Editing Cosmic microwave background (section)

===Alternative theories===
{{main| Non-standard cosmology }}
The standard cosmology that includes the Big Bang "enjoys considerable popularity among the practicing cosmologists"<ref name=NarlikarPadmanabhan>{{Cite journal |last1=Narlikar |first1=Jayant V. |last2=Padmanabhan |first2=T. |date=September 2001 |title=Standard Cosmology and Alternatives: A Critical Appraisal |url=https://www.annualreviews.org/doi/10.1146/annurev.astro.39.1.211 |journal=Annual Review of Astronomy and Astrophysics |language=en |volume=39 |issue=1 |pages=211–248 |doi=10.1146/annurev.astro.39.1.211 |bibcode=2001ARA&A..39..211N |issn=0066-4146}}</ref>{{rp|211}}
However, there are challenges to the standard big bang framework for explaining CMB data. In particular standard cosmology requires [[Fine-tuning (physics)|fine-tuning]] of some free parameters, with different values supported by different experimental data.<ref name=NarlikarPadmanabhan/>{{rp|245}}
As an example of the fine-tuning issue, standard cosmology cannot predict the present temperature of the relic radiation, <math>T_0</math>.<ref name=NarlikarPadmanabhan/>{{rp|229}} This value of <math>T_0</math> is one of the best results of experimental cosmology and the [[steady state model]] can predict it.<ref name="Apeiron2_3_79"/>
However, alternative models have their own set of problems and they have only made post-facto explanations of existing observations.<ref name=NarlikarPadmanabhan/>{{rp|239}} Nevertheless, these alternatives have played an important historic role in providing ideas for and challenges to the standard explanation.<ref name=HistoryOfAlternatives/>