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The Friedmann Equations — The Shape of the Universe - Leejohnston - 01-08-2026
The Friedmann Equations — The Shape of the Universe
The Friedmann equations describe how the universe expands over time.
Core equation:
(ȧ / a)² = (8πGρ / 3) − (k / a²) + (Λ / 3)
Where:
a = scale factor of the universe
ȧ = rate of expansion
ρ = energy density
k = curvature of space
Λ = cosmological constant
What this means:
The expansion of the universe depends on:
• Matter
• Radiation
• Dark energy
• Geometry
Key insight:
• Predicts expansion or collapse
• Explains dark energy
• Forms the backbone of modern cosmology
Why this matters:
Every model of the universe — Big Bang, inflation, cosmic acceleration — starts here.