Red Shift

[JonStar]

Question: Compared to the emission from our sun, the galaxies in the universe each have a red shift. Are all the emission lines for a given star shifted by the same amount? Or are the ultraviolet frequencies shifted more or less than those in the yellow frequencies or the red frequencies. Logic would indicate every emission line is shifted lower in energy, but are the shifts the same amount for every one?
But then again, my logic would indicate that a photon of a certain frequency would just get tired in the cold of space and six billion years, losing energy and shifting to the red. If that is the case, the universe would not be expanding.

[Ellimist]

Question: Compared to the emission from our sun, the galaxies in the universe each have a red shift. Are all the emission lines for a given star shifted by the same amount? Or are the ultraviolet frequencies shifted more or less than those in the yellow frequencies or the red frequencies. Logic would indicate every emission line is shifted lower in energy, but are the shifts the same amount for every one?

z or redshift for emission or absorption lines from a single source have been found to be constant. Lights of all wavelengths travel at the same speed, so the amount of expansion space undergoes in the time the photons take from going from the source to the destination is same.

But then again, my logic would indicate that a photon of a certain frequency would just get tired in the cold of space and six billion years, losing energy and shifting to the red. If that is the case, the universe would not be expanding.

The tired light hypotheses cannot be used to explain redshift of light coming from distant astronomical objects entirely. One of the problems would be that loss of energy would lead to scattering, and distant galaxies would appear blurred. Also, space is mostly empty. It is generally accepted that the wavelength of the light is stretched with the expansion of the universe which leads to redshift.


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I'm neither an astronomer nor a student of physics, so the things I post are to the best of my knowledge and may be wrong

[Chris Peterson]

Are all the emission lines for a given star shifted by the same amount?

Yes... but the shift is multiplicative, not additive. The formula is (z + 1)λ_emit = λ_obs. So the observed wavelength will always be scaled by z+1. A 550 nm source with a redshift of 2 will be observed at 1650 nm, a threefold shift, but an absolute shift of 1100 nm. A 700 nm source with a redshift of 2 will be observed at 2100 nm, again a threefold shift, but now an absolute shift of 1400 nm.

But then again, my logic would indicate that a photon of a certain frequency would just get tired in the cold of space and six billion years, losing energy and shifting to the red.

Your logic would fail, in that case. Tired light scenarios violate well tested theories of electromagnetism, and are invalidated by a number of lines of experimental and observational evidence.