<p>If the universe wasn't expanding, would light still be redshifted after traveling some distance?</p>
<p>Is there a way of being sure that it's the expansion that causes light to redshift and not just a natural phenomenon for light to redshift as it travels, regardless of whether space is expanding. In the latter case, the only way expansion of space could affect the redshift would be by making light travel a longer distance.</p>
<p>Edit: So I've come across the term 'Tired light' in an SE answer but it doesn't really explain why there aren't supporters for this theory. So, why aren't there?</p>

CC BY-SA 4.0
2020-06-22T09:33:02.023Z
Does this answer your question? [Is there another explanation, apart from the doppler effect, for the redshift observed in distant galaxies?](https://astronomy.stackexchange.com/questions/1973/is-there-another-explanation-apart-from-the-doppler-effect-for-the-redshift-ob)
ProfRob
CC BY-SA 4.0
2020-06-22T09:34:20.580Z
See also https://astronomy.stackexchange.com/questions/29061/are-there-other-proofs-of-the-expanding-universe-apart-from-the-redshift
ProfRob
CC BY-SA 4.0
2020-06-22T09:38:41.577Z
And perhaps more detail: https://physics.stackexchange.com/questions/300365/time-dilation-of-distant-cosmic-events-what-is-it
ProfRob
CC BY-SA 4.0
2020-06-22T16:43:09.980Z
@RobJeffries https://astronomy.stackexchange.com/questions/1973/is-there-another-explanation-apart-from-the-doppler-effect-for-the-redshift-ob This question does introduce "Tired light" but doesn't quite explain why no one supports this theory.
https://astronomy.stackexchange.com/questions/29061/are-there-other-proofs-of-the-expanding-universe-apart-from-the-redshift Same goes for this. It focuses on the expansion of the universe rather than 'can the redshift be caused by something else'
Arnab Chowdhury
<cosmology><light><redshift>
Is cosmological redshift caused due to expansion of space or distance traveled by light?
Arnab Chowdhury
# Is cosmological redshift caused due to expansion of space or distance traveled by light?

(Asked by: username_0 on 2020-06-22)

If the universe wasn't expanding, would light still be redshifted after traveling some distance?

Is there a way of being sure that it's the expansion that causes light to redshift and not just a natural phenomenon for light to redshift as it travels, regardless of whether space is expanding. In the latter case, the only way expansion of space could affect the redshift would be by making light travel a longer distance.

Edit: So I've come across the term 'Tired light' in an SE answer but it doesn't really explain why there aren't supporters for this theory. So, why aren't there?

**Tags:** cosmology, light, redshift

> **Comments:**
> **username_1**: Does this answer your question? [Is there another explanation, apart from the doppler effect, for the redshift observed in distant galaxies?](https://astronomy.stackexchange.com/questions/1973/is-there-another-explanation-apart-from-the-doppler-effect-for-the-redshift-ob)  
> **username_1**: See also https://astronomy.stackexchange.com/questions/29061/are-there-other-proofs-of-the-expanding-universe-apart-from-the-redshift  
> **username_1**: And perhaps more detail: https://physics.stackexchange.com/questions/300365/time-dilation-of-distant-cosmic-events-what-is-it  
> **username_0**: @RobJeffries https://astronomy.stackexchange.com/questions/1973/is-there-another-explanation-apart-from-the-doppler-effect-for-the-redshift-ob This question does introduce "Tired light" but doesn't quite explain why no one supports this theory. https://astronomy.stackexchange.com/questions/29061/are-there-other-proofs-of-the-expanding-universe-apart-from-the-redshift Same goes for this. It focuses on the expansion of the universe rather than 'can the redshift be caused by something else'  

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