Expansion and relic radiation support an earlier hot, dense Universe.
Key knowledge
The hot Big Bang model describes the observable Universe evolving from an earlier hot, dense state as space expands and cools. The cosmic microwave background is relic radiation released when matter became sufficiently neutral for light to travel freely; its spectrum and small variations constrain cosmological models.
Conditions and scope
The large-scale model assumes approximate homogeneity and isotropy; it does not describe every local structure as expanding.
This record does not establish a physical singularity, a cause of the Universe or the microscopic nature of dark matter and dark energy.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
ESA's account of CMB observations, expansion and large-scale model assumptions; no CMB map or parameter estimate was newly analysed.
2026-10-10 · English hot-state/expansion and relic-radiation scope checked against ESA's Planck page; precise cosmological ages and densities are excluded.
Foundational review
2026-10-10 · Fresh primary-source inspection of the complete compact record, including every statement, equation, quantity and material condition, followed by independent AI editorial review. This check does not certify all linked lessons or every passage of every cited publication.
Sources from other places
Agreement within this scope
Expanding hot early Universe, relic CMB and cosmological constraints.
Model constraints do not settle every question about the earliest state.
Cosmological redshift describes the stretching of light wavelengths as the universe expands during propagation. Inferring a distance from redshift requires an expansion model and a definition of distance. A simple nearby Hubble relation is a limited approximation, rather than a universal conversion at all redshifts.
Cosmological wavelength stretching is interpreted within an expanding-universe model.
Temperature and polarization statistics of the cosmic microwave background can be compared with predicted spectra to constrain cosmological parameters. Planck releases provide likelihoods, parameter chains and best fits for stated models and data combinations; the inferred parameters are not direct readings from a sky-map pixel.
CMB statistics constrain parameters within an explicitly stated cosmological model.
The hot expanding universe passed through changing particle and radiation conditions. Light nuclei formed before neutral atoms; later declining free-electron abundance allowed photons to propagate much more freely. The cosmic microwave background preserves radiation from this last-scattering era, rather than light emitted at the first instant.
This separates physical eras within the hot-universe evidence.