Claim: The Hubble Constant Describes the Universal Rate of Expansion
It has been revised by 90% since its first measurement. Three current methods give three different values. A fundamental constant of nature does not behave this way.
Edwin Hubble reported in 1929 that distant galaxies were receding from us, and that their recession velocities were proportional to their distances. The constant of proportionality — now called the Hubble constant, H₀ — was measured at approximately 500 km/s/Mpc. This implied a universe approximately 2 billion years old: younger than the Earth, as then understood, by a factor of more than two.
The history of H₀ since 1929 is a history of revision. Not incremental refinement, but fundamental revision. From 500 to 180 to 75 to 50 to the current contested range of 63 to 74 km/s/Mpc. A reduction of approximately 87% from the original value.
This history is not a sign of science correcting itself, as the standard narrative suggests. It is a sign that the quantity being measured is not a fundamental constant of nature.
The Three Current Values
As of the time of writing, three independent, well-validated measurement methodologies return three distinct values of H₀:
73.04 ± 1.04 km/s/Mpc — from the Cepheid variable star distance ladder, used by the SH0ES collaboration (Riess et al., 2022). This is the local measurement, calibrated using stars in the nearby universe and extended to Type Ia supernovae at cosmological distances.
67.4 ± 0.5 km/s/Mpc — from the Cosmic Microwave Background as analysed by the Planck satellite (Planck Collaboration 2018). This is the early-universe measurement, derived from fitting the acoustic peak structure of the CMB within the LCDM model framework and extrapolating forward.
63 ± 6 km/s/Mpc — from galaxy group infall dynamics applied to the M81 and Centaurus A groups (Wagner, Benisty and Karachentsev, 2026). This is the most recent independent measurement, probing the dynamical properties of well-studied nearby galaxy groups and finding a value lower than either of the two established values.
The discrepancy between the Cepheid value and the Planck value has now exceeded 6 sigma. In any other area of physics, a 6-sigma discrepancy between two measurements of the same quantity would be interpreted as one or both measurements being wrong, or the theoretical framework connecting them being incorrect. In cosmology, it has been given a name — the Hubble tension — and treated as a puzzle to be resolved by new physics.
What a True Constant Would Look Like
A fundamental constant of nature is the same regardless of how you measure it. The speed of light in vacuum is 299,792,458 m/s whether you measure it with lasers, atomic clocks, or interferometers. The fine structure constant is 1/137.036 in every experiment ever conducted. The gravitational constant G is the same at every scale and epoch where it has been measured.
H₀ returns different values from different methods, different scales, and different epochs. The Planck measurement probes the universe at redshift z ≈ 1100. The Cepheid measurement probes the universe at z < 0.1. The galaxy group measurement probes z < 0.01. Three different epochs, three different scales, three different values with a directional trend: lower values at smaller scales and more recent epochs.
This is not the behaviour of a constant. It is the behaviour of a statistical property that varies with the sample being measured.
The BFUT Prediction
In the Big Flare-Up Theory, the Hubble relationship is an emergent statistical property of a gravitationally sorted galaxy population. Different measurement methods probe different scales and epochs of the sorting process and are expected to return different values. The directional trend — lower values at smaller scales and more recent epochs — reflects the fact that gravitational sorting has proceeded further in the local universe than at large cosmological distances.
BFUT Prediction 5, stated in the research paper before the Wagner et al. (2026) result was available, reads: "the Hubble tension will persist and local measurements will trend downward as measurement precision improves." The 63 km/s/Mpc result confirmed this prediction at the time of the paper's submission.