Linear cosmological matter growth
For small sub-Hubble-scale perturbations of pressureless matter in a homogeneous expanding background, the Newtonian growing-density model obeys δ̈+2Hδ̇−4πGρ̄_mδ=0.
Key knowledge
For small sub-Hubble-scale perturbations of pressureless matter in a homogeneous expanding background, the Newtonian growing-density model obeys δ̈+2Hδ̇−4πGρ̄_mδ=0. Gravity drives growth while expansion affects it through H. In an Einstein–de Sitter matter-only flat model, independent solutions are δ∝a and δ∝a⁻³ᐟ²; a general background requires its own growth solution.
Values and equations
δ̈+2Hδ̇−4πGρ̄_mδ=0; EdS: δ_grow∝a, δ_decay∝a^(−3/2)
- δ,a
- matter density contrast and dimensionless scale factor 1
- H
- background Hubble expansion rate s⁻¹
- ρ̄_m
- mean gravitating matter mass density kg m⁻³
- G
- gravitational constant m³ kg⁻¹ s⁻²
- t
- cosmic time for dotted derivatives s
Conditions and scope
- |δ|≪1,δ=(ρ_m−ρ̄_m)/ρ̄_m, cosmic time and negligible pressure/velocity-dispersion effects; the gravitational source and background components must be consistently specified.
- Radiation, freely streaming particles, horizon-scale gauge effects and nonlinear collapse require broader perturbation theory. Dark-matter particle identity is not resolved by this model; no dated best-fit cosmological parameters are asserted.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Read the actual Newtonian linear equation45 and its sub-Hubble/pressureless and nonlinear-limit paragraphs. The Einstein–de Sitter modes are independently obtained by substituting H=2/(3t),ρ̄_m=1/(6πGt²),δ=t^p, giving p=2/3 and−1. Excluded dated parameter estimates and the nearby inconsistent curvature-sign shorthand.
2026-10-10 · Independent AI editorial review: All44 exact root-authored compact records, equations/variable units/conditions and140 origin edges accepted after independently reading final6/18 with bounded primary bodies and matching prior38/122 scientific fingerprints unchanged. Exact claim/edge review is distinct from combined inventory scope and separate CLE26 approval; no entire cited books or old-corpus experimental revalidation is asserted. Receipt: cosmos-completion-independent-content-and-inventory-review.1.
Entry details
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- uni-cosmos-linear-density-growth
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- University core expansion