Webb and Hubble confirm Universe's expansion rate

Hubble tension and what Webb adds

• Thread centers on the “Hubble tension”: local measurements of the Hubble constant (73 km/s/Mpc) vs CMB-inferred value (67 km/s/Mpc) whose error bars no longer overlap.
• JWST observations of Cepheids and supernovae match Hubble’s results, strongly reducing the chance that the tension is due to Hubble measurement error.
• Commenters stress: the tension remains unresolved; Webb confirmed Hubble, not the CMB result.

Methods for measuring expansion rate

• Two main approaches discussed:
  • Early‑universe: infer today’s H₀ from CMB anisotropies within the ΛCDM model.
  • Late‑universe: build a “cosmic distance ladder” (parallax → Cepheids → Type Ia supernovae, plus other anchors) and fit redshift vs distance.
• Some share technical notes on error budgets (e.g., Cepheid reddening, SN statistics, anchor distances) and alternative anchors (megamasers, Gaia, eclipsing binaries).

Interpretations and implications

• Suggested explanations for the tension: unknown systematics, incorrect ΛCDM assumptions, or genuinely “new physics” (dynamic dark energy, modified gravity, etc.).
• Several see it as strong evidence current large‑scale models are incomplete but effective approximations. Others emphasize how well ΛCDM still fits most data.

Time, physical laws, and philosophy

• Long subthread on whether “rate of time” is meaningful, invariance of physical laws across cosmic history, and the problem of induction.
• Noether’s theorem and energy conservation are invoked; some note cosmology already tolerates non‑conservation of energy at large scales and dark energy’s odd behavior.
• Debate over how much we can ever know about the very early universe and whether overconfidence is a problem.

Alternative cosmological ideas

• “Tired light” (photon energy loss over distance), gravitational background noise, changing constants, cyclic or static universes, and CMB as dust emission are floated.
• Others point out these ideas generally conflict with multiple observations (spectral shapes, lack of blurring, structure formation) and have largely been disfavored.
• Mention of the CMB “Axis of Evil” alignment as another puzzling anomaly.

Expansion, motion, and “expanding into what?”

• Repeated confusion over expansion of space vs galaxies “moving through” static space; balloon and bedsheet analogies recur.
• Clarifications: peculiar velocities vs Hubble flow, superluminal recession as metric expansion, local systems (galaxy clusters) not following expansion.

Human reaction

• Many express awe at what can be inferred from sparse photons and clever geometry, alongside skepticism about how final any of these conclusions are.