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def definition def or abbrev

critical_density

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formal statement (Lean)

  64noncomputable def critical_density : ℝ :=

proof body

Definition body.

  65  -- H₀ ~ 70 km/s/Mpc ~ 2.3e-18 s⁻¹
  66  3 * (2.3e-18)^2 / (8 * Real.pi * G)
  67
  68/-! ## Why Is Flatness A Problem? -/
  69
  70/-- The equation for Ω evolution:
  71
  72    |Ω - 1| ∝ a²(t) in radiation domination
  73    |Ω - 1| ∝ a(t) in matter domination
  74
  75    So deviations from 1 GROW with time!
  76    Ω = 1 is an unstable equilibrium (like balancing a pencil). -/

depends on (14)

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