# Universe not expanding after all?

**URL:** <https://boards.straightdope.com/t/universe-not-expanding-after-all/663920>\
**Category:** Factual Questions\
**Created:** [July 19, 2013, 9:35am UTC](https://boards.straightdope.com/t/universe-not-expanding-after-all/663920 "2013-07-19T09:35:43Z")\
**Posts on this page:** 2\
**Page:** 2

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**Author:** ![Yumblie](https://avatars.discourse-cdn.com/v4/letter/y/76d3ee/32.png) [@Yumblie](https://boards.straightdope.com/u/Yumblie)\
**Post date:** [July 21, 2013, 6:03pm UTC](https://boards.straightdope.com/t/universe-not-expanding-after-all/663920/21 "2013-07-21T18:03:53Z")

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> [@Asympotically\_fat](#):
>
> AFAIK there isn’t a huge amount of evidence for expansion that is independent of redshift, but there is some. In the big bang model the temperature of the CMB decreases in time, whereas in most steady-state models the CMB would be expected to have a constant temperature.
> 
> [[1012.3164] The evolution of the Cosmic Microwave Background Temperature: Measurements of TCMB at high redshift from carbon monoxide excitation](http://arxiv.org/abs/1012.3164)

Maybe I’m missing something obvious, but in a steady-state universe why would there be a CMB at all? I can’t think of any explanation for such a uniform, isotropic source of radiation other than the universe being hot and dense in the past.

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**Author:** ![Half\_Man\_Half\_Wit](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/half_man_half_wit/32/21766_2.png) [@Half\_Man\_Half\_Wit](https://boards.straightdope.com/u/Half_Man_Half_Wit)\
**Post date:** [July 21, 2013, 6:09pm UTC](https://boards.straightdope.com/t/universe-not-expanding-after-all/663920/22 "2013-07-21T18:09:12Z")

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> [@Yumblie](#):
>
> Maybe I’m missing something obvious, but in a steady-state universe why would there be a CMB at all? I can’t think of any explanation for such a uniform, isotropic source of radiation other than the universe being hot and dense in the past.

One explanation for the CMB in a steady-state universe I recall (due to Fred Hoyle, I believe) was that the light of old stars might be scattered by peculiar needle-shaped grains of iron, but I don’t think this is in line with modern precision measurements anymore (but you’re right to note that the CMB is a great problem for all steady-state theories, being often considered the ‘smoking gun’ of the big bang, to mix some metaphors).

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