The Inverse Ladder, Run End to End: DESI Distances Plus the BBN Baryon Density Return H0 = 69.0
Year: 2026
Type: article
Abstract: The inverse distance ladder — baryon acoustic oscillations calibrated by a sound horizon computed from the baryon density that nucleosynthesis measures — is the early-universe side's answer to the local ladder, and it is usually quoted from large joint analyses whose inner workings are hard to inspect. This paper runs the whole chain openly, in one computation, with every step stated: the baryon density fixed at Omega_b h^2 = 0.02237 from the primordial deuterium abundance; the sound horizon computed by direct integration for each trial cosmology rather than assumed; the eleven DESI 2024 distance measurements fitted over the two background parameters (H0, Omega_m) of a flat cosmological-constant history. The chain's control is exact: at the Planck densities it returns a sound horizon of 146.97 Mpc against the published 147.09. The fit returns H0 = 69.0 km/s/Mpc with a profiled one-sigma range of 68.25 to 69.75, matter fraction 0.305 (range 0.290–0.320), physical matter density 0.1452, sound horizon 146.41 Mpc, and a chi-squared of 13.97 for eleven points. The result sits 1.77 sigma above the Planck value and 3.15 sigma below the SH0ES value: the inverse ladder, run transparently on current data, lands between the disputants but much closer to the early universe, and it excludes the ladder's central value at a level set by the acoustic distances rather than by any microwave-background modelling. Imposing the SH0ES value with the standard matter fraction degrades the fit to a chi-squared of 31.38. Nothing in the chain uses the microwave background's anisotropy data at all — the baryon prior is nucleosynthesis's, the ruler is an integral, and the distances are DESI's — which is what makes the result an independent line rather than a restatement of Planck. This study is computed from published values and stated assumptions; it is not a measurement.
Author: Aldred, William Alexander
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7225772952
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