The Hubble tension and the observer's causal diamond
Description
The Hubble constant from the local distance ladder exceeds the cosmic microwave background (CMB) value by more than 5σ, and baryon acoustic oscillations (BAO) return an intermediate value. Proposed changes to early- or late-time physics have not yet resolved the tension.
This paper explores whether the ladder, BAO and CMB values can be reconciled within a quantum recording architecture that operationalises Wheeler's participatory universe. The proposed mechanism is an endpoint gate on the boundary of the observer's causal diamond that shortens the distance scale recorded by a measurement. The diamond can change in five directions: its size, the time of its centre and the three spatial coordinates of its centre. Each direction that a probe fixes in setting its scale passes through the gate once and survives with probability σ = exp(−3/(16π²)). A probe that fixes m of these five directions, its metrological rank, records a Hubble length shortened by σ^m and reads σ^(−m) times the Hubble constant of the realised geometry. The CMB takes its scale from last scattering, rank zero. BAO fix separations across and along the line of sight, rank two. The ladder's chain of distances can fix all five, and the ladder data select rank five.
A CMB fit with three parameters fixed by the architecture gives H0* = 66.80 km s⁻¹ Mpc⁻¹ for the realised geometry. The predicted readings 66.8, 69.4 and 73.5 match the CMB, BAO and ladder without fitting a continuous parameter to late-time data. With the rank left free, DESI DR2 BAO prefer 1.72 ± 0.26, close to rank two. Reading BAO at rank two lowers the preference for evolving dark energy from 2.5–4.0σ to 0.3–1.6σ across three supernova samples.
A recording architecture centred on the observer may reconcile the ladder, BAO and CMB values. The main current limitation is that the physical process by which the gate shortens the scale recorded by each measurement has not yet been derived. Falsifiable predictions are presented for forthcoming surveys.
Notes
First public release (v1, 27 October 2026).
This release presents an initial proposal for a new conceptual framework, and the work remains under active development. The results are conditional on the assumptions stated in the Supplemental Material. Later versions will update the paper as the open problems are addressed, and comments are welcome.
Contents. The main text sets out the endpoint factor, the metrological rank of each probe class, the distance ladder, the comparison with current data and the predictions. The Supplemental Material gives the derivations, the SH0ES reconstruction, the DESI DR2, joint-fit and evolving-dark-energy analyses, the candidate landing places of the endpoint factor (Table S13) and the derivation status of every result (Table S15).
Status of results. Table S15 gives the status of each quantitative result and the assumptions on which each result rests. Three choices were made with the data in view (the designation of the distance ladder, the form of the dressed background and rank zero for the CMB), and the choices not fixed by the construction are charged in the model comparison (Supplemental Material, S13).
Open problem. The physical process by which the gate shortens the scale recorded by each measurement has not yet been derived. The Supplemental Material states the requirements on that process and the routes already excluded, and work on the process is ongoing.
Companion papers. The CMB anomalies, Standard Model, dark sector, primordial cosmology and foundations papers listed under related works supply the architecture, the background parameters and the survival factor. Companion papers are cited by their concept DOIs. The foundations paper is under revision, and its concept DOI resolves to the latest version.
Code. The deposit holds eleven scripts in paper order, four modules, the numbers file used by the figures and three data archives (the runs of scripts 10 and 11, and the CMB-alone minima used for comparison in script 10). The file 00_README_S20_v1.md maps each script to its section. Scripts 01 to 04 and 09 reproduce the calculations from public data. The joint CMB and BAO fits come from the multi-start script 10, whose configurations, minima and logs are deposited, as are those of script 11. These fits need the Planck, ACT, DESI and supernova likelihoods.
Files
HubbleTension_v1_27Oct26.pdf
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Additional details
Dates
- Created
-
2026-10-27