Matter, radiation and vacuum expansion solutions
Research context
research method · conditional · As of 2026-10-10
Combining a conserved component with flat single-component Friedmann expansion yields matter a∝t^(2/3), radiation a∝t^(1/2) and vacuum exponential expansion.
Key knowledge
Combining a conserved component with flat single-component Friedmann expansion yields matter a∝t^(2/3), radiation a∝t^(1/2) and vacuum exponential expansion. Multi-component transitions require the total-density solution; these powers are not valid across the entire cosmic history.
Values and equations
a∝(t-t0)^[2/(3(1+w))]; χ_h(t)=integral_tinitial^t c dt'/a(t'); r_s(t)=integral_tinitial^t c_s(t') dt'/a(t')
- a
- Dimensionless scale factor 1
- w
- Constant equation-of-state parameter 1
- t,t0,tinitial
- Cosmic times with declared origin/lower bound s
- χ_h,r_s
- Comoving particle-horizon and sound distances m
- c,c_s
- Light and appropriate fluid sound speeds m s^-1
Conditions and scope
- Expanding flat branch, w>-1 for the big-bang power law; vacuum solution has w=-1 and positive constant density.
- Horizon and sound distances integrate the actual time-dependent scale factor and sound speed.
- Power law requires flat independently conserved single-component domination and w>-1; for w=-1, a=a0 exp[H(t-t0)].
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Cosmology: the expanding universe: Sections 1.2–1.3: continuity and component expansion solutions (selected source body inspected).
2026-10-10 · Bounded source check of the recorded statement and conditions. This does not certify a unique physical model, reproduce the cited study or replace independent branch review.
Entry details
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- research-earth-component-expansion
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