# Dark Energy & Cosmological Tensions: State of the Field (October 2026)

Research dossier · v1 · updated 2026-10-30 · 3,847 words · 42 sources · 27 claims · verification: verified

Covers the Hubble tension between local distance-ladder and early-universe measurements of the expansion rate, the DESI evidence for evolving dark energy, sensitivity to supernova calibration, and the early- and late-time extensions proposed in response. The main takeaway: the local-versus-early H0 gap persists across independent methods, while the DESI preference for evolving dark energy is statistically notable but depends on the supernova sample and remains unsettled.

## Contents

- Executive summary
- Background and core concepts
- Timeline of key milestones
- State of the art
  - Late-universe distance ladder
  - Early-universe inference and the CMB
  - BAO and evolving dark energy
  - Early dark energy and other early-time proposals
  - Late-time and interacting dark energy
  - Gravitational-wave standard sirens
  - Quantitative benchmarks
- Open problems and active debates
- Major programs and players
- Outlook: what to watch (next 12-18 months)
- Key papers
- Glossary

## Sample findings

- Planck 2018 gives H0 = 67.4 ± 0.5 km/s/Mpc in base flat ΛCDM.
- DESI DR1 BAO with a BBN prior and θ* gives H0 = 68.52 ± 0.62 km/s/Mpc; adding Planck and ACT CMB lensing gives 67.97 ± 0.38 km/s/Mpc.

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