{"dataset":{"slug":"cosmological-parameters","title":"Cosmological Parameters","description":"The numbers that describe the universe as a whole — the matter density (Ωm), the dark-energy density (ΩΛ), the amplitude of fluctuations (σ8), and the scalar spectral index (ns).","version":"1.0.0","lastGenerated":"2026-06-29","license":"CC BY-SA 4.0","entityCount":4,"sources":["planck"]},"entities":[{"id":"cosmological_parameter:sigma-8","name":"Amplitude of Fluctuations (σ8)","type":"cosmological_parameter","domain":"science","description":"A measure of how clumpy the universe is — the amplitude of matter-density fluctuations averaged over spheres of 8 megaparsecs. It links the smooth early universe to today's web of galaxies, and a mild disagreement between its early-universe and weak-lensing determinations — usually quantified through the related combination S8 — is known as the S8 tension.","entryPath":"/distance-ladder/sigma-8"},{"id":"cosmological_parameter:dark-energy-density","name":"Dark Energy Density (ΩΛ)","type":"cosmological_parameter","domain":"science","description":"The fraction of the universe's total energy density carried by dark energy — the component driving the accelerating expansion. In the standard model it is the cosmological constant Λ, and it makes up the majority of the present-day energy budget.","entryPath":"/distance-ladder/dark-energy-density"},{"id":"cosmological_parameter:matter-density","name":"Matter Density (Ωm)","type":"cosmological_parameter","domain":"science","description":"The fraction of the universe's total energy density that is in matter — dark matter plus ordinary baryonic matter — today. Together with the dark-energy density it sets the geometry and the fate of the universe; it is measured most precisely from the cosmic microwave background.","entryPath":"/distance-ladder/matter-density"},{"id":"cosmological_parameter:scalar-spectral-index","name":"Scalar Spectral Index (ns)","type":"cosmological_parameter","domain":"science","description":"The 'tilt' of the spectrum of primordial density fluctuations laid down by inflation — whether fluctuations have slightly more or less power on large scales than on small. A value just below one is a key prediction of, and constraint on, inflationary models, and is measured from the CMB.","entryPath":"/distance-ladder/scalar-spectral-index"}]}