Webb and Hubble confirm Universe's expansion rate
New measurements from the James Webb Space Telescope closely match Hubble’s earlier estimates of the universe’s expansion rate, strengthening confidence in the “distance ladder” method based on Cepheid variables and supernovae. However, this leaves unresolved the so‑called Hubble tension: these late‑universe measurements still disagree with values inferred from the cosmic microwave background, suggesting either unrecognized systematics or missing physics such as evolving dark energy or modified gravity. Commenters explore the limits of our cosmological models, the assumptions behind time invariance and energy conservation, and how techniques like the cosmic distance ladder let us infer vast scales from tiny signals.
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.