Jim Peebles calculated the recombination history of the early cosmic plasma. His treatment followed how electrons and protons form neutral hydrogen while the expanding background changes the conditions for atomic transitions.
An equilibrium abundance alone is insufficient when photons from atomic transitions are repeatedly reabsorbed and the expansion competes with reaction rates. Following this nonequilibrium history helps determine when the cosmic microwave background ceases to scatter efficiently. The calculation connects atomic physics to the observable last-scattering epoch.[ref]
Recombination of the Primeval Plasma by P. J. E. Peebles. Abstract and opening kinetic discussion: non-equilibrium recombination and cosmological radiation
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Portrait of Jim Peebles
. Juan Diego Soler; 17 May 2010; existing Commons crop and levels adjustment by WikiPedant. CC BY 2.0, via Wikimedia Commons. Source. Articles by others on the same topic
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Jim Peebles is a renowned Canadian-American astrophysicist known for his significant contributions to the understanding of the universe's evolution, particularly in the areas of cosmology and theoretical physics. He has been particularly influential in the study of the cosmic microwave background radiation and the large-scale structure of the universe. Peebles was awarded the Nobel Prize in Physics in 2019, together with Michel Mayor and Didier Queloz, for his theoretical discoveries in physical cosmology.