What causes the Hubble tension? · revision history

Revision 2

Accepted · core change · record

Changes against revision 1:

Title
What causes the Hubble tension?
Plain
Two careful ways of measuring how fast the universe expands today give different answers. The cause could be a measurement error or new physics.
Precise · changed · core
Revision 1: Write $H0 = h x 3.24e-18\ \mathrm{s}^{-1}$. The SH0ES Cepheid plus type Ia supernova ladder gives $h = 0.730 \pm 0.010$, while Planck CMB in LCDM gives $h = 0.674 \pm 0.005$. Identify whether the discrepancy comes from distance-ladder systematics, from physics before recombination that shrinks the sound horizon, or from late-time physics, with a model that fits all data at least as well as LCDM.
Revision 2: Write $H0 = h x 3.24 \times 10^{-18}\ \mathrm{s}^{-1}$. The SH0ES Cepheid plus type Ia supernova ladder gives $h = 0.730 \pm 0.010$, while Planck CMB in LCDM gives $h = 0.674 \pm 0.005$. Identify whether the discrepancy comes from distance-ladder systematics, from physics before recombination that shrinks the sound horizon, or from late-time physics, with a model that fits all data at least as well as LCDM.
Settled by
Independent one-percent $H0$ measurements that agree with one side, plus a model or systematic that removes the discrepancy without spoiling other fits.
Kind
phenomenon
Answer type
identification
References
(empty)
Literature status
contested
Status note
2025 to 2026 JWST cross-checks by SH0ES find Cepheid, TRGB and JAGB distances agree within about 0.03 mag, while CCHP finds $h$ near 0.70.
Posed since
(empty)

Decisions