Cosmological redshift and expansion
In an FLRW expansion model, light emitted and observed by comoving observers is stretched by the ratio of their scale factors.
Key knowledge
In an FLRW expansion model, light emitted and observed by comoving observers is stretched by the ratio of their scale factors. A spectral redshift therefore connects emission epoch to expansion history. Local peculiar motion and gravitational effects can also contribute to an observed redshift.
Values and equations
1 + z = λobs/λemit = aobs/aemit
- z
- cosmological redshift 1
- λobs,λemit
- observed and emitted wavelengths m
- aobs,aemit
- scale factors at observation and emission same scale-factor convention
Conditions and scope
- The displayed relation concerns the cosmological component for comoving emission and observation.
- Redshift alone does not determine a unique distance without an expansion and geometry model.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Read wavelength/scale-factor ratios and redshift definition; excluded dated highest-redshift statements and model-dependent identification of z=∞ with every possible beginning.
2026-10-10 · Independent AI editorial review: All26 Life-authored Cosmos compact statements, conditions, displayed equations and all56 origin semantic links read. Entire26-entry author statement/source matrix and explicit exclusions assessed. Targeted independent primary sections are listed below; this does not claim every referenced source body or proof was independently re-read. This is scoped AI reference-content review, not human disciplinary certification or whole-field completion. Receipt: cosmos-life-independent-content-review.1.
Entry details
Permanent link to this entry ↗- Record identity
- uni-cosmos-redshift-scale-factor
- Revision
- core.1
- Structured reference record
- University core expansion