted meets N material particles in its path and transfers a part of its energy to the material particles, supposing all the material particles interact equally with the photon, a differential equation for the energy of the photon is obtained with coefficient k as follows: dE dN ¼ kλ0E: (1) The solution, from the condition E ¼ E0 when N ¼ 0, is E ¼ E0 exp ð Þ kNλ0 (2) The energy loss of the photon is ΔE ¼ E0 E. Thus, there is ΔE ¼ E0 1 1 exp ð Þ kNλ0 : (3) The expression for the redshift is Z ¼ λλ0 λ0 . It can be written as Z ¼ ν0ν ν ¼ E0E E . Then, it obtains, Z ¼ ΔE E : (4) From Eqs. (2)–(4), Z ¼ exp ð Þ kNλ0 1:
Reference: Page 7. The equation of the cosmological redshift Tired Light Denies the Big Bang