Hubble Expansion & Cosmological Redshift
Every galaxy recedes — velocity proportional to distance: v = H₀·d
Scale Factor: 1.00
H₀: 70 km/s/Mpc
Time: 0.0 Gyr
Redshift z: 0.00
Hubble's Law (1929): recession velocity v = H₀·d, where H₀ is the Hubble constant (~70 km/s/Mpc). This is not motion through space — space itself expands.
Galaxies (dots) are colored by recession velocity: blue-shifted (nearby) → orange → red-shifted (far).
The Friedmann equation governs expansion: (ȧ/a)² = H²(Ω_m/a³ + Ω_Λ). Dark energy (Ω_Λ) causes accelerating expansion — galaxies beyond the Hubble horizon are forever unreachable.
Cosmological redshift: z = 1/a - 1, where a is the scale factor when light was emitted.