Mathematica(@mathemetica):Deriving cosmic expansion from Einstein: The slide shows how Einstein's field equations R_μν − ½ g_μν R = 8π G_N T_μν + Λ g_μν, for a perfect fluid T_μν = −p g_μν + (p + ρ) u_μ u_ν, yield the Friedmann-Lemaître equation H² ≡ (Ṙ/R)² = 8π G_N ρ/3 − k/R² + Λ/3. Here H(t) is the Hubble parameter and Λ the cosmological constant. The equation powers models of universe evolution, helps estimate its age and density from observations, and underpins studies of dark energy with telescopes like Hubble and JWST.

2026.08.26 11:25

Deriving cosmic expansion from Einstein: The slide shows how Einstein's field equations R_μν − ½ g_μν R = 8π G_N T_μν + Λ g_μν, for a perfect fluid T_μν = −p g_μν + (p + ρ) u_μ u_ν, yield the Friedmann-Lemaître equation H² ≡ (Ṙ/R)² = 8π G_N ρ/3 − k/R² + Λ/3. Here H(t) is the Hubble parameter and Λ the cosmological constant. The equation powers models of universe evolution, helps estimate its age and density from observations, and underpins studies of dark energy with telescopes like Hubble and JWST.