Friedmann Equations & Cosmological Parameters Explained
The Friedmann equations describe how the universe expands.
Einstein’s general relativity inspires them. Alexander Friedmann derived these key equations in 1922.
The first Friedmann equation links expansion rate to energy content. It shows the Hubble parameter squared equals a combination of matter, radiation, curvature, and dark energy terms.
The second equation tracks how the expansion rate changes over time. It reveals acceleration or deceleration depending on the universe’s contents.
Hubble parameter H₀ measures current expansion speed. Astronomers express it in km/s/Mpc. Current best estimates place H₀ around 67–74 km/s/Mpc. This value sparks lively debate in cosmology.
Ωm represents matter density parameter. It includes ordinary matter plus dark matter. Today, Ωm sits near 0.3. So matter makes up roughly 30% of the total energy budget.
ΩΛ stands for dark energy density parameter. It drives the universe’s accelerated expansion. Current data show ΩΛ ≈ 0.7. Therefore dark energy dominates the cosmos now.
The flatness problem ties everything together. Observations indicate the total density parameter Ωtotal ≈ 1. This means Ωm + ΩΛ + Ωr ≈ 1 (radiation term Ωr is tiny today).
Cosmologists use these parameters to build models. The standard Lambda-CDM model relies heavily on them. It assumes flat geometry, cold dark matter, and a cosmological constant.
Planck satellite data refined these values precisely. JWST observations continue testing them today.
H₀ tension challenges the picture. Different methods give slightly conflicting numbers. This puzzle drives new physics research.
Friedmann equations remain powerful tools. They connect theory to real observations beautifully.
Master these parameters. Then the story of our expanding universe becomes much clearer.