Editing Cosmic microwave background (section)

=== Progress on theory ===
In the 1970s numerous studies showed that tiny deviations from isotropy in the CMB could result from events in the early universe.<ref name=PartridgeReview/>{{rp|8.5.1}}
Harrison,<ref>
{{cite journal|last=Harrison|first=E. R.|date=1970|title=Fluctuations at the threshold of classical cosmology|journal=[[Physical Review D]]|volume=1|pages=2726–2730|doi=10.1103/PhysRevD.1.2726|bibcode = 1970PhRvD...1.2726H|issue=10 }}</ref> Peebles and Yu,<ref>{{cite journal|last1=Peebles|first1=P. J. E.|last2=Yu|first2=J. T.|date=1970|title=Primeval Adiabatic Perturbation in an Expanding Universe|journal=[[Astrophysical Journal]]|volume=162|pages=815–836|doi=10.1086/150713|bibcode=1970ApJ...162..815P}}</ref> and Zel'dovich<ref>
{{cite journal|last=Zeldovich|first=Y. B.|date=1972|title=A hypothesis, unifying the structure and the entropy of the Universe|journal=[[Monthly Notices of the Royal Astronomical Society]]|volume=160|pages=1P–4P|doi=10.1093/mnras/160.1.1P |doi-access=free |bibcode=1972MNRAS.160P...1Z}}</ref> realized that the early universe would require quantum inhomogeneities that would result in temperature anisotropy at the level of 10<sup>−4</sup> or 10<sup>−5</sup>.<ref name=PartridgeReview/>{{rp|8.5.3.2}} [[Rashid Sunyaev]], using the alternative name ''relic radiation'',  calculated the observable imprint that these inhomogeneities would have on the cosmic microwave background.<ref>{{cite journal|author=Sunyaev RA|author2=Zel'dovich YB|title=Small-scale fluctuations of relic radiation|journal=Astrophys. Space Sci.|volume=7|issue=1|pages=3–19|date=1970|bibcode=1970Ap&SS...7....3S|doi=10.1007/BF00653471|s2cid=117050217|url=https://link.springer.com/article/10.1007/BF00653471}}</ref>