<p><a href="http://en.wikipedia.org/wiki/Tired_light" rel="nofollow"><em>Tired light</em></a> has been used as an explanation before, whereby light loses energy whilst travelling through space---a sort of drag effect. </p>

<p>I don't think anyone actually supports it nowadays, though.</p>

CC BY-SA 3.0
2014-03-20T20:50:41.187Z
Especially given the new gravity wave observational support for inflationary theory.
called2voyage
CC BY-SA 3.0
2014-03-20T11:07:20.990Z
2014-03-20T13:07:24.247Z
2014-03-20T13:07:24.247Z
Sirius
<p>In Cosmology, the main contribution to redshift would be cosmological redshift. Namely the redshift that occurs due to the Hubble flow. According to Hubble's law,</p>

<p><span class="math-container">\begin{equation}
v = H_0 d
\end{equation}</span>
The further two objects are away from each other, the faster they are moving. Of course, all this is under the assumption of an expanding universe, such as the widely accepted <span class="math-container">$\Lambda CDM$</span> model. </p>

<p>The Hubble flow is in a sense a type of "speed", but this velocity can be faster than the speed of light. This is chiefly because the space between two points is expanding, causing the wavelength of the light to be stretched out.</p>

<p>There is also gravitational redshift, something that occurs due to gravity's effect on spacetime. Although it might be better to think that <em>anything</em> that can stretch the wavelength of light can cause redshift, suppose there exist some kind of <em>god hand</em> that allows one to just pull and subsequently stretch the <em>light wave</em> this would also cause redshift.</p>

CC BY-SA 4.0
2019-04-09T18:27:27.300Z
2019-04-09T18:27:27.300Z
chou
<p>On episode 10 of the original Cosmos TV series, Carl Sagan mentions that some scientist don't agree that the redshift observed in distant galaxies is evidence of the big bang, stating that probably the doppler effect is not responsible for this effect. What other explanations are there?</p>

CC BY-SA 4.0
2019-12-20T09:03:55.010Z
The original Cosmos TV series is from the 80's. A lot of things have been discovered in cosmology since.
usernumber
CC BY-SA 3.0
2014-03-15T16:50:04.327Z
The alternative was around the shift being an actual wavelength shift due to the age of those galaxies. Not sure that argument stacks up any more though (and it was always a bit difficult to argue)
Rory Alsop
<galaxy><big-bang-theory><radio-astronomy><astrophysics><redshift>
Is there another explanation, apart from the doppler effect, for the redshift observed in distant galaxies?
Eduardo Serra
# Is there another explanation, apart from the doppler effect, for the redshift observed in distant galaxies?

(Asked by: username_0 on 2014-03-15)

On episode 10 of the original Cosmos TV series, Carl Sagan mentions that some scientist don't agree that the redshift observed in distant galaxies is evidence of the big bang, stating that probably the doppler effect is not responsible for this effect. What other explanations are there?

**Tags:** galaxy, big-bang-theory, radio-astronomy, astrophysics, redshift
> **Comments:**
> **username_2**: The alternative was around the shift being an actual wavelength shift due to the age of those galaxies. Not sure that argument stacks up any more though (and it was always a bit difficult to argue)  
> **username_1**: The original Cosmos TV series is from the 80's. A lot of things have been discovered in cosmology since.  

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## 2 answers

### Answer by username_3 on 2014-03-20. Score: 5

[*Tired light*](http://en.wikipedia.org/wiki/Tired_light) has been used as an explanation before, whereby light loses energy whilst travelling through space---a sort of drag effect.

I don't think anyone actually supports it nowadays, though.

> **Comments:**
> **username_4**: Especially given the new gravity wave observational support for inflationary theory.  

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### Answer by username_5 on 2019-04-09. Score: 1

In Cosmology, the main contribution to redshift would be cosmological redshift. Namely the redshift that occurs due to the Hubble flow. According to Hubble's law,

\begin{equation}
v = H\_0 d
\end{equation}
The further two objects are away from each other, the faster they are moving. Of course, all this is under the assumption of an expanding universe, such as the widely accepted $\Lambda CDM$ model.

The Hubble flow is in a sense a type of "speed", but this velocity can be faster than the speed of light. This is chiefly because the space between two points is expanding, causing the wavelength of the light to be stretched out.

There is also gravitational redshift, something that occurs due to gravity's effect on spacetime. Although it might be better to think that *anything* that can stretch the wavelength of light can cause redshift, suppose there exist some kind of *god hand* that allows one to just pull and subsequently stretch the *light wave* this would also cause redshift.


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