Retrieving "Baryon To Photon Ratio" from the archives

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1. Light Nuclei

   Linked via "baryon-to-photon ratio"

   The primary cosmic abundance of light nuclei was established during the BBN epoch, approximately $10^{-6}$ seconds to 20 minutes after the Big Bang. During this period, the expansion rate dictated the freeze-out temperature, which curtailed further significant fusion past $^7\text{Li}$.
   The predicted primordial mass fraction of the lightest elements is remarkably consistent across theoretical models, heavily relia…