Equation 9 · Part 2 · From Origins to Frontier: A History of Precision Cosmology
subscript
subscript
What this part means
The lower label selects a particular version, component, or indexed member of the quantity. For example, x₀ and xₜ can be values at different positions.
Its job in the formula
A subscript distinguishes a version, component, step, or member of a quantity. It does not automatically mean multiplication.
Full expression→subscript→Article meaning
The passage around this formula
where is the physical size of the sound horizon at recombination — how far a pressure wave in the primordial plasma could travel before the plasma became neutral and transparent — and is the angular diameter distance to that same epoch. Planck measures directly from the angular spacing of peaks in the CMB power spectrum to extraordinary precision; converting that angle into a present-day expansion rate requires assuming a cosmological model (matter content, radiation content, and the equation of state of dark energy) to relate and to . This is the crux of the tension discussed below: Planck’s is a model-dependent inference from an early-universe…
Learn the underlying idea
A subscript is a label attached below a symbol. It often selects a time step, component, category, or member of a sequence.
Open the illustrated subscripts: which member of a family? guide →
Sources cited in the article section
- [5] Nine-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Cosmological Parameter Results ↗
- [6] Planck 2018 results. VI. Cosmological parameters ↗
These citations provide research context; check each source for the exact claim it supports.