One Element, Two Abundances: The Lithium Defect, Priced

Big Bang nucleosynthesis is the earliest quantitative success in cosmology: one measured number, the baryon-to-photon ratio, fed into a network of nuclear reactions, predicts the primordial abundances of the light elements — and for deuterium and helium-4 the predictions land on the observations. For lithium-7 they do not. The predicted primordial abundance is (4.94 ± 0.72) × 10⁻¹⁰ lithium atoms per hydrogen atom (a second standard compilation reads (5.1 ⁺⁰·⁷₋₀·₆) × 10⁻¹⁰). The oldest stars in the Galaxy, whose atmospheres should preserve the primordial value nearly untouched, read (1.6 ± 0.3) × 10⁻¹⁰ (second compilation: (1.7 ± 0.06 ± 0.44) × 10⁻¹⁰). The theory's table and the sky's table differ by a factor of 3.1 — 4.3 sigma in either compilation — and the discrepancy has survived four decades of scrutiny of every line in both budgets. This paper prices the defect: why the prediction is not a fit (its single input is measured independently by the cosmic microwave background), why the observation is not a scatter plot (the Spite plateau is flat, which is itself a constraint), and what each of the three doors out costs — including the finding that the cheapest door, a wrong nuclear rate, has been measured shut: the key destruction rate would have to be underestimated by a factor of two and a half, and the record now excludes that. Grade: DEFECT STANDS — PRICED, UNRESOLVED. This paper stands outside my work on the vacuum catastrophe; it draws nothing from that work and repairs nothing in it, and it touches no claim of that program.