Watching the Expansion Move: Redshift-Drift Predictions Separate the Normalisation Dispute from the Dark-Energy One
Year: 2026
Type: article
Abstract: The redshift drift — the slow change in a distant object's redshift as the expansion evolves — is the only proposed measurement of the expansion history in real time, requiring no calibration, no ruler, and no model of the source. This paper computes the spectroscopic velocity drift over a twenty-year baseline for three histories and asks which of the current disputes the drift can actually settle. The Planck history predicts drifts from +4.89 cm/s at redshift 0.5 through zero near redshift 2 to −15.79 cm/s at redshift 5 over twenty years. The small-ruler history, carrying the ladder's expansion rate, separates from the Planck prediction by 1.70 cm/s at redshift 0.5 and by 3.29 to 3.42 cm/s at redshifts 3 to 5: at redshift 3 the separation reaches a representative 2 cm/s measurement precision in about 12 years of baseline. The evolving-dark-energy history, by contrast, separates from the Planck history by at most 0.53 cm/s anywhere in the range, and would need about 100 years of baseline at redshift 3 to reach the same 2 cm/s threshold. The redshift drift is therefore, on human timescales, a direct arbiter of the Hubble tension's normalisation dispute — it reads H0 and the intermediate expansion rate off the sky with no intermediaries — and nearly useless, on those same timescales, for grading dark-energy dynamics. Programmes should be designed and advertised accordingly. This study is computed from 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: W7225776018
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